CA1235146A

CA1235146A - High thermal conductivity ceramic body

Info

Publication number: CA1235146A
Application number: CA000495936A
Authority: CA
Inventors: Irvin C. Huseby; Carl F. Bobik
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1984-11-26
Filing date: 1985-11-21
Publication date: 1988-04-12
Also published as: GB8526830D0; GB2167771A; DE3541398C2; US4578365A; JPH075374B2; GB2167771B; DE3541398A1; JPS61219763A

Abstract

HIGH THERMAL CONDUCTIVITY CERAMIC BODY

ABSTRACT OF THE DISCLOSURE

A process for producing an aluminum nitride ceramic body having a composition defined and encompassed by polygon PINIKJ but not including lines KJ and PIJ of Figure 4, and a thermal conductivity greater than 1.00 W/cm?K at 25°C which comprises forming a mixture comprised of aluminum nitride powder containing oxygen, yttrium oxide, and free carbon, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges between points K and Pl of Figure 4, said compact having an equivalent % composition of Y, Al, O and N outside the composition defined and encompas-sed by polygon PINIKJ of Figure 4, heating said compact up to a temperature at which its pores remain open reacting said free carbon with oxygen contained in said aluminum nitride producing a deoxidized compact, said deoxidized compact having a composition wherein the equivalent % of Al, Y, O and N is defined and encompassed by polygon PINIKJ but not including lines KJ and PIJ of Figure 4, and sintering said deoxidized compact at a temperature of at least about 1860°C producing said ceramic body.

Description

RD-16,434 :~'J''~5~6 HIGH THERMAL CONDUCTIVITY CERAMIC BODY

The present invention relates to the production of a liquid phase sistered polycrystalline aluminum nitride body having a thermal conductivity higher than loo W/cm~K
at 25~C, and preferably at least about 1.50 W/cm-K at 25C.
In one aspect of the present process, aluminum nitride is deoxidized by carbon to a certain extent, and then it is further deoxidized and/or sistered by utilizing yttrium oxide to produce the present ceramic.
A suitably pure aluminum nitride single crystal, containing 300 ppm dissolved oxygen, has been measured to have a room temperature thermal conductivity of 2.8 W/cm-K, which is almost as high as that of Boo single crystal, which is 3.7 W/cm-K, and much higher than that of AYE single crystal, which is 0.44 W/cm-K. The thermal conductivity of an aluminum nitride single crystal is a strong function of dissolved oxygen and decreases with an increase in dissolved oxygen content. For example, the thermal conductivity of aluminum nitride single crystal having 0.8 wit% dissolved oxygen, is about 0.8 W/cm-K.
Aluminum nitride powder has an affinity for oxygen, especially when its surface is not covered by an oxide. The introduction of oxygen into the aluminum nitride lattice in aluminum nitride powder results in the formation of Al vacancies via the equation:

I

, ~5~'~6 RD-16,g3~

3N-3 ' 30 2 + V (1) (N-3) (N-3) (Al 3) Thus, the insertion of 3 oxygen atoms on 3 nitrogen sites will form one vacancy on an aluminum site. The presence ox oxygen atoms on nitrogen sites will probably have a neglig-isle influence on the thermal conductivity of Awn. However, due to the large difference in mass between an aluminum atom and a vacancy, the presence of vacancies on aluminum sites has a strong influence on the thermal conductivity of Awn and, for all practical purposes, is probably responsible for all of the decrease in the thermal conductivity of Awn.
There are usually three different sources of oxygen in nominally pure Awn powder. Source #l is discrete particles of Aye. Source #2 is an oxide coating, perhaps as Aye, coating the Awn powder particles. Source #3 is oxygen in solution in the Awn lattice. The amount of oxygen present in the Awn lattice in Awn powder will depend on the method of preparing the Awn powder. Additional oxygen can be introduced into the Awn lattice by heating the Awn powder at elevated temperatures. Measurements indicate that at ~l900~C the Awn lattice can dissolve -1.2 wit% oxygen. In the present invention, by oxygen content of Awn powder, it is meant to include oxygen present as sources #1, #2 and #3.
Also, in the present invention, the oxygen present with Awn powder as sources #1, #2 and #3 can be removed by utilizing free carbon, and the extent of the removal of oxygen by carbon depends largely on the composition desired in the resulting sistered body.
According to the present invention, aluminum nitride powder can be processed in air and still produce a ceramic body having a thermal conductivity greater than 1.00

-2-1 ' " , 1 ;~35~46 ROD 16,434 W/cm at 25C, and preferably at least about 1.50 W/cm HO at 25~C.
In one embodiment of the present invention, the aluminum nitride in a compact comprised of particulate aluminum nitride of known oxygen content, free carbon and yttrium oxide, is deoxidized by carbon to produce a desired equivalent composition of Al, N, Y and O, and the deoxidized compact is sistered by means of a liquid phase containing mostly Y and O and a smaller amount of Al and N.
Those skilled in the art will gain a further and better understanding of the present invention from the detailed description set forth below, considered in conjunction with the figures accompanying and forming a part of the specification in which:
FIGURE 1 is a composition diagram (also shown as Figure 1 in U.S. Pal. Jo. 4,547,471 issued October 15, 1985 and assigned to the assignee herein) showing the subsolidus phase equilibria in the reciprocal ternary system comprised of Alp, YIN Yo-yo and Aye. Figure 1 is plotted in equivalent % and along each axis of ordinates the equivalent % of oxygen is shown (the equivalent of nitrogen is 100~ minus the equivalent % of oxygen).
Along the axis of abscissas, the equivalent % of yttrium is shown the equivalent of aluminum is 100~
minus the equivalent % of yttrium). In Figure 1, line ABCDEF but not lines CUD and EN encompasses and defines the composition of the sistered body of U.S. Patent No. 4,547,471. Figure 1 also shows an example of an ordinates-joining straight line ZZ' joining the oxygen contents of an YIN additive and an aluminum nitride powder. From the given equivalent % of yttrium and Al at any point of an ordinates-joining line passing through the polygon ABCDEF, the required amounts of yttrium additive and Awn for producing the composition ,., ~3S~6 ROD 16,434 of that point on the ordinates-joining line can be calculated;
FIGURE 2 is an enlarged view of the section of Figure 1 showing the composition of the polycrystalline body of U.S. Pat. No. 4,547,471;
FIGURE 3 is a composition diagram showing the subsolidus phase equilibria in the reciprocal ternary system comprised of Awn, YIN, Yo-yo and Aye. Figure 3 is plotted in equivalent and along each axis of ordinates the equivalent % of oxygen is shown (the equivalent of nitrogen is 100 the equivalent of oxygen). Along the axis of abscissas, the equivalent % of yttrium is shown (the equivalent % of aluminum is 100% minus the equivalent % of yttrium). In Figure 3, line, i.e.
polygon, PlNlKJ but not including lines KJ and Ply encompasses and defines the composition of the sistered body produced by the present process; and FIGURE 4 is an enlarged view of the section of Figure 3 showing polygon PlNlKJ and also showing polygon QTXJ.
Figures 1 and 3 shown the same composition diagram showing the subsolidus phase equilibria in the reciprocal ternary system comprised of Awn, YIN, Yo-yo and AYE and differ only in that Figure 1 shows the polygon ABCDÉF of U.S. Pat.
No. 4,547,471 and the line ZZ', whereas Figure 3 shows the polygon PlNlKJ. The composition defined and encompassed by the polygon ABCDEF does not include the composition of the present invention.
Figures 1 and 2 were developed algebraically on the basis of data produced by forming a particulate mixture of YIN of predetermined oxygen content and Awn powder of predetermined oxygen content, and in a few instances a mixture of Awn, YIN and Yo-yo powders, under nitrogen gas, shaping the mixture into a compact . ., -- . .. .

51~6 ROD 16,434 under nitrogen gas and sistering the compact for time periods ranging from 1 to 1.5 hours at sistering temperatures ranging from about 1860C to about 2050C
in nitrogen gas at ambient pressure. More specifically, the entire procedure ranging from mixing of the powders to sistering the compact formed therefrom was carried out in a non oxidizing atmosphere of nitrogen.
Polygons PlNlY~J and QTXJ of Figures 3 and 4 also were developed algebraically on the basis of data produced by the examples set forth herein as well as other experiments which included runs carried out in a manner similar to that of the present examples.
The best method to plot phase equilibria that involve oxynitrides and two different metal atoms, where the metal atoms do not change valence, is to plot the compositions as a reciprocal ternary system as is done in Figures 1 and 3. In the particular system of Figures 1 and 3 there are two types of non-metal atoms (oxygen and nitrogen) and two types of metal atoms (yttrium and aluminum). The Al, Y, oxygen and nitrogen are assumed to have a valence of +3, +3, -2, and -3, respectively. All of the Al, Y, oxygen and nitrogen are assumed to be present as oxides, nitrides or oxynitrides, and to act as if they have the aforementioned valences.
The phase diagrams of Figures 1 to 4 are plotted in equivalent percent. The number of equivalents of each of these elements is equal to the number of moles of the particular element multiplied by its valence. Along the ordinate is plotted the number of oxygen equivalents multiplied by 100~ and divided by the sum of the oxygen equivalents and the nitrogen equivalents. Along the abscissa is plotted the number of yttrium equivalents multiplied by 100%
and divided by the sum of the yttrium equivalents and ~5~46 the aluminum equivalents. All compositions of the Figures 1 to 4 are plotted in this manner.
Compositions on the phase diagrams of Figures 1 to 4 can also be used to determine the weight percent and the volume percent of the various phases. For example, a particular point in the polygon PlNlKJ in Figure 3 or 4 can be used to determine the phase composition of the polycrystalline body at that point.
Figures 1 to 4 show the composition and the phase equilibria of the polycrystalline body in the solid state.
In U.S. Pat. No. 4,547,471, in the names of I. C. Huseby and C. F. Bobik there is disclosed the process for producing a polycrystalline aluminum nitride ceramic body having a composition defined and encompassed by line ABCDEF but not including lines CUD
and EN of Figure 1 therein (also shown as prior art Figure 1 herein), a porosity of less than about 10~ by volume of said body and a thermal conductivity greater than 1.0 W/cm-K at 22C which comprises forming a mixture comprised of aluminum nitride powder and an yttrium additive selected from the group consisting of yttrium, yttrium hydrides yttrium nitride and mixtures thereof, said aluminum nitride and yttrium additive having a predetermined oxygen content, said mixture having a composition wherein the equivalent % of yttrium, aluminum, nitrogen and oxygen is defined and encompassed by line ABCDEF but not including lines CUD
and EN in Figure 1, shaping said mixture into a compact, and sistering said compact at a temperature ranging from about 1850C to about 2170C in an atmosphere selected from the group consisting of nitrogen, argon, hydrogen and mixtures thereof to produce said polycrystalline body.
U.S. Pat. Jo. 4,547,471 also discloses a ~S1~6 ROD 16434 polycrystalline body having a composition comprised of from greater than about 1.6 equivalent % yttrium to about 19.75 equivalent % yttrium, from about ~0.25 equivalent aluminum up to about 98.4 equivalent %
aluminum, from greater than about 4.0 equivalent oxygen to about 15.25 equivalent oxygen and from about 84.75 equivalent nitrogen up to about 96 equivalent % nitrogen.
U.S. Pat. No. 4,547,471 also discloses a polycrystalline body having a phase composition comprised of Awn and a second phase containing Y and 0 wherein the total amount of said second phase ranges from greater than about 4.2% by volume to about 27.3%
by volume of the total volume of said body, said body having a porosity of less than about 10~ by volume of said body and a thermal conductivity greater than Lo W/cm~K at 22~C.
Briefly stated, the present process for producing the present sistered polycrystalline aluminum nitride ceramic body having a composition defined and encompassed by line, i.e. polygon, PlNlKJ
but not including lines KJ and Ply of Figures 3 or 4, a porosity of less than about 10~ by volume, and preferably a minimum of about 1.50 W/cm.K at 25C
comprises the steps:
(a) forming a mixture comprised of aluminum nitride powder containing oxygen, yttrium oxide or a precursor therefore and a carbonaceous additive selected from the group consisting of free carbon, a carbonaceous organic material and mixtures thereof, said carbonaceous organic material thermally decomposing at a temperature ranging from about 50DC
to about 1000C to free carbon and gaseous product of decomposition which vaporizes away, shaping said ~35~6 RD-16,434 mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges between points X and PI of Figures 3 or 4, which is from greater than about 0.35 equivalent % to less than about 4.4 equivalent % yttrium and from greater than about 95.6 equivalent % to less than about 99.65 equivalent % aluminum, said compact having an equivalent % composition of Y, Al, 0 and N outside the composition defined and encompassed by polygon PlNlKJ of Figures 3 or 4, (b) heating said compact in a non oxidizing atmosphere at a temperature up to about 1200C thereby providing yttrium oxide and free carbon, (c) heating said compact in a nitrogen-containing non oxidizing atmosphere at a temperature ranging from about 1350C to a temperature sufficient to deoxidize the compact but below its pore closing temperature reacting said free carbon with oxygen contained in said aluminum nitride producing a deoxidized compact, said deoxidized compact having a composition wherein the equivalent % of Al, Y, 0 and N is defined and encompassed by polygon PlNlKJ but not including lines KJ and Ply of Figure 3 or 4, said free carbon being in an amount which produces said deoxidized compact, and (d) sistering said deoxidized compact in a nitrogen-containing non oxidizing atmosphere at a temperature of at least about 1860 producing said polycrystalline body.
In the present process, the composition of the deoxidized compact in equivalent % is the same as or does not differ significantly from that of the resulting sistered body in equivalent %.
In the present invention, oxygen content can be determined by neutron activation analysis.

RD-16,434 ,51~6 By weight % or % by weight of a component herein, it is meant that the total weight % of all the components is 100%.
By ambient pressure herein, it is meant atmosphere to or about atmospheric pressure.
By specific surface area or surface area of a powder herein, it is meant the specific surface area act cording to BET surface area measurement.
Briefly stated, in one embodiment, the present process for producing a sistered polycrystalline aluminum nitride ceramic body having a composition defined and encompassed by line, i.e. polygon, QTXJ but not including lines QJ and XJ of Figures 3 or 4, a porosity of less than about 10% by volume, and preferably less than about 2% by volume of said body and a thermal conductivity greater than 1.00 W/cm-K at 25C, and preferably greater than 1.50 W/cm-K
at 25C comprises the steps:
(a) forming a mixture comprised of aluminum nitride powder containing oxygen, yttrium oxide, and a carbonaceous additive selected from the group consisting of free carbon, a carbonaceous organic material and mixtures thereof, said carbonaceous organic material thermally decomposing at a temperature ranging from about 50C to about 1000C to free carbon and gaseous product of decomposition which vaporizes away, said free carbon having a specific surface area greater than about 100 mug the aluminum nitride powder in said mixture having a specific surface area ranging from about 3.4 mug to about 6 mug shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges from point X up to point Q of Figures 3 or 4, which is from greater than about 0.8 equivalent ye to about 3.2 equivalent % yttrium and from about 96.8 equivalent % to less than ~D-16,434 So 6 about 99.2 equivalent % aluminum, said compact having an equivalent % composition of Y, Al, 0 and N outside the composition defined and encompassed by polygon ~lNlKJ of Figures 3 or 4, the aluminum nitride in said compact con-twining oxygen in an amount ranging from greater than Abbott% by weight to less than about 4.50% by weight of said aluminum nitride, (b) heating said compact in a non oxidizing atmosphere at a temperature up to about 1200C thereby providing yttrium oxide and free carbon, (c) heating said compact at ambient pressure in a nitrogen-containing non oxidizing atmosphere containing at least about 25% by volume nitrogen at a temperature ranging from about 1350C to a temperature sufficient to deoxidize the compact but below its pore closing temperature reacting said free carbon with oxygen contained in said aluminum nitride producing a deoxidized compact, said deoxidized compact having a composition wherein the equivalent % of Al, Y, 0 and N is defined and encompassed by polygon QTXJ but not including lines QJ and XJ of Figure 3 or 4, the aluminum nitride in said compact before said deoxidation by said carbon having an oxygen content ranging from greater than about 1.4% by weight to less than about 4.5% by weight of said aluminum nitride, said free carbon being in an amount US which produces said deoxidized compact, and (d) sistering said deoxidized compact at ambient pressure in a nitrogen-containing non oxidizing atmosphere containing at least about 25% by volume nitrogen at a temperature ranging from about 1910C to about 2000C, preferably from about 1910C to about 1950C, and in one embodiment from about l950GC to about 2000C, producing said polycrystalline body.

RD-16,434

3 ~i5~46 Briefly stated, in another embodiment, the present process for producing the present sistered polycrystalline aluminum nitride ceramic body having a composition defined and encompassed by line, i.e. polygon, PlNlKJ but not including lines KJ and Ply of Figures 3 or 4, a porosity of less than about 10% by volume, and preferably less than about 4% by volume of said body and a thermal conductivity greater than 1.00 W/cm-K at 25C, and preferably a minimum of 1.5 W/cm-K at 25C comprises the steps:
(a) processing an aluminum nitride powder into a compact for deoxidation by free carbon by providing an aluminum nitride powder having an oxygen content ranging up to about 4.4% by weight of said aluminum nitride powder, forming a mixture comprised of said aluminum nitride powder, yttrium oxide or precursor therefore and a carbonaceous additive selected from the group consisting of free carbon, a carbonaceous organic material and mixtures thereof, said carbonaceous organic material thermally decomposing at a temperature ranging from about 50C to about 1000C to free carbon and gaseous product of decomposition which vaporizes away, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent %
of yttrium and aluminum ranges between points K and PI of Figures 3 or 4, which is from greater than about 0.35 equivalent % to less than about 4.4 equivalent % yttrium and from greater than about 95.6 equivalent % to less than about 99.65 equivalent % aluminum, said compact having an equiva-lent % composition of Y, Al, 0 and N outside the composition defined and encompassed by polygon PlNlKJ of Figures 3 or 4, during said processing said aluminum nitride picking up oxygen, the oxygen content of said aluminum nitride in said compact before said deoxidation by carbon ranging from greater than about 0.6% by weight, and preferably greater . .

. . .

RD-16,434 1 2;~5146 than about 1.40% by weight, up to about 4.50% by weight of said aluminum nitride, (b) heating said compact in a non oxidizing atmosphere at a temperature up to about 1200~C thereby providing yttrium oxide and free carbon, (c) heating said compact in a nitrogen-containing non oxidizing atmosphere at a temperature ranging from about 1350C to a temperature sufficient to deoxidize the compact but below its pore closing temperature reacting said free carbon with oxygen contained in said aluminum nitride producing a deoxidized compact, said deoxidized compact having a composition wherein the equivalent % of Al, Y, 0 and N is defined and encompassed by polygon PlNlKJ but not including lines KJ and Ply of Figure 3 or 4, said free carbon being in an amount which produces said deoxidized compact, and (d) sistering said deoxidized compact in a nitrogen-containing non oxidizing atmosphere at a temperature of at least about 1860C producing said polycrystalline body.
Briefly stated, in another embodiment, the present process for producing a sistered polycrystalline aluminum nitride ceramic body having a composition defined and encompassed by polygon QTXJ but not including lines QJ and XJ of Figures 3 or 4, a porosity of less than about 10% by volume and preferably less than about 2% by volume of said body and a thermal conductivity greater than 1.00 W/cm-K at 25C, and preferably greater than about 1.50 W/cm~K at 25C
comprises the steps:
(a) processing an aluminum nitride powder into a compact for deoxidation by free carbon by providing an aluminum nitride powder having an oxygen content ranging from greater than about 1.00% by weight to less than about

4.00% by weight of said aluminum nitride powder, forming a I

, RD-16,434 ~5~46 mixture comprised of said aluminum nitride powder, yttrium oxide or precursor therefore and a carbonaceous additive selected from the group consisting of free carbon, a carbonaceous organic material and mixtures thereof, said carbonaceous organic material thermally decomposing at a temperature ranging from about 50C to about 1000C to free carbon and gaseous product of decomposition which vaporizes away, said free carbon having a specific surface area greater than about lo mug the aluminum nitride powder in lo said mixture having a specific surface area ranging from about 3.4 mug to about 6 mug shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges from point X up to point Q of Figures 3 or 4, which is from greater than about 0.8 equivalent % to about 3.2 equivalent % yttrium and from about 9.6.8 equivalent % to less than about 99.2 equivalent % aluminum, said compact having an equivalent % composition of Y, Al, 0 and N outside the composition defined and encompassed by polygon PlNlKJ of Figures 3 or 4, during said processing said aluminum nitride picking up oxygen, the oxygen content of said aluminum nitride in said compact before said deoxidation by carbon ranging from greater than about 1.40% by weight up to about 4.50% by weight of said aluminum nitride and being greater than said oxygen content of said starting aluminum nitride powder by an amount rang no from greater than about 0.03% by weight up to about 3.00% by weight of said aluminum nitride, (b) heating said compact in a non oxidizing atmosphere at a temperature up to about 1200C thereby providing yttrium oxide and free carbon, (c) heating said compact at ambient pressure in a nitrogen-containing non oxidizing atmosphere containing at least about 25% by volume nitrogen at a temperature ranging . .

RD-16,434 ~35~46 from about 1350C to a temperature sufficient to deoxidize the compact but below its pore closing temperature thereby reacting said free carbon with oxygen contained in said aluminum nitride producing a deoxidized compact, said deoxidized compact having a composition wherein the equiva-lent % of Al, Y, O and N is defined and encompassed by polygon QTXJ but not including lines QJ and XJ of Figure 4, said free carbon being in an amount which produces said deoxidized compact, and lo sistering said deoxidized compact at ambient pressure in a nitrogen-containing non oxidizing atmosphere containing at least about 25% by volume nitrogen at a temperature ranging from about l910~C to about 2000DC, preferably from about 1910C to about 1950C, and in one embodiment from about 1950C to about 2000C, producing said polycrystalline body.
In another embodiment of the present process, said mixture and said compact have a composition wherein the equivalent % of yttrium end aluminum ranges between points K
and P but does not include points K and P of Figure 4, said yttrium ranging from greater than about Owe equivalent % to less than about 4.4 equivalent %, said aluminum ranging from greater than about 95.6 equivalent % to less than about 99.45 equivalent %, and said sistered body and said Dixie-dozed compact are comprised of a composition wherein the equivalent percent of Al, Y, O and N is defined and encom-passed by polygon PUNK but does not include lines KJ and PI
of Figure 4.
In another embodiment of the present process, said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges from point N up to point Pi of Figure 4, i.e. said yttrium ranging from greater than about 0.35 equivalent % to about 2.9 equivalent RD-l6,434 ~.~3S1~6 % and said aluminum ranging from about 97.1 equivalent % to less than about 99.65 equivalent %, and said sistered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, O and N is defined and encompassed by polygon PININOP but does not include line PIP of Figure 4.
In another embodiment of the present process, to produce a sistered polycrystalline aluminum nitride ceramic body having a composition defined and encompassed by polygon QTYlY2 but excluding line QUEUE of Figure 4, said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges from point Ye up to point Q, i.e. said yttrium ranging from greater than about 0.8 equivalent % to about 2.0 equivalent % and said aluminum ranging from about 98.0 equivalent % to less than about 99.2 equivalent %.
In another embodiment of the present process, said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges between points K
and P but does not include points K and P of Figure 4, i.e.
said yttrium ranging from greater than about 0.55 equivalent % to less than about 4.4 equivalent % and said aluminum ranging from greater than about 95.6 equivalent % to less than about 99.45 equivalent %, and said sistered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, O and N is defined and encompassed by polygon PONKJ but does not include lines NO, KJ and PI of Figure 4.
In yet another embodiment of the present process, said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges from point No up to point K of Figure 4, i.e. said yttrium ranging from about 1.9 equivalent % to less than about 4.4 equivalent % and RD-1~,434 said aluminum ranging from greater than about 95 6 equiva-lent % to about I 1 equivalent %, and said sistered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, 0 and N is defined by line Ilk but excluding point K of Figure 4 In another embodiment of the present process to produce a sistered polycrystalline aluminum nitride ceramic body having a composition defined and encompassed by polygon QTXJ but not including lines QJ and XJ of Figure 4 and a porosity of less than 1% by volume of the body, the free carbon has a specific surface area greater than about 100 mug the aluminum nitride in said mixture has a specific surface area ranging from about 3 7 mug to about 6 0 mug all firing of the compact is carried out in nitrogen, and at a sistering temperature ranging from about l910~C to about 1950DC, the resulting sistered body has a thermal conductive fly greater than 1 50 W/cm-K at 25 DC, and at a sistering temperature ranging from about 1950C to about 2000C, the resulting sistered body has a thermal conductivity greater than about 1 67 W/cm-K at 25C
In another embodiment of the present process, to produce a sistered polycrystalline aluminum nitride ceramic body having a composition defined and encompassed by polygon QTYlY2 but excluding line QUEUE of Figure 4 which contains carbon in an amount of less than about 04% by weight of the sistered body and has a thermal conductivity greater than 1 77 W/cm-K at 25C and a porosity of less than 1% by volume of the body, the aluminum nitride in said mixture has a specific surface area ranging from about 3 4 mug to about 6 0 mug the free carbon has a specific surface area greater than 100 m go all firing of the compact is carried out in nitrogen and the sistering temperature ranges from about 1950~C to about 2000C.

RD-16,434 1~3S~46 In another embodiment of the present process, to produce a sistered polycrystalline aluminum nitride body having a composition defined and encompassed by polygon QTYlY2 but excluding line QUEUE of Figure 4 which contains carbon in an amount of less than about .04% by weight of the sistered body and has a thermal conductivity greater than 1.68 W/cm-K at 25C and a porosity of less than 1% by volume of the sistered body, the aluminum nitride in said mixture has a specific surface area ranging from about 3.7 mug to about 6.0 mug the free carbon has a specific surface area greater than 100 mug all firing of the compact is carried out in nitrogen and the sistering temperature ranges from about 1910C to about 1950C.
In another embodiment of the present process, to produce a sistered polycrystalline aluminum nitride ceramic body having a composition defined and encompassed by polygon QTYlY2 but excluding line QUEUE of Figure 4 which has a thermal conductivity greater than 1.57 W/cm-K at 25~C and a porosity of less than 1% by volume of the scented body, the aluminum nitride in said mixture has a specific surface area ranging from about 3.7 mug to about 6.0 mug the free carbon has a specific surface area greater than 100 mug all firing of the compact is carried out in nitrogen and the sistering temperature ranging from about l910~C to about 1950C.
In another embodiment of the present process, said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges between points K
and P but does not include points K and P of Figure 4, i.e.
said yttrium ranging from greater than about 0.55 equivalent % to less than about 4.4 equivalent and said aluminum ranging from greater than about 95.6 equivalent % to less than about 99.45 equivalent %, and said sistered body and ...... ...... . . .

~51~6 RD-16,434 said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, 0 and N is defined and encompassed by polygon PONKJ but does not include lines NO, KJ and PI of Figure 4, said free carbon has a specific surface area greater than about 100 mug said aluminum nitride powder in such mixture has a specific surface area ranging from about 3.4 mug to about 6.0 mug said stinter-in atmosphere is nitrogen, said sistering temperature is from about 1965DC to about 2050DC, and said sistered body has a porosity of less than about 2% by volume, and prefer-ably less than about 1% by volume, of said body and has a thermal conductivity greater than 1.67 W/cm-K at 25C.
In yet another embodiment of the present process, said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges from point No up to point K of Figure 4 and said sistered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, 0 and N is defined by line Ilk but excluding point K of Figure 4, said free carbon has a specific surface area greater than about 100 mug said aluminum nitride powder in said mixture has a specific surface area ranging from about 3.6 mug to about 6.0 mug said sistering atmosphere is nitrogen, said sistering temperature is from about 1970C to about 2050C, and said sistered body has a thermal conductivity greater than 1.50 W/cm-K at 25C.
The calculated compositions of particular points in Figures 3 or 4 in the polygon PlNlKJ are shown in Table I
as follows:

RD-16, 434 ~35~46 TABLE I
Composition (Equivalent I) Vow I and (Wit I of Phases*
Point Y Oxygen Awn Yo-yo YO-YO

P 0.55 1.1598.7(98.2) - 1.3(1.8) o 0.6 1.1 98.7(98.1) 0.2( 0.3) 1.1(1.6) N 2.9 2.9 94.9(92.4) 5.1( 7.6) K 4.4 4.4 92.4(88.7) 7.6(11.3) J 2.5 4.1 94.0(91-9) 6.0(8.1) Q 0.8 1.55 98.1(97.3) - 1.9(2.7) T 1.0 1.55 97.8 0.7 1.5 X 3.2 4.2 93.4 2.8 3.8 Ye 2.0 2.75 95.8 1.5 2.7 Ye 1.9 3.15 95.5 - 4.5 No 1.9 1.9 96.7(94.9) ~.3(5.1) Pi 0.35 0.8599.2(98.8) - 0.8(1.2) * - Wit % is given in parentheses, Vow % is given without parentheses The polycrystalline aluminum nitride body produced by the present process has a composition defined and encom-passed by polygon, i.e. line, PlNlRJ but not including lines KJ and Ply of Figures 3 or 4. The sistered polycrystalline body of polygon PlNlKJ but not including lines Jo and Ply of Figures 3 or 4 produced by the present process has a combo-session comprised of from greater than about 0.35 equivalent % yttrium to less than about 4.4 equivalent % yttrium, from greater than about 95.6 equivalent % aluminum to less than about 99.65 equivalent % aluminum, from greater than about 0.85 equivalent % oxygen to less than about 4.4 equivalent %

: : :

,, ` RD-16,434 51'~

oxygen and prom greater than about 95.6 equivalent % vitro-gun to less than about 99.15 equivalent % nitrogen.
Also, the polycrystalline body defined and encom-passed by polygon PlNlKJ but not including lines KJ and Ply of Figure 3 or 4 is comprised of an Awn phase and a second phase which ranges in amount from greater than about 0.8% by volume at a composition next to point Pi to less than about 7.6% by volume at a composition adjacent to point K of the total volume of the sistered body, and such second phase can be comprised of YO-YO or a mixture of Yoga and Yo-yo. When the second phase is comprised of Yo-yo, i.e. at line Ilk, it ranges in amount from about 3.3% my volume to less than about 7.6% by volume of the sistered body. However, when the second phase is a mixture of second phases comprised of Yo-yo and YO-YO, i.e. when the polycrystalline body is defined and encompassed by polygon PlNlKJ excluding lines KJ, Ply and Ilk, such mixture of phases ranges in amount from greater than about I by volume to less than about 7.6% by volume of the sistered body. Specifically, both of these second phases are always present in at least a trace amount, i.e. at least an amount detectable by X-ray diffract lion analysis, and in such mixture, the Yo-yo phase can range to less than about 7.6% by volume of the sistered body, and the YO-YO phase can range to less than about 6.0% by volume of the total volume of the sistered body. More specifically, when a mixture of Yoga and Yo-yo phases is present, the amount of YO-YO phase decreases and the amount of Yo-yo phase increases as the composition moves away from line Ply toward line Ilk in Figure 4. Line Ply in Figure 4 is comprised of Awn phase and a second phase comprised of YO-YO.
The sistered polycrystalline body of polygon PONKJ
but not including lines KJ and PI of Figures 3 or 4 produced . .

RD-16,434 Sly by the present process has a composition comprised of from greater than about 0.55 equivalent yttrium to less than about 4.4 equivalent % yttrium, from greater than about 95.6 equivalent % aluminum to less than about 99.45 equivalent %
aluminum, from about 1.1 equivalent % oxygen to less than about 4.4 equivalent % oxygen and from greater than about 95.6 equivalent % nitrogen to about 98.9 equivalent %
nitrogen.
Also, the polycry~talline body defined and encom-passed by polygon PONKJ but not including lines KJ and PI of Figure 3 or 4 is comprised of an Awn phase and a second phase which ranges in amount from about 1.3% by volume at line PO to less than about 7.6% by volume at a composition next to point K of the total volume of the sistered body, and such second phase can be comprised of Yo-yo or a mixture of YO-YO and Yo-yo. When the second phase is comprised of Yo-yo, i.e. at line NO, it ranges in amount from about 5.1%
by volume to less than about 7.6% by volume of the sistered body. however, when the second phase is a mixture of second phases comprised of Yo-yo and YO-YO, both of these second phases are always present in at least a trace amount, i.e.
at least an amount detectable by X-ray diffraction analysis, and in such mixture, the Yo-yo phase can range to less than about 7.6% by volume of the sistered body, and the YO-YO
phase can range to less than about 6.0% by volume of the total volume of the sistered body. More specifically, when a mixture of YO-YO and Yo-yo phases is present, the amount of YO-YO phase decreases and the amount of Yo-yo phase increases as the composition moves away from line PI toward line NO in Figure 4. Line PI in Figure 4 is comprised of Awn phase and a second phase comprised of YO-YO.
-RD-16,434 51~6 As can be seen from Table I, the polycrystalline body at point K composition would have the largest amount of second phase present which at point K would be Yo-yo.
In another embodiment, the polycrystalline alum-nut nitride body produced by the present process has composition defined and encompassed by polygon PlNlNOP but not including line Pup of Figures 3 or 4. The sistered polycrystalline body of polygon PlNlNOP but not including line Pup of Figures 3 or 4 produced by the present process has a composition comprised of from greater than about 0.35 equivalent % yttrium to about 2.9 equivalent % yttrium, from about 97.1 equivalent % aluminum up to about 99.65 equiva-lent % aluminum, from greater than about 0.85 equivalent %
oxygen to about 2.9 equivalent % oxygen and from about 97.1 equivalent % nitrogen to less than about 99.15 equivalent %
nitrogen.
Also, the polycrystalline body defined and encom-passed by polygon PlNlNOP but not including line Pup of Figures 3 or 4 is comprised of an Awn phase and a second phase which ranges in amount from greater than about 0.8% by volume at a composition next to point Pi to about 5.1% by volume at point N of the total volume of the sistered body, and such second phase can be comprised of YO-YO or a mixture of Y4Al2Og and YO-YO. When the second phase is comprised of YO-YO, i.e. at line Nun, it ranges in amount from about 3.3%
by volume to about 5.1% by volume of the sistered body.
However, when the second phase is a mixture of second phases comprised of YO-YO and Y4Al2Og, i.e. when the polycrystalline body is defined and encompassed by polygon PlNlNOP excluding lines Pup and Nun, such mixture of phases ranges in amount from greater than about 0.8% by volume to less than about

5.1% by volume of the sistered body. Specifically, both of these second phases are always present in at least a trace , ..

RD-16,434 1~35146 amount, i.e. at least an amount detectable by X-ray diffract lion analysis, and in such mixture, the Yo-yo phase can range to less than about 5.1% by volume of the sistered body, and the YO-YO phase can range to less than about 1.3% by volume of the total volume of the sistered body. More specifically, when a mixture of YO-YO and Yo-yo phases is present, the amount of YO-YO phase decreases and the amount of Yo-yo phase increases as the composition moves away from line Pup toward line Nun in Figure 4. Line Pup in Figure 4 is comprised of Awn phase and a second phase comprised of YO-YO.
In another embodiment, the polycrystalline alum-nut nitride body produced by the present process has a composition defined and encompassed by polygon, i.e. line, QTXJ but not including lines QJ and XJ of Figures 3 or 4.
The sistered polycrystalline body of polygon QTXJ but not including lines QJ and XJ of Figures 3 or 4 produced by the present process has a composition comprised of from greater than about 0.8 equivalent % yttrium to about 3.2 equivalent % yttrium, from about 96.B equivalent % aluminum up to about 99.2 equivalent % aluminum, from greater than about l.S5 equivalent % oxygen to about 4.2 equivalent oxygen and from about 95.8 equivalent % nitrogen to less than about 98.45 equivalent % nitrogen.
Also, the polycrystalline body defined and encom-passed by polygon QTXJ but not including lines QJ and XJ of Figure 3 or 4 is comprised of an Awn phase and a second phase which ranges in amount from greater than about 1.9% by volume to less than about 6.6~ by volume of the total volume of the sistered body, and such second phase is comprised of a mixture of YO-YO and Yo-yo. Specifically, the Yo-yo phase ranges from a trace amount, i.e. at least an amount detect-able by X-ray diffraction analysis, to less than about 2.8%

RD-16,434 1~35146 by volume of the sistered body, and the Y4Al2Og phase ranges from about 1.5% by volume to less than about 6.0% by volume of the sistered body. More specifically, the amount of Y4Al2Og phase decreases and the amount of Yo-yo phase in-creases as the composition moves away from line QJ toward line TX in Figure 4.
In one embodiment, the present polycrystalline body has a composition defined and encompassed by polygon PONKJ but not including lines NO, KJ and PI of Figures 3 or 4, i.e. it has a composition comprised of from greater than about 0.55 equivalent % yttrium to less than about 4.4 equivalent % yttrium, from greater than about 95.6 equiva-lent % aluminum to less than about 99.45 equivalent %
aluminum, from about 1.1 equivalent % oxygen to less than about 4.4 equivalent % oxygen and from greater than about 95.6 equivalent % nitrogen to about 98.9 equivalent % vitro-gent In this embodiment, the phase composition of the sistered body is comprised of Awn and a mixture of second phases comprised of Yule and YO-YO. This second phase mixture ranges in amount from about 1.3% by volume to less than about 7.6% by volume of the body and always contains both Y4Al2Og and YO-YO at least in a trace amount, i.e. at least in an amount detectable by X-ray diffraction analysis.
Specifically, in this embodiment, the amount of YO-YO phase can range to less than about 7.6% by volume of the sistered body, and the amount of Y4Al2Og phase can range to less than about 6.0% by volume of the sistered body.
In another embodiment, the present process pro-dupes a sistered body defined by line Ilk but not including point K of Figure 4 which has a phase composition comprised of Awn and YO-YO wherein the YO-YO phase ranges from about 3.3% by volume to less than about 7.6% by volume of the body. Line Ilk but not including point K of Figure 4 has a .. ..

RD-16,434 ~35~6 composition comprised of from about 1.9 equivalent % to less than about 4.4 equivalent % yttrium, from greater than about 95.6 equivalent % to about 98.1 equivalent % aluminum, from about 1.9 equivalent % to less than about 4.4 equivalent %
oxygen and from greater than about 95.6 equivalent % to about 98.1 equivalent % nitrogen.
In another embodiment, the present process pro-dupes a sistered body defined by polygon QTYlY2 but excludes line QUEUE of Figure 4 which has a phase composition comprised of Awn and a second phase mixture of Yo-yo and YO-YO
wherein the total amount of this second phase mixture ranges from greater than about 1.9% by volume to less than about 4.5% by volume of the total volume of the body. Specific-ally, the Yo-yo phase ranges from a trace amount, i.e. at least an amount detectable by X-ray diffraction analysis, to about 1.5% by volume of the total volume of the sistered body, and the YO-YO phase ranges from about 1.5~ by volume to less than about 4.5% by volume of the body. Polygon QTYlY2 of Figure 4 has a composition comprised of from greater than about 0.8 equivalent % to about 2.0 equivalent % yttrium, from about 9B.0 equivalent % to less than about 99.2 equivalent % aluminum, from greater than about 1.55 equivalent % to less than about 3.15 equivalent % oxygen and from greater than about 96.P5 equivalent % to less than about 9B.45 equivalent % nitrogen.
In the present process, the aluminum nitride powder oak be of commercial or technical grade. Specifically-lye it should not contain any impurities which would have a significantly deleterious effect on the desired properties of the resulting sistered product. The starting aluminum nitride powder used in the present process contains oxygen generally ranging in amount up to about 4.4% by weight and usually ranging from greater than about 0.5% by weight to -R~-16,434 So 46 less than about 4.0~ by weight, i.e. up to about 4% by weight, and in one embodiment ranging from greater than about 1.00% by weight to less than about 4.00% by weight.
Typically, commercially available aluminum nitride powder contains from about 1.5 weight % (2.6 equivalent %) to about 3 weight % (5.2 equivalent %) of oxygen and such powders are most preferred on the basis of their substantially lower cost.
Generally, the present starting aluminum nitride lo powder has a specific surface area which can range widely, and generally it ranges up to about 10 mug Frequently, it has a specific surface area greater than about lo mug and more frequently of at least about 3.0 mug usually greater than about 3.2 mug and preferably at least about 3.4 mug Generally, the present aluminum nitride powder in the present mixture, i.e. after the components have been mixed, usually by milling, has a specific surface area which can range widely, and generally it ranges to about lo mug Frequently, it ranges from greater than about 1.0 mug to about lo mug and more frequently from about 3.2 mug to about lo mug and preferably it ranges from about 1.5 mug to about 5 mug and in one embodiment it ranges from about 3.4 mug to about 5 mug according to BET surface area measurement. Specifically, the minimum sistering tempera-lure of a given composition of the present invention in-creases with increasing particle size of the aluminum nitride.
Generally, the yttrium oxide (Yo-yo) additive in the present mixture has a specific surface area which can range widely. Generally, it is greater than about 0.4 mug and generally it ranges from greater than about 0.4 mug to about 6.0 mug usually from about 0.6 mug to about 5.0 RD-16,434 ~235~

mug more usually from about 1.0 mug to about 5.0 mug and in one embodiment it is greater than 2.0 mug In the practice of this invention, carbon for deoxidation of aluminum nitride powder is provided in the form of free carbon which can be added to the mixture as elemental carbon, or in the form of a carbonaceous additive, for example, an organic compound which can thermally deco-pose to provide free carbon.
The present carbonaceous additive is selected from I the group consisting of free carbon, a carbonaceous organic material and mixtures thereof. The carbonaceous organic material pyrolyzes, i.e. thermally decomposes, completely at a temperature ranging from about 50C to about 1000C to free carbon and gaseous product of decomposition which vaporizes away. In a preferred embodiment, the carbonaceous additive is free carbon, and preferably, it is graphite.
ugh molecular weight aromatic compounds or materials are the preferred carbonaceous organic materials for making the present free carbon addition since they ordinarily give on pyrolyzes the required yield of portico-late free carbon of sub micron size. Examples of such aromatic materials are a phenol formaldehyde condensate resin known as Novolak which is soluble in acetone or higher alcohols, such as bottle alcohol, as well as many of the related condensation polymers or resins such as those of resorcinol-formaldehyde, aniline-formaldehyde, and crossly-formaldehyde. Another satisfactory group of materials are derivatives of polynuclear aromatic hydrocarbons contained in coal tar, such as dibenzanthracene and chrysene. A
preferred group are polymers of aromatic hydrocarbons such as polyphenylene or polymethylphenylene which are soluble in aromatic hydrocarbons.

, .

RD-16,434 5~46 The present free carbon has a specific surface area which can range widely and need only be at least sufficient to carry out the present deoxidation. Generally, it has a specific surface area greater than about 10 mug preferably greater than 20 McKee, more preferably greater than about 100 mug and still more preferably greater than 150 mug according to BET surface area measurement to insure intimate contact with the Awn powder for carrying out its deoxidation.
Most preferably, the present free carbon has as high a surface area as possible. Also, the finer the particle size of the free carbon, i.e. the higher its surface area, the smaller are the holes or pores it leaves behind in the deoxidized compact. Generally, the smaller the pores of a given deoxidized compact, the lower is the amount of liquid phase which need be generated at sistering temperature to produce a sistered body having a porosity of less than about 1% by volume of the body.
By processing of the aluminum nitride powder into a compact for deoxidation by free carbon, it is meant herein to include all mixing of thy aluminum nitride powder to produce the present mixture, all shaping of the resulting mixture to produce the compact, as well as handling and storing of the compact before it is deoxidized by carbon.
In the present process, processing of the aluminum nitride powder into a compact for deoxidation by fret carbon is at least partly carried out in air, and during such processing of the aluminum nitride powder, it picks up oxygen from air usually in an amount greater than about 0.03% by weight of the aluminum nitride, and arty such pick up of oxygen is controllable and reproducible or does not differ signify-gently if carried out under the same conditions. If desire Ed the processing of the aluminum nitride powder into a RD-16,434 ~l5~4~

compact for deoxidation by free carbon can be carried out in air.
In the present processing of aluminum nitride, the oxygen it picks up can be in any form, i.e. it initially may be oxygen, or initially it may be in some other form, such as, for example, water. The total amount of oxygen picked up by aluminum nitride from air or other media is less than about 3.00% by weight, and generally ranges from greater than about 0.03% by weight to less than about 3.00% by weight, and usually it ranges from about 0.10% by weight to about 1.00% by weight, and preferably it ranges from about 0.15% by weight to about 0.70% by weight, of the total weight of the aluminum nitride. Generally, the aluminum nitride in the present mixture and compact prior to dockside-lion of the compact has an oxygen content of less than Abbott% by weight, and generally it ranges from greater than about 0.6% by weight, preferably greater than about l.40% by weight, to less than about 4.50% by weight, and usually it ranges from about 2.00% by weight to about 4.00% by weight, and more usually it ranges from about 2.20% by weight to about 3.50% by weight, of the total weight of aluminum nitride.
The oxygen content of the starting aluminum nitride powder and that of the aluminum nitride in the compact prior to deoxidation is determinable by neutron activation analysis.
In a compact, an aluminum nitride containing oxygen in an amount of about 4.5% by weight or more general-lye is not desirable.
In carrying out the present process, a uniform or at least a significantly uniform mixture or dispersion of the aluminum nitride powder, yttrium oxide powder and carbonaceous additive, generally in the form of free carbon RD-16,434 I

powder, is formed and such mixture can be formed by a number of techniques. Preferably, the powders are ball milled preferably in a liquid medium at ambient pressure and temperature to produce a uniform or significantly uniform dispersion. The milling media, which usually are in the form of cylinders or balls, should have no significant deleterious effect on the powders, and preferably, they are comprised of steel or polycrystalline aluminum nitride, preferably made by sistering a compact of milling media size of Awn powder and Yo-yo scenting additive. Generally, the milling media has a diameter of at least about 1/4 inch and usually ranges from about 1/4 inch to about 1/2 inch in diameter. The liquid medium should have no significantly deleterious effect on the powders and preferably it is non-aqueous. Preferably, the liquid mixing or milling medium can be evaporated away completely at a temperature ranging from above room or ambient temperature to below 300C leaving the present mixture. Preferably, the liquid mixing medium is an organic liquid such as Hutton or hexane. Also, preferably, the liquid milling medium con-twins a dispersant for the aluminum nitride powder thereby producing a uniform or significantly uniform mixture in a significantly shorter period of milling time. Such dispel-sent should be used in a dispersing amount and it should evaporate or decompose and evaporate away completely or leave no significant residue, i.e. no residue which has a significant effect in the present process, at an elevated temperature below 1000C. Generally, the amount of such dispersant ranges from about 0.1% by weight to less than about 3% by weight of the aluminum nitride powder, and generally it is an organic liquid, preferably oleic acid.
In using steel milling media, a residue of steel or iron is left in the dried dispersion or mixture which can . .

RD-16,434 1~35146 range from a detectable amount up to about 3.0% by weight of the mixture. This residue of steel or iron in the mixture has no significant effect in the present process or on the thermal conductivity of the resulting sistered body.
The liquid dispersion can be dried by a number of conventional techniques to remove or evaporate away the liquid and produce the present particulate mixture. If desired, drying can be carried out in air. Drying of a milled liquid dispersion in air causes the aluminum nitride to pick up oxygen and, when carried out under the same conditions, such oxygen pick up is reproducible or does not differ significantly. Also, if desired, the dispersion can be spray dried.
A solid carbonaceous organic material is prefer-by admixed in the form of a solution to coat the aluminum nitride particles. The solvent preferably is non-aqueous.
The wet mixture can then be treated to remove the solvent producing the present mixture. The solvent can be removed by a number of techniques such as by evaporation or by freeze drying, i.e. subliming off the solvent in vacuum from the frozen dispersion. In this way, a substantially uniform coating of the organic material on the aluminum nitride powder is obtained which on pyrolyzes produces a sub Stan-tidally uniform distribution of free carbon.
The present mixture is shaped into a compact in air, or includes exposing the aluminum nitride in the mixture to air. Shaping of the present mixture into a compact can be carried out by a number of techniques such as extrusion, injection molding, die pressing, isostatic pressing, slip casting, roll compaction or forming, or tape casting to produce the compact of desired shape. Any lubricants, binders or similar shaping aid materials used to aid shaping of the mixture should have no significant RD-16,434 5~6 deteriorating effect on the compact or the present resulting sistered body. Such shaping-aid materials are preferably of the type which evaporate away on heating at relatively low temperatures, preferably below 400C, leaving no significant residue. Preferably, after removal of the shaping aid materials, the compact has a porosity of less than 60% and more preferably less than 50% to promote densification during sistering.
If the compact contains carbonaceous organic material as a source of free carbon, it is heated at a temperature ranging from about 50C to about 1000C to pyrolyze, i.e. thermally decompose, the organic material completely producing the present free carbon and gaseous product of decomposition which vaporizes away. Thermal decomposition of the carbonaceous organic material is carried out, preferably in a vacuum or at ambient pressure, in a non oxidizing atmosphere. Preferably, the non oxidizing atmosphere in which thermal decomposition is carried out is selected from the group consisting of nitrogen, hydrogen, a noble gas such as argon and mixtures thereof, and more preferably it is nitrogen, or a mixture of at least about 25% by volume nitrogen and a gas selected from the group consisting of hydrogen, a noble gas such as argon and mixtures thereof. In one embodiment, it is a mixture of nitrogen and from about 1% by volume to about 5% by volume hydrogen.
The actual amount of free carbon introduced by pyrolyzes of the carbonaceous organic material can be determined by pyrolyzing the organic material alone and determining weight loss. preferably, thermal decomposition of the organic material in the present compact is done in the sistering furnace as the temperature is being raised to deoxidizing temperature, i.e. the temperature at which the RD-16,434 351~6 resulting free carbon reacts with the oxygen content of the Awn.
Alternately, in the present process, yttrium oxide can be provided by means of an yttrium oxide precursor. The term yttrium oxide precursor means any organic or inorganic compound which decomposes completely at a temperature below about 1200C to form yttrium oxide and by-product gas which vaporizes away leaving no contaminants in the sistered body which would be detrimental to the thermal conductivity.
Representative of the precursors of yttrium oxide useful in the present process is yttrium acetate, yttrium carbonate, yttrium oxalate, yttrium nitrate, yttrium sulfate and yttrium hydroxide.
If the compact contains a precursor for yttrium oxide, it is heated to a temperature up to about 1200~C to thermally decompose the precursor thereby providing yttrium oxide. Such thermal decomposition is carried out in a non oxidizing atmosphere, preferably in a vacuum or at ambient pressure, and preferably the atmosphere is selected from the group consisting of nitrogen, hydrogen, a noble gas such as argon and mixtures thereof. Preferably, it is nitrogen, or a mixture of at least about 25% by volume nitrogen and a gas selected from the group consisting of hydrogen, a noble gas such as argon and mixtures thereof.
In one embodiment, it is a mixture of nitrogen and from about 1% by volume to about 5% by volume hydrogen.
The present deoxidation of aluminum nitride with carbon, i.e. carbon-deoxidation, comprises heating the compact comprised of aluminum nitride, free carbon and yttrium oxide at deoxidation temperature to react the free carbon with at least a sufficient amount of the oxygen contained in the aluminum nitride to produce a deoxidized compact having a composition defined and encompassed by I; -33-Jo .

. .

RD-16, 434 ~;~35~6 polygon Pl~lKJ but not including lines KJ and Ply of Figures 3 or 4. This deoxidation with carbon is carried out at a temperature ranging from about 1350C to a temperature at which the pores of the compact remain open, i.e. a tempera-lure which is sufficient to deoxidize the compact but bullets pore closing temperature, generally up to about 1800C, and preferably, it is carried out at from about 1600DC to 1650C.
The carbon-deoxidation is carried out, preferably at ambient pressure, in a gaseous nitrogen-containing non oxidizing atmosphere which contains sufficient nitrogen to facilitate the deoxidation of the aluminum nitride. In accordance with the present invention, nitrogen is a wrier-Ed component for carrying out the deoxidation of the come pact. Preferably, the nitrogen-containing atmosphere is nitrogen, or it is a mixture of at least about 25% by volume of nitrogen and a gas selected from the group consisting of hydrogen, a noble gas such as argon, and mixtures thereof.
Also, preferably, the nitrogen-containing atmosphere is comprised of a mixture of nitrogen and hydrogen, especially a mixture containing up to about 5% by volume hydrogen.
The time required to carry out the present carbon-deoxidation of the compact is determinable empirically and depends largely on the thickness of the compact as well as the amount of free carbon it contains, i.e. the carbon-deoxidation time increases with increasing thickness of the compact and with increasing amounts of free carbon contained in the compact. Carbon-deoxidation can be carried out as the compact is being heated to sistering temperature provide Ed that the heating rate allows the deoxidation to recompleted while the pores of the copycat are open and such heating rate is determinable empirically. Also, to some extent, carbon deoxidation time depends on deoxidation "I

RD-16,43~
1~351~6 temperature, particle size and uniformity of the particulate mixture of the compact i.e. the higher the deoxidation temperature, the smaller the particle size and the more uniform the mixture, the shorter is deoxidation time. Also, to some extent, deoxidation time depends on its final position on the phase diagram, i.e. as line Ilk is approach-Ed deoxidation time increases. Typically, the carbon-deox-ideation time ranges from about hour to about 1.5 hours.
Preferably, the compact is deoxidized if. the sistering furnace by holding the compact at deoxidation temperature for the required time and then raising the temperature to sistering temperature. The deoxidation of the compact must be completed before sistering closes off pores in the compact preventing gaseous product from vapor-icing away and thereby preventing production of the presentsintered body.
In the present deoxidation with carbon, the free carbon reacts with the oxygen of the aluminum nitride producing carbon monoxide gas which vaporizes away. It is believed that the following deoxidation reaction occurs wherein the oxygen content of the aluminum nitride is given as Aye:

Al 0 + 3C + No 3C~( ) + Allen (2) In the deoxidation effected by carbon, gaseous carbon-cor.taining product is produced which vaporizes away thereby removing free carbon.
If the compact before deoxidation is heated at too fast a rate through the carbon-deoxidation temperature to - sistering temperature, and such too fast rate would depend largely on the composition of the compact and the amount of carbon it contains, the present carbon-deoxidation does not RD--16, 4 34 ~'~35~4~

occur, i.e. an insufficient amount of deoxidation occurs, and a significant amount of carbon is lost by reactions (3) and/or (PA).

C I Awn Alan (3) - C + 1/2 No con (PA) The specific amount of free carbon required to produce the present deoxidized compact can be determined by a number of techniques. It can be determined empirically.
Preferably, an initial approximate amount of carbon is lo calculated from Equation (2), that is the stoichiometric amount for carbon set forth in Equation (2), and using such approximate amount, the amount of carbon required in the present process to produce the present sistered body would require one or a few runs to determine if too much or too little carbon had been added. Specifically, this can be done by determining the porosity of the sistered body and by analyzing it for carbon and by X-ray diffraction analysis.
If the compact contains too much carbon, the resulting deoxidized compact will be difficult to stinter and will not produce the present sistered body having a porosity of less than about 10% by volume and preferably less than about 4%
by volume of the sistered body, or the sistered body will contain carbon in an excessive amount. If the compact contains too little carbon, X-ray diffraction analysis of the resulting sistered body will not show any YO-YO phase and that its composition is not defined or encompassed by the polygon PlNlKJ not including lines KJ and Ply of Figure 4.
The amount of free carbon used to carry out the present deoxidation should produce the present deoxidized RD-16,434 SLY

compact leaving no significant amount of carbon in any form, i.e. no amount of carbon in any form which would have a significantly deleterious effect on the sistered body. More specifically, no amount of carbon in any form should be left in the deoxidized compact which would prevent production of the present sistered body, i.e. any carbon content in the sistered body should be low enough so that the sistered body has a thermal conductivity greater than 1.00 W/cm-K at 25~C.
Generally, the present sistered body may contain carbon in some form in a trace amount, i.e. generally less than about .08% by weight, preferably in an amount of less than about .065% by weight, and more preferably less than about .04% by weight, and most preferably less than .03% by weight of the total weight of the sistered body.
A significant amount of carbon in any form remain-in in the sistered body significantly reduces its thermal conductivity. An amount of carbon in any form greater than about 0.065% by weight of the sistered body is likely to significantly decrease its thermal conductivity.
The present deoxidized compact is densified, i.e.
liquid-phase sistered, at a temperature which is a sistering temperature for the composition of the deoxidized compact to produce the present polycrystalline body having a porosity of less than about 10% by volume, and preferably less than about 4% by volume of the sistered body. For the present compositions defined and encompassed by polygon PlNlKJ of Figure 4 excluding lines KJ and Ply, this sistering tempera-lure generally is at least about 1860CC and generally ranges from about 1860C to about 2050C with the minimum sistering temperature increasing generally from about 1860C for a composition represented by a point next or nearest to point J to generally about 1960C for a composition represented by a point next to point K to about 1980~C at point No and less I, RD-16,434 1~35~46 than about 2000C for a composition next to point Pi of Figure 4. Minimum sistering temperature is dependent most strongly on composition and less strongly on particle size.
More specifically, in the present invention, for the present deoxidized compact having a constant particle size, the minimum sistering temperature occurs at a compost-lion represented by a point next to point J within the polygon PlNlKJ and such temperature increases as the combo-session moves away from point J toward any point on line KNlPl.
Specifically, the minimum sistering temperature is dependent largely on the composition (i.e., position in the Figure 4 phase diagram), the green density of the compact, i.e. the porosity of the compact after removal of shaping aid materials but before deoxidation, the particle size of aluminum nitride, and to a mush lesser extent the particle size of yttrium oxide and carbon. The minimum sistering temperature increases within the polygon PlNlKJ as the composition moves from next or nearest to point J to line KNlPl, as the green density of the compact decreases, and as the particle size of aluminum nitride, and to a much lesser extent, yttrium oxide and carbon increases. For example, for a composition represented by a point within polygon PlNlKJ of Figure 4 and nearest to point J, the minimum sistering temperature varies from about 1860~C for the particle size combination of aluminum nitride, yttrium oxide and carbon of about 5.0 mug 2.8 mug and 200 mug respectively, to about 1890C for the particle size combing anion of aluminum nitride, yttrium oxide and carbon of about 0.5 mug 0.5 m go and 20 mug respectively. Also, at point K, or a composition represented by a point nearest to point K within polygon PlNlKJ, the minimum sistering temper-azure varies from about 1960~C for the particle size `:
;

RD-16,434 ~35~

combination of Awn, Yo-yo and carbon of about 5.0 mug 2.8 mug and 200 mug respectively, to about 2000C for the particle size combination of Awn, Yo-yo and carbon of about 1.2 mug 0.6 mug and 20 mug respectively. Also, for example, at point No, the minimum sistering temperature for the particle size combination of Awn, Yo-yo and carbon of about 5.0 mug 2.8 mug and 200 mug respectively, is about 1980C.
To carry out the present liquid phase sistering, the present deoxidized compact contains sufficient equiva-lent percent of Y and 0 to form a sufficient amount of liquid phase at sistering temperature to density the carbon deoxidized compact to produce the present sistered body.
The present minimum densification, i.e. sistering, tempera-lure depends on the composition of the deoxidized compact. the amount of liquid phase it generates. Specifically, for a sistering temperature to be operable in the present invention, it must generate at least sufficient liquid phase in the particular composition of the deoxidized compact to carry out the present liquid phase sistering to produce the present product. For a given composition, the lower the sistering temperature, the smaller is the amount of liquid phase generated, i.e. densification becomes more difficult with decreasing sistering temperature. However, a sistering temperature higher than about generally 2050C provides no significant advantage.
In one embodiment of the present invention, the sistering temperature ranges from about 1910C to about 2050C, and in another embodiment from about 1965C to about 2050C, and in another embodiment from about 1970C to about 2050C, and in yet another embodiment from about 1950C to about 2000C, and still in another embodiment from about :

RD-16,434 1~;35146 1910C to about 1950C, to produce the present polycrystal-line body.
For compositions defined and encompassed by the polygon QTXJ excluding lines QJ and XJ of Figure 4, the sistering temperature ranges from about 1910C to about 2000~C, and the minimum sistering temperature is about l910~C to produce the present sistered body having pros-fly of less than about 2% by volume of the body.
The deoxidized compact is sistered, preferably at ambient pressure, in a gaseous nitrogen-containing nonoxi-dozing atmosphere which contains at least sufficient vitro-gun to prevent significant weight loss of aluminum nitride.
In accordance with the present invention, nitrogen is a necessary component of the sistering atmosphere to prevent any significant weight loss of Awn during sistering, and also to optimize the deoxidation treatment and to remove carbon. Significant weight loss of the aluminum nitride can vary depending on its surface area to volume ratio, i.e.
depending on the form of the body, for example, whether it is in the form of a thin or thick tape. As a result, generally, significant weight loss of aluminum nitride ranges from in excess of about 5% by weight to in excess of about 10% by weight of the aluminum nitride. Preferably, the nitrogen-containing atmosphere is nitrogen, or it is a mixture at least about 25% by volume nitrogen and a gas selected from the group consisting of hydrogen, a noble gas such as argon and mixtures thereof. Also, preferably, the nitrogen-containing atmosphere is comprised of a mixture of nitrogen and hydrogen, especially a mixture containing from about 1% by volume to about 5% by volume hydrogen.
Sistering time is determinable empirically.
Typically, sistering time ranges from about 40 minutes to about 90 minutes.

. -` ' .

i Z.35146 RD-16,434 In one embodiment, i.e. the composition defined by polygon PlNlKJ but not including lines Ilk, Ply and KJ of Figure 4, where the aluminum nitride in the carbon-deoxidiz-Ed compact contains oxygen, the yttrium oxide further deoxidizes the aluminum nitride by reacting with the oxygen to form YO-YO and Yo-yo, thus decreasing the amount of oxygen in the Awn lattice to produce the present sistered body having a phase composition comprised of Awn and a second phase mixture comprised of Yo-yo and YO-YO.
In another embodiment, i.e. line Ilk but excluding point K of Figure worry the aluminum nitride in the carbon-deoxidized compact contains oxygen in an amount significantly smaller than that of polygon PlNlKJ but not including lines Ilk, Ply and KJ of Figure 4, the resulting sistered body has a phase composition comprised of Awn and Yo-yo .
The present sistered polycrystalline body is a pressure less sistered ceramic body. By pressure less stinter-in herein it is meant the densification or consolidation of the deoxidized compact without the application of mechanical pressure into a ceramic body having a porosity of less than about 10% by volume, and preferably less than about 4% by volume.
The polycrystalline body of the present invention is liquid-phase sistered. I.e., it stinters due to the presence of a liquid phase, that is liquid at the sistering temperature and is rich in yttrium and oxygen and contains some aluminum and nitrogen. In the present polycrystalline body, the Awn grains have about the same dimensions in all directions, and are not elongated or disk shaped. General-lye the Awn in the present polycrystalline body has an average grain size ranging from about 1 micron to about 20 microns. An inter granular second phase of Yo-yo or a mixture 5~4~ ' of Yo-yo and Yule is present along some of the Awn grain boundaries. The morphology of the micro structure of the present sistered body indicates that this inter granular second phase was a liquid at the sistering temperature. As the composition approaches line KJ in Figure 4, the amount of liquid phase increases and the Awn grains in the present sistered body become more rounded and have a smoother surface. As the composition moves away from line KJ in Figure 4 and approaches point Pi, the amount of liquid phase decreases and the Awn grains in the present sistered body become less rounded and the corners of the grains become sharper.
The present sistered body has a porosity of less than about 10% by volume, and generally less than about 4%
by volume, of the sistered body. Preferably, the present sistered body has a porosity of less than about 2% and most preferably less than about 1% by volume of the sistered body. Any pores in the sistered body are fine sized, and generally they are loss than about 1 micron in diameter.
Porosity can be determined by standard metallographic procedures and by standard density measurements.
The present process is a control process for producing a sistered body of aluminum nitride having a thermal conductivity greater than 1.00 W/cm K at 25C, and preferably greater than 1.50 W/cm-K at 25C. Generally, the thermal conductivity of the present polycrystalline body is less than that of a high purity single crystal of aluminum nitride which is about 2.3 W/cm-K at 25C. If the same procedure and conditions are used throughout the present process, the resulting sistered body has a thermal conduct tivity and composition which is reproducible or does not differ significantly. Generally, thermal conductivity increases with a decrease in volume % of second phase, and I

RD-16,434 1 ~5~'~6 for a given composition with increase in sistering tempera-lure.
In the present process, aluminum nitride picks up oxygen in a controllable or substantially controllable manner. Specifically, if the same procedure and conditions are used in the present process, the amount of oxygen picked up by aluminum nitride is reproducible or does not differ significantly. Also, in contrast to yttrium, yttrium nitride and yttrium hydrides yttrium oxide does not pick up oxygen, or does not pick up any significant amount of oxygen, from air or other media in the present process.
More specifically, in the present process, yttrium oxide or the present precursor therefore does not pick up any amount of oxygen in any form from the air or other media which would have any significant effect on the controllability or reproducibility of the present process. Any oxygen which yttrium oxide might pick up in the present process is so small as to have no effect or no significant effect on the thermal conductivity or composition of the resulting stinter-Ed body.
Examples of calculations for equivalent % are as follows:
For a starting aluminum nitride powder weighing 89.0 grams measured as having 2.3 weight % oxygen, it is assumed that all of the oxygen is bound to Awn as Allah, and that the measured 2.3 weight % of oxygen is present as 4.89 weight % Aye so that the Awn powder is assumed to be comprised of 84.65 grams Awn and 4.35 grams Allah.
A mixture is formed comprised of 89.0 grams of the starting Awn powder, 4.72 grams of Yo-yo and 1.4 grams free carbon.

.

RD-16,434 ~.~3514~;

During processing, this Awn powder picks up additional oxygen by reactions similar to (4) and now contains 2.6 weight % oxygen.

2 Awn + 3H20 Aye + 2NH3 The resulting compact now is comprised of the following composition:

89.11 grams Awn powder containing 2.6 weight % oxygen, (84.19g Awn + 4.92g Allah), 4.72 grams Yo-yo and 1.4 grams carbon.
\

lo During deoxidation of the compact, all the carbon is assumed to react with Allah via reaction (5) Allah + 3C + No ' Allen + KIWI (5) In the present invention, the carbon will not reduce Yo-yo, but instead, reduces Allah.
15 After reaction (5) has gone to completion, the deoxidized compact now is comprised of the following combo-session which was calculated on the basis of Reaction (5):

88.34 grams Awn powder containing 0.5 weight % oxygen (87.38 grams Awn + 0.96 slams Allah) and 4.72 grams Yo-yo prom this weight composition, the composition in equivalent % can be calculated as follows:

. .

., :

5~6 RD-16,434 Wit (g) Moles Equivalents Awn 87.38 2.132 6.395 Aye 0.958 9.40 x 10 3 5.640 x 10 2 Yo-yo 4.72 2.090 x 10 2 0.125 TOTAL EQUIVALENTS = 6.577 V = Valence M = Moles = Wit MY
MY = molecular weight En = Equivalents En = M X V
Valences: Al + 3 Y + 3 En % Y in deoxidized compact =
nosy equivalents x 100% (6) nosy equivalents + nodal equivalents = 0.125 x 100% = 1.91%

6.577 Erg % O in deoxidized compact =
no. O e ~ivalents x 100% (7) no. O equivalents + noun equivalents .= 5.64 + 0-125 x 100% = 2.76% (~) 6.577 This deoxidized compact as well as the sistered body contains about 1.91 equivalent % Y and about 2.76 equivalent % Oxygen.

!` .

RD-16,434 I

To produce the present sistered body containing 2.0 equivalent % Y and 2.8 equivalent % O, i.e. comprised of 2 equivalent % Y, 98 equivalent % Al, I equivalent % O and 97.2 equivalent % N, using an Awn powder measured as having 2.3 weight % Oxygen (4.89 weight % AYE), the following calculations for weight % from equivalent % can be made:

100 grams = weight of Awn powder x grams = weight of YO-YO powder z grams = weight of Carbon powder Assume that during processing, the Awn powder picks up additional oxygen by reaction similar to (9) and in the compact before deoxidation now contains 2.6 weight %
oxygen (5.52 weight % AYE) and weighs 100.12 grams Allen + OWE ' AYE + 2N~3 (9) After processing, the compact can be considered as having the following composition:

Weight (g) Moles Equivalents Allen 2.308 6.923 AYE . 0.0542 0.325 YO-YO x 4.429 x 10 3x 0.02657x C z .0~333z During deoxidation, 3 moles of carbon reduce 1 mole of AYE and in the presence of No form 2 moles of Awn by the reaction:

Aye No Sal (lo) RD-16,434 1~5~

After deoxidation, all the carbon will have reacted and the compact can be considered as having the following composition:

Weight (g) Moles Equivalents Awn 94.59 + 2.275z 2.308 + 0.05551z 6.923 + 0.1665z Aye 5.53 - 2.830z 0.0542 - 0.02775z 0.325 - 0.1665z Yo-yo x 4.429 x 10 3 x 0.02657 x T = Total Equivalents - 7.248 + 0.02657 x Equivalent Fraction of Y = 0.02 = 0.02657 x (11) T
Equivalent Fraction of 0=0.028=0.325-0.1665z + 0.02657x (12) Solving Equations (11) and (12) for x and z:
x = 5.57 grams of Yo-yo powder z = 1.60 grams of free carbon A body in a form or shape useful as a substrate, i.e. in the form of a flat thin piece of uniform thickness, or having no significant difference in its thickness, usually referred to as a substrate or tape, may become non-flat, for example, warp, during sistering and the resulting sistered body may require a heat treatment after sistering to flatten it out and make it useful as a sub-striate. This non-flatness or warping is likely to occur in the sistering of a body in the form of a substrate or tape having a thickness of less than about .070 inch and can be eliminated by a flattening treatment, i.e. by heating the sistered body, i.e. substrate or tape, under a sufficient applied pressure at a temperature in the present sistering " .

RD-16,43~
Sue temperature range of from about 1860~C to about 2050C for a period of time determinable empirically, and allowing the sandwiched body to cool to below its sistering temperature, preferably to ambient or room temperature before recovering the resulting flat substrate or tape.
Specifically, in one embodiment of this flattening process, the non-flat substrate or tape is sandwiched between two plates and is separated from such plates by a thin layer of Awn powder, the sandwiched body is heated to its sistering temperature, i.e. a temperature which is a sistering temperature for the sandwiched sistered body, preferably in the same atmosphere used for sistering, under an applied pressure at least sufficient to flatten the body, generally at least about .03 psi, for a time period suffix client to flatten the sandwiched body, and then the sand-wicked body is allowed to cool to below its sistering temperature before it is recovered.
One embodiment for carrying out this flattening treatment of a sistered thin body or substrate tape comprise en sandwiching the sistered non-flat substrate or tape between two plates of a material which has no significant deleterious effect thereon such as molybdenum or tungsten, or an alloy containing at least about >30% by weight of tungsten or molybdenum. The sandwiched substrate or tape is separated from the plates by a thin layer, preferably a discontinuous coating, preferably a discontinuous monolayer, of aluminum nitride powder preferably just sufficient to prevent the body from sticking to the surfaces of the plates during the flattening heat treatment. The flattening pressure is determinable empirically and depends largely on the particular sistered body, the particular flattening temperature and flattening time period. The flattening treatment should have no significant deleterious effect on ROD- 1 6 , 43 us ~.~35146 the sistered body. A decrease in flattening temperature requires an increase in flattening pressure or flattening time. Generally, at a temperature ranging from about 1~60DC
to about 2050C, the applied flattening pressure ranges from about .03 psi to about 1.0 psi, preferably from about .06 psi to about .50 psi, and more preferably from about .10 psi to about .30 psi. Typically, for example, heating the sandwiched sistered body at the sistering temperature under a pressure of from about .03 psi to about .5 psi for 1 hour in nitrogen produces a flat body useful as a substrate, especially as a supporting substrate for a semiconductor such as a silicon chip.
The present invention makes it possible to fabric gate simple, complex and/or hollow shaped polycrystalline aluminum nitride ceramic articles directly. Specifically, the present sistered body can be produced in the form of a useful shaped article without machining or without any significant machining, such as a hollow shaped article for use as a container, a crucible, a thin walled tube, a long rod, a spherical body, a tape, substrate or carrier. It is useful as a sheath for temperature sensors. It is especial-lye useful as a substrate for a semiconductor such as a silicon chip. The dimensions of the present sistered body differ from those of the unsintered body, by the extent of shrinkage, i.e. densification, which occurs during stinter-in.
The present ceramic body has a number of uses. In the form of a thin flat piece of uniform thickness, or having no significant difference in its thickness, i.e. in the form of a substrate or tape, it is especially useful as packaging for integrated circuits and as a substrate for an integrated circuit, particularly as a substrate for a semi conducting So chip for use in computers.

,,, .. . .

1~5~6 RD-16,434 The invention is further illustrated by the following examples wherein the procedure was as follows, unless otherwise stated:
The starting aluminum nitride powder contained oxygen in an amount of less than 4% by weight.
The starting aluminum nitride powder was greater than 99% pure Awn exclusive of oxygen.
In Examples BAY 8B, PA and 9B of Table II and AYE
and 30B of Table III, the starting aluminum nitride powder 10 had a surface area of 3.84 mug (0.479 micron) and contained 2.10 wit% oxygen as determined by neutron activation anal-skis.
In the remaining examples of Table II, the start-in aluminum nitride powder had a surface area of 4.9~ mug 15 (0.371 micron) and contained 2.25 wit% oxygen as determined by neutron activation analysis.
In all of the examples of Table II and Examples AYE and 30B of Table III, the Yo-yo powder, before any mixing, i.e. as received, had a surface area of about 2.75 mug The carbon used in the examples of Tables II and III was graphite and except as indicated in Table III, it had, before any mixing, a specific surface area of 200 mug (0.017 micron) as listed by the vendor.
Non-aqueous Hutton was used to carry out the mixing, i.e. milling, of the powders in all of the examples of Tables II and III.
In all of the examples of Tables II and III, the milling media was hot pressed aluminum nitride in the approximate form of cubes or rectangles having a density of about 100%.
In Examples 8-9, 11 and 15 of Table II and all of the examples of Table III, the Awn, Yo-yo or yttrium . ~^' RD-16,434 S ~16 carbonate and carbon powders were immersed in non-aqueous Hutton containing oleic acid in an amount of about 0.7% by weight of the aluminum nitride powder in a plastic jar and vibratory milled in the closed jar at room temperature for a period of time which varied from about 15 hours to about 21 hours producing the given powder mixture. In the remaining examples of Table II, no oleic acid was used, and the Awn, Yo-yo and carbon powders were immersed in non-agueous Hutton in a plastic jar and vibratory milled in the closed jar at room temperature for a period of time which varied from about 18 hours to about 68 hours depending on the mixture producing the given powder mixture.
In all of the Examples of Tables II and III, the milled liquid dispersion of the given powder mixture was dried in air at ambient pressure under a heat lamp for about 20 minutes and during such drying, the mixture picked up oxygen from the air.
In all of the Examples of Tables II and III, the dried milled powder mixture was die pressed at 5 Kpsi in air at room temperature to produce a compact having a density of roughly 55% of its theoretical density.
In those examples of Tables II and III wherein the sistered body is given as being of A size, the compacts were in the form of a disk, in those examples wherein the stinter-Ed body is given as being of C size, the compacts were in the form of a bar, and in those examples wherein the stinter-Ed body is given as being of D size, the compacts were in the form of a substrate which was a thin flat piece, like a tape, of uniform thickness, or of a thickness which did not differ significantly.
In all of the examples of tables II and III, except Examples 17-20, the given powder mixture as well as the compact formed therefrom had a composition wherein the RD-16,434 ~;~3S~46 equivalent of yttrium and aluminum ranged between points K
and Pi of Figure 4.
In Examples 17-20 of Table II, the given powder mixture as well as the compact formed therefrom had a composition wherein the equivalent % of yttrium and aluminum were outside the range of from point K to point Pi of Figure 4.
The equivalent % composition of Y, Al, 0 and N of the compacts of all of the Examples of Tables II and III, i.e. before deoxidation, was outside the composition defined and encompassed by polygon PlNlKJ of Figure 4.
In all of the examples of Tables II and III, the aluminum nitride in the compact before deoxidation contained oxygen in an amount ranging from greater than about 1.40% by weight to less than about 4.50% by weight of the aluminum nitride.
In each of the examples of Tables II and III, one compact was formed from the given powder mixture and was given the heat treatment shown in Tables II and III. Also, the examples in Tables II and III having the same number but including the letters A or B indicate that they were carried out in an identical manner, i.e. the powder mixtures was prepared and formed into two compacts in the same manner and the two compacts were heat treated under identical condo-lions, i.e. the two compacts were placed side by side in the furnace and given the same heat treatment simultaneously, and these examples numbered with an A or B may be referred to herein by their number only.
In all of the examples of Tables II and III, the same atmosphere was used to carry out the deoxidation of the compacts as was used to carry out the sistering of the deoxidized compact except that the atmosphere to carry out the deoxidization was fed into the furnace at a rate of 1 ,- ..

RD-16,434 ~Z~5~6 SKIFF to promote removal of the gases produced by dockside-lion, and the flow rate during sistering was less than about .1 SKIFF.
The atmosphere during all of the heat treatment in all of the examples in Tables II and III was at ambient pressure which was atmospheric or about atmospheric pros-sure.
The furnace was a molybdenum heat element furnace.
The compacts were heated in the furnace to the given deoxidation temperature at the rate of about 100C per minute and then to the given sistering temperature at the rate of about 50C per minute.
The sistering atmosphere was at ambient pressure, i.e. atmospheric or about atmospheric pressure.
At the completion of heat treatment, the samples were furnace-cooled to about room temperature.
All of the examples of Tables II and III were carried out in substantially the same manner except as indicated in Tables II and III and except as indicated herein.
Carbon content of the sistered body was determined by a standard chemical analysis technique.
Based on the predetermined oxygen content of the starting Awn powders and the measured compositions of the resulting sistered bodies, as well as other experiments, it was calculated or estimated that in every example in Table II, the aluminum nitride in the compact before deoxidation had an oxygen content of about 0.3% by weight higher than that of the starting aluminum nitride powder.
Measured oxygen content was determined by neutron activation analysis and is given in wit%, which is % by weight of the sistered body.

' ; -"'"

RD-16,434 Lucille _ -In Tables II and III, in those examples where the oxygen content of the sistered body was measured, the equivalent % composition of the sistered body was calculated from the starting powder composition and from the given measured oxygen content of the sistered body. The Y, Al, N
and oxygen are assumed to have their conventional valences of: +3, +3, -3, -2, respectively. In the sistered bodies, the amount of Y and Al was assumed to be the same as that in the starting powder. During processing, the amount of oxygen gain and nitrogen loss was assumed to have occurred by the overall reaction:

2 Awn 3/202 Aye 2 (13) During deoxidation, the amount of oxygen loss and nitrogen gain was assumed to have occurred by the overall lo reaction:

Aye 3C No (14) The nitrogen content of the sistered body was determined by knowing the initial oxygen content of the starting aluminum nitride powder and measuring the oxygen content of the sistered body and assuming that reactions 13 and 14 have occurred.
In Tables II and III, an approximation sign is used in front of the equivalent percent oxygen for sistered bodies whose oxygen content was not measured. Since exam-pies having the same number but including the letter A or Were carried out under the same conditions to produce the given pair of sistered bodies simultaneously, this pair of sistered bodies will have the same oxygen content, and therefore, the oxygen content of one such sistered body is Y ..

RD-16,434 ~35146 assumed to be the same as the measured oxygen content of the other such sistered body. Also, in Table II, the oxygen content of the sistered body of Example 3 (Sample 88Dl) is assumed not to differ significantly from the oxygen content of Example lo (Sample Allah). Also, the sistered body of Example 21 (Sample 92C) is assumed to have an oxygen content which does not differ significantly from that of Example 6 (Sample Allah).
The equivalent percent oxygen content of the sistered body of Example 8B (Sample AYE) and of example 9B
(Sample clue) was calculated from the equation:

0 = (1.34R + 1.81) Y
1.88 where 0 = equivalent percent oxygen Y = equivalent percent yttrium R = v/o YO-YO
v/o YO-YO + v/o Yo-yo The equivalent percent oxygen contents of the sistered bodies of Examples PA and 8B are assumed to be the same.
The equivalent percent oxygen contents of the sistered bodies of Examples PA and 9B are assumed to be the same.
The equivalent % oxygen content of the sistered bodies of Examples 22-25, 27, 29B and 26B (Samples AYE, AYE, AYE, AYE, AYE, 131Dl and 170B) was calculated from the equation 0 = (2.91R + 3.~32) Y
3.86 .

. . .

RD-16,434 1~351~6 The equivalent % oxygen content of the sistered bodies in Examples 29 and 31 (Samples AYE and AYE) was estimated from the X-ray diffraction analysis data. The equivalent %
oxygen content of the sistered bodies of examples 26 and 32 (Samples AYE and 175B) was assumed to be the same as that of Examples 27 and 31 (170B and AYE), respectively.
Weight loss in Tables II and III is the difference between the weight of the compact after die pressing and the resulting sistered body.
Density of the sistered body was determined by the Archimedes method.
Porosity in % by volume of the sistered body was determined by knowing the theoretical density of the stinter-Ed body on the basis of its composition and comparing that to the density measured using the following equation:

porosity - (1 - measured density _) 100% (15) theoretical density Phase composition of the sistered body was deter-mined by optical microscopy and X-ray diffraction analysis, and each sistered body was comprised in % by volume of the sistered body of aluminum nitride phase and the given volume % of the given second phases. The X-ray diffraction anal-skis for volume % of each second phase is accurate to about + 20% of the given value.
The thermal conductivity of the sistered body of the examples was measured at 25C by a steady state heat-flow method using a rod shaped sample ~0.4 cm x 0.4 cm x 2.2 cm sectioned from the sistered body. This method was originally devised by A. Regret in 1888 and is described in an article by G. A. Slack in the "Encyclopedic Dictionary of Physics", Ed. by J. Thewlis, Pergamon, Oxford, 1961. In I

...... . .

~.~35~6 RD-16,434 this technique the sample is placed inside a high-vacuum chamber, heat is supplied at one end by an electrical heater, and the temperatures are measured with fine-wire thermocouples. The sample is surrounded by a guard Solon-don. The absolute accuracy is about 3% and the repeat-ability is about t 1%. As a comparison, the thermal con-ductility of an Aye single crystal was measured with a similar apparatus to be 0.44 W/cm-K at about 22C.
In Tables II and III, the size of the resulting sistered body is given as A, C or D. The body of A size was in the form of a disk about .17 inch in thickness and about .32 inch in diameter. The body of C size was in the shape of a bar measuring about 0.16 inch x 0.16 inch x 1.7 inches.
The body of D size was in the form of a substrate, i.e. a thin piece of uniform thickness, or of no significant difference in thickness, having a diameter of about 1.5 inch and a thickness of about .044 inch.
In all of the examples of Tables II and III, the compacts were placed on a molybdenum plate and then given the heat treatment shown in Tables II and III.
In all of the Examples of Tables II and III
wherein the sistered body was of C size or of D size, the starting compact was separated from the molybdenum plate by a thin discontinuous layer of Awn powder.
The sistered body of Example 21 exhibited some non-flatness, i.e. exhibited some warping, and was subjected to a flattening treatment. Specifically, the sistered body produced in Example 21 was sandwiched between a pair of molybdenum plates. The sandwiched sistered body was swooper-ted from the molybdenum plates by a thin discontinuous coating or monolayer of aluminum nitride powder which was just sufficient to prevent sticking of the sistered body to the plates during the flattening treatment period. The top .

RD-16,434 ~5~46 molybdenum plate exerted a pressure of about 0.11 psi on the sistered body. The sandwiched sistered body was heated in nitrogen, i.e. the same atmosphere used to stinter it, to about l900~C where it was held for about 1 hour and then furnace cooled to about room temperature. The resulting sistered body was flat and was of uniform thickness, i.e.
its thickness did not differ significantly. This flat sistered body would be useful as a supporting substrate for a semiconductor such as a silicon chip.

1.98 grams of Yo-yo powder and 0.443 grams of graphite powder were added to lo grams of aluminum nitride powder and the mixture, along with aluminum nitride milling media, was immersed in Nancy Hutton in a plastic jar and vibratory milled in the closed jar at room temperature for about 68 hours. The resulting dispersion was dried in air under a heat lamp for about 20 minutes and during such drying, the aluminum nitride picked up oxygen from the air.
During milling, the mixture picked up 0.370 gram Awn due to wear of the Awn milting media.
Equivalent portions of the resulting dried mixture were die pressed producing compacts.
Two of the compacts were placed side by side on a molybdenum plate.
US The compacts were heated in nitrogen to 1600C
where they were held for 1/2 hour, then the temperature was raised to 1750C where it was held for 1/2 hour, and then the temperature was raised to 2000~C where it was held for 1 hour.
This example is shown as Examples lo and lo in Table II. Specifically, one of the sistered bodies, Example I .

.....

-.

RD-16,434 isle lo, had a measured oxygen content of owe by weight of the body and contained carbon in an amount of 0.021% by weight of the sistered body. Also, it had a phase composition comprised of Awn, 0.7% by volume of the body of YIN phase, 0.6% by volume of the body of YO-YO and 5.8% by volume of the body of Yo-yo. Also, it had an equivalent % composition comprised of 3.73% 0, (100~-3.73%) or 96.27% N, 3.80% Y and (100%-3.80%) or 96.20% Al.

The compacts used in Examples PA, 2B, and 3 were produced in Example 1. In Examples PA and 2B, the two compacts were heated at a rate of about l90DC per minute directly to the sistering temperature of 2000C where they were held for 1 hour.
In Example 3, one compact was heated to 1660C
where it was held for 1 hour and then the temperature was raised to 1940C where it was held for 1 hour.
In Example 5, i.e. PA and 5B, the two compacts were heated to 1600C where they were held for 1 hour and 20 then to 1900C where they were held for 1 hour.
In Example 6, one compact was heated to 1600C
where it was held for 1 hour and then the temperature was raised to l900DC where it was held for 1 hour.
Examples PA and 4B, and lo and lob were carried out in the same manner as Examples lo and lo except as indicated herein and except as shown in Table II.
In Example B, i.e. PA and 8B, the two compacts were heated to 1500C where they were held for 1/2 hour, then the temperature was raised to 1600C where it was held 30 for 1 hour, and then the temperature was raised to 1900C
where it was held for 1 hour.

RD-16,434 ~35146 In Example 9, i.e. PA and 9B, the two compacts were heated to 1500C where they were held for 1/2 hour, then the temperature was raised to 1600C where it was held for 1 hour and then it was raised to 1950C where it was held for 1 hour.
Examples 7, 11 and 21 were carried out in the same manner as Example 6 except as indicated herein and except as shown in Table II.
Examples 13-20, i.e. AYE and B to AYE and B, were carried out in the same manner as Example 5, i.e. PA and B, except as indicated herein and except as shown in Table II.
.

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> _ _ o`

r ¦ O 1" N N n o o -- o o o o o u '?~ ¦ O o N N
> > 0 Z I ,- I , , , , , , , , , o o o O
Kiwi V I I N I V V V V N N -- N N
O eye---U ¦ I N I N _ N N O I 0 I
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r ,~, ~Z35~46 RD-16,434 Examples PA, 53, 6, PA, 8B, PA, 9B, loan lob 11, AYE, 12B, AYE, 14B, and 21 illustrate the present invention, and the sistered body produced in these examples is useful for packaging of integrated circuits as well as for use as a substrate or carrier for a semiconductor such as a silicon chip.
In Examples lay lo and 3, too much free carbon was added to the powder mixture which caused too much dockside-lion of the aluminum nitride producing sistered bodies which had compositions slightly outside polygon PlNlKJ of Figure 4 and slightly below line NO. However, Example 3 does thus-irate the operability of 1940C as a sistering temperature in this composition area for aluminum nitride powder having a specific surface area of 4.96 mug In Examples PA and 2B, the rate at which the compacts were heated to 2000C was insufficient to deoxidize the compacts before sistering as shown by the large amount of carbon remaining in the sistered body of Example 2B.
A comparison of Examples PA and 4B with Examples lo and lo shows that even though more free carbon was added to the powder mixture of Examples PA and 4B, the resulting sistered bodies had almost the same composition. This shows that with increasing amounts of free carbon in the powder mixture, the compositions of the resulting sistered bodies do not get significantly below line NO of Figure 4.
Examples PA and SUB illustrate the present invent lion. The sistered bodies of Examples PA and 5B have the same composition, the same porosity and the same thermal conductivity. Based on a comparison of Examples PA and 5B
with Example PA which has a very similar composition, and based on other work, it is known that the sistered bodies of Examples PA and 5B have a thermal conductivity greater than 1.50 W/cm-K at 25C, i.e. approximately 1.68 W/cm-K at 25C.

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X35~46 - -Example 6 illustrates the present invention.
Based on a comparison of Examples 6 and BY which do not differ significantly in composition, and based on other work, it is known that the sistered body of Example 6 has a thermal conductivity greater than 1.50 W/cm-K at 25C, i.e.
approximately 1.72 W/cm-K at 25C.
Example 7 illustrates that even though there was an extensive deoxidation step carried out, the use of the hydrogen atmosphere during deoxidation and sistering result-Ed in a sistered body which contained an excessive amount of carbon, and based on other work, it is known that this sistered body containing 0.3% carbon has a thermal conduct tivity below l.00 W/cm-K at 25C. Also, the hydrogen atmosphere in Example 7 caused an excessive amount of weight loss.
Examples PA and 8B illustrate the present invent lion. The sistered bodies of Examples PA and By have the same composition, the same porosity and the same thermal conductivity.
Examples PA and 9B illustrate the present invent lion. The sistered bodies of Examples PA and 9B have the same composition, the same porosity and the same thermal conductivity. A comparison of Examples PA and PA shows that the higher sistering temperature in Example PA produced a sistered body with a higher thermal conductivity.
Based on other work and a comparison of Examples loan lob and if with Examples PA and PA, it is known that the sistered bodies of Examples lo and B and if would have a thermal conductivity greater than 1.00 W/cm-K at 25DC.
Examples lo and 11 of Table II, and Example 29 of Table III illustrate the present invention even though there was a small amount of YIN phase formed in the sistered body.
Specifically, sectioning of the sistered body of these ~5146 RD-16,434 examples showed that this ON phase was located only in the center of the body, i.e. the YIN phase was black and was surrounded by the present composition which was tan. The formation of this YIN phase was due to the thickness of the sistered body and its composition, and it is caused by an oxygen gradient. Specifically, from the center of the sistered body the concentration of oxygen increases by a small amount and the concentration of nitrogen decreases by a small amount occasionally resulting in the formation of a small amount of YIN phase in the center of the body when it has a composition in the polygon PlNlKJ of Figure 4, which is close to line Ilk or on line Ilk.
Examples AYE and 12B illustrate the present invention. The sistered bodies of Examples AYE and 12B have the same composition, the same porosity and the same thermal conductivity. Based on a comparison of Examples AYE and 12B
with Example BAY and based on other work, it is known that the sistered bodies of Examples AYE and 12B have a thermal conductivity greater than 1.50 W/cm-K at 25~C, i.e. approx-irately greater than 1.72 Wok at 25~C.
In Examples AYE and 13B too much free carbon was added to the powder mixture which caused too much dockside-lion of the aluminum nitride producing sistered bodies with a composition outside polygon PlNlKJ below line NlPl in Figure 4 which is a composition area difficult to stinter as illustrated by the resulting high porosity of these sistered bodies.
The composition of the sistered bodies of Examples AYE and B is within experimental error of lying within polygon PlNlKJ. Based on other work and a comparison of Examples AYE and B with Examples PA and PA, it is known that the sistered bodies of Examples AYE and B would have a thermal conductivity greater than 1.00 W/cm-K at 25C.

I' RD-16,434 ~.~35~46 The equivalent % composition of the sistered bodies of Examples 15-20 fell outside polygon PlNlKJ of Figure 4 and specifically they fell below line NlPl of Figure 4. The sistered bodies of Examples 15-20 had a porosity higher than 10% by volume of the body which thus-trades the difficulty of sistering in this composition area below line NlPl of Figure 4.
Example 21 illustrates the present invention. The sistered body of Example 21 does not differ significantly in composition and porosity from the sistered body of Example 6. Also, based on a comparison of Example 21 with Example PA, and based on other work, it is known that the sistered body of Example 21 has a thermal conductivity greater than 1.50 W/cm-K at 25C, i.e. approximately 1.72 W/cm-K at 25C.
Table III shows additional examples. Specifically-lye Table III shows the composition of the powder mixture, i.e. powders added, in each example as well as the specific surface area of some of the powders added.
The examples in Table III were carried out in substantially the same manner as disclosed for Example 6 or as disclosed for Example PA and B except as shown in Table III or as noted herein.

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So Example 29 of Table III illustrates the present invention. Based on other work and especially a comparison of Examples 29 and AYE, it is known that the sistered body of Example 29 would have a thermal conductivity greater than 1.00 W/cm.K at 25C. The sistered body produced in Example 29 would be useful for packaging of integrated circuits as well as for use as substrates for semiconductors such as a silicon chip.
In each of the examples of Table III, except Example 29, insufficient carbon was added to the powder mixture thereby resulting in a deoxidized compact and a sistered body having a composition outside the polygon PlNlKJ of Figure 4. However, Examples 22-25 illustrate the operability of relatively coarse powders for these compositions to produce sistered bodies having a porosity of less than 10~ by volume. Examples 26-and 27 illustrate that for this composition and powders of relatively coarse particle size, increasing the sistering temperature significantly decreased the porosity of the resulting sistered body. Example 28 illustrates the use of yttrium carbonate as a precursor for yttrium oxide to produce a sistered body with low porosity. Examples AYE and B illustrate the operability of an atmosphere comprised of a mixture of hydrogen and 25% by volume nitrogen. Examples 31 and 32 illustrate that for this composition and particle size combination, sistering could not be effected to produce a sistered body having a porosity of less than about 10% by volume.
Reference is made to U.S. Patent 4,478,785 entitled HIGH THERMAL CONDUCTIVITY ALUMINUM NITRIDE
CERAMIC BODY issued October 23, 1984 in the names of I. C. Huseby and C. F. Bobik and assigned to the assignee hereof which discloses a process comprising .

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forming a mixture comprised of aluminum nitride powder and free carbon wherein the aluminum nitride has a predetermined oxygen content higher than about 0.8% by weight and wherein the amount of free carbon reacts with such oxygen content to produce a deoxidized powder or compact having an oxygen content ranging from greater than about 0.35~ by weight to about 1.1 by weight and which is at least 20~ by weight lower than the predetermined oxygen content, heating the mixture or a compact thereof to react the carbon and oxygen producing the deoxidized aluminum nitride, and sistering a compact of the deoxidized aluminum nitride producing a ceramic body having a density greater than 85% of theoretical and a thermal conductivity greater than 0.5 W/cm~K at 22C.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for producing a sintered polycrys-talline aluminum nitride ceramic body having a composition defined and encompassed by polygon PINIKJ but not including lines KJ and PIJ of Figure 4, a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm?K at 25°C which comprises the steps:
(a) forming a mixture comprised of an oxygen-contain-ing aluminum nitride powder, yttrium oxide, and free carbon, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges between points K and Pl of Figure 4, said yttrium ranging from greater than about 0.35 equivalent % to less than about 4.4 equivalent %, said aluminum ranging from greater than about 95.6 equivalent %
to less than about 99.65 equivalent %, said mixture and said compact having an equivalent % composition of Y, Al, O and N
outside the composition defined and encompassed by polygon PINIKJ of Figure 4, (b) heating said compact in a nitrogen-containing nonoxidizing atmosphere at a temperature ranging from about 1350°C to a temperature sufficient to deoxidize the compact but below its pore closing temperature reacting said free carbon with oxygen contained in said aluminum nitride producing a deoxidized compact, said deoxidized compact having a composition wherein the equivalent % of Al, Y, O
and N is defined and encompassed by polygon PINIKJ but not including lines KJ and PIJ of Figure 4, said free carbon being in an amount which produces said deoxidized compact, and (c) sintering said deoxidized compact in a nitrogen-containing nonoxidizing atmosphere at a temperature of at least about 1860°C producing said polycrystalline body.

2. The process according to claim 1 wherein said nitrogen-containing atmosphere in step (b) contains suffi-cient nitrogen to facilitate deoxidation of the aluminum nitride to produce said sintered body.

3. The process according to claim 1 wherein said nitrogen-containing atmosphere in step (c) contains suffi-cient nitrogen to prevent significant weight loss of said aluminum nitride.

4. The process according to claim 1 wherein said process is carried out at ambient pressure.

5. The process according to claim 1 wherein the aluminum nitride in said compact in step (a) before said deoxidation of step (b) contains oxygen in an amount ranging from greater than about 0.6% by weight to less than about 4.5% by weight of said aluminum nitride.

6. The process according to claim l wherein said aluminum nitride in step (a) has a specific surface area ranging up to about 10 m2/g and said free carbon has a specific surface area greater than about 10 m2/g.

7. The process according to claim 1 wherein said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges between points K
and P of Figure 4, said yttrium ranging from greater than about 0.55 equivalent % to less than about 4.4 equivalent %, said aluminum ranging from greater than about 95.6 equiva-lent % to less than about 99.45 equivalent %, and wherein said sintered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, O
and N is defined and encompassed by polygon PONKJ but not including lines KJ and PJ of Figure 4.

8. The process according to claim 1 wherein said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges from point N up to point P1 of Figure 4, said yttrium ranging from greater about 0.35 equivalent % to about 2.9 equivalent %, said aluminum ranging from about 97.1 equivalent % to less than about 99.65 equivalent %, and wherein said sintered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, O and N is defined and encompassed by polygon PININOP but not including line PIP of Figure 4, and said sintering temperature is at least about 1900°C.

9. The process according to claim 1 wherein said free carbon has a specific surface area greater than about 100 m2/g, said aluminum nitride powder in said mixture has a specific surface area ranging from about 3.4 m2/g to about 6.0 m2/g, wherein said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges between points K and P of Figure 4, said yttrium ranging from greater than about 0.55 equivalent % to less than about 4.4 equivalent %, said aluminum ranging from greater than about 95.6 equivalent % to less than about 99.45 equivalent %, said sintering atmosphere is nitrogen, said sintering temperature is from about 1965°C to about 2050°C, said sintered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, O and N is defined and encompassed by polygon PONKJ
but does not include lines NK, KJ and PJ of Figure 4, and said sintered body has a porosity of less than about 2% by volume of said body and has a thermal conductivity greater than 1.67 W/cm?K at 25°C.

10. The process according to claim 1 wherein said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges from point Nl up to point K of Figure 4, said yttrium ranging from about 1.9 equivalent % to less than about 4.4 equivalent %, said aluminum ranging from greater than about 95.6 equivalent %
to about 98.1 equivalent %, and wherein said sintered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, O and N is defined by line NIK but not including point K of Figure 4, and said sintering temperature is at least about 1960°C.

11. A process for producing a sintered polycrys-talline aluminum nitride ceramic body having a composition defined and encompassed by polygon QTXJ but not including lines QJ and XJ of Figure 4, a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.50 W/cm?K at 25°C which comprises the steps:
(a) forming a mixture comprised of an oxygen-containing aluminum nitride powder, yttrium oxide, and free carbon, said free carbon having a specific surface area greater than about 100 m2/g, the aluminum nitride powder in said mixture having a specific surface area ranging from about 3.4 m2/g to about 6.0 m2/g, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges from point X up to point Q of Figure 4, said yttrium in said compact ranging from greater than about 0.8 equivalent % to about 3.2 equivalent %, said aluminum in said compact ranging from about 96.8 equivalent % to less than about 99.2 equivalent %, said compact having an equivalent % composition of Y, Al, O and N outside the composition defined and encompassed by polygon PINIKJ of Figure 4, the aluminum nitride in said compact containing oxygen in an amount ranging from greater than about 1.40% by weight to less than about 4.50% by weight of said aluminum nitride, (b) heating said compact at ambient pressure in a nitrogen-containing nonoxidizing atmosphere containing at least about 25% by volume of nitrogen at a temperature ranging from about 1350°C to a temperature sufficient to deoxidize the compact but below its pore closing temperature thereby reacting said free carbon with oxygen contained in said aluminum nitride producing a deoxidized compact, said deoxidized compact having a composition wherein the equiva-lent % of Al, Y, O and N is defined and encompassed by polygon QTXJ but not including lines QJ and XJ of Figure 4, the aluminum nitride in said compact before said deoxidation by said carbon having an oxygen content ranging from greater than about 1.40% by weight to less than about 4.50% by weight of said aluminum nitride, said free carbon being in an amount which produces said deoxidized compact, and (c) sintering said deoxidized compact at ambient pressure in a nitrogen-containing nonoxidizing atmosphere containing at least about 25% by volume nitrogen at a temperature ranging from about 1910°C to about 2000°C
producing said polycrystalline body.

12. The process according to claim 11 wherein the sintering temperature ranges from about 1910°C to about 1950°C, said aluminum nitride powder in said mixture has a specific surface area ranging from about 3.7 m2/g to about 6.0 m2/g, and said sintered body has a porosity of less than about 1% by volume of said body.

13. The process according to claim 11 wherein the sintering temperature ranges from about 1950°C to about 2000°C, and said sintered body has a porosity of less than about 1% by volume of said body and a thermal conductivity greater than about 1.67 W/cm?K at 25°C.

14. A process for producing a sintered polycrys-talline aluminum nitride ceramic body having a composition defined and encompassed by polygon P1N1KJ but not including lines KJ and P1J of Figure 4, a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm?K at 25°C which comprises the steps:
(a) forming a mixture comprised of aluminum nitride powder, yttrium oxide or precursor therefor, and a carbona-ceous additive selected from the group consisting of free carbon, a carbonaceous organic material and mixtures there-of, said carbonaceous organic material thermally decomposing at a temperature ranging from about 50°C to about 1000°C to free carbon and gaseous product of decomposition which vaporizes away, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges between points K
and P1 of Figure 4, said yttrium ranging from greater than about 0.35 equivalent % to less than about 4.4 equivalent %, said aluminum ranging from greater than about 95.6 equiva-lent % to less than about 99.65 equivalent % aluminum, said compact having an equivalent % composition of Y, Al, O and N

outside the composition defined and encompassed by polygon PINIKJ of Figure 4, (b) heating said compact in a nonoxidizing atmosphere at a temperature up to about 1200°C thereby providing yttrium oxide and free carbon, (c) heating said compact in a nitrogen-containing nonoxidizing atmosphere at a temperature ranging from about 1350°C to a temperature sufficient to deoxidize the compact but below its pore closing temperature reacting said free carbon with oxygen contained in said aluminum nitride producing a deoxidized compact, said deoxidized compact having a composition wherein the equivalent % of Al, Y, O
and N is defined and encompassed by polygon PINIKJ but not including lines KJ and PIJ of Figure 4, said free carbon being in an amount which produces said deoxidized compact, and (d) sintering said deoxidized compact in a nitrogen-containing nonoxidizing atmosphere of at least about 1860°C
producing said polycrystalline body.

15. The process according to claim 14 wherein said nitrogen-containing atmosphere in step (c) contains sufficient nitrogen to facilitate deoxidation of the alumi-num nitride to produce said sintered body.

16. The process according to claim 14 wherein said nitrogen-containing atmosphere in step (d) contains sufficient nitrogen to prevent significant weight loss of said aluminum nitride.

17. The process according to claim 14 wherein said process is carried out at ambient pressure.

18. The process according to claim 14 wherein the aluminum nitride in said compact in step (a) before said deoxidation of step (c) contains oxygen in an amount ranging from greater than about 0.6% by weight to less than about 4.5% by weight of said aluminum nitride.

19. The process according to claim 14 wherein said aluminum nitride in step (a) has a specific surface area ranging up to about 10 m2/g and said free carbon has a specific surface area greater than about 10 m2/g.

20. The process according to claim 14 wherein said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges between points K
and P of Figure 4, said yttrium ranging from greater than about 0.55 equivalent % to less than about 4.4 equivalent %, said aluminum ranging from greater than about 95.6 equiva-lent % to less than about 99.45 equivalent %, and wherein said sintered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, O
and N is defined and encompassed by polygon PONKJ but not including lines KJ and PJ of Figure 4.

21. The process according to claim 14 wherein said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges from point N up to point Pl of Figure 4, said yttrium ranging from greater than about 0.35 equivalent % to about 2.9 equivalent %, said aluminum ranging from about 97.1 equivalent % to less than about 99.65 equivalent %, and wherein said sintered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, O and N is defined and encompassed by polygon PININOP but not including line P1P of Figure 4, and said sintering temperature is at least about 1900°C.

22. The process according to claim 14 wherein said free carbon has a specific surface area greater than about 100 m2/g, said aluminum nitride powder in said mixture has a specific surface area ranging from about 3.4 m2/g to about 6.0 m2/g, wherein said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges between points K and P of Figure 4, said yttrium ranging from greater than about 0.55 equivalent % to less than about 4.4 equivalent %, said aluminum ranging from greater than about 95.6 equivalent % to less than about 99.45 equivalent %, said sintering atmosphere is nitrogen, said sintering temperature is from about 1965°C to about 2050°C, said sintered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, O and N is defined and encompassed by polygon PONKJ
but does not include lines NK, KJ and PJ of Figure 4, and said sintered body has a porosity of less than about 2% by volume of said body and has a thermal conductivity greater than 1.67 W/cm?K at 25°C.

23. The process according to claim 14 wherein said mixture and said compact have a composition wherein the equivalent % of yttrium and aluminum ranges from point N1 up to point K of Figure 4, said yttrium ranging from about 1.9 equivalent % to less than about 4.4 equivalent %, said aluminum ranging from greater than about 95.6 equivalent %
to about 98.1 equivalent %, and wherein said sintered body and said deoxidized compact are comprised of a composition wherein the equivalent percent of Al, Y, O and N is defined by line NIK but not including point K of Figure 4, and said sintering temperature is at least about 1960°C.

24. A process for producing a sintered polycrys-talline aluminum nitride ceramic body having a composition defined and encompassed by polygon QTXJ but not including lines QJ and XJ of Figure 4, a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.50 W/cm K at 25°C which comprises the steps:
(a) forming a mixture comprised of an oxygen-containing aluminum nitride powder, yttrium oxide or precursor therefor, and a carbonaceous additive selected from the group consisting of free carbon, a carbonaceous organic material and mixtures thereof, said carbonaceous organic material thermally decomposing at a temperature ranging from about 50°C to about 1000°C to free carbon and gaseous product of decomposition which vaporizes away, said free carbon having a specific surface area greater than about 100 m2/g, the aluminum nitride powder in said mixture having a specific surface area ranging from about 3.4 m2/g to about 6.0 m2/g, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges from point X up to point Q
of Figure 4, said yttrium ranging from greater than about 0.8 equivalent % to about 3.2 equivalent %, said aluminum ranging from about 96.8 % equivalent % to less than about 99.2 equivalent %, said compact having an equivalent %
composition of Y, Al, O and N outside the composition defined and encompassed by polygon PINIKJ of Figure 4, the aluminum nitride in aid compact containing oxygen in an amount ranging from greater than about 1.40% by weight to less than about 4.50% by weight of said aluminum nitride, (b) heating said compact in a nonoxidizing atmosphere at a temperature up to about 1200°C thereby providing yttrium oxide and free carbon, (c) heating said compact at ambient pressure in a nitrogen-containing nonoxidizing atmosphere containing at least about 25% by volume nitrogen at a temperature ranging from about 1350°C to a temperature sufficient to deoxidize the compact but below its pore closing temperature thereby reacting said free carbon with oxygen contained in said aluminum nitride producing a deoxidized compact, said deoxidized compact having a composition wherein the equiva-lent % of A1, Y, O and N is defined and encompassed by polygon QTXJ but not including lines QJ and XJ of Figure 4, the aluminum nitride in said compact before said deoxidation by said carbon having an oxygen content ranging from greater than about 1.40% by weight to less than about 4.50% by weight of said aluminum nitride, said free carbon being in an amount which produces said deoxidized compact, and (d) sintering said deoxidized compact at ambient pressure in a nitrogen-containing nonoxidizing atmosphere containing at least about 25% by volume nitrogen at a temperature ranging from about 1910°C to about 2000°C
producing said polycrystalline body.

25. The process according to claim 24 wherein the sintering temperature ranges from about 1910°C to about 1950°C, said aluminum nitride powder in said mixture has a specific surface area ranging from about 3.7 m2/g to about 6.0 m2/g, and said sintered body has a porosity of less than about 1% by volume of said body.

26. The process according to claim 24 wherein the sintering temperature ranges from about 1950°C to about 2000°C, and said sintered body has a porosity of less than about 1% by volume of said body and a thermal conductivity greater than about 1.67 W/cm K at 25°C.

27. A polycrystalline aluminum nitride body having a composition defined and encompassed by polygon P1N1KJ but not including lines KJ and P1J of Figure 4, a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm K at 25°C.

28. A polycrystalline aluminum nitride body having a composition defined and encompassed by polygon P1N1NOP but not including line P1P of Figure 4, a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm K at 25°C.

29. A polycrystalline aluminum nitride body having a composition defined and encompassed by polygon PONKJ but not including lines KJ and PJ of Figure 4, a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm-K at 25°C.

30. A polycrystalline aluminum nitride body having a composition defined and encompassed by polygon QTXJ
but not including lines QJ and XJ of Figure 4, a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm.K at 25°C.

31. A polycrystalline body having a composition defined and encompassed by polygon P1N1KJ of Figure 4 but excluding lines KJ and P1J which is comprised of from greater than about 0.35 equivalent % yttrium to less than about 4.4 equivalent % yttrium, from greater than about 95.6 equivalent % aluminum to less than about 99.65 equivalent %
aluminum, from greater than about 0.85 equivalent % oxygen to less than about 4.4 equivalent % oxygen and from greater than about 95.6 equivalent % nitrogen to less than about 99.15 equivalent % nitrogen, said polycrystalline body having a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm.K at 25°C.

32. A polycrystalline body having a composition defined and encompassed by polygon PlNlNOP of Figure 4 but excluding line PlP which is comprised of from greater than about 0.35 equivalent % yttrium to about 2.9 equivalent %
yttrium, from about 97.1 equivalent % aluminum to less than about 99.65 equivalent % aluminum, from greater than about 0.85 equivalent % oxygen to about 2.9 equivalent % oxygen and from about 97.1 equivalent % nitrogen to less than about 99.15 equivalent % nitrogen, said polycrystalline body having a porosity of less than about 10% by volume of said body and a minimum thermal conductivity greater than 1.00 W/cm.K at 25°C.

33. A polycrystalline body having a composition defined and encompassed by polygon PONKJ of Figure 4 but excluding lines KJ and PJ which is comprised of from greater than about 0.55 equivalent % yttrium to less than about 4.4 equivalent % yttrium, from greater than about 95.6 equiva-lent % aluminum to less than about 99.45 equivalent %
aluminum, from about 1.1 equivalent % oxygen to less than about 4.4 equivalent % oxygen and from greater than about 95.6 equivalent % nitrogen to about 98.9 equivalent %
nitrogen, said polycrystalline body having a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm.K at 25°C.

34. A polycrystalline body having a composition defined and encompassed by polygon QTXJ of Figure 4 but excluding lines QJ and XJ which is comprised of from greater than about 0.8 equivalent % yttrium to about 3.2 equivalent % yttrium, from about 96.8 equivalent % aluminum up to about 99.2 equivalent % aluminum, from greater than about 1.55 equivalent % oxygen to about 4.2 equivalent % oxygen and from about 95.8 equivalent % nitrogen to less than about 98.45 equivalent % nitrogen, said polycrystalline body having a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm.K at 25°C.

35. A polycrystalline body having a composition defined and encompassed by polygon PONKJ but excluding lines NK, KJ and PJ of Figure 4 which is comprised of from greater than about 0.55 equivalent % yttrium to less than about 4.4 equivalent % yttrium, from greater than about 95.6 equiva-lent % aluminum to less than about 99.45 equivalent %
aluminum, from about 1.1 equivalent % oxygen to less than about 4.4 equivalent % oxygen and from greater than about 95.6 equivalent % nitrogen to about 98.9 equivalent %
nitrogen, said polycrystalline body having a porosity of less than about 4% by volume of said body and a minimum thermal conductivity of 1.50 W/cm.K at 25°C.

36. A polycrystalline body having a composition defined by line NlK of Figure 4 but excluding point K which is comprised of from about 1.9 equivalent % yttrium to less than about 4.4 equivalent % yttrium, from greater than about 95.6 equivalent % aluminum to about 98.1 equivalent %
aluminum, from about 1.9 equivalent % oxygen to less than about 4.4 equivalent % oxygen and from greater than about 95.6 equivalent % nitrogen to about 98.1 equivalent %
nitrogen, said polycrystalline body having a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm.K at 25°C.

37. A polycrystalline body having a composition defined and encompassed by polygon QTY1Y2 but excluding line QY2 which is comprised of from greater than about 0.8 equivalent % yttrium to about 2.0 equivalent % yttrium, from about 98.0 equivalent % aluminum to less than about 99.2 equivalent % aluminum, from greater than about 1.55 equiva-lent % oxygen to less than about 3.15 equivalent % oxygen and from greater than about 96.85 equivalent % nitrogen to less than about 98.45 equivalent % nitrogen, said polycrys-talline body having a porosity of less than about 2% by volume of said body and a thermal conductivity greater than 1.50 W/cm.K at 25°C.

38. A polycrystalline body having a phase compo-sition comprised of A1N, Y2O3 and Y4A12O9 wherein the total amount of said Y2O3 and Y4A12O9 phases ranges from greater than about 0.8% by volume to less than about 7.6% by volume of the total volume of said body, said Y2O3 and Y4A12O9 phases being present in at least a trace amount, said Y2O3 phase ranging to less than about 7.6% by volume of said sintered body, said Y4A12O9 phase ranging to less than about 6.0% by volume of said sintered body, said body having a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm.K at 25°C.

39. A polycrystalline body having a phase compo-sition comprised of A1N, Y2O3, and Y4A12O9 wherein the total amount of said Y2O3 and Y4A12O9 phases ranges from greater than about 0.8% by volume to less than about 5.1% by volume of the total volume of said body, said Y2O3 and Y4A12O9 phases being present in at least a trace amount, said Y2O3 phase ranging to less than about 5.1% by volume of said sintered body, said Y4A12O9 phase ranging to less than about 1.3% by volume of said sintered body, said body having a porosity of less than about 10% by volume of said body and a minimum thermal conductivity of greater than 1.00 W/cm.K at 25°C.

40. A polycrystalline body having a phase compo-sition comprised of A1N, Y2O3, and Y4A12O9 wherein the total amount of said Y2O3 and Y4A12O9 phases ranges from about 1.3% by volume to less than about 7.6% by volume of the total volume of said body, said Y2O3 and Y4A12O9 phases being present in at least a trace amount, said Y2O3 phase ranging to less than about 7.6% by volume of said sintered body, said Y4A12O9 phase ranging to less than about 6.0% by volume of said sintered body, said body having a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm.K at 25°C.

41. The polycrystalline body according to claim 40 wherein said body has a porosity of less than about 2% by volume of said body and a thermal conductivity greater than 1.67 W/cm.K at 25°C.

42. A polycrystalline body having a phase compo-sition comprised of A1N and Y2O3 wherein the total amount of said Y2O3 phase ranges from about 3.3% by volume to less than about 7.6% by volume of the total volume of said body, said body having a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.00 W/cm?K at 25°C.

43. A polycrystalline body having a phase compo-sition comprised of AlN, Y2O3 and Y4Al2O9 wherein the total amount of said Y2O3 and Y4Al2O9 phases ranges from greater than about 1.9% by volume to less than about 6.6% by volume of the total volume of said body, said Y2O3 phase ranging in amount from at least a trace amount to less than about 2.8%
by volume of said body, said Y4Al2O9 phase ranging from about 1.5% by volume to less than about 6.0% by volume of said body, said body having a porosity of less than about 2%
by volume of said body and a thermal conductivity greater than 1.50 W/cm?K at 25°C.

44. The polycrystalline body according to claim 43 wherein said body has a porosity of less than about 1% by volume of said body and a thermal conductivity greater than 1.67 W/cm?K at 25°C.

45. A polycrystalline body having a phase compo-sition comprised of A1N, Y2O3 and Y4Al2O9 wherein the total amount of Y2O3 and Y4Al2O9 phases ranges from greater than about 1.9% by volume to less than about 4.5% by volume of the total volume of said body, said Y2O3 phase ranging from a trace amount to about 1.5% by volume of the sintered body, said Y4Al2O9 phase ranging from about 1.5% by volume to less than about 4.5% by volume of the sintered body, said body having a porosity of less than about 2% by volume of said body and a thermal conductivity greater than 1.50 W/cm?K at 25°C.

46. The polycrystalline body according to claim 45 wherein said body has a porosity of less than about 1% by volume of said body and a thermal conductivity greater than 1.68 w/cm-K at 25°C.