US1609129A - Microfurnace - Google Patents

Description

H. s. ROBERTS Nov. 30 1926' MICROFURNAGE Filed May 15 1925 4 Sheets-Sheet 1 Nov. 30 1926.

H. S. ROBERTS MICROFURNAGE Nov. 30 1926.

H. S. ROBERTS MICROFURNACE 15 4 Sheets-Sheet 3 Filed M Nov. 30;1926. 3 1,609,129 I H. S. ROBERTS MICROFURNACE Filed May 15. 1925 -4 Sheets-Sheet 4 as W A110 ibu-{n'l conerilibr liwaraastlgzez-as Patented Nov. 30, 1926.

UNITED. STATES PATENT OFFICE.

HOWARD S. ROBERTS, OF WASHINGTON, DISTRICT 01? COLTIMBIA, ASSEGNOR TO CARNEGIE INSTITUTION 0F WASZ-Ifi'TG-TUN, OF WASHINGTON, DZESTBICT OF CO- LUMBIA.

Application filed May 15, 1925.

By the microscopic study of coals and carbonaceous shales a large amount of information has beenob'tained as to the botany of the plants which contrilnited to their formation. In the continuance of these in vestigations it was found desirable to heat thin sections of the coal or shale in an inert atmosphere and to observe the phenomena which take place such as the melting and volatilization thereof and the temperatures at which the phenomena occur. This was first done by a small resistancefurnace of the cylindrical type, but this was inadequate for the examination of much of the material since the minute detail of the specimens in many cases necessitated the high magni- "fication thereof for proper study.

In the case of the cylindrical furnace referred to, as is the case with all furnaces hitherto used in high temperature microscopy, the specimen to be examined is placed within a heated-chamber; it is supplied with heat, chiefly by radiation and convection, from the walls of the chamber, and loses heat by radiation outward thru the openings which must be provided for observing the specimen. In order to increase the useful magnification of the specimen the solid angle subtended at the specimen by these openings must be increased. Thus it is found that to attain a useful magnification 'of 300 diameters most of the heating must be from the sides of the specimen and as a consequence it is impossible to obtain a sufliciently uniform temperature across the ex tent of the specimen or to measure its temperature with sufii'cientaccuracy.

In the furnace which forms the subject matter of the'present invention heat is supplied to the specimen chiefly by conduction thru two strips of silica glass or other transparent material, being placed between them and in contact with both. The strips in turn are placed between and in good thermal contact with two flat heating elements. Since the heating elements are close to the specimen the openings for observing the specimen may be :kept small without constricting the large angle of viewnecessitated by the high magnification desired. As a consequenceth'e temperature across the specifn'en is suflicieritl'y uniform. The'temperatux-Wot til'ls'epecimen ismeasured in the usual MIOEL'OF'URNACE.

Serial No. 305633;

way by means of a thermocouple whose junction is welded to one heating element or located at definite point between the two heating elements, an experimentally determined correction being applied to allow for whatever difference there may be between the temperature of the thermocouple junction and that of the specimen.

This furnace permits the heating to high temperatures under such conditions as permit the employment of a microscope objective of large aperture having a working distance as small as 5 millimeters while keeping the objective reasonably cool. It is'possible to measure the temperature readily and with sufiicient accuracy. Oxidation of the specimen is prevented by keeping the furnace closed and passing a current of helium or other inert gas through it to excludeth'e a1r.

Other objects of the invent-ion will be ap parent from the following detailed description and the appended claims.

In the drawings:

Figure 1 is aside elevation of a micro.- seope with the furnace in place on the supporting table or stage thereof.

Figure 2 is a perspective View of the furnace.

Figure 3 is a top plan view of the furnace with parts broken away.

Figure 4 is a longitudinal section on the line 4.4i of Figure '3.

Figure 5 is a transverse section on the line 5*5 of Figure 3.

Figure 6 is a transverse section on the line 66 of Figure 3. I

Figures 7 to 13 inclusive disclose a modified form of furnace.

Figure 7 is a top plan view thereof.

Figure 8 is a sect-ion on the line 8-8 of Figure 7.

Figure 9 is a section on the line 99 of Figure 7 Figure 10 is, a similar section with the top removed.

Figure 11 shows two forms. of'on'e'felement of the heater;

Figure 12 is a cross section of the heater.

Figure 13 is a perspective View of the heatenits support, and the thermocouple.

In the form of :the inventiondisolosed in Figures .1. to 6, inclusive, the furnace is sub stantially rectangular and adapted to be placed upon the table A of a microscope 13 of any usual or desired type. The furnace casing is composed of an upper brass plate 1 and a lower brass plate 2 which form a relatively massive brass housing adapted to contain the elements to be described. The upper plate 1 has an internal conduit 3 to which water may be admitted by pipe 4 and from which it is discharged by pipe 5 or vice versa. Similarly the lower plate 2 has an internal conduit 6 to which water may be admit-ted by pipe 7 and may be discharged by pipe 8 or vice versa. The pipes 5 and 7 may be connected by a short tube 9 if desired and a continuous circulation of water is thus provided for. The two portions of the casing may be connected by screws 2.

The heating element is a thin ribbon of nichrome bent double so as to form, in eftec two substantially plane and parallel heaters, 11 and 12. The upper end of the ribbon is turned up adjacent the outside of the easing, and the lower end 13 turned down outside the casing. The end 10 is fastened by screws l t to a terminal block 15 which is insulated from the casing as indicated at 16 and 17, and this terminal block is fastened to the casing by screws 18 which are also provided with insulation 19 as shown in Figure 6. The screws hold in position the lead-in member 20 to which one of the circuit wires 21 may be attached. The circuit is completed through the heating element, the end 13 of which is attached to the lower member 2 of the casing by screws 22 and through the casing member 2 to the lead-out member 23 attached by screws 24 to said lower member 2 and to which the other circuit wire 25 may be attached.

Aligned openings26 and 27 are provided in the heating element in order to see through it. The spaces above and below the heater are filled with strips of mica 28 and 29 which have been previously heated for some hours at a temperature of about 950 C. which drives off the water and causes the mica to swell to several times its original thickness. It thus forms a fairly good ther mal insulator and at the same time has sutlieient mechanical strength to keep the heater centered. Openings 30 and 31 are provided in the strips of mica in register with the openings 26 and 27. Similar openings 32 and 33 are formed in the brass sections or plates 1 and 2, and in these are placed windows 34 and 35 of thin silica glass.

The temperature of the furnace is measured by a thermocouple 36 having its junction 37 located in a notch 38 in the porcelain block 39 which is placed between the layers 11 and 12 of the heating element. The wires of the thermocouple may pass out through glass tubes 40 and 4:1, and the thermocouple will be calibrated by noting its readings when a standard substance in the furnace is held at its melting point.

In order to prevent oxidation of the material being investigated it is in many cases found desirable to fill the furnace with an atmosphere of helium or some similar inert gas. This is admitted to the body of the furnace through the pipe 42 and will escape through the opening 13 through which the slides are introduced.

The specimen to be investigated is placed between two silica glass strips 4.4. and 45 and may be introduced through the opening 43 and moved about considerably without moving the furnace. If the furnace is filled with an atmosphere of helium, the heater requires a current of about 40 ampercs to reacl 800 C. and this may be supplied in any desired manner, as by an 11 volt sign-lighting: transformer controlled by a rheostat and an'nneter-in series with the primary winding! of the transformer.

The modification illustrated in Figures 7 to 13 inclusive invo ves the same fundamental principles but differs considerably in details. In this form the casing; consists of a base member 6 substantially circular and adapted to fit in a similarly shaped opening: in the table A, of the microscope and be supported thereon by a flange, and a top member d7, the two members being; screw threaded to engage as at 48. The opposing central portions of the two parts are hollowed to form a chamber 49. A pipe admits water into a conduit 51 in the upper member 47 and the water passes off through a pipe A similar conduit in the lower member has an inlet connected to a pipe 5 1 and an outlet 55. An observation opening 56 in the upper casing member 47 is pro vided with a glass window 57 and a similar opening 58 in the lower member is provided with a glass window 59. Helium or other inert gas is supplied to the chamber 4-9 through a pipe 60.

The heating element comprises an open ended silver box 61 shown in perspective in Figure 13, in longitudinal section in Fig;- ures 9 and 10, in cross section in FlfjUlQ'lQ. and also diagrannnatically in longitudinal section in Figure 11. This box has thin layers of mica 62 on its sides and is wound with a fine resistance wire 63. (e. nichrome chromel, etc), one terminal 64 of which passes out through. a glass tube 65 and the other terminal 66 through a similar tube 67. the wires and tubes being preferably sealed with cement or otherwise to prevent diffusion of air into the chamber 49. The upper and lower sides of the box will be formed with openings 68 and 69 respectively if the ltlll to be examined by reflected light, the two forms being shown in Figure 11. It is ob- .Vious that the upper and lower sides of the box correspond to the upper and lower pm; tions 11 and 12 of the ribbon in the form of furnace shown in Figures 1 to 6.

This heating element issupp'orte'd in the chamber 49 by two identical supporting elements 71, each compris ng a unitary member having feet 72 through which pass screws 7 3 which secure the member to the lower or base member 46 of the casing, and each having at its top two inturne d ears .74 which fit into the open ends of the box 61 as clearly shown in Figure 13. These supports arevery light and may each be stamped out of a piece of sheet metal of some alloy of low thermal conductivity,

The two wires, 76 and 77. which tormthe thermocouple are here welded to the silver box 61, one on either side of and close to tlie ippei' opening; 68 with the two wires 76 and 77 leading off as shown in Figure 7 and Figure 13. y

To position the specimen it is necessary to unscrew the top member 47 ot the casing", after which the specimen, enclosed between two transparent plates as usual. can be introduced into the interior of the heating element through an open end as indicated at C in Figure 10. l

Either form of the invention permits the specimen to be heated to a high temperature which may be measured and varied at will, and maintained at a remarkably uniform temperature during its exam nation through a high power microscope. It is obvious that various details may be changed and that portions of the invention may be used alone or in other combinations without in any way departing from the spirit of the invention which is to be regarded as limited only by the scope of the appended claims.

I claim as my invent-ion:

1. A micro-furnace comprising a casing having a central chamber and a heating element within said chamber and having upper and lower portions spaced apart sufficiently so as substantially to contact with and surround a specimen carrying slide inserted therebetween.

2. A micro-furnace comprising a casing having a central chamber, a heating element within said chamber and having upper and lower port ons spaced apart sufliciently so as substantially to contact with and surround a specimen carrying slide inserted therebetween, and means for cooling the casing.

3. A micro-furnace comprising a casing having a central chamber, a heating e ement within said chamber and having upper and lower portions spaced apart sufficiently so as substantially to contact with and surround a specimen carrying slide inserted therebetween, and conduits in said casing through which water is circulated for cooling the casing.

I 4. A microfurnace comprising a cas ng having a central chamber, a heating element within said chamber and having upper and lower portions spaced apart suiiiciently so as substantially to contact with and surround a specimen carrying slide inserted therebetween and means for introducing inert gas into said chamber.

5. A micro-furnace comprising a casing having a central chamber, a heating element within said chamber and having upper and lower portions spaced apart sutiiciently so as substai'i'tially to contact with and surround a specimen carrying slide inserted therebetween, means for cooling said casing, and nieans for introducing inert gas into saic chamber. y

y 6. A micro-furnace comprising a casing having a central chamber, a heating element within said chamber and having upper and lower portions spaced apart suflic'iently so as si'ibstantially to contact with a specimen carrying slide inserted therebetween, a block between and contacting with said portions, and a thermocouple carried by said block.

7 A micro-furnace comprising a casing having a central chamber, a heating element within said chamber and having upper and lower portions spaced apart sutiiciently so as substantially to contact with a specimen car'- rying slide inserted I therebetween, a block between and contacting with said portions, a thermocouple carried by said block, and means for introducing inert gas into said chamber.

8. A micro-furnace comprising a casing having a central chamber, and a heating element in the form of a nichrome ribbon supported in said chamber with its sides spaced apart sufiiciently so as substantially to contact with and surround a specimen carrying slide inserted therebetween.

9. A micro-furnace comprising a casing having a central chamber, a heating element in the form of a nichrome ribbon supported in said chamber with its sides spaced apart sufficiently so as substantially to contact with a specimen carrying slide inserted therebetween, and layers of mica between the sides of said ribbon and the casing.

10. A micro-furnace comprising a casing having a central chamber, a heating element in the form of a nicrome ribbon supported in said chamber with its sides spaced apart sufiiciently so as substantially to contact with a specimen carrying slide inserted th-erebetween, and layers of mica between the sides of said ribbon and the casing, said casing, heating element, and mica being provided with alined observation openings.

11. A micro-furnace comprising a casing having a central chamber, a heating element in the form of a nichrome ribbon supported in said chamber with its sides spaced apart sufficiently so as substantially to contact with a specimen carrying slide inserted therebetween, and layers of mica between the sides of the ribbon and the casing, the ends of the ribbon being extended to the outside of the casing for connection to the terminals of a circuit.

12. A micro-furnace comprising a casing having a central chamber, a heating element in the form of a nichrome ribbon supported in said chamber with its sides spaced apart sufliciently so as substantially to contact with a specimen carrying slide inserted therebetween, and a thermocouple lying between the sides of the ribbon and substantially surrounded thereby;

13. A micro-furnace comprising a casing having a central chamber, a heating element in the form of a nichrome ribbon supported in said chamber with its sides spaced apart sufiiciently so as substantially to contact with a specimen carrying slide inserted therebetween; layers of mica between the sides of the ribbon and the casing, and means for cooling the casing. V

14:. A micro-furnace comprising a casing having a central chamber and a heating element therein in the form of a ribbon of metal folded to form spaced upper and lower portions having their ends extended to the outside of the casing for connection to the terminals of a circuit, said upper and lower portions adapted to receive between them a specimen carrying slide.

15. A micro-furnace comprising a casing having a central chamber, a heating element therein in the form of a ribbon of metal folded to form spaced upper and lower portions having their ends extended to the outside of the casing for connection to the terminals of a circuit, said upper and lower portions adapted to receive between them a specimen carrying slide, and a thermocouple located between the sides of the ribbon and adjacent said slide.

16. A micro-furnace comprising two heating elements having substantially plane parallel surfaces separated by a short distance, aligned openings through each heating element for observation, in combination with a slide comprising strips of transparent material carrying between them the specimen, said slide being in good thermal contact with the heating elements when placed therebetween.

17. A micro-furnace comprising two heating elements having substantially plane parallel surfaces separated by a short distance aligned openings through each heating element for observation, in combination with a slide con'iprisingstrips of transparent material carryil'ig between them the specimen, said slide being in good thermal contact with the heating elements when placed t-herebetween, and a thermocouple between said heating elements and adjacent the specimen to indicate the temperature of the latter.

In testimony whereof, I have hereunto subscribed my name.

HOWARD s. ROBERTS.

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