US3407327A - High pressure electric discharge device containing mercury, halogen, scandium and alkalimetal - Google Patents

Description

Oct. 22, 1968 KOURY ET AL 3,407,327

HIGH PRESSURE ELECTRIC DISCHARGE DEVICE CONTAINING MERCURY, HALOGEN, SCANDIUM AND ALKALI METAL Filed Dec. 21, 1967 Y H RM U OMR KYO m m w F E DN E H R 0 F u United States Patent 3 407,327 HIGH PRESSURE ELEiJTRIC DISCHARGE DEVICE CONTAINING MERCURY, HALOGEN, SCANDI- UM AND ALKALI METAL 3,407,327 Patented Oct. 22, 1968 "ice emission characteristics of mercury and the light emitting metal are what would be expected to result from the combination.

We have discovered, however, that when thorium and Frederic Koury, Lexington, and John F. Waymouth, Essex 5 scandium atoms are added to a lamp fill as the light County, Mass., assignors to Sylvania Electric Products emitting metals, together with mercury, halogen and alkali Inc., acorporation of Delaware metal atoms, that the light produced by the device is coimnugtuigzzilafit of a iphcgatrori) serzzNoi 9 6 :35 entirely different that that would be normally predicted 32 575 ls app on from known data giving the intensities of spectral lines 7 Claims .(CL 313 229) 10 of either of the two metals alone. In particular, both scandium and thorium would be predicted to have strong ultraviolet and blue emissions because their principal emis- ABSTRACT OF THE DISCLOSURE sion lines are in that region. When either of the two are A h r 1 t h d h its used together with an alkali iodide however, this is not 6 66 m arge evlce. W em the case. The radiation which is produced from arc tubes an vlslble colors m the Spectrum appear. hues gellerauy using fills including scandium is a spectrum containing i than 5 apart and contammg a mclud all colors, the spacing between the lines would average mg scandlllm i P and i alkah metal about 20 A. The emission is a discrete line pattern when when thonum 1S mduded m the ml, the hues 9 the spec' measured on an instrument of moderate resolution. If

trum appear generally less than about 5 umts apart 20 thorium is added also, the thorium spectrum with its forest of lines, substantially a continum, appearing generally less than 5 A. apart will be seen, as mentioned in Cross reference to related apphcanons our copending application, Ser. No. 230,944, filed Oct. 16,

This application is a continuation in part of our co- 1962. Because of the pressure of mercury, the typical merpending application Ser. No. 555,914, filed June 7, 1966, lly lines 4048, 4348, 5461, 577 0 and 5790 A. will be entitled High Pressure Electric Discharge Device which in imposed upon the spectrum.

turn is a continuation in part of our copending applica- Accordingly, the primary object of our invention is tion Ser. No. 324,265, filed Nov. 11, 1963 entitled High the use of scandium and thorium, with mercury, halogen Pressure Electric Discharge Device, now abandoned, and alkali metal atoms to attain light emission from high which in turn is a continuation in part of our copending 0 pressure electric discharge devices different from that applications Ser. No. 209,974, filed July 7, 1962, entitled which would be expected from the intensities of the spec- High Pressure Electric Discharge Device and Ser. No. tral lines of each.

230,944, filed Oct. 16, 1962, entitled Electric Discharge The many objects, features and advantages of our in- D i vention will become manifest to those conversant with This invention relates to high pressure electric discharge the art upon reading the following specification when devices and particularly to those containing atoms of taken in conjunction with the accompanying drawings.

other mercury, light-emitting metals, and alkali and halo- In the devices having the fill of our invention, we have gen. Specifically, this invention relates to the discovery selected various segments of the emission and measured that two particular light emitting metals used conthe total energy emitted in that region. Each of the segjunctively in such devices produce spectral energy line ments are compared to the emission energy data pubintensities which are different than each would be exlished in the Tables of Spectral Line Intensities, issued pected to produce individually. by the National Bureau of Standards, Monograph Num- In high pressure electric discharge devices containing ber 32, Part I, on Dec. 29, 1961.

TABLE I [scandium] Col. 1 Col. 2 Col. 3 Col. 4 Col. 5 Col. 6

Relative Relative energy of the Normalized emission Spectrum energy portion of the spectrum Normalized resulting from Color measured from attributable to scandium emission of scandium in tables inalamp containing scandium from scandium-sodium (arbitrary scandium and sodium tables (Col. 3) lamp (001. 4)

units) (arbitrary units) Blue 4246-4358 2, 303 25 1.00 1.00 Green. 5071-5711 503 04 .24 2. Red 6210-6305 275 34 .12 1.36

[Thorium] Col. 7 001. s 601.9 001. 10 001. 11 001. 12

Relative Relative energy of the Normalized emission Spectrum energy portion of the spectrum Normalized resulting from Color measured from attributable to thorium emission of thorium in a (A.) tables in a lamp containing thorium from thorium-sodium (arbitrary thorium and sodium tables (Col. 9) lamp (Col. 10)

units) (arbitrary units) Blue".-. 3975-4025 650 45 1.00 1.00 Green- 5725-5775 34.5 40 .053 .89 Red---" 6575-6625 10.0 23 .015 .51

mercury alone, the spectral emission in only the characteristic lines expected, to be produced by mercury. When the lamp fill is modified to include mercury, a halogen and a light emitting metal, the spectral emission is changed to a superposition of the spectral lines of the light emitting metals upon the mercury lines. The spectral energy From the foregoing table, a lamp containing scandium alone would be expected from column 3 to have only about one quarter of the energy emitted in the green region as in the blue region and about one tenth the energy emitted in the red region as in the blue region. Surprisingly, in a halide-containing lamp with scandium and sodium atoms (see col. 4) about two and a half times more energy is emitted in the green region than in the blue region of the energy attributable to scandium and about one and a third as much energy is emitted in the red region than the blue region.

On the other hand, a lamp containing thorium alone would be expected from column 9 to have only about five one-hundredths of the emission in the green region as in the *blue region and about one one-hundredths of the energy emitted in the red region as in the blue region. But with a halide containing lamp with sodium and thorium atoms (see col. 9), the energy emitted in the green region and attributable to thorium is about nine-tenths of the energy emitted in the blue region and about one-half as much energy is emitted in the red region as in the blue region.

Hence, viewing the National Bureau of Standards Tables, a lamp with scandium alone would be expected to be a bluish-ultraviolet emitting lamp with only a moderate amount of green and less blue. Surprisingly, of the energy attributable to scandium the green portion predominates in scandium-sodium lamp. Large amounts of red energy are emitted also, whereas only small quantities would be predicted from the Bureau of Standards Tables. Hence, the ligth emission of these two light emitting metals in an arc tube is not merely the sum of each metal taken separately.

Referring to the figure, an elevational view of a high pressure electric discharge device is shown. For clarity of presentation, the outer bulbous envelope and the base of the lamp are shown in phantom lines surrounding the arc tube harness and the arc tube. The device, such as shown in the drawing, comprises an outer vitreous envelope or jacket 2 of generally tubular form having a central bulbous portion 3. The jacket is provided at its end with a re-entrant stem having a press seal through which extend relatively stiff lead-in wires 6 and 7 connected at their outer ends to the electrical contacts of the usual screw type base 8 and at their inner ends to the arc tube and the harness.

The are tube is generally made of quartz although other types of glass may be used such as alumina glass or Vycor, the latter being a glass of substantially pure silica. Sealed in the arc tube 12, at the opposite ends thereof are main discharge electrodes 13 and 14 which are supported on lead-in wires 4 and respectively. Each main electrode comprises a core portion which may be a prolongation of the lead-in wires 4 and 5 and may be prepared of a suitable metal such as for example molybdenum or tungsten. The prolongations on these lead-in wires 4 and 5 can be surrounded by molybdenum or tungsten wire helixes.

An auxiliary starting probe or electrode 18, generally prepared of tantalum or tungsten is provided at the base end of the arc tube 12 adjacent the main electrode 14 and comprises an inwardly projecting end of another lead-in wire.

Each of the current lead-in wires described have their ends welded to intermediate foil sections of molybdenum which are hermetically sealed within the pinched sealed portions of the arc tube. The foil sections are very thin, for example approximately 0.0008 inch thick and go into tension without rupturing or scaling off when the heated are tube cools. Relatively short molybdenum wires 23, 24 and are welded in the outer ends of the foil and serve to convey current to the various electrodes inside the arc tube 12.

Metal strips and 46 are welded onto the lead-in wires 23 and 24 respectively. A resistor 26 is welded to foil strips 45 which in turn is welded to the are tube harness. The resistor may have a value of for example, 40,000 ohms and serves to limit current to auxiliary electrode 18 during normal starting of the lamp. Metal foil strip 46 is welded at one end to a piece of molybdenum foil sealed in the arc tube 12 which in turn is welded to main electrodes 13 and 14. Metal foil strip 47 is welded to one end of the lead-in 35 and at the other end to the harness. The pinched or flattened end portion of the arc tube 12 form a seal which can be of any desired width and can be made by flattening or compressing the ends of the are tube 12 while they are heated.

A U-shaped internal wire supporting assembly or are tube harness serves to maintain the position of the arc tube 12 substantially coaxially within the envelope 2. To support the arc tube 12 within the envelope, stiif lead-in wire 6 is welded to the base 53 of the harness. Because stiff lead-in wires 6 and 7 are connected to opposite sides of a powder line, they must be insulated from each other, together with all members associated with each of them. Clamps 56 and 57 hold the arc tube 12 at the end portions and are fixedly attached to legs 54 of the harness. A rod 57 bridges the free ends of the U-shaped support wire 54 and is fixedly attached thereto for imparting stability to the structure. The free ends of the U-shaped wire 54 are also provided with a pair of metal springs 60, frictionally engaging the upper tubular portion of the lamp envelope 2. A heat shield 61 is disposed beneath the are tube 12 and above the resistor 26 to protect the resistor from any excessive heat generated during lamp operation.

The are tube 12 is provided with a filling of mercury which reaches pressures in the order of one half to several atmospheres during normal lamp operation at temperatures of 450 to 700 C. In addition, the are tube is provided with halogen atoms, iodine being preferred and except fluorine, the quantity being suflicient to form a ratio of 0.025 to 0.85 atom of halogen per atom of mercury. Generally, approximately 2.5 l0 to 8.0)(10- gram atoms of mercury are added per centimeter of arc length, arc length being measured as the distance between opposing tips of the electrodes.

The scandium content of the arc tube is between about 2.5 10 to 1.5 10 gram atoms/cm. of arc length and the thorium content is between about 5 l0 to 1x 10- gram atoms/cm. of arc length and either can be present in quantities between 10 to mole percent of the total of the thorium and scandium concentration.

Below the lower limits, the emission of the metals will not be sufficient because inadequate quanities are present. In addition to the thorium and scandium, between -1.0 l0 to l.0 gm. atoms/cm. of arc length of an alkali metal, preferably sodium is present in order to maintain a stable are.

In addition to providing an excellent source of colorblended light, the combination of scandium and thorium in an arc tube tends to improve the operating characteristics of the lamp. The production of light by an arc tube discharge source requires an electrical breakdown of the gap between the electrodes producing an are. With high pressure devices, a subsequent increase in gas pressure is produced by the heating due to the are and must occur before the light emission of the source can reach its full equilibrium value. Lamps containing metal iodides in addition to mercury have, frequently, extinguished during their warming up period. Such extinction has been found to be due to a high voltage required to re-ignite the lamp, each half cycle of the alternating current. This re-ignition voltage maximizes at 30 to seconds after ignition, and results from the presence of excessive quantities of iodine in the vapor phase before the total pressure has increased to the operating level. If the reignition voltage required by the lamp exceeds that delivered by the ballast, the lamp extinguishes. When scandium and thorium are used eonjunctively, together with other materials in the are tube, this re-ignition voltage is minimized substantially. It appears that scandium helps to maintain the pressure of iodine in the vapor phase during the warm up period at a low level, thereby minimizing the re-ignition voltage required by the lamps.

Hence, the presence of scandium yields a means of maintaining a low amount of iodine in the vapor state during the early stages of a cycle of lamp operation.

The fabrication of the envelope, sealing techniques and positioning of the electrodes in the high pressure electric discharge device according to our invention takes place in a manner quite similar to that known to the art with conventional mercury lamps. And further, the mercury may be added to the arc tube by techniques well known to the art. To prepare the arc tube, we pump down an envelope having a pair of electrodes disposed at either end thereof, and spaced about 7 cm. from each other, through an exhaust tubulation extending from the surface of the envelope and disposed in communication with the interior thereof. The envelope is then electrically baked and filled with argon to flush out residual impurities, it is quite important to eliminate or substantially eliminate hydrogen from the arc tube.

Also, the electrodes can be vacuum baked at 600 to 800 C. for a few hours before their use to eliminate hydrogen which might occur due to processing, Furthermore, care should be exercised when sealing the electrodes into the arc tube to prevent hydrogen-containing, combustion gases from seeping in or becoming absorbed upon the surface.

The pump and fill procedure above described is usually repeated three to four times and then an arc is struck between the electrodes while there is a filling of argon gas. This operation of the arc removes any residual impurities from the electrodes and these contaminants can then be easily drawn from the system when the argon filling is pumped out. We then add approximately 46 milligrams of mercury, 7.5 milligrams of mercuric iodide, 0.5 milligram of scandium and 0.5 mg. of thorium and 19 mg. of sodium iodide to an envelope having an arc length of approximately 4.5 centimeters. The arc tube is then filled to atmospheric pressure with argon gas which is slowly leaked out until a pressure of about 23 millimeters of mercury is obtained. Subsequently, the exhaust tubulation is tipped off and the envelope is sealed.

It is apparent that modifications and changes may be made within the scope of the instant invention. It is our intention however to be limited only by the scope of the appended claims.

As our invention, we claim:

1. A high pressure electric discharge device emitting a visible spectrum of all colors with spectral lines appearing generally less than about 5 A. apart, said device comprising: an arc tube having an electrode disposed at each end thereof; a vaporizable fill disposed within said are tube, said fill comprising at least one halogen selected from the group consisting of iodine, bromine and chlorine, together with atoms of mercury, thorium, scandium and alkali metal, said halogen and mercury being present in an atomic ratio of halogen to mercury between about 0.025 to 0.85, said mercury being present in sufficient quantities to be completely vaporized at normal operating temperatures of said are tube and to form a restricted arc therein, said thorium being present in said are tube in quantities between about 5 X 10- to 1 10- gram atoms/cm. of arc length, said scandium being present in said arc tube in quantities between about 2.5 10 to 1.5 10 gram atmos/cm. of arc length, said thorium concentration in said are tube being between about 10 to of the total of the scandium and thorium concentration.

2. The device according to claim 1 wherein mercury is present in quantities between about 2.5 10 to 8.0)(10 gram atoms/cm. of arc length.

3. The device according to claim 1 wherein the alkali metal is sodium and there are 1.0)(10 to 1.0X10- gram atoms of sodium per cm. of arc length.

4. A high pressure discharge device emitting a visible spectrum of all colors with spectral lines appearing generally less than about 20 A. apart, said device comprising: an arc tube having electrodes at either end thereof and a vaporizable filling of atoms of scandium and a halogen selected from the group consisting of chlorine, bromine and iodine; atoms of mercury and an alkali metal; said halogen and mercury being present in an atomic ratio between 0.025 to 0.85; said mercury being present in sufficient quantities to be completely vaporized at normal operating temperatures of said are tube and to form a restricted arc therein, said scandium being present in quantities in the range of 2.5 10- to 1.5 10 gram atoms per centimeter of arc length, said alkali metal atoms being present in quantities of 1 10- to 1.0X10* gram atoms per centimeter of arc length.

5. The high pressure discharge device according to claim 4 wherein the alkali metal is sodium.

6. The high pressure discharge device according to claim 4 wherein at least a part of said mercury is added as mercuric iodide.

7. The device according to claim 4 wherein iodine is the halogen.

References Cited UNITED STATES PATENTS 3,234,421 2/1966 Reiling 313--229 X 3,351,798 11/1967 Bauer 313-229 X JAMES W. LAWRENCE, Primary Examiner.

R. L. JUDD, Assistant Examiner.

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