US2176134A - Electric gaseous discharge device - Google Patents

Description

Oct. 17, 1939. G. IY-IOLST 2,176,134

ELECTRIC GASEOUS DISCHARGE DEVICE Filed March 17, 193':

INVENTOR Gllles Holst Y Haw-a6.

ATT NEY Patented Oct. 17, 1939 ELECTRIC GASEOUS DISCHARGE DEVICE Gilles Holst, Eindhoven, Netherlands, assignor to General Electric Company, a corporation of New York Application March 17, 1937, Serial No. 131,489

Germany March 27, 1936 1 Claim.

The present invention relates to electric gaseous discharge devices, and particularly to devices of this. type which operate at relatively high temperatures.

A particular object of the invention is to pro-' vide an electric gaseous discharge device which will operate at an elevated temperature for extended periods without change in its electrical characteristibs. tion is to provide a gaseous discharge device in which the gaseous content of said device is retained despite operation of said device at a temperature at which marked diffusion of the gas through the container occurs. -Another object of the invention is to increase the energy capacity of a device of given size. Another object of the invention is to provide a light source of high efliciency. A further objectof the invention is to provide a gaseous discharge device having a long useful life. Still other objects and advantages of the invention will appear from the following detailed specification or from an inspection of the accompanying drawing.

The invention consists in the new and novel combination of elements hereinafter set forth and claimed.

In the interest of high luminous efliciency the modern electric gaseous discharge lamps are ordinarily designed to operate at a relatively high temperature, which is frequently just below the softening point of the vitreous envelope employed. Most of these devices employ a fixed gas either for use in facilitating starting of a discharge or .to sustain the discharge during continued operation of the lamp, and I have found that some of they gases employed in these devices rapidly escape at these elevated temperatures through the vitreous envelopes commonly employed. This loss of gas causes a marked change in the characteristics of the device which is frequency undesirable. This is particularly true, for example, in the case of high pressure mercury vapor tubes of the so-called capillary type, which are commonly made of fused silica. These tubes, which are ordinarily designed to operate with wall temperatures in excess of 500 C., contain a small quantity of mercury together.

A further object of the inventhrough the wall of the envelope, with the result that it becomes increasingly diflicult to initiate a discharge therein, more and more potential being required for this purpose until eventually the device will not start at all on the available potential. As a result the useful life of these devices has been materially shortened.

I 'have now discovered that this difliculty is entirely overcome by enclosing these devices within an outer envelope which likewise contains neon, or whatever other gas tends to difiuse through the inner envelope. Since this outer envelope or jacket is necessarily larger it will be at a lower temperature than the inner one, and hence there will be no appreciable loss of neon through this outer envelope. The pressure of the neon in this jacket "is preferably so chosen with respect to the pressure of the neon in the inner envelope that under designed operating conditions these pressures will be equal, despite the difference in the average temperature of the gas in the two compartments. Under these conditions the lamp will neither gain nor lose neon during operation, but will operate with' the neon in the two compartments in equilibrium. In some cases, however, higher or lower relative pressures of neon may be used in the outer jacket, in which case there will be some diffusion of neon through the lamp envelope, but at a much reduced rate. Where the outer pressure is higher, during operation, than that within the lamp envelope the leakage will, of course, be inward, and will compensate for any neon lost by clean-up during operation of the lamp.

The neon in this jacket increases the heat transfer from the lamp envelope to the jacket and thus aids in dissipating heat from the lamp. In many cases this is desirable, since, as compared to an evacuated jacket, it permits more energy to be impressed on the lamp, with a consequent increase in luminous efliciency. This heat transfer is further increased, where desired, by the addition of another gas, such as nitrogen, which will not diffuse through the lamp envelope when hot to the neon within the jacket.

For the purpose of illustrating my invention I have shown a lamp constituting one embodiment thereof in the accompanying drawing".

As shown in this drawing the discharge tube I is of the capillary type which is now on the market for the emission of visible light or ultraviolet rays. This tube,'which is of fused silica, has an inside diameter of 4 mm., andan outside diameter of 7.5 mm. This tube is provided at the ends with the electrode chambers 2, in which I are sealed the thermionic cathodes 3, which preferably consist of tungsten coated with barium oxide. These electrodes, which are of the type which are heated to electron emission by the discharge, are separated by 18 mm.

Within said discharge tube 5 there is a small amount of mercury and a rare gas filling which consists of neon with a sufilcient addition of argon to reduce the breakdown potential between the electrons 3 to a value less than that with pure neon. Thus in practice the argon ordinarily is of the order of .2% of the neon. The

pressure of the mixture is of the order of 20 mm. r

at room temperature.

The discharge tube l is suspended from the stem 6 of the glass envelope 1 by means of the current inlead wires 4 and 5. This envelope or jacket I is filled with a mixture of neon and nipressure of neon within the jacket 1.

trogen. At room temperature the pressure of this mixture is 500 mm., while the partial pressure of the neon is of the order of mm., although in some cases it is varied from 5 to 250 mm., with from 20 to mm. being a favorable range. It will be noted that no provision of argon within the outer jacket is necessary to prevent change in the argon concentration within the inner envelope, since argon does not diffuse through the fused silica even at the tem peratures which render it highly pervious to neon.

In the useof this lamp sufiicient electrical energy is ordinarily impressed thereon to raise the mercury vapor pressure within the tube l to of the order of 10 atmospheres or more. Under these conditions the fused silica wall of this tube reaches a temperature of 500 C. or more. At this temperature, with its correspondingly high partial pressure of .the neon, a very considerable diffusion of neon would take place through the fused silica if it were not for the Under operating conditions, however, the neon pressure is substantially the same, in the preferred case, or does not markedly vary, on opposite sides of the fused silica wall of the tube I, and hence there is no change in the neon content of the tube I, or at most only a slight change where the pressures are not exactly equal.

The gas within the jacket 1 produces an increased heat transfer, due largely to increased convection currents, from the tube l toward this jacket so that the energy impressed upon the tube l for a given heating thereof is greater than would be the case if there were a vacuum within this jacket. This increase in energy consumption results not only in a greater light output, but also in a higher luminous eificiency. The nitrogen which is added to the neon in this jacket aids in this heat transfer without creating any problem of difiusion into the tube l, due to the fact that the nitrogen will not diffuse through the fused silica. Any other suitable gas which would not diffuse through the fused silica might be used in a similar manner.

It is likewise to be understood that while I have disclosed my invention by reference to a particular device using neon and a fused silica envelope, that it is equally applicable to all other similar cases where a gas is enclosed within an envelope of glass or other material which is or becomes pervious thereto under operating conditions. It is also to be understood that various other additions, changes or omissions, within the scope of the appended claims, may be made in the structure disclosed without departing from the spirit of my invention.

What I claim'asnew and desire to secure by Letters Patent of the United States, is:

An electric gaseous discharge device comprising a sealed envelope, electrodes therein, a gaseous atmosphere within said envelope consisting of neon with a small percentage of argon intermixed therewith, and a sealed jacket about said envelope containing nitrogen intermixed with a small quantity of neon, whereby the neon concentration within said sealed envelope is maintained substantially constant despite long continued maintenance of said envelope at a temperature above that at which neon will diffuse therethrough.

GILLES HOLST.

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