US2280618A - Electric gaseous discharge device - Google Patents

Description

A ril 21, I942. RgBESSON 2,239,613

ELECTRIC GASEOUS DISCHARGE DEVICE Fil ed March 23, 1 959 FI QI I INVENTOR I Raoul. Besson TORNEY and claimed.

Patented Apr. 21, 1942 UNITED STATES PATENT FFICE 2,280,618 swo'rarc'qsssousmscnancn DEVICE Raoul Besson, Paris, France, assignor to General Electric Company, a corporation of New York Application March 23,1939,- Serial No. 263,763

- In Switzerland March 25, 1938 The present invention relates to electric gas eous discharge devices and particularly to those devices in which a critical mixture of gases or vapors is utilized to permit starting of a dis charge at a low potential.

A particular object of the invention is to provide means whereby such a critical mixture of gases may be maintained substantially constant throughout the life of the device. Another object of the invention is to provide means to feed gas to a tube at a substantially constant rate to compensate for gas lost to the tube through the from an inspection of the accompanying drawing.

The invention consists in the new and novel combination of elements hereinafter set forth Discharge tubes with a gaseous atmosphere containing a rare main gas and a slight proportion of at' least one auxiliary rare gas or metal vapor, are well known.- In the following, the

term auxiliary gas" applies to the latter of-these two: gases; thus, in order to lower the starting potential of a discharge tube, there is added vto the main rare gas a trace of an auxiliary gas whose ionization potential is lower'than the excitation potential for the metastable state of the main gas. For instance", in the case of a neon tube, one adds xenon, krypton, argon, ormercury vapor. Another case is that of the tubes which are filled in very difierent proportion s'- with divers gases, for the purpose of combining their luminous spectra.

However, during the service of such tubes the,

the walls, electrodes, etc., and in this manner the 7 '3 Claims. (01. 176-125) 7 exists in the tube (that is to say, on the operating condition of the tube), so that the mass of vaporized mercury cannot, during thenormal operation, be adjusted as a function of the mass of vapor that has disappeared. 7

According to the present invention, it has been found that it is possible to overcome the disappearance of the auxiliary gas by placing the tube atmosphere in permanent contact with a body that retains auxiliary gas at the time of its introduction in thetube, and which, together with that auxiliary gas, brings about a system of. chemical divariant equilibrium, which admits as a gaseous phase, said gas or vapor. The nongaseous phase of that system preferably consists, in the case of an auxiliary rare gas, of a silica gel, active carbon, alumina, or the. like, which has adsorbed that gas. In the case where the auxiliary gas is a vapor, the nongaseous phasepreferably'consistsof an alloy of suitable dissociation potential, especially zinc or tin amalgam, for instance with 10, per cent zinc or tin, if it is requiredto'lower the. starting-poten- .tial of .the. tube. it is preferably to prepare it by fusion, since the Wherea'n amalgam is used,

contact-type amalgam may permit a relatively important amount of free mercury to subsist, whose excessive tension would make the lumi nous emission of, mercury predominant;

Under the preceding condition, the two varipendsare the temperature and the proportion of gas ofmercurywhich is retained in said body.

the latter variable. being independent of the tube,

operation'. In thisman'ner the desired pressure of the gas or of the additional vapor is; main- .tained by selecting a system in which a body readvantage which might be derived from using I these'gases is entirely lost after a very short period of operation. This loss obviously cannot be a avoided by a'simple increase inthe quantity of auxiliary gas initially introduced, forby increa ing that quantity the electric and lumino s tains this :yauxiliary'gas totlie desired' deg-ree,

which depends upon the current utilized in the discharge tube. Thus high current density permits utilizing a system with a relatively high gas pressure, since such acurrent causes such a rapid decrease of the pressure of .the auxiliary gas inthe tube'that after a fewseconds only the main gas is excited. 0n the other hand, a

1 low current density requires a system with a low drops in the tube and then take advantage of Y the-1 balance which isbstablished between. that vapor and the corresponding liquid for suitable losing with vapor in the tube, since the vapor, tension depends only on the temperature which gas pressure, otherwise'th'e main .gas emission would bealtered by-iemission of auxiliarygas.

In practice, thepres'sure of equilibrium of the gas retaining bodymay .gb'e selected in such a way that the quantity of 'liberated'gas or vapor' v that iabsorbed in the will be slightly l ower ihan" 7 tube. durlng-operation.g

ables on-which" the balance of the system .de-

. It'must be notedthat the m t-o the1in-' ventibu is app icable iieqaiise oft e' twctouowing i'acts: one that the auxiliary gaseous atmosphere behaves, as far as the equilibrium is concerned, Just as if the main gas did not exist. Second, its partial pressure is low; as a result,

the speed of dissociation of the emitting system will sufllce for producing the desired gaseous discharge. In fact this speed. is the higherwthe lower the gaseous pressure which intervenes in adsorbed xenon and this tends to re-establish continuously the xenon pressure, which otherthat equilibrium, and the higher the relative-- pressure variation due to the absorption in the tube of the auxiliary gaseous atmosphere.

The attached figures give by way of non-limiting examples, physical embodiments of the present invention. v

Figs. 1, 2 and 3 show discharge devices con: taining amalgam, and represent various methods of arranging thatamalgam in the tube: Fig. 4 shows a device utilizing an auxiliary rare gas.

when the amalgam is used, the latter, which is represented at 3, may be placed in the sealing tube 2, of the discharge tube I, and outside (Fig. 1) or inside (Fig. 2) of this tube. The amalgam may be also placed in a perforated glass ball 4, arranged within the tube (Fig. 3), or directly in the tube (not shown). The only condition to be met is to avoid that the amalgam may lodge itself on the electrode, where, in view of the high temperature reigning there, it would be likely to become toorapidly dissociated. It is nevertheless possible to take even that case into consideration, when electrodes of large surface areas are used, provided the amalgam is placed at the far end of the electrode. In the case where the device is used for bringing about a reduction in the striking voltage, the following phenomena occur: At the start. the neon tube. with its amalgam, will light up and give a blue color, which is due to the lowtension of the mercury vapor of the amalgam: in a few seconds, the entire positive column assumes the orange color of neon. When the tube is disconnected, the mercury vapor continues to evolve from the amalgam and becomes gradually diffused inthe tube, which, after a few hours of rest, first lights up with an entirely blue color, and then again becomes orange after a few seconds of operation. By virtue of the amalgam, a neon tube of 80 cm. length, and 40 mm. diameter, in conformity with the invention, lights up at about 450 volts D. C. This tube can be used for thousands of hours on a EGO-volt D. C. system; it will be most reliable in starting. However, the same tube, without amalgam, and requiring 700 volts for starting, cannot be utilized.

In Fig. 4, the neon tube which I have shown is provided with an appendix I which is closed within the tube by a very fine point 0, and which terminates at the other extremity by a stem I. Through 1, the carbon may be purged under vacuum, by suitable heating. After the carbon wise would decrease as time goes on. A few grams of carbon will insure a. sufficient pressure for several thousand operating hours.

Letters Patent of the United States, is:

1. An electric gaseous discharge device com-- prising -a sealed envelope containing a rare gas intermixed with a critically small percentage of another gaseous element having a lower ionizing potential than the metastable potential of the rare gas to lower the starting potential of said device and an additional supply of said gaseous element located out of the path of the discharge within said envelope and .bonded to another element in such a manner that its gaseous pressure is "reduced prior to the initiation of a discharge in said device,'to a value substantially equal to the partial pressure of the critically small percentage thereof required for lowering the starting potential of the device, the quantity of said gaseous element evolved from said bonded supply being less than the quantity thereof lost by clean-up during operation of the device whereby said device has the low starting potential characteristic of the gaseous mixture and emits light characteristic of the rare gas during operation.

2. An electric gaseous discharge device comprising a sealed envelope containing a principal gas intermixed with a critically small percentage of mercury vapor, the metastable potential of the principal gas being higher than the ionizing potential of the mercury vapor, said mercury vapor lowering the starting potential of said device, the partial pressure of said mercury vapor being less than that corresponding to mercury at room temperature, and an amalgam within said envelope at a point where it is not directly exposed to said discharge, the vapor pressure of the mercury in said amalgam being substantially equal to thepartial pressure of said mercury in the vapor-phase. prior to the initia tion of a discharge in said device, the quantity of mercury evolved from said amalgam being less than the quantity of mercury lost by clean-up during the operation of the device.-wherebysaid device has the low starting potential character-. istic of the gaseous mixture and emits light characteristic of the principal gas duringoperation.

60 vapor being less than that corresponding to meris cooled, xenon is introduced in 8 under a pressure of several mm. of mercury, after which the stem 1 is sealed. The discharge tube is now closed in the well known manner and, the electrodes and the tube being thoroughly freed of gas, a high vacuum is produced in the tube by means of the evacuating stem I. After this has been done, point I is broken in vacuum by any well known means (steel ball or high frequency), and one. adds the xenon, through pumping, into the tube, until the desired pressure is obtained (a few hundredths of a mm. if it is desired to' bring about a lowering of the starting potentiah a few tenths oi a mm. if. it is a question of obtaining 3. An electric gaseous discharge device comprising a sealed envelope containing neon intermixed with a critically small percentage of mercury vapor, the partial pressure of said mercury cury at room temperature and an amalgam within said'envelope at a point where it is not directly exposed to said discharge, the vaporpressure of the mercury in said amalgam being substantially equal to the partial pressure of said mercury in the vapor phase prior to the initiation of a discharge in said device, the quantity" of mercury evolved from said amalgam being less than the quantity of mercury lost by clean-up during operation of the device, whereby the device has the low starting potential characteristic of the gaseous mixture and emits light characteristic of the neon during operation.

' RAOUL BESSON.

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