US1971891A - Electric discharge tube and process of operating same - Google Patents

Description

Aug. 28, 1934. ZECHER 1,971,891

ELECTRIC DISCHARGE TUBE AND PROCESS OF OPERATING SAME Filed May 22. 1930 In ved'or,

A ctc' r/ze y- Patented Aug. 28, 1934 UNITED STATES ELECTRIC DISCHARGE TUBE AND PROCESS OF OPERATING SADIE Gustav Zecher, Eindhoven, Netherlands, assignor, by mesne assignments, to GeneralElectric Company, a corporation of New York Application May 22, 1990, Serial No. 454,606 In the Netherlands June 8, 1929 12 Claims. (o1. 176-42) This invention relates to an electrical discharge tube, used either as an illuminating element, or as a generator of special properties radiation, such as ultra-violet rays. For such purposes the tube contains electrode material consisting of an alloy or mixture of metals in the form of an amalgam, say cadmium amalgam. In this way it is possible to obtain light or other radiation from the tube showing the characteristic spectrum of a metal found in the amalgam without danger of cracking the tube when its liquid electrodes solidify, whereas, if such metal, say cadmium, or sodium, is used by itself as electrode material there is risk that the tube will break either when the metal cools to a solid or when the tube is again started.

If a suitable alloy or mixture of metals is made the basis for the introduction of any metal whose spectrum is desired, it is found that the danger of destroying the tube is greatly lessened compared to the risks run when that particular metal is used as a sole electrode material. Discharge tubes of the kind in question, however, when operated with electrodes consisting of a mixture or alloy of metals present the disadvantage that the light or radiation from the discharge exhibits essentially the spectrum of the most volatile metal in the mixture, consequently, if an amalgram is used, the spectrum would be essentially that of mercury. For this reason it has been found necessary to connect a condensing chamber to the discharge tube of such a size as to be just capable of storing all the vapor of the most volatile metal of the alloy, the mercury, for

instance, in case an alloy is used as electrode material.

For some time after such a discharge tube, to which a condensing chamber or vesselis connected, is put into service the discharge will take place essentially through the vapor of the least volatile metal, hence the light given ofi will exhibit essentially the spectrum of the vapor of said metal. After the discharge has been interrupted the metal which has collected in the condensing chamber must be again mixed with the less volatile metal, which may be effected by tipping the discharge tube, otherwise the tube might crack. It has been found, however, that a suflicient admixture does not take place in every case so that in certain instances a breakage of the tube may result. Accordingly when using such discharge tubes care must be taken that when the discharge is interrupted the metal collected in the condens- 7 done automatically but the necessary devices materially complicate the apparatus.

As one feature of this invention it has been discovered that tubes of the kind described can be operated safely and continuously without a condensing chamber connected to the discharge tube, that is, it is possible to suppress the separate condensing vessel heretofore connected to the discharge tube, and it is one of the objects of the invention to do so.

According to the invention the discharge tube used therein preferably contains an alloy or mixture of metals constituting an electrode of the tube. This alloy or mixture may consist for example of an amalgam, say cadmium amalgam. Furthermore the structure of the tube is so de signed as to present a discharge space through which passes a separate channel serving to constantly return the metal condensed in the operation of the tube, say mercury, to the space that contains the electrode alloy or mixture of metals. In this way it is possible to obtain a light spec-- trum from the discharge tube which is essentially that of the least volatile metal, and this is a further object of the invention. The particular structure of the tube will be described in detail below.

In the drawing which is to be considered as part of this specification: Fig. 1 is a diagrammatic illustration of a discharge tube, exhibiting one form of my invention as described in this specification. Figs. 2 and 3 show diagrams of modifications of the invention.

Referring to Figure 1, the discharge tube 1 is shaped as a reversed, U tube. The limb 2 contains an alloy or mixture of metals 3 which may consist of an amalgam, say cadmium amalgam,'or of an alloy of bismuth and mercury. Good results have, for example, been obtained with a cadmium amalgam containing 20% of cadmium. The alloy 3 constitutes an electrode of the discharge tube and is connected to a leading-in wire-4, taken through the wall of the tube. The limb 5 of the discharge tube contains an electrode which consists, for example, of a supply of mercury 6 connected to the leading-in wire '7. Obviously this electrode may consist of a solid substance, or of the same alloy as the electrode 3, and it may be preferable for the ends of the'tube to be spherically enlarged. A short distance above the electrode 6 a small tube 8 is sealed into limb 5 and opens out just above the electrode 6. This tube 8 has a bent, or zigzag, shape and has its other end sealed to the lower end of limb 2.

' discharge;

Discharge tubes of the kind illustrated will not run on the usual operating voltage until they have been ignited. This is accomplished in various ways, well known in the art, for instance the tube may be tilted or inclined to bring about an instantaneous contact between the metals of the running electrodes, and in this connection it is necessary to provide that the opening of tube 8 above electrode 6 should be so located and of such a character that no electrode material can flow into tube 8. Another way to effect preliminary ignition is to temporarily apply a very high voltage, and in some cases amalgam 3 is heated.

Supposing the tube to be successfully started by one of the well known methods referred to, with amalgam 3 as anode and electrode '7 as cathode, the first effect will be to primarily volatilize the mercury contained in amalgam 3. Consequently, in addition to the spectrum of the cadmium, supposing a cadmium amalgam, the light generated will show many mercury lines. The mercury volatilized condenses in the upper part of limb 5, thusincreasing the quantity of mercury in that limb. When the meniscus of electrode 6 reaches the opening of tube 8 the condensed mercury will be led back through the said tube to the lower part of limb 2. It has been found after the tube has been running for some time the surface of electrode3 substantially becomes cadmium and that the discharge takes place essentially in a vapor of cadmium of high pressure. The light generated by this discharge contains many ultra-violet rays, which will pass freely through the wall of the tube if thesaid wall is of quartz or other transparent material for such rays. Thus the tube can be used as a generator of ultra-violet rays, and serve as an artificial sunlight, or a source of radiation for sterilization purposes.

It has been found that with continued operation of the tube the quantity of mercury which volatilizes is but slight and does not effect the spectrum of the light emitted to any extent. Furthermore the device very greatly reduces the risk of breakage on starting or stopping the tube for the constant return or circulation of the condensed mercury keeps the average percentage of metals forming the amalgam electrode 3 nearly constant.

The discharge tube shown in Figure 2 has a straight cylindrical part 9, the spherically enlarged end of which contains an alloy or mixture of metals, say cadmium amalgam or a mixture of mercury, cadmium and bismuth 10 electrically connected to leading-in wire 11 The upper part of tube 9 has sealed to it, a short distance from the end, a cup. shaped enlarged cylinder 12 into which the end of tube 9 projects, the projection forms a circular-channel, or chute, at the base of cup 12 that connects with a tube 18 extending parallel to tube 9 and sealed into the spherical enlargement ,of said tube 9. Tube 18 as shown is considerably smaller than tube 9 and extends well below the surface of the electrode 10, which prevents any possibility of the condensed vapor carried by tube '18 congealing, or solidifying when about to discharge into the electrode 10.

Tube 9 may contain a suitable gaseous filling, for instance, one of the rare gases, the presence of which will assist the initial ignition of the The enlargement 12 carries a stem sealed therein to support an incandescent cathode 14 of the filament type, which is heated by wires 15 and 16 passing through stem 13 and forming one electrode of the tube 9. The other electrode 10 is connected to the external circuit by wire 11.

The function of tube 18 is to return the condensed vapor of mercury, or more broadly of the most volatile constituent of the amalgam electrode 10. Once the tube has settled into steady running relation there will be only a slight flow through tube 18 and as explained above it is found that in this modification also the cadmium of the amalgam collects essentially on the surface of the electrode 10, thus giving a discharge through tube 9 practically wholly in cadmium vapor with its resulting spectrum in radiation.

The form of the invention shown in Fig. 3 is similar to Fig. 2 in regard to arrangement of the discharge portion of the tube and its provisions for circulating condensed vapors back to the electrode pool of amalgam, but all the leadin wires are disposed at one end of the tube which has advantages for certain purposes, as sunlight lamps and sometimes in ultra-violet ray work.

As shown in Figure 3 lead-in wire 19, running to the electrode at the far end of the tube passes through the tube which serves also to return or circulate back the condensed vapors from the top condensing chamber to the lower electrode of amalgam. The wire 19 is protected by a tube 20 of insulation material to prevent damage by contact with the vapor flowing in the return tube.

While the channel or tube for returning the condensed vapor to the amalgam pool is shown outside the main discharge tube in the forms of the invention illustrated, it will be understood that it might also be run through the discharge space of the tube. The essential feature, broadly, being that the vapor of the most volatile constituents of the amalgamated metals in the electrode is collected by condensation and caused to fiow through a return conduit to again unite with the body of the electrode, and this process or method of operation is continued until the discharge settles down to give a spectrum of practically the least volatile metal vapor. The invention is not to be restricted to any particular apparatus or agencies for draining the easily vaporizable metals of the mixture back to the electrode pool.

What I claim is:

1. An electrical discharge tube containing a mixture of vaporizable electrode metals having different temperatures of vaporization, a discharge space, a condensation space and a conduit leading from said condensation space to the part of the tube containing said mixture of electrode metals., and discharging below the surface of said mixture.

2. An electrical discharge tube containing an electrode consisting of a mixture of vaporizable metals, one of said metals having a lower vaporization temperature than the others, said tube comprising a discharge space, a condensation space and channel means leading. from said condensation space to the part of the tube containing said electrode, and extending below the surface of said electrode.

3. An electrical discharge tube containing an electrode of mercury amalgamated with a metal having a higher vaporization temperature than mercury, said tube comprising a discharge space portion, a condensation space portion and a conduit leading from the condensation space to the portion of the -tube containing said amalgam and opening out below the surface of the amalgam.

4. An electrical discharge tube shaped substantially as an inverted U tube, an electrode material in one limb of the U tube consisting of different metals and an electrode in the other limb of a single metal in combination with a conduit connecting the lower portion of said first named electrode with the tube above the second named electrode.

5. A vapor discharge tube comprising an electrode portion containing a vaporizable electrode material containing at least two metals, a discharge portion and a condenser portion provided with a cooperating electrode and a drain tube adapted to deliver products of condensation below the surface of the two-metal electrode.

6. The process of operating electrical discharge tubes which consists in passing an electrical current through a composite electrode contained in the tube, decomposing the composite electrode and reuniting its constituents below the surface of said electrode during operation of the tube for the purpose of obtaining radiation of given spectrum characteristics.

7. A process of operating metal vapour lamps having an arc vessel containing electrode means comprising an alloy of metals of different boiling point and specific gravity, comprising the steps of condensing the constituent electrode metals after vaporization in the are, collecting the condensate of the light high boiling metal so as to be adjacent to the arc, and collecting the condensate of the heavy low boiling metals so that it is separated by virtue of its lower specific gravity from the are by a layer of said constituent of said high boiling metal.

8. A process of operating metal vapour lamps having an arc vessel containing electrode means comprising an alloy of metals of different boiling point and specific gravity, comprising the steps or condensing high boiling light constituents of said alloy inside the arc vessel, leading said condensed high boiling constituents directly after condensation to the metal at the electrodes, condensing heavy lower boiling constituents of said alloy outside the arc vessel, collecting said condensed low boiling constituents separately from said high boiling constituents, and causing said condensed low boiling constituents to flow continually back to the metal at the electrodes at the coldest parts thereof.

9. Metal vapour lamps, comprising the combination of an arc vessel having electric pole means and an electrode consisting of an alloy of metals of different boiling point and specific gravity, with receiver means for the low boiling heavy constituents of said alloy, downward flow conduit means leading from said receiver means, and inlet means whereby the low boiling constituent from said conduit means is returned to said are vessel at a point below the surface of the electrode means so as to be separated from the are by a layer of high boiling constituent.

10. A process of operating metal vapor lamps comprising a composite electrode which comprises the steps of separating the constituents of the composite electrode, leading one of the separated constituents back to the part of the electrode contiguous to the discharge and leading the other of said constituents below the surface of the electrode.

11. An electric discharge device comprising a tubular container, electrodes sealed therein, elec trode leads sealed therein at one end thereof, one of said electrodes being of vaporizable material and-located at the end of said container opposite that end into which said inleads are sealed, said container having a discharge portion and a condenser portion provided with a cooperating electrode and a drain tube adapted to deliver products of condensation below the surface of said vaporizable electrode, the lead for said vaporizable electrode being led through said drain tube.

12. An electric discharge device comprising a tubular container, electrodes sealed therein, electrode leads sealed therein at one end thereof, one of said electrodes being acomposite electrode of vaporizable material and located at the end of said container opposite that end into which said inleads are sealed, said container having a discharge portion and a condenser portion provided with a cooperating thermionic electrode and a drain tube adapted to deliver products of condensation below the surface of said vaporizable electrode, the'lead for said vaporizable electrode being led through said drain tube.

GUSTAV ZECHER.

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