US2006081A - Electrode for vapor electric devices - Google Patents

Description

Jun 25, 1935.

W. T. ANDERSON, JR ET AL ELECTRODE FOR VAPOR ELECTRIC DEVICES Filed March '2, 1954 2 a J 5 5 J v f FHOCOJ/ 0Z7 ATTdRNEY Patented June 25, 1935 PATENT OFFICE ELECTRODE FOR VAPOR ELECTRIC DEVICES William T. Anderson, Jr., and Lester F. Bird, Newark, N. J., assignors to Hanovia Chemical and Manufacturing Company, Newark, N. J a corporation of New Jersey Application March 2, 1934, Serial No. 713.630

'3 Claims.

This invention relates to vapor electric devices employing a rare gas and a vaporizable metal filling, and more particularly to improvements in self-heating incandescent activated electrodes for use'in such devices.

It is an object of the invention to provide automatic regulation of the electron emitting surfaces of electrodes whereby the most eflicient op erating temperature can be quickly obtained and excessive destructive temperatures are prevented; and whereby the vaporizable metal is provided in adequate concentration of vapor almost immediately after the device has been started.

The invention applies specifically to an arc lamp of the enclosed type having all the generalcharacteristics of the metal vapor arc, such as a negative volt-ampere characteristic and the necessity for an electrical circuit comprising either a ballast resistance or a choke. The rare gas, such as argon, serves in this device primarily for the initiation of the discharge which vaporizes the metal and establishes the arc. Any readily vaporizable metal such as mercury or cadmium can be employed. The electrodes are designed to be self-heating and activated with alkaline earth metal combinations, and operate at incandescence.

The invention applies specifically to such a lamp in which the electrodes are of a novel design; and in which an arrangement is provided to assist in the rapid volatilization of the metal for the arc. The electrodes are classified as belonging to the solid, incandescent, activated type which are heated directly by the vapor discharge instead of by an auxiliary electrical circuit. Electrodes of this type have at room temperature, when the discharge is initiated, a very small electron emission. The electrodes are heated by the proximity of the arc stream and by the dissipation of energy at the cathode during the emission of electrons. The Electrodes heat to incandescence, the resulting electron emission at this temperature being many times that of the cold electrode.

Self-heating thermionic electrodes for discharge lamps and are lamps have been described in the prior art and have been made in a large number of designs. They have consisted of single wires, groups of wires, cups, cylinders, and twisted ribbons, to mention a few. They have usually consisted of a refractory core metal with a coating which resists disintegration and which has a high thermionic emission at reduced temperatures. A very large variety of core metals and coating materials have been employed.

lCl. 176 122) It is of utmost importance with this type of electrode that the cathode should warm very rapidly to the operating temperature. Failure to accomplish this results in rapid destruction of the electrode and a shortened useful life for the 5 lamp. Prior to our invention, this result has been obtained by constructing the-cathode with a small mass in the form of laminations or fine wires. This construction offered to the discharge a relatively small surface for contact and 10 resulted in poor thermal conductivity to other cooling areas. As a result there was a rapid heating of the emissive surfaces, but also there was the very imminent danger that the metal core be overheated and destroyed unless very 15 critical conditions involving the proportioning of the vitreous envelope, the quantity of vaporizable metal, and the electrical operating conditions be very carefully considered and controlled. It is equally essential after the electrode has attained 20 the efiicient operating emission temperature, that further increases in temperature, which would fuse and volatilize the materials composing the electrode, and which would thereby destroy the lamp, should be prevented. 25

By means of our invention, We have perfected a mechanical structure for an electrode which results in the rapid heating of the electron emissive surface to the operating temperature, and which by virtue of unique automatically operative cooling devices prevents overheating and destruction of this surface, thereby eliminating the necessity of maintaining critical manufacturing conditions, involving careful proportioning of the vitreous envelope, and theexercising 35 of great care in measuring the quantity of vaporizable metal admitted, and the providing of critically designed electrical control apparatus for operation of the lamp. All these are conditions which must be met by the prior art in order that operative lamps possessing a reasonable practical life can be produced. Our invention results in the producing of lamps which compare most favorable with any heretofore known but which are more simplified in their construc- 45 tion.

These and other advantageous objects, which will later appear, are accomplished by the simple and practical construction and arrangement of parts hereinafter described and exhibited in the 50 accompanying drawing, forming part hereof, and in which:

Fig. 1 is a sectional view of an electrode embodying our invention,

Figs. 2, 3, 4, 5 and .6 are perspective views of 55 modified forms of electrodes embodying ourinvention,

Fig. 7 is a sectional view 0! a'portion of a vapor electric lamp showing a further modified form of electrode embodying our invention; and disclosing the use of an auxiliary external heating coil in series with the electrode, and

ll 'lg.v 8 is a sectional view of a portion of a vapor electric'lamp showing a further modified form of electrode embodying our invention; and disclosing the use of an auxiliaryinternal heating coil in series with the electrode.

Referring to the drawing, in Fig. 1 the invention is shown to consist essentially in presenting to the discharge a small area in the form of a thin edge of metal and inpreventing the destruction of this thin edge by its location with respect to cooling means.

In Fig. 1, the electrode is shown to comprise a plurality of nested metal cups 9 which are electrically connected by a weld or other suitable means, and separated by a coating In of a material which is a poor heat conductor when cold, and a good heat conductor when hot.

For example, in the modified form shown in Fig. 2, the cathode electrode can be constructed in the form of a cone H with the edge in the direction of the discharge. The inside of the cone and the edge contain and support the thermionic material, such as alkaline earth metals, the use of which for this purpose is old in the art. This cone I is nested into a second similar cone l2; which extends almost to the edge of the first cone.

The two cones are mechanically and electrically connected at some point, for example, at the bottom by a weld, Between the surfaces of the two cones is placed a material l3 0! such character that it has a very poor thermal con ductivity when cold and a very good thermal conductivity when hot. Examples of such materials are the refractory oxides of aluminum, zinc, and zirconium which are excellent insulators to both heat and electricity at room tem peratures, but which become increasingly conductive as incandenscence is approached. As a result of this laminated arrangement, when the electrode is cold, the two cones are thermally insulated from each other (excepting at the point of weld) and only a relatively small quantity of heat is required to warm the innermost cone to emissive temperature. Before the inner cone attains a destructive high temperature, the intermediate layer of materials will have warmed sufiiciently to permit the passage of a greater amount of heat energy to the outer cone, there by improving the thermal connection between the inner and outer cones and in effect increasing the radiating area of the inner cone so that its temperature cannot continue to rise. Additional radiating cones I4 and intermediate materials can be employed if desired, but the principle of operation will be the same. As a result of this novel arrangement the inner cone II is automatically protected from destruction by high temperatures and at the same time the advantage of a very rapid warming up period which is so essential for the satisfactory operation of a self-heating cathode, is maintained. This arrangement simplifies what otherwise constitutes difiicult manufacturing procedure, and it is not necessary to consider critical tube proportions nor is it necessary to avoid an excess of the vaporizable metal. By our novel electrode design tube proportions and metal content can be varied over very wide limits without slice the functim of the lamp.

In Fig. 3there is shown a modified form in which the electrode II isshownintheformofa cup with a ragged edge. The cup II is connected toasecondcup l'byaweldthecupsbeingseparated byamaterial llsuehasabove described;

the second cup II is connected to a third cup I! by a weld.

In the modified form shown in Fig. 4, the electrode has a structure of a basket weave, having longitudinal strips II and bands I interwoven with the strips, the parts being coated with a material It as above described.

In Fig. 5 the electrode I! is mounted in a reflecting cup I'I having a rounded edge ll, the electrode It and the cup being coated with the material l3 as above described.

In Fig. 6, the electrode is in the form of a mesh I! which is coated with the material I! as above described.

In Fig. '7 there is shown a modified form in which the electrode 3| is cup-shaped and is connected by a weld 3| or similar means to a disc 32 which is also electrically connected to a disc 33. Interposed between the cup and the discs are layers of a material 34 which is a poor heat conductor when cold, and a good heat conductor when hot.

In Fig. 8, the electrode 4. is cup-shaped and is electrically connected by a weld, or similar means to bowl-shaped members 4|, 2, said members and cup being separated by a layer of a material which is a poor conductor of heat when cold and a good conductor of heat when hot.

When metals which are not so readily volatile, such as cadmium, are employed for the metal vapor filling. we have found it desirable to supplement the heat produced by the e of the discharge through the lamp and the electrodes by an ohmic resistance 2| in series with the electrode and located immediately below it, as shown in Fig. '7. This heating device is not to be confused with the parallel circuit heaters of a filamentary nature which are old to the art of heated thermionic electrodes. The heater employed in our lamp is in series electrically with each electrode, which itself has only one current lead wire 2| to it. The electrical circuit is completed through the discharge in the lamp. The current through our lamp is substantially greater when the lamp is just being started than after stable operating conditions have been attained. For example, the starting current may be 8 amperes and the operating current at equilibrium only 3 amperes. Our heater is most effective therefore just after the lamp has been started, and the heat generated in it is employed to assist in the metal volatilization and the rapid establishment of stable operating conditions.

In Figs. 7 and 8 the vitreous envelope 5! of the vapor electric device is shown to have condensation chambers 5| in close proximity to the lead-in wires and the heaters. This structure obviously hastens the vaporization of the vaporizable metal 52, which condenses into chambers 5|. In accordance with our invention lamps have been constructed which operate with argon gas at pressures 1 to 8 millimeters of mercury and with a mercury vapor filling at pressures between 200 and 800 millimeters of mercury. We have made the envelope of either commercial glass or fused quartz. The electrodes, two in number, consist each of three cones II, l2, l3, (see Fig. 2) formed of metallic nickel having a melting point at 1450 degrees centigrade. Their wall thickness is about 0.009 inch. Their diameter at the top of the cone is 11 millimeters and at the bottom of the cone 7 millimeters. Their form enables them to be nested together quite closely. The inside of the two outer cones is completely covered with a thin layer of the temperature controlling materials. A very large variety of these materials alone and in mixture have been found efllcacious. We have found that any of the weakly basic metals, such as aluminum, zinc, and zirconium, which form oxides resistant to high temperatures and which are not readily reduced to the metal, are possessed of the necessary temperature regulating properties. The oxides, or compounds which yield the oxides of such metals, are formed into a thin slime employing as a vehicle a liquid hydrocarbon such as carbitol, which does not flow too freely. The treated cones are baked at a red heat in air and in vacuum. During the process the metallic oxides form an adherent layer upon the inside of the cones, this layer having very poor thermal conductivity when cold, but conducting heat readily when warmed to about 900 degrees centigrade.

When one of these cones is inserted into a second cone, the two can make thermal contact principally through these poorly conducting layers l3. The layer I3 is also, when cold, a poor conductor of electrical energy. It is therefore necessary to make electrical contact between the metal cones at some point. This is most conveniently accomplished at the bottom of the cones by means of a small spot weld, which also serves to mechanically attach the cones. The two cones are then inserted into the third and attached in a similar manner. The outside cone I4 is attached to the support rod 22 which is in turn fused into the glass or fused quartz. This support rod may be made of tungsten, and in the form of a straight rod. or as an inside heating coil 25 (see Fig. 8). The inside of the innermost cone II is treated with the thermionic materials, such as employed in the familiar Wehnelt electrode.

Before assembly in the lamp, the completed electrodes are heated to incandescence in vacuum, during which process the oxides in the layers form more compact attachment between the The electrodes are then assembled into cones. the envelope and the whole degassed in the usual manner. The metal vapor and the rare gas are introduced, and the tube is sealed by fusion.

If the additional heating coil is desired and if it has not been incorporated as a portion of the support rod. it can be provided in the form of a small external heating coil (see Fig. '7) in series with the lead-in wire 2| and encircling the lead-in seal; or as an internal heating coil in series with the lead-in wire 26 as shown in Fig. 8. A chromium-nickel alloy is satisfactory material for the heater.

The lamp which we have described requires a voltage shock for the establishment of the discharge. This is provided by any one of the inductive methods which are well known to the art. The lamp for alternating current operation employs a stabilizing reactance in series with one of related to cones, it is evident that the underlying principles of our invention are equally applicable to other forms of laminated structures, such as shown in Figs. 1, 3, 4, 5, 6, 7 and 8.

The foregoing disclosure is to be regarded as descriptive and illustrative only, and not as 'restrictive or limitative of the invention, of which obviously an embodiment may be constructed including many modifications without departing from the general scope herein indicated and denoted in the appended claims.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent, is:

1. A self-heating incandescent activated electrode for vapor electric discharge devices comprising at least two pieces of core metal, a layer of a material of variable heat conductivity comprising a metallic compound of the group including aluminum, zinc, and zirconium, separating the core pieces substantially throughout their area in such a way that when the electrode struc-' ture is cold, heat is poorly conducted from one piece of the core metal to another piece of the core, and so that heat is readily conducted be tween the parts of the core materials when the electrode is at an elevated temperature to pro-' vide a self-regulating temperature control for the portion of the electrode that is exposed to electronic or molecular bombardment by an automatically efiective increase in the radiation surface and mass of the electron emissive surface, and means to electrically connect the parts of the laminated core structure.

2. A self-heating activated electrode for a vapor electric discharge device composed of a laminated structure of core material, inorganic metallic compoundsof the group including aluminum, zinc, and zirconium, separating individual parts of said structure, said inorganic metallic compounds having relatively poor heat conductivity when at room temperature and relatively good heat conductivity when at a red heat or at higher temperatures, so that one portion of the electrode structure can be warmed to red heat while thermally insulated from other portions of the electrode structure, and becomes automatically thermally connected to the other portions of the electrode as soon as red heat or higher temperatures have been attained.

3. In a vapor electric device, an envelope containing rare gas and a vaporizable metal and electrodes, at least one of said electrodes being of the self-heating incandescent activated type and comprising a laminated core construction of alternate layers of metal and compounds of the group including aluminum, zinc, and zirconium, which are good thermal insulators at normal temperatures and good thermal conductors at high temperatures, said substances preventing heat passing readily from the portion of the electrode bearing the electron emissive surface when the electrode is below 600 degrees centigrade and enabling heat to pass readily from one portion of the electrode to other parts when the electron emissive surface has attained temperatures above 600 degrees centigrade. and means to electrically connect the alternate layers of metal.

4. In a vapor. electric device, a cathode structure comprising alternate layers of substances that are good thermal conductors and radiators at all temperatures and of compounds of the group including aluminum, zinc, and zirconium, that are poor heat conductors at normal temperatures but good heat conductors at high temperatures, said arrangement of heat conductors providing an automatic temperature control for the thermionic surface of the self-heating cathode, and means to electrically connect the layers of substances that are good thermal conductors and radiators at all times.

5. In a vapor electric discharge device composed of an envelope, electrodes mounted at opposite ends of the envelope, a filling of an excess of an easily vaporizable metal and a rare gas, at least one of said electrodes being of the selfheating activated type having a single lead-wire, condensation chambers located in close proximity to the lead-in wires and seals of the electrodes, and a heating coil in series with the self-heating activated electrode so that the current flowing to the electrode passes through the heating coil so that the heat generated by the heating coil assists and controls to some extent the pressure of the metal vapor content of the lamp.

6. In a vapor electric device, an envelope containing rare gas and an excess of vaporizable metal, electrodes of the self-heating incandescent activated type mounted in said envelope, each electrode comprising a laminated core construction of alternate layers of metal and substances which are good thermal insulators at normal temperatures and good thermal conductors at high temperatures so that heat cannot pass readily from the portion of the electrode bearing the electron emissive surface when the electrode is below 600 degrees centigrade and can pass readily from one portion of the electrode to the other parts when the electron emissive surface has attained temperatures above 600 degrees centigrade, and condensation chambers located in close proximity to the lead-in wires and seals of the electrodes, and heating coils in series with the electrodes such that the current flowing to the electrodes passes through the heating coils to assist and control to some extent the pressure of the metal vapor within the lamp.

7. In a vapor electric device, an electrode of the self-heating activated type, comprising at least two metal members, one of said members having an electron emissive surface, means for electrically connecting said members, and an inorganic substance separating said members, said substance being a compound of any of the weakly basic metals which form oxides resistant to high temperatures and which are not readily reduced to the metal and having poor heat conductivity when cold and good heat conductivity when hot.

WILLIAM T. ANDERSON. JR. LESTER F. BIRD.

CERTIFICATE or CORRECTION.

Patent No. 2,006,081. I June 25, 1935.

WILLIAM T. ANDERSON, m, ET AL.

it is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, second column, lines 33 and 34, claim 1, strike out the words "the parts of the laminated core structure" and insert the words said core pieces; and line 50, claim 2, after "attained" insert the words and means to electrically connect the parts of the laminated core structure; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 13th day of August, A. D. 1935.

Leslie Frazer (Seal) Acting Commissioner of Patents.

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