US2128270A - Lighting device - Google Patents

Description

2 Sheets-Sheet 1 R R a K INVENTOR Hans J Spanner av Wrz'ab Doe/171 MLA ATTORNEY Aug. 30, 1938. H. JfSPANNER ET AL LIGHTING DEVICE Filed March 30, 1929 Aug. 30, 1938. H. J. SPANNER ET AL LIGHTING DEVICE Filed March 250, 1929 2 Sheets-Sheet 2 ma N e a I I I I l I I y.

11 011.5 BY Vln'ck Patented Aug. 30, 1938 UNITED STATES PATENT OFFICE LIGHTING DEVICE Application March 30, 1929, Serial No. 351,368 In Germany April 30, 1928 13 Claim.

This invention relates to gaseous discharge devices and more particularly to gaseous discharge illuminating devices adapted to furnish either or both visible and ultra-violet radiation by a lumi- 6 nous electrical discharge from a hot cathode.

Heretofore tubes of the type commonly known as neon or gaseous discharge tubes have em ployed an electrical discharge through a tube filled with an inert gas such as neon. In such tubes the discharge usually takes place between cold electrodes and is characterized by a high voltage drop which takes place near the cathode and is called the cathode drop. These tubes require a very high voltage which, as stated, is largely consumed in the cathode drop, which high voltage is in itself capable of supporting and maintaining the discharge. Inasmuch as in such tubes the discharge provides its own ions it can be readily understood that the discharge is extremely sensitive to slight changes in gas pressure, impurities contained in the gas, and so forth. The high voltage required is also a disadvantage because of the extra cost of the high voltage transformer required and because of the personal hazard involved when such high voltages are brought onto the premises oi the ordinary customer of the lighting company. Furthermore the high voltage cathode drop produces a high velocity of the ions within the tube and 8 the resulting ionic bombardment oi the cathode disintegrates it and the tube consequently has a short life.

Oxide coated cathodes both filaments and indirectly heated sleeves, etc., have been commonly used in radio tubes and the eil'ect of the oxide coating to activate or increase the electron emission of the heated cathode is well known. It has also been suggested to use cathodes or this type in gaseous discharge tubes, but this has not been considered satisfactory because of phenomena such as ion bombardment which occur in gaseous discharge tubes but are not encountered in vacuum tubes such as thermionic valves.

One object of our invention is to provide in gaseous discharge tubes operating at widely dlfferent gas pressures and with rare gases or metal vapors or both, and with various current inputs,

a thermionic cathode which will give full advantage of the activation with an electron emittingmaterial, but which, unlike other devices of this nature known prior to our invention, will maintain its desirable characteristics over a long useful life.

Another object of our invention is to provide a device of the character described in which the electrode drop is so far reduced by activation that the device may be operated by direct connection to a. low voltage distributing circuit.

Another object of the invention is to simplify the construction and operation of devices of the character described by the elimination of the necessity for heating transformers and even by the entire elimination of heating circuits.

Other objects and advantages of our invention will be apparent to those skilled in the art from the following description and drawings.

In the accompanying drawings we have shown a preferred embodiment of our invention and various modifications thereof which we have chosen with a view to explaining the principles involved in our invention and the method of applying them to practical use. These, of course, are not to be taken as limiting, but merely illustrative of our invention.

Fig. l is a longitudinal ,section of a lighting tube, the external connections thereof being shown in diagrammatic form;

Fig. 2 is an enlarged section of one of the oathodes oi' the tube shown in Fig. 1;

Fig. 3 is an enlarged section of another form of cathode;

Fig. 4 is an enlarged longitudinal section of the cathode filament as used in another form of the invention;

Fig. 5 is an enlarged longitudinal section of still another form of a cathode filament;

Fig. 6 is a detailed sectional view of another cathode employing a diilerent form of insulation;

Fig. 7 is a detailed sectional view of still another i'orm of cathode; and I Fig. 8 is a sectional view of another form of gas discharge lighting device, the external connections being shown in diagrammatic form.

A suitable container or tube for the gaseous discharge is shown at H and has enlarged portions i2 and III at each end for the reception of electrodes. This tube may be of ordinary glass or if it is desired to make use of the ultra-violet radiation it may be of quartz or suitable material which permits the ultra-violet rays to pass through, or special effects may be attained by the use of colored or fluorescent material such as lead glass, glass with an addition of scandium or with varnishes of fluorescent materials. The tube may be filled with a rare gas or a gas or vapor of a chemically inert substance such as mercury vapor. Or preferably an inert gas and a metal vapor are used together, the gas serving to provide a medium for carrying the initial discharge when the device is started and the mercury vapor becoming available after starting as the heating of the initial discharge vaporiaes the metal.

The detailed construction of one o! the electrodes which is specially adapted for use as a cathode in such a lighting tube is shown in Fig. 2. The complete tube illustrated in Fig. l is shown connected to an alternating circuit and therefore each electrode is 01' this special form. It should be understood that when used on a direct current circuit it is only necessary to have one electrode in this special cathode form and the other electrode or anode may be constructed oi. graphite or other suitable material.

The reference character it indicates an inclosing shell which may be cylindrical in form and may be one of the metals which form amphoteric oxides. As illustrative of the class or compounds known as amphoteric oxides may be mentioned aluminum oxide, zirconium oxide, nickel oxide, iron oxide, copper oxide, cobalt oxide, and chromium oxide. On this shell It as a support may be provided a layer is of highly emissive material whose electrons work function is less than three volts and which does not attack the glass of the container, such as barium, strontium, calcium, or thorium, or some compound thereof such as an oxide, carbide or silicide. A layer oi the amphoteric oxide may advantageously lie between the metal base and the activating surface mass. The nickel, or other material. of the shell diiiuses slowly through the barium in the form of an amphoterlc oxide and tends to prevent the too rapid dissipation of the barium. Insteadot the coating on a metal which forms an amphoteric oxide, a coating may be used which is a mixture of an emissive substance such as barium oxide, with an amphoteric compound such as aluminum oxide, zirconium oxide or nickel oxide. The amphoteric oxides unite with the emissive oxides to form compounds such as barium aluminate, barium zirconate, barium nickelate, and so i'orth.

The emissive material may also with advantage be distributed throughout the body oi the cathode so that the emlssive substance, as it is slowly released by heating and action oi the discharge, may difluse to the outside of the cathode and become effective.

A cathode constructed as indicated above is particularly suitable for use because it is resist-t able to ion bombardment and is not subject to mechanical disintegration by crumbling away. By the above means such highly emissive substances as caesium and rubidium have been satisiactorily used for the cathode material which were impossible to use heretofore because 01 their disassociation tendency, vapor pressure, and so forth.

The materials used for their emissive properties may be used as oxides and because 0! improved ignition and reliability they may also be used in the form of such compounds as hydrides, nitrides, cyanides, asides, and so forth, which decompose by heating and tree the metal. The metal is held by the amphoterlc oxide probably by ejecting some of the aluminum, nickel, and so forth, or by forming so called complex compounds, e. g. by means of additional valences.

Within the shell it there may be provided a separate heating element which as shown is in the form of a double helix II oi wire with which are connected two leading-in terminals l1 and It. The space within the shell It not occupied by the heating element may be iilled with elecareas-1o trical insulating material is. By thus lnclosing the heating element and shielding it from the space in which the gaseous discharge takes place it is possible to operate the filament at a higher voltage such as directly from the line without in any way aflecting the gaseous discharge. With such higher voltages the selection oi the proper insulating materials becomes a matter of considerable importance.

Heretoiore quartz has sometimes been used but is open to the objection that it will combine with tungsten at the higher temperatures to form tungsten silicate with the result that the tungsten is gradually eaten away. Another objection to quartz as well as to certain other materials is that at red temperatures there takes place electrolytic current flow because oi the sodium or potassium ions which are always present. To some extent magnesium either in the form of oxide or in the form of steatite has been used. This also is open to the objection that it attacks tungsten chemically and moreover its resistance tails oi! rapidly at the higher temperatures.

Besides the requirement that there shall be little or no electrolytic current flow or actual movement of ions it is also necessary that the metallic or electronic conductivity shall be low. In general, electronic conductivity is inversely proportional to the electrons work-function.

Materials which are particularly adapted for use in accordance with the above requirements are compounds, especially oxides of zirconium and beryllium and also 01' pure aluminum and scandium. Furthermore, the oxide of beryllium and zirconium have a very, high melting point and remain chemically quite indiil'erent to such materials as are used for filaments and heating elements. These materials may be used as a powdered mass and they may also be used by being sprayed on the heating body and filament and thereafter sintered at a temperature at about 2000' centigrade so as to form a covering or enamel on the wire.

Referring again to Fig. 1 the terminals l1 and it of the filament it are connected to conductors 20 and 2|. The conductor 2| is connected directly to one terminal 01 a line switch 22 and the other conductor 20 is connected through a resistance 23 to a conductor 2! which is connected to the other terminals of the switch 22. The

shell oi one of the cathodes is connected through a terminal 2! to the conductor 2| while the shell oi' the other cathode is connected through a terminal 26 to the conductor 24. The conductor 2| may have connected in its circuit an inductance coil 21 which limits the current passing through the gaseous discharge path between the two electrodes. The cathode connected to the conductor 2|. has positioned adjacent thereto an auxiliary anode 22 which anode has a terminal 29 which is connected through a high resistance 30 to the conductor 20. Likewise the cathode connected to the conductor 2| has positioned adjacent thereto an auxiliary anode 3i which has a terminal 32 connected through a high resistance 33 to the conductor 2i.

In operation the switch 22 is closed and the current passes through the resistance 23 and into the terminals l1 and ID of both cathodes and heats the emissive material on the cathodes. When the temperature on the cathodes is suinciently high and the rate of emission is suiflcientiy great a gaseous discharge starts between the auxiliary anode 28 and the cathode adjacent thereto and also from the auxiliary anode aisasvo II and the cathode adjacent thereto. Because of the high resistances 30 and Il in series with these auxiliary anodes the current flow to the auxiliary anodes is limited and the discharge is transferred for the most part to the gaseous path between the main electrodes.

Because of the emissive materials on the oathodes there is no so-called cathode drop and the tube operates on the ordinary voltages of a distribution circuit such as 110 volts or 220 volts. The use of the amphoteric oxides or materials capable of forming such amphoteric oxides prevents the cathode irom disintegrating rapidly and results in a tube having a longer life than has heretofore been possible with gaseous discharge devices having a hot cathode.

The form of cathode shown in Fig. 3 is somewhat similar to that shown in Fig. 1. The heating element 36, however, is in the form of a single helix instead of a double helix as in Fig. 1. The resistance of a heating element of this form is less than that of a double helix and it is more adapted to carry heavy currents at lower potentials across its terminals. With such lower potentials across its terminals it is not so likely to interfere with the current distribution of the gaseous discharge in the neighborhood of the cathode and if the potential is sufliclently low the filling of insulating material may be omitted.

Fig. 4 shows a filament which acts both as a cathode and as a carrier for the current used for heating the cathode. A support 31 of nickel or some material adapted to form an amphoteric oxide is coated with a layer 38 of a highly emissive material such as barium oxide. Such a construction is particularly adapted for use where a low voltage is used for heating the filament.

In Fig. a supporting core 39 is covered with an intermediate layer I of an amphoteric oxide which in turn is covered with a layer ll of a highly emissive material. The layer ill of amphoteric material may be used in metallic form in which case the core may be plated with the metal in question. The core in such cases may be of tungsten. platinum. or molybdenum. When the core is plated with a metal suitable for torming an amphoteric oxide it is desirable to oxidize the surface so that thin but even and cohesive coatings may be obtained.

In Fig. 6 the metal shell II has an external emissive layer I5 and has positioned therewithin a helix 42 of wire which provides the initial heating of the cathode. The helix 4! is wound on a hollow cylinder 43 of insulating material such as zirconium or beryllium oxide. The leading-in wire I l is carried through the interior opening of the cylinder 43 and is connected to one terminal of the helix 42. The other leading-in wire I! is connected to the remaining terminal of the helix. A second hollow cylinder of insulating material 44 surrounds the helix ".and disks 4i and 46 are positioned at the ends so that the coil of helix 42 is substantially inclosed although not gas tight. In making these preformed pieces of insulating material such as cylinders, tubes, disks, etc., the substances may be ground in a colloid mill, then small amounts of acid and water added thereto to form a paste. After the paste has been given a suitable form it is then burned at a temperature somewhat higher than usually required for porcelain, clay. and so forth. a temperature of about 2200 centigrade being suitable. It may also be desirable to furnish the filament of the helix 42 with a protecting surface layer as indicated at "a in Fig. 6. This layer may be an oxide or a nitride which may be formed by bringing the filament to an incandescent temperature in an atmosphere of nitrogen or air.

Similar protection can also be obtained by a covering or layer of the borlde oi the core metal.

In Fig. '7 the emissive material is shown embedded as at l! in the body of the supporting shell Ila and a thin layer of emissive material is also provided as at ii. In Fig. 8 electrodes SI and I! are provided which have no internal means for heating the cathode but are dependent entirely upon the heating received from the gaseous discharge. either from the main discharge or from auxiliary electrodes to be presently described. Each eiectrode II and i! has posle tioned adjacent thereto auxiliary electrodes 53 and 54 respectively. A leading-in wire I! for the electrode II is connected by means of a conductor it to one of the conductors I1 01' a supply circuit. The other conductor 58 of the supply circuit is connected through an inductance coil 5!. A leading-in wire 60 for the electrode 52 is connected by means of a conductor 6| to the conductor 58 from the supply circuit. A leadingin wire 82 for the auxiliary electrode 58 is connected through a high resistance 63 to the conductor 68 from .the supply circuit and similarly a leading-in wire 64 from the auxiliary electrode 54 is connected through a. resistance 85 to the conductor 51 of the supply circuit.

Referring to Fig. 8, when the tube is first put into operation. by closing the switch which con-' nects the supply lines, the electrical potential is only suflicient to start an auxiliary discharge between the main electrode 5i and the auxiliary electrode 53, as indicated at 66. and a similar discharge as indicated at 61. These auxiliary discharges gradually heat the electrodes BI and 52 until the main discharge takes place as indicated at 88.

By the foregoing means a device has been obtained which has electrodes specially adapted for use in a gaseous discharge tube for either lighting or ultra-violet radiations. A reasonable long life is obtained, the operation is rendered simple, and the connections may be made directly from the supply line and the heating filament can also be directly connected to the supply line without employing a transformer. The electrodes can be built in any desired size which means that it is possible to operate such tubes or lamps with rare gases or metal vapors at different gas pressures and with different amperes input without noticeable disintegration, lnactlvation, or burning out by uneven action of the gaseous discharge on the heated cathode.

We claim:

1. A radiant electrical discharge device which comprises an envelope permeable to at least a part oi the radiation from the discharge, an ionizable filling adapted to carry said discharge, a plurality of electrodes permanently spaced apart therein at least one of which serves as a cathode and has an activating mass comprising iree metal of the electropositive group Ba. Sr, Ca, Cs, Rb and a refractory insulating material.

2. A radiant electrical discharge device which comprises an envelope permeable to at least a part of the radiation from the discharge, an ionizable filling adapted to carry said discharge. a plurality oi electrodes permanently spaced apart therein at least one oi which serves as a cathode and has an activating mass comprising a material of the electropositive group Ba, 8;, Ca, Cs, Rb and a reiractory insulating material, all

given strength and resistance to disintegration under ionic bombardment by heating and a part of the material of the electropositive group is free metal and a part is combined in a compound adapted to be slowly reduced by the action, of the discharge whereby to serve as a reservoir of the activating metal.

3. A radiant electrical discharge device as defined in claim 1 in which the refractory insulating material comprises a refractory oxide partially combined with the activating metal of said electro-positive group. a

4. A radiant electrical discharge device as defined in claim 1 in which the refractory insulating material comprises a silicon compound.

5. A radiant electrical discharge device as defined in claim 1 in which the refractory insulating material comprises a refractory .oxide of the group zirconium oxide. aluminum oxide.

6. In an electrical discharge device an indirectly heated cathode having a conducting member forming the cathode proper and a heating element and insulation between them consisting essentially of at least one of the pure oxides of the group beryllium oxide, zirconium oxide. scandium oxide, aluminum oxide.

7. In an electrical discharge device an indirectly heated cathode as defined in claim 6 in which the insulating oxide material is in the form of a sintered mass intimately fitting on the heating element.

8. In an electrical discharge device an indirectly heated cathode as defined in claim 6 in which the insulating oxide and the heating ele- 5 ment are separated by a protective layer oi a araaavo material or the group. nitrides and borides of the metals of the heating element.

8. The method of activating an electrode which comprises coating it with a refractory amphcteric oxide and a compound of an electropositive metal with a reducing ion constituent, mounting said electrode in a discharge tube, evacuating said tube and decomposing the compound of the electropositive metal by heating.

10. The method as defined in claim 9 in which the surface of the electrodeon which the activation is applied comprises a metal which forms an amphoteric oxide and is oxidized to form such amphoteric oxide before the compound of the electropositlve metal is applied.

11. The method of activating an electrode which comprises coating it with an activation material including a hydride of a strongly electropositive metal, mounting it in a discharge tube, evacuating the tube and heating the electrode to decompose the hydride at least partially.

12. The method of' activating an electrode which comprises coating it with an activation material including a silicide of a strongly electropositive metal, mounting it in a discharge tube, evacuating the tube and heating the electrode to decompose the carbide at least partially.

13. The method of activating an electrode which comprises coating it with an activation material including a silicide of a strongly electropositive metal, mounting it in a discharge tube, evacuating the tube and heating the electrode to decompose the silicide at least partially.

HANS J. BPANNER. ULRICH DOERING.

CERTIFICATE OF CORRECTION Patent No. 2,128,270.

August 50, 193B- HANS J. SPANNER, ET AL,

It is hereby certified that error appears in the printed specification of the above nunbered patent requiring correction'as follows: Page h, second column, line 21 claiml2, for the word "silicide" read carbide; and that the said Letters Patent should be read with this correction therein that the same conform to the record of the case in the Patent Office.

Signed and sealed this 11th day-of October, A. D. 1938.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

given strength and resistance to disintegration under ionic bombardment by heating and a part of the material of the electropositive group is free metal and a part is combined in a compound adapted to be slowly reduced by the action, of the discharge whereby to serve as a reservoir of the activating metal.

3. A radiant electrical discharge device as defined in claim 1 in which the refractory insulating material comprises a refractory oxide partially combined with the activating metal of said electro-positive group. a

4. A radiant electrical discharge device as defined in claim 1 in which the refractory insulating material comprises a silicon compound.

5. A radiant electrical discharge device as defined in claim 1 in which the refractory insulating material comprises a refractory .oxide of the group zirconium oxide. aluminum oxide.

6. In an electrical discharge device an indirectly heated cathode having a conducting member forming the cathode proper and a heating element and insulation between them consisting essentially of at least one of the pure oxides of the group beryllium oxide, zirconium oxide. scandium oxide, aluminum oxide.

7. In an electrical discharge device an indirectly heated cathode as defined in claim 6 in which the insulating oxide material is in the form of a sintered mass intimately fitting on the heating element.

8. In an electrical discharge device an indirectly heated cathode as defined in claim 6 in which the insulating oxide and the heating ele- 5 ment are separated by a protective layer oi a araaavo material or the group. nitrides and borides of the metals of the heating element.

8. The method of activating an electrode which comprises coating it with a refractory amphcteric oxide and a compound of an electropositive metal with a reducing ion constituent, mounting said electrode in a discharge tube, evacuating said tube and decomposing the compound of the electropositive metal by heating.

10. The method as defined in claim 9 in which the surface of the electrodeon which the activation is applied comprises a metal which forms an amphoteric oxide and is oxidized to form such amphoteric oxide before the compound of the electropositlve metal is applied.

11. The method of activating an electrode which comprises coating it with an activation material including a hydride of a strongly electropositive metal, mounting it in a discharge tube, evacuating the tube and heating the electrode to decompose the hydride at least partially.

12. The method of' activating an electrode which comprises coating it with an activation material including a silicide of a strongly electropositive metal, mounting it in a discharge tube, evacuating the tube and heating the electrode to decompose the carbide at least partially.

13. The method of activating an electrode which comprises coating it with an activation material including a silicide of a strongly electropositive metal, mounting it in a discharge tube, evacuating the tube and heating the electrode to decompose the silicide at least partially.

HANS J. BPANNER. ULRICH DOERING.

CERTIFICATE OF CORRECTION Patent No. 2,128,270.

August 50, 193B- HANS J. SPANNER, ET AL,

It is hereby certified that error appears in the printed specification of the above nunbered patent requiring correction'as follows: Page h, second column, line 21 claiml2, for the word "silicide" read carbide; and that the said Letters Patent should be read with this correction therein that the same conform to the record of the case in the Patent Office.

Signed and sealed this 11th day-of October, A. D. 1938.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

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