US2924737A

US2924737A - Glow discharge tube

Info

Publication number: US2924737A
Application number: US660323A
Authority: US
Inventors: Elings Garmt Allard; Verweij Evert Johannes Willem; Klasens Hendrik Anne
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1957-05-20
Filing date: 1957-05-20
Publication date: 1960-02-09
Anticipated expiration: 1977-02-09

Description

Feb. 9, 1960 e. A. ELINGS ET AL GLOW DISCHARGE TUBE Filed May 20, 1957 K I 3 i INVENTOR GARMT ALLARD ELINGS ARIE KOE LEWI EVERT JOHANNES WILLEM VERWE HENDRIK ANNE KLASENS BY a e.

AG NT flied m P w O 1,924,737 GLOW DISCHARGE TUBE Application May 20, 1957, Serial No. 660,323

5 Claims. (Cl. 313-355) This invention relates to a glow discharge tube containing a cathode which is coated with alkaline earth metal oxides. The invention also relates to a method of producing such a tube.

In the known glow discharge tubes provided with a barium oxide-coated cathode, the barium oxide layer is activated by means of current pulses, in which process it is partially decomposed. The liberated oxygen is absorbed by the getter in the tube. Activation by current pulses is necessary, since the pure barium oxide layer is not conductive.

This known method suffers from the disadvantage that a comparatively large amount (20%-50%) of the coating material becomes detached within the tube and that the life of the tubes, measured by the operating or ignition voltage or both, is comparatively variable. The detached material may give rise to short-circuiting between the auxiliary anode and the cathode.

It is an object of the present invention to provide a cathode coating and a method of producing a tube pro vided with such a cathode coating, which ofler advantages over previously known coatings and methods.

In a glow discharge tube containing a cathode coated with alkaline earth metal oxides, according to the invention, the oxide layer contains lanthanum oxide or cerium oxide or both, in an amount which corresponds to about 0.1 atomic percent-40 atomic percent of at least one of the latter metals relative to the total amount of metal atoms. Preferably, the alkaline earth metal is barium containing at most about 40% of strontium or calcium, or both.

According to the invention, the cathode coating is produced by applying the carbonates of the metals concerned to the metal cathode body. The assembly is subsequently heated within a few seconds to a temperature between 900 C. and 1250 C., the layer changing visibly, presumably owing to melting or sintering, the temperature being subsequently held at about 800 C.-900 C. for further degassing of the cathode.

Cathodes in accordance with the invention, which have been subjected to the above treatment, have the advantage that no further activation is required, that is to say, the coating layers show suflicient emission.

Cathodes in accordance with the invention can be further improved if at most 40% of the oxygen of the oxides is replaced by fluorine.

In order that the invention may readily be carried out, one embodiment thereof will now be described with reference to the accompanying diagrammatic drawing in which a tube having a cathode in accordance with the invention is shown and with reference to a number of examples of the composition of the layer and the manner in which it is treated.

In the figure, reference numeral 1 denotes a sectional view of the bulb of the tube in which a cathode plate 2 made of 0.2 mm. sheet-nickel is arranged. This plate is coated with an activated layer 3 of 5;; thickness. Two

nickel wires 4 having a diameter of 0.6 mm. are spaced 0.3 mm. away from the cathode. A nickel tube 5 of diameter 2 mms. is spaced away from the cathode by 3 mms. The wires 4 are the auxiliary anodes and the nickel tube 5 is the main anode. The tube is filled with argon under a pressure of 18 mms. pressure. In the production of the tube, one side of the cathode plate is coated with a layer of carbonates and, as the case may be fluorides of the metals which must be provided in the activating layer. The cathode plate is then mounted in the tube which is subsequently connected to the pump. By means of high-frequency current, the cathode plate is heated in about 2.5 seconds to a temperature between 900 C. and 1250 C. so that the changed appearance of the layer shows that the latter melts or, as the case may be, sinters. Thereupon the temperature is reduced to about 900 C. for one minute. The getter is evaporated and subsequently the tube is filled with argon to the correct pressure and operated for a certain period of time.

Satisfactory results were obtained when cathodes were coated with a coating obtained in the following way.

milligram atom of Ba(NO solution was poured into an excess of (NH CO solution. The precipitated carbonate was filtered, washed with water and with alcohol and dried. Thereafter the carbonate was mixed with butyl alcohol and some binder in a mortar. A quantity of hydrofluoric acid diluted with alcohol was added such that 0.5% of the carbonate was converted into fluoride. The product thus obtained was applied onto a cathode plate and treated as described.

Another coating was prepared in the same way as above which originally departed from 100 milligram atom Ba(NO with 1 milligram atom of La(NO or 10 milligram atom of La(NO In the last case results were obtained also when 5.15 or 50% of the carbonate was converted into fluoride.

In another experiment the carbonate was prepared from 100 milligram atom Ba(NO l0 milligram atom La(NO 1 milligram atom Ce(NO 0.5% of the carbonate was converted into fluoride. Also 30 milligram atom of Sr(NO could be added or only 15 milligram atom of Sr(NO and the La(NO left out but 5% of the carbonate converted into fluoride.

Another carbonate was prepared from 100 milligram atom of Ba(NO and 3 milligram atom of Ce(NO Here also 1.5% of the carbonate could be converted into fluoride in the Way described or 3 milligram atom of Ni(NO was converted into carbonate.

What is claimed is:

1. A glow discharge tube having a cathode coated with a layer consisting essentially of alkaline earth metal oxides and an oxide selected from the group consisting of lanthanum oxide and cerium oxide in an amount corresponding to about 0.1 to 40 atomic percent of at least one of the latter metals relative to the total number of metal atoms in the layer.

2. A glow discharge tube as claimed in claim 1 in which less than about 40% of the oxides are replaced by the corresponding fluorides.

3. A method of manufacturing a glow discharge tube comprising the steps, coating a support with a layer consisting essentially of alkaline earth metal compounds which decompose upon heating to form the corresponding oxides and a compound of metal selected from the group consisting of lanthanum and cerium which also decomposes upon heating to form the corresponding oxide, said layer containing an amount of the compound of said latter metal which corresponds to about 0.1 to 40 atomic percent of at least one of the latter metals relative to the total number of metal atoms in the layer,

3 4 heating the coated support to a temperature of about 900 to 1250 C. to produce a visible change in the coating, thereby forming a cathode for the glow discharge tube, and introducing an ionizable gaseous medium into an envelope surrounding said cathode.

4. A method as claimed in claim 3 inywhich less than about 40% of the compounds of the alkaline earth metal which decompose upon heating to form the corresponding oxides are replaced by the corresponding fluorides.

5. A method as claimed in claim 3 in which the coated support is heated in the envelope and the envelope degassed after the cathode is formed.

5 References Cited in the tile of this patent UNITED STATES PATENTS I 1,922,244 Hunter Aug. 15, 1933 2,273,762 Reerink Feb. 17, '1942 10 2,586,768

Bash Feb. 26,- 1952 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,924,737

February 9, 1960 Garmt Allard Elings et a1.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should readas corrected below.

Column 3,

line 8, before "which" insert and the latter metal Signed and sealed this 12th day of July 1960.

(SEAL) Attest:

EKARL H. AXLINE ROBERT c. WATSON Attesting Officer Commissioner Of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION February 9, 1960 Patent Noa 2,924,737

Garmt Allard Elings et alt It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below. I p

i In the heading to the printed specification between lines 8 and 9 insert Claims priority, application Netherlands May 29 1956 Signed and sealed this 25th day of October 1960 (SEAL) Attest:

KARL Ho AXLINE ROBERT c. WATSON Commissioner of Patents Attesting Officer

Claims

1. A GLOW DISCHARGE TUBE HAVING ACATHODE COATED WITH A LAYER CONSISTING ESSENTIALLY OF ALKALINE EARTH METAL OXIDES AND AN OXIDE SELECTED FROM THE GROUP CONSISTING OF LANTHANUM OXIDE AND CERIUM OXIDE IN AN AMOUNT CORRESPONDING TO ABOUT 0.1 TO 40 ATOMIC PERCENT OF AT LEAST ONE OF THE LATTER METALS RELATIVE TO THE TOTAL NUMBER OF METAL ATOMS IN THE LAYER.