US2488727A

US2488727A - Electrode for electric discharge devices

Info

Publication number: US2488727A
Application number: US854A
Authority: US
Inventors: Klasens Hendrik Anne; Junction Mitcham; Holmes Thomas
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1947-01-13
Filing date: 1948-01-07
Publication date: 1949-11-22
Anticipated expiration: 1966-11-22

Description

Nav. 22, 1949 H. A. KLAsENsET AL 2,483,727

ELECTRODE FOR ELECTRIC DISCHARGE DEVICES Filed Jan. 7, 1948 Patented Nov. 22, 1949 ELECTRODE FOR ELECTRIC DISCHARGE DEVICES Hendrik Anne Klasens, Mitcham Junction, and Thomas Holmes, London, England, assignors to General Electric Company, a corporation of New York Application January 7, 1948, Serial No. 854 In Great Britain January 13, 1947 1 Claim.

This invention relates to electric discharge devices and in particular to discharge lamps of the cold starting type filled with gas and/or metal vapor at a low pressure. When a sumciently high voltage is applied between the electrodes of such a tube the lamp strikes. The cathode losses are high initially but decrease when the electrodes are heated up by the discharge until a final equilibrium is reached whereby the voltage drop near the cathode is small but just enough to keep it at the requisite emitting temperature.

It is a disadvantage of the conventional types of electrodes, consisting of a metal wire coated with emitting material, that the coating disintegrates during life, especially during the period when the electrodes are heating up and the cathode losses are high. The life of the lamps is shortened by this disintegration. Moreover the sputtered material will be deposited on the glass wall near the electrodes causing an unsightly blackening. It is known that the life of the tube can be improved by using a solid rod of emitting material enclosed in a wire helix. The emitting surface still disintegrates but the emission is continuously restored by diiiusion of the emitting material, for example an alkaline earth metal, from the inside to the surface. This does not prevent however the deposition of sputtered material on the glass.

It is an object of our invention to provide an electrode of the cold starting type which will have a very long life. Other objects are to provide an electrode which is highly resistant to disintegration, heats up quickly upon starting of the discharge and requires only a small voltage drop to keep it at the requisite temperature during operation, and minimizes or' practically eliminates blackening of the surrounding envelope.

Other objects and advantages of our invention will appear from the following description and from the drawing which is a somewhat diagrammatic elevation of one end of a gaseous discharge lamp embodying an electrode comprising our invention. 7

According to the present invention, in an electric discharge lamp of the type referred to above and comprising a sealed envelope l filled with gas and/or metal vapor at low pressure, the electrodes 2 are constituted of hollow bodies made of an alloy of one or more alkali metals or alkaline earth metals with a metal or metal alloy capable of forming a substantially homogeneous alloy therewith. Preferably the alkaline earth or a nickel-copper alloy. The surface of such emissive alloys can be made strongly emitting by mild oxidation (e. g., by heating in an atmosphere of oxygen) whereby a thin layer of metal oxide is formed, followed by heating in a vacuum at such temperature that the alkali metal or alkaline earthdifiuses to the surface. In this way a surface layer is formed, comprising inter alia the free alkali metal(s) or the free alkaline earth metal(s) or a mixture of these metals, together with the oxide(s) of the said metal(s).

The said alloy may be made by melting together nickel and barium in the absence of air, e. g., in the atmosphere of argon. To prevent evaporation of barium, chromium may be added, and a certain percentage of copper may also be added to increase the solubility of the barium.

A suitable composition is:

Per cent Barium 0.5 Chromium 1.0 Copper 10.0

Nickel, balance.

The material is drawn into tube form, and

the tubes are activated by heating for about 20 seconds in oxygen at 10- mm. pressure, for inlamp the discharge covers only the inside of the tube, i. e., the so-called hollow cathode effect is obtained. In the case of a discharge lamp filled with argon at about 3 mm. pressure,

an internal diameter of 2 mm. is satisfactory.

It will be understood that each end of the envelope 1 is provided with an electrode 2 which may be supported by a lead-in conductor 3.

According to a further feature of the invention a shield 4 which may be in the form of a plate may be positioned adjacent the open end of the electrode 2 so as to cover the opening while leaving suflicient space for the discharge to pass between the shield and the inside of the electrode. In this way any blackening of the envelope of the lamp near the electrode, which in any case is greatly diminished because the sputterlng takes place only inside the electrode and nearly all the sputtered material is collected on the electrode itself, is substantially eliminated metal used is barium and itis alloyed with nickel as sput material escaping from e p n 3 A end of the electrode will be collected on the shield. A slight bombardment of the outside of the electrode may still take place and cause sputtering of metal and blackening of the envelope, but this may be prevented by coating the outside of the electrode with an insulator, such as glass as indicated by the dotted outline 5.

Electrodes made according to the invention have a very long life, not only because the emitting layer strongly adheres to the metal carrier but also because any loss in emitted material is replenished from the body of the electrode. Another advantage is that heat losses by convection are low, so that the electrodes are heated up very quickly on starting and only a small voltage drop is necessary to keep them at the requisite temperature during operation of the lamp.

What we claim as new and desire to secure by Letters Patent of the United States is:

In a gaseous electric discharge device, an electrode comprising a hollow body composed of a substantially homogeneous alloy containing mainly nickel together with approximately 10% copper, 1% chromium and 0.5% barium.

HENDRIK ANNE KLASENS. THOMAS HOLMES.

REFERENCES CITED The following references are of record in the