US2913298A

US2913298A - Cold and hollow electrode

Info

Publication number: US2913298A
Application number: US701671A
Authority: US
Inventors: Lemaigre-Voreaux Pierre
Original assignee: Claude Paz et Visseaux SA
Current assignee: Claude Paz et Visseaux SA
Priority date: 1956-12-19
Filing date: 1957-12-09
Publication date: 1959-11-17
Anticipated expiration: 1976-11-17

Description

5 P. LEMAlGRE-VOREAUX 2,913,293

COLD AND HOLLOW ELECTRODE Filed Dec. 9, 1957 [/v l/E/V 70/2 PIERRE Lmlmlazz-l oflz'fiux United States Patent COLD AND HOLLOW ELECTRODE Pierre Lemaigre-Voreaux, Paris, France, assignor to Claude Paz et Visseaux, Paris, France Application December 9, 1957, Serial No. 701,671

Claims priority, application France December 19, 1956 1 Claim. (Cl. 316-26) This invention relates to cold and hollow electrodes for gaseous electric discharge lamps and is an improvement in or modification of the invention described in the specification of my prior patent application No. 562,565 filed January 31, 1956, titled Cold' and Hollow Electrode and owned by the present assignee.

In the specification of the prior patent application above referred to there is described a cold and hollow electrode for an electric discharge lamp containing gas and mercury vapour such electrode having aflixed to the inner wall thereof at least one small piece comprising, mainly or solely, one or more rare earth metals such as lanthanum in a metallic condition. In such an electrode, the total area of the piece, or pieces, is small and remains small, as compared with the area of the inner wall of the electrode and preferably is smaller and remains smaller than one tenth of the area of such wall, at least during almost the whole life of the electrode.

In a copending patent application No. 670,714 filed July 9, 1957 is disclosed an improved step in the formation process of electrodes according to the above patent application, such step comprising a heat treatment in an atmosphere of nitrogen.

An important object of the present patent application is to provide electrodes of the kind disclosed in the patent application No. 562,565 the voltage drop of which remains still longer relatively low.

The present invention is characterized in that the electrode, provided with its piece, or pieces, comprising rareearth metal, is subjected to electric discharges in an atmosphere of helium with an atmosphere of a few millimeters of mercury when cold. The helium used contains at most a relatively small proportion of impurities, especially as regards the oxygen content.

This improvement applies whatever may be the nature of the discharge atmosphere wherein the electrode will normally be required to operate whether such atmosphere contains helium or not, the latter case being by far the most frequent occurrence.

Like nitrogen, used in the process described in the prior patent application No. 670,714, the employment of a helium atmosphere will reduce considerably the oxidation of the surface of the rare earth metal pieces as compared with a similar treatment efiected in traces of air which may remain after a moderate pumping. The use of helium as opposed to nitrogen offers the following advantage: it reduces considerably or eliminates entirely, depending upon its nitrogen content and upon the treatments to which the electrode is subjected, the superficial nitrogenation of the lanthanum or other rare earth metal (including cerium) or alloy. This nitrogenation would decrease the absorption capacity of the metal for gas and might result in an excessive evolution of nitrogen if the electrode were used for too high currents in view of its dimensions. Electrodes, treated according to the present invention utilize better than those of the patent application No. 670,714 the advantageous properties of the metals or alloys in question, while with- 2,913,298 Patented Nov. 17, 1959 application No. 562,565, is described hereinafter, by way of example, with reference to the accompanying drawing which shows said electrode in longitudinal section.

As described in the specification of the patent application No. 562,565, the electrode may comprise a cylinder 1 of nickel plated sheet .iron at the ends of which two steatite pieces are located such pieces comprising a bottom 7 and a ring 2 the latter incorporating an orifice 3 and a collar 5 which serves to protect the edge 4 of the cylinder 1. A current lead-in wire 8 is welded to the cylinder 1 and one or more sections 6 of lanthanum wire have been welded inside the cylinder in the vicinity of the bottom piece 7.

After the various portions of the electrode have been assembled, the electrode is subjected to a degassing and formation treatment, which, at the same time, degasses the inner surface of the envelope inside which said electrode is mounted. Such treatment may, for example, be as follows:

Two similar electrodes are sealed in a vacuum-tight manner, respectively, at the ends of a glass tube provided with an exhaust tube. The tube is then connected, by means of exhaust tube, to a vacuum pump, so as to drain it fairly completely of air. The tube is then filled with commercial helium under a pressure of the order of one or two millimeters, and the two electrodes are connected to a current source so as to set up between them, an electric discharge, the intensity of which is gradually in creased. This discharge heats up the glass of the tube and raises the electrodes to dull red. When the heating is sufficient, the evacuation of the tube is resumed and the discharge is stopped while continuing the pumping, until a fairly good vacuum is obtained, so as to eliminate the gases which have been released from the electrodes and from the inner wall of the tube, as well'as the rest of the helium which was introduced.

In the case of an electrode designed for a current of 0.1 ampere in normal operation, the intensity of the discharge used for the above treatment may for example increase from 0.1 to about 0.3 ampere the duration of the treatment being about three minutes. Such a discharge is less powerful than that which would be required to be used if the electrodes did not include any lanthanum but it is suflicient in the circumstances however, since the lanthanum will then absorb whatever traces there may be of harmful. gas. There are several advantages in employing a relatively weak discharge. The equipment required for manufacture is simplified and the fluorescent material which possibly coats the tube is affected but very slightly by the treatment. The advantages of use of helium in the treatment have been indicated above.

Discharge tubes, the electrodes of which have been treated in the manner above described may have any atmosphere used normally in cold cathode tubes and may contain nitrogen or not.

The piece of lanthanum may be changed to pieces comprising mainly lanthanum or other rare earth metals or alloys.

What I claim is:

In a process for manufacturing a cold and hollow electrode for an electric discharge device having a gas and mercury vapor atmosphere, said electrode comprising at least one small metal piece fixed to the inner surface of the hollow of said electrode, said metal comprising mainly at least one rare-earth metal in a metallic condition, the step of subjecting the electrode provided with said piece and placed in an enclosure'to electric discharges in an atmosphere of helium with an absolute pressure of a few millimeters of mercury when cold, the helium containing at most a relatively small proportion andthe intensity of said dischargesbeing at least equal to the normal working intensity of the electrode, and the subsequent step of pumping said enclosure.

References Cited in the file of this patent of impurities, especially as regards the oxygen content 10 2,456,968

UNITED STATES PATENTS Longini Dec. 21, .1948