GB411669A - Improvements in and relating to gaseous electric discharge devices - Google Patents

Abstract

411,669. Discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Foulke, T. E. ; 30, Evelyn Place, Nutley, New Jersey, U.S.A.) May 15, 1933, No. 14078. Convention date, May 13, 1932. [Class 39 (i).] A method of producing a gaseous electric discharge device comprises coating the electrodes with a decomposable nitrogen compound of an alkali or alkaline earth metal, reducing the compound partly to the metal and partly to another nitrogen compound without exposing said electrodes to deleterious gases and oxidizing treatment, evacuating, introducing the desired filling and sealing-off the device. In one example electrodes of nickel, iron, molybdenum or copper, or nickel plated with another metal are used and are roughened, for instance by dipping in nitric and citric acid, drying and electrolytically etching in sulphuric acid. The electrodes are then coated with a mixture of barium and caesium azides by dipping in a water solution of 10 to 20 per cent barium azide and 0.5 per cent caesium azide. The electrodes are dried and assembled in the device without heating. The electrodes are then heated to 150‹ C., reducing the barium azide to nitride, and then to 180‹ C. producing some metallic barium. To protect the electrodes from gases evolved from the envelope the envelope is heated to 300‹ C. in a furnace giving low radiant heat so that before the electrodes reach 150‹ C. it is gas-free. Several methods of controlling the furnace temperature are described. The device is evacuated, filled with a mixture of neon and 0.4 per cent argon at a pressure of 30 to 35 mm. and sealed off. The device is then activated by an alternating- current high intensity discharge which reduces the caesium azide to caesium and caesium nitride. The electrodes may be coated with barium azide or strontium azide, or either of these with caesium azide, or rubidium azide or caesium azide, or either of these with barium azide or strontium azide or with barium azide and strontium azide, or amides or other nitrogen compounds may be used. Fig. 2 shows a lamp having electrodes made in accordance with the invention. The electrodes 4 which may simulate a candle-flame, or stars, or crosses, or letters or insignia, are spaced about 1 mm. apart at their upper end. A mica disc 7 shields them from the heat of the sealing-off flame. A resistance 6 is mounted on the cap 5. The lower part 8 of the lamp is covered with a material such as that known under the Registered Trade Mark "Duco" to simulate a wax candle, or the envelope may be wrapped in paper or the like. Specification 362,347 is referred to.