GB450035A - Improvements in electrodes for high-pressure metallic vapour electric discharge tubes - Google Patents

Abstract

450,035. Discharge lamps. TENNANT, W. J., 111, Hatton Garden, London.-(Soc. Anon. pour les Applications de l'Electricite et des Gaz Rares Etablissements Claude-Paz & Silva; 8, Rue Cognacq-Jay, Paris) May 7, 1935, No. 13471. [Class 39 (i)] In high-pressure, metal-vapour tubes containing auxiliary inert gases, electrodes of metal or alloy coated with emissive oxide and heated directly by the discharge without the intervention of auxiliary heating have an emissive surface of not less than 20 sq. cms. per c.c. of electrode volume and preferably 5-10 sq. cms. per amp. of discharge current, and are emissive only on their internal surfaces. The electrodes heat up rapidly by the discharge and reduce blackening of the walls of the tube. Vapour pressures of 500 mm. to atmospheric pressure are specified. The electrode contains oxide-coated cells 6, Fig. 1, having a supporting metal of the nickel or platinum group and its external cylindrical surface 1 is scoured so that the discharge cannot start therefrom. In a modification, an electrode of height equal to its width is formed from a metal ribbon wound into a spiral with its turns almost touching and coated with barium dioxide except on the external face of its outer turn. A ribbon of refractory metal such as molybdenum may be coated as by metallization or electrodeposition with a metal of the nickel or platinum groups before coating with oxide. The ribbon may be corrugated or crimped to increase its surface. The lead 11, Fig. 3, of the auxiliary electrode 15 for a glow discharge at starting is brought out with the lead 12 of the electrode 1 through a bead 16 of glass known under the Registered Trade Mark " Pyrex." The bead 16 is sealed at 13 to the walls 17 and remains cool so that electrolysis of the glass is avoided.