GB507122A - - Google Patents

Abstract

507,122. Photo - electric cathodes. ELECTRICAL RESEARCH PRODUCTS, Inc. June 23, 1938, No. 18627. Convention date, June 26, 1937. [Class 39 (i)] The cathode in a photo-cell is formed by diffusion of caesium or rubidium, lithium, potassium or sodium into a layer of silver sulphide formed on a silver backing by means of a glow discharge in an atmosphere of hydrogen sulphide. A number of cells 5-in each of which the anode 9, silver cathode plate 12 and caesium emitting pellet 14 are already mounted-are attached by the exhaust ring tubes 16 to a header 20, Fig. 2, which is connected to pumping apparatus comprising a liquid air trap 29, two McLeod gauges 30, 31, mercury vapour pump 32, mercury cut off 33 and vacuum pump connected to tube 34 ; an ionization manometer 40 is attached to the tube 20 and three gas supply vessels 35, 36, 37 to the pump side. An electric heater 25 comprising removable chimneys 27 is placed under the cells. The cells are evacuated, the liquid air trap being cooled with a mixture of solid carbon dioxide and a material known by the Registered Trade Mark as " Cellosolve " acetate. Oxygen from the vessel 35 is next admitted and an electric discharge passed to first oxidize the silver plate and then reduce it, by heating, to form a matte surface. The oxygen is evacuated and hydrogen sulphide is admitted from the vessel 36 ; the electric processing circuit is changed to give condenser discharges through the cells to form silver sulphide, excess gas being subsequently evacuated. The pellets 14-each carried by a copper ring 13-are now heated and the mixture of Ca2CrO4, Cr2O3 and A1 produces caesium vapour which diffuses on the glass envelope, a shield 15 preventing flow to the cathode plate. The heater, 25 which is used in various stages of the processing with or without the chimneys 27, is then employed to vaporize the caesium from the envelope on to the plate. Argon is subsequently admitted as a filling at a pressure of 5 x 10<-2> mm. of Hg. The silver surface may be formed on a backing of nickel or copper. As finished the cathode surface may contain in addition to the mixture of caesium. sulphide and metallic silver, some caesium alloyed or absorbed in free silver particles.