GB345375A - Improvements in the manufacture of photoelectric cathodes - Google Patents

Abstract

345,375. Photo-electric cells. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and CAMPBELL, N. R., of General Electric Co., Wembley, Middlesex. Jan. 6, 1930, No. 482. [Class 39 (i).] In the manufacture of a photoelectric cathode by the deposition of a highly electropositive metal such as an alkali or alkaline-earth metal on a support coated with a compound with which the metal reacts, the cathode is maintained at a temperature considerably above 50‹ C., and preferably at 200‹ C., while the metal is introduced gradually into its neighbourhood in the form of vapovr ; the rate of entry is limited preferably by a constriction in the supply tube. The cell a containing a coating of silver or a silver plate forming the cathode support, and an anode e in the form of a rod or wire frame, has a tube g leading to an exhaust pump, and a closed tube h containing caesium oxide and connected with the cell by a constriction k which is longer or narrower than that usually provided for sealing off. After the cell has been baked and evacuated, the silver is oxidized to a deep blue colour by admitting oxygen to a pressure of 1 mm. and passing a glow discharge with the silver as cathode. Oxygen is removed and the cell and the tube h are heated to 200‹ C. by lowering an oven, the pump being maintained in action. The electrodes are connected in series with a galvanometer and a source of 20 volts the silver being negative. The current, which is due to thermionic emission, reaches a maximum after about 10 minutes and then falls rapidly to zero or to a current which is unsaturated, the tube h being then sealed off. The cell is heated again for half an hour to remove excess caesium ; a rare gas may be admitted and the cell sensitized by the process described in Specification 332,002, [Class 39 (i), Electric lamps, Arc &c.].