GB500531A - Improvements in or relating to photosensitive electrodes - Google Patents

Abstract

500,531. Photo - electric cells. ELECTRICAL RESEARCH PRODUCTS, Inc. Aug. 11, 1938, No. 23709. Convention date, Aug. 26, 1937. [Class 39 (i)] A photosensitive electrode, particularly a cathode for a photo-electric cell is formed by applying to a conducting support a layer of an easily reducible metallic compound such as silver oxide, tin oxide or copper oxide mixed with a stable refractory compound, such as zirconium oxide, aluminium oxide or aluminium silicate, reducing the metallic compound so as to leave metallic particles intimately mixed with the refractory compound, and applying an alkali metal to the layer in the presence of heat so as to cause the alkali metal to penetrate into the surface of the layer. The cell comprises a cathode 12 in the form of a semi-cylindrical plate mounted on the stem 6 by support wires 8, 8a, 8b, and a nickel wire anode 9. A heavy copper wire 13 partially encircling the stem carries between its ends a metallic capsule 14 enclosing a mixture which produces caesium vapour when heated, and a nickel shield 15 is supported between the capsule and the cathode. Current is induced in the wire 13 by an external coil 17 for heating the capsule. An apparatus for treating four cells simultaneously is described and comprises an electric heater, a liquid air trap, two McLeod gauges, a mercury vapour pump, a mercury cut-off, a vacuum pump, an ionization micrometer, and two gas supply units, one. containing hydrogen for use in the reduction of tin and copper oxides, and the other argon for introduction into the finished cell. In one method, the concave surface of the nickel cathode is roughened and coated with a suspension of silver and zirconium oxides in water to which a small amount of zirconium nitrate has been added. The cell is then sealed in the heater, evacuated and heated to raise the cathode temperature to 300-400‹ C. so that the silver oxide is reduced. The coil 17 is connected to a source of high frequency current to " flash " the capsule 14 whereby caesium vapour is deposited on the glass walls of the cell. The cell is subsequently heated by air currents to transfer the caesium to the cathode. An electric circuit is described whereby the sensitivity of the cells can be indicated by an ammeter. When the required sensitivity is reached, the cells are allowed to cool and argon is admitted. Methods are described of producing a cathode with a matrix of caesium, tin and aluminium oxide and a cathode with a matrix of caesium, copper and aluminium silicate. Potassium, sodium, rubidium or lithium may be used in place of caesium.