Improvements in thermionic cathodes of vacuum electric tube devices

摘要

365,185. Thermionic cathodes. ROBINSON, E. Y., Garvary, Dryden Road, Bush Hill Park, BARTON, F., 41, Glebe Avenue, both in Enfield, Middlesex, and ASSOCIATED ELECTRICAL INDUS - TRIES, Ltd., Crown House, Aldwych, London. Aug. 18, 1930, No. 34763/31. Divided on 364,136. [Class 39 (i).] The heater of an indirectly heated cathode is provided with an insulating covering of aluminium oxide by applying to the heater a coating of aluminium hydroxide and converting it into the oxide. In one method the heater which may be a tungsten wire is drawn over a grooved wheel rotating in a bath containing a gelatinous suspension of aluminium hydroxide in water. The coated wire is then heated from 150 to 250‹ C. in a flame or oven and subsequently to a high temperature in a blowpipe flame or electric oven. To assist in the bonding a small quantity of silica gel or other fluxing material may be added to the aluminium hydroxide suspension, and an agglomerant such as starch, dextrin, tragacanth, or gum arabic may also be added. The suspension may comprise aluminium hydroxide in glycerine. To increase the amount of material picked up by the wire, the latter may be wound with cotton and the whole dipped in nitric acid to form a sheath of cellulose nitrate. This is then dipped in the aluminium hydroxide suspension and the coated wire is then subjected to the action of acetone vapour which coagulates the cellulose nitrate covering. The coated wire is then heated to ignite the cellulose nitrate and leave aluminium oxide on the wire. Specification 278,787, [Class 39 (i), Electric lamps, Arc &c.], is referred to.