GB201900A - Improvements in and relating to electrodes having a high electron emissivity and method of making them - Google Patents

Abstract

201,900. British Thomson - Houston Co., Ltd., (Assignees of Fernberger, H. M.). Aug. 3, 1922, [Convention date]. Vacuum tubes.-An electrode having high electron emissivity is prepared by intimately mixing a reducing agent such as carbon, and an oxide, with a refractory metal such as tungsten, sintering the mixture into an ingot, and mechanically working the ingot. The oxide may consist of thoria, calcium oxide, or other oxides of the alkaline or rare earths. The powdered materials are pressed into a bar 1/4" square before sintering. In one method powdered tungsten is prepared by reducing in hydrogen tungstic oxide made in any known way, as by firing in the air para ammonium tungstate. crystal formed from a solution of ammonium tungstate, and then mixing with the powdered carbon. In the preferred method powdered carbon is mixed with powdered thoriated tungsten prepared by evaporating an ammonium tungstate solution to obtain crystals of para ammonium tungstate, which are dried, powdered and mixed with sufficient thorium hydroxide to give a mixture of tunstic oxide and thoria containing from 0.5 to 1.6 per cent by weight of thoria. This mixture when reduced in hydrogen produces tungsten containing 0.6 to 2 per cent of thoria. The thorium hydroxide may be prepared by dissolving thorium nitrate in water, precipitating with a slight excess of ammonia water, and washing the precipitate free of ammonium salts. The para ammonium tungstate crystals and thorium hydroxide are mixed by ball milling until the mixture becomes a creamy mass, which is then dried, passed through a sieve, and heated in thin layers in silica dishes to convert it. into tungstic oxide containing thoria, which is then reduced in hydrogen. Carbon, in the form of lamp black, up to about 0.5 per cent, but preferably 0.3 per cent by weight, is added and thoroughly mixed and sifted. or thoriated tungstic oxide is mixed with sufficient powdered carbon to reduce the oxide, and then fired in a crucible in the absence of air to reduce tungstic oxide to thoriated tungsten containing carbon. The wire after drawing may be brought to a temperature of 2200‹ K. for a few minutes. Specification 184,446 is referred to.