GB506432A - Improvements in the manufacture and production of fine metal and alloy powders - Google Patents

Abstract

506,432. Metal powders; alloys; soldering. POWELL, A. R., and JOHNSON, MATTHEY, & CO., Ltd. Dec. 20, 1937, No. 35273. [Class 82 (i)] [Also in Group XXII] Fine metal or alloy powders for use in decorating ceramics, the production of conducting surfaces on nonconductors, the production of metal paints, or for use as soldering powders, are produced by reduction or dissociation of compounds at temperatures below the melting points of the metals or alloys in the presence of a distributing or dispersing agent which can be removed without detriment to the powdered metal or alloy formed. For example, an oxide, hydroxide or carbonate of a metal is co-precipitated with a distributing-agent consisting of an oxide, hydroxide or carbonate of a metal incapable of reduction or dissociation, and the mixed precipitate is subjected to dissociation or reduction treatment; alternatively, the distributing-agent is impregnated with a solution of a compound of the metal. The distributing-agent is finally removed, or the metal powder is floated away from the distributing-agent. When a mixture of metal compounds is used, a powdered alloy is formed by selecting a suitable temperature ; a tin compound must be mixed with a metal compound capable of reduction at a temperature below the melting point of the alloy formed. With copper and precious metal compounds, tin compounds may be used in any proportion, the reduction temperature being above 600‹ C., and cadmium and zinc compounds may be used in amounts not exceeding 10 per cent, the temperature being between 700 and 800‹ C. In examples: (1) an aqueous solution of a mixture of silver nitrate and calcium or magnesium nitrate is poured into a boiling solution of sodium carbonate or caustic soda, the precipitate is washed and dried and is dissociated by heating in air or is reduced by heating in hydrogen. Silver powder dispersed in a distributing-agent consisting of calcium or magnesium carbonate or oxide is thus produced. The distributing-agent is leached out with acetic acid ; (2) copper powder is produced by using mixtures of copper and calcium nitrates, copper and magnesium sulphates, or copper and magnesium chlorides; (3) gold and platinum powders are obtained by impregnating calcium or magnesium carbonates with solutions of the chlorides of the metals, drying the mixed precipitate and heating it in the presence of a reducing-agent. The distributing-agent is leached out with dilute hydrochloric acid ; (4) a finely powdered alloy of iron, copper and nickel is produced by mixing an aqueous solution of iron, copper and nickel sulphates with a solution of magnesium sulphate, the mixed solution is poured into a hot aqueous solution of sodium carbonate, the precipitate is heated in hydrogen, and the distributing-agent is removed by dilute sulphuric acid.