GB679172A - Improvements in or relating to the production of metal or metal oxide powders and products therefrom - Google Patents

Abstract

Insoluble metal oxalates used for making finely divided metals or metal oxides by decomposition of the oxalates (see Groups II and III) are prepared by a precipitation method comprising the addition of oxalic acid to an aqueous solution of the corresponding sulphates, which solution contains at least one sulphate which is a lower valency sulphate of a metal exhibiting variable valency, said precipitation taking place at a temperature between 40 DEG and 90 DEG C. in the presence of an organic reducing agent not substantially more readily oxidized in the solution than formaldehyde, e.g. formaldehyde or a sugar such as glucose, and also in the presence of an amount of sulphuric acid sufficient to bring the pH of the solution to a value not exceeding 3. The reducing agent prevents formation of the higher valency sulphates, the acid prevents formation of basic sulphates and the temperature prevents adsorption of sulphate ions by the precipitate. Reference is made to the production of alloys of iron, nickel and cobalt such as those capable of being sealed through the glass of vacuum tubes and to magnetic bodies formed of mixed oxides of two or more metals such as the magnetic spinels. In examples: (1) in producing a 50 : 50 cobalt-iron alloy, mixed oxalates are precipitated by oxalic acid from an aqueous solution of cobaltous and ferrous sulphates containing sulphuric acid and glucose at 70 DEG C., the precipitate is washed, dried and powdered; (2) in producing a magnetic spinel formed of zinc oxide, nickel oxide and ferric oxide in the solar ratios of 35, 15 and 50 per cent respectively, the mixed oxalates are precipitated from an aqueous solution of zinc, nickel and ferrous sulphates containing sulphuric acid and glucose at 70 DEG C., the precipitate is washed, dried and sieved; (3) in producing a magnetic alloy containing nickel, molybdenum and iron in the proportions 78.5, 4 and 17.5 per cent, the mixed oxalates are precipitated as in (1) from a solution of nickel sulphate, ferrous sulphate and molybdenum sulphate.ALSO:A process for making finely divided metal oxides by the decomposition of insoluble oxalates of the metals includes the precipitation of metal oxalates by the addition of oxalic acid to an aqueous solution of the corresponding sulphates which solution contains at least one sulphate which is a lower valency sulphate of a metal exhibiting variable valency in which said presipitation takes place at a temperature between 40 DEG and 90 DEG C in the presence of an organic reducing agent not substantially more readily oxidized in the solution than formaldehyde, e.g. formaldehyde or a sugar such as glucose, and also in the presence of an amount of sulphuric acid sufficient to bring the pH of the solution to a value not exceeding 3. The reducing agent prevents formation of the higher valency sulphates, the acid prevents formation of basic sulphates and the temperature prevents adsorption of sulphate ions by the precipitate. The precipitated oxalates are heated to between 400 DEG and 800 DEG C in the presence of air or oxygen to form the metal oxides. The resulting metal oxide powders are made into solid bodies by pressing and sintering and to obtain a high density, it is preferred to use a mixture of powders formed by decomposition of the oxalates at different respective temperatures. Reference is made to the production of magnetic bodies formed of mixed oxides of two or more metals such as the magnetic spinels. In one example, a magnetic spinel formed of zinc oxide, nickel oxide and ferric oxide in the molar ratios of 35, 15 and 50 per cent respectively is prepared by co-precipitating the mixed oxalates by addition of oxalic acid to an aqueous solution of zinc, nickel and ferrous sulphates containing sulphuric acid and glucose at 70 DEG C, the precipitate is washed, dried and sieved and then decomposed in air in two batches at 750 DEG and 600 DEG C to form mixed oxides which are used to form an inductance core (see Group XXXV).ALSO:A process for making finely divided metals by the decomposition of insoluble oxalates of the metals includes the precipitation of metal oxalates by the addition of oxalic acid to an aqueous solution of the corresponding sulphates which solution contains at least one sulphate which is a lower valency sulphate of a metal exhibiting variable valency in which said precipitation takes place at a temperature between 40 DEG and 90 DEG C in the presence of an organic reducing agent not substantially more readily oxidized in the solution than formaldehyde, e.g. formaldehyde or a sugar such as glucose, and also in the presence of an amount of sulphuric acid sufficient to bring the pH of the solution to a value not exceeding 3. The precipitated oxalates are heated to between 400 DEG and 800 DEG C in the presence of an atmosphere of hydrogen preferably containing between 1 2 and 10 per cent of water vapour to form the metals. The resulting metal powders are made into solid bodies by pressing and sintering and to obtain a high density, it is preferred to use a mixture of powders formed by decomposition of the oxalates at different respective temperatures. Reference is made to the production of alloys of iron, nickel and cobalt such as those capable of being sealed through the glass of vacuum tubes. In examples (1) a 50 : 50 cobalt-iron alloy is prepared by co-precipitation of the mixed oxalates from an aqueous solution of cobaltous and ferrous sulphates containing sulphuric acid and glucose at 70 DEG C, the precipitate is washed, dried, powdered and reduced in hydrogen in two batches at 525 DEG C and 675 DEG C, and the resulting powdered metals are mixed in the proportions of 16 per cent of the first batch and 84 of the second batch and then pressed to desired shape and sintered to form thin discs, e.g. telephone diaphragms; (2) a magnetic alloy containing nickel, molybdenum and iron in the proportions 78.5, 4 and 17.5 per cent is prepared by co-precipitating the mixed oxalates as in (1) from a solution of nickel sulphate, ferrous sulphate and molybdenum sulphate, reducing the mixed powdered oxalates in hydrogen in two batches at 700 DEG C and 575 DEG C, mixing the resulting metal powders in the proportions 84 : 16 per cent and then pressing and sintering to desired shape. The Provisional Specification refers to the production of cores of loading coils or other inductances, pole pieces of telephone receiver magnets and telephone or telegraph relay magnets.