GB799912A - Magnetic impulse record carriers - Google Patents

Abstract

The magnetic coating on a magnetic impulse record carrier comprises in a non-magnetic binder, a magnetic iron oxide powder of which 2.5-4 atom per cent of iron are substituted by cobalt, and a magnetic iron oxide in which iron is the sole metal. In making the mixed oxide, mixed hydroxides are precipitated by adding a solution of iron and cobalt sulphates to a solution of NaOH and NaClO, under nitrogen. The suspension is heated under nitrogen to 80 DEG C. and mixed with a solution of NaNO3. The precipitate is decanted, dried at 100 DEG C. and oxidized in air at 280 DEG C. The simple iron oxide is made by precipitating iron hydroxide by adding NaOH to a solution of FeSO4. After the addition of iron scrap, the suspension is heated to 60 DEG C. and air passed through. The iron hydroxide filtrate is heated to 350 DEG C. and converted into Fe2O3, and then reduced by gas to Fe3O4. This is cooled to 200 DEG C. in nitrogen and oxidized to Y-Fe2O3 at 200 DEG C. in air. Alternatively, the suspended hydroxide is converted to Fe3O4 by heating to 80 DEG C. and adding NaNO3 and afterwards to Y-Fe2O3 by heating at 260 DEG C. in air. Other starting salts may be the chlorides, nitrates or acetates of iron and cobalt, and the precipitating agent may be potassium or calcium hydroxide or ammonia. Other oxidizing agents referred to are potassium and ammonium nitrates, sodium chlorate, potassium persulphate, hydrgoen peroxide and oxygen. Methods of making the record carrier from the oxides are described (see Group XXXV).