The preparation of iron powders consisting of submicroscopic elongated particles by pseudomorphic reduction of iron oxides

The preparation of submicroscopic elongated iron particles by pseudomorphic reduction of α-FeOOH with hydrogen has been studied. At a temperature of 350°C rapid sintering occurs of the iron particles formed. At temperatures below 300°C sintering is largely absent but the reaction is too slow. It has been found that the reduction rate at low temperatures can be increased, and hence sintering diminished, by absorption of Ag+ or Co+ ions on the surface of the iron oxide particles, leading to iron powders with improved magnetic properties. When Sn²⁺is adsorbed the reaction rate decreases. Yet the coercivity of the iron powders obtained is considerably increased, probably also due to a diminished sintering.