GRANULAR POWDER OF PLANAR MAGNETITE AND ITS PRODUCTION

PURPOSE:To directly form the fine granular powder of unsintered nonporous planar magnetite from an aq. soln. by using a ferrous salt aq. soln. and an alkali carbonate aq. soln. and adopting a specified method. CONSTITUTION:Granular powder of planar magnetite which has 0.03-0.5mum average diameter and 7-30m /g specific surface area and is nonporous and unsintered is formed by the following method. In other words, oxygen-contg. gas is introduced into an aq. soln. incorporating FeCO3 which is obtained by allowing a ferrous salt aq. soln. to react with an alkali carbonate aq. soln. and it is oxidized. In this case, the ferrous salt aq. soln. is allowed to react with the alkali carbonate aq. soln. wherein equivalent ratio of alkali carbonate for ferrous salt incorporated in this ferrous salt aq. soln. is one equivalent or above and the amount is not more than the value shown in a formula I. Furthermore 0.01-2.0mol.% citric acid or its salt for Fe is previously added to any one of the ferrous salt aq. soln., the alkali carbonate aq. soln. and the FeCO3-contg. aq. soln. before passing oxygen-contg. gas to perform oxidation and thereafter the FeCO3-contg. aq. soln. is oxidized by passing the oxygen- contg. gas.