PRODUCTION OF ACICULAR MAGNETIC IRON OXIDE GRANULAR POWDER

PURPOSE:To provide the method for producing acicular magnetic iron oxide granular powder which has a large aspect ratio, uniform particle size without coexisting of branched particles, and thereby has excellent coercive force distribution and each particle is independent from another. CONSTITUTION:A suspension of >=pH 11 containing ferrous oxide is prepared by the reaction of an aq. ferrous salt soln. and an alkali soln. Preliminarily, a water-soluble silicate and a water-soluble aluminum salt are added into the suspension, into which oxygen-contg. gas is introduced to cause the oxidation reaction and to produce acicular goethite particlar powder containing Si and Al. Then these particles are reduced to obtain acicular magnetite particles, or further the particles are oxidized to obtain acicular maghemite particles, or both of particles are modified with Co to obtain acicular magnetic iron oxide particles. Since the production amt. of goethite is increased to >=6.3g/l/ hour by this method, magnetic oxide particles can be obtd. advantageously in industry and economics.