| 摘要 |
PURPOSE:To provide a method for production in which needlelike magnetic iron oxide grain powder, having a uniform grain size and a high axial ratio (diameter of the major axis/diameter of the minor axis), excellent in coercive force distribution and simultaneously better in squareness ratio and orientation degree without any dendritic grains mixed therein is industrially obtained. CONSTITUTION:An oxygen-containing gas is passed through a reaction solution between an aqueous solution of a ferrous salt and an alkaline aqueous solution in an amount less than equiv. to produce needlelike goethite nuclear grains, and a reaction solution of the ferrous salt containing the aforementioned needlelike goethite nuclear grains is kept at <=75 deg.C and the temperature is then reduced to <=60 deg.C and, as necessary, further kept at <=60 deg.C in a nonoxidizing atmosphere. An alkaline carbonate in >=an equiv. amount based on Fe<2+> in the above-mentioned reaction solution of the ferrous salt is subsequently added. An oxygen-containing gas is then passed therethrough to grow the aforementioned nuclear grains and produce needlelike goethite grains, which are subsequently reduced to afford needlelike magnetite grains or, as necessary, further oxidized to provide needlelike maghemite grains. Both the above- mentioned grains, as necessary, are modified with Co to afford the objective needlelike magnetic iron oxide grain powder. |
