| 摘要 |
PURPOSE:To obtain a uniform goethite needlelike crystal which is suitable as a starting raw material for producing ferromagnetic metallic powder by introducing an O2-contg. gas into the reaction liquid of an aq. ferrous salt soln. and an aq. alkali (hydrogen) carbonate soln. CONSTITUTION:An aq. ferrous salt soln. and an aq. alkali carbonate or alkali hydrogencarbonate soln. are brought into reaction to form the colloid of ferrous carbonate. An O2-contg. gas, for example, air or the like is introduced at 20- 80 deg.C into the aq. soln. which contains the ferrous carbonate colloid and is adjusted to 0.05-2mol/l concn. of the excess alkali carbonate therein to effect an oxidation reaction. Green rust is then formed first and as the oxidation progresses, a goethite needlelike crystal is formed. The crystal consists of the particles having a narrow grain size distribution width of an average length of the long axis l = about 0.1-0.3mu and an average axial ratio, the length of the long axis/the length of the short axis = about 5-10 and having the uniform shape contg. substantially no dendrite crystals. If such particles are treated by the conventional method, the ferromagnetic metallic powder suitable for providing the higher density recording to a magnetic recording medium is obtd. |
