| 摘要 |
PURPOSE:To obtain acicular magnetic iron oxide powder which is excellent in magnetic characteristics and also excellent in dispersion properties of paint by adding an organic compd. to alpha-hematite at the specified temp. and heating the mixture in an inert gas and reducing it and thereafter oxiding it. CONSTITUTION:An organic compd. is added in the temp. range of 150-350 deg.C to alpha-hematite (alpha-Fe2O3) which is obtained by dehydrating and calcining acicular hydrated iron oxide and the mixture is reduced in an inert gas stream. Then acicular gamma-hematite particles (gamma-Fe2O3) are obtained by oxidizing it. As the most important point in the above-mentioned method, the addition of the organic compd. is performed in the temp. range of 150-350 deg.C. At <150 deg.C temp. in the addition, the coercive force of gamma-hematitie obtained after oxidation is low and the amount of residual carbide is large and trouble is caused in dispersion properties of paint in a time for producing a magnetic recording medium. On the other hand, at >350 deg.C temp. in the addition, reduction is not fully advanced and the reduction of saturation magnetization is caused. |
