| 摘要 |
PURPOSE:To obtain ferromagnetic metal powder having uniform and highly densed oxide film and excellent magnetic characteristics by a method wherein the surface of the metal powder is subjected to slow oxidation while the increase in partial pressure of oxygen is being conducted at a fixed speed. CONSTITUTION:Ferromagnetic metal powder mainly composed of iron is fluidized in a fluidized bed at a temperature of 30 deg.C or higher using inert gas. Oxygen gas is mixed therein at an introducing speed with the fixed increment rate of 10ml/nin<2> or less per 1 gram of metal magnetic powder. When an oxide film, which is necessary for stabilization of the ferromagnetic metal powder, is formed by continuously conducting a slow oxidation treatment uniformly, an oxidative reaction is automatically stopped. This oxidative reaction can be traced by monitoring the temperature of the fluidized bed. To be more precise, when the reaction temperature comes down and the oxygen density on the outlet side is detected, the fluidized bed is cooled down to the room temperature, the oxidative reaction is completely stopped, and the stabilization treatment is finished. As a result, an oxide film is formed uniformly and in high density on the grain surface of the ferromagnetic metal powder, and the ferromagnetic metal powder, having no danger of ignition, excellent magnetic characteristics and lesser deterioration with time, can be obtained. |
