| 摘要 |
PURPOSE:To prevent sintering of magnetic powder by making silicon adhere in a large quantity with a (hydrous) iron oxide by a method wherein water-soluble silicate is added to water suspension of an iron oxide or a hydrous iron oxide and pH is designated as being 10.5 or more, then pH is designated as being 10 or less at specific speed. CONSTITUTION:An iron oxide and/or a hydrous iron are suspended to water and pH is designated as being 10.5 or more by adding an alkaline compound, then pH is designated as being 10.5 or more by adding water-soluble siliate thereto or the alkaline compound therewith at the time of termination on adding the water-soluble siliate pH is lowered by adding acid such as phosphoric acid or sulfuric acid to the water suspension, then the water-soluble siliate is nutralized and SiO2 is separated out adhered to the surface of the iron oxide and/or the hydrous iron oxide. While pH is lowered to 10.0, if desirable, from 10.0 to 9.5 speed is set so that the time required to lower pH by 1 takes 5min or more. If desirable, speed is set so that the time required to lower pH by 1 takes 10-100min. The iron oxide and/or the hydrous iron oxide are turned into magnetic powder by performing filtration, cleaning, dry and performing such as reduction and oxidization etc. |
