MANUFACTURE OF ACICULAR ALPHA-FEOOH FOR MAGNETIC RECORDING MATERIAL

摘要

PURPOSE:To enable alpha-FeOOH having a sharp grain size distribution, less branching and a clear crystalline form to be obtained by maturing the suspension, resulted by partially neutralizing and oxidizing a ferrous salt solution to generate an alpha-FeOOH nucleus crystal, at a temperature not lower than 50 deg.C and higher than the temperature of generating the nucleus crystal. CONSTITUTION:First a ferrous salt solution is partially neutralized and oxidized so as to change a portion of the Fe content in the solution to an alpha-FeOOH nucleus crystal. The concen tration of the ferrous salt solution is normally 30-90g/l, and the quantity of an alkali to be added is that required to precipitate 5-50% of the Fe ions in the mother liquor. The maturing temperature is to be not lower than 50 deg.C and to be higher than the temperature of generating the nucleus crystal. If below 50 deg.C, the dissolving and separating reaction of the nucleus crystal is suppressed, and it is difficult to generate grains having a sharp grain size distribution and less branching, requiring a longer maturing time. This is industrially disadvantageous. Normally, alpha-FeOOH nucleus crystal applied with the maturing process is successively subjected to a reaction for growing the nucleus crystal to provide alpha-FeOOH of a predetermined grain size. This growth reaction is performed by oxidizing the matured suspension, or after adding a ferrous salt solution thereto, by adding an oxidizing agent such as air while adding an alkali.