| 摘要 |
<p>A method of manufacturing a magnetic pigment of gamma -Fe2O3 particles in which the process starts with an alkaline or acid reacting aqueous dispersion of gamma -Fe2O3. According to the invention, a water-soluble ammonium salt, which is derived from a low molecular weight, weakly acidic organic acid, is added to the aqueous dispersion, the gamma -Fe2O3 particles flocculating. The flocculated gamma -Fe2O3 is separated, washed with water which preferably also comprises such a water-soluable ammonium salt, and is then dried. The ammonium salt volatilizes in the drying process used either as such or after decomposition. A suitable ammonium salt is ammonium acetate. The pigment obtained according to the invention has a low content of salt absorbed at the surfaces of the pigment particles, for example, a content lower than 0.1 and, for example 0.03% by weight. A magnetic recording element which is based on the pigment obtained according to the invention shows an improved life time in particular upon storage or during use in moist environments.</p> |
