| 摘要 |
PURPOSE: To provide a granular magnetite particle powder and the producing method, which has 150-300Oe coercive force and is excellent in heat resistance and coloring ability. CONSTITUTION: The granular magnetite particle having the particle surface covered with Znx Fex+y Oz (where, 0.4<=x<=1.0, x+y=1, 4.0<=z<=4.3) is formed by adding and mixing 1-26mol.% ferrous salt aq. solution expressed in terms of Fe<2+> to total Fe in the granular magnetite particle, 0.5-4.0mol.% zinc salt aq. solution expressed in terms of Zn and an alkali hydroxide aq. solution in a water dispersion containing the granular magnetite particle under a non- oxidizing atmosphere, adjusting OH group concn. in the dispersion to 0.3-1.0mol/l and after that, passing an oxygen containing gas at >=50 deg.C. Next, the granular magnetite particle powder is obtained by adding at least one kind of a compound selected from a Si compound, Al compound and Ti compound and after that, adjusting the pH to 5-9 to cover with at least one kind of the added compound. |
