MAGNETIC PARTICULATE POWDER AND PRODUCTION THEREOF

摘要

PURPOSE:To produce magnetic particles having excellent dispersibility, by coating the surfaces of magnetic particles with hydrated alumina having a boehmite structure and a (hydr)oxide layer containing Al or Si. CONSTITUTION:An aqueous solution of an acid or alkali is added to a mixed suspension at pH >=9 or pH <=4 containing magnetic particles and hydrated alumina particles of a boehmite structure in an amount of 0.05-5.0wt.% expressed in terms of Al2O3 based on the magnetic particles to adjust the pH to 6.5-8.5 and provide a suspension of the magnetic particles having hydrated alumina particles deposited on the surfaces of the magnetic particles. An aqueous solution of an alkalis is then added to the above-mentioned suspension to adjust the pH to >=10. A compound (e.g. sodium aluminate) containing Al and/or compound (e.g. sodium silicate) containing Si in an amount of 0.01-5.0wt.% expressed in terms of Al2O3 or SiO2 based on the magnetic particles is added thereto and an acid is subsequently added to adjust the pH to 6.5-8.5 and form a (hydr)oxide layer of Al and/or Si on the surfaces of the magnetic particles having deposited hydrated alumina particles.