Magnetoplumbite-type hexaferrite powder, for ceramic magnets and magnetic recording supports, is produced using a microstructure control agent addition to allow simple disintegration of the calcined biscuit

摘要

Magnetoplumbite-type hexaferrite powder production, in which a microstructure control agent is added so that conventional calcined biscuit fine grinding can be replaced by simple disintegration, is new. Production of powders or biscuits of M-type hexaferrites of formula AFe12O19 (A = Ba, Sr, Ca and/or Pb) comprises: (a) mixing Fe2O3 and an A compound in a Fe2O3/AO molar ratio of 5.7-6.1 and simultaneously or subsequently grinding to a uniform mixture of 0.25-1 microns m average particle size, with addition of a microstructure control agent before or during grinding; and (b) agglomerating and calcining the mixture at 1100-1300 deg C to form a porous ferrite biscuit exhibiting a crystallized M-type ferrite conversion yield of greater than 95%, an apparent density of less than 3.5 (preferably less than 3) or a porosity of greater than 30 (preferably greater than 40)% and a low primary particle grain boundary cohesion energy providing a high friability so that conventional fine grinding can be replaced by simple disintegration of the biscuit. Independent claims are also included for the following: (i) a hexaferrite biscuit having an apparent density of less than 3 and an average particle size of 0.25-1 mu m, obtained by the above process; (ii) a fine hexaferrite powder obtained by disintegration of the above biscuit; (iii) magnets produced from the above powder; and (iv) magnetic recording supports produced from the above powder.