Patent ID: 6761830
Filing Date: 2004-07-13
Classification: C01G,C01P,C04B,G11B,H01F

Abstract:
Method for manufacturing M type hexaferrites of formula AFe12O19 where A is a metal selected from the group consisting of Ba, Sr, Ca, Pb and mixtures thereof, comprising the steps of:a) mixing iron oxide Fe2O3 and an A compound with a molar ratio n=Fe2O3/AO of between 5.7 and 6.1, simultaneously with said mixing or subsequently thereto, grinding said mixture to an average particle size between 0.25 and 1 &mgr;m, with a predetermined degree of homogeneity, and simultaneously with of before said grinding, adding to said mixture a microstructure controlling agent; b) shaping said ground mixture in the form of agglomerates of shape and size adapted to calcination, and calcining the shaped mixture in an oven at between 1100Â° C. and 1300Â° C., in such a way as to form M type ferrite material in the form of a porous cake having: a transformation yield in crystallized M ferrite greater than 95%, an apparent density da lower than 3.5, or a porosity higher than 30%, and low cohesion energy at grain boundaries between primary particles leading to high brittleness; and c) optionally grinding or dispensing by simple dispersion said porous cake to form a fine powder.