Strontium and/or barium ferrite powder prodn. - by spray drying mixed salt soln. to give prod. with high coercivity, useful for hard magnets

摘要

Prodn. of Sr and/or Ba ferrite powder, opt. contg. Pb, for the prodn. of hard ferrite magnets, is carried out by heat treatment of a mixt. of solns. of Fe, Sr and/or Ba and opt. Pb salts at 900-1300 degrees C, pref. in a spray drying tower. It is pref. to use a mixt. of aq. 0.1-1 M chloride and/or nitrate solns. with a molar ratio of Fe:Sr/Ba/(Pb) of 4.5-6:1. A ferrite powder with few defects can be produced, giving a much high coercivity JHc (of 430-460kA/m) than usual at the same specific magnetic satn. polarisation (over 6mTcm3/g). Also the individual grains are not so strongly sintered together, so that grinding is easier and leads to fewer additional 'mechanical' defects. The ferrite is useful for making hard magnets for small motors, starter motors, etc.