Process for preparing strontium ferrites

The process for preparing a metal ferrite of the formula MO.multidot.nFe.sub.2 O.sub.3 wherein M is strontium and n has a value of from 3 to 6.5, said ferrite having an average crystallite size of not greater than 2.5 microns, a normal coercive force of greater than about 3600 oersteds, a remanence of greater than about 3600 gauss and at least about 90% crystallite orientation, which comprises the steps of:

• a. preparing solid particles comprising intimate agglomerates of (i) less than 0.1 micron grains of strontium oxide and (ii) less than 0.1 micron grains of ferric oxide, having a molar ratio of ferric oxide to divalent metal oxide of from 3:1 to 6.5:1;
• b. maintaining the solid particles of agglomerated oxides at temperatures of from about 800.degree. C to 1100.degree. C for a period of from about 0.1 to about 24 hours, thereby forming less than 0.5 micron average diameter crystallites of divalent metal ferrite;
• c. sintering the crystallites from about 0.1 to about 2 hours at a temperature of form 800.degree. C to 1300.degree. C and from about 100 to 30,000 psi into a solid ductile body having a uniform average grain size of less than 1 micron;
• and
• d. hot forging the solid ductile body by applying a pressure of from 1000 psi to 30,000 psi and a temperature of from 800.degree. C to 1300.degree. C, said pressure and temperature being selected to give a strain rate of from about 1%/minute to about 500%/minute.