Process for preparing microcrystalline barium ferrite platelets

摘要

A process for preparing microcrystalline barium ferrite platelets comprises the formation of an aqueous alkaline dispersion which contains coprecipitates of the hydroxides of barium ions, iron(III) ions and, if desired, ions of a substituted element, heating the dispersion to a temperature of not less than 50@C and not more than the boiling point of the dispersion under atmospheric pressure to convert the coprecipitates into precursors of barium ferrite, and calcining the precursors to produce microcrystalline barium ferrite platelets, and is characterised by a step of addition of a carbonate-forming agent such as sodium carbonate to the aqueous alkali dispersion before or after heating the aqueous alkaline dispersion, so as to make the water-soluble barium ions present therein insoluble, and a step of calcining the precursors of the barium ferrite in the presence of sodium sulphate at temperatures of from 700@C to 900@C to produce microcrystalline barium ferrite platelets having a mean particle size of from about 0.03 to 0.1 mu m and a planarity ratio (aspect ratio) of from 2 to 5.