Preparation and magnetic properties of barium ferrite fine particles by the coprecipitation salt-catalysis method

The authors describe catalytic action by NaCl in the reaction between alpha -Fe/sub 2/O/sub 3/ and BaCO/sub 3/ and the development of a new process for manufacturing barium ferrite fine particles. Pure alpha -FeOOH and reagent-grade BaCO/sub 3/ are mixed and heated at temperatures from 300 to 800 degrees C with and without NaCl. The BaCO/sub 3/ and alpha -Fe/sub 2/O/sub 3/ powders which are formed during heating react and change to barium ferrite at temperatures 100 degrees C lower than NaCl than without it. A hematite defect structure is maintained up to a relatively high temperature due to the presence of the salt, which promotes the formation of barium ferrite. The manufacturing process involves mixing an aqueous solution of metallic chlorides with a mixture of NaOH and Na/sub 2/CO/sub 3/. This alkaline coprecipitate slurry is then neutralized by HCl solution, filtered, and dried. The dried powder, containing salts produced by the reaction, is heated at 840 degrees C. After the salts are dissolved in water, barium ferrite fine particles are obtained.<
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