PREPARATION AND MAGNETIC-PROPERTIES OF BARIUM FERRITE FINE PARTICLES BY THE COPRECIPITATION SALT CATALYSIS METHOD

We describe a catalytic action of NaCl in the reaction between alpha-Fe2O3 and BaCO3 and development of a new process of manufacturing barium ferrite fine particles using NaCl as a catalyst. Barium ferrite particles provide promising prospects for particulate media for high-density magnetic tapes because they are extremely small, and have a narrow SFD value. Pure alpha-FeOOH and reagent-grade BaCO3 are mixed and heated at temperatures from 300 to 800-degrees-C with and without NaCl. The powders of BaCO3 and alpha-Fe2O3 which are formed during heating react and change to barium ferrite particles at temperatures 100-degrees-C lower with NaCl than they do without the salt. A defect structure of hematite is maintained up to a relatively high temperature by the presence of the salt, which promotes the formation of barium ferrite. The developed manufacturing process involves mixing an aqueous solution of metallic chlorides with a mixture of NaOH and Na2CO3. This alkaline slurry of coprecipitate is then neutralized by HCI 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.