Process for the production of needleshaped, cobalt-containing gamma-ferric oxide crystalline particles

Claim 1

A PROCESS FOR THE PRODUCTION OF FERROMAGNETIC, NEEDLE-SHAPED, COBALT-CONTAINING GAMMA-FERRIC OXIDE PARTICLES HAVING A LENGTH BETWEEN ABOUT 0.5 AND ABOUT 3 MICRONS AND A WIDTH BETWEEN ABOUT 0.05 AND ABOUT 1.5 MICRONS WHICH COMPRISES (A) ADMIXING, AT A TEMPERATURE BETWEEN ABOUT 0 AND ABOUT 30*C., (I) AN AQUEOUS MEDIUM CONTAINING A BASE OF THE GROUP CONSISTING OF LITHIUM, SODIUM, POTASSIUM, CALCIUM, AND BARIUM HYDROXIDES, WITH (II) AN AQUEOUS SOLUTION CONTAINING A WATER-SOLUBLE FERROUS SALT OF THE GROUP CONSISTING OF FERFOUS, SULFATE, FERROUS NITRATE, AND FERROUS CHLORIDE, AND A WATER-SOLUBLE COBALTOUS SALT OF THE GROUP CONSISTING OF COBALTOUS SUFLATE, COBALTOUS NITRATE, AND COBALTOUS CHLORIDE, THE ATOMIC RATIO OF THE COBALT TO THE IRON IN THE SAID SOLUTION BEING BETWEEN ABOUT 1 AND ABOUT 10 PARTS OF COBALT TO 100 PARTS OF IRON, UNTIL A PH BETWEEN ABOUT 4.5 AND ABOUT 6.5 IS ATTAINED, (B) TREATING AND RAPIDLY STIRRING THE RESULTING MIXTURE AT THE SAID TEMPERATURE WITH AIR AT A RATE BETWEEN ABOUT 5 AND ABOUT 10 VOLUMES PER VOLUME OF MIXTURE PER MINUTE TO CONVERT THE FERROUS OXIDE HYDRATE TO FERRIC OXIDE HYDRATE, (C) THEREAFTER, IN A SECOND STEP OF THE PROCESS, IN ORDER TO BRING THE COBALT-CONTAINING FERRIC OXIDE PARTICLES TO THE REQUISITE DIMENSIONS, ADDING TO THE RESULTING REATION MIXTURE FURTHER QUANTITIES OF THE SAID AQUEOUS BASIC MEDIUM (I) AND THE AQUEOUS SOLUTION CONTAINING FERROUS AND OBALTOUS SALTS (II) WHILE MAINTAINING THE PH BETWEEN ABOUT 4.5 AND ABOUT 6.5, (D) TREATING AND RAPIDLY STIRRING THE RESULTING MIXTURE WITH SUCH A FURTHER QUANTITY OF AIR THAT THE ADDITIONAL QUANTITY OF THE PRECIPITATED PRODUCT FORMED IN STEP (C) IS CONVERTED INTO COBALT-CONTAINING FERRIC OXIDE HYDRATE, (E) SUBSEQUENTLY SEPARATING AND DEHYDRATING THE THUS OBTAINED NEEDLE-SHAPED, COBALT-CONTAINING FERRIC OXIDE HYDRATE PARTICLES HAVING THE REQUISITE DIMENSIONS, AND (F) REDUCING AND REOXIDIZING THE PARTICLES OF MIXED OXIDES THUS OBTAINED TO CONVERT THEM INTO PARTICLES OF FERROMAGNETIC, NEEDLE-SHAPED, COBALT-CONTAINING GAMMA-FERRIC OXIDE HAVING THE REQUISITE DIMENSIONS.