PROCESS FOR THE PREPARATION OF COBALTIC GAMMA IRON (III) OXIDE AND MAGNETIC MEMORIES AND PARTS THEREOF, INCLUDING THE COBALIC GAMMA IRON (III) OXIDE PREPARED

摘要

1482157 Co-modified acicular Fe 2 O 3 PFIZER Inc 8 Oct 1974 [6 May 1974] 43625/74 Heading C1A An acicular -ferric oxide containing at least 0À25 atomic per cent of combined cobalt, (based on the iron content) which when incorporated with recording binder at a level of 75% by weight of the total formulation, provides a magnetic recording member having a magnetic stability coefficient of 4,000-10,000, is claimed per se. It may be prepared by (a) introducing an acqueous alkali solution into an aqueous ferrous chloride solution which contains 0À25- 0À7 pound FeCl 2 per gallon, the alkali solution being added at the rate of 0À03-0À2 equivalents per minute per mole of dissolved FeCl 2 whilst maintaining the temperature at 60-90‹ F., the addition proceeding until 20-85% of the dissolved iron has been added, (b) passing an oxygen containing gas into the aqueous mixture until the pH is between 2À6 and 4À1, (c) adding a water soluble cobaltous salt to the resulting lepidocrocite seed slurry in an amount equivalent to at least 0À25 atomic per cent cobalt based on the total iron introduced, (d) maintaining the slurry at 80-160‹ F. and a pH of 2À6-4À1 whilst simultaneously and continuously introducing an aqueous solution of alkali and an oxygen-containing gas until the iron content is completely precipitated as lepidocrocite, (e) continuing the process of step (d) until a pH of at least 7 is achieved so as to precipitate all of the cobalt on to the surface of the lepidocrocite and (f) reducing the co-modified lepidocrocite to co-modified Fe 3 O 4 at 650-800‹ F. and subsequently oxidizing to co-modified acicular -ferric oxide.