SYNTHETIC GAMMA FERRIC OXIDE

摘要

1392196γ-FeO.OH andγ-Fe 2 O 3 PFIZER Inc 10 March 1972 [17 March 1971 11 Feb 1972] 11412/72 Heading C1A [Also in Division C3] A novel form ofγ-FeO.OH particles at least 70% by volume of which have a length : width ratio greater than 10 : 1 and a length of up to 2Á are prepared by reacting an aqueous FeCl 2 solution of concentration 0À25-5 lb. per U.S. gal. with an O 2 -containing gas and an aqueous base until the pH is 2À9-4À1 to form a seed slurry of FeO.OH and then maintaining a temperature of 80-140‹ F. and a pH of 2À9-4À1 in the presence of FeCl 2 and simultaneously and continuously introducing a base and an O 2 - containing gas until 1À2 to 5 parts by weight of product are formed per part of seed. The aqueous base may be NaOH, NH 4 OH or Ca(OH) 2 . Metallic iron may be present during the second part of the process. FeSO 4 and Fe(NO 3 ) 2 may be used along with FeCl 2 .γ-Fe 2 O 3 may be obtained by reducing the FeO.OH to Fe 3 O 4 with H 2 at 600-800‹ F. and oxidizing to Fe 2 O 3 with air at 450-720‹ F. The FeO.OH may first be coated with an aliphatic monocarboxylic acid having 8-24 C atoms, e.g. coconut oil fatty acid or lauric acid, and the H 2 for reduction may then be omitted. The product may be densified by milling.