METHODS OF MANUFACTURING FERROMAGNETIC CARBON MODIFIED CHROMIUM OXIDE AND COMPOSITIONS AND RECORDING MEDIA CONTAINING SAME

1409090 Ferromagnetic chromium oxide INTERNATIONAL BUSINESS MACHINES CORP 29 Nov 1972 [27 Dec 1971] 55079/72 Addition to 1317216 Heading C1A Ferromagnetic chromium oxide composition of tetragonal crystal structure containing from 58À5 to 62% by weight of chromium oxygen and from 0À05 to 0À9% by weight of carbon is prepared by forming an intimate modifying mixture of a chromium salt (e.g. chromium halide, sulphate, nitrate or acetate) and a source of elemental carbon (e.g. acetylene black, bone black, carbon black, charcoal, graphite, lamp black or carbon oxide) mixing the modifying mixture thus formed with chromium trioxide and then heating the resultant reaction mixture at a temperature within the range from 450‹ to 850‹ F. under a pressure within the range 730 p.s.i. to 44,000 p.s.i. Iron and tin may be included in the composition in amounts of 0À15 to 1À6% and 0À01 to 0À35% by weight respectively. The composition may be in the form of particles of 1 micron average length which may be mixed with organic binders and applied to suitable substrates in the preparation of magnetic recording media.