SE365492

1287614 Chromium oxide FARBENFABRIKEN BAYER AG 7 Oct 1969 [11 Oct 1968] 49137/69 Heading C1A [Also in Division H1] Ferromagnetic CrO 2 is made by (1) heating CrO 3 with a modifier to 200-380‹ C. to form a chromium oxide in which the chromium has an average valency of above 4 but below 6; (2) heating this chromium oxide with CrO 3 in the presence of water to 200-400‹ C. at a pressure of 1 to 500 kg./cm.2, using 1-40% wt. per cent of the chromium oxide product of (1) based on the weight of CrO 3 used in the second stage. The modifier, which may comprise 1-30 wt. per cent of the CrO 3 used in stage (1), may be tellurium or tellurium and/or antimony compounds with or without iron oxides or hydroxides. In examples, the products from stage (1) are Cr 3 O 8 or a mixture of Cr 3 O 8 and Cr 2 O 5 modified with TeO 2 , Sb 2 O 3 or α-FeOOH. The CrO 2 products may have a remanence of 400-500 Gauss cm.3g.-1 and a coercivity of 200-500 Ve and consist of acicular particles 0À1-2 Á x 0À02-0À1 Á.