PATENTS

      85.              ------.  [BADISCHE ANILIN- UND SODA-FABRIK]  (I. G. Farbenindustrie A. G. “In Auflosung”).  Making Magnetic Iron Oxides.  British Patent 677,878, Aug. 20, 1952.  Chem. Abs., vol. 47, 1953, p. 800.

Magnetic Fe oxides for magnetic sound recorders are produced directly from Fe carbonyl by burning it in an amount of O₂ producing an atom ratio of O: Fe substantially less than 3:2 by using a burner similar to those used for liquid fuel at 100°-1,500°.  The nature of the Fe oxides formed is influenced by the combustion temperature and the cooling rate.  Fe oxide obtained with a restricted supply of O₂ is oxidized to y-Fe₂O₂ by introducing additional O₂ while still hot, preferably under 500°, because at a higher temperature y-Fe₂O₂ is converted into the stable nonmagnetic a form.  When Fe₃O₄ is oxidized to y-Fe₂O₂ the permeability and remanence become functions of the oxidation temperature.  The values of the permeability and remanence are 32, 35, 21, 8, and 64, 61, 56, 16, respectively, at 90°, 250°, 405°, 585°.