GB747737A - Improvements in or relating to methods of manufacturing non-metallic permanent magnets - Google Patents

Abstract

747,737. Magnetic compositions. PHILIPS ELECTRICAL INDUSTRIES, Ltd. July 3, 1953 [July 7, 1952], No. 18502/53. Class 38 (2). A permanent magnet having a (BH) max value of more than 2.3 X 10<SP>6</SP> Gause-Oersted is made from crystals having a magnetoplumbite structure and of composition MO.6Fe 2 O 3 where M represents at least one of the metals barium, strontium and lead of which metals at most <SP>2</SP>/ 5 may be replaced by calcium, e.g. the compositions forming the subject of Specification 708,127, which crystals are powdered and, after the addition of a substance which inhibits crystal growth during heating, or a material which turns into such a substance during heating, converted into a magnetically-anisotropic body, e.g. as in materials forming the subject of Specification 747,724, and then heated to between 1150‹ and 1350‹ C. To produce a barium composition, barium carbonate and iron oxide are ground in alcohol, heated to 1250‹ C., cooled, reground, reheated and sintered at 1340‹ C., cooled and reground, 0.5 per cent by weight of lanthanum oxide as modifier is then added, followed by a liquid such as water, alcohol and acetone, and the mixture is compressed in a magnetic field, and reheated to 1200-1225‹ C. The grinding may be in water, and there may be only one heating to 1270‹ C. before the lanthanum oxide, to the extent of 0.25 per cent by weight, is added, the final heating being at 1320‹ C. The inhibiting substance may be 0.5 per cent of basic bismuth carbonate, 0.25 or 1 per cent of calcium carbonate and slightly different temperatures for heat treatment are specified. Times of grinding and rates of heating and cooling are specified together with details of the magnetic properties obtained. Other materials added as or to produce inhibiting substances may be barium sulphate, barium oxide, barium ferrite, calcium oxide, calcium ferrite, bismuth oxide, boric acid, arsenic trioxide or antimony pentoxide. In forming the magnetically anisotroped body the powdered crystals may be orientated in a magnetic field when, for example, they are suspended in an inert liquid which is subsequently removed by compression.