GB879794A - A process for the manufacture of non-metallic or ceramic permanent magnets - Google Patents

Abstract

879,794. Magnetic compositions. LIGNES TELEGRAPHIQUES ET TELEPHONIQUES. Dec. 10, 1957 [Dec. 14, 1956], No. 38351/57. Drawings to Specification. Class 38 (2). A permanent magnet material which may be represented by the formula expressed in molecular percentages (1-0.01y) (85.7-x) Fe 2 O 3 , (1-0.01y) (14.3+2) BeO, y SiO 2 , where x is 0-4 is made by compressing at 0.5-20 tons/sq. cm. a mixture of particles of iron or barium oxides or compounds which convert to oxides and sintering it for about 10 minutes at 1150-1300‹ C. 83Fe 2 O 3 , 17BaO was made by ball milling Fe 2 O 3 and barium carbonate with water for 24 hours, drying, screening, compressing at 5 tons/sq. cm., sintering for 4 hours at 1280‹ C. and cooling for 15 hours. This material has high values and low temperature coefficients of B r , He and BH (max). Magnetically anisotropic material having improved magnetic properties in the direction in which the pressure is applied is obtained by presintering the material at 1200‹ C. for three hours in air, cooling for 12 hours and regrinding to particles of 1 micron size before compressing. Further improvement in He is obtained by adding 0.1-6% preferably 1-2% of silica or a material which converts to silica on heating, during either of the grinding steps. Examples are described of the production of materials having the formulµ 81.5 Fe 2 O 3 , 16.7 BaO, 1.8 SiO 2 and 82.6 Fe 2 O 3 , 16.9 BaO, 0.5 SiO 2 . A machinable material is produced by sintering the material of the first in the above processes before the compression step at 1250‹ C. for four hours, cooling it in 15 hours, regrinding and mixing with it a binder such as a condensation polymer in a solvent which slowly evaporates, compressing at below 0.5 20 tons/sq. cm. and heating e.g. at 180‹ C. to eliminate the solvent and harden the binder. Suitable binders are epichlorhydrine, diphenolpropane or epoxy or silicone varnishes.