Improvements in and relating to the manufacture of ferrimagnetic materials
Номер патента: GB1045432A
Опубликовано: 12-10-1966
Автор(ы):
Принадлежит: Chevron Research and Technology Co, Chevron Research Co
Опубликовано: 12-10-1966
Автор(ы):
Принадлежит: Chevron Research and Technology Co, Chevron Research Co
Реферат: A process for manufacturing a ferrimagnetic material in the form of sintered finely divided particles comprises converting at least one salt of a divalent metal and at least one salt of a trivalent iron, in the presence of an epoxy compound and a source of hydroxyl groups, to a sol containing a mixture of the corresponding hydroxides which is then converted into the desired ferrimagnetic material by heating. The salts may be chlorides, bromides or iodides, and the divalent metal may be cobalt. The sol is converted into a gel and the other reaction products are driven off before the mixture is heated to form the ferrimagnetic matetial. The ferrimagnetic particles of the invention may be coated with an antiferromagnetic material for example a Fe2O3, coupled by exchange anisotropy (that is to say, the spin systems of the ferrimagnetic and antiferromagnetic phases are coupled) which gives material with a higher coercivity than the ferrimagnetic material above. The product of the Microgel process has pores smaller than 1000 <\>rA diameter and surface areas above 2 m.2/gram. Because of this porosity it can be ground more easily than the products of conventional processes. The epoxy compound may be a lower alkylene oxide (ethylene, propylene or butylene oxide) or an epichlorohydrin, and the source of hydroxyl groups may be water. A polar solvent (water or a lower alkanol) which is more polar than the epoxy compound may be present. The ferrimagnetic materials produced may have spinel, garnet, magneto-plumbite or perovskite structure. To give particles with an insulating coating the gel produced above is ground with aluminium chloride (for a coating of Al2O3) and a lower alkanol. A lower alkylene oxide is then added resulting in a dispersion of the ferrimagnetic precursor particles in an Al(OH)3 gel. Heating yields ferrimagnetic particles coated with Al2O3. Silica, magnesia, or zirconia may be used instead of alumina.
Improvements in and relating to machines for the manufacture of electric incandescent lamps and similar articles
Номер патента: GB252395A. Автор: . Владелец: British Thomson Houston Co Ltd. Дата публикации: 1926-09-09.