Sintered ferrite magnet and its production method
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United States of America Patent
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Mar 21, 2017
Grant Date -
Aug 6, 2015
app pub date -
Jul 24, 2013
filing date -
Jul 31, 2012
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Abstract
A sintered ferrite magnet comprising main phases of ferrite having a hexagonal M-type magnetoplumbite structure, first grain boundary phases existing between two main phases, and second grain boundary phases existing among three or more main phases, the second grain boundary phases being dispersed in its arbitrary cross section, and the second grain boundary phases having an average area of less than 0.2 μm2, are produced by calcining, pulverizing, molding and sintering raw material powders having the general formula of Ca1-x-yLaxAyFe2n-zCoz, wherein 1−x−y, x, y and z and n representing a molar ratio are in desired ranges; 1.8% or less by mass of SiO2 and 2% or less by mass (as CaO) of CaCO3 being added to a calcined body after calcining and before molding; and the sintering step being conducted with a temperature-elevating speed of 1-4° C./minute in a range from 1100° C. to a sintering temperature, and a temperature-lowering speed of 6° C./minute or more in a range from the sintering temperature to 1100° C.
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