Sintered ferrite magnet and its production method

摘要

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.

主权项

1. A method for producing 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; said second grain boundary phases being dispersed in an arbitrary cross section of said sintered ferrite magnet; and said second grain boundary phases having an average area of less than 0.2 μm2; said method comprising the steps of
preparing raw material powders comprising metal elements of Ca, La, an element A which is Ba and/or Sr, Fe and Co, which are represented by the general formula of Ca1-x-yLaxAyFe2n-zCoz, wherein 1−x−y, x, y and z representing the atomic ratios of said metal elements, and n representing a molar ratio meet: 0.3≦1−x−y≦0.65, 0.3≦x≦0.65, 0≦y≦0.2, 0.25≦z≦0.65, and 4.5≦n≦7; calcining said raw material powders to obtain a calcined body; pulverizing said calcined body to powder; molding said powder to obtain a green body; and sintering said green body to obtain a sintered body; 0-1.8% by mass of SiO2 and 0-2% by mass (as CaO) of CaCO3 being added to 100% by mass of said calcined body after calcining and before molding; and said sintering step being conducted with a temperature-elevating speed of 1-4° C./minute in a temperature range from 1100° C. to a sintering temperature, and a temperature-lowering speed of 6° C./minute or more in a temperature range from the sintering temperature to 1100° C.