Anisotropic ferrite produced with coarse particles milled from sintered magnets

摘要

Anisotropic ferrite sintered magnets are usually produced by the sintering of wet pressed bodies previously oriented by a magnetic field. It is well known that the orientation is efficient for very fine single crystalline particles. The use of dry pressing reduces the orientation capability, since the mobility of fine particles can be reduced by their agglomeration. However, the use of coarse powders obtained by milling sintered anisotropic magnets should facilitate the orientation during dry pressing. These coarse particles are composed of grains with the same crystallographic directions, so they could be oriented by a magnetic field. The goal of this paper is to investigate this possibility. In this work the sintered strontium ferrite magnets were milled and the obtained powder was classified, oriented and dry isostatically pressed. Sintering was conducted in a dilatometer furnace and shrinkage was monitored. The magnetic properties of the samples were evaluated by VSM. Microstructure was also evaluated. Magnetic properties were dependent of the particle size, and orientation and shrinkage were quite low for coarse particles.