Hard ferrite

Hard ferrite can be called permanent magnet material, mainly including: magnetoplumbite-type Ba-ferrite, Sr-ferrite, Pb-ferrite, spinel-type CO-ferrite, etc. .

The production of hard ferrite requires not only high purity of raw materials and precise formulation composition, but also appropriate magnet grain size, uniform distribution, reasonable orientation and compact structure.

The pre-sintering temperature of hard ferrite is generally 1100～1300℃. The sintering temperature is carried out in an oxidizing atmosphere at 1150 to 1250°C. For example, Ba-ferrite is made by pre-sintering the raw material at a temperature of 1100～1200℃, and sintering it at a temperature of 1150～1250℃ after forming. Co-ferrite is pre-fired at a temperature of about 900°C, then sintered at a temperature of 1100°C under reduced pressure, applied a magnetic field at a Curie temperature of 300°C, and then slowly cooled. .

The sintered density of ferrite is related to the size of the residual magnetic induction. The denser the ferrite, the greater the residual magnetic induction. Although increasing the firing temperature can increase the magnet density, it will cause the magnetic phase crystal grains to grow, which is unfavorable to the magnetic induction intensity. The correct method is to introduce additives to speed up the sintering speed, increase the density, and effectively inhibit the growth of magnet grains. Commonly used additives are: Al2O3, AS2O3 and Bi2O3.

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