Reductive synthesis of Fe@Al2O3 micro powders with high permeability and low magnetic loss in the MHz range

Abstract

Magnetic powders with high permeability and low loss in MHz range have gained ever-increasing attention. In this work, spherical FeCO3 particles have been firstly oxidized in air, then coated with Al(OH)3 insulation shell and finally reduced by hydrogen at different temperature. The results show that as the reduction temperature increases, reduced products would gradually be converted into Fe/Fe3O4@Al2O3 and Fe@Al2O3. Meanwhile, the increase of reduction temperature leads to a gradual increase in the content and crystal size of Fe. Owing to the protection from Al2O3 layer, spherical morphology can be well preserved in reduced products, while holes would be generated in spherical particles, due to the release of gaseous products. Further investigation on magnetic properties shows that with the increment of reduction temperature, permeability would be improved, and magnetic loss would be basically decreased in the frequency range of 1–30 MHz. It should be mentioned that reduction product at high temperature (600 °C) has larger permeability and weaker magnetic loss than that of carbonyl iron powder with similar particle size. This work may provide useful reference for the development of micro magnetic powders and high-performance soft magnetic composites.