Effects of SiO2 on magnetic-properties of Al2O3-coated acicular α-Fe particles

(SiO₂, Al₂O₃)-coated acicular α-Fe particles were obtained by first coprecipitating Si and Al ions on the surface of α-FeOOH particles and next the α-FeOOH particles were dehydrated and reduced by hydrogen. The effects of Si ion on Al₂O₃-coated α-Fe particles are as follows: (1) it prevented the acicular α-Fe particles from particle growth and grain growth during reduction; (2) a suitable amount of Si ion (0.3 wt%) in the particles only slightly decreased the σ_s value but significantly increased the _iH_c value of the particles; (3) 0.3 wt% of Si ion effectively prevented the σ_s value of the Al₂O₃-coated α-Fe particles from deteriorating with time, higher Si ion content was required to prevent the _iH_c from deteriorating: and (4) Si ion could not prevent the magnetics of the Al₂O₃-coated α-Fe particle from deteriorating under severe surroundings