PREPARATION AND MAGNETIC-PROPERTIES OF AL2O3-COATED ACICULAR ALPHA-FEPARTICLES

Al-modified acicular alpha-Fe particles were produced using the chemic al precipitation method by adding Al ion on the surface of alpha-FeOOH . This was followed by air oxidation, dehydration, and hydrogen reduct ion processes. Various dehydration, reduction temperatures and times w ere also studied. The addition of Al ion impeded the interparticle sin tering, spherization, and grain growth processes which were found to o ccur during dehydration and reduction. Consequently H-i(c) increased w ith the addition of Al ion, reached a maximum at 3 wt.% Al and later d ecreased again. The addition of Al ion always decreased the sigma valu e of alpha-Fe particles. The addition of Al ion prevented the alpha-Fe particles from deteriorating. At room temperature, 3 and 1.5 wt.% of Al ions would be required, respectively, for stabilizing the sigma and H-i(c) values of alpha-Fe particles. At elevated temperature, H-j(c) would deteriorate faster than the sigma value.