Morphology of ultra fine iron particles

Variation in morphology of the silica thin film coated ultra fine goethite particles(length:140 nm, aspect ratio:11/1, surface area:95 m²/g, SiO2/Fe:3.4 wt%) in the process of decomposition and subsequent reduction was examined by means of gas adsorption and electron microscopy. Microporous hematite particles, prepared by decomposition of the silica-coated ultra fine goethite particles at 250°C in vacuo, were subjected to heat-treatment at 700°C in air to form the nonporous hematite particles without degradation of the acicular shape. The highly acicular and nonporous ultra fine iron particles(length:110 nm, aspect ratio:10/1, surface area: 80 m²/g) were obtained as a result of shrinkage of the particles in the reduction process of the nonporous hematite particles at 400°C in hydrogen gas. Coercivity of the ultra fine iron particles was 1660 Oe.