Hematite powders synthesized by mechanochemical processing

The mechanochemical synthesis of ultrafine hematite powders via solid-state reactions involving FeCl3 and CaO or Ca(OH)(2), respectively, has been investigated. Mechanical milling of 2FeCl(3)+3CaO led to a nanocrystalline mixture of these two compounds. Fe2O3 formed only after heat treatment at 150 degrees C or above. A dilution of CaCl2 into the starting mixture caused a significant decrease in particle size, resulting in 10-30 nm mono-disperse particles of Fe2O3. Nanocrystalline akaganeite, FeOON, together with calcium chloride was formed by milling 2FeCl(3)+3Ca(OH)(2). Conversion of FeOOH to Fe2O3 by dehydration occurred during subsequent heat treatment. Ultrafine Fe2O3 particles of 20-50 nm were obtained after removal of the CaCl2 by-product phase. (C) 1997 Acta Metallurgica Inc.