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, ha s been investigated. Mechanical milling of 2FeCl(3)+3CaO led to a nano crystalline mixture of these two compounds. Fe2O3 formed only after he at treatment at 150 degrees C or above. A dilution of CaCl2 into the s tarting mixture caused a significant decrease in particle size, result ing in 10-30 nm mono-disperse particles of Fe2O3. Nanocrystalline akag aneite, FeOON, together with calcium chloride was formed by milling 2F eCl(3)+3Ca(OH)(2). Conversion of FeOOH to Fe2O3 by dehydration occurre d during subsequent heat treatment. Ultrafine Fe2O3 particles of 20-50 nm were obtained after removal of the CaCl2 by-product phase. (C) 199 7 Acta Metallurgica Inc.