MICROSTRUCTURAL EVOLUTION DURING HIGH-ENERGY BALL-MILLING OF FE2O3-SIO2 POWDERS

The reaction of a 25 mol% Fe2O3-SiO2 (hematite-amorphous silica) powde r mixture during high energy ball milling in both closed and open cont ainers has been studied by x-ray diffraction and Mossbauer spectroscop y. After around 21 h of milling, the alpha-Fe2O3 powders with an avera ge particle size of 15 nm have formed and no reaction between alpha-Fe 2O3 and SiO2 is found in the two types of milling containers. This dem onstrates that the high energy mechanical milling technique is able to prepare a dispersion of ultrafine alpha-Fe2O3 particles. After extend ed milling in the open container all iron atoms are found in a hematit e phase. In the closed container the hematite phase transforms into an iron-rich spinel phase and some of the iron atoms react with the amor phous SiO2, forming a new Fe(II)-containing silicate compound.