Microstructural evolution during high energy ball milling of Fe2O3-SiO2 powders

The reaction of a 25 mol% Fe2O3-SiO2 (hematite-amorphous silica) powder mixture during high energy ball milling in both closed and open containers has been studied by x-ray diffraction and Mossbauer spectroscopy. After around 21 h of milling, the alpha-Fe2O3 powders with an average particle size of 15 nm have formed and no reaction between alpha-Fe2O3 and SiO2 is found in the two types of milling containers. This demonstrates that the high energy mechanical milling technique is able to prepare a dispersion of ultrafine alpha-Fe2O3 particles. After extended milling in the open container all iron atoms are found in a hematite phase. In the closed container the hematite phase transforms into an iron-rich spinel phase and some of the iron atoms react with the amorphous SiO2, forming a new Fe(II)-containing silicate compound.