Mechanochemical reaction between ilmenite (FeTiO3) and aluminium

A natural ilmenite (FeTiO3) and aluminium powder have been mechanically milled together for 100 h in a laboratory ball mill. The as-milled powder and an unmilled powder of identical composition were annealed at up to 1200 degrees C and examined by X-ray diffraction and differential thermal analysis (DTA). The unmilled sample showed aluminium melted prior to an exothermic reaction starting at -850 degrees C. The milled powder showed no thermal activity, other than a reversible phase transition at 1067+/-4 degrees C, indicating that reaction occurred within the mill. The products of both powders were the same, TiAl3, Fe4Al3, and Al2O3, although in the milled powder these phases were nanocrystalline until annealing caused crystallite growth. The thermal reaction seemed to occur in two stages, formation of TiAl3, Al2O3 and elemental iron followed by a slower, diffusion controlled reaction between the elemental iron and residual aluminium to form Fe4Al13. The reaction during milling was attributed to increased intermixing between the ilmenite and aluminium causing a change in the rate determining step from solid-state diffusion to another, unknown, controlling mechanism. (C) 1998 Elsevier Science S.A.