Effects of the Ti/Fe ratio on the phase composition and magnetic properties of mechanochemically activated Ti-Fe_2O_3 mixtures

摘要

The mechanochemical activation of Ti-Fe_2O_3 powder mixtures with molar ratio 1 and 1.5 was performed with the aim of understanding the effects of the starting composition on the reactivity and structure of the produced phases. The solid mixture was characterized by scanning electron microscopy, X-ray diffraction, vibrating sample magnetometry and Mossbauer spectroscopy. The consumption of the reactants and the formation of metallic iron are observed at short activation times. After 3 h, the redox reaction completes, yielding a composite powder formed by nanocrystalline Fe particles dispersed in an oxide matrix. The mixture with the highest Ti/Fe ratio leads to the formation of a TiO_2 matrix, whereas the other composition forms FeTiO_3. Both composite materials have very high saturation magnetization and moderate coercivities. Under subsequent thermal treatment at 700℃, the activated solids show a progressive crystalline ordering with partial oxidation of Fe (mainly to FeTiO_3 and Fe_2O_3) and crystallization into the rutile phase of TiO_2.This leads to a significant decrease of magnetization and coercivity.