INFLUENCE OF THE NATURE OF MILLING MEDIA ON PHASE-TRANSFORMATIONS INDUCED BY GRINDING IN SOME OXIDES

Polymorphic transformations induced by dry ball milling in an argon at mosphere have been investigated in various oxides (TiO2, SnO2, Y2O3, W O3) by X-ray diffraction, Mossbauer spectroscopy and transmission elec tron microscopy (TEM). The transformations have been found to depend o n the nature of the milling media, particularly when reduction reactio ns take place between grinding tools and oxide particles. When ground with steel tools, cubic yttria is transformed into a monoclinic modifi cation as reported in the literature, while tin oxide is reduced. When ground with zirconia tools, cubic yttria with a bixbyite type structu re is transformed into cubic yttria with a fluorite type structure, wh ile monoclinic tungsten oxide is transformed into a cubic oxide with a n ReO3 type structure. Plausible structural explanations are proposed. In all cases, nanometre-sized domains have been observed by TEM even after grinding times as short as some minutes.