Kinetics of formation of nanocrystalline phases by mechanochemical reaction between Ti and RuO2

The structural evolution of a mixture of Ti and RuO2 mechanically alloyed over a period of 40 h was followed with respect to time by X-Ray diffraction. The structural parameters were extracted from the XRD traces by performing a Rietveld refinement analysis. The phase formation occurs in three distinct stages. In stage I (first 10 min of milling), RuO2 and Ti reacts to form RuTi, Ru, and TiO, with some other oxide phases of titanium (Ti2O3, and TiO2). In stage II (between 10 and 60 min), the reaction slows down and the titanium dioxides are being reduced. In stage III, decomposition of RuTi through reaction with Ti2O3 occurs, to yield to the formation of TiO and Ru. In stage I, the reaction rate is very high, for example, 34.7 wt % of RuTi is formed after only 10 min of milling. It is argued that such rapid reaction rate is due to the enthalpy of the redox reaction occurring between Ti and RuO2 which raised the local temperature and thus favors the atomic interdiffusion. Finally, a series of experiments performed as a function of the milling intensity points to the existence of an energy threshold below which the combustion reaction between Ti and RuO2 does not occur. (C) 1999 Kluwer Academic Publishers.