Initial stage of mechanochemical synthesis in the Ti-C exothermic system

Nanocrystalline titanium carbide is obtained by mechanochemical synthesis in a planetary ball mill AGO-2S from a powder mixture Ti(50)C(50) (at %) of titanium and graphite. Either gradual or abrupt reaction occurs, depending on the power intensity of the mill. The critical power intensity for the transition from the gradual to abrupt kinetics is found. By X-ray diffraction, X-ray photoelectron spectroscopy, and temperature monitoring, it is shown that the state of Ti-C system directly before the beginning of the reaction is identical irrespective of the subsequent kinetics of mechanosynthesis. This state is characterized by the nanocrystalline structure of titanium (grain size, ∼20 nm), no reflexes of graphite, the presence of a diffuse halo in X-ray diffractograms, and the presence of chemical interatomic Ti-C type bonds. The doses of mechanical energy necessary for the beginnings of both gradual and abrupt reactions are equal and do not depend on the power intensity of the mill.