Ball milling-induced combustion in powder mixtures containing titanium, zirconium, or hafnium

Ball milling induces self propagating high temperature reactions in many highly exothermic powder mixtures. This phenomenon has been studied in a variety of reactions with titanium, zirconium, and hafnium. Several oxides (CuO, Cu2O, NiO, Fe3O4, and ZnO) were reduced with Ti, Zr, and Hf and the borides, carbides, silicides, and sulfides of these metals were prepared from elemental mixtures. The ignition time is much shorter with Zr than with either Ti or Hf whenever oxygen or sulfur is involved in the reaction, but no similar variation is observed for the formation of borides, carbides, and silicides. It is suggested that the fast diffusion of oxygen in ZrO2 and very likely of sulfur in ZrS2 are responsible for this behavior. (C) 1996 Academic Press, Inc.