Nucleation and growth kinetics of reaction-product formation for copper–titanium and silver–titanium alloys on alumina

A nucleation and growth mechanism is proposed for the formation of the reaction product at the interface between polycrystalline alumina and liquid-metal alloy drops containing titanium. The reaction product had been previously identified to be an oxide of titanium. The growth of reaction product islands was clearly observed at the alumina–metal interface using optical microscopy after dissolving the metal droplets with acid. The fractional coverage was quantified as a function of time and, by assuming Avrami-type reaction kinetics, surface reaction rate constants, k, were calculated for copper–titanium and silver–titanium alloys on alumina. Reaction rate constants between 1.4 × 10^-4 and 18 × 10^-4 s^-2 were obtained for copper–titanium alloys on alumina. The k values for silver–titanium alloys were found to be an order of magnitude lower (2.5 × 10^-6 and 7.2 × 10^-6 s^-2) then the k values obtained for copper–titanium alloys on alumina. This revised version was published online in November 2006 with corrections to the Cover Date.