Reactive diffusion in the system vanadium-silicon

The diffusion-controlled growth of vanadium silicides (V3Si, V5Si3, V6Si5, VSi2) was studied on bulk V–Si diffusion couples annealed for 2–36 h at 1150–1390°C. The layer growth kinetics was parabolic for all of the silicides. Only at 1150 and 1200°C was an induction period observed before the formation of a continuous V6Si5 layer. The parabolic growth constants of the II kind for the exclusive growth of each silicide from the adjacent phases were calculated from the parabolic constants of the I kind measured on the V–Si diffusion couples. The rate constants of the II kind were in turn related to the diffusion properties of the silicides. As a result, the interdiffusion coefficient, taking into account the diffusion of both elements, was obtained for each phase. The resulting activation energies were 240 kJ mol-1 for V3Si, 250 kJ mol-1 for V5Si3 and 190 kJ mol-1 for VSi2. The activation energies scale well with the melting point of the compounds. For V6Si5, the activation energy is strongly dependent on the set of thermodynamic data used in the calculation owing to the uncertainty in the decomposition temperature of this phase.