Kinetics of Decomposition of Titanium Tetraiodide

Abstract

      The rate of growth of an incandescent filament exposed to a steady stream of titanium tetraiodide vapour was determined from changes in the electrical conductance of the filament, and used to calculate the rate of decomposition of titanium tetraiodide at 1100-1500°C and at various vapour pressures. The method used eliminates the effects of titanium evaporation, counter-current gaseous diffusion, and the iodide synthesis reaction, which have influenced previous work. The results show that the rate of decomposition is proportional to the vapour concentration but independent of the surface area for a given length of filament. The decomposition rate varies with temperature according to an Arrhenius-type relationship, leading to a provisional estimate for the energy of activation of 28.6 kcal/mole. Under suitable conditions high deposition rates are obtained. The decomposition appears to proceed as a first-order, homogeneous, gas-phase reaction in a hot reaction zone around the filament, rather than heterogeneously on the surface.