COMBUSTION SYNTHESIS IN THE TI-C-NI-MO SYSTEM .2. ANALYSIS

Combustion-wave arrest experiments provide the means of greater understanding of the physical phenomena which occur during the propagation of a combustion wave within a Ti-C-Ni-Mo powder mixture. The apparent activation energy for the process (E approximate to 120 +/- 40 kJ/mol) and the observations reported in the companion article indicate that the rate-limiting step in the reaction between Ti and C is the dissolution of C into the Ti-Ni-C melt. Temperature profile analysis indicates that the 2 mu m C flakes are completely consumed within approximately 0.2 seconds. The formation of TiCx spherules and their subsequent detachment is explained in terms of compressive stresses established in the growing TICx layer on the C particle. The compressive stresses are estimated to exceed 1 GPa, and an energy balance analysis predicts the formation of spherules for layer thicknesses on the order of 1 mu m, consistent with the experimental results.