Kinetics of Combustion Synthesis in the Ti-C and Ti-C-Ni Systems

The kinetics and mechanisms of combustion reactions in the Ti-C and Ti-C-Ni systems were studied. Samples were produced by igniting compacts of elemental Ti, C, and Ni powders with a tungsten heating coil under an inert argon atmosphere. Using an elementary model of the process, the "apparent" activation energies of these highly exothermic reactions were determined by measuring combustion wave velocities and combustion temperatures. For the Ti + C ⇒ TiC reaction, two different combustion regimes were found. The first, for combustion temperatures greater than 2711 K, was postulated to be controlled by the dissolution of carbon into a titanium melt with an apparent activation energy of 124 ± 31 kJ · mol⁻¹. The second, for combustion temperatures less than 2711 K, was postulated to be controlled by the diffusion of carbon through a solid TiC layer with an apparent activation energy of 364 ± 25 kJ · mol⁻¹. For the reaction Ti + C + 25 wt% Ni ⇒ TiC + 25 wt% Ni the apparent activation energy was measured to be 133 ± 50 kJ · mol⁻¹, corresponding to the dissolution of carbon into a Ti-Ni melt. Temperature profile and microstructural information are also presented.