(694g) Solid Flame: Experimental Validation
Based on the thermodynamic calculations, it has long been hypothesized that a true solid-state combustion reaction could occur . However, in every previously investigated case, due to the presence of impurities, one of the reactants experienced a phase transition (e.g. melting), or there was some transport-assisted process occurring. For example, it is well known that the pure tantalum-carbon system should not experience any phase transitions during combustion since its adiabatic temperature (2743 K) is well below the eutectic point (4242 K) of the system. But it has been previously shown that combustion wave propagation in this system occurs with the help of gas-phase transport agents, which are formed through reaction between carbon and the metal oxide layer [cf. 2]. Through use of high energy ball milling in an inert atmosphere, the oxygen free Ta/C composite particles were prepared. It was experimentally proven that these particles possess the ignition temperature on the order of 1300 K and that the true solid flame reaction may propagate along the heterogeneous media, which consist of such particles. A number of studies were done to define the morphology and microstructure of the reactants and reaction products, the apparent activation energy, and other relevant characteristics.
 Merzhanov, A. G., Self-propagating high-temperature synthesis: Twenty years of search and findings. In “Combustion and Plasma Synthesis of High-Temperature Materials” (Z. A. Munir and J. B. Holt, eds.). VCH Publishers, New York, 1990, p. 1.
 Merzhanov, A. G., Rogachev, A. S., Mukasyan, A. S., Khusid, B. M., Borovinskaya, I. P., and Khina, B. B., The role of gas-phase transport in combustion of tantalum-carbon system. J. Eng. Phys.Thermophys.. 59,809 (1990).