Role of Convective Heat Transfer in Gasless Combustion by the Example of Combustion of the Ti–C System

Abstract

Combustion of mixtures of transition metals with nonmetals began to be actively studied after Merzhanov, Borovinskaya, and Shkiro discovered a new method for producing inorganic substances by combustion, which was called self-propagating high-temperature synthesis [1]. The first studies were performed on small-sized samples in a constant-pressure vessel (bomb) and showed that the combustion velocity and the structure and composition of the final products are independent of the external gas pressure [1‐3]. Therefore, such combustion was called gasless combustion and such systems were named gasless systems. The theory developed for describing the combustion of these systems is based on the assumption of a conductive mechanism of heat transfer in the combustion wave and ignores the effect of impurity gas release and convective heat transfer by the metal melt on combustion [2, 4]. However, at the present time, many experimental data have been accumulated on the combustion of mixtures of metals (Ti, Zr) with nonmetals (C, B, Si) (gasless mixtures) that cannot be explained within the framework of the existing theory of gasless combustion, which is based on the assumption of a conductive mechanism of heat transfer in the combustion wave [5‐7]. Among such data are a high velocity of combustion of compacted samples, the dependence of the combustion velocity both on the amount of impurity gases in the mixture and on the external pressure at which the synthesis is performed [5], the existence of a maximum in the combustion velocity versus density curve [3], and an increase in the combustion velocity with a decrease in the sample diameter [6] and after thermal vacuum treatment of the initial samples [7]. To explain these experimental facts, we put forth the hypothesis that the mechanism of combustion of fast-burning gasless systems under constant external pressure, as well as in directed filtration of impurity gases [8, 9], is determined by both convective and conductive heat transfer. In this case, the convective heat transfer is caused by the motion of the melt of the low-melting component