Experimental and Theoretical Study of the Effect of a Porous Medium Structure and Impurity Gas Release on Ti–Si–C Combustion

This paper describes the combustion of powder and granulated mixtures $$(1-X)(\textrm{Ti}+\textrm{C})+X(5\textrm{Ti}+3\textrm{Si})$$ ( $$0\leqslant X\leqslant 1$$ ). Experimental values of the burning rate of the powder mixtures depend on fraction $$X$$ of the 5Ti $$+$$ 3Si binary mixture, on the characteristic size of titanium particles $$d$$ (Ti) in the charge, and on the value of a free volume above the charge in the reactor. The results are explained using the convective-conductive combustion model. It is shown that the nature of the change in the burning rate of powder mixtures with increasing $$X$$ associated with fulfillment or nonfulfillment of conditions for charge particle heating and impurity gas desorption ahead of the combustion front. A large amount of the liquid phase at $$0.4<X<0.6$$ prevents gas pressure equalization ahead of and behind the melt layer, which ensures maximum burning rates of the ternary mixture at $$d(\textrm{Ti})=120$$ $$\mu$$ m [or minimum at $$d(\textrm{Ti})=20$$ $$\mu$$ m according to other studies]. Experimental burning rates of mixtures with 0.6- and 1.7-mm granules are applied to calculate the combustion transfer time between granules and the burning rate of the substance inside the granules, i.e., the burning rate of powder mixtures minus the effect of gas release. The dependence of the burning rate of the granule substance on $$X$$ is close to linear. It is shown for 5Ti $$+$$ 3Si that, in contrast to Ti $$+$$ C, the impurity gas release behind the melt layer contributes to the fact that the combustion front velocity in the powder mixture exceeds the combustion velocity of granulated mixtures and the substance combustion velocity inside the granules.