Experimental and theoretical study of the influence of porous medium structures and impurity gas release on Ti–Si–C combustion

The combustion of powder and granulated mixtures (1 - $X$)(Ti + C) + $X$ (5Ti + 3Si), 0 $\le X\le$ 1 was studied. The experimental values of the combustion rate of powder mixtures depended on the fraction $X$ of the binary mixture 5Ti + 3Si, on the characteristic size of titanium particles $d$(Ti) in the charge and on the value of the free volume above the charge in the reactor. The convective-conductive combustion model was used to explain the results. It was shown that the nature of the change in the combustion rate of powder mixtures with increasing $X$ is associated with the fulfillment or nonfulfillment of the conditions for heating the charge particles and desorption of impurity gas in front of the combustion front. A large amount of liquid phase at 0.4 $<X<$ 0.6 prevents equalization of gas pressure in front of and behind the melt layer, which ensures maximum combustion rates of the ternary mixture at $d$(Ti) = 120 $\mu$m (or minimum at $d$(Ti) = 20 $\mu$m according to other authors). Based on the experimental combustion rates of mixtures with granules measuring 0.6–1.7 mm, the combustion transfer time between granules and the combustion rate of the substance inside the granules were calculated, i.e., the combustion rate of powder mixtures with the effect of gas evolution leveled out. The dependence of the combustion rate of the granule substance on $X$ is close to linear. For the 5Ti + 3Si composition, it is shown that, in contrast to the Ti + C mixture, due to the release of impurity gases behind the melt layer, the combustion front velocity in the powder mixture exceeds the combustion velocity of granulated mixtures and the combustion velocity of the substance inside the granules.