Specific Features of Heat and Mass Transfer during Combustion of a Granular Zr + 0.5C Mixture in an Argon Coflow

In this study, the synthesis patterns of ZrC_0.5 ceramics from a granulated mixture in a coflow of argon were investigated for the first time. Preliminary experiments without an argon purge showed that the impurity gas does not affect the combustion rate of Zr + 0.5C mixtures, and combustion transfer from granule to granule is ensured by movement of the zirconium melt. In an argon coflow, a new combustion mode of granular mixtures was discovered, characterized by high-speed combustion front propagation and accompanied by a decrease in both the longitudinal and transverse size of the burnt sample with the formation of a so-called “finger.” The set of observed phenomena can be explained by the assumption that due to significant shrinkage of the sample in the longitudinal direction, the permeability of the products decreases, which prevents filtration of argon through the products, directing the gas flow to the side surface of the cylindrical reactor into the resulting finger. An increase in the gas flow in a narrow channel along the side surface of the reactor in turn causes an increase in the apparent velocity and an increase in the combustion temperature of the mixture at the periphery of the sample. The experiments and calculations conducted show that the reduction in the dimensions of the sample in the longitudinal direction is ensured by the pressure difference of the filtered gas, and in the cross section, by the action of surface tension forces due to the temperature gradient.