Conductive and convective combustion modes of granular mixtures of Ti–C–NiCr

The combustion modes of powder and granular mixtures (100 – X)(Ti + C) + XNiCr (X = 0–30%) containing Ti powders of different dispersion with different amounts of impurity gases in them were investigated. The experimental setup provided filtration of impurity gases released during combustion in the cocurrent direction or through the side surface of the sample. The difference between the experimental burning velocities of powder mixtures with titanium of different fineness is explained using a convective-conductive combustion model. For granular mixtures based on Ti powder with a characteristic size of 120 μm, it was shown that combustion occurs in the conductive mode. Comparison of the combustion velocities of granular mixtures containing Ti powder with particles of a characteristic size of 60 μm in the absence and presence of gas filtration through the sample indicates the transition of combustion to the convective regime. The necessary and sufficient conditions for the transition from conductive to convective combustion are formulated, which makes it possible to determine the composition of the mixture whose combustion occurs in the boundary region. In mixtures based on Ti with a particle size of 60 μm, the conductive combustion regime is observed during the combustion of granules 0.6 mm in size and a mixture with X = 30% of granules 1.7 mm in size. For mixtures with X = 0–20% with granules 1.7 mm in size, burning in the convective regime, the interfacial heat transfer coefficients were evaluated using experimental data. Their values are more than an order of magnitude higher than the theoretical ones. The XPA results of the combustion products showed that in order to obtain synthesis products without side phases of intermetallic compounds, it is necessary to use finely dispersed titanium powder.