Investigation of Macrokinetic Parameters of Combustion of (Ti + C)-Based Powder and Granular Mixtures: Elucidation of the Negative Activation Energy Paradox

For the first time, a comparative study is carried out of the macrokinetic parameters of the combustion of powder and granular mixtures of Ti + C when diluted by metal powders. The burning rates of powder mixtures (Ti + C) + 20% Me (Me = Ni, Cu) turned out to be higher than those of Ti + C mixtures, despite the lower temperature of combustion. This contradicts the theoretical models of the dependence of the combustion rate on the maximum temperature in condensed heterogeneous media. When diluting a Ti + C mixture with Ti or TiC powders, such a contradiction does not occur. The data obtained are explained using the convective-conductive model of combustion by the strong influence of the impurity gas release from titanium ahead of the combustion front. The values of the time of the transition of combustion between the granules and the burning rate of the material inside the granules, as well as a quantitative assessment of the decelerating effect of impurity gases in powder mixtures, are obtained using the values of combustion rates of the mixtures with granules of different sizes. For the (Ti + C) + 20% Ni mixture, the ignition time of the granules turned out to be less than 1 ms. The efficiency of the combustion transition between granules in the presence of a hot Ni melt is explained by comparing the combustion parameters of granular mixtures of Ti + C diluted with other metal powders and titanium carbide.