Reason for the increasing burning rate of $\mathrm{Ti} +\mathrm{C}$ powder mixture when diluted with copper

For the first time, a comparative study of the combustion of powder and granular mixtures $\mathrm{Ti} +\mathrm{C}$, $(\mathrm{Ti} +\mathrm{C})+20\%\mathrm{Cu}$ with granules of different sizes with varying the particle size of titanium from 31 to 142 $\mu$m was performed. It has been found that the combustion rate of the $(\mathrm{Ti} +\mathrm{C})+20\%\mathrm{Cu}$ powder mixture is higher than that of the $\mathrm{Ti} +\mathrm{C}$ mixture, despite the lower combustion temperature. The use of the “gasless” combustion theory to determine the kinetic parameters of the process from the burning rate of the powder mixture leads to a negative value of the apparent activation energy, which shows the inapplicability of the traditional approach. The results are explained within the framework of the convective-conductive model of combustion by the retarding effect of impurity gases released during heating of component particles ahead of the combustion front. Using the values of the burning rate of granular mixtures with granules $0.6-1.7$ mm, the burning rate of the substance of the granules is calculated, i.e. the burning rate of the powder mixture, in which the influence of impurity gases is leveled. The ratio of the burning rates of a substance inside granules and powder samples determines the measure of the influence of impurity gas evolution on the burning rate of a powder mixture.