Combustion modes of the $\mathrm{Ti}+\mathrm{C}$ granular mixture with different content of gasifying additive

The influence of the content of polyvinyl butyral $(0\div2.3\%)$ on the combustion of a granular mixture of $\mathrm{Ti}+\mathrm{C}$ with titanium of different grades is investigated. The experiments were carried out in the absence of an external gas flow; therefore, due to the low decomposition temperature and a small amount of polyvinyl butyral, a conductive combustion mode was expected. However, for rapidly burning mixtures, a convective combustion mode was found due to the ignition of the granule surface with hot gaseous decomposition products of polyvinyl butyral. The mechanism of falling of undecomposed polyvinyl butyral behind the ignition front is explained. It was found that the combustion mode of the $\mathrm{Ti}+\mathrm{C}$ granular mixture depends on the rate of its combustion in the absence of a gas flow through the sample. Based on the experimental and theoretical analysis of the combustion process, it has been established that the ignition of granules in the convective mode occurs at the temperature of the $\alpha\to\beta$-transition in titanium. A qualitative explanation is given for the different effect of the content of polyvinyl butyral on slow and fast burning mixtures $\mathrm{Ti}+\mathrm{C}$.