Abstract
Combustion of cylindrical \(\textrm{Hf}+0.5\) C samples pressed from hafnium powder mixtures with soot in nitrogen is investigated. Nonactivated mixtures and compositions subjected to preliminary mechanical activation in a planetary mill are studied. Nitrogen pressure in the experiments reaches \(0.2{-}4\) MPa. It is revealed that the combustion conditions of samples from the nonactivated mixture depends on the nitrogen pressure. The front propagation is self-oscillatory at a pressure below 2 MPa and stationary at high pressures. The combustion of samples from the mechanically activated mixture is stationary over the entire pressure range, while their burning rate ( \(50{-}100\) )-fold exceeds the burning rate of samples from the nonactivated mixture. This is due to the difference in the microstructures of these mixtures and, accordingly, to different reaction mechanisms. The mechanical activation of the mixture is accompanied by the formation of composite particles, whose hafnium–carbon contact area is orders of magnitude greater than the same contact area in the case of an nonactivated mixture. As a result, the hafnium–carbon interaction plays the leading role in the combustion of the samples from mechanically activated mixtures. This interaction improves the gas permeability of the sample and leads to subsequent nitriding. The leading role in the combustion of the sample from an nonactivated mixture is played by hafnium nitriding occurring at a low rate due to filtration difficulties.
