Study of conditions and specific features of Hf + 0.5 C combustion in nitrogen: effect of mechanical activation

Combustion of cylindrical Hf + 0.5 C samples pressed from hafnium powder mixtures with soot in nitrogen is investigated. Non-activated mixtures and compositions that had undergone preliminary mechanical activation in a planetary mill were studied. The nitrogen pressure in the experiments was 0.2–4 MPa. It was found that the combustion mode of samples from the non-activated mixture depends on the nitrogen pressure. At a pressure below 2 MPa, the front propagates in a self-oscillating mode, and at high pressures – in a stationary mode. The combustion of samples from the mechanically activated mixture proceeds in a stationary manner over the entire range of studied pressures, while the combustion rate is 50–100 times higher than the combustion rate of samples from the non-activated mixture. This is due to the difference in the microstructures of these mixtures and, accordingly, to different reaction mechanisms. During mechanical activation of the mixture, composite particles are formed, the contact area of carbon and hafnium in which is orders of magnitude greater than the contact area between them in the case of a non-activated mixture. As a result, the leading role in the combustion of samples from mechanically activated mixtures is played by the interaction of hafnium with carbon, which leads to an improvement in the gas permeability of the sample and subsequent nitriding. In samples from a nonactivated mixture, the leading role is played by the nitriding of hafnium, which occurs at a low rate due to filtration difficulties.