Effect of aluminum additives on the ignition of tungsten–teflon mixtures

Abstract

Abstract Thermodynamic analysis and studies of combustion and structure formation of products were carried out in the powder mixtures of tungsten and polytetrafluoroethylene (Teflon, Tf) with aluminum additives. The mixture components were selected to fabricate high-density condensed products with high ignition temperature. Aluminum was used as an energetic additive accelerating the ignition process and increasing the mixture combustion temperature. In mixtures, a tungsten/Tf ratio was fixed; the aluminum content was varied according to the formula (1 − x)(0.8W + 0.2Tf) + xAl = const. Mechanically activated mixtures were pressed into the samples and heated in special crucible with controlled heating rate. It was shown that an increase in the heating rate changes insignificantly the ignition temperature of systems, but strongly affects the structure of combustion products. The ignition and combustion of compositions with low aluminum content results a large volume of gaseous products, which fly apart or form a high-porous structure. At high Al concentration, the results of experiments and thermodynamic calculations are sufficiently different that can be explained by the lack of thermodynamic data on tungsten aluminides in the used program and by the fact that real conditions of reaction are far from equilibrium and adiabatic ones. The calculated and experimental data showed that the optimal aluminum content to form melted products with a high density (ρ(W2C) = 17.2 g/cm3) is about 10 wt %. At high Al concentration, the main combustion product (tungsten aluminide WAl4) has the lower density (ρ(WAl4) = 6.6 g/cm3) that is insufficiently for practical application.