Combustion Wave Speeds of Sol−Gel-Synthesized Tungsten Trioxide and Nano-Aluminum:  The Effect of Impurities on Flame Propagation

Abstract

Nanoparticles of tungsten trioxide (WO 3 ) were synthesized using sol−gel chemistry and combined with nanoscale aluminum (Al) particles to form a thermite. The as-made sol−gel-derived WO 3 aerogel contains impurities such as hydroxyl groups that are inherent to the synthesis process. These impurities can be removed via heat-treating the powder, and both as-made and heat-treated mixtures were examined for ignition and flame propagation as a function of the mixture bulk density. Results showed that the hydroxyl impurity impedes flame propagation in high density (compressed pellets) by acting as a heat sink and absorbing energy during flame propagation. In loose powders (low density mixtures), convection plays a more dominant role in flame propagation, such that the reduced particle size of the as-made WO 3 produces higher flame propagation speeds than the enhanced thermal transport properties associated with the heat-treated WO 3 .