Ignition and Combustion Performance of B@HMX Composite Microunit Prepared by Recrystallization of Solvent Evaporation

Fuel boron (B) has the advantage of a high calorific value. However, a coating of boron oxide (B₂O₃) is present on the outermost layer of the B particles, which will greatly hinder the oxidation of B. In this study, the high-energy 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) is used to increase the activity of B powder, so as to enhance the ignition and combustion performance of B. Samples with various HMX contents are successfully prepared by recrystallization of the solvent evaporation method. The study of morphology and composition reveals that HMX is coated on the surface of B particles to form composite microunits. Interestingly, the heat and gas released during the decomposition of HMX facilitated the evaporation and destruction of the oxide film. Consequently, this promotes the oxidation reaction of B and results in a reduction in its initial oxidation temperature to 762.45 °C. The results of ignition and combustion tests show that the shortest ignition delay time of the sample with the mass ratio of B to HMX of 1:5 is 1.11 s, which is 0.38 s earlier than that of the physical mixed sample. In addition, the maximum height and width of the combustion flame are the largest. These results show that B@HMX composite microunits with a high energy activation effect provide an effective strategy for better application of B powder.