The preparation and combustion performances of boron-based composites containing AlB₂ and MgB₂

In order to address the problems of low combustion efficiency and ignition difficulties associated with boron (B) particles, the B-based composites with high calorific values and enhanced combustion performance have been designed and prepared. These composites are obtained by combining nanoscale B powders (nB) with AlB₂ and MgB₂ using a ball-milling technique. Notably, the composite with an AlB₂: nB mass ratio of 5.5:1 shows relatively high calorific value of 39.7 kJ g⁻¹ or 108.7 kJ cm⁻³ in equivalence. The results of the thermal analysis indicate that AlB₂ and MgB₂ may enhance the thermal stability of nB, but they would promote its oxidative exothermic reactions at elevated temperature. In addition, the composites BM-AlB₂/nB and BM-MgB₂/nB exhibit superior ignition and combustion performance, specifically with respect to ignition delay and the maximum combustion temperature, when compared to pure nB, AlB₂ and MgB₂. The BM-AlB₂/nB with the highest calorific value is then coated with a typical hybrid oxidizer containing ammonium perchlorate (AP) and polyvinylidene fluoride (PVDF) using a spray-drying technique to demonstrate their oxidation efficiency as pseudo solid propellants. The core-shell (BM-AlB₂/nB)@(AP/PVDF) composite exhibits reduced smoke, a centralized flame structure, and sustainable high combustion temperature. Potential combustion reaction pathways of B-based composites are also proposed to understand their combustion chemistry.