Nano-carbides as accelerants for boron oxidation reaction

Nano-materials are potential substitutes for micro-sized solid propellant ingredients for improving energy density and reaction activity. So far, several nano-carbides act as accelerants for boron (B) oxidation reaction but their promotive effects and corresponding action mechanisms have rarely been reported. In this work, four nano-carbides [nano-boron carbide (nB(4)C), nano-titanium carbide (nTiC), nano-zirconium carbide (nZrC), and nano-silicon carbide (nSiC)] were evaluated by thermogravimetric differential scanning calorimetry-combined thermal analysis system and thermodynamic software FactSage 6.2. Among the four nano-carbides, nTiC ranked as the best accelerant by reducing the initial oxidation temperature of B by 10.7% and increasing heat release by 16.0%. By comparison, nB(4)C and nZrC were ranked as second and third best accelerants with abilities of decreasing the initial oxidation temperature (by 5.4% and 3.3%, respectively) and raising heat release (both by 6.2%). On the other hand, though nSiC slightly decreases the initial oxidation temperature of B, heat release of B + nSiC was lower than that of original B. The action mechanisms of nano-carbides were found complex, and one nano-carbide can accelerate B oxidation following one or several approaches. First, the nano-carbide can be oxidized before B to offer extra heat and induce the oxidation of B. The produced gaseous oxidation product CO2 by nano-carbide may then help break down the liquid oxide film deposited on B particle surface. Third, the reaction between nano-carbide and B would generate borides, which may diminish accumulated liquid oxide film at low temperatures. Finally, the corresponding oxide will be produced to catalyze the oxidation of B. Overall, these findings look promising for future performance improvement of B-based solid propellants.