Multi-scale modified nitramine crystals with conjugated structure intercalation and thin-layer catalyst coating for well-controlled energy release rate

High-energy solid propellants with lower pressure exponent, lower burn rate but with high combustion efficiency are usually desired. The use of catalysts in less amount but maintained high efficiency is essential for high-energy content and better combustion performances. The fine combination of catalyst with energetic fillers as oxidizer has been found to be a promising strategy to achieve this goal. In this paper, a widely used nitramine oxidizer, cyclotrimethylenetrinitramine (RDX) has been selected as a typical example, which was first intercalated for lower sensitivity and lower burn rate, and then it was coated with in-situ synthesized nanosized metal oxides as catalysts for lower pressure exponent using polydopamine as the interfacial binding layer. Two types of catalyst-coated hybrid RDX crystals (named as qy-RDX@Fe₂O₃ and qy-RDX@CuO) have been prepared and characterized. It is found that the in-situ grafted nano-Fe₂O₃ and CuO crystals have significant catalytic effect on qy-RDX, which increased the heat release of qy-RDX@Fe₂O₃ and qy-RDX@CuO from 1747 J·g⁻¹ to 2159 J·g⁻¹ and 2133 J·g⁻¹, respectively. The results show that both qy-RDX@Fe₂O₃ and qy-RDX@CuO could reduce the ignition delay time and largely improve the burn rate of corresponding propellants at lower pressure (e.g. increased from 3.14 mm·s⁻¹ to 5.50 mm·s⁻¹ at 1 MPa) by coating only 0.13 wt% Fe₂O₃ and 0.15 wt% CuO catalysts, resulting in much lower pressure exponent (from 0.32 to 0.15). In particular, the decomposition heat of propellant containing only 10 wt% of qy-RDX@CuO is 1.5 times higher than the reference blank sample, so that its flame temperature was increased from 1800 °C to 2400 °C due to higher combustion efficiency with more energy release.