Unexpected burning rate independence of composite propellants on the pressure by fine interfacial control of fuel/oxidizer

In this paper, micro-spherical Al@PDA@RDX composites with fine interfacial control have been fabricated by spray-drying technique, where poly-dopamine (PDA) is employed as a binding layer. These composites have been applied in HTPB/AP/RDX/Al propellants, which have the same theoretical formulation and hence identical specific impulse (I-sp). However, these propellants differ in the interfacial structure due to different ways of assembling the ingredients, resulting in significant changes in their combustion performance. The thermal reactivity, burning rate, flame structure and the morphology of condensed combustion products (CCPs) of the prepared propellants have been investigated comprehensively. It has been shown that the pressure exponent (1-4 MPa) can be decreased from 0.236 to 0.024 (10 times lower) by the fine interfacial control, with more than 500 degrees C increase in flame temperature and 45.5% drop-off in the flame stand-off distance. In addition, the CCPs size distributions of the propellants have shown the enhanced interfacial interaction from Al@PDA@RDX composites can greatly inhibit the large-sized agglomeration of Al particles during the burning process.