Influence of AP Particle Size on Burning Characteristics of HMX/AP Propellants Supplemented with Fe2O3

Nitramine propellants have attracted considerable attention in the domain of solid rockets and gun propulsion because of their energetic and smokeless features. Ammonium perchlorate (AP) is the widely used oxidizer in propellants owing to the excellent burning characteristics. In this study, the burning rates of cyclotetramethylenetetranitramine (HMX)/AP propellant, prepared with varying mass ratios of AP to whole oxidizer (xi) using Fe2O3 as a catalyst, were investigated. Fine AP (FAP) and coarse AP (CAP) were used as the AP samples. The burning rates of HMX/FAP propellants were higher than those of HMX/CAP propellants. The burning rates increased with increasing xi and with the Fe2O3 addition. The burning characteristics of the HMX/AP propellant displayed unique dependencies on the AP particle size, xi, and pressure. The maximum effect of Fe2O3 on the increase in burning rate was obtained when xi = 0.6 because the increase in the catalytic effect for the AP propellant due to the increase in xi could not be entirely compensated for by the decrease in xi for the HMX propellant. When xi < 0.4, the propellant comprising Fe2O3 displayed a non-luminous flame below 1 MPa; the length of the non-luminous flame decreased with increasing pressure and xi and did not depend on the AP particle size. The flame of the HMX/AP propellants at low xi would be described as a two-stage flame comprising two reaction zones: the first-stage reaction zone and the preparation zone. The combustion processes in the first-stage reaction zone significantly affected the burning characteristics of HMX/AP propellants.