Influence of iron oxide on thermal decomposition behavior and burning characteristics of ammonium nitrate/ammonium perchlorate-based composite propellants

The thermal decomposition behavior and burning characteristics of ammonium nitrate(AN)/ammonium perchlorate(AP) propellants supplemented with Fe2O3 were investigated. Based on these data, the performance differences between the propellants with Fe2O3 and those without Fe2O3 were investigated to reveal the influence of Fe2O3 on the thermal decomposition behavior and burning characteristics of AN/AP-based composite propellants. TG-DTA showed the peak temperature and temperature range of thermal decomposition due to AN decomposition to be independent of the presence of Fe2O3. The peak and the offset temperature of thermal decomposition due to AP decomposition decreased owing to the addition of Fe2O3, while the onset temperature did not vary. The burning rate of the AN/AP propellant was increased by the addition of Fe2O3; the effect of Fe2O3 on increasing the burning rate was influenced by the type of oxidizer, AP content in the oxidizer (ξ), and AP size. Furthermore, Fe2O3 allowed the suppression of the remarkable heterogeneity of the combustion wave of the AN/AP propellant without Fe2O3. The ignitability of the AN/AP propellant was improved by the addition of Fe2O3, except for the propellant with a ξ of 0.4. The cause of depressed ignitability by the addition of Fe2O3 for the propellant with a ξ of 0.4 is discussed based on thermogravimetry-differential thermal analysis, the visual observations of the unignited propellant surfaces, and the decomposition phenomena of the propellants using a high-temperature observation equipment. A large quantity of AN remained on the surface of the unignited propellant at 0.5 MPa. The cause of the depressed ignitability is that AN, AP, and HTPB do not simultaneously decompose and as a result AN remains on the burning surface. Thus, the burning surface of AN did not regress simultaneously with the burning surface of the AP-filled region, the matrix of AP, and HTPB.