Thermal decomposition of phase-stabilised ammonium nitrate (PSAN), hydroxyl-terminated polybutadiene (HTPB) based propellants. The effect of iron(III) oxide burning-rate catalyst

Abstract

Phase-stabilised ammonium nitrate (PSAN) and hydroxyl-terminated polybutadiene (HTPB) are the main ingredients of propellants used with success in some pyrotechnic igniter components of the VULCAIN liquid rocket engine for the ARIANE 5. Small amounts of selected additives play an important role in solving some of the problems presented by composite propellants that include ammonium nitrate (AN). Iron(III) oxide (Fe 2O 3), for example, can be used as a burning-rate modifier in PSAN/HTPB propellants and although its effect on the burning rate is well known, its mechanism of action is not well understood. Thermogravimetry (TG), differential thermogravimetry (DTG) and differential thermal analysis (DTA) have been applied to study the slow thermal decomposition of selected compositions to investigate the mechanism of action of Fe 2O 3 as a burning-rate modifier of PSAN/HTPB propellants. The compositions evaluated include PSAN, Fe 2O 3 and HTPB cross-linked with isophorone diisocyanate (IPDI) as ingredients. No effect of Fe 2O 3 on PSAN decomposition is found. Fe 2O 3 shows an effect on the kinetics of the first stage of HTPBIPDI decomposition and increases the exothermicity of HTPBIPDI decomposition. In the decomposition of PSAN HTPBIPDI Fe 2O 3 propellants, the effect of Fe 2O 3 is also observed and a synergetic interaction between PSAN and HTPBIPDI is found, for which a physical-chemical explanation is given.