Comparative study on aluminum agglomeration characteristics in HTPB and NEPE propellants: The critical effect of accumulation.

In this study, we investigate the aluminum agglomeration characteristics in hydroxyl‑terminated polybutadiene (HTPB) and nitrate ester plasticized polyether (NEPE) propellants during combustion. Based on thermogravimetric-differential scanning calorimetry (TG-DSC), sample quenching, microscope diagnoses, and collection of condensed combustion product, the effects of oxidants and binders on the thermal decomposition and surface characteristics of quenched samples, and combustion and agglomeration characteristics of propellants were analyzed. The Al/AP/HTPB composite has a one-step exothermic process with a heat of 1723 J·g−1, which is divided into two exothermic reactions with the addition of hexogen (RDX), with the first heat release being only 102.8 J·g−1. The first heat release of NEPE propellant is 1059 J·g−1, while CL-20 reduces it to only 520.5 J·g−1. At 14 MPa, the agglomerated peak particle size of AP/HTPB propellant is the smallest (50 µm), and the agglomerated particle size of AP/RDX/HTPB is 63 µm. The aggregation peak particle size of HMX/AP/NEPE propellant is 56 µm at 14 MPa, and the aggregation peak particle size of CL-20/HMX/AP/NEPE propellant is the largest among all samples (79 µm). The agglomeration of the two propellants is all controlled by the characteristics of the melting layer on the burning surface. The existence of pockets composed by large particle ammonium perchlorate (AP) in HTPB propellant also plays an important role in the agglomeration process of aluminum particles, which is different from NEPE propellant. The decomposition of melted binder leads to the accumulation of unlighted aluminum particles, and the size of agglomerates is mainly affected by the accumulation process. The distributed heat of different kinds of oxidants during propellant combustion may lead to the rapid decomposition of the binder before aluminum ignition, leading to the aggravation of the accumulation process and the increase of the agglomerated particle size. [ABSTRACT FROM AUTHOR]