Thermal decomposition behaviour and chemical kinetics of tungsten based electrically controlled solid propellants

Abstract

In recent times, there is a growing interest in the development of electrically controlled solid propellants (ECSPs) because they offer various advantages over conventional solid propellants. However, the fundamental understanding on the complex reaction mechanism of decomposition/combustion of these ECSPs is still limited. The present study attempts to expand the knowledge on thermal decomposition mechanisms of ECSPs based on lithium perchlorate (LP) oxidizer and poly vinyl alcohol (PVA) binder, and to further investigate the influence of tungsten (W) as a metal additive, using thermal analysis. The chemical kinetic parameters for different metallized samples are obtained and compared with the non-metallized baseline propellant. Decomposition of non-metallized sample occurs over three stages involving primary reactions between molten oxidizer and pyrolysis products of PVA, and secondary gas-phase reactions overlapping with pyrolysis of unreacted LP. However, metallized ECSPs exhibit only single step decomposition that incorporates metal oxidation as well. It is obtained that the initial decomposition temperature of non-metallized ECSP is 349 °C with a heat release from the overall decomposition reaction of 2043 J/g. Addition of W increases this overall heat release up to 43% for ECSP-M1 containing 5% W, whereas the decomposition temperature is reduced by ∼60 °C, when compared to the non-metallized case. This indicates that the thermal stability of ECSPs is lowered due to the inclusion of W particles. Further increase in W content diminishes the overall heat release by 10% and 13% with correspondingly more unreacted samples, and rises the effective activation energy by 36% and 60% for ECSP-M2 and ECSP-M3, respectively, relative to ECSP-M1. Based on the present findings, we propose the global reaction mechanism for both non-metallized and metallized ECSPs.