Investigation of aging induced processes on thermo-kinetic and combustion characteristics of tungsten pyrotechnic delay composition

Abstract

A degradation in performance parameters related to thermal decomposition and combustion behaviour of tungsten based pyrotechnic delay composition can occur when subjected to accelerated aging conditions in a controlled environment. The present study utilizes various methods to quantify the extent of degradation in thermo-kinetic and burning characteristics as well as to postulate a fundamental aging mechanism for traditional tungsten (W) pyrotechnic delay material, which has not been attempted in the past. The delay composition based on metallic fuel (W) and perchlorate oxidizer is subjected to aging at constant temperature of 71 °C and 95% relative humidity, for 2 and 12 weeks, respectively. Experiments including thermal analysis, combustion temperature profile and burning rate measurements are conducted together with numerical simulation of an actual pyrotechnic delay device. Moreover, the reaction mechanism, chemical kinetics, and combustion behaviour between pristine and aged cases are examined. Results illustrate that there exist two aging induced processes, which increases the presence of large agglomerated particles, high metal oxide content by thickening the outer oxide layer of metallic fuel, and more unreacted oxygen to instigate incomplete combustion in aged samples. This alters the reaction pathway of combustion process, lowers average thermal conductivity, and reduces diffusion of reactants in aged samples, thus causing significant decrement in the heat of reaction (31%), combustion zone temperature (10%), reactivity (12%), and burning rates (10%), such that the overall pyrotechnic delay device experiences misfiring during operation or a failure in accomplishing its actual intended task.