Taguchi method-based evaluation of thermal hazard of lift-off pyrotechnics under various storage conditions

Abstract

This study employed the Taguchi method and analysis of variance to investigate the factors that influence the deterioration of the lift-off pyrotechnics when they are stored under various relative humidity (RH) and temperature conditions. A field emission scanning electron microscope and an energy-dispersive X-ray spectroscope were used to observe the microstructures and elements of pyrotechnic samples. Differential scanning calorimetry (DSC) and Vent Sizing Package 2 (VSP2) were applied to measure the relationship between the trace heat flow of the samples and temperature as well as the thermal runaway reactions in a pseudo-adiabatic environment. A DSC analysis and a thermodynamic ASTM E698 analysis were combined to explore the safety of lift-off pyrotechnics and the related thermal hazards.The energy-dispersive X-ray spectroscopy and DSC experimental results revealed that KNO3 is highly soluble. However, when RH and exposure time increased, the surface dissolution of oxidants decreased the height of the second exothermic peak, resulting in incomplete combustion and ignition failure. The ASTM E698 thermokinetic analysis results indicated that the apparent activation energy (Ea) of the samples increased substantially after being immersed in deionized water. Notably, the Ea of colored smoke increased from 46.88 to 155.91 kJ/mol, indicating that the examined pyrotechnics were more sensitive to a decrease in temperature than to an increase in humidity. A large amount of water can be used to alleviate the reactivity of pyrotechnics and thus reduce pyrotechnic hazards. The VSP2 analysis results indicated that the self-boosting rate of the samples was greater under 40% RH than under pristine conditions; however, this rate decreased substantially under 80% RH and after immersion in deionized water. The results of the Taguchi experiment and analysis of variance revealed that humidity contributed 63.60% and 50.86% to Ea and maximum pressure, respectively. Accordingly, controlling humidity should be prioritized to diminish the hazard of storing pyrotechnics.