Effects of Moisture Content on the Thermal Stability and Combustion Performance of HMX

Abstract 1,3,5,7-Tetranitro-1,3,5,7-tetraazacyclooctane (HMX) is a widely used energetic material with high energy density but limited thermal safety. In this work, we systematically investigate the effects of moisture on the thermal stability and combustion behavior of HMX using HMX/H2O mixtures with mass ratios of 10:0, 9:1, 8:2, and 7:3. Polarizing microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy results showed that the addition of water does not alter the crystal phase or molecular structure of HMX. As the moisture content increased, the peak temperature of thermal decomposition for HMX samples treated with different water ratios shifted slightly to higher values, while the friction sensitivity decreased significantly. In addition, the 5-second explosion point temperature rose and the ignition delay time was prolonged, along with decreased flame luminosity and burning rate. These combined experimental observations demonstrate an improvement in the overall thermal safety performance of the samples. Under the specific conditions of this study, compared with samples of other mass ratios, 10 wt % water provides a favorable balance between reduced sensitivity and retained combustion performance. It is worth noting that the open-air combustion experimental results show that when the water content increases to 20 wt %, complete combustion cannot be achieved despite further enhanced thermal stability. These findings illustrate the regulatory role of water in the thermal decomposition, thermal explosion, ignition, and combustion behaviors of HMX. This study provides valuable insights into the safe disposal and combustion applications of energetic materials.