Research on the thermal decomposition kinetics and the isothermal stability of HMX

Abstract

During the thermal decomposition of cyclotetramethylene tetramine (HMX), the endothermic process of melt disturbed exothermic decomposition, which brought deformation in its thermal graphs. Hence, exact kinetic parameters of the thermal decomposition of HMX could not be calculated by the thermal measuring method. The thermal stability in low temperature also couldn’t be described by the decomposition kinetics of the temperatures higher than the temperature of melt. Thermogravimetric (TG) measures the sample’s mass loss in the process of the thermal decomposition which will reduce the impact of the melting process to a certain extent. In this study, the combined TG (thermogravimetric analyzer)/DSC (differential scanning calorimetry) method was used to investigate the thermal behavior of HMX. Based on the experimental data of TG, the kinetic model and parameters of the thermal decomposition of HMX was studied by the multivariate nonlinear regression method. The isothermal DSC test has certain advantages for studying the thermal behavior of materials at low temperature. In this paper, the isothermal DSC test was used to investigate the thermal behavior of HMX. The kinetic parameters obtained by the Friedman method with heat balance were analyzed and used for simulating the adiabatic behavior time to the maximum rate under adiabatic conditions (TMRad). The results indicated that the decomposition process of HMX could be described by the kinetic equation: $${\text{d}}\alpha /{\text{d}}t = 10^{38.2} \exp ( - \,432200/RT)(1 - \alpha )(1 + 10^{1.41} \alpha )$$ , which was autocatalytic decomposition. The TD8 and TD24 (the temperatures when the adiabatic behavior time to the maximum rate under adiabatic conditions were 8 and 24 h, respectively) of HMX were 214.6 and 204.5 °C, respectively.