Comparison of the thermal decompositions of HMX and 2,4-DNI for evaluation of slow cookoff response and long-term stability

摘要

Thermal decomposition of HMX between 175C and 200C was studied using the simultaneous thermogravimetric modulated beam mass spectrometer with focus on initial stages of the decomposition. Thermal decomposition products are the same as in previous higher temperature experiments. The initial stages of the decomposition have an induction period followed by two acceleratory periods. Arrhenius parameters for the induction and two acceleratory periods are (Log(A)= 18.2 (plus minus) 0.8, Ea = 48.2 (plus minus) 1.8 kcal/mole), (Log (A) = 17.15 (plus minus) 1.5 and Ea = 48.9 (plus minus) 3.2 kcal/mole), (Log (A) = 19.1 (plus minus) 3.0 and Ea = 52.1 (plus minus) 6.3 kcal/mole). This data can be used to calculate the time and temperature required to decompose a desired fraction of a test sample testing the effect of thermal degradation on sensitivity or bum rates. It can also be used to estimate the extent of decomposition expected under normal storage conditions for munitions containing HMX. This data, along with previous mechanistic studies conducted at higher temperatures, suggest that the process that controls the early stages of decomposition of HMX in the solid phase is scission of the N-NO(sub 2) bond, reaction of the N0(sub 2) within a lattice cage to form the mononitroso analogue of HMX and decomposition of the mononitroso HMX within the HMX lattice to form gaseous products that are retained in bubbles or diffuse into the surrounding lattice. These methods evaluating HMX can be used to evaluate new energetic materials such as 2,4-DNI. The early 2,4-DNI thermal decomposition is characterized by an initial decomposition, an apparent induction period, then an initial acceleratory period. The main gaseous products are NO, C0(sub 2), HNCO, H(sub 2)0, N(sub 2), CO, HCN and C(sub 2)N(sub 2). The presence of adsorbed and occluded H(sub 2)0 is the major cause of the early decomposition.