Through the use of simultaneous thermogravimetry modulated beam mass spectrometry (STMBMS) measurements, time-of-flight (TOF) velocity-spectra analysis, and H-2, C-13, N-15, and O-18 labeled analogues of 1,3,5-trinitrohexahydro-s-triazine (RDX), the thermal decomposition products of RDX have been identified as H2O, HCN, CO, CH2O, NO, N2O, NH2CHO, NO2, HONO, (CH3)NHCHO, oxy-s-triazine (OST), and 1-nitroso-3,5-dinitrohexahydro-s-triazine (ONDNTA) and all of their gas formation rates have been measured as a function of time. From these results the primary reaction pathways that control the decomposition of RDX in both the solid and liquid phases have been discovered. Four primary reaction pathways control the decomposition of RDX in the liquid phase between 200 and 215-degrees-C. Two pathways are first-order reactions solely in RDX. One produces predominantly OST, NO, and H2O and accounts for approximately 30% of the decomposed RDX, and the other produces predominantly N2O and CH2O with smaller amounts of NO2, CO, and NH2CHO and accounts for 10% of the decomposed RDX. The third pathway consists of formation of ONDNTA by reaction between NO and RDX, followed by the decomposition of ONDNTA to predominantly CH2O and N2O. The fourth reaction pathway consists of decomposition of RDX through reaction with a catalyst that is formed from the decomposition products of previously decomposed RDX. The third and fourth reaction channels each account for approximately 30% of the decomposed RDX. Experiments with solid-phase RDX have shown that its decomposition rate is very much slower than that of liquid-phase RDX. ONDNTA is the only product that appears to be formed during the early stages of the decomposition of RDX in the solid phase. As the solid-phase decomposition progresses, N2O and lesser amounts of CH2O start to evolve and their rates of evolution increase until products associated with the liquid-phase RDX decomposition appear and the rates of gas formation of all products rapidly increase. This behavior strongly suggests that the decomposition of solid RDX occurs through formation of ONDNTA within the lattice, the subsequent decomposition of it within the lattice to N2O and CH2O, followed by the dispersion of CH2O in the RDX, leading to its eventual liquefaction and the onset of the liquid-phase decomposition reactions.
