Comparative analysis of vaporization and thermal decomposition of cyclotrimethylenetrinitramine (Rdx)

Considering the need for accurate vaporization rates in the propellant combustion models, sublimation and vaporization rates of cyclotrimethylenetrinitramine (RDX) have been estimated over a wide range of temperatures. Simultaneous thermal analysis was carried at various slow heating rates, 5, 10, and 15°C/min, using a coupled TGA/DSC-FTIR system. In the solid phase, the mass loss occurs mainly due to the sublimation of RDX, whereas, in the liquid phase, both vaporization and thermal decomposition play a significant role. The extent of thermal decomposition was estimated using a computational model based on a recently developed detailed liquid-phase decomposition mechanism for RDX. For each of the heating rates, a suitable match between computational and experimental mass loss and species evolution profiles was achieved. As evident from the FTIR data, a major part of the mass loss occurs because of the evolution of decomposition products, such as N₂ O, CH₂ O, NO₂, NO, HCN, H₂ O, CO, and CO₂ . Results show that vaporization accounts for 29.6, 34, and 35.9% of the total mass loss for the 5, 10, and 15°C/min heating rates, respectively. Relatively more RDX vaporizes at higher heating rates because of the initiation of the boiling phenomenon at higher sample temperatures.