Bimolecular crystal CL-20 with 7H-tris(1,2,5oxadiazolo)3,4-b:3',4'-d:3',4'-fazepine Experimental enthalpy of formation and thermal stability

摘要

The standard enthalpies of combustion and enthalpy of formation (EF) of 7H-tris([1,2,5]oxadiazole)[3,4-b:3',4'-d:3",4"-f]azepine (Az), its bimolecular crystal (BMC) with CL-20 γ-polymorph in molar ratio 1:1, and the γ-polymorph of CL-20 itself have been experimentally determined. It has been established that the difference between EF of BMC (1007.5±6.7 kJ/mole) and EF of the equimolecular mechanical mixture γ -CL-20 and Az (995.9 kJ/mole) differ by no more than 12 kJ/mole, that is a level of a measurement deviation. Quantum-chemical calculations have shown that the BMC does not possess any additional energy as compared to the total energy of the original isolated Az crystals and y -CL-20 and the value of the standard EF can be considered to a first approximation as the sum of the EFs of the original crystals. This difference does not affect the energy performance of compositions. It has been established that during thermal decomposition of the BMC y -CL-20 with Az the main contribution to the heat release rate and the process heat makes the decomposition of CL-20. Compound Az presented in the BMC, even inhibits the thermal decomposition of CL-20. This phenomenon lets to increase the shelf life of the BMC compared to the shelf life of the original CL-20.