Crystal structure and thermal decomposition kinetics of 1,3,5-trinitro-4,6-diazidobenzene

Abstract

Two different single crystals of 1,3,5-trinitro-4,6-diazidobenzene (C₆HN₉O₆) were measured by X-ray single-crystal diffraction. The molecular weight of C₆HN₉O₆ is 295.16. Crystal I system is orthorhombic, and space groups are Pbca, a = 10.5199 (19) nm, b = 13.436 (3) nm, c = 15.235 (3) nm, β = 90°, V = 2153.4 (7) nm³, Z = 8, Dc = 1.821 g cm⁻³, μ = 0.164 mm⁻¹, F(000) = 1184. Crystal II system is tetragonal, and space groups are P42/no a = b = 19.412 (5) nm, c = 5.9603 (17) nm, β = 90°, V = 2246.0 (13) nm³, Z = 8, Dc = 1.746 g cm⁻³, μ = 0.157 mm⁻¹, F(000) = 1184. Enthalpy of formation and detonation properties were calculated at the DFT-B3LYP/6-311++G ** level. It shows that these two compounds all have good detonation performance, among which crystal I has higher detonation velocity (8.81 km s⁻¹) and detonation pressure (34.65 GPa) than those of crystal II. The thermal behavior of the crystal I was studied by differential scanning calorimetry (DSC)–thermal gravimetric (TG) analysis, melting peak is at 94.80 °C, and two decomposition exothermic peaks are at 126.39 °C and 212.10 °C, respectively, in DSC curve. According to the Kissinger and Flynn–Wall–Ozawa methods, the activation energy (E) calculated for the first decomposition of the crystal I is 109.25 kJ mol⁻¹ and 110.67 kJ mol⁻¹, respectively, and second decomposition is 121.05 kJ mol⁻¹ and 124.35 kJ mol⁻¹, respectively. In addition, the accelerating rate calorimeter (ARC) was used to further study the adiabatic decomposition behavior. The E of the two decompositions is 128.70 kJ mol⁻¹ and 302.55 kJ mol⁻¹, respectively, and the pre-exponential (A) is 1.02 × 10¹⁶ s⁻¹ and 2.01 × 10³⁵ s⁻¹, respectively, by ARC data. The mechanism functions were f(α) = 2α^0.5 (first decomposition) and f(α) = 3α^2/3 (second decomposition).