Crystal structure, thermal decomposition, mechanical sensitivity of Na[CL-14·2H2O] and its catalytic effect on the thermal decomposition of ammonium nitrate

Abstract

A one-dimensional energetic complex (Na[CL-14·2H₂O]) constructed from sodium and 5,7-diamino-4,6-dinitrobenzofuroxan (CL-14) was synthesized, and its crystal structure was analyzed by X-ray diffraction. The crystal belongs to a monoclinic system with space group P2₁/c. The complex possesses a one-dimensional coordination framework based on the [ONaN]_n chain, which might result in its low sensitivity and high heat resistant. The thermal decomposition mechanism of Na[CL-14·2H₂O] was predicted by means of TG-DSC, TG-MS and FTIR analyses. The thermal decomposition of Na[CL-14·2H₂O] contains one endothermic and one exothermic processes in the temperature range of 25–500 °C with NaNCO, Na₂CO₃, H₂O, NO and CO₂ as the final products. The non-isothermal kinetic and thermodynamic parameters for the first exothermic process of the Na[CL-14·2H₂O] have been studied, with the apparent activation energy, pre-exponential factor, entropy of activation, enthalpy of activation and free energy of activation of 280.7 kJ mol⁻¹, 57.8, 282.7 J mol⁻¹ K⁻¹, 276.2 kJ mol⁻¹ and 154.8 kJ mol⁻¹, respectively. The impact sensitivity and friction sensitivity of Na[CL-14·2H₂O] was tested according to general methods, with the values of 27 J and 360 N, respectively. Na[CL-14·2H₂O] has been investigated as an energetic catalyst in ammonium nitrate (AN) by means of TG-DTG, TG-MS, DSC and extent of conversion (α)–T kinetic curve analyses. And the thermal kinetic constants for the catalytic and noncatalytic decomposition of AN samples were calculated using Kissinger's and Ozawa–Doyle's equations. The possible catalytic mechanism was also discussed and proposed. The results show that Na[CL-14·2H₂O] decreases the peak temperature and activation energy value of the complete decomposition process for AN by 41.3 °C and 10.9 kJ mol⁻¹, respectively. Furthermore, the thermal decomposition of AN in the presence of Na[CL-14·2H₂O] starts at significantly lower temperature (about 30 °C) than that of pure AN. Apparently, Na[CL-14·2H₂O] could be incorporated as a potential energetic catalyst in AN-based propellants.