Nonisothermal decomposition and safety parameters of HNIW/TNT cocrystal

Abstract

To explore the thermal decomposition behavior and evaluate the thermal safety of the cocrystal 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW)/2,4,6-trinitrotoluene (TNT), its thermal and kinetic behaviors were studied by differential scanning calorimetry (DSC) technique. With the help of onset temperature (T_e) and maximum peak temperature (T_p) from the non-isothermal DSC curves of HNIW/TNT cocrystal at different heating rates (β), the following were calculated: the value of specific heat capacity (C_p) and the standard molar enthalpy of formation , the apparent activation energy (E_K and E_O) and pre-exponential constant (A_K) of thermal decomposition reaction obtained by Kissinger's method and Ozawa's method, density (ρ) and thermal conductivity (λ), the decomposition heat (Q_d, as half-explosion heat), Zhang–Hu–Xie–Li's formula, Smith's equation, Friedman's formula, Bruckman–Guillet's formula, Frank-Kamenetskii's formula and Wang–Du's formulas, the values (T_e0 and T_p0) of T_e and T_p corresponding to β → 0, thermal explosion temperature (T_be and T_bp), adiabatic time-to-explosion (t_tiad), 50% drop height (H₅₀) for impact sensitivity, critical temperature of hot-spot initiation (T_cr), thermal sensitivity probability density function [S(T)] vs. temperature (T) relation curves with radius of 1 m and ambient temperature of 300 K, the peak temperature corresponding to the maximum value of S(T) vs. T relation curve (T_S(T)max), safety degree (SD) and critical ambient temperature (T_acr) of thermal explosion. Results show that the kinetic equation describing the exothermic decomposition reaction of HNIW/TNT cocrystal is The following thermal safety parameters for the HNIW/TNT cocrystal are obtained: T_e0 = 464.45 K; T_p0 = 477.55 K; T_be = 472.82 K; T_bp = 485.89 K; t_tiad = 4.40 s, 4.42 s, and 4.43 s for n = 0, 1, and 2, respectively; T_cr = 531.90 K; H₅₀ = 19.46 cm; and the values of T_acr, T_S(T)max, SD and P_TE are 469.69 K, 470.58 K, 78.57% and 21.43% for sphere; 465.70 K, 470.58 K, 78.17% and 21.83% for infinite cylinder; and 459.39 K, 464.26 K, 77.54% and 22.46% for infinite flat.