Thermal decomposition kinetics and thermal safety of HNF

To understand the thermal decomposition kinetics and thermal safety of hydrazinium nitroformate (HNF), thermal decomposition characteristics of HNF were studied by vacuum stability test(VST), differential scanning calorimetry (DSC) and thermogravimetry (TG). According to peak temperatures of DSC curves and conversion degrees(α) of TG curves at 5, 10, 15℃·min-1 and 20℃·min-1, the apparent activation energy(Ek and Ea) and pre-exponential factor (Ak)for thermal decomposition reaction of HNF were calculated by Kissinger's method and Ozawa's method, respectively. The kinetic equations describing the exothermic decomposition process of HNF were presented. Thermodynamic parameters (free energy of activation ΔG , enthalpy of activation ΔH and entropy of activation ΔS ) for thermal decomposition reaction of HNF and thermal safety parameters (critical temperature of thermal explosion Tbpo and self-accelerating decomposition temperature TSADT) for HNF were calculated. Results show that the volume of gas evolved for HNF is 0.41 mL·g-1, which does not exceed the standard of 2 mL·g-1, revealing that HNF has good thermal stability. The exothermic decomposition process of HNF after melting can be divided into two stages. Ek=257.10 kJ·mol-1, Ak=1.74×1033 s -1, ΔG =103.37 kJ·mol-1, ΔH =253.82 kJ·mol-1, ΔS =380.78 J·K-1·mol-1, Tbpo=400.28 K and TSADT=395.10 K. The kinetic equation of exothermic decomposition reaction may be described as: for the first stage in the α range of 0.20~0.65, dα/dt=kf(α)=Ae-E/(RT)f(α)=5.14×1021×(1-α)[-ln(1-α)]1/2exp(- (1.81×104)/T), and for the second stage in the α range of 0.65~0.80, dα/dt=kf(α)=Ae-E/(RT)f(α)=3.30×1014×(1-α)[-ln(1-α)]-1exp(- (1.33×104)/T). ©, 2014, Institute of Chemical Materials, China Academy of Engineering Physics. All right reserved.