Evaluation of isothermal kinetics of the thermal decomposition of guanidine nitrate in constant volume

Abstract

ABSTRACTIn this paper, thermal decomposition characteristics of guanidine nitrate (GN) are studied by both dynamic and isothermal differential scanning calorimetry (DSC) tests in constant volume. The dynamic curve (1°C/min) shows that at least two overlapped peaks exist in the decomposition curve of GN, whereas the decomposition peaks of each isothermal experiment (305–320°C) can be clearly taken as a combination of three decomposition peaks. Besides, an isothermal kinetic model is studied. AKTS is used to decouple the isothermal decomposition peaks, to obtain three separate peaks, i.e., one decelerating model peak and two sigmoidal model peaks. An Nth order kinetic model is established for the first decomposition stage, and an autocatalytic model is established to describe the left two stages. The kinetic parameters of each stage are calculated by nonlinear fitting. The equation describing the reaction rate for the Nth order kinetic model as below, dα/dt = exp(8.92)exp(−67730/RT)(1−α)1.020, the second and the third steps can be described by the equations of dα/dt = exp(26.15)exp(−165570/RT)(1-α)0.508+ exp(23.87)exp(−159360/RT)(1-α)0.508α0.150 and dα/dt = exp(24.03) exp(−166070/RT)(1-α)0.082+exp(23.28)exp(−160000/RT)(1−α)0.082α0.210, respectively. The results calculated by these models fit well the experimental data, proving that the kinetic parameters are reliable and accurate.