Effect of morphology on the isothermal decomposition kinetics of nitroguanidine

The thermal stability of nitroguanidine (NQ) with different morphologies was studied using a self-developed isothermal decomposition gas manometric device at both high and low temperatures. At 443.15-463.15 K, the total decomposition of needle-like NQ (N-NQ) and hexagonal block-shaped NQ (H-NQ) proceeded in two stages: a fast decomposition stage after heating, and a much slower decomposition stage later. It was indicated that all the models for N-NQ and H-NQ at the first stage followed the Avrami-Erofeev equation but with different values of n, while all the models at the second stage conformed to Parabola order. The decomposition rate of H-NQ was faster than N-NQ after heating, showing a better stability of N-NQ. At 373.15-413.15 K, the initial decomposition kinetics were calculated. The activation energy calculated by mode-fitting method was 146.33 kJ/mol and 182.71 kJ/mol for N-NQ and H-NQ, respectively, which was consistent with the results obtained through model-free method. The average activation free energy (Delta G(not equal)), enthalpy (Delta H-not equal) and entropy (Delta S-not equal) for N-NQ were 148.30 kJ/mol, 142.03 kJ/mol, and -15.81 J/(mol.K), respectively, while they were 139.61 kJ/mol, 184.42 kJ/mol, and 107.14 J/(mol.K) for H-NQ. The storage life of N-NQ and H-NQ at 298.15 K were extrapolated to 21.58 and 29.44 years, respectively.