Study on the thermal behavior, kinetics, thermodynamics and chemical reactions of double-base propellant under multiple heating rates

The present study investigates the thermal behavior, devolatilization index, heat variations, kinetic and thermodynamic characteristic parameters, volatile components and possible chemical reactions of double-base propellant pyrolysis. Thermogravimetric analysis (TGA), in-situ Fourier transform infrared spectroscopy (FTIR) and online TGA-FTIR mass spectrometry are employed. The findings indicate that alterations in temperature and heating rate significantly affect the pyrolysis process, exhibiting a triphasic behavior, where the initial stage may be considered as a single-step reaction, primarily involving the pyrolysis of nitroglycerin. The pyrolysis of nitrocellulose predominantly occurs in the third stage. With the increase of heating rate, the reaction rate of the first stage decreases, whereas that of the second stage increases, resulting in a temperature hysteresis phenomenon. The maximum instantaneous heat flow and the total heat flow both increases, while the full width at half maximum decreases, thereby enhancing the combustion performance and reaction intensity of double-base propellant, while reducing the thermal stability. 450–550 K is the main exothermic temperature range. The average activation energies for the first and second stages of double-base propellant pyrolysis, determined using three effective kinetic methods, are 107.14 kJ/mol and 379.14 kJ/mol. The model g(α) = (1− (1− α)^(1/3))² can accurately characterize the first pyrolysis stage from a kinetic perspective. The average values of ∆H, ∆G and ∆S are 231.83 kJ mol⁻¹, 231.83 kJ mol⁻¹ and − 35.06 J K⁻¹. The pyrolysis of double-base propellant is an unstable and non-spontaneous endothermic reaction with decreasing stability as the reaction progresses. The major components of volatiles produced and the potential chemical reactions involved are identified.