Decoupling Of Thermal Effects Of Decomposition Reaction With Coupling Of Endothermic Phase Change And Exothermic Decomposition

Exothermic decomposition reaction appears immediately after melting endothermic peak in a variety of chemicals, the phenomenon here is called as coupling phenomenon of heat absorption and generation. The chemical with this characteristic, which also has a relatively low decomposition temperature, is very dangerous, since it can lead to fire and explosion accident easily due to thermal effects during production, usage, storage and transportation. So it is necessary to obtain accurate thermal behaviors and safety parameters such as adiabatic induction period of coupling materials. The coupling phenomenon made the decomposition curve deformed. If the thermal decomposition kinetics are calculated without decoupling, the prediction will be wrong, which is bad for accident prevention and risk control. Therefore, we should decouple first, then study the exothermic decomposition and endothermic melting processes separately to obtain their kinetic and thermodynamic parameters, and make correct prediction finally.Firstly, three kinds of coupling materials azobisisobutyronitrile (AIBN), RDX (RDX) and salicylaldehyde hydroxamic acid (SHA) were tested by differential scanning calorimetry (DSC) and adiabatic accelerating calorimetry (ARC) to analyze their thermal behaviors under dynamic, isothermal and adiabatic conditions. Kissinger method, isothermal method and adiabatic induction period method were employed to calculate the activation energies. The results showed that:under dynamic condition, AIBN and RDX both showed coupling phenomena, but SHA had a special, no endothermic peak appeared at a heating rate of less than 4℃/min. The overlapping existed at heating rates higher than 4℃/min. Under isothermal condition, the three coupling materials all showed bell-shaped curves and S-type conversion curves, indicating that their thermal decomposition had autocatalytic characteristics. Under adiabatic condition, self-heating rates of the three coupling materials were very low at the initial stage of reactions, and the corresponding pressure grew slowly. It was probably due to the interference of endothermic melting to the exothermic decomposition.RDX and SHA are not suitable for MATLAB method due to their complex decomposition mechanism, so only the AKTS decoupling method was used for RDX and SHA. Meanwhile, the decoupling correctness of AIBN was verified by thermodynamics. Comparing the decoupling results of solvent and mathematical methods, it was found that the decomposition activation energies had the same trend after decoupling by solvent and MATLAB methods, the results showed that the decoupling results were credible.