Isoconversional kinetic analysis of thermal decomposition of 1-butyl-3-methylimidazolium hexafluorophosphate under inert nitrogen and oxidative air atmospheres

Non-isothermal decomposition of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF₆) in inert nitrogen and air atmospheres was investigated by means of multiple heating-rate thermogravimetric analysis. The results obtained under the heating rates of 5–20 K min⁻¹ show that the [bmim]PF₆ pyrolysis mainly occurred from 600 to 800 K and its oxidative thermal decomposition mainly from 550 to 750 K. Kinetic thermal decomposition processes have been analyzed with differential Friedman method and three integral Flynn–Wall–Ozawa, Coats–Redfern and Vyazovkin–Dollimore methods. Through these model-free isoconversional methods, the activation energy and pre-exponential factor over the entire conversion range have been successfully estimated. By using the Coats–Redfern method, the diffusion-controlled D5 model is found to be the best reaction mechanism function for describing two-stage pyrolysis and one-stage oxidative thermal decomposition and leads to very satisfactory calculation performances. The short-term stability and long-term thermal stability are discussed as well.