A thermogravimetric study on the catalytic decomposition of ammonium perchlorate from activation energy normalised through kinetic compensation

摘要

Though the reaction temperatures of both low (LTD) and high temperatuare (HTD) decompositions of ammonium perchlorate (AP) are lowered by CuO catalyst, the activation energy (E) for the reactions, computed from TG data shows an increase for LTD and a decrease for HTD. The values of both E and A (pre-exponential factor) for LTD and HTD are altered in the presence of the catalyst, thereby making it not feasible to have a direct correlation of activation energy with the effect of the catalyst in enhancing the reaction rate. However, when E values are normalised for the variation in the values of A, the activation energy is lower for both the stages of decomposition of AP in the presence the catalyst. In order to establish the normalisaltion procedure, the first two stages of the thermal decomposition of calcium oxalate monohydrate are chosen as model reactions. The values of E and A from both isothermal and non-isothermal experiments carried out under different experimental conditions of heating rate and sample mass of CaC_2O_4.H_2O show interdependence through kinetic compensation (KC) effect. The KC effect is also shown by the kinetic parameters from a single non-isothermla experiments, when they are calculated for different values of n. In all these cases, the values of E derived from the KC plots for a fixed value of A are remarkably constant and independent of the variations in experimental conditions for both the stages of decomposition of CaC_2O_4.H_2O. The pragmatic application of the newly proposed KC correction method of deriving consistent values of E, normalised for the variations in A values, has been demonstrated in the catalytic thermal decomposition of AP.