Kinetic analysis of overlapping multistep thermal decomposition comprising exothermic and endothermic processes: thermolysis of ammonium dinitramide

Abstract

This study focused on kinetic modeling of a specific type of multistep heterogeneous reaction comprising exothermic and endothermic reaction steps, as exemplified by the practical kinetic analysis of the experimental kinetic curves for the thermal decomposition of molten ammonium dinitramide (ADN). It is known that the thermal decomposition of ADN occurs as a consecutive two step mass-loss process comprising the decomposition of ADN and subsequent evaporation/decomposition of in situ generated ammonium nitrate. These reaction steps provide exothermic and endothermic contributions, respectively, to the overall thermal effect. The overall reaction process was deconvoluted into two reaction steps using simultaneously recorded thermogravimetry and differential scanning calorimetry (TG-DSC) curves by considering the different physical meanings of the kinetic data derived from TG and DSC by P value analysis. The kinetic data thus separated into exothermic and endothermic reaction steps were kinetically characterized using kinetic computation methods including isoconversional method, combined kinetic analysis, and master plot method. The overall kinetic behavior was reproduced as the sum of the kinetic equations for each reaction step considering the contributions to the rate data derived from TG and DSC. During reproduction of the kinetic behavior, the kinetic parameters and contributions of each reaction step were optimized using kinetic deconvolution analysis. As a result, the thermal decomposition of ADN was successfully modeled as partially overlapping exothermic and endothermic reaction steps. The logic of the kinetic modeling was critically examined, and the practical usefulness of phenomenological modeling for the thermal decomposition of ADN was illustrated to demonstrate the validity of the methodology and its applicability to similar complex reaction processes.

Studies on multistep thermal decomposition behavior of polytriazole polyethylene oxide‐tetrahydrofuran elastomer

“…According to previous studies, 27,28 there is a linear relationship between the value of E a and ln A for a nonisothermal experiment, which lies in the regression line of their compensation. A set of E a and ln A can be obtained for each model.…”

Ignoring heat inertia impairs accuracy of determination of activation energy in thermal analysis

“…Therefore, the published values of activation energy may not be authoritative, as they may be off by as much as several tens of percent . It is worthy of note that the relative (per gram) value of thermal inertia is the same for large and small samples.…”

“…Determination and publication of values of activation energy of reactions is common and has become the subject of many documents dealing with thermal physics of materials . It has appeared in a variety of journals to name but a few latest ones . Nonisothermal measurement under a constant heating rate using various experimental methods has led to development of a range of methods for utilization of kinetic data.…”

“…[1][2][3] It has appeared in a variety of journals to name but a few latest ones. [4][5][6][7][8][9] Nonisothermal measurement under a constant heating rate using various experimental methods has led to development of a range of methods for utilization of kinetic data. That is done on the basis of the most common thermoanalytical techniques, such as DTA (differential thermal analysis) and TG (thermogravimetry), [10][11][12][13] which are still popular today.…”

“…The best example is the domain of solid-state kinetics [1][2][3][4][5][6][7][8][14][15][16][17] where Piloyan et al 12 published a simple method of calculation of activation energy from DTA measurements almost half a century ago. It is based on calculating the logarithm of the temperature difference between the sample and the reference, kept in the same environment.…”