A. Jeya Rajendran, T. Lekshmana Thanulingam, A. Meisudar and U. Manikandan
Abstract: Dynamic, non-isothermal analysis of the pyrotechnic mixture of a sound-producing fire cracker, KNO3/Al/S/H3BO3,was carried out under N2 atmosphere by using a simultaneous thermogravimetric and differential thermal analyser. Intermediates and the residue formed in each stage of thermal decomposition of the pyrotechnic mixture were characterised by X-ray diffraction analysis and the most probable reaction pathway was proposed. Thermogravimetric (TG) and differential thermogravimetric data (DTA) were used for the interpretation of the mechanisms and kinetics of decomposition by means of a model-fitting method, the Coats–Redfern equation, and model-free methods, the Arrhenius and Kissinger methods. The values of activation energy (E) were calculated as 11–16 kJ mol−1, 24–53 kJ mol−1 and 15–56 kJ mol−1 for stages I, II and III respectively by the model-fitting method, with the Avrami–Erofe’ev model (A2), two-dimensional model, nucleation and growth mechanism. The pre-exponential factor (ln A) of each stage of thermal decomposition at various linear heating rates was calculated and the probable decomposition mechanism was proposed for the first decomposition step as the expulsion of sulphur, and the second and third decomposition steps as the conversion of aluminium to alumina are obtained. Similarly, the reaction was also found to be first order.
Keywords: pyrotechnics, fireworks, thermal analysis, activation energy, Coats–Redfern equation.
Ref: JPyro, Issue 31, 2012, pp34-48 (J31_34)
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