Kinetic Analysis of Thermal Decomposition of Unirradiated and γ-Irradiated Tris(ACEtylacetonato)-Ruthenium(III) [Ru(acac)3]

Abstract

The thermal decompositions of unirradiated and γ-irradiated Ru(acac)3 were studied in air. The results show that decomposition proceeds in one major step in the temperature range of 150-250°C with the formation of RuO2 as a final solid residue for unirradiated Ru(acac)3. For γ-irradiated Ru(acac)3, with a total γ-ray dose of 102kGy, the decomposition goes eventually to completion with almost 100% decomposition and proceeds in one major step which contains four overlapping decomposition stages in the temperature range of 200 −320°C. The kinetics were followed isothermally and non-isothermally using both model-fitting and model-free approaches. IR spectroscopy and X-ray powder diffraction techniques were employed to follow the chemical composition of the solid residues obtained at different temperatures. In a model-fitting approach, the kinetic triplet, i.e. the apparent activation energy Ea, the pre-exponential factor, ln A, and the reaction model f (α), were analyzed and calculated using straight line plots, and reduced time plots by isothermal measurements. For non-isothermal measurements we have applied the Coats and Redfern, and Kennedy and Clark methods. In the model-free approach, the non-thermal data for both unirradiated and γ-irradiated Ru(acac)3 samples were analyzed using the Flynn-Wall-Ozawa (FWO), Tang (T), and Vyazovkin (Vyz) isoconversional methods. The results of application of model-free and model-fitting approaches to the thermal decompositions of both unirradiated and γ-irradiated Ru(acac)3 were compared and evaluated to deduce the most probable kinetic triplet that describes correctly the thermal behavior of Ru(acac)3. Discussion of the results is preceded by a short review of the models relevant to this study.