Evaluation of Kinetic Parameters and Thermal Stability of Melt-Quenched Bi_xSe_100-xAlloys (x ≤7.5 at%) by Non-Isothermal Thermogravimetric Analysis

Abstract

Non-isothermal thermogravimetry (TG) measurements on melt-quenched Bi x Se 100-x specimens (x=0, 2.5, 7.5 at%) were made at a heating rate β=10°C/min in the range T=35°C~950°C. The as-measured TG curves confirm that Bi x Se 100-x samples were thermally stable with minor loss at T≲400°C and mass loss starts to decrease up to 600°C, beyond which trivial mass loss was observed. These TG curves were used to estimate molar (Se/Bi)-ratios of Bi x Se 100-x samples, which were not in accordance with initial composition. Shaping features of conversion curves α(T)-T of Bi x Se 100-x samples combined with a reliable flow chart were used to reduce kinetic mechanisms that would have caused their thermal mass loss to few nth-order reaction models of the form f [α(T)][1-α(T)]n (n=1/2, 2/3, and 1). The constructed α(T)-T and (dα(T)/dT)-T curves were analyzed using Coats-Redfern (CR) and Achar-Brindley-Sharp (ABS) kinetic formulas on basis of these model functions, but the linearity of attained plots were good in a limited α(T)-region. The applicability of CR and ABS methods, with model function of kinetic reaction mechanism R0 (n=0), was notable as they gave best linear fits over much broader α(T)-range.