METHOD OF ASSESSING SOLID-STATE REACTIVITY ILLUSTRATED BY THERMAL-DECOMPOSITION EXPERIMENTS ON SODIUM-BICARBONATE

The thermal decomposition of sodium bicarbonate (NaHCO3) was studied under different atmospheres (dry nitrogen, air, and carbon dioxide), with various heating rates in order to characterize the substance. Various non-isothermal methods of kinetic analysis were employed in estimating the Arrhenius kinetic parameters, the activation energy and the frequency factor. All show that the most probable reaction mechanism under dry nitrogen and air is the first-order deceleratory mechanism, whereas under carbon dioxide it is the Avrami-Erofeev equation, with n = 1.5. Thermogravimetric and derivative thermogravimetric analysis (TGA and DTG) were employed for comparing the solid state reactivity of different samples of sodium bicarbonate. The reaction parameters, the extent of the reaction (alpha) and the reaction temperature were used in comparing the reactivities of various samples of sodium bicarbonate differing in particle size and surface area produced by grinding the substance in a ball mill. A method was utilized, termed here the alpha(sample)-alpha(reference) (alpha(S)-alpha(T)) method, by which the solid state reactivity of these samples could be compared with that of a reference. The terms alpha(S), alpha(T) refer to the extent of reaction (here the extent of decomposition) at the same temperature for the sample (s) and reference (r).