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

The thermal decomposition of sodium bicarbonate (NaHCO3) was studied u nder different atmospheres (dry nitrogen, air, and carbon dioxide), wi th various heating rates in order to characterize the substance. Vario us non-isothermal methods of kinetic analysis were employed in estimat ing the Arrhenius kinetic parameters, the activation energy and the fr equency factor. All show that the most probable reaction mechanism und er dry nitrogen and air is the first-order deceleratory mechanism, whe reas 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 dif ferent samples of sodium bicarbonate. The reaction parameters, the ext ent of the reaction (alpha) and the reaction temperature were used in comparing the reactivities of various samples of sodium bicarbonate di ffering in particle size and surface area produced by grinding the sub stance in a ball mill. A method was utilized, termed here the alpha(sa mple)-alpha(reference) (alpha(S)-alpha(T)) method, by which the solid state reactivity of these samples could be compared with that of a ref erence. The terms alpha(S), alpha(T) refer to the extent of reaction ( here the extent of decomposition) at the same temperature for the samp le (s) and reference (r).