Investigation of the reaction mechanism and kinetics of production of anhydrous sodium metaborate (NaBO2) by a solid-state reaction

In this study, the solid-state reaction mechanism and kinetics were investigated for production of anhydrous sodium metaborate (NaBO2), an industrially and technologically important boron compound. To assess the kinetics of solid-state production of NaBO2, the chemical reaction between borax (Na2B4O7) and sodium hydroxide (NaOH) was investigated by use of the thermal analysis techniques thermogravimetry (TG) and differential thermal analysis (DTA). DTA curves obtained under non-isothermal conditions at different heating rates (5, 10 and 20 A degrees C/min), revealed five endothermic peaks corresponding to five solid-state reactions occurring at 70, 130, 295, 463, and 595 A degrees C. The stages of the solid-state reaction used for production NaBO2 were also analyzed by XRD, which showed that at 70 and 130 A degrees C, Na2B4O7 and NaOH particles contacted between the grains, and diffusion was initiated at the interface. However, there was not yet any observable formation of NaBO2. Formation of NaBO2 was initiated and sustained from 295 to 463 A degrees C, and then completed at 595 A degrees C; the product was anhydrous NaBO2. Activation energies (E (a)) of the solid-state reactions were calculated from the weight loss based on the Arrhenius model; it was found that in the initial stages of the solid-state reaction E (a) values were lower than in the last three steps.