Characterization and thermal dehydration kinetics of zinc borates synthesized from zinc sulfate and zinc chloride

Abstract

Zinc borate hydrate (Zn3B6O12 center dot 3.5H(2)O) was synthesized from zinc sulfate heptahydrate (ZnSO4 center dot 7H(2)O), anhydrous zinc chloride (ZnCl2), and boric acid (H3BO3). The product was characterized by X-ray diffraction, Fourier-transform infrared and Raman spectroscopy, and thermal gravimetry and differential thermal gravimetry. The effects of reaction time and temperature on product morphology were studied by use of scanning electron microscopy. Results from thermal analysis showed that dehydration occurred in two steps. Thermal dehydration kinetics were investigated by use of the Coats-Redfern and Horowitz-Metzger non-isothermal kinetic methods. In the Coats-Redfern method, activation energies were found to be 225.40 and 570.63 kJ/mol for the first and second steps, respectively. In the Horowitz-Metzger method, activation energies were found to be 254.33 kJ/mol for the first step and 518.22 kJ/mol for the second step.