Thermal Kinetics and Thermodynamics of the Dehydration Reaction of Inyoite (Ca2B6O6(OH)10 ⋅ 8H2O)

Abstract The inyoite mineral was identified with X-ray diffraction and the bonds of triangular BO3 and tetrahedral BO4 ions were characterized using Fourier-transform Infrared Spectroscopy. Two steps of decomposition (dehydration and dehydroxylation) were interpreted with kinetic and thermodynamic modelling using the Coats–Redfern non-isothermal kinetic method. Different reaction models (chemical reaction order, diffusion, and phase interfacial reaction) were applied. The thermodynamic (ΔH, ΔG, and ΔS) and kinetic (E, ko, n, mechanism, and model) parameters were determined. Thermal decomposition of inyoite occurred in the range of 32–660°C through a two-step reaction. Higher correlation factors were obtained at the chemical reaction order of 1.7 for the first step and 1.3 for the second step. The activation energy averages were 71.61 and 30.71 kJ/mol for the first and second steps of water removal, respectively. The positive values of ΔH and ΔG indicated an endothermic and non-spontaneous reaction, whereas the negative value of ΔS signified the reaction was slow and decreased the system disorder.