Thermal dehydration kinetics of SrB6O10·5H2O with different morphologies

Abstract

The globular-like, sheet-like, coral-like SrB6O10·5H2O was prepared by hydrothermal method, and characterized by X-ray powder diffractometer(XRD), thermogravimetry(TG), differential thermal analysis(DTA), scanning electron microscopy(SEM). The activation energy of the thermal dehydration of SrB6O10·5H2O with different morphologies was calculated by Ozawa-Flynn-Wall (OFW) method. The most probable mechanism function of the dehydration reaction was determined by master-plots method, and the average pre-exponential factor of the thermal dehydration of the sample was calculated. The results show that the thermal dehydration of SrB6O10·5H2O is divided into two steps. The activation energy of thermal dehydration reaction is affected by the morphology and size. The activation energy of SrB6O10·5H2O in the first step of thermal dehydration is close, while there is a significant difference in the activation energy value of SrB6O10·5H2O in the second step of thermal dehydration. The order of activation energy, as well as the order of the average pre-exponential factor, is consistent with the size order of the constituent units of the sample microstructure. The first-step thermal dehydration mechanism functions of SrB6O10·5H2O (globular-like, sheet-like, coral-like) are all [-ln(1-α)]3, which belongs to random nucleation and growth, and the second-step thermal dehydration mechanism functions are α2(one-dimensional diffusion), α+(1-α)·ln(1-α) (two-dimensional diffusion), and [-ln(1-α)]3 (random nucleation and growth), the reasons for the difference of their two-step mechanistic functions are analyzed.