Effect of Heat Treatment on the Structural Characteristics and Dehydroxylation Kinetics of the Tunellite

Abstract

The effect of heat treatment on the structural properties of the tunellite has been investigated in the present study. The tunellite samples were calcined in a furnace for 5 h at three different temperatures, 400, 710, and 800°C. These temperatures were determined with respect to the DTA/TG curve. The calcined tunellite samples were characterized by X-Ray Diffraction (XRD). It was found that with increasing calcination temperatures, a veatchite phase was observed. The morphology of the calcined tunellite samples was characterized by Scanning Electron Microscope (SEM). According to the results of the analyses, it was observed that the calcination temperature influenced the shape of the tunellite. The Brauner-Emmett-Teller (BET) analysis revealed that the specific surface area of the samples decreased with an increasing calcination temperature due to the shrinkage of the agglomerates. In addition, the dehydroxylation kinetics of the tunellite was studied by the thermogravimetric technique. The non-isothermal kinetic data were analyzed and the kinetic parameters for the dehydroxylation stage were computed by 21 solid-state mechanisms. In addition, the kinetic compensation effect (KCE) was also used in order to correlate the pre-exponential factor with the activation energy.