Abstract: Titanium dioxide is an anorganic polymorfic compound that exists in different crystallographic structures. Three most common crystallographic structures are anatase, rutile and brookite. The most common use of TiO2 is in the form of a white pigment, which contains rutile and is used to deliver opacity and whiteness in paints, packaging and other materials. For production of white pigment, sulfate or chloride processes are known. In the sulfate process during calcination at high temperatures, a phase transformation from anatase TiO2 to rutile occurs. Given the exact temperature and time of a complete phase transformation, heating time of titania in oven can be shortened. This way, a lot of energy and production costs can be saved.
In this master's thesis, three samples of white pigment were analysed. The samples were taken from the production of TiO2 by sulfate process, before the calcination. Samples were analysed by thermogravimetric and differential thermal analysis, coupled with mass spectrometry. Afterwards XRD and HTXRD analyses were done. First, each sample was heated to a certain temperature and termostated, afterwards XRD measurements of cooled samples were made. At the same temperatures HTXRD measurements were also conducted. While thermostating at a certain temperature, every 10 minutes a diffractogram was recorded. This way the transformation from anatase to rutile was observed at different temperatures. The Rietveld method was used to obtain the phase content data in order to calculate the conversion, needed for the kinetic analysis of a phase transformation. Using a mathematical model, kinetic parameters were found. The Avrami method and the linearisation method, which is a linear form of the Avrami method equation, were used for calculations. Kinetic parameters were calculated by finding the function that best fits the experimental data by one method or the other. Using either of the two methods, comparable values of kinetic parameters were obtained, where values of calculated activation energies were in the same range. Complexity of the process makes the assumption of the actual activation energy imprecise, meaning that the term of the activation energy is in fact referred to the apparent activation energy.
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