X-ray powder diffraction is one of the basic methods for characterising crystalline materials. Using this method, I analysed 11 samples of tempera and 10 samples of water-based paints from two different manufacturers. Qualitative analysis was carried out using Crystallographica Search-Match program (CSM) and Powder Diffraction File (PDF-2). By comparing the diffractogram of standard and sample, I determined the crystalline phases in each sample. This was followed by a quantitative analysis in TOPAS program to determine the mass fractions of previously identified phases.
I have found out that calcite, rutile and dolomite are the most commonly used fillers in Aero and Fila tempera and water-based paints. The most represented compound in all analysed samples is calcite. There is more than 59 % calcite in each paint. Dolomite and rutile represent lower mass fractions. Tempera and water-based paints also contain pigments. These are organic or inorganic compounds that are used for colouring. The mass fractions of organic pigments are very low – mostly less than 1 %. Inorganic pigments are found in higher quantities, e. g. tens of percent. These were mostly various iron oxides or sodalite tectosilicates. On the diffractogram of samples containing different iron minerals as pigments, we observed a linear increase in the background with increasing diffraction angle, as a result of appearance of fluorescence. In some samples, I was not able to identify all diffractions peaks. I assume that this is because there was no appropriate standard in the database. Although the fact that there was no declaration on packaging of tempera and water-based paints about their composition which would enable comparison, I think the results of my analyses are reasonable based on the existing literature.
|
