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Open AccessArticle

Investigations of Feldspar-Quartz Raw Materials After Firing: Effect of Various Na2O/K2O Ratio and Synthetic Pigments Addition

1
Mineral and Energy Economy Research Institute of the Polish Academy of Sciences, J. Wybickiego 7A, 31-261 Kraków, Poland
2
Faculty of Materials Science and Ceramics, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Kraków, Poland
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(7), 646; https://doi.org/10.3390/min10070646
Received: 10 July 2020 / Revised: 20 July 2020 / Accepted: 20 July 2020 / Published: 21 July 2020
Different techniques (chemical analysis, X-ray diffraction, Mössbauer spectroscopy, UV-Vis-NIR spectrophotometry and chromaticity measurements) were used to study the color variation of feldspathic raw materials after firing at 1200 °C. Two varieties of feldspar-quartz grits (with Na2O or K2O prevalence) doped with synthetic pigments (hematite and rutile) were heat-treated in an oxidizing atmosphere. The results obtained indicate that the color of the ceramic body after firing may not only depend on the presence and analytical content of coloring elements (such as iron and titanium), but on their valence state and the chemical characteristics of the melt itself. The prevalence of larger alkali K+ ions over Na+ ions may cause the reduction of the coordination number of iron. This has a significant effect on the length of the Fe–O bond, which in turn influences the capacity for light absorption of a specific wavelength. The results of spectrophotometric measurements showed pronounced disparity between the raw materials and samples doped with coloring oxides. The introduction of synthetic pigments caused clear changes in the spectral dependence of the total absorbance. The absorbance increased in the whole measuring range, in particular in the visible part of the spectrum. Furthermore, a red-shift of the absorption bands towards longer wavelengths attributed to oxygen-metal charge transfer (OMCT) interactions between Fe3+ and O2− ions as well as to d-d transitions within Fe3+ ions was observed. View Full-Text
Keywords: potassium- and sodium-rich feldspar-quartz; coloring oxides; Mössbauer spectroscopy; UV-Vis-NIR spectrophotometry; color after firing potassium- and sodium-rich feldspar-quartz; coloring oxides; Mössbauer spectroscopy; UV-Vis-NIR spectrophotometry; color after firing
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MDPI and ACS Style

Lewicka, E.; Trenczek-Zajac, A. Investigations of Feldspar-Quartz Raw Materials After Firing: Effect of Various Na2O/K2O Ratio and Synthetic Pigments Addition. Minerals 2020, 10, 646. https://doi.org/10.3390/min10070646

AMA Style

Lewicka E, Trenczek-Zajac A. Investigations of Feldspar-Quartz Raw Materials After Firing: Effect of Various Na2O/K2O Ratio and Synthetic Pigments Addition. Minerals. 2020; 10(7):646. https://doi.org/10.3390/min10070646

Chicago/Turabian Style

Lewicka, Ewa; Trenczek-Zajac, Anita. 2020. "Investigations of Feldspar-Quartz Raw Materials After Firing: Effect of Various Na2O/K2O Ratio and Synthetic Pigments Addition" Minerals 10, no. 7: 646. https://doi.org/10.3390/min10070646

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