Papers by Author: Thomas Kronberg

Abstract: The influence of wollastonite and dolomite on melting behaviour and crystallization was studied for 25 raw glazes. The melting behaviour was observed by hot-stage microscopy. The glazes were also fired industrially both in a fast-fired gas kiln for floor tiles (50 min) and in a traditional gas kiln for sanitaryware (25 hours). The surface composition and structure of the glazes were studied by SEM/EDXA. The crystalline phases in the glazes were identified by XRD. Main crystalline phases found in the glazes were wollastonite and diopside. Fusibility and surface structure on the raw glazes containing wollastonite and dolomite as raw materials depended both on the total content and the ratio of CaO and MgO in the glaze. Low content of alkaline earths gave incomplete fusion, while high content gave extensive crystallization. The results can be applied to tailor raw glaze compositions for a desired surface structure to be fired at a certain fusion temperature.

Abstract: The goal of this work was to establish the compatibility of mat glazes with functional films known to render the surfaces with self-cleaning or easy-to-clean properties. Glazes with wollastonite, pseudowollastonite, diopside and zircon as the main crystalline phases in the surfaces were coated with fluoropolymer as well as ceramic, sol-gel derived titania and zirconia films. The glazes were soaked in typical detergent solutions used in everyday life up to four days. The surface roughness was measured with confocal optical microscope and the surface was imaged and analyzed with SEM/EDXA. When applied on wollastonite and pseudowollastonite containing glazes the functional films readily reacted in water solutions by pitting of the surface in the vicinity of the crystals. The ceramic titania and zirconia films showed better chemical resistance on wollastonite –free glazes, while the fluoropolymer film corroded in the most alkaline environments. The results indicate that functional films could be used also on rough surfaces without markedly affecting the surface topography. However, the films should be applied only on glazes with an excellent chemical resistance.