Thomas Kronberg

Durability of Mat Glazes in Hydrochloric Acid Solution

The influence of composition on durability of fast-fired mat raw glazes in hydrochloric acid was studied with several different methods. The appearance of the corroded glazes was classified according to a standardised visual method. The surface composition of the glaze was studied by SEM/EDXA. The crystalline phases in the glaze were identified by XRD. Changes in surface topography on micro-range were observed by AFM, while macro-range related changed were examined by a non-contact optical profiler. The concentration of dissolved ions in the acid solution after the corrosion test was analysed by ICPS. The results indicate that besides chemical composition also phase composition and surface morphology should be taken into account in corrosion studies of mat glazes. Corrosion of both amorphous and crystalline phases could be detected. The proportion of unreacted raw material in the glaze also strongly affected the corrosion behavior.

Corrosion of Glazes Coated with Functional Films in Detergent Solutions

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.

Easy-to-Clean Coatings on Glass and Glazed Surfaces

Glass and glazes are easy-to-clean surfaces often used in everyday environments where the surface needs to repel soils and deposits. In general, these surfaces have good chemical durability in everyday environments. However, the durability is rapidly degraded in solutions of high or low pH. This kind of surface corrosion has been found to diminish the cleanability. Surface topography has also a certain influence on the soil attachment and cleanability. Self-cleaning and easy-to-clean coatings have been employed to enhance the cleanability of surfaces. In this report surface properties of three coatings reported to enhance the cleanability of glass and glazed surfaces are summarized. The properties discussed are the surface appearance, roughness, wettability, soil attachment and soil removal. Also the chemical and mechanical durability of the coatings are discussed. The coatings studied were a commercial fluoropolymer film applied at room temperature, an experimental sol-gel derived TiO2 coating calcined at 500°C, and an experimental liquid flame sprayed TiO2-Ag coating applied on the substrates at 500-800°C. The advantages of the fluoropolymer coating are easy application and soil good soil repellence, but the coating has limited chemical and mechanical durability. The manufacture of the sol-gel TiO2 coating requires several processing steps. The coated surface showed excellent cleanability, and good chemical and mechanical durability. The liquid flame sprayed coating has potential to be applied online in the material manufacture. However, the processing parameters should be optimized in order to achieve desired improvements in the cleanability.

Melting Behaviour and Surface Structure of Glazes Containing Wollastonite and Dolomite

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.