Dr. Minna Piispanen - Characterization of Functional Coatings on Ceramic Surfaces
Classification
Glass, Glazes, Coatings, characterization, chemical and mechanical durability, self-cleaning and cleanability.
Abstract
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 also have a very good chemical durability. The durability, however, is rapidly degraded in solutions of high or low pH. This kind of surface corrosion diminishes the cleanability. The surface topography also influences the soil resistance and cleanability of the surface. To enhance the surface cleanability and chemical resistance, self-cleaning and/or easy-to-clean coatings have been employed to glass and glazes. The coatings we studied were a commercial hydrophobic fluoropolymer coating, two experimental coatings based on titania, and one experimental sol-gel based zirconia coating applied on glazed tiles and sanitary ware ceramics and float glass. The effect of a smooth transparent glaze was also tested on an opaque glaze surface containing zircon. One of the titania coatings was applied via the sol-gel route, while the other one also containing silver was manufactured via the liquid flame spray method.
We measured the effect of the coatings on the appearance, roughness, and wettability of the surfaces. The chemical resistance and mechanical durability of the surfaces were also compared. Finally, the interaction of the surfaces with different model soils was studied. The easy-to-clean and self-cleaning capabilities of the coatings were compared with a commercial self-cleaning float glass surface.
The results showed that the hydrophobic fluoropolymer coating changes the surface properties, so that soil attachment clearly decreased without affecting the surface appearance. The functionality, however, disappeared in alkaline environments. Its mechanical durability was also poor. The titania coating applied via the sol-gel route was hydrophilic and photocatalytically active. Thus, the coating showed self-cleaning capability. The tests suggested that the experimental sol-gel coating had similar or better self-cleaning properties than the commercial self-cleaning float glass surface. The chemical and mechanical durability of the coating was good. The coating slightly changed the surface appearance. The coating containing titania and silver did not show the desired functionality. This was assumed to partly depend on insufficient coating thickness. Thus, further development is needed to make this coating an alternative to be considered. The silver addition is also likely to give the coating antimicrobial properties. The interaction of the coating with microbes was not tested. The sol-gel derived zirconia coating enhances the chemical durability of the surface. The coating does not have any self-cleaning capability. The smooth glossy additional glaze effectively decreased the roughness. The coating, however, had lower mechanical resistance than the substrate opaque glaze containing zircon crystals.
Some of the studied coatings show promise regarding self-cleaning and easy-to-clean properties of the surfaces. As the results showed, however, the functionality of the surfaces can easily diminish as a result of chemical and mechanical loading. Since ceramic surfaces are often subjected to mechanical abrasion and different aqueous solutions, the long term performance of the coatings should be known. Our results provide guidelines for selecting additional coatings on ceramic silicate surfaces used in different environments.
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