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Development of self-cleaning clay roofing tiles

Self-cleaning clay roofing tiles with improved resistance to the action of microorganisms will be developed. Nanocrystalline photocatalytic coatings applied to the ceramic surface will be superhydrophilic, well bonded and durable.

Clay roofing tiles are ceramic systems with a relatively high amount of porosity (from 8% up to 14%) produced from plastic clay-like materials rich in iron and/or carbonates. During their long-life exploitation, these systems are exposed to physical (frost), chemical (atmospheric acid gases) and biological degradation (microorganism actions, lichens) and in such an environment they are often partially deteriorated. In recent years there have been different approaches to the production of bio-resistant clay roofing tiles: application of different chemical agents (Cu slag, CuO powder, copper-exchanged montmorillonite) as additives for the basic raw material compositions or designs of hydrophobic self-cleaning coats (lotus effect). All these approaches suffer from a number of drawbacks that have prevented their widespread application. It was difficult for small quantities of additives to be well homogenised in a large quantity of raw materials, while batch processing of hydrophobic material (lotus effect) was a costly and time consuming technique, depending heavily on the surface structure of the tiles. The problem to a great extent could be solved by application of hydrophilic photocatalytic coatings, which chemically breakdown organic dirt (microorganisms such as lichens, algae, etc.) during exposure to sunlight, and transforming them into harmless components. In this way the biodegradation process is disabled. The technology of self-cleaning materials has been developed rapidly in recent years. For a commercial product, its potential is huge and the market truly global. Because of the wide range of possible applications, from window glass and cement to textiles, self-cleaning coatings may become an important labour-saving device. Some of this potential has already been realised: self-cleaning paints are already available in Europe, while self-cleaning windows have made an impact within the past few years as well as several multinational glazing companies. Many materials such as metal oxides or sulphides could be applied as a photocatalytic active material, but the widely used photocatalytic material is the anatase type of TiO2 (titanium dioxide) with nano-size particles. It is a very effective agent against organic and inorganic material as well as against bacteria and fungi. Its advantages in comparison with the other photocatalytic material are: low cost, quite fast reaction under mild operating conditions and the possibility of a wide spectrum of organic contaminants being converted to water and CO2 (redox reactions and molecular transformations). The technology of self-cleaning clay roofing tiles is at the very beginning. Although there are outdoor applications of TiO2 photocatalysis, in literature very little information on the interaction between titanium dioxide and traditional building materials like concrete, mortar plaster or clay roofing tiles are available. By coating the original ceramic support (clay roofing tile) with a super hydrophilic photo-catalyst, the dirt of the roof could be washed away by rain - the roof will be kept clean for a long time. Two effects would be considered: firstly, the formation of a super-hydrophilic surface (nano-sized coating) which would have a higher affinity to water than oil, and secondly, the utilisation of a photocatalytic material which, after the ultraviolet illumination, would contain a photo-generated hole-electron pair that reacts with oxygen and water in the environment, generating potential cleaning agents on the surface of the coated material. The agents (.OH, .OOH) will decompose large organic molecules to smaller fragments. The combination of photocatalysis and super-hydrophilicity allows grease and dirt to be swept away with water. The possibilities of fixing the photocatalytic materials on the surface of clay roofing tiles will be investigated: application of the spray-coating technology, as well as application of the sedimentation technology. The next step is the photocatalytic decomposition of organic materials (methylene blue, rhodamine B) - model substances for organic contaminants, and the photocatalytic decomposition of the microorganisms - inoculated fungi. Time-dependent measurements of the decomposition reaction will also be investigated. Thus, we will focus on the areas of materials properties and lighting techniques trying to achieve the desired effects. The potential for the widespread use of photocatalysts in clay roofing tiles looks promising as a new way to minimise contaminants and improve the aesthetic quality of our urban environments. Keywords: clay roofing tiles, self-cleaning effect, semiconductors.
Acronym: 
CLEANTILE
Project ID: 
3 969
Start date: 
01-01-2007
Project Duration: 
30months
Project costs: 
500 000.00€
Technological Area: 
Building Materials, Components and Methods
Market Area: 
Manufacture of Building Materials

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