Oct 31 2005
Dirt in the wrong place can destroy entire production batches in many branches of industry. But constant cleaning is expensive. Specially coated easy-to-clean surfaces can considerably reduce the amount of cleaning involved, thus bringing down costs.
Sparkling and shining, the surfaces in a freshly cleaned commercial kitchen are a credit to the cleaners who have to remove all traces of grease and food from them every day. But it is not just in the catering business and food industry that cleanliness is essential – the requirements have grown more stringent in the production sector, too. Dirt in the manufacture of microchips and pharmaceuticals, for example, can result in faulty products and cause heavy financial loss. But is frequent, costly and time-consuming cleaning the only option? Research scientists at the Fraunhofer Institute for Electron Beam and Plasma Technology FEP in Dresden are working on an alternative approach: easy-to-clean surfaces which prevent the deposition of dirt and thus reduce the expense and effort of cleaning.
“We functionalize the surfaces with a titanium dioxide coating,” explains Frank-Holm Rögner of the FEP. “If they are then radiated with UV light, a self-cleaning effect is produced.” To create the coating the research scientists use the PVD process – short for physical vapor deposition. This involves vaporizing pure titanium metal in a vacuum plasma, adding oxygen and depositing the reaction product on the cooler surface to be coated. UV light – from sunlight or commercial fluorescent tubes – then initiates photocatalytic oxidation processes in the titanium dioxide coating, combating germs and particles of organic dirt. Light also changes the wetness properties of the photohydrophylic surface: Water flows off more easily and takes particles of dirt with it.
These advantages of a titanium dioxide coating have been known for quite some time and coating methods already exist, too. “The oxide can also be applied using sol-gel techniques or mixed in paint,” says Rögner. “But the advantage of our technique is that we do not need any auxiliary material such as paint. This enables us to obtain a very pure, dense and completely transparent coating which shows outstanding photocatalytic and photohydrophylic activity.” The scientists can tailor the hardness and thickness of their easy-to-clean coatings to requirements. Even the crystalline structure of the oxide and therefore its properties can be controlled by the deposition temperature. “The PVD process is especially suitable for large, flat surfaces made of metal, glass, ceramics and some plastics,” concludes Rögner. “The only limitation is that the material can withstand temperatures of around 130 °C.”
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