PUHTEET 2 and 3 projects focused on study of thin film coatings (sol-gel and ALD-based) which are aimed to provide additional value for different metal materials and products. The aim was to gain the long term corrosion and wear resistance, anti-scratch and easy-to-clean properties as well as take into account the decorative aspects. In addition, the suitability of the sol-gel coatings for roll-to-roll (R2R) coating of metallic coils was investigated. Furthermore, novel surface pre-treatments (PET-electric disharhage, atmospheric plasma, and dry ice cleaning) to be used for cleaning of metallic substrates prior deposition of sol-gel coating were studied. Coating development concentrated on the influence of inorganic (e.g. SiO2, Al2O3, ZrO2) and organic (e.g. vinyl, acryl, metacryl and epoxy) components to desired properties of the coatings. Also, the effectivity of the corrosion inhibitors and influence on different dyeing agents were investigated. The effect of different curing methods and processes for sol-gel based coatings were investigated as well as industrial scale and industrial environment coating procedures. A novel pre-treatment method (electropolishing with electric discharge method, PET) using environmentally ammonium sulphate based electrolytes was investigated and it was found to be feasible also in continuous process for metal coils. Dry ice (solid CO2) cleaning was also studied as a pre-treatment method for a reel-to-reel coating of metal coils. It was found that the dry ice treatment produces sufficient surface quality for further surface coating with sol-gel coatings and good adhesion of the coating, especially when used with copper based materials which are sensitive for oxidation after a traditional surface pre-treatment. A novel forming method (Incremental Sheet Forming) was used for moulding of sol-gel coated metal sheets to investigate the behaviour of the coatings and influence of forming parameters. Sol-gel coated metal sheets could be formed with this method and the coatings resisted forming in some level though the forming parameters and properties of the coatings had very strong effect on degradation of the coating. Environmental aspects of the sol-gel coatings were investigated. It was verified that all the coatings used in the project fulfilled the demands concerning volatile organic compound (VOC) emissions set by the directive 2004/42/EC. The long-term corrosion resistance and dirt repellancy of the coated materials were investigated with the field corrosion tests on an isle located in the Gulf of Finland. The duration of the tests was around 550 days. Only the thickest coatings (ca. 30-50 μm) were still protecting the base material after this environmental exposure. Thinner sol-gel coatings with a thickness of sub-micrometer to couple of micrometers or ALD/TiO2-coatings with a thickness of couple of tens or hundreds of nanometers could not fully protect the base material, especially if the base material was electronegative/sensitive to corrosion. Though, even the reference material, uncoated stainless steel (grade EN 1.4301 or AISI 304) showed corrosion in these severe environmental conditions. On the other hand, the hot-dip zinc galvanized steel with sol-gel coating gave very promising results. A company project in which VTT's and Millidyne's coatings were used was carried out simultaneously with these projects. Parts of ventilation system manufactured by Fläkt Woods Ltd. Copyright © VTT 2009.
|Place of Publication||Espoo|
|Publication status||Published - 2009|
|MoE publication type||D4 Published development or research report or study|
|Name||VTT TIEDOTTEITA - RESEARCH NOTES|
- sol-gel coating, ALD-TiO2-coating, HVOF-coating, corrosion resistance, wear behaviour, environmentally friendly metal products, easy to clean, photocatalytic, roll-to-roll process, PET-process electric discharge, dry ice (solid CO2), stainless steels and