||Surface Activation by Corona for Adhesive Multi-layer Coatings on Aluminium
Ambat, Rajan (Materials Science and Engineering, Department of Mechanical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
||Møller, Per (Materials Science and Engineering, Department of Mechanical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Kingshott, Peter (Solar Energy Programme, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
||Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
||Conversion coatings using chromium have long been used for aluminium alloys as an intermediate layer to improve corrosion resistance and for better adhesion of paint layers. Although chrome conversion coating offers many advantageous coating properties, its use of hexavalent chromium is strictly regulated due to its toxicity and suspected carcinogenicity. For this reason, manufacturers have begun to identify, evaluate, and implement acceptable alternatives for chrome conversion coatings where feasible. These alternative technologies commonly generate less pollution than chrome conversion coatings and have fewer associated health and safety risks.
However, so far no single treatment has been found that could effectively compete with the properties of chrome conversion coatings. Research is underway to identify inorganic or organic coatings or a combination of both as a replacement for chrome coatings. Silane monolayers have long been used in the glass fiber industries to provide a chemical bonding between silicon dioxide and polymers. Such monolayers are also applicable for achieving a chemical bridging between the aluminium surface and the paint layer. Therefore, silane based coatings have been tried on aluminium as an intermediate layer to replace chromium. However important issues on how the aluminium pre-treatment affects the silane coverage are still not fully understood.
In general, studies have shown that the oxide layer of the aluminium surface is of high importance to the performance of the silane coating. Atmospheric plasmas have traditionally been used as a non-chemical etching process for polymers, but the characteristics of these plasmas could very well be exploited for metals as well. This project focuses on how the corona discharge process is affecting the aluminium AA 1050 alloy surface, how it affects the corrosion properties and whether it can be used as a method of initiating chemical reactions on the surface. The corona discharge is found to grow an oxide layer at the surface. This oxide is characterized using XPS, SEM/EDS and FIB-FESEM. Potentiodynamic electrochemical experiments show that the corona treatment gives a very good anodic protection of the surface, and a moderate reduction of the cathodic reactivity.
The influence of the corona discharge to the interfacial bonding to the bis(1,2 triethoxysilyl)ethane (BTSE) silane is investigated by XPS and potentiodynamic experiments and the corona treatment is found to give an increase to the silane bonding
A novel process where the BTSE is evaporated to the surface has been attempted, and good silane coverage is found by this method, though optimization of process parameters is needed.
Additional corona treatment to this silane layer is found to create a heterogeneous surface containing BTSE silane and silicon dioxide.
Creation date: 2007-07-25
Update date: 2011-09-27