| Abstract |
Cr(VI)-based pre-treatments have been in use for long time on several materials, however, they are target of great criticism and in the near future they could be definitely banned. The actual alternatives to Cr(VI) show pros and cons when sets of key properties are considered such as: corrosion resistance, adhesion of organic coatings, fatigue resistance, reliability and quality control. However, some of the possible alternatives show high potential, if some improvements are carried out and the if mechanisms involved are more deeply understood. The present work focus on the use of rare earth (Ce, La) salts and bis-sulphur silane (BTESPT) as chromate substitutes for galvanised steel. These compounds when applied by immersion and subsequent curing originate films that improve corrosion resistance and paint adherence. The films were characterised by Auger and XPS spectroscopy. The corrosion resistance was assessed by electrochemical impedance spectroscopy and dc polarisation. Comparison with the chromate conversion pre-treatment is also carried out simultaneously with discussion of the possible mechanisms involved in the different processes. (C) 2004 Elsevier Ltd. All rights reserved. |
