Cr (VI) free, water-based sol-gel systems for metal corrosion protection

Chromating and Phosphating are very well established surface treatment processes and are of utmost economic significance. However, chemicals with a high environmental impact are still widely used in these processes. Many industries do not approve the use of chromating process with Cr(VI) due to changing regulations. Evonik’s new Multifunctional Silanes Systems® offer performance similar to Chromium (VI) but without affecting the environment and simplify the pre-treatment process.

Water-borne sol-gel systems based on silanes are very promising for the treatment of metal substrates. They can react with the metal surface and can passivate the substrate. The water-based systems offer an extremely low volatile organic compound (VOC) level and maximum corrosion protection without the use of Chromium (VI) in the system. The new products offer protection against abrasion and chemicals and also provide excellent adhesion of coatings.

A hydrophobic protection layer can be formed to protect from corrosion and the adhesion of a subsequent coating can be improved. However, sol-gel systems do not give an active but a passive corrosion protection. The corrosion protection of water-based sol-gel systems can be improved when these systems are used as a binder in formulations. The major advantages of such formulations are:

• different types of metals can be treated with a single formulation
• curable at fairly low temperatures
• silane systems are environmentally safe

During this presentation, recent corrosion test results of different coated and uncoated metal surfaces will be presented.