Galvanising is one of the most common and effective methods of protecting steel against corrosion and relies on the increased anodic activity of zinc, which provides cathodic protection to the underlying substrate. However, galvanizing primarily takes place via a hot dipping process whereby steel components/structures are submerged within a molten bath of the coating metal. This process cannot be completed onsite of the application by the manufacturer and the coating process therefore results in substantial economic costs. One alternative to hot dip galvanising is the application of zinc rich coatings which consist of zinc particles dispersed in a binder. Such systems are available in a liquid form and can be applied to steel substrates as a paint. However, issues with this technology need still be addressed.

For example, it is critical that corrosion protection capability is not compromised. Secondly, aesthetics demands mean that coatings must be coloured without affecting corrosion protection properties, Industrial practice at the moment is to apply a multi coat system and this may contain three or even more layers. Thickness of the coating, environmentally friendliness and ease of application are other factors to be considered during the development of novel zinc rich coatings.

This work describes the development of zinc based coating systems which are able to provide reliable corrosion protection whilst meeting customer demands with respect to aesthetics.

Quantitative and qualitative details of the corrosion protection performance of the developed coatings are obtained to benchmark the performance with other commercial coating systems. Other than accelerated cyclic corrosion test exposure and subsequent periodic semi-quantitative assessment of defects, scanning vibrating electrode technique (SVET) is also used to investigate the extent to which the different coatings are able to offer sacrificial protection in the case that the size of the exposed area is systematically changed.

Details of this development will be presented together with corrosion evaluation results. Industrial challenges facing the zinc coating industry, examples of commercial coating failure mechanisms, and the requirements of new generation zinc coatings will also be discussed.