The why's and how's of protective coatings: An overview

Prof A. S. Khanna discusses the importance, purposes and various classifications of protective coatings

- Prof. A.S. Khanna

Protection by coatings is one of the five methods of protecting a metal from corrosion. The other four methods are: better material selection, anodic/cathodic protection, better design and last but not least protection by inhibitive chemicals. Coming to protective coatings, there is broad classification of different coatings, based upon the method of application: brush/roller, spray method, hot dip, thermal spray, PVD/CVD, chemical conversion, laser surface modifications etc. Out of all these, the paint coating, appears to be the most trivial method of surface modification. It is usually applied using a brush to give a barrier coating of paint which is generally an insulating coating, and helps in preventing corrosion. However, paint coatings cannot be considered as a very simple technique when applied on industrial systems, where durability and its functionality become very important. There are various varities of paint coatings based upon its utility, purpose and function. In a very simple classification, it can be divided into two main types: decorative and industrial. Decorative paints are usually applied to enhance the aesthetics of the object while industrial paints are mainly for corrosion protection. But there are several new requirements for decorative paints: long durability and stability from UV light, antidust, hydrophobic, anti-fungal and anti-graffiti. Thus many decorative coatings require one or more additional features in to serve the purpose of protecting, concrete buildings, flyovers, bridges and multiplexes.