Ethyl silicate binders for high performance coatings

Surface coatings based on ethyl silicate binders are categorised as inorganic coatings, whereas the conventional surface coatings which are mainly based on organic binders are referred to as organic coatings. Zinc-rich inorganic coatings based on ethyl silicate are quite successful for the protection of steel against corrosion under severe exposing conditions such as underground, marine atmosphere, industrial atmosphere, nuclear power plants, etc. These coatings provide unmatched corrosion protection to steel substrates exposed to high temperatures. Because of the formation of conductive matrix out of the binder after film curing, zinc-rich coatings based on ethyl silicate binder offer outstanding cathodic protection to steel structures. These coatings are mostly solvent-borne, but recently water-borne versions of the same have also been developed. However, the commercial success of water-borne systems is not yet well established. In the present article, the processes of hydrolysis of ethyl silicate in the presence of acidic and alkaline catalysts have been elaborated to produce ethyl silicate hydrolysates of desired degree of hydrolysis. Effect of various factors such as amount of catalysts, amount of water, type and amount of solvent, reaction temperature and reaction time has been discussed. Calculations to find out the amount of water and solvent required to yield the product of desired degree of hydrolysis have also been illustrated. Typical recipes useful for the preparation of ethyl silicate hydrolysates suitable for use as coating binders have also been presented. The chemistry and mechanism involved in the preparation of binder and the curing of film has also been discussed. This article also summarises the effect of various factors, viz. particle size and shape of zinc pigment, presence of extenders in the formulations, and the application technique on film performance.