Development of an Electroless Method to Deposit Corrosion-Resistant Silicate Layers on Metallic Substrates

A novel electroless method for depositing corrosion-resistant silicate layers on metallic substrates from aqueous solutions has been developed. The silicate layer was deposited from an aqueous solution of sodium silicate 3.22 weight ratio sodium silicate, 37.5% solution in water from PQ Corporation and sodium borohydride. The technique is demonstrated by forming a passive film on galvanized steel. Deposition parameters such as concentration of the bath, temperature, and pH have been optimized based on the corrosion characteristics of the final coating. Studies on the coating reveal the formation of a very thin 5n m zinc disilicate layer followed by a much thicker 500 nm silica layer. Accelerated corrosion tests showed that the silicate coatings have higher corrosion resistance and better stability when compared to chrome passivates. Silica coatings developed by this method show promise as an alternative to chrome passivation for corrosion protection.