Ceramic coatings on metals prepared by sol-gel technique for corrosion resistance study

Aluminium metal substrates were coated with silica, titania and silica-titania using the alkoxide precursors. The coating solutions were prepared by hydrolysis and condensation reactions of the alkoxide precursors. The metal substrates were pre-treated and coatings were prepared by dip coating the substrates in coating solutions of suitable consistency. They were withdrawn at a constant rate of 1 mm/sec. The coated substrates were heat treated in the temperature range of 350–500°C for 2 hrs. The corrosion resistance of coated substrates was measured by potentio-dynamic polarization test using 5% H₂SO₄ as well as 3.5% NaCI solutions and the results were compared with corrosion of bare. metal. From the above study, it was observed that the corrosion rate of aluminium metal was reduced by 86% for silica coatings, 25% for titania coatings and 77% for silicatitania coatings in 5% H₂SO₄ solutions. Similarly, the corresponding reduction of corrosion rates was 99%, 90% and 95% respectively in 3.5% NaCl solution. The corrosion resistance of silica coatings was very good compared to poor resistance of pure titania coatings. The addition of silica increases the corrosion resistance of titania appreciably.