Sol-gel-derived alumina/polyvinylpyrrolidone hybrid nanocomposite film on metal for corrosion resistance

With the addition of polyvinylpyrrolidone (PVP), alumina sol with an aluminum sec-butoxide/water molar ratio of 1 : 45 was synthesized. The surface tension of this alumina sol was found to be lower by 35% than the sol without PVP. Alumina/PVP hybrid film with a critical thickness up to 2 μm was fabricated by dip-coating method. The heat treatment between 200 and 300°C could produce a film with perfect hybrid nanocomposite structures. Alumina particles with a size of about 20 nm were uniformly distributed in this material. The hardness of the film samples increased with the increment of heat treatment temperature, and hardness values higher than the original metal were detected after heat treated above 400°C. The film-coated metals that were heat treated below 150°C or above 400°C exhibited relatively weak adhesion, but strong adhesion was obtained when heat treated between 200 and 300°C for 30 min. The corrosion rate of the film-coated metal that was heat treated between 200°C and 300°C for 30 min was lower by 95% than the uncoated metal.