Formation and Surface Structural Features of Crystalline Ceramic Nanocomposite Coatings on Aluminium Using Lithium Sulphate with Silicate Additive

Abstract

We have synthesized a series of the ceramic coatings by anodization of aluminium using lithium sulphate and sodium silicate additive. Our experiments show that the present coatings are nanocomposites in nature, consisting of a mixture of nanocrystalline alumina, silica, aluminium silicate and mullite; the formation of alumina was similar to conventional anodizing technology, while the formation of mullite was attributed to an addition of sodium silicate. The microhardness of the coatings progressively increased with the increasing current density up to 0.2 A/cm2, which could mainly be attributed to the decrease of porosity in the interfacial region of the oxides up to the range. From the performance of the coatings against corrosion (Tafel/Nyquist plots), it was inferred that the coatings fabricated by lithium sulphate–sodium silicate bath have enhanced corrosion resistance (R p = 3.12 kΩ), as well as better microhardness value than that of the lithium sulphate bath alone (R p = 660.96 Ω) which confirm the perception that the silica particles included in the anodized alumina matrices randomly. Presence of Al, Si and O indicated that the electrolyte components had been intensively incorporated into the coatings.