Zirconia primers for corrosion resistant coatings

The recent restriction in the use of chromium VI gave a new impulse in the field of anti-corrosion treatment for an alternative solution. A promising route seems to be the deposition of a thin ceramic layer on the metallic surface. In this study, four zirconia primers have been deposited on 1050 aluminium sheets by sol–gel process. Sol preparation was obtained starting from two different precursors and two curing temperatures were tested. Surface microstructure and chemical composition were determined by AFM and XPS for all samples. Electrochemical Noise Analysis (ENA) was used in Harrison's solution to evaluate the corrosion resistant features of the samples. Tests have been also performed on samples protected by polyester topcoat deposited on the aforesaid primers. AFM analysis revealed that, for all the samples, covering and structure of the coating were uniform. XPS depth profiling allowed concluding that film thickness was in the range from 18 to 30 nm and that chemical composition was constant through primer thickness. Corrosion tests demonstrated that zirconia primers showed good performances in terms of corrosion resistance, comparable to chromate and fluotitanate layers industrially prepared. Topcoated samples gave an optimal corrosion resistance.