Study of the effect of mechanically treated CeO2 and SiO2 pigments on the corrosion protection of painted galvanized steel

The effectiveness of mechanically treated CeO2 particles and SiO2 particles as active fillers into an organic coating was investigated. For this purpose, different combinations of CeO2 and SiO2 particles were added to an epoxy-polyester polymeric matrix: mechanically treated CeO2 particles, mechanically treated CeO2/SiO2 particles and mechanically treated SiO2 powders (used for comparison). The particles were dispersed into the polymeric matrix and HDG steel panels were coated with the different paints. A strontium chromates containing paint was used as a reference to compare the performances of the other samples. The salt spray results proved the good performance of coatings containing combinations of ceria and silica especially where these had been mechanically treated in a co-milling operation. The paint containing only the mechanically treated SiO2 particles showed a fairly good resistance in the salt spray chamber considering the scratched samples. The EIS measurements evidenced the good corrosion protection properties of the paints containing the different combinations of mechanically treated CeO2 and SiO2 particles. After about 1000 h of immersion in 0.1 M NaCl solution, the samples containing the mix of mechanically treated CeO2/SiO2 particles showed impedance values which were comparable with the chromate control sample. The cathodic polarization tests evidenced the low extent of detachment of the coating containing the mix of mechanically treated CeO2/SiO2 particles. The electrochemical characterization and neutral salt spray test results proved the effectiveness of the mechanical treated cerium (IV) oxides treated together with SiO2 as active pigments to improve the corrosion protection of the substrate. The reasons for the synergistic effect of the milled (together or separately) SiO2 and CeO2 particles was not clear at all, but a few hypothesis were discussed. (C) 2011 Elsevier B.V. All rights reserved.