Preparation of cerium doped silica sol-gel coatings on glass and aluminum substrates

A. PEPE,; M. APARICIO; S. CERÉ; A. DURÁN

JOURNAL OF NON-CRYSTALLINE SOLIDS

Elsevier

Año: 2004 vol. 348 p. 162 - 171

0022-3093

Chromates are among the most common substances used as corrosion inhibitors. However, these compounds are highly toxic,and an intense effort is being undertaken to replace them. Cerium compounds seem to fulfil the basic requirements for considerationas alternative corrosion inhibitors. The aim of this work was to study the effect of the incorporation of cerium ions in silica sol–gelcoatings on aluminum alloys as potential replacement of chromate treatments. The main idea was to combine the
barrier effect ofsilica coatings with the
corrosion inhibitor effect of the cerium inside the coatings. Thin (below1 lm for a single layer) and transparentcerium doped silica sol–gel coatings were prepared by dipping 3005 aluminum alloys in sol–gel solutions. Ultra-violet–visiblespectra (UV–vis) showthat cerium ions, Ce3+ and Ce4+, always are present in the coatings, independently of the cerium salt or firingatmosphere used. Active protection with single and two layer coatings prepared with Ce (IV) salt seems to improve corrosion protectionof the coated aluminum while coatings prepared with Ce(III) salt only entails a protection when applied as a two layer, possiblydue to sealing of pre-existent defects in the first layer. The improvement of active protection with immersion time would implythat corrosion is inhibited by cerium ions that migrate through the coating to the site of the attack (a defect in the coatings) and thenreact to passivate the site.