Influence of sol-gel process parameters on the protection properties of sol-gel coatings applied on AA2024

Abstract

The present work explores effects of shelf-life, temperature and the presence of cerium nitrate additive on the protective performance of sol-gel coatings applied on AA2024. These are important parameters when industrial applicability of coating formulations is considered. The studied sol-gel system is based on a combination of metalorganic precursor titanium(IV) propoxide and hybrid epoxy silane 3-glycidoxypropyltrimethoxysilane. The synthesized sol-gel formulations without or with addition of 0.007 M Ce(NO3)(3) were aged during different times at temperatures 25 degrees C or 6 degrees C. FTIR results show that the intensities of the bands associated to Si- O-Si increase with respect to Si-OH groups during the aging process as a result of extended condensation. However, such transformations occur less rapidly at low temperature. The electrochemical impedance spectroscopy measurements clearly show that sol-gel coatings corresponding to the sol-gel aged at low temperature exhibit similar corrosion protective capabilities compared to the coating obtained without sol-gel aging. It is also observed that the protection performance of the sol-gel coatings with cerium nitrate obtained after two weeks of sol-gel aging is lower compared to the coatings without cerium additive. This effect is attributed to the enhanced reactivity of the sol-gel due to cerium(III) presence. (C) 2014 Elsevier B.V. All rights reserved.