Analytical characterisation and corrosion behaviour of bis-aminosilane coatings modified with carbon nanotubes activated with rare-earth salts applied on AZ31 Magnesium alloy

The present work investigates the corrosion behaviour of AZ31 Magnesium alloy (Mg AZ31) substrates pretreated with a water soluble bis-aminosilane modified with multiwall carbon nanotubes (CNTs). Prior addition to the silane solution, the CNTs were submitted to a treatment in an aqueous solution containing cerium nitrate or lanthanum nitrate. The chemical composition of the treated CNTs and of the modified silane coatings was assessed by X-ray Photoelectron spectroscopy (XPS). The thickness and the morphology of the silane coatings were investigated by scanning electron microscopy (FEG/SEM). The pre-treatment of the Mg AZ31 was performed by dipping the metallic coupons in the silane solution modified with the CNTs. The electrochemical behaviour of the silane coated coupons was studied during immersion in 0.05 M NaCl solutions, using the scanning vibrating electrode technique. The electrochemical investigation showed that the activation of the CNTs with the rare-earth salt delays the corrosion activity of the Mg AZ31 substrates. The analytical and microscopic study suggested that the CNTs are homogeneously dispersed in the silane coating and that the CNTs act as support for inhibitor storage. (C) 2008 Elsevier B.V. All rights reserved.