Corrosion resistance of phytic acid / Ce (III) nanocomposite coating with superhydrophobicity on magnesium

Abstract

By alternative immersion into the aqueous solutions of phytic acid (PA) and CeCl3 for n cycles, a nanocomposite coating coded as (PA/Ce)n was fabricated on the magnesium substrate. The Ce3+ ions were supposed to coordinate with the phosphate groups of the PA molecules and the (PA/Ce)n coatings adhered to the substrate firmly (5B according to the ASTM D 3359 method). Compared with the PA coating, the Ce3+ ions enhanced the corrosion resistance of the PA/Ce nanocomposite coating. To further improve the corrosion resistance, the (PA/Ce)n coatings were immersed into the ethanol solution of hexadecyltrimethoxysilane (HDMS) and followed by heating in air. The so-obtained sample coded as Mg-H2O-(PA/Ce)n-HDMS was superhydrophobic and possessed much better corrosion resistance as compared with the Mg-H2O-(PA/Ce)n sample due to the retained thin layer of air at the solid/water interface in the NaCl aqueous solution. For four cycles, the Mg-H2O-(PA/Ce)4-HDMS sample showed the most excellent superhydrophobicity with a contact angle of 167.3 ± 2.1° and a sliding angle of 2.7 ± 0.8° due to its hierarchical surface morphology. Moreover, for four cycles, the retained air was most durable and remained intact after immersion for 80 h; consequently, the corrosion resistance of the Mg-H2O-(PA/Ce)4-HDMS sample was found the best. In one word, the corrosion resistance of PA to the Mg substrate was improved by incorporating with Ce3+ ions and further modifying by HDMS molecules. The present study provided a new conversion coating by combining the synergistic anti-corrosion effect of PA, Ce3+ ions, and the surface superhydrophobicity.