PROCESSING AND PROPERTIES OF ENVIRONMENTALLY FRIENDLY CORROSION RESISTANT HYBRID NANOCOMPOSITE COATINGS

摘要

Chromate compounds-free hybrid silicone based nanocomposite coatings have been formulated under purely aqueous conditions and fully characterized. The hybrid nanocomposite coatings were synthesized by acid-catalyzed hydrolysis and condensation of organo-functional siloxane precursors, resulting in the formation of self assembled nanoscale composite SNAP. The cross-linking of the SNAP conversion coating was done with a primary and secondary amino silane; APTEOS and ETDA respectively. Small amount (0.05-0.2%) of organoclay, Cloisite 15A, clay was added to the coatings as a reinforcement and diffusion barrier phase. Corrosion inhibition of the coatings was determined by using DC Polarization test (DCPT) and Electrochemical Impedance Spectroscopy (EIS). The DCPT test results were used to optimize the processing conditions and structure of the hybrid nanocomposite. The corrosion performance of the bi-layer coatings was shown to be about three orders of magnitude higher than that of the one layer coating system (conversion and bulk). The corrosion inhibition of the coatings was significantly improved in the presence of 0.2% of clay or multi-functional co-reactants. The clay/bi-layer polysiloxane coating's impedance was significantly high (E+6 Ohms), and remained unchanged after about 8 weeks of exposure to 3.5% NaCl solution.