Inhibition of copper corrosion by silane coatings

OFHC copper specimens were pre-filmed in hydro-alcoholic solutions of various silanic agents (3-mercapto-propyl-trimethoxy-silane, PropS-SH; bis-triethoxy-silyl-ethane, BTSE; n-octadecyl-trimethoxy-silane, OctadecS; phenyl-trimethoxy-silane, PhS) to evaluate the influence of the silane molecule structure towards copper corrosion protection. Linear polarization resistance, potentiodynamic polarization curves, and electrochemical impedance spectroscopy tests were performed in 0.6 M NaCl. The thiolate bond caused a good anchoring of the silane molecule on the copper surface, which determined a noticeable hindrance to the anodic reaction of copper oxidation. Since this bond was found to be stronger than that of the oxane bond, the PropS-SH coating was more corrosion resistant and more persistent than the other tested silane coatings. The optimum pre-treatment solution pH was 4, although PropS-SH coating presented some imperfections. At this pH the coating was thicker than that at pH 10, when the silanized layer completely covered the copper surface. Nevertheless, the defects of this layer were so small that they could be plugged, for a prolonged time, by the copper corrosion products.