Electrodeposition Of Silane Sol-gel Films And Silane-contained Primers

Silane sol-gel films have been widely applied in surface modification, optical materials, electroanalysis and biosensors, corrosion protection of metals, etc. Silane sol-gel films are usually prepared by dip-coating, spin-coating and spraying. However, in these methods, the requirement for the stability of silane solutions limits the tendency for the formation of silane films. Recently, a novel electrodeposition method, which relies on the facilitation of silane film formation by cathodically generated OH"ions, has been well developed. In this thesis, some key issues in the electrodeposition of silane sol-gel films were investigated, the application of electrodeposition method was expanded, and the controllable local electrodeposition of silane sol-gel films on either conducting or insulating substrates using SECM feedback mode was first proposed. The main contents are listed as follows:(1) The influence of nitrate ions on the electrodeposition of silane sol-gel films was investigated. It is observed that proper concentration of nitrate could reduce to nitrite on the cathode, producing OH- ions that would facilitate the deposition of silane films, leading to the enhancement in the compactness, thickness and corrosion resistance of the electrodeposited films. However, extra high concentration of nitrate would probably "over-catalyze" the condensation of silane in the precursor, resulting in the deterioration of electrodeposited films' protectiveness.(2) Silane films doped with SiO2 nanoparticles were prepared by electrodeposition method. Tiny amount of SiO2 nanoparticles could improve the corrosion resistance of silane films on aluminum, while extra high amount of SiO2 nanoparticles would make the silane films porous and deteriorate films' protectiveness. Electrodeposition at proper potentials could further improve the corrosion resistance of silane/SiO2 composite films via cathodically generating OH- ions, while electrodeposition at extra negative potentials would deteriorate the films' protectiveness due to the H2 evolution. The i-t curves recorded during the electrodeposition indicate that SiO2 nanoparticles might involve in the electrodeposition process.(3) The controllable local electrodeposition of silane sol-gel films on either conducting or insulating substrates was achieved using SECM feedback mode. The size of the locally electrodeposited films could be tuned by adjusting deposition conditions such as tip potential, deposition time and tip-substrate distance. The locally electrodeposited silane films have potential applications in binding Au nanoparticles for "local catalysis".(4) The anodic electrodeposition of silane sol-gel films was preliminarily investigated. We clarified that the color change of glassy carbon electrodes possibly arises from the oxidation of glassy carbon substrates and the electro-polymerization of ethanol, thus it could not be used as the sole indicator of silane film formation. The anodically electrodeposited TMOS silane films were further examined by XPS, and the results indicate that silane could be anodically electrodeposited from precursors containing different electrolytes (including KC1).(5) The epoxy-acrylate superprimer coatings were electrodeposited on galvanized steel. Cathodic current may facilitate the deposition of silane, while the anionic primer tends to deposit with anodic current. Thereby, a novel "cathodic + anodic" electrodeposition mode, that is, cathodic electrodeposition followed by anodic electrodeposition, was proposed. The coatings prepared by "cathodic + anodic" electrodeposition perform better corrosion resistance than the cathodic-only or anodic-only electrodeposited coatings. During the "cathodic + anodic" electrodeposition, the cathodic process could lead to the formation of a silane-rich layer, which may act as a pretreatment to the substrates improving the adhesion and corrosion resistance of the following anodically electrodeposited primers.