Electrochemically Tuning Deposition Of Sol-gel Films Under A Thin Electrolyte Layer And Under Light Irradiation

Sol-gel method has been widely used in preparing silane film, which is generally applied in such fields as protective pre-treatment of metal material, electrochemical analysis and biosensor, catalyst film and surface modification. Electro-assisted cathodiclly deposition adopts the mechanism of "local alkalization", concerning both the stability of sol-gel system in acid bulk solution and the condensation reactions above the substrate in basic local area. Because of the advantages of this method, it has been concerned and developed widely in recent years. In this thesis, the cathodic electrodeposition progress occurred under local area has been researched and it is further expanded in both theory and technology fields. The main issues are listed as follow:(1) According to the theory of mass transfer in solution, the active molecules would diffuse rapidly with the favorably diffused gradient resulting from the decrease of the thin electrolyte film. Under the condition of thin electrolyte layer (TEL), the dissolved O2above the electrode could diffuse to the substrate surface easily and then was reduced to produce the catalysts of OH-, which led to the deposition of silane film with thicker, more compact and highly protective properties. However, once the thickness of electrolyte film reached a critical value, the continuous decrease of it would reversely damage to the anti-corrosion ability of silane films.(2) The p-type semiconductor excited by photo would induce the separation progress of electron-hole pair. The electrons in conductive band (CB) would pass into the solution on some conditions and then were reduced to produce the catalysts of OH’, increasing the OH-concentration high enough for preparing silica films, while the area without photo exciting would not appear any products. This novel method would be used to control the silane films deposited in some special areas by simply manipulating the irradiation and expand the applied fields of cathodic electrodeposition of silane films. The photo density, applied potential and deposition time all contributed to the thickness and roughness of the deposited films and the morphology and size of silica particles, especially the photo density perform the key point in such a method.