The Adsorption And Film Forming Kinetics Mechanisms Of Silane Molecules On Metal Surface

Each year, worldwide scrapped metal due to corrosion accounted for about1/3of the annual production of metal, direct economic losses reached$700billion. Organic coating as the most effective means to protect metal surface from corrosion, in order to enhance the adhesion properties between the substrate and the organic coating, a variety of pretreatment processes were develop. Traditional Metal surface pretreatment process (as parkerising and chromate passivation), prevalence of complex construction process and serious environmental pollution during use. With the growing voice of environmental protection, the use of these traditional techniques are limited, develop a new, non-polluting metal surface pretreatment method is extremely urgent. The metal surface silanization which developed in recent years using ultra-thin organic coating instead of the traditional crystalline phosphate layer, as the construction process is simple, environment-friendly, low-cost, is considered as the potential replacement for chromate passivation and phosphatizing technology, and it can realized the coating process non-phosphorus, does not contain nickel-manganese-chromium and other heavy metals, eliminate nitrite carcinogens, and compatible with the existing coating processes and equipment, with irreplaceable advantages of environmental protection, is expected to bring significant changes to the traditional surface preparation techniques.The research of silanization pretreatment technology focuses on the performance of the silane film and the process influencing factors, such as the concentration of the silane solution, immersion time and so on. The research generally agreed that:the adsorption and film-forming kinetic processes of silane molecules (film-forming mechanism, the molecular arrangement after film-forming, bonding method and structure) are key factors to determine the interfacial bonding properties and the film performance, the silanization pretreatment effect are closely related to the surface state of the metal, the structure and orientation of the silane molecules. Therefore, find out the adsorption and film forming kinetics mechanisms of silane molecules on metal surface and the key factors that affect the mechanism, not only can provide theoretical guidance for the design, screening and synthesis of the outstanding performance silane molecules, but also can provide theoretical support for the rapid development and industrialization of the silane pretreatment technology.This dissertation paid attention to the following work:selecting two kinds of silanes y-GPS and γ-APS, studying the adsorption and film forming kinetics mechanisms of γ-GPS and γ-APS. As a result, some conclusions with strong application were obtained.The adsorption behavior of γ-GPS on low carbon steel surfaces was systematically investigated by RA-IR, EIS and AFM, focusing on the changes in γ-GPS chains alignment during the adsorption process and the influence of assembly time on the chemical structures, three-dimension morphology and corrosion resisting property of γ-GPS films. The results indicated that the adsorption of γ-GPS exhibited an oscillatory phenomenon, which experienced rapid adsorption firstly, then reached maximum adsorption capacity, subsequently suffered extensive desorption, finally went through irreversible slow adsorption. The growth behavior and protective performance of γ-GPS films was closely related to the adsorption capacity and the alignment of silanol monomers. As more silanol monomers were adsorbed, the stronger the intermolecular van der Waals interactions between the γ-GPS chains would be, resulting in highly ordered γ-GPS films with excellent performance. The proposed adsorption models were used to simulate the experimental phenomena and determine the adsorption mechanisms taking place on the low carbon steel surfaces.The influence of pH to the self-assembled film forming dynamic process of γ-APS on low carbon steel surfaces was systematically investigated by RA-IR and EIS, focus on the relationship between the pH of the hydrolyzate and the adsorption orientation, the adsorption capacity and the film performance of γ-APS, confirmed the optimal pH of the silane hydrolyzate.The results showed that:there exist multi-center active adsorption of γ-APS on low carbon steel surface, amino groups and-Si-OH groups are in competitive adsorption on metal surfaces, the adsorption orientation of γ-APS are closely related the pH of the hydrolyzate; the protection performance of γ-APS film mainly depends on the adsorption capacity of γ-APS molecules, associated little with the adsorption orientation. Within the pH range in the entire study, the peak intensity of Si-O-Fe peaks are weak, but with the rise of pH of the hydrolyzate, slightly lower, show that with the increase of the pH value of the hydrolyzate, silanol monomer to the amino end down adsorption gradually increased,-Si-OH end down adsorption gradually reduced. The amount of Si-O-Si in film gradually increased with the pH value of the hydrolysis increases, indicated that the solution in an alkaline environment can promote the adsorption and condensation of the silanol monomers in the surface of the substrate. Moreover, in the conditions of natural pH of γ-APS solution (optimum pH value), we change the micro pH value of the adsorption interface with cathodic electrodeposition method, found that the increase of micro pH value in adsorption interface catalytic condensation reaction between silanol monomers, thickness, better corrosion resistance silane films were obtained.