| Surface modifications of metals with a relative high chemical activity have been applied in different fields, such as electronic, mechanical, aerospace industry. Electroplating technology is one of the important methods of surface modification, which can electrodeposit selectable functional coatings with high chemical inertness on the surface of active metals. The decision criteria for choosing the metal coatings deposited on different substrates for surface modification by electroplating technology is a puzzle for the researchers. Materials Studio is a kind of materials science modeling and simulation software, which can be adopted to study the structures and properties of varied materials in molecular scale using the first principle theory. The software has been widely used in material, chemistry, condensed matter physics, biology, pharmaceutical etc.In this thesis, the Materials Studio was employed to complete the following tasks: based on the optimized bulk structure of metal crystals (Au, Cu, Ni and Fe), different crystal faces were structured, and corresponding surface energies were calculated though further structure optimization. At the same time, the electronic state densities of those crystal faces were also analyzed using first principle. The calculation results showed that the (111) face of Au, Cu, and Ni had the lowest surface energy, while for Fe crystal, the (211) face exhibits the lowest surface energy. By comparing the simulation results of the above four metals, it was found that the surface energy of Au, Cu, Ni, and Fe increased in turn, indicating the corresponding stability decreased in turn. Those results confirmed the chemical stability of plating pieces could be improved by electroplating Au coating on Cu surface or electroplating Ni on Fe surface.In electroplating technology, this thesis researched a new kind of non-cyanogens gold-plating process in detail. Firstly, a water-soluble non-cyanogens gold salt was prepared and characterized; it was found that the new gold salt presented composite complexation structure and high stability in water. The gold-platting process with the water-soluble gold salt was studied. The test results showed that the bath stability and current density range, coating quality were similar to those in traditional cyanide gold-plated system. Hence the non-cyanogens gold-plating process could substitute the existing cyanide gold-plated system. In addition, the process of plating Ni on Fe surface was also studied, and the coating structure and properties were tested. Corrosion resistance of Cu plating pieces was evaluated by nitric acid steam test.The results showed that serious corrosion occurred on bared Cu substrate, while no corrosion phenomena was observed after plating Au coating on Cu surface, which indicating that the surface modification of plating pieces by plating gold could improve the chemical stability. The materials studio calculation results showed that the surface energy of Au(111) and Cu(111) faces were 0.790 and 1.367 J/m~2, respectively, which provided a microscopic theory for the results of nitric acid steam test.Salt spray test was used to evaluate the corrosion resistance of Fe plating pieces. The results showed that serious corrosion occurred on bared Fe substrate, while no corrosion phenomena was observed after plating Ni coating on Fe surface, which indicating that the surface modification of plating pieces by plating Ni could also improve the chemical stability. With the help of Materials Studio, the surface energy of Ni(111) and Fe(211) faces were calculated to be 1.959 and 2.215 J/m~2, respectively, which can explain the results of salt spray test based on atom scale. |
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