Preparation Of Alkanethiol Composite Organic Molecular Films On Copper And The Investigation Of Their Corrosion Inhibition Properties

Copper and its alloys are widely used in industry as constructional or functional materials. Upon exposure to humid atmosphere or corrosive solutions, they are easily corroded and discolored, which has an impact on their excellent properties and decorative performance. Therefore, it is of great significance to develop an efficient, convenient, low-cost and environment friendly technology to prevent copper from corrosion.Self-assembled monolayers?SAMs? are highly ordered, densely packed,thermodynamically stable molecular films, which form by spontaneous chemisorption of active molecules onto solid surface. The preparation of SAMs has the advantages of mild condition, simple process and low energy consumption. And the prescence of SAMs will not significantly change the appearance or most other characteristics of substrate except the surface properties. Obviously, SAMs provide a great possibility to protect copper in various corrosive circumstances. In this thesis, octadecanethiol(C₁₈SH)SAMs, C₁₈SH-BTA composite molecular films, L-cysteine?L-Cys? and C₁₈ SH composite molecular films were prepared in aqueous solution, and their corrosion inhibition performance was systematically studied. The main results are as follows:?1? The aqueous solution containing C₁₈ SH was prepared taking advantage of solubilization of surfactants and C₁₈ SH SAMs on copper were prepared by immersion of substrate in microemulsion at room temperature and atmospheric pressure. The corrosion morphology observed by SEM shows that C₁₈ SH SAMs can provide effective and long-term protection in chloride-containing solution. The electrochemical measurements show that after modified by C₁₈ SH SAMs, the electrochemical behavior of copper electrode changes greatly. C₁₈ SH SAMs improves the charge transfer resistance significantly and prevents the contact between the metal substrate and the corrosive solution as a hydrophobic barrier layer. As the time of assembly and the concentration of C₁₈ SH increase, the coverage of C₁₈ SH SAMs on the surface improves. The adsorption behavior of C₁₈ SH fits the Langmiur isotherm well.?2? We modified the C₁₈ SH SAMs with BTA and studied the protective performance and the mechanism of the composite molecular films. The results of SEM and the polarization curves indicate that the composite anticorrosion systems have great synergistic corrosion inhibition effect.Both anodic and cathodic electrochemical processes, especially the anodic dissolution of copper, were inhibited effectively. Electrochemical impedance spectroscopy shows that the charge transfer resistance of composite layer is much higher than those of single monolayers. The way of cooperating has a significant influence on the electrochemical performance of composite layers. Among them, C₁₈SH-BTA composite SAMs have the best barrier properties, its inhibition efficiency reaching 99.87%. SERS and FTIR spectroscopy prove that the composite SAMs have stronger ability to maintain their barrier properties.?3? L-Cys monolayers, L-Cys modified C₁₈ SH composite molecular films and L-Cys and C₁₈ SH mixed assembled layers were prepared by self-assembly, and their corrosion inhibition properties were investigated by electrochemical measurements. The results show that L-Cys SAMs were able to prevent metal substrate from corrosion effectively. Moreover, L-Cys modified C₁₈ SH SAMs presents better inhibiting properties than L-Cys SAMs and C₁₈ SH SAMs, the inhibition efficiency improves to 99.89%. The corresponding adsorption models were proposed to explain the different electrochemical performances resulting from different preparation methods.The L-Cys and C₁₈ SH mixed SAMs are denser and more stable, which is indicated by the enhanced charge transfer resistance and decreased capacitance, showing excellent performance against corrosion and discoloration.