Surface Modification Of Copper And Carbon Steel And The Investigation Of Their Corrosion Inhibition In Seawater

Copper and carbon steel are important materials related to the national economic development and have been widely used in social production and people's daily life. However, there is different degrees corrosion existing in them in different application environments, especially in strong corrosive medium. So the metal corrosion brings severe economic losses to production and daily life. Therefore, it is a very meaningful work to search corrosion inhibitor for copper and carbon steel which is more ideal, environmentally friendly and non-toxic.The thesis is mainly divided into two sections:The first section is"Investigation of the corrosion resistance of n-tetradecanoic acid and its hybrid film with bis-silane on copper surface in seawater". Studying the super-hydrophobic film preparation on copper surface adopted orthogonal experimental method and obtained the best condition of forming super-hydrophobic film. The best condition of forming super-hydrophobic film was an ethanol solution of n-tetradecanoic acid (0.05mol/L) at 35oC water bath for 7 days. The surface morphology of n-tetradecanoic acid super-hydrophobic film was studied by contact angle measurement and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy. Vertical rod structures evenly attaching to copper surface can be observed and its contact angle (CA) has reached 153°. Their corrosion resistance was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization which revealed that copper corrosion was effectively inhibited by n-tetradecanoic acid super-hydrophobic film, but the capacity of ordinary n-tetradecanoic acid film was inferior. In addition, the adsorption behavior of n-tetradecanoic acid molecules at the copper surface was explored by Gaussian (R) 03 software. During the experiment we found that the interaction of n-tetradecanoic acid super-hydrophobic film and copper substrate was relatively weak, so selected silane coupling agent bis-[(triethoxysilyl) propyl] tetrasulfide (BTESPT) to increase their interaction. Although the contact angle of the hybrid film decreased which was about 125o, the electrochemical experimental results showed that the corrosion resistance of the hybrid film markedly improved compared to the single n-tetradecanoic acid polymer film. Also its compactness and soundness was greatly improved.The second section is"Silylation treatment of carbon steel and the study of its corrosion resistance in sea water". BTESPT silane film and different cerium silane films were successfully prepared on the carbon steel surface. Using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and Infrared Spectroscopy studied the hydrolysis solvent, hydrolysis time, solution concentration and pH value of BTESPT which proved that the mixture of water and ethanol is ideal hydrolysis solution of BTESPT, pH=4.5, the optimum hydrolysis time is two days and the optimum concentration is BTESPT/DI water/ethanol=2/3/95(v/v/v). The corrosion resistance of all kinds of silane films in sea water was investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and 3%CuSO4 pitting experiments. The electrochemical experimental results showed that the protective capacity of silane film with Ce2(SO4)3 was better than the silane film without Ce3+. The silane films had a good protective effect to carbon steel substrate and delayed its corrosion process. However, the capacity of silane films to protect substrate against corrosion reduced with the immersion time. At the same time, the surface morphology of silane film was studied by scanning electron microscopy (SEM). An energy dispersive X-ray spectrum (EDS) was also used to analyze the micro zone composition of the surface. As can be seen from the SEM photographs the silane film prepared on the carbon steel surface are dense and uniform.