| Copper is one of the most important metal materials owing to its high electrical and thermal conductivities, mechanical workability, and its relatively noble properties. It is thus widely used in petroleum pipeline, seawater pipeline, industrial water utilities, seawater desalination, heat exchangers system and relative industrial manufacture. Normally, copper has a good corrosion resistance performance. Although copper has widespread applications in these systems, it is prone to suffer from corrosion attack in aggressive medium when exposed to the high concentration of Cl– solutions, which results in enormous economic losses and many potential safety problems.Various strategies have been developed to address the growing need for the inhibition of copper corrosion. One of the most efficient approaches for protecting copper against aggressive attack is the use of organic compounds to form tight films. The majority of the well–known inhibitors are organic compounds containing heteroatoms, such as oxygen, nitrogen, or sulfur, and multiple bonds, which allow adsorption on the metal surface and block the active sites on the surface, thereby reducing the corrosion rate. Unfortunately, some of the corrosion inhibitors are toxic and hazardous to both human beings, raising a series of additional environmental issues. Hence, considerable effort has been devoted to looking for effective and environmentally acceptable corrosion inhibitors as alternatives of toxic inhibitors. In this article, we selected three eco-friendly compounds as corrosion inhibitors to study inhibition performance.Phytic acid calcium(PAC) is a natural and non-toxic phosphoric acid compound, which extract from cereal grains and seeds. It is widely used in the fields of food, grease,medicine and daily chemicals industry. Due to the six phosphate groups attached to the inositol in the PAC molecular structure, so it possesses a powerful capability of chelating with different metal ions, such as Zn2+, Fe2+, Cu2+, and Mg2+ ions.Methionine( L–MTI)is an essential amino acids in human body. It is available for preventing and treating of chronic hepatitis, cirrhosis and other liver diseases. N-(2-Mercaptopropionyl)glycine( MPG)is an amino acid derivative, which contain free thiol. It can be used for fatty liver, alcoholic liver and heavy metal detoxification.These two kinds of amino acids both contain S–H bond, –N–H bond and COO– in their molecular structure. It is beneficial to chelat with the metal ions. Therefore, amino acids and amino acid derivatives are also potential corrosion inhibitor.Surface-enhanced Raman Scattering(SERS) can provide abundant information of adsorbed species at electrode surface under(sub) monolayer with highly sensitive surface effect. In this paper, Raman spectrum, electrochemical impedance, Potentiodynamic polarization and optical microscope were used to investigate the adsorption behavior and inhibition property of inhibitor on the metal surface. Moreover, we have also discussed the adsorption mechanism. The results are as follows:1. In this chapter, the copper electrodes were immersed into the PAC aqueous solution with different assembly conditions to form L–MTI modified copper electrodes. The inhibition efficiencies of PAC film with different assembly concentrations and time were investigated by using electrochemistry and spectroscopic methods, recorded in 3 wt% Na Cl solution. EIS and polarization curve results suggested the maximum inhibition efficiency η of 92.53 % is achieved at 5h and 10?3M. SERS spectrum elucidate the PAC molecules were chemically attaching to the copper surface via P–O groups as well as P=O groups. The adsorption of PAC film on the copper surface obeyed the Langmuir adsorption isotherm. Furthermore, the value of Gibbs energy revealed that reaction was via spontaneous process and mainly chemisorbed fashion.2. In this chapter, the aim of this work was to improve the inhibition efficiency of L–MTI coating through understanding the concentration–dependent and p H–dependent adsorption behavior of L–MTI molecules on the copper surface. All the experiments were done in neutral 3 wt% Na Cl solution. The maximum values of resistance, phase angle and the minimum value of corrosion current were observed when the assembly concentration is 10–2 M concentration and p H is 7. Electrochemical experiments suggested that inhibition efficiency is 95 %. At this optimum condition, the inhibition efficiency increased with increasing the assembly concentration and the maximum value of inhibition efficiency could reach up to 93.3 % for copper with L-MTI film. SERS showed that L-MTI molecules adsorped on the copper surface via C–S and C–N groups as well as COO– group to form the compact and uniform L–MTI film.3. In this chapter, we discussed the inhibition performance of amino acid derivatives MPG for metallic silver, to examine the possibility of amino acid derivatives used as corrosion inhibitor. Under the condition of different concentrations and p H, we mainly studied the compactness for MPG film and the adsorption conformation of MPG molecules on the silver surface. In case of the p H 7, MPG molecules were adsorped on the silver surface via formation of C-S groups. Based on electrochemical results and the related surface analyses, we concluded that the MPG films were not compact. But it can be effective in protecting the metal. |
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