| Admittedly, copper, as a traditional industry metal material, has been extensively used in harsh surroundings due to its mechanical workability, thermal conductivities and corrosion resistance. Particularly its noble character, to some extent, exhibits more excellent performance compared with other metals. However, in marine media, the existence of chloride ion is inevitable, which will significantly restrict the engineering applications of copper in industry. Currently, numerous effective methods have been taken to alleviate the corrosion of copper and its alloys. Among them, the use of inhibitors is a cost-effective and practical choice to protect copper and its alloys in marine medium. Particularly those organic compounds, which mainly contain either N, O, S atoms or π-bonds, have attracted a lot of attention as inhibitors for the aqueous corrosion of copper. Organic molecules, which can donate electrons to unoccupied d-orbitals of metal atoms to form coordinate covalent bonds and can also accept free electrons from the metal surface by using their anti-bonding orbitals to form feedback bonds, demonstrate excellent corrosion inhibition as inhibitors. Unfortunately, many widely used inhibitors are harmful to humans, hazardous to environment and difficult to be degraded by microorganism. Therefore, it is necessary to develop green and high-efficiency organic molecules as new and better copper inhibitors. Because pharmaceutical drugs ubiquitously consist of carbocyclic and heterocyclic systems and most of them are non-toxic to human health and aquatic environment. The use of pharmaceutical drugs as corrosion inhibitors for metals in diverse aggressivesurroundings has attracted much attention in these years. Some antibiotics, such as cloxacillin, fluconazole, ketoconazole and azithromyrin, have demonstrated their good applicability in the corrosion inhibition of metals in various harsh environments.At the same time, among various approaches to improve the protective efficiency of copper in corrosive environment, self-assembled monolayer of organic inhibitors also has been proved to be one of the most fascinating approaches owing to its high efficiency and convenient operation. Self-assembled monolayer is usually formed through a simple chemisorptions process, conform like a kind of ultra thin hydrophobic coatings and offers great prospect to protect metal substrate from corrosion. Currently, substantial organic inhibitive compounds have been investigated, such as benzotriazole, thiol, dithiol and dithiocarboxylic, silane, triazinedithiol. Considering that each category of organic inhibitors possesses limited functional groups which either react with copper surface or resist corrosion limitedly, attentions are mainly concentrated on developing more desirable inhibitors, which means not only more reactive sites to generate a highly packed self-assembled monolayer but excellent hydrophobic property, isolating metal from corrosive media. Thiol, which could react with metal and form chemical chelates with metal, is considered as one of the most desirable functional groups. Moreover, Hydrophobic groups, such as hydrocarbon, phenyl or aromatic derivative and chain alkane, are in possession of the ability to separate metal from corrosive agents, water and chloride ions, for example. According to many experiments, if a molecule consists of both thiol and hydrocarbon groups, it will probably be an effective inhibitor to preserve copper in corrosive conditions.In this paper, our work consists of three parts:Firstly, 4,6-diamino-2-mercaptopyrimidine(DAMP), which is a non-poisonous, economical and eco-friendly medical intermediate and commonly used in biological field, was selected as a corrosion inhibitor for copper. DAMP contains a mercapto group, two amino groups and a nitrogen-containing six-membered heterocyclic ring. The inhibition effect of DAMP as a corrosion inhibitor for copper in 3.5 wt.% Na Cl solution was investigated by using weight loss measurement, electrochemical impedancespectroscopy(EIS) and potentiodynamic polarization. The surface morphologies were observed by scanning electron microscopy(SEM) and energy dispersive spectrometer(EDS). Quantum chemical calculation using density functional theory(DFT) was employed to explain the experimental results obtained in this study and to give further insight into the inhibition action of DAMP on the copper surface.Secondly, self-assembled monolayers(SAMs) formed by 1,3,5-Benzenetrithiol(BTT) and TBBT on the surface of copper were explored in our study for the first time. SAMs formed by BTT and 4,4’-Thiobisbenzenethiol(TBBT) as a copper inhibitor is investigated in 3.5 wt.% Na Cl solution by means of weight loss measurement and electrochemical methods. Scanning electron microscopy(SEM), as well as contact angle, is used to examine the surface morphologies and Fourier transform infrared(FTIR) is used to detect the compositions of the copper surfaces. The integral adsorption configuration of BTT molecule on Cu(1 1 1) was established by molecular stimulation. Other theoretical methods were also applied to analyzing the interactive reaction mechanism between BTT and TBBT molecule and copper surface.1. Experimental and theoretical studies of 4,6-diamino-2-mercaptopyrimidine as a copper inhibitor in 3.5 wt.% Na Cl solution.Inhibition effect of 4,6-diamino-2-mercaptopyrimidine(DAMP) as a copper corrosion inhibitor in 3.5 wt.% Na Cl solution was investigated by weight loss, electrochemical impedance spectroscopy, and potentiodynamic polarization. The inhibition efficiency increased with increasing DAMP concentration in the range of 1.0 to 2.0 m M DAMP and decreased with increasing temperature. The obtained results showed that DAMP inhibited both the anodic and cathodic currents and the maximum inhibition efficiency reached 93.2% at 2.0 m M DAMP. The inhibition performance of DAMP was confirmed by SEM and EDS. Quantum chemical calculations revealed that the DAMP molecule was adsorbed on copper surface in a paralleled way through S, N atoms and pyrimidine ring. Adsorption of DAMP was found to obey the Langmuir adsorption isotherm2. Investigation of corrosion inhibition performance of 1,3,5-benzenetrithiol self-assembled monolayer on copper in 3.5 wt.% Na Cl solutionCorrosion inhibition performance of 1,3,5-benzenetrithiol(BTT) self-assembled monolayer on copper was investigated by weight loss, electrochemical impedance spectroscopy and potentiodynamic polarization. The obtained results showed that BTT self-assembled monolayer could suppress both anodic and cathodic currents remarkably, which means that BTT molecule worked as a mixed inhibitor. The maximum value of inhibition efficiency reached 92.2% at 1 m M BTT. Scanning electron microscope and energy dispersive spectrometer were employed to give further insights of the adsorption of BTT. Quantum chemical calculations indicated that the BTT molecule could be adsorbed on copper surface in a paralleled way through S atoms. Adsorption of BTT was found to follow the Langmuir adsorption isotherm.3. Inhibition of copper corrosion in 3.5 wt.% Na Cl solution by modification of 4,4’-Thiobisbenzenethiol self-assembled monolayer4,4’-Thiobisbenzenethiol(TBBT) self-assembled monolayer(SAM) was prepared on copper surface and investigated by weight loss measurement and electrochemical methods. The results indicated that TBBT can inhibit both the anodic and the cathodic corrosion of copper and the inhibition efficiency of TBBT are closely associated with concentrations and assembly time. FT-IR and contact angle(CA) results confirmed the adsorption of TBBT SAM and formation of a hydrophilic film. Quantum chemical calculations were employed to analyze the structure of TBBT and correlate the adsorption mechanism between TBBT molecule and copper surface. Adsorption of TBBT on copper surface obeys the Langmuir isotherm. |
PDF Full Text Request