碳钢缓蚀剂和铜基自组装膜的研究

【作者】 陈文；

【导师】 李念兵；

【作者基本信息】 西南大学 ， 分析化学， 2012， 博士

【摘要】 铜和钢作为重要的常用金属材料,被广泛地应用于交通运输、建筑、机械、化工、电子、国防工业等领域。由于它们的化学性质较为活泼,在使用环境中易被腐蚀。尤其在比较恶劣的条件下,比如在酸液、含氧水中及含C1-,S042-等离子的溶液中腐蚀会更加强烈。因此,铜和钢的腐蚀防护问题一直受到腐蚀科学领域学者们的密切关注。常用的金属腐蚀防护技术中,合理添加缓蚀剂是一种有效的防腐手段。随着人们环境保护意识的增强,高效、环保型缓蚀剂的开发和研究成为当今腐蚀科学的重要课题之一自组装膜是活性分子通过化学键自发吸附在固/液或固/气界面,从而形成具有一定取向、排列紧密的有序分子膜,属于热力学稳定体系。自组装成膜制备方法简单,不受基底形状限制,且形成的膜致密有序,成为具有广泛应用前景的成膜技术之一。金属表面上组装高效的缓蚀剂分子不仅可拓宽缓蚀剂的应用范围,而且自组装膜技术可以通过分子设计和优化组装过程来改变组装膜的物化性质,这就为在二维乃至三维领域内研究其物理性质提供了可能,也为进一步探索缓蚀剂的作用机理,研究和开发新型缓蚀剂开拓了新途径。本文研究工作共分两个部分：第一部分,选取了有机杂环化合物和有机磷酸盐作为缓蚀剂,分别研究了它们在硫酸和氯化钠溶液中对碳钢的缓蚀行为,并结合现代表征技术和量化计算对相应的缓蚀机理进行了阐释。第二部分,利用杂环化合物多吸附中心的特点在铜基上组装了缓蚀功能膜,运用电化学方法研究了组装膜在不同腐蚀介质中对铜的腐蚀抑制行为,考察了组装条件对膜质量的影响,并对膜的吸附和缓蚀机理进行了探索。主要研究工作如下：1.2,5-二巯基-1,3,4-噻二唑在硫酸中对碳钢的缓蚀行为研究运用失重法和电化学方法研究了2,5-二巯基-1,3,4-噻二唑(DMTD)在硫酸中对碳钢的腐蚀抑制行为,并采用扫描电子显微镜(SEM),傅立叶变换红外光谱(FTIR)对碳钢表面缓蚀剂的吸附进行表征和分析。Tafel曲线结果说明DMTD作为一种混合型缓蚀剂抑制了碳钢在硫酸中的腐蚀,但并未改变阴极氢气析出的机制。极化电阻和电化学阻抗图谱(EIS)测试显示,DMTD的添加改变了碳钢表面的双电层结构,增大了腐蚀反应的极化电阻。由失重实验数据求得相关热力学和动力学参数,分析结果表明DMTD分子在碳钢表面的吸附是个自发的放热过程且满足Langmuir吸附等温模型。电容-电位曲线测试表明DMTD吸附前后的碳钢表面在硫酸中均带有正电荷。根据实验结果和计算的量子化学参数,DMTD分子在碳钢上的吸附机理可能是以静电引力和共价键的形成为驱动力的混合吸附过程。2.复合膦(磷)酸盐在氯化钠溶液中对碳钢的缓蚀行为研究利用Tafel曲线、电化学阻抗图谱研究了三聚磷酸钠和苯乙烯膦酸钠对碳钢在3%氯化钠溶液中的缓蚀性能。Tafel曲线结果表明,三聚磷酸钠为阳极型缓蚀剂,而苯乙烯膦酸钠为混合型缓蚀剂,对钢的阴、阳极腐蚀反应有明显的抑制。相比于单种缓蚀剂,复合膦(磷)酸盐对碳钢有更好的腐蚀抑制作用。同时,电化学测试表明复合膦(磷)酸盐在钢表面存在竞争性吸附,不利于保护膜的生成。3.5-巯基-3-苯基-1,3,4-噻二唑-2(3H)硫酮钾盐自组装膜在氯化钠溶液中对铜的缓蚀行为研究在铜电极表面制备了5-巯基-3-苯基-1,3,4-噻二唑-2(3H)硫酮钾盐(MPTT)自组装膜。利用Tafel曲线和电化学阻抗图谱考察了自组装条件对自组装膜缓蚀性能的影响,结果显示,较高的MPTT浓度、合适的组装时间、适当的高温有助于增强自组装膜的缓蚀能力。自组装吸附过程包括初始期的快速吸附和后期的结构重排。适当的延长组装时间和提高组装温度有助于MPTT分子重排而得到一个低缺陷的自组装膜。同时发现MPTT的吸附满足Langmuir吸附等温式,并且是一个自发的混合性的吸附过程。根据量化计算,红外光谱和接触角测试等结果,MPTT分子可能是以原子S和N作为吸附中心,取代基苯环通过π-π相互作用排列在吸附层外部,从而形成一个致密的疏水性保护膜。4.三聚硫氰酸自组装膜在盐酸中对铜腐蚀的缓蚀行为研究利用自组装技术在硝酸刻蚀的铜基上自组装了三聚硫氰酸(TTCA)薄膜。红外光谱证实了TTCA分子在铜表面的吸附,接触角测试和扫描电子显微镜显示自组装膜为亲水性的层状吸附结构。运用电化学方法研究了自组装膜对铜在盐酸中的腐蚀抑制行为,发现自组装膜的缓蚀性能与组装浓度和组装时间有关,最佳条件为在2.5mM TTCA乙醇溶液中组装12小时。Tafel曲线测试表明自组装膜作为混合型缓蚀剂抑制了铜的阴、阳极腐蚀反应,最高缓蚀效率达到91.2%。电化学阻抗图谱说明TTCA分子在铜表面的吸附降低了金属/溶液界面的电容,增大了腐蚀反应的电荷转移电阻。量子化学计算结果显示,TTCA分子的吸附可能以物理吸附为主,原子S和N以在金属表面成键的方式参与吸附。5.三聚硫氰酸自组装膜在氯化钠中对铜腐蚀的缓蚀行为研究采用浸泡法在不同pH值的TTCA水溶液中将TTCA分子组装在未刻蚀的铜基表面。运用电化学阻抗图谱对组装条件进行优化,测试表明在0.1mM TTCA酸性(pH=4.25)水溶液中浸泡3小时制备的自组装膜对铜具有更好的缓蚀效果。同时,通过改变溶液中氯离子浓度和浸蚀时间来考察自组装膜的耐蚀性能,发现自组装膜在氯化钠溶液中具有较好的稳定性和耐蚀性。根据电化学实验、红外光谱、接触角测试等结果,TTCA在酸性水溶液中的自组装膜可能是由TTCA分子和[Cu-TTCA]络合物组成的混合膜,它作为一个阻止溶液中氧和氯离子侵蚀铜基的屏障,有效地保护了基底金属。更多还原

【Abstract】 Copper and steel are primary metallic materials and are widely used in transportation, construction, machinery, chemicals, electronics, national defense industry, and so on. But they are susceptible to corrosion in the environment due to their active chemical nature. They would be corroded markedly especially in harsh conditions, such as acid solutions, aqueous solutions containing Cl-, SO42-and dissolved oxygen. Thus, the corrosion of copper and steel has become an important subject for the corrosion researchers. The use of inhibitor is an effective method in common corrosion protection technology. With increased environmental awareness, the development and investigation for highly efficient and environmentally friendly corrosion inhibitors has been an important issue t issue in the field of corrosion science.Self-assembled monolayers (SAMs) are well ordered and dense monolayers formed by the spontaneous adsorption of active molecules via chemical bonds on the solid/liquid or solid/gas interface, which are belong to the thermodynamic stability system. Because the preparation method for self-assembled monolayers is simple, independent of substrate shape, and the film formed is compact, it has become one of the film technologies with broad application prospects. Efficient inhibitor molecules assembled on the metal surface could widen the scope of application of the inhibitor. Furthermore, self-assembly technology could adjust the physical and chemical properties of the assembled film by designing molecule and optimizing the assembly process. This offers the possibility to study physical properties of inhibitors in two-dimensional and even three-dimensional field for exploring their inhibition mechanism, and provides a new avenue to develop and research new-type corrosion inhibitors.In this paper, the work is divided into two parts:The first, we selected an organic heterocyclic compound and an organic phosphonate as inhibitors, and investigated their inhibition performance on the corrosion of mild steel in sulfuric acid and sodium chloride solution, respectively. The corresponding inhibition mechanisms were discussed based on the modern characterization techniques and quantum chemical calculations.The second, some heterocyclic compounds with multi-center adsorption sites were assembled on copper surface. The electrochemical methods were used to investigate the inhibition effects of self-assembly monolayers on the copper in different corrosive media and influence of assembly conditions on the SAMs quality. The relevant adsorption and corrosion inhibition mechanism of SAMs have also been explored.1. Inhibition effect of2,5-dimercapto-1,3,4-thaidizole on the corrosion of mild steel in sulphuric acid solutionThe effect of2,5-dimercapto-1,3,4-thaidizole (DMTD) on the corrosion of mild steel (MS) in sulphuric acid solution was investigated using weight loss and various electrochemical techniques. Scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy were used to determine characteristic of the inhibitor adsorbed on the carbon steel. The results of Tafel curves indicated the DMTD acted as mixed-type inhibitor for corrosion of carbon steel, but did not change the mechanism of the cathodic hydrogen evolution. Linear polarization resistance and electrochemical impedance spectroscopy (EIS) measurements revealed that the addition of DMTD changed the electrical double layer structure of the carbon steel surface and increased the polarization resistance of the corrosion reaction. Relevant thermodynamic and kinetic parameters obtained by the weight loss measurement showed that the adsorption of DMTD molecules on the carbon steel surface is a spontaneous and exothermic process and obey the Langmuir isothermal adsorption model. Capacitance-potential curve tests indicated carbon steel surface in sulfuric acid carried positive charges before and after adsorption of DMTD molecules. According to the results of experiments and quantum chemical parameters, the adsorption mechanism of DMTD on carbon steel surface could be a mixed adsorption process through both the electrostatic attraction and formation of covalent bond as driving forces.2. Inhibition effect of a composite phosphonate on the corrosion of mild steel in sodium chloride solutionsTafel curves and electrochemical impedance spectroscopy were used to investigate the inhibition effect of sodium tripolyphosphate and sodium1-phenylvinyl phosphate on the carbon steel corrosion in3%sodium chloride solution. Tafel curves tests revealed sodium tripolyphosphate acted as an anodic inhibitor, but sodium1-phenylvinyl phosphate was a mixed-type inhibitor with strong inhibition performance on both the anodic and cathodic corrosion reaction. Compared with single inhibitor, composite inhibitors performed a better corrosion inhibition on carbon steel. At the same time, the electrochemical tests revealed that a competitive adsorption would occur between the two kinds of inhibitors in composite phosphonate system, which is disadvantageous for the formation of protective film.3. Potassium5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione self-assembled monolayer against copper corrosion in sodium chloride solutionPotassium5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione (MPTT) was self-assembled on copper surface. The influence of assembly conditions on the SAM inhibition properties was investigated by Tafel curves and EIS measurements, and the results indicated that high MPTT concentration, suitable assembly time, and elevated temperature could enhance the inhibitive effect of SAM on copper corrosion under experimental conditions. The self-assembly process includes initial fast adsorption and following structural rearrangement stage. Suitable prolonging assembly time and elevating assembly temperature could promote the rearrangement process of MPTT molecules, and decrease defect density of the SAM on copper surface. It was also found that the adsorption of MPTT obeys the Langmuir adsorption isotherm, and is a spontaneous and composite adsorption process. According to quantum chemical calculations, infrared spectroscopy and contact angle measurement, MPTT molecules may be adsorbed on the copper through the electronegative atoms S and N as adsorption centers, and substituent benzene ring was arranged outside the adsorption layer through π-π interactions, thus forming a compact and hydrophobic protective film.4. Inhibition of copper corrosion in hydrochloric acid solution by the self-assembled monolayers of trithiocyanuric acidThe trithiocyanuric acid (TTCA) molecules were prepared on the etched copper surface in ethanol solution by using self-assembly technique. The FTIR confirmed that the TTCA molecules were adsorbed on the copper surface, and the contact angle and SEM measurements revealed the self-assembly film has a layered structure with hydrophobic nature. The inhibition effect of self-assembly film on the copper corrosion was investigated by electrochemical methods and the results revealed that it was related to the assembly concentration and assembly time. The optimal condition for assembly process is immersion in2.5mM TTCA ethanol solution for12h. Tafel curves tests showed that the self-assembled monolayers acted as a mixed type inhibitor against both cathodic and anodic corrosion reactions, and the highest inhibition efficiency reached91.2%. EIS measurement indicated TTCA molecules adsorbed on copper surface decreased the total capacitance of the metal/solution interface, and increased the charge-transfer resistance of the corrosion reaction. Quantum chemical calculations showed that the adsorption of TTCA molecules may be dominated by physical interaction, and the electronegative atoms of S and N may participate in bonding with the metal surface.5. Corrosion inhibition of copper in sodium chloride solution by self-assembled monolayers of trithiocyanuric acidThe trithiocyanuric acid (TTCA) molecules were assembled on the non-etched copper surface in aqueous solution at different pH values by using immersion method. The assembly conditions were optimized by using electrochemical impedance spectroscopy measurements, and the results revealed that the TTCA films could provide better protection performance against copper after3h of assembly in0.1mM TTCA acidic aqueous solution. Meantime, the inhibition performance of the films was investigated by changing the concentration of chloride ions and the corrosive immersion time of TTCA-modified electrodes in corrosive media, and the results revealed that the TTCA films possess good stability and durability in sodium chloride solution. According to electrochemical experiments, FTIR and contact angle measurements, the TTCA film assembled in acidic solution could be mixed films involving TTCA molecules and [Cu-TTCA] complex, which could act as a barrier to hinder aggressive species from attacking the underlying copper substrate and provide good protection for copper in sodium chloride solution.更多还原