【作者】 艾俊哲；

【导师】 郭兴蓬；

【作者基本信息】 华中科技大学 ， 材料学， 2006， 博士

【摘要】 大型复杂系统工程如海上石油钻采平台、苛刻复杂腐蚀环境中的油气井系统等在构建上不可避免地使用高等级耐蚀合金,耐蚀合金与碳钢的组合使用提高了系统整体可靠性和经济性。但异种金属组合产生的电偶腐蚀成为这些大型复杂系统工程中腐蚀控制的薄弱环节。大多数的缓蚀剂对电偶腐蚀的抑制效果较差,而关于缓蚀剂抑制电偶腐蚀机理方面的文献报道非常少。因此,开展电偶腐蚀及缓蚀剂抑制电偶腐蚀机理研究具有重大的理论与现实意义。论文采用腐蚀失重、极化曲线、交流阻抗、电偶电流、原子力显微镜及傅立叶红外光谱等实验方法研究了二氧化碳环境中S31803不锈钢与N80碳钢耦接产生的电偶腐蚀,以电极表面过剩电荷分布状态为切入点着重研究了二氧化碳腐蚀体系中偶合金属的电偶腐蚀行为、金属表面过剩电荷对缓蚀剂吸附行为的影响。通过实验揭示了缓蚀剂在电偶电极阴阳极区的吸附机理,进而根据电偶电极表面过剩电荷状态,有针对性地研究了缓蚀剂对电偶腐蚀的抑制作用与协同机制。主要研究结果如下:咪唑啉酰胺是一种性能优良的二氧化碳腐蚀缓蚀剂。该缓蚀剂主要抑制了碳钢在二氧化碳饱和的含氯离子介质中腐蚀的阳极过程,是一种阳极抑制型缓蚀剂。缓蚀剂在碳钢表面的吸附满足El-Awady动力学模型,符合Flory-Huggins吸附等温式。根据该模型,温度较低时一个咪唑啉酰胺分子取代了1或2个吸附水分子,占据了1或2个活性点;温度较高时一个咪唑啉酰胺分子至少取代了2个吸附水分子并占据了2个以上活性点。虽然咪唑啉酰胺对二氧化碳环境中碳钢腐蚀的抑制效率很高,但它与一些常用缓蚀剂一样对碳钢电偶腐蚀的缓蚀效率不高。饱和CO₂的含氯离子介质中,在金属自腐蚀电位下,不锈钢表面带有过剩正电荷,而碳钢表面带有过剩负电荷;两电极偶合后,在混合电位下,不锈钢表面带有过剩负电荷,而碳钢表面带有过剩的正电荷。偶合金属阴阳极区表面的过剩电荷与单独金属的表面过剩电荷状态具有显著的差异。月桂酸盐对碳钢在饱和CO₂的含氯离子介质中的腐蚀抑制效果较差,但对碳钢/不锈钢偶对的电偶腐蚀抑制效果较好。在加有月桂酸盐缓蚀剂的饱和CO₂的含氯离子介质中,不锈钢和碳钢表面均带有过剩正电荷。该缓蚀剂溶液中两电极偶合后,在混合电位下,不锈钢表面带有过剩负电荷,而碳钢表面带有过剩的正电荷。缓蚀剂在碳钢、不锈钢及偶对的阴阳极表面均能吸附,其在偶对阳极（碳钢）表面的吸附强度和覆盖度较之未耦合时增大。咪唑啉季胺盐化合物与KI对碳钢/不锈钢偶对的电偶腐蚀具有较好的协同抑制效果,抑制了电偶腐蚀的阴极过程。I-能显著改善电偶电极表面过剩电荷状态。加入KI后,咪唑啉季胺盐化合物与KI的协同作用增强了缓蚀剂在电偶电极表面的吸附,提高了对电偶腐蚀的抑制效果。金属表面过剩电荷的分布状态显著地影响缓蚀剂分子的吸附行为。在二氧化碳的含氯离子介质中,碳钢表面带有过剩负电荷,不锈钢表面带有过剩正电荷;碳钢与不锈钢耦接后,其表面电性均发生了逆转。具有阳离子特性的缓蚀剂能较好地吸附在带有过剩负电荷的金属表面而抑制金属腐蚀,但在带过剩正电荷的电偶对阳极表面的吸附较弱,使得其对电偶腐蚀的抑制作用也相应较差;阴离子缓蚀剂能较好地吸附在带过剩正电荷的电偶对阳极表面而对电偶腐蚀具有较好的抑制效果;无机阴离子能改善电偶对表面的过剩电荷状态,使得其阳极表面带过剩负电荷,其与阳离子缓蚀剂的协同作用显著增强缓蚀剂在电偶对阳极表面的吸附,从而较好地抑制电偶腐蚀。更多还原

【Abstract】 It is unavoidable to use noble anticorrosion alloys in huge complicated systems such as offshore drilling & recovery platform and oil & gas system in rigorous complex environment. The whole reliability and economy are improved by assembling the noble anticorrosion alloys and carbon steel. The safety problem arising from galvanic corrosion has been the weakest portion for corrosion protection in the systems. Most common corrosion inhibitors have poor inhibition on galvanic corrosion. Furthermore, reports of inhibition mechanism on controlling galvanic corrosion by inhibitors are rather few. Therefore, it is significant for both theoretical and practical aspects to investigate galvanic corrosion and inhibition mechanism of inhibitors.In this paper, galvanic corrosion of N80 carbon steel coupled with stainless steel in CO₂-containing corrosion media was investigated by various experimental methods including weight loss, polarization curve, electrochemical impedance spectrum, galvanic current, atomic force microscopy and Fourier transform infrared spectroscopy. By studying the distribution state of surface excess charge, the galvanic corrosion behavior and effect of surface excess charge on adsorption are stressed. The mechanism of inhibitor adsorption on both cathodic and anodic areas of galvanic electrode is proposed. Based on the charge distribution state of the galvanic electrode, special studies are carried out to make it clear the inhibition and synergistic effect on galvanic corrosion. The main results are listed blow.The inhibitor, imidazoline amide, is of anodic adsorption type and mainly inhibits anodic process of carbon steel corrosion in CO₂-saturated solution containing Cl-. It is also an effective corrosion inhibitor for carbon steel in this solution. The adsorption meets the El-Awady thermodynamic kinetic model, and is in line with the Flory-Huggins isotherm. According to the model, at relative lower temperature, an inhibitor molecule replaces one or two water molecules, and it occupies one or two active spots accordingly; at relative higher temperature, an inhibitor molecule replaces at least two water molecules, and it occupies more than two active spots accordingly.Although imidazoline amide has high inhibition efficiency for carbon steel in corrosion environment containing carbon dioxide, like some other corrosion inhibitors, it is non-effective for galvanic corrosion either. In CO₂-saturated solution containing Cl-, at their corrosion potentials, stainless steel and carbon steel carry positive and negative excess charges. However, when stainless steel and carbon steel is coupled in the same solution, at the mixed potential, stainless steel and carbon steel carry negative and positive excess charges respectively. The surface charges on cathodic and anodic areas of galvanic couple are much different from those on single metals.Sodium laurate is not effective for carbon steel corrosion in CO₂-saturated solution containing Cl-, but it is effective for galvanic corrosion of galvanic couple （stainless steel/carbon steel）. In the presence of laurate inhibitor, positive excess charges would be carried on both stainless steel and carbon steel. When stainless steel and carbon steel is coupled in the inhibitor solution, at the mixed potential, stainless steel and carbon steel carry negative and positive excess charges respectively. The inhibitor can adsorb to the surface of both carbon steel and stainless steel whether they are alone or coupled. Comparing to the adsorption on carbon steel uncoupled, the adsorbability and coverage of the inhibitor film on the carbon steel of the couple is bigger and larger.There exists synergistic inhibition on galvanic corrosion for the couple （stainless steel/carbon steel） between imidazoline quaternary compound and inorganic ion I-, they remarkbly inhibit the cathodic process of galvanic corrosion. Ion I- can improve the metal surface excess charge on galvanic electrode significantly. The adsorption is strengthened by the synergistic effect of quaternary compound and inorganic ion I-, thus the galvanic corrosion is well controlled.Surface excess charge on metals can significantly affect the adsorption behavior of inhibitors. In CO₂-saturated solution containing Cl-, at their corrosion potentials, stainless steel and carbon steel carry positive and negative excess charges respectively. However, charges change to be inverted when two metals are electrically coupled. Cationic inhibitors can adsorb on the metal carrying negative excess charge, thus the corrosion is inhibited; Cationic inhibitors are difficult to adsorb on the anode of galvanic couple carrying positive excess charge, thus is non-effective to galvanic corrosion. However, high inhibition efficiency for galvanic corrosion can be obtained by using anionic inhibitors. Inorganic anion can change positive charges into negative charges on the anode of the galvanic couple, thus helps cationic inhibitors to be easily adsorbed on it. The adsorption is strengthened remarkably by the synergistic inhibition of cationic inhibitor and inorganic anion, thus the galvanic would be better controlled.更多还原