【作者】 袁传军；

【导师】 梁成浩；

【作者基本信息】 大连理工大学 ， 化学工程， 2010， 博士

【摘要】 铝、锌、镁及其合金是阴极保护系统中常用的电极材料。然而,铝合金牺牲阳极的溶解不均匀,锌参比电极在海水中的环境影响,以及镁合金牺牲阳极在青藏高原低温冻土层中的电化学性能的研究报道较少。因此,研究铝合金牺牲阳极的溶解不均匀性、锌参比电极在海水中的环境影响和镁合金牺牲阳极在冻土层中的电化学性能具有重要的现实意义。本文采用电化学测试技术,研究了合金元素Ga对Al-Zn-In系合金牺牲阳极的作用,考察了海水中的各种因素对锌参比电极电位稳定性的影响,并探讨了冻土层中镁合金系列牺牲阳极的电化学性能,借助扫描电镜、X-射线衍射等现代物理测试技术进行了表征,深入研究了合金元素作用机理和电极溶解机理。结果表明：Ga均匀地固溶于铝合金中,而In在阳极表面产生局部富集、形成富In第二相。随着Ga含量的增加,Al-Zn-In阳极工作电位负移,电流效率下降,孔蚀愈严重。在模拟海水中,Al-4%Zn-0.022%In-0.015%Ga牺牲阳极工作电位为-1039 mV,电流效率为96.3%,溶解均匀,具有良好的阳极极化性能和耐孔蚀性能,是一种理想的新型高效牺牲阳极；Al-In-Zn-Ga合金由于In3+的活化作用,破坏了表面钝化膜,使电极电位显著负移,从而激活了Ga3+的活性,使得Ga3+、In3+、Zn2+等产生共同沉积,维持了较高的阳极活性溶解,导致了合金的“溶解—再沉积”的过程。高纯锌、Zn-Al-Cd合金在海水、淡海水和淡水中电位稳定,适宜充当长效参比电极,其中Zn-Al-Cd合金的电化学性能较佳。在Cl-浓度小于0.1496 mol/L的溶液中,随着Cl-浓度的增大,锌电极电位呈线性负移的趋势；但当Cl-浓度大于0.1496 mol/L时,锌的电极电位基本不受Cl-浓度的影响。海水pH值对高纯锌、Zn-Al-Cd合金电位影响不明显。海水流速增加,锌电极电位正移。10μA/cm2的阳极电流明显改善高纯锌的电极电位稳定性；高纯锌、Zn-Al-Cd合金表面膜主要由ZnO、Zn2(OH)2CO3等组成,Cl-、金属表面微观组织的不均匀性等因素的作用产生小范围的电位波动。青藏高原冻土层中,高纯镁的腐蚀电位最负,MGAZ31B镁合金阳极的腐蚀电位最正；合金的溶解活性依次为MGAZ63B镁合金、MGAZ31B镁合金、MGMlC镁合金和高纯镁；MGAZ63B镁合金电化学性能较优,工作电位为-1630 mV,电流效率为61.77%,适宜做冻土层中的牺牲阳极。镁合金阳极表面呈现出沟槽或第二相腐蚀,腐蚀表面的主要元素为Mg、O以及镁合金中的基体元素,主要腐蚀产物为Mg(OH)2。以边界元为计算方法,应用Matlab为开发工具,计算出的冻土层中镁牺牲阳极-碳钢热管阴极保护系统中碳钢表面的电位分布与实测值的误差最大不超过10%,说明电位的数值计算是可靠有效的,为今后稳定冻土层路基和铺设管道阴极保护设计提供了参考。更多还原

【Abstract】 Aluminum, zinc, magnesium and their alloys are commonly used in CP engineers. But, research work such as local dissolution of aluminum alloy sacrificial anodes, effects of external mediums on zinc reference electrodes in seawater, electrochemical performances of magnesium alloy sacrificial anodes in Qinghai-Tibetan plateau frozen soil have not been reported. Therefore, study on the above-mentioned problems is of importance. Centered on the above problems, electrochemical methods were used to study the followings: effects of Ga on Al-Zn-In performances, effects of medium on zinc reference electrodes in seawater, magnesium alloy performance in frozen soil. Modern physical methods including SCE and XRD were used to characterize some relevant problems in order to discuss the activation mechanism and dissolution mechanism.Results show:Ga dissolves in the alloy uniformly but In segregates in the boundary, which forms a In-rich secondary phase. With the increase of Ga contents, the work potential of Al-Zn-In anodes shifts to a more negative value, the current coefficient drops and more serious pit corrosion happens. Al-4%Zn-0.02%In-0.015%Ga alloy is a kind of new ideal high-effective anode in man-mad seawater because of its potential (-1039 mV), current efficiency (96.3%), uniform dissolution, excellent anodic polarization performance and resistance to pit corrosion. In3+destroys the passivation membrane and shifts the potential to a more negative value and activates Ga3+. This promotes ions including Ga3+, In3+and Zn2+to precipitate together and maintains the dissolution of Al-Zn-In alloy. The process is called "dissolution-reprecipitation".Both high purity zinc and Zn-Al-Cd alloy are liable to establish a stable potential in seawater, diluted seawater and tap water. The two electrodes could be used as reference electrodes in cathodic protection engineering. The performance of Zn-Al-Cd alloy reference electrodes is better than that of high purity zinc. When Cl- concentration is below 0.1496 mol/L in tap water and diluted seawater, zinc electrode potentials shows a linear relationship with the increase of Cl" concentration. When Cl- concentration is higher, zinc electrode potentials have no relationships with Cl- concentration. As seawater flow velocity goes up, zinc potentials shift to more positive values. Seawater pH has no obvious effect on zinc potentials.10μA/cm2 anodic current improves the potential stability of high purity zinc remarkably. In simulated frozen soil, open potential of high purity magnesium is the most negative one and that of MGAZ31B is the most positive one. The sequence of dissolution activation and reaction activation from high to low is MGAZ63B, MGAZ31B, MGMIC and pure magnesium. Electrochemical performance of MGAZ63B with higher current efficiency is the best, MGAZ63B is suitable to act as a sacrificial anode in Qinghai-Tibetan plateau frozen soil. Grooving corrosion or secondary phase corrosion presents on the surface. The main elements appearing on the surface include Mg, O and bulk elements, which mainly form Mg(OH)2.Potential distributions on the steel protected by magnesium were calculated by BEM and Matlab. The errors between calculated potential, and measured ones is less than 10 percents. This illustrate that numerical calculation is reliable and effective. Numerical calculation could serve for the further CP in frozen soil.更多还原