铝阳极在氯化物溶液中的溶解行为与机理

【作者】 熊伟；

【导师】 郭兴蓬； 齐公台；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2011， 博士

【摘要】 铝合金是在含氯离子介质中应用广泛的牺牲阳极材料。虽然有很多关于铝阳极的研究,但是偏析相在铝合金阳极溶解过程中的电化学行为、偏析相影响铝阳极溶解的机理以及铝阳极微观组织结构与宏观电化学性能的关联性是改进铝阳极性能的关键性问题,缺乏系统性的研究。本文制备了Al-Zn-In-Sn、Al-Zn-In-RE、Al-Zn-In-Te和Al-Zn-In-Sn-Te四种阳极,通过线性极化、交流阻抗、ICP-MS及扫描电镜等技术研究了不同固溶处理时间及溶液中Sn4+离子对铝阳极溶解过程的影响,探讨了氯化钠溶液中添加不同浓度的CeCl3时铝阳极的溶解机理,同时研究了添加Te元素的新型铝阳极的电化学性能和溶解机理,以及在阳极铸造过程中不同的保温时间对铝阳极电化学性能的影响。研究结果表明在Al-Zn-In-Sn及其固溶处理后的试样中Sn元素富集于晶界上的半球形偏析物。铝阳极的活化溶解开始于半球形偏析物,Sn元素作为阳极相优先溶解。Al-Zn-In-Sn固溶处理后电流效率提高,析氢自腐蚀降低,开路电位更负,具有更高的活性,表现出优良的牺牲阳极性能。但当Al-Zn-In-Sn阳极固溶处理时间过长时将导致偏析相减少并出现断裂的现象,并且含有Sn的半球形偏析物中Mg富集明显,自腐蚀严重,恶化了电化学性能。Sn4+增强了Al-Zn-In和Al-Zn-In-Sn阳极的表面活性,促进了阳极的活化溶解,并且提高了铝阳极的电流效率。在添加了SnCl₄的氯化钠溶液中,Al-Zn-In-Sn阳极的腐蚀比Al-Zn-In阳极更加均匀。稀土合金元素和氯化物溶液中的Ce3+离子改善了Al-Zn-In日极的电流效率Al-Zn-In日极在加入了CeCl3的氯化钠溶液中的阳极溶解开始于Ce富集的圆形沉积物附近。大多数含Ce的圆形沉积物分布在Al基体。Ce的沉积促进了铝牺牲阳极表面的活化。溶液中添加的Ce3+抑制了Al-Zn-In-RE阳极中合金元素Ce的活化溶解。添加了合金元素Te的Al-Zn-In-Te阳极具有更低含量的有害物质Fe和Si,更低的腐蚀电位,较低的自腐蚀速率和更高的电流效率。Al-Zn-In-Sn-Te系列阳极比Al-Zn-In-Te阳极腐蚀电位更负,电流效率更高。但过量的Te导致铝阳极的电化学性能损失。添加Te元素的Al-Zn-In-Te阳极的腐蚀开始于在晶界和晶间上Zn和Te富集的半球形偏析相。铸造过程中适当增加保温时间能使铝阳极的活化元素在半球形偏析物中更加富集,促进铝阳极表面活化,减少析氢自腐蚀,提高电流效率。当保温时间过长,达到45min时,铝阳极表面的偏析相大量减少,抑制了活性元素在铝阳极表面的富集,降低铝阳极表面活性。偏析相的数量和分布影响腐蚀形貌和电化学性能。更多还原

【Abstract】 Al alloys were widely used as sacrificial anodes in the solution containing chloride ion. Although there were many investigations on the Al anodes, the electrochemical behavior of segregations in the dissolution processes of Al anodes, the effect of segregations on the dissolution mechanism of Al anodes and the relationship between microstructure and macroscopic electrochemical properties of Al anodes had important effect on the properties of Al anodes, which needed systematic investigations. Four kinds of Al anodes were prepared, such as Al-Zn-In-Sn, Al-Zn-In-RE, Al-Zn-In-Te and Al-Zn-In-Sn-Te. The effect of different solution treatment time and Sn4+ in the solution on the dissolution processes of Al anodes was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, inductively coupled plasma mass spectrometry and scanning electron microscopy with energy-dispersive X-ray analysis techniques. The dissolution mechanism of Al anodes in the NaCl solution with different concentration of CeCl3 was studied. Meanwhile, the electrochemical properties and dissolution mechanism of new Al anodes with Te as the alloying element were investigated. Furthermore, the effect of different heat reservation treatment time on the electrochemical properties was investigated.The results showed that Sn element was enriched in the hemispherical segregations at the grain boundary of Al-Zn-In-Sn anode after solution treatment. The active dissolution initiated at the hemispherical segregations and Sn as the anodic phase dissolved first. After the solution treatment, Al-Zn-In-Sn anodes exhibited higher current efficiency, lower self-corrosion of hydrogen evolution, more negative open-circuit potential, and more active surface, which were desirable for sacrificial anodes. After the overlong time of solution treatment, Al-Zn-In-Sn anodes exhibited less and broken segregations, and the enrichment of harmful Mg in the hemispherical segregations containing Sn, which caused serious self-corrosion and loss of electrochemical properties. Sn4+ enhanced the activation on the surface and the active dissolution, and improved the current efficiency of Al anodes. In the NaCl solution containing SnCl4, the Al-Zn-In-Sn anode exhibited a more even corrosion than the Al-Zn-In anode.RE as the alloy element and Ce3+ as the additive in a chloride solution, enhanced current efficiency for Al alloys. The anodic dissolution of Al-Zn-In anodes, in the NaCl solution with the addition of CeCl3, began around the hemispherical precipitations where Ce is enriched. Major hemispherical precipitations containing Ce were distributed in the Al matrix. The precipitations of Ce enhanced activation on the surface of Al anodes. Ce3+ as the additive in the solution inhibited the active dissolution of Ce as the alloying element of the Al-Zn-In-RE anode.With the addition of Te as the alloying element, the Al-Zn-In-Te anode exhibited lower harmful impurity content of Fe and Si, more negative corrosion potential, the lower self-corrosion and higer current efficiency. Al-Zn-In-Sn-Te series anodes showed more negative corrosion potential and higher current efficiency than Al-Zn-In-Te series anodes. However, excessive addition of Te led to the loss of electrochemical properties of Al anodes. The corrosion of the Al-Zn-In-Te anode initiated at the Zn and Te enriched hemispherical segregation in grain boundaries and interdendritic zones.Properly increasing the time of heat reservation treatment during the cast process could enrich the active element in the hemispherical segregations of Al anodes, enhance the activation on the surface of Al anodes, reduce the self-corrosion of hydrogen evolution, and improve the current efficiency. Al-Zn-In-Sn anodes after the overlong time (45min) of heat reservation treatment exhibited much less segregations and the inhibition of enrichment of the active element on the surface of Al anodes which led to the inactivation on the surface of Al anodes. The quantity and distribution of segregations influenced the corrosion morphology and the electrochemical performance.更多还原