In situ aqueous stability of Mg-Li-(Al-Y) alloy: role of Li

P. Volovitch, A. Maltseva, Yuan-Wei Yan, K. Ogle, N. Birbilis
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Abstract

The role of lithium in the mechanisms of aqueous stability of Mg-Li alloys was explored by combining in situ and ex situ surface and solution characterization. In situ surface evolution of a corrosion resistant Mg-Li(-Al-Y-Zr)-alloy in aqueous NaCl solution was studied by confocal Raman Microscopy and Kinetic Raman Mapping [1], real time solution analysis was made with Atomic Emission SpectroElectroChemistry [2]. Additional ex situ surface characterizations by Photoluminiscence Spectroscopy, Auger Electron Spectroscopy and Glow Discharge Optical Emission Spectroscopy were made immediately after the aqueous exposure and after exposure to ambient air. In situ analyses demonstrated that both Li and Mg dissolved in aqueous solutions from visually intact anodic areas, leaving a Li-depleted metallic layer under an approximately 100 nm thick Li-doped MgO. Interestingly, in these areas the growth of magnesium hydroxide (Mg(OH)2) was very slow than in pure Mg, suggesting that the kinetics of the transformation MgO→Mg(OH)2 was strongly inhibited. On the cathodic areas, local accumulation of Li2[Al2(OH)6]2·CO3·nH2O (Li-Al layered double hydroxide), LiAlO2, Y2O3 and Mg(OH)2 was observed. Li2CO3, previously considered as a component of a protective film responsible for corrosion resistance of Mg-Li alloys [3], was not present in situ on the surface evolving in aqueous solution and was detected only ex situ after the exposure to ambient air. The proposed corrosion mechanism attributes the improvement of aqueous corrosion resistance of Mg-Li alloys to the increase of the chemical stability of MgO doped by Li+ [4]. The latter could be formed thanks to selectively leached in the solution Li+. Additionally, cathodic activation of Mg can be reduced on Li-doped MgO and Li-Al layered double hydroxide, detected in situ on cathodic areas. Pilling Bedworth ratios (PBR), calculated for lithium doped MgO film on Mg-Li alloys with different Li content, demonstrated that the condition of a protective film on Mg-Li alloy (PBR>1) requires a minimal Li concentration in the alloy close to 15-18 at. %. [1] A. Maltseva, V. Shkirskiy, G. Lefevre, P. Volovitch, Corrosion Science, 153 (2019) 272-282. [2] Y. Yan, P. Zhou, O. Gharbi, Z. Zeng, X. Chen, P. Volovitch, K. Ogle, N. Birbilis, Electrochemistry Communications, 99 (2019) 46-50 [3] L. Hou, M. Raveggi, X.-B. Chen, W. Xu, K.J. Laws, Y. Wei, M. Ferry, N. Birbilis, Journal of The Electrochemical Society, 163 (2016) C324-C329 [4] Y.M. Yan, A. Maltseva, P. Zhou, X.J. Li, Z.R. Zeng, O. Gharbi, K. Ogle, M. La Haye, M. Vaudescal, M. Esmaily, N. Birbilis, P. Volovitch, Corrosion Science, 2020, 164, 108342
Mg-Li-(Al-Y)合金原位水稳定性:Li的作用
结合原位、非原位表面和溶液表征,探讨了锂在Mg-Li合金水稳定性中的作用机制。采用共聚焦拉曼显微镜和动力学拉曼映射[1]研究了耐腐蚀Mg-Li(-Al-Y-Zr)-合金在NaCl水溶液中的原位表面演化,并用原子发射光谱电化学[2]进行了实时溶液分析。通过光致发光光谱、俄歇电子光谱和辉光放电光学发射光谱,在水暴露和暴露于环境空气后立即进行了额外的非原位表面表征。原位分析表明,Li和Mg溶解在水溶液中,从视觉上完整的阳极区域,在大约100纳米厚的掺杂锂的MgO下留下一个耗尽锂的金属层。有趣的是,在这些区域,氢氧化镁(Mg(OH)2)的生长速度比纯Mg慢,这表明MgO→Mg(OH)2的转化动力学被强烈抑制。在阴极区域,Li2[Al2(OH)6]2·CO3·nH2O (Li-Al层状双氢氧化物)、LiAlO2、Y2O3和Mg(OH)2局部富集。Li2CO3,以前被认为是负责Mg-Li合金[3]耐腐蚀的保护膜的组成部分,在水溶液中不存在于表面的原位演变,只有在暴露于环境空气后才被检测到。提出的腐蚀机理将Mg-Li合金耐水腐蚀性能的提高归因于Li+[4]掺杂MgO的化学稳定性的提高。后者可通过选择性浸出在Li+溶液中形成。此外,在锂掺杂的MgO和Li-Al层状双氧根上,可以原位检测到Mg的阴极活化。对不同锂含量Mg-Li合金上掺锂MgO膜的起球Bedworth比(PBR)进行了计算,结果表明,在Mg-Li合金上形成保护膜的条件(PBR>1)要求合金中Li的最小浓度接近15-18 at。%。[10]刘建军,李建军,李建军,等。金属腐蚀与腐蚀学报,2019,32(1):387 - 387。[3]严勇,周平,曾志刚,陈晓霞,P. Volovitch, K. Ogle, N. Birbilis,电化学通讯,99(2019)46-50[3]侯立,M. Raveggi, x.b b。陈伟,徐伟,罗克杰,魏勇,M. Ferry, N. Birbilis,电化学刊,163 (2016)C324-C329 bbb .阎彦明,A. Maltseva,周鹏,李晓军,曾志荣,O. Gharbi, K. Ogle, M. La Haye, M. Vaudescal, M. Esmaily, N. Birbilis, P. Volovitch,腐蚀科学,2020,164,108342
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