【作者】 罗伟；

【导师】 吴希俊；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2006， 博士

【摘要】 本文采用溶液浸泡法、阳极极化法、循环伏安法和电化学阻抗谱法，结合X射线衍射（XRD）、场发射扫描电镜（FEGSEM）和X射线能量色散谱（EDS）等检测手段，较系统研究了惰性气体沉积—原位温压法（IGCWC）制备的大三维尺寸块体纳米晶Cu在酸性硫酸铜溶液（CuSO₄+H₂SO₄）、中性含氯钠盐溶液（Na₂SO₄+NaCl）、Na₂SO₄溶液和NaCl溶液中的腐蚀行为与机理，研究了SO₄^2-浓度、Cl^-浓度、腐蚀介质温度和pH值以及纳米晶Cu的晶粒尺寸和制备过程中产生的制备缺陷对纳米晶Cu的腐蚀行为的影响，并比较分析了纳米晶Cu与多晶Cu在相同环境中的腐蚀机理的差异。研究结果表明：1．纳米晶Cu的腐蚀行为存在晶粒尺寸效应。在酸性硫酸铜溶液中，晶粒尺寸减小，纳米晶Cu的致钝电流密度I_cr、维钝电流密度I_P和过钝化电位E_tp均增大，致钝电位E_cr减小。另外，纳米晶Cu的自腐蚀电位E_corr随晶粒尺寸减小而负移，说明晶粒尺寸效应引起的表面活性增大是影响E_corr的重要因素。纳米晶Cu晶粒尺寸减小，晶界所占比例大，原子活性大，钝化能力增强，同时所形成的钝化膜溶解速率增大，极化电阻R_p大大减小，腐蚀电流密度增大，导致其耐蚀性降低。2．在酸性硫酸铜溶液中，纳米晶Cu的I_cr和I_p均比多晶Cu大，E_corr比多晶Cu低，表明纳米晶Cu的耐蚀性比多晶Cu差。电化学阻抗谱分析，纳米晶Cu极化电阻R_p较多晶Cu小许多，且孔蚀诱导期早于多晶Cu，证实了纳米晶Cu耐蚀性不及多晶Cu。3．在中性含氯钠盐溶液中，纳米晶Cu的I_cr和I_p均比多晶Cu小，E_corr比多晶Cu高。虽然Cl^-对于稳定钝化膜的形成有一定的抑制作用，但因为纳米晶Cu的纳米晶粒尺度效应，比多晶Cu更易钝化，表面所形成的钝化膜保护效果也好于多晶Cu，所以纳米晶Cu的耐蚀性比多晶Cu好。循环伏安特性分析证实了这一点。纳米晶Cu和多晶Cu在中性含氯溶液中的钝化区比在酸性硫酸铜溶液中要窄得多，这正是因为Cl^-对形成稳定钝化膜的抑制作用的结果。4．在中性含氯钠盐溶液中，纳米晶Cu腐蚀形态完全不同于多晶Cu，呈现均匀的表面溶解并伴随有不均匀的局部腐蚀，而多晶Cu则是分布均匀的晶界腐蚀。此外，纳米晶Cu还发生了晶粒长大，且与溶液直接接触的最外层表面晶粒长大远比次表层要快，晶粒长大是非均匀性的。5．纳米晶Cu对溶液中的氧痕量更为敏感。究其原因，是因为纳米晶Cu晶界处原子活性大，有利于氧的自由传输。另外，在浸泡或极化过程中，纳米晶Cu表面有S的聚积，而多晶Cu则无S的聚积。6．纳米晶Cu在极化过程中扩散的影响作用不可忽视，而多晶Cu在整个极化过程中，主要受电荷转移过程而非扩散等传质过程控制，更多地受到中间产物或吸附的影响。7．在0.47wt.％NaCl溶液中，纳米晶Cu的E_corr和Tafel斜率与多晶Cu基本一致，但其E_cr、I_cr和I_p都比多晶Cu大，说明纳米尺度效应增强了阳极溶解动力学，纳米晶Cu的抗蚀性不及多晶Cu。另外，纳米晶Cu无二次钝化，而多晶Cu的二次钝化非常明显，这与两阶段保护膜的形成有关。8．SO₄^2-浓度对纳米晶Cu的阳极极化行为有重要影响，纳米晶Cu的I_cr随SO₄^2-浓度的增加而增大，且logI_cr与SO₄^2-有较好的线性关系：logI_cr=0.01158[SO₄^2-]+0.14142。然而，纳米晶Cu的E_cr却随SO₄^2-浓度的增加而降低。9．0.3wt.％Na₂SO₄溶液中加入10⁴ppm Cl^-，纳米晶Cu阳极极化行为发生明显变化，Cl^-在纳米晶Cu表面形成难溶于水的CuCl保护钝化膜，因此，纳米晶Cu电极溶解速率受CuCl和Cu₂O的双重抑制，从而降低纳米晶Cu的I_cr，并显著减缓活化—钝化过渡区的电流密度下降速率。10．在活化—钝化过度区纳米晶Cu阳极极化区存在“斜率转折点电位”。本文提出“静电离子团”模型很好地解释了纳米晶Cu的存在的“斜率转折点电位”和I_cr随SO₄^2-浓度增加而增大的现象。动力学分析，纳米晶Cu电极的溶解电流与电位E、SO₄^2-浓度、溶液pH值和温度T、Cu⁺在纳米晶Cu表面氧化膜内的扩散系数D以及氧化膜厚度d有关：11．溶液温度T对纳米晶Cu的阳极极化行为有重要影响，在3.3wt.％Na₂SO₄溶液中，纳米晶Cu的I_p、I_cr和E_cr均随温度T升高而增大，且logI_cr与1／T之间有较好的线形关系：logI_cr=-669.94（1／T）+2.4388。温度由25℃升高到30℃，Tafel斜率明显增大；温度继续升高，但Tafel斜率保持不变。温度升高，纳米晶Cu极化后表面Cu₂O立方晶体堆积相对疏松，但晶体尺寸更为细小、均匀。Cu₂O堆积疏松导致出现表面腐蚀孔洞。12．随着溶液pH值的降低，纳米晶Cu的I_cr逐渐增大，I_p亦呈上升趋势，且logI_cr=-0.0287pH+0.25。pH值降低，2Cu_sur⁺+OH^-（?）Cu₂O+H⁺反应受到抑制，即抑制了纳米晶Cu电极表面氧化膜的生成，从而减弱了对纳米晶Cu阳极的保护作用，其溶解速率增大。13．纳米晶Cu制备过程中产生的微缺陷对其耐蚀性有不利影响，存在微缺陷部位是纳米晶Cu的腐蚀薄弱部位，微缺陷可能导致纳米晶Cu的局部腐蚀。更多还原

【Abstract】 Anodic polarization, electrochemical impedance spectroscopy （EIS）, cyclic voltammetry （CV） electrochemical methods and XRD （X-ray diffraction）, EDS （energy-dispersive spectroscopy）, FEGSEM （Field emission gun scanning electron microscopy） technique were used to experimentally investigate the corrosion behavior of bulk nanocrystalline （nc） copper prepared by IGCWC （inert gas condensation and in situ warm compress） in acid copper sulphate solution （CUSO₄+H₂SO₄）, neutral solution containing chlorides （Na2SO₄+NaCl）, Na₂SO₄ and NaCl solutions. The influences of sulfate ions, chloride ions, pH value and temperature of solution, grain size of nc copper and defects produced in the fabrication of the sample on the corrosion behaviour of nc copper were studied. Meanwhile, the differences in corrosion behavior between nc copper and coarse copper at the same corrosin condition were analysed.The conclusions are listed below.1. Grain size of nc copper played an important role in its corrosion behaviour. With decreasing grain size, passive current density Ip, critical current density for passivity I_cr and transpassive potential E_tp of nc copper increased but primary passive potential E_cr of nc copper decreased. In addition to self-corrosion potential E_corr of nc copper decreased and the corrosion current density increases notably as grain size decreased. Those results showed that the corrosion resistance of nc copper decreased as grain size reduced. which was mainly attributed to the high activity of surface atoms and intergranular atoms resulted from the reduction of grain size.2. In acid copper sulphate solution, I_p and I_cr of nc copper were greater than that of coarse copper but E_corr of nc copper was negative than that of coarse copper indicating that nc copper had lower corrosion resistance than coarse copper. EIS study demonstrated that R_p of nc copper was lower than that of coarse copper and the original pitting corrosion seemed to happen earlier on nc copper surface than on the coarse copper surface. Compared with coarse copper, nc copper decreased in resistance to corrosion.3. In neutral solution containing chlorides solution, I_p and I_cr of nc copper were lower than that of coarse copper but E_corr of nc copper was positive than that of coarse copper indicating that nc copper exhibited higher corrosion resistance than coarse copper. The formation of the stable passivity film was restrained by chloride ions, leading to a narrowing of the range of passivation of nc copper in neutral solution containing chlorides solution than in acid copper sulphate solution. Because of thenano-scale effect nc copper was much easier to passivate than coarse copper. The protective film on the surface of nc copper had a better protection than that on the surface of coarse copper. CV study demonstrated that nc copper exhibited a higher corrosion resistance than coarse copper.4. In neutral solution containing chlorides solution, nc copper exhibited uniform dissolution of the surface and discrete localized corrosion typically, but conventional coarse copper exhibited considerable preferential attack along the grain boundaries with signs of pitting corrosion dispersed throughout the surface uniformly. In addition to the grain growth of nc copper in solution was observed. The intrinsic grain growth of nc copper was much slower than the apparent growth in solution.5. Nc copper was much sensitive to the oxygen content in the solution. This sensitivity is mainly attributed to the high activity of surface atoms and intergranular atoms. The high activity of surface atoms and intergranular atoms, resulting from the reduction of grain size, leads to an enhancement of free transfer of oxygen. In addition to there was accumulation of sulphur on the sarface of nc copper but there was no on sarface of coarse copper.6. For nc copper the diffusion effect in the polarization was important For coarse copper the polarization was mainly controlled by the transfer but not by diffusion. The intermediate or soiption results had a great effect on the polarization of coarse copper.7. In 0.47wt.% NaCl solution, nc copper exhibited a different anodic polarization behavior from coarse copper. There was no second passivity for nc copper, while there was a notable second passivity for coarse copper. The second passivity was was attributed to the formation of the two steps protective films. In addition to the self-corrosion potential and the Tafel slope of nc copper almost equated to that of coarse copper but I_P, I_cr and E_cr were higher than that of coarse copper. It revealed that nano-scale effect accelerate the dissolution of nc copper.8. In Na₂SO₄ solution the sulfate ion concentration played an important role in the anodic polarization behaviour of nc copper. With increasing sulfate ion concentration, I_cr increased but E_cr decreased. The relationship between loglcr and 1/T fitted a linear equation of logI_cr=0.01158[SO₄^2-] +0.14142.9. Adding 10⁴ ppm Cl^- in 0.3wt.% Na₂SO₄ solution, the anodic polarization behavior of nc copper changed significantly. I_cr decreased and the decreasing rate of anodic current intensity lowed notably in the range of activity-passivity zone. These changes were attributed to the CuCl protective film on the nc copper.10. The decreasing rate of anodic current intensity lowed notably in the range of activity-passivity zone. A model of "static ion congeries" was proposed to explain this notable change of the decreasing rate of anodic current intensity and the case of I_cr increased with increase of sulfate ion concentration. Kinetics analysis revealed that the dissolution current of nc copper was dependent on potential, sulfate ion concentration, pH value, temperature, the diffusion coefficient of Cu+ in the oxidation film and the thickness of the oxidation film on the surface of nc copper.11. Temperature T played an important role in the anodic polarization behaviour of nc copper. With increasing temperature T, I_p, I_cr and E_cr of nc copper increased. The relationship between logI_cr and 1/T fitted a linear equation of logI_cr= —669.94 （1/T） + 2.4388. The CU₂O film on the surface of nc copper after polarization became loose but the grain size of Cu₂O film became small with increasing temperature.12. With increasing pH value of the solution, I_cr and I_p of nc copper increased and the relationship between logI_cr and pH fitted a linear equation of logI_cr = —0.0287pH+0.25. Due to the reaction 2Cu_sur⁺ +OH^-（?） Cu₂O + H⁺ was restrained as pHvalue of the solution increased. In other words, the formation of the oxidation film on the surface of nc copper was restrained, therefore, the protective effect lowered leading to an increase in the rate of dissolution.13. Defects such as micro-gap produced in the fabrication of nc copper sample had great effect on the overall corrosion performance of nc copper sample, which were weakness to corrosion更多还原