吴晓晓, 孔纲, 孙子文, 车淳山
华南理工大学材料科学与工程学院 广州 510640
WU Xiaoxiao, KONG Gang, SUN Ziwen, CHE Chunshan
中图分类号: TB304, TG174.4
文章编号: 1005-3093(2016)04-0269-08
通讯作者:
收稿日期: 2015-07-7
网络出版日期: 2016-04-25
版权声明: 2016 《材料研究学报》编辑部 《材料研究学报》编辑部
基金资助:
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摘要
在热浸镀Galfan镀层表面制备了镧盐转化膜, 采用扫描电镜及能谱分析(SEM/EDS)、X射线光电子能谱分析(XPS)、原子力扫描探针显微分析(AFM)研究镧盐转化膜的表面形貌、化学成分和结构。通过中性盐雾试验、电化学极化分析和电化学阻抗研究膜层的耐腐蚀性能, 确定最佳成膜时间。结果表明: 镧盐转化膜成膜不均匀, 优先在晶界或相界等活性区域; 随着处理时间的延长, 膜层的厚度增加; 膜层上存在裂纹, 且裂纹随着处理时间的延长而变宽, 处理时间超过30 min时, 膜层脱落, 耐腐蚀性能降低; 镧盐转化膜由La的氧化物/氢氧化物以及少量的Al和Zn的氧化物/氢氧化物组成。与未经处理的热浸镀Galfan镀层相比, 镧盐转化膜显著减低基体的腐蚀速率, 明显提高其耐腐蚀性能。
关键词：
Abstract
Lanthanum nitrate conversion coating was prepared on a hot-dip Galfan steel by dipping in a passivation solution of La(NO3)3. The surface morphology, chemical composition and structure of the coating were characterized by scanning electron microscopy (SEM) with X-ray energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). The corrosion resistance of the conversion film coated steel was assessed by neutral salt spray tests (NSS), electrochemical polarization curve and electrochemical impedance spectroscopy (EIS). The results showed that the conversion coating was not uniform, which had grown preferentially on grain- and phase-boundaries as well as other active sites. The thickness of the coating increased, while cracks in the coating expanded gradually with the increasing dipping-time. The coating spall off after dipping for more than 30 min, and therewith the protective performance of the coating degraded. In comparison with the blank Galfan steel, the corrosion rate of the conversion film coated Galfan steel lowered down significantly.
Keywords：
热浸镀是钢铁防大气腐蚀最经济有效的方法之一, 常规热浸镀锌镀层在潮湿环境中易腐蚀产生白锈, 从而影响钢件外观质量。随着热浸镀产品应用的多元化, 对其耐腐蚀性能提出了更高的要求, 其中锌-铝合金镀层成为研究热点[1, 2]。国际铅锌研究组织(ILZRO)研究并开发了Galfan (Zn-5%Al-0.1%RE) 镀层[3], 试验证明, Galfan镀层在大气环境中的耐腐蚀性能是常规镀锌层的2-3倍[4]。目前Galfan镀层的耐腐蚀机理为, 在Galfan镀层表面形成一层致密的Al2O3保护膜[5], 成为阻止腐蚀的屏障; Galfan镀层的外层是富Zn相和富Al相交替的共晶组织, 富Zn相作为阳极先发生腐蚀, 生成的腐蚀产物填充表面, 即镀层表面转为富Al相与Zn的腐蚀产物的复合物, 从而阻止腐蚀的进一步延伸[6]; Galfan镀层的内层和镀层晶间中充满了非晶态Al合金物质[7], 减缓了镀层间晶腐蚀速度并提高了整个镀层的抗腐蚀能力。
为提高镀层的耐腐蚀性能, 通常在金属表面做铬酸盐钝化处理。但是六价Cr有剧毒, 给环境和人体带来严重的危害, 因而受到严格的限制。近年来, 国内外学者致力于无铬钝化技术的研究, 可以分为无机物钝化[8-11]、有机物钝化[12, 13]及其复合物钝化[14, 15]。其中稀土钝化因其无毒无污染、耐蚀性能好等优点成为研究的热点[16, 17]。Olivier等[18]研究发现稀土盐(La、Ce和Y)对锌合金均有明显的缓蚀作用。Conde等[19]将铝合金浸入稀土钝化液中获得的转化膜降低基体的腐蚀速率, 提高其耐腐蚀性能。顾宝珊等[20]在铝合金表面制备了稀土转化膜, 结果表明, 膜层由稀土氧化物/氢氧化物及铝的氧化物混合组成。研究还发现稀土转化膜产生点蚀后还具有一定的修复能力。然而稀土转化膜的质量和耐腐蚀性能与铬酸盐钝化膜还存在一定的差距。
目前国内外对Galfan镀层表面稀土转化膜的研究甚少。本文选用La(NO3)36H2O为主盐, 在Galfan镀层表面制备镧盐转化膜, 通过采用SEM/EDS、AFM和XPS研究膜层的表面形貌、化学成分和结构, 进而分析膜层的生长过程。采用中性盐雾实验(NSS)、电化学极化曲线和电化学阻抗谱(EIS)来评价膜层的耐腐蚀性能。
实验基体材料选用尺寸为50 mm×40 mm×0.8 mm的Q235冷轧钢板, 前处理条件为: 15% NaOH热碱浴除油→热水冲洗→15% HCl酸洗除锈→冷水冲洗→助镀剂助镀→烘干。将前处理后的试样置于盛有熔融Galfan (Zn-5% Al-0.1% RE, 质量分数)的SG2-7.5-10石墨坩埚中热浸镀, 镀锌温度为(410±5)℃, 浸渍时间约为1 min, 之后缓慢提出锌液面, 立即水冷, 获得所需试样。采用STH-1型测厚仪测得镀层厚度为12 μm左右。本文采用镧盐转化膜工艺为: La(NO3)36H2O 20 g/L、H2O2 10 ml/L、NaF 0.1 g/L, 处理温度 70℃, 处理时间10 s~60 min, 在室温条件下自然干燥。
采用LEO1530VP型扫描电子显微镜 (SEM)以及Inca300型能谱仪(EDS)分别观察分析膜层的微观形貌和化学成分。采用ESCALAB250型光电子能谱仪(XPS)分析膜层的元素组成和元素价态。采用SPM3800N型原子力扫描探针显微镜(AFM)观察膜层的表面形貌和结构。通过YWX/Q-150型号盐雾箱的中性盐雾试验(NSS)来评价膜层的耐腐蚀性能, 测试溶液为质量分数为5%NaCl的水溶液, 喷雾8 h、停16 h为一个周期, 记录试样表面的腐蚀面积随喷雾周期的变化。电化学测试在CHI604B电化学工作站上进行, 采用三电极体系, 工作电极为待测试样(用石蜡封闭后露出10 mm×10 mm膜层表面), 辅助电极为铂电极, 参比电极为饱和甘汞电极, 测试溶液采用未除气的5%NaCl溶液, 室温条件。极化曲线测量的扫描速率为1 mV/s, EIS测试频率范围为10 mHz~ 100.00 kHz, 测量信号的幅值为10 mV。
图1为热浸镀Galfan试样经镧盐钝化液处理10 s~60 min的表面形貌的SEM图。由图1可见, 当处理时间为10 s时, 试样表面形貌与Galfan镀层表面形貌相似, 可明显看到不同晶粒及层片状共晶组织。当处理时间延长到1 min时, 晶界及某些相界附近产生了膜层的局部堆积和突起, 这是因为晶界及相界等处活性较高, 镧盐转化膜的成膜速率较快。随着处理时间延至10 min时, 膜层堆积不断变大、变连贯, 然后布满整个表面, 膜层逐渐增厚, 同时出现微小细裂纹。当处理时间为30 min时, 膜层进一步增厚, 膜层中的裂纹变多、变宽, 同时在局部区域开始出现上翘现象, 这是因为膜层增厚内应力增大。当处理时间延至60 min时, 膜层脱落, 变得不连续, 此时试样表面分成两层, 剥落处可看到与基体形貌完全不同的新生膜层。
图1 不同处理时间镧盐转化膜的SEM像
Fig.1 SEM images of Galfan coating treated in lanthanum salt bath for (a) 10 s; (b) 1 min; (c) 10 min; (d) 30 min; (e) 60 min
表1为图1中各微区的EDS分析结果, 由于EDS分析中采集的区域深度较大, 分析结果中会包含很多基体的信息, 膜层越薄, 基体信息越强。因此EDS结果并不能完全反应表面膜层的成分, 但是能够在一定程度上反映膜层中各元素含量的变化。从表1看出, 镧盐转化膜主要由Zn、Al、O和La元素组成。总体上来看, 随着处理时间的增长, 膜层中Zn含量减少, Al含量先增加后减少, La含量对应增加, 这表明随着处理时间的延长, 膜层的厚度增加。从表1还可以看出, 膜层的堆积处La和O含量相对于平坦处较高, Zn和Al含量较少, 这说明成膜过程中堆积处的膜层比平坦处的膜层厚, 成膜不均匀。处理时间为60 min试样的剥落处没有检测到La和Al元素, 这是因为新生膜层极薄, 基体信息太强。考虑到EDS检测不到H元素, 可以认为膜层由La的氧化物/氢氧化物、以及少量的Al和Zn的氧化物/氢氧化物组成。
表1
Table 1 EDS analysis results for the different micro squares in
| Analytical area | Treatment time | Zn | Al | O | La |
|---|---|---|---|---|---|
| 1 | 10 s | 88.12 | 11.88 | - | - |
| 2 | 1 min | 72.01 | 13.82 | 13.71 | 0.46 |
| 3 | 1 min | 49.58 | 12.05 | 36.22 | 2.15 |
| 4 | 10 min | 49.52 | 7.71 | 39.34 | 3.43 |
| 5 | 10 min | 16.04 | 2.54 | 68.91 | 12.50 |
| 6 | 30 min | 34.07 | 1.57 | 54.07 | 10.29 |
| 7 | 60 min | 8.96 | 1.07 | 72.92 | 17.05 |
| 8 | 60 min | 89.05 | 10.95 | - | - |
图2和图3分别为经镧盐钝化液处理时间为1 min试样表面的XPS全谱图和Zn2p, La3d, Al2p, O1s的高分辨谱图。从图2看出, 镧盐转化膜表面含有Zn、La、Al和O等元素, 考虑到XPS检测不到H元素, 推测镧盐转化膜表面由Al的氧化物/氢氧化物, La的氧化物/氢氧化物以及Zn的氧化物/氢氧化物组成。图3a为Zn2p的高分辨率谱图, 结合能为 1021.50 eV和1044.26 eV的峰分别对应于Zn2p3/2和Zn2p1/2, 这说明Zn是以Zn2+的形式存在, 其中结合能为1021.50 eV对应于ZnO的Zn2p3/2[21]。图3b为La3d的高分辨谱图, 出现了4个峰, 是两组成对出现的自旋-轨道分裂峰, 结合能分别为833.89 eV, 837.45 eV, 850.59 eV和854.47 eV, 前两个峰对应La3d2/5, 后两个峰对应La3d3/2, 且837.45eV和854.47eV的峰位是La3+的卫星峰, 这说明膜层中含有La3+[22], 833.89 eV和850.59 eV两个峰之间的自旋轨道分裂值约为16.80 eV, 说明膜层中存在La2O3[23]。图3c为Al2p的高分辨谱图, 峰值的结合能为74.60 eV与Al2O3的Al2p一致。图3d中O1s的谱图经分峰拟合后得到2个峰, 结合能分别为531.19 eV和532.40 eV。由标准谱图可知, 其中531.19 eV对应Al2O3, Al(OH)3, ZnO和La(OH)3[24], 532.40 eV对应La2O3和Zn(OH)2。因此推测: 镧盐转化膜由La2O3、La(OH)3、Al2O3、Al(OH)3、ZnO和Zn(OH)2组成。
图2 处理时间为1 min得到的镧盐转化膜的XPS全谱图
Fig.2 XPS surface analysis of conversion film formed on Galfan coating with 1 min treatment
图3 Zn2p, La3d, Al2p, O1s的XPS高分辨谱图
Fig.3 High resolution XPS spectra of Zn2p (a), La3d (b), Al2p (c), O1s (d)
图4为处理时间为1 min试样距表面不同深度位置的成分分析。从图4可知, 膜层表面Al、La和O含量较高, Al含量沿着深度的方向先增加后减少, 然后趋于稳定, La和O含量沿深度方向逐渐减少; 而表面Zn含量较低, 随着深度的增加, Zn含量逐渐增加。这说明在短时间处理条件下成膜主要是Al(OH)3/Al2O3及La(OH)3/La2O3的沉积。
图4 处理时间为1 min得到的镧盐转化膜的XPS深度分析
Fig.4 XPS depth analysis profiles of four elements in Galfan coating with 1 min treatment
图5为Galfan试样经镧盐钝化液处理时间为10 s和1 min的AFM图, 从图5可以看出, 镧盐转化膜表面不平整, 呈现出一座座耸立的小山峰, 处理时间为10 s的试样表面的山峰呈现针尖状, 处理时间为1 min的试样表面的山峰宽且高耸。图中颜色的深浅代表高度差, 随着处理时间的延长, 膜层的高度起伏变大。Ra表示膜层平均粗糙度, Rq表示膜层表面粗糙度的均方根。由粗糙度数据知, 处理时间为10 s和1 min试样的Ra值分别为9.342 nm和44.481 nm, Rq分别为12.477 nm和60.935 nm。这说明随着处理时间的延长, 膜层的表面粗糙度变大, 进一步证明镧盐转化膜成膜不均匀。
图5 Galfan镀层镧盐转化膜试样AFM图
Fig.5 AFM micrographs of Lanthanum conversion coating formed after passivation treatment for (a) 10 s; (b) 1 min
图6为热浸镀Galfan和不同处理时间的镧盐转化膜试样的中性盐雾测试结果。从图6可以看出, 未处理的Galfan试样经过一个周期的喷雾, 腐蚀面积已经达到80%, 而经过镧盐钝化液处理10 min的试样经3个周期的喷雾, 腐蚀面积仅为15%左右。当处理时间小于10 min时, 随着处理时间的延长, 膜层耐腐蚀性能逐渐增强, 这是因为随着处理时间的延长, 膜层的厚度增加。当处理时间超过10 min后, 膜层耐腐蚀性能随着处理时间的延长而逐渐下降, 这是因为膜层中出现的裂纹随着处理时间的延长变多变宽, 最后脱落。由此可见, 处理时间为10 min获得的镧盐转化膜耐腐蚀性能最优。
图6 Galfan与不同处理时间获得的镧盐转化膜的NSS结果
Fig.6 NSS results of Galfan coating without and with passivation treatment for different time
图7为热浸镀Galfan和不同处理时间的镧盐转化膜在5%NaCl溶液中的Tafel极化曲线。从图7可以看出, 与未处理的热浸镀Galfan试样相比, 经过镧盐钝化液处理的试样的极化曲线的阳极分支和阴极分支均向低电流密度的方向移动, 这表明镧盐转化膜同时抑制腐蚀反应的阳极过程和阴极过程, 从而抑制整个腐蚀反应, 提高基体的耐腐蚀性能。当处理时间为10 min时, 抑制腐蚀反应的阴极过程和阳极过程最显著, 说明此时试样的耐腐蚀性能最优。表2给出了图7中极化曲线经过电化学工作站自带处理软件拟合所得的相关电化学腐蚀参数。其中Ecorr为自腐蚀电位, Ep为极化电阻, Icorr为腐蚀电流密度。从表2可知, 与未处理的热浸镀Galfan试样相比, 镧盐转化膜的极化电阻明显提高, 腐蚀电流显著降低, 其耐腐蚀性能大幅度提高。经镧盐钝化液处理10 min获得的镧盐转化膜试样的极化电阻(56690.0 kΩcm2)相对于未处理Galfan试样(1546.3 kΩcm2)提高了30多倍, 其腐蚀电流密度(0.1178 μAcm-2) 相对于Galfan试样(5.430 μAcm-2)降低了40多倍, 这说明镧盐转化膜显著的提高了基体的耐腐蚀性能。
图7 Galfan 和不同处理时间的镧盐转化膜在5% NaCl溶液中的极化曲线
Fig.7 Electrochemical polarization curves of Galfan coating without and with Lanthanum conversion treatment for different time in 5% NaCl solution
表2
Table 2 Electrochemical polarization parameters corresponding to
| Sample | Ecorr/V | Rp/Ωcm2 | Icorr/μAcm-2 |
|---|---|---|---|
| Galfan | -1.062 | 1546.3 | 5.430 |
| 10 s | -1.068 | 2687.6 | 3.101 |
| 1 min | -1.060 | 3494.0 | 2.242 |
| 10 min | -1.041 | 56690.0 | 0.1178 |
| 30 min | -1.052 | 22930.2 | 0.3530 |
| 60 min | -1.077 | 9441.9 | 0.8021 |
图8为Galfan和经镧盐钝化液处理不同时间的试样在5%NaCl溶液中的Nyquist图。由图8知, Galfan和经过镧盐钝化液处理的试样均具有高频容抗环和低频容抗环, 其中高频容抗弧对应着膜层的保护作用, 低频容抗环表征膜层/基底界面的电极反应[25]。当处理时间小于10 min时, 随着处理时间的延长, 高频容抗弧和低频容抗弧的半径增长, 这说明随着处理时间的延长, 膜层对基体的覆盖率增大, 膜层增厚阻碍了电荷的转移和电解质在膜层中的扩散, 从而提高了基体的耐腐蚀性能。当处理时间大于10 min时, 高频容抗环和低频容抗环的半径均随着处理时间的延长而逐渐减小。这是因为随着处理时间的继续延长, 膜层虽然继续增加, 但是膜层中出现的裂纹变多, 变宽, 膜层与基体的结合力减弱, 最后膜层脱落, 导致膜层对基体的保护作用遭到破坏。此时膜层难以有效的阻止电解质在膜层中的扩散, 其耐腐蚀性能下降。从图8中看出, 当处理时间为10 min试样的阻抗实部Z '最大, 耐腐蚀性能最优。
图8 Galfan和不同处理时间的镧盐转化膜在5%NaCl溶液中的电化学阻抗谱
Fig.8 EIS of Galfan coating without and with Lanthanum conversion treatment for different time in 5% NaCl solution, (a) Nyquist plots; (b) local amplification of
将热浸镀Galfan试样浸入添加了NaF的镧盐钝化液中, 由于溶液中含有具有腐蚀性的F-, 在酸性条件下能加快试样表层氧化铝的的溶解:
由于试样表面存在不同活性的部分或不同金属元素等原因, 构成众多的微电池反应[26]。
微阳极区域:
微阴极区域:
在成膜过程中可以观察到, 有气泡产生并吸附于试样表面, 可以推测成膜过程中存在以下反应:
由于钝化液中添加了H2O2, 微阴极区域还会发生以下反应:
由式(4)和式(5)知, 反应式(4)消耗了微阴区附近的H+, 使微阴区的pH值升高。另外钝化液中的H2O2发生式(5)反应产生大量的OH-, 使基体表面的OH-浓度急剧上升, 促进微阴区附近的pH值升高, 为成膜提高碱性条件, 促进膜层的生成。
当微阴极区域的pH达到一定值时, Al3+、Zn2+和La3+会与溶液中的OH-发生反应生成不溶性的氢氧化物覆盖在试样的表面, 形成转化膜。
根据Al-H2O系E-pH图, 当pH处于4.6~8.3时[27]:
根据Zn-H2O系E-pH图, 当pH处于8.4~10.4时[28]:
另外, 根据La-H2O系E-pH图, 当pH超过8.1时[29]:
Al(OH)3、Zn(OH)2和La(OH)3的溶度积分别为1.3×10-33、1.2×10-17、2.0×10-19, 初始钝化液pH值为4左右, 所以Al(OH)3最先沉积, La(OH)3次之, Zn(OH)2最后析出。
根据以上分析, 结合SEM/EDS、XPS分析结果知, 成膜前期以Al(OH)3/Al2O3及La(OH)3/La2O3沉积为主, 后期以La(OH)3/La2O3、少量的Zn(OH)2/ZnO沉积为主。
1. 镧盐转化膜成膜过程是不均匀的, 优先在晶界或相界等活性区域成膜。随着处理时间的延长, 膜层的厚度增加, 同时膜层上会出现裂纹, 且裂纹随着成膜时间的延长而变宽, 当处理时间超过30 min时, 膜层脱落。
2. 镧盐转化膜由La的氧化物/氢氧化物, 以及少量Al和Zn的氧化物/氢氧化物组成。在成膜过程中, 前期以Al(OH)3/Al2O3、La(OH)3/La2O3沉积为主, 后期以La(OH)3/La2O3、Zn(OH)2/ZnO沉积占主导。
3. 在热浸镀Galfan镀层表面制备的镧盐转化膜具备优异的耐腐蚀性能。处理时间为10 min所获得的镧盐转化膜较未经处理的热浸镀Galfan的腐蚀电流密度明显降低, 而极化电阻和电化学阻抗显著增大, 耐腐蚀性能最好。
The authors have declared that no competing interests exist.
| [1] |
Investigation into the effects of metallic coating thickness on the corrosion properties of Zn-Al alloy galvanising coatings , |
| [2] |
Effect of Al on the galvanic ability of Zn-Al coating under thin layer of electrolyte ,
<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">The effect of Al on the galvanic ability of Zn–Al coating has been studied under thin electrolyte layers by measuring surface potential and surface pH. The changes of surface potential and surface pH over Zn–Al/steel galvanic couple corroding in artificial sea water (ASW) were measured at 60% and 90% RH at 298 K. In the initial stage of corrosion, Zn–55Al coating has shown better galvanic protection ability than Zn–5Al coating in both 60% and 90% RH. However, Zn–5Al coating was better in long term corrosion. The better galvanic ability of Zn–55Al coating in the initial stage of corrosion was related to the observation of pH as low as low as 2 on its surface. The low pH value was due to hydrolysis of Zn<sup>2+</sup> and Al<sup>3+</sup> ions. The low pH value was further confirmed by observing evolution of gas due to H<sup>+</sup> reduction on the Zn–55Al coating. With the progress of corrosion, the low pH region of coating layer extended towards the base steel. This helped expand the deposition of zinc corrosion products on the steel surface. The enhanced dissolution of zinc in Zn–55Al coating led to the formation of a barrier layer which limited the galvanic protection of remaining steel. This was not the case in Zn and Zn–5Al coating. The X-ray analyses of the corroded samples have shown the deposition of zinc corrosion products on the steel surface, which greatly depended on the RH value. The part of the steel surface covered with zinc corrosion products has shown relatively less noble potential than other part indicating that zinc corrosion products took a role to protect the base steel against corrosion. The results from surface potential and surface pH measurements were substantiated by the surface observation of the corroded sample during and after the corrosion test.</p>
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| [3] |
Application of EIS to assess the effect of rare earths small addition on the corrosion behaviour of Zn-5%Al (Galfan) alloy in neutral aerated sodium chloride solution ,
<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">The effect of rare earth metal (Gd, Dy, Er, and Y) small additions on the corrosion behaviour of Zn–5% Al (Galfan) alloy has been investigated. The corrosion resistance of Zn–5Al–0.1Gd, Zn–5Al–0.1Dy, Zn–5Al–0.1Er, and Zn–5Al–0.1Y alloys has been assessed by electrochemical impedance spectroscopy (EIS) measurements carried out in a 0.1 M NaCl solution, at approximately neutral pH, without stirring and in contact with the air. For comparison, the electrochemical tests have also been carried out on the Galfan alloy. EIS results showed that rare earths’ addition significantly improves the corrosion behaviour of Galfan. This improvement is most likely due to enhanced barrier properties of the corrosion products layer and additional active corrosion protection originated from the inhibiting action of the lanthanide ions entrapped as oxides/hydroxides in this surface layer.</p>
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| [4] |
Progress in research of hot-dipped Zn-Al alloying coating ,热浸Zn-Al合金镀层的研究进展 ,
综述了近年来国内外对热浸Zn-Al合金镀层的研究,包括含Al 量不同时镀层的组织与性能特点以及添加元素RE,Mg,Si的作用.介绍了Zn-5Al-RE、Zn-5Al-Mg、Zn-55%Al-1.6Si镀层和 Zn-23%Al-Si镀层的组织结构、性能和防腐蚀机理及其应用场合以及Zn-Al合金镀层应用于批量热镀锌的研究与进展.
|
| [5] |
XPS study of the surface chemistry of conventional hot-dip galvanised pure Zn, galvanneal and Zn-Al alloy coatings on steel ,
<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">This study uses X-ray photoelectron spectroscopy (XPS) to analyse the outer surfaces of galvanised, galfan and galvanneal metallic coatings obtained by hot dipping. Considerable aluminium segregation towards the surface, principally as Al<sub>2</sub>O<sub>3</sub>, has been seen in all the studied coatings. The aluminium content on the surface was surprisingly similar to or even greater than the zinc content, which is the major element in the chemical composition of these coatings. The formation of Al<sub>2</sub>O<sub>3</sub> seems to prevent the oxidation of the zinc in the metallic coating.</p>
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| [6] |
Atmospheric corrosion behavior of aluminum-zinc alloy-coated steel , |
| [7] |
The microstructure of Zn-5%Al hot dip coating and study on its corrosion resistant mechanism ,Zn-5%Al合金热浸镀层微结构及其防腐机理研究 , |
| [8] |
Formation and corrosion resistance of titanium containing conversion film on hot-dip Galvanized steel ,热浸镀锌层钛盐转化膜的制备和耐蚀性能 ,
<p>制备了热浸锌层钛盐转化膜, 采用SEM、EDS表征了转化膜的表面形貌、化学成分, 采用XPS技术分析了膜层的组成, 探讨了膜层的生长过程。通过中性盐雾试验、电化学极化分析和电化学阻抗研究了膜层的耐蚀性能。结果表明, 膜层主要由含结晶水的Ti(OH)<sub>4</sub>/TiO<sub>2</sub>和Zn(OH)<sub>2</sub>/ZnO组成, 随着处理时间的增加钛盐转化膜逐渐增厚, 膜层中的Ti含量逐渐增加。与未经处理的热浸镀锌层比较, 转化膜层腐蚀电流密度减小, 极化电阻和电化学阻抗显著增大, 耐蚀性明显增强。</p>
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| [9] |
Molybdate conversion coatings on AZ31 magnesium alloy ,
AZ31镁合金钼酸盐转化膜 ,
利用钼酸盐溶液在AZ31镁合金表面获得棕黄色的转化膜.用扫描 电镜(SEM)和X射线光电子能谱(XPS)对膜层的形貌和组分进行研究,采用动电位极化曲线测试对膜层的耐蚀性进行研究.结果表明:膜的微观形态由球形 颗粒构成,膜层厚度约12μm,对镁合金的覆盖作用良好;转化膜表层中Mo元素主要以MoO3形式存在,在膜的内部钼主要以MoO3和MoO(OH)2存 在,并含有部分MoO3;钼酸盐转化膜在阳极极化过程中发生明显的钝化,腐蚀电位正移683 mV,腐蚀电流密度降低2个数量级,明显提高AZ31镁合金的耐蚀性能.同时对镁合金表面钼酸盐转化膜的成膜机理进行初步探讨.
|
| [10] |
An atomic emission spectroelectrochemical study of passive film formation and dissolution on galvanized steel treated with silicate conversion coatings ,
The effect of a silicate conversion coating, which was applied on electrogalvanized steel (EG) and hot dip galvanized steel (HDG), on zinc passivation and dissolution is investigated by atomic emission spectroelectrochemistry (AESEC) using anodic/cathodic cycles in a neutral borate buffer solution. We are able to decompose the total zinc oxidation rate into a soluble (dissolution) and insoluble (passivation) component. It is found that the silicate conversion coating reduces the soluble component with no measurable effect on the insoluble component. The results imply that zinc passive film formation occurs unhindered underneath the silicate film but the film effectively blocks zinc dissolution.
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| [11] |
Effect of size of silica powder on preparation of silicate conversion coatings on Galvanized steel ,二氧化硅粉体粒度对硅酸盐转化膜制备的影响 ,
<p>用微米和纳米粒度的SiO<SUB>2</SUB>粉体分别配制SiO<SUB>2</SUB>质量分数为5%、模数(SiO<SUB>2</SUB>/Na<SUB>2</SUB>O摩尔比)为3.50的硅酸钠溶液, 并用之浸泡热镀锌钢制备了硅酸盐钝化膜。用X射线衍射(XRD)、反射红外光谱(RA-IR)分析二氧化硅粉体, 用透射红外光谱(FT-IR)和核磁共振(NMR)分析硅酸钠溶液的结构, 用原子力显微镜(AFM)、电化学阻抗谱(EIS)分析转化膜的结构。结果表明: 与微米级二氧化硅相比, 纳米级二氧化硅含有Si-OH键较多, 用它配制的硅酸钠溶液中硅酸负离子的聚合程度较低, 成膜过程脱水量较多而生成微观孔隙较多的转化膜。</p>
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| [12] |
The adsorption of an epoxy acrylate resin on aluminum alloy conversion coatings ,
A thermodynamic study of the adsorption of an epoxy acrylate resin used for UV-cured coatings on two different anticorrosion pretreatments on aluminium alloys relevant to aerospace industry has been undertaken. Aluminium alloy Al2219 specimens, treated with an inorganic chromate based conversion coating (Alodine 1200S) and an organic titanium based conversion coating (Nabutan STI/310), were immersed in solutions of different concentrations of the resin and adsorption isotherms were determined by assessing the uptake of the adsorbate, as a function of solution concentration, by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results show different behaviour for the two substrates, which can be attributed to the organic component of the titanium based coating. In the case of the inorganic conversion coating a clear plateau is achieved at relatively low concentrations and at a lower level of adsorption than for the hybrid coating. The data for both the coatings conform well to the Langmuir model, the organic coating, as well as showing a higher level of adsorption of the resin, also presents oscillatory behaviour at low concentration, which is shown to be complementary to the behaviour of the reactive diluent included with the epoxy acrylate to aid processing. A discussion of this competitive adsorption of the epoxy resin and the diluent on the different substrates is presented, based on considerations of the chemistry of the systems under investigation. (C) 2011 Elsevier Ltd. All rights reserved.
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| [13] |
Study of composition and corrosion protection afforded by phytic acid conversion coatings applied to AZ91 magnesium alloy ,AZ91D镁合金植酸转化膜组成与耐腐蚀性能研究 , |
| [14] |
Composition and Corrosion resistance of molybdate/silane composite films on Galvanized steel, Journal of South China University of Technology ( 镀锌钢上钼酸盐/硅烷复合膜的组成与耐蚀性 ,
分别采用一步法和两步法在热镀锌钢板表面获得钼酸盐/硅烷复合 膜,通过X射线光电子能谱分析(XPS)、俄歇电子能谱剥层分析(AES)、盐雾腐蚀试验(NSS)及Tafel极化曲线等对两种复合膜的化学成分和耐蚀 性能进行了研究,并将它们与单独的钼酸盐转化膜、硅烷膜进行对比.结果表明:一步法和两步法制备的复合膜具有相似的双层结构,内层以钼酸盐转化膜(含O、 Mo、Zn、P)为主,外层以硅烷膜(含C、O、Si)为主,内外层之间及膜与锌基体之间的化学成分呈梯度变化;与单独的钼酸盐膜、硅烷膜相比,两种复合 膜对腐蚀的阴极过程的抑制明显增强,自腐蚀电流减小至单层膜的1/5以下,耐蚀性显著提高;两步法制备的复合膜耐蚀性超过常规铬酸盐钝化膜,而一步法制备 的复合膜的耐蚀性比由两步法制备的稍差,但仍接近常规铬酸盐钝化膜.
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| [15] |
Modification of bis-silane solutions with rare-earth cations for improved corrosion protection of galvanized steel substrates ,
The present work aims at assessing the corrosion behaviour of hot dip galvanised steel substrates pre-treated with bis-[triethoxysilylpropyl]tetrasulfide and bis-1,2[triethoxysilyl]ethane silane solutions doped with cerium nitrate or doped with lanthanum nitrate. The effect of the dopants on the barrier properties of the silane film and its corrosion-inhibition ability is studied via electrochemical impedance spectroscopy. Complementary studies using atomic force microscopy and surface analysis were also performed. The results show that the corrosion resistance of substrates pre-treated with the silane solutions doped with the rare-earth cations increases by more than one order of magnitude when compared with the non-doped pre-treatments. The results also show that the protective behaviour of the pre-treatment is dependent on the dopant and on the silane film. The work discusses the role of the dopant on the anti-corrosion properties of the pre-treated substrates.
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| [16] |
Growth behavior of lanthanum conversion coating on hot-dip galvanized steel ,
La conversion coatings in various growth stages were obtained by immersing hot-dip galvanized (HDG) sheets in the lanthanum nitrate solution for different times from 10s to 240min. A growth process model of the La conversion coating on hot-dip galvanized steel was suggested. It is shown that the conversion coating grows more quickly by the zinc grain boundaries, where the cracks occur first and develop gradually on the whole surface of the conversion coating. When the immersion time is increased (more than 60min), some rod-like precipitations containing more Zn and less La are deposited on the conversion coating. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurement results reveal that, with increasing immersion time, the protective property of the La conversion coatings is gradually increased in the early growth stage and then decreased when the cracks develop.
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| [17] |
Growth mechanism of cerium salt conversion coating modified with citric acid on galvanized steel ,热镀锌层柠檬酸改进型铈盐转化膜的生长机理 ,
将热镀锌钢板浸入含有25 g/L Ce(NO3)3·6H2O、4～6 g/L H2O2(30％)、15～20 g/L H3Cit的处理液中,在70℃下处理10 s～240 min,从而在其表面获得铈盐转化膜.采用中性盐雾试验(NSS)和电化学极化曲线来分析膜层耐蚀性能,确定最佳成膜时间范围.采用扫描电镜(SEM)观 察膜层的微观形貌,利用能谱仪(EDS)、X射线光电子能谱仪(XPS)、红外吸收光谱仪(IR)分析膜层的化学组成.结果表明:处理时间为10 min左右的铈盐转化膜耐腐蚀性能最优,最佳工艺条件下得到的铈盐转化膜的耐蚀性能与铬酸盐转化膜的相当；随着处理时间的延长,膜的厚度增加,膜层的裂纹 变宽；处理时间超过10 min后膜层逐步产生脱落,耐腐蚀性能也随之降低;转化膜的生长过程中,前期以柠檬酸铈吸附膜的沉积为主,后期以Ce(OH)3/Ce2O3及 Ce(OH)4/CeO2的沉积占主导.
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| [18] |
Influence of oxidizing ability of the medium on the growth of lanthanide layers on galvanized steel ,
<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">Protection mechanisms offered to galvanized steel by lanthanide salts in a 0.1 M NaCl solution were investigated by using electrochemical techniques such as polarization curves, electrochemical impedance spectroscopy (EIS), scanning vibrating electrode technique (SVET) and surface analysis such as scanning electron microscope (SEM) and glow discharge optical emission spectrometry (GDOES).</p><p id="">The role of the oxidizing ability of the medium was studied by changing the aeration conditions: aerated, saturated, deaerated and acid deaerated solutions.</p><p id="">In aerated solution, the cerium deposition quickly offers an inhibition of the oxygen reduction. Current density cartographies (SVET) are consistent with surface analysis and other electrochemical techniques.</p>
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| [19] |
Effective corrosion protection of 8090 alloy by cerium conversion coatings ,
<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">Conversion treatments based on immersion in Cr(VI) aqueous solutions are key technologies that combine low cost, easy application and high performance. However, they are environmentally problematic due to their carcinogenity and genotoxicity. Among the potential alternatives, treatments based on rare-earth compounds have drawn attention due to the stability of their oxides and their environmental acceptability. Despite the amount of work published, there is not yet an industrially suitable alternative treatment for aircraft aluminium alloys that is able to provide the required corrosion protection. A common feature of these alloys is the high level of copper in their chemical composition. Although the presence of copper in an alloy may enhance cerium deposition, high copper content alloys (AA2024, AA7075) have proven the most difficult to protect with Ce conversion coatings.</p><p id="">In the present work, a commercial 8090-T8 aluminium alloy containing 1.15 weight percent (wt.%) Cu was coated with a Ce conversion coating at room temperature from a Ce bath without prior pretreatment of the specimens. Polarisation curves revealed that the presence of a cerium conversion coating (CeCC) reduces by two orders of magnitude the corrosion rate of the AA8090 alloy in a sodium chloride solution. Impedance measurements exhibited capacitive behaviour for the CeCC up to 216 h, showing that the cerium layer protects the bare alloy in the aggressive solution.</p><p id="">Electrochemical tests have therefore revealed that these conversion layers afford long-lasting protection; withstanding up to 168 h in Salt Spray test.</p>
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| [20] |
Study on performance and corrosion resistance mechanism of rare metal conversion coating on Al alloy surface ,铝合金表面稀土转化膜性能与耐蚀机理研究 ,
在全面分析国内外稀土转化膜的 研究成果和存在问题的基础上,结合前期稀土对铝合金缓蚀机理、成膜机理研究成果,对含氧化促进剂的化学方法形成的稀土铈转化膜进行了研究。采用扫描电子显 微镜(SEM)、X射线散射能谱分析(EDS)和X射线衍射(XRD)分析、X射线光电子能谱(XPS)的Survey谱图分析转化膜的主要成分和铈的价 态。结果表明:铝合金表面稀土转化膜主要由非晶态的四价Ce氧化物/氢氧化物和铝氧化物的混合物组成;在整个转化膜中Ce元素总体分布均匀;转化膜致密均 匀,局部镶嵌一些富含Ce沉积物。电化学研究证明,在NaCl溶液中含氧化促进剂H2O2形成致密的非晶态的铈转化膜能够阻止水和Cl离子在转化膜中的渗 透,同时抑制了铝合金表面发生电化学腐蚀的阴极过程和阳极过程,稀土转化膜产生点蚀后还具有一定的自修复能力。
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| [21] |
Electronic structures of MRhO2, MRh2O4, RhMO4 and Rh2MO6 on the basis of X-ray spectroscopy and ESCA data , |
| [22] |
Lanthanum-based conversion coating on Mg-8Li alloy , |
| [23] |
Microstructure and dielectric properties of La2O3 films prepared by ion beam assistant electron-beam evaporation, Journal of |
| [24] |
Characterization of Venezuelan Laterites By X-Ray Photoelectron Spectroscopy ,
X-ray photoelectron spectroscopy, together with some bulk sensitive techniques, has been used to characterize a set of Venezuelan laterites which are potential catalysts in various industrially important reactions. Our studies reveal the occurrence of certain phase transformations and allow us to give the surface composition of these samples. It has been possible to show that Si and Fe are present not in oxide form but in other phases.
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| [25] |
Effect of the anionic part of various Ce(III) salts on the corrosion inhibition efficiency of AA2024 aluminium alloy ,
Systematic investigations on the inhibitive efficiency of different Ce(III) salts against the corrosion of AA2024 in 0.01M NaCl are performed. Various concentrations (from 10 615 to 10 612 M) for each Ce-salt are investigated after different exposure periods up to 600h. Their inhibitive abilities were evaluated by: Linear Sweep Voltammetry (LSV) and Electrochemical Impedance Spectroscopy (EIS) combined with SEM observation and EDX analysis. A strong influence of the Ce-salts anionic parts on the inhibitive efficiencies and the mechanism of the protective behaviour are found. The inhibitive efficiencies of the Ce(III) salts are ordered as: Ce(NO 3 ) 3 >(NH 4 ) 2 Ce(NO 3 ) 5 >Ce 2 (SO 4 ) 3 >CeCl 3 .
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| [26] |
Corrosion protection of in situ Al-based composite by cerium conversion treatment ,
Cerium conversion films were deposited on the surface of in situ aluminum-based composite in solutions containing different cerium chloride (CeCl) and hydrogen peroxide (HO) concentrations at 30 掳C. The morphology and composition of conversion films deposited in various solutions were investigated using scanning electron microscopy, energy dispersive x-ray analysis, and x-ray photoelectron spectroscopy (XPS). SEM observations revealed that only patches of film can be deposited on the composite surface when immersed in solutions with low CeCland HOconcentrations. However, entire composite surface was covered with a compact film when immersed in a solution containing 10 g/L CeCland 100 mL/L HO. XPS results indicated that cerium was incorporated as Cespecies in the hydrated oxide film. The formation of such hydrated conversion film on the composite resulted in low anodic current density and more noble pitting potential when exposed to 3.5% NaCl solution.
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| [27] |
Measurement of aluminium corrosion potential-pH and the polarization curve ,铝的电位-pH图及铝腐蚀曲线的测定 ,
测定了在ｐＨ＝２～１６范围内，铝的腐蚀电位－ｐＨ图，对铝腐蚀电位－ｐＨ图中的各临界线上的反应进行了分析，得到了铝在水溶液中腐蚀的钝化ｐＨ值范围，并建立了在不同ｐＨ值范围内，铝的腐蚀电位方程；还测定了在ｐＨ＝７时，纯水及人造海水中铝的腐蚀极化曲线。
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| [28] |
Investigation on the mechanism of forming rare earth conversion coating on zinc plating ,锌镀层表面稀土转化膜成膜机理分析 , |
| [29] |
Inhibitive mechanism of Ce-ion and La-ion for carbon steel in NaCl solution ,稀土Ce和La对碳钢在NaCl溶液中的缓蚀机理 ,
采用盐水滴腐蚀试验、腐蚀产物SEM及XPS分析、极化曲线测试分别研究了Ce3+和La3+对碳钢在氯化钠溶液中的缓蚀机理，并利用热力学数据绘制了Ce-H2O及La-H2O二元电位－pH相图。结果表明Ce3+和La3+能够在pH值较高的阴极区沉淀，阻碍O及电子在碳钢表面和溶液之间的转移和传递，通过抑制阴极反应从而减缓腐蚀的进行。热力学计算及电位 － pH图表明Ce3+在有氧时可被氧化成沉淀倾向更强的Ce4+，在酸性溶液中Ce4+化合物的稳定性要高于La3+化合物，因此Ce3+的缓蚀效果要好于La3+。
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