锰和锑元素对锌腐蚀的影响及其机理研究

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	锰和锑元素对锌腐蚀的影响及其机理研究
	尚秀玲
学位类型	博士
导师	柯伟 ; 张波
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	腐蚀科学与防护
关键词	Zn-0.4mn Zn-1.2sb 钝化大气腐蚀 Xps Zn-0.4mn Zn-1.2sb Passivation Atmospheric Corrosion Xps
摘要	" Zn具有良好的耐大气腐蚀性能且电化学活性比Fe高，因此Zn主要用于锌镀层，覆盖在钢材表面以减缓钢铁的大气腐蚀速率。在现有的镀锌方法中，热浸镀锌在工业中的应用最为广泛。随着工业上对可以长期服役的热浸锌镀层需求的增长，需要开发新的耐蚀的热浸锌镀层。其中添加合金元素是提高镀Zn钢耐腐蚀性能的一个可能途径。有研究表明添加Mn和Sb元素能提高热浸锌镀层的耐蚀性，但对其作用机理尚缺乏深入研究。为此，本论文主要选择Mn和Sb元素为主要合金元素，采用多种表面分析和微观观察技术系统地研究了添加Mn和Sb锌合金的大气腐蚀，活性腐蚀和钝化行为；并深入分析了含Mn和Sb锌合金的钝化和腐蚀行为和机制。首先，根据相图、热浸镀锌生产工艺和文献报道等综合结果确定了Mn和Sb合金元素的添加量分别为0.4wt%和1.2wt%。微观成分分析和微观组织观察表明：Zn-0.4Mn中的Mn元素几乎完全固溶在Zn基体中；而在Zn-1.2Sb合金中，Sb在基体中完全不能固溶，只存在于富Sb相中。采用XPS、AFM等实验方法研究了添加少量Mn(0.4 wt %)对纯Zn在0.1M NaOH溶液中的钝化行为的影响。结果表明添加0.4wt% Mn能降低纯Zn钝化区间的钝化电流密度。XPS结果表明Mn以+2价态存在于钝化膜中，且Mn元素在钝化膜中的含量高于基体。Mott-Schottky分析结果揭示Zn-0.4Mn合金表面钝化膜的缺陷浓度低于纯Zn钝化膜的缺陷浓度。AFM观察发现Zn-0.4Mn钝化膜的颗粒尺寸小于纯Zn，这表明Mn能促进ZnO形核。此外，AFM结果表明添加Mn可以降低纯Zn在0.1M NaOH溶液中表面粗糙度。根据以上结果提出了Mn提高纯Zn钝化性能的主要机制，即Mn能促进ZnO形核并降低钝化膜的孔隙率，同时Mn还能减低钝化膜的缺陷浓度从而抑制钝化膜中离子的传输。通过SEM、TEM和电化学测试研究了Zn-1.2Sb合金中富Sb相的微观结构和电化学性质。TEM/EDX 分析表明Zn-1.2Sb合金中的富Sb第二相Zn：Sb原子比约为3：2。电化学试验发现富Sb相电化学活性比Zn低。在近中性溶液中(0.1M NaCl)中，Sb相对纯Zn的腐蚀作用不明显，对阳极和阴极反应均没有显著的促进作用。然而在酸性溶液(0.1M NaCl+0.001MHCl)中，富Sb相促进析氢反应，而对氧还原反应没有明显的促进作用。研究了合金元素Mn和Sb在工业大气和海岸工业大气环境中对纯Zn大气腐蚀性能的影响，并对合金元素的作用机理进行了分析。在海岸工业大气环境中，添加少量Mn(0.4 wt%)可以显著减少纯Zn在大气腐蚀过程中的局部腐蚀。而在工业大气环境中，添加少量Mn(0.4 wt%)对纯Zn在大气腐蚀过程中局部腐蚀的影响不明显。纯Zn和Zn-0.4Mn合金在工业大气环境中腐蚀产物的主要成分为Zn5(CO3)2(OH)6和Zn4SO4(OH)6。其中，Zn4SO4(OH)6分布在整个腐蚀产物内，且在点蚀坑内部浓度最高。海岸工业大气环境中则为Zn5(CO3)2(OH)6，Zn4SO4(OH)6 和 NaZn4Cl(OH)6SO4·6H2O。其中，Zn4SO4(OH)6分布在整个腐蚀产物内，在点蚀坑内部浓度最高，而NaZn4Cl(OH)6SO4·6H2O主要分布在腐蚀坑上部。在两种环境中，添加少量Mn对腐蚀产物的成分没有影响。在只有SO2存在且浓度较高时，Mn可以降低均匀腐蚀速率。在SO2和Cl-共同存在的环境中，发现Mn能显著抑制纯Zn的局部腐蚀。在大气环境下，Mn元素的作用机制为通过缓解局部酸化来减少局部腐蚀，此外Mn促进ZnO形核使腐蚀产物更均匀从而降低均匀腐蚀速率。激光共聚焦显微镜结果表明在工业大气和海岸工业大气环境中，添加少量Sb(1.2 wt.%)对减少纯Zn在大气腐蚀过程中的局部腐蚀作用并不明显。与纯Zn的大气腐蚀产物相似，Zn-1.2Sb合金在工业大气环境中腐蚀产物的主要成分也为Zn5(CO3)2(OH)6和Zn4SO4(OH)6；在海岸工业大气环境中为Zn5(CO3)2(OH)6，Zn4SO4(OH)6 和 NaZn4Cl(OH)6SO4·6H2O。添加少量Sb对腐蚀产物的成分及分布规律没有明显影响。添加少量Sb(1.2 wt.%)对纯Zn在工业大气和海岸工业大气环境中大气腐蚀失重没有明显的作用，这些结果由富Sb相电化学性质来解释，即富Sb相阳极活性比Zn基体低，但对氧还原反应没有促进作用。"
其他摘要	"Atmospheric corrosion is the most prevalent type of corrosion for zinc, owing to extensive outdoor applications of hot-dip galvanized steels. Nearly half of the zinc produced is used for this purpose. The zinc coating which has high corrosion resistance is required along with the development of industry. Alloying elements have significant effects on the atmosphere corrosion and adding beneficial alloying elements have been an important way to improve the atmosphere corrosion resistance of zinc. Recently, it has been reported that Mn and Sb can be successfully added into molten zinc and can increase the corrosion resistance of hot-dip galvanized coating. However, there is still a lack of full understanding of the effect of Mn and Sb on the corrosion mechanism of zinc. In this study, many technologies were used to understand the effect of Mn and Sb on the corrosion mechanism of zinc. Pure Zn (99.995 wt%), Zn-0.4Mn alloy (containing 0.4 wt% Mn ) and Zn-1.2Sb (containing 1.2 wt%Sb) were used in this study. Zn-0.4Mn and Zn-1.2Sb alloy were successfully made by adding 0.4 wt% Mn and 1.2wt% Sb in the molten Zn bath (99.995 wt%) respectively. After being cooled in air, the alloy was cut into required sizes by electronic discharge machining. Most majorities of Mn additions are dissolved in the Zn matrix with occasionally tiny amounts of Mn-rich intermetallic particles and there were significant Sb-rich intermetallic particles formed on Zn-1.2Sb as confirmed by SEM/EDX analysis (not shown). No detectable Sb was found in Zn matrix. The passivation of pure Zn (99.995 wt%) and Zn-0.4Mn (0.4 wt% Mn) alloy in a deaerated 0.1M NaOH solution (pH 12.9) was investigated by electrochemical measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The potentiodynamic polarization and electrochemical impedance measurements show that addition of 0.4 wt% Mn can decrease the passive current density of Zn in the passive region. XPS surface analysis indicates that there is approximately 1.0-2.0 at% Mn2+ being incorporated into the passive film on Zn-0.4Mn alloy with Mn content being higher in the outer layers. Mott-Schottky analysis shows that the incorporated Mn can decrease concentration of defects in the film. AFM observations disclose that Mn can decrease the grain size of the film. The mechanism by which Mn additions improve the passivity of Zn is that the incorporated Mn can inhibit ions transportation in the film and inhibit its growth. Meanwhile, Mn can also promote the nucleation of Zn oxides and decrease film porosity. The structure of Sb-rich intermetallic phase in Zn-1.2Sb (1.2 wt%Sb) alloy has been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and transmission electron diffractions. TEM analysis shows that the Sb-rich phase may be a new phase, and it has no obvisous effect on oxygen reduction reaction and hydrogen evolution reaction 0.1 M NaCl. In acidic solution (0.1M NaCl+0.001M HCl), the Sb-rich phase can promote the hydrogen evolution reaction, nevertheless, has no obvisous effect on oxygen reduction reaction. The formation mechanism of atmosphere corrosion products inside pits and the role of small Mn and Sb addition on localized corrosion of Zn have also been discussed. The corrosion performances of pure Zn and Zn-0.4Mn alloy exposed in marine (Qingdao, east of China) and industrial (Shenyang, northest of China) environment have been studied after exposure for three years. After exposure in Qingdao for three years, pitting corrosion occurs on both pure Zn and Zn-0.4Mn with fewer and smaller pits found on Zn-0.4Mn alloy by confocal scanning laser microscope (CSLM), which indicates that the addition of Mn can reduce the localized corrosion of Zn. After exposure in Shenyang for three years, small addition of Mn can reduce the uniform corrosion rate of pure Zn. Corrosion products formed on pure Zn and Zn-0.4Mn have been characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe micro-analyzer (EPMA). The main crystalline phases identified by XRD are Zn5(CO3)2(OH)6, Zn4SO4(OH)6 after exposure in Shenyang for three years, and the main crystalline phases identified by XRD are Zn5(CO3)2(OH)6, Zn4SO4(OH)6 and NaZn4Cl(OH)6SO4·6H2O after expose in Qingdao for three years. Small amounts of ZnO and Zn(OH)2 were also found which mainly present on top surface of corrosion films as revealed by XPS. Combined results of XRD and EPMA indicate that Zn4SO4(OH)6 and NaZn4Cl(OH)6SO4·6H2O are the main compounds inside the pits with Zn4SO4(OH)6 locating at the pit bottom. Addition of 1.2wt% Sb has no obvisous effect of atmosphere corrosion in both marine and industrial environment. The main crystalline phases identified by XRD are Zn5(CO3)2(OH)6, Zn4SO4(OH)6 after exposure in Shenyan for three years, and the main crystalline phases identified by XRD are Zn5(CO3)2(OH)6, Zn4SO4(OH)6 and NaZn4Cl(OH)6SO4·6H2O after exposure in Qingdao for three years. Small amounts of ZnO and Zn(OH)2 were also found which mainly presented on top surface of corrosion films as revealed by XPS analysis. Addition of Sb has no obvisous effect on elements distributing. Compared with Zn matrix, Sb-rich phase is less active. The Sb-rich phase is found to have no effect on oxygen reduction reation rate, thus the less active Sb-rich phase may have a beneficial effect on atomosphere corrosion performance of Zn. However, the possobility of pitting may be increased since it promotes hydrogen evolution in acid environment. "
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64499
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	尚秀玲. 锰和锑元素对锌腐蚀的影响及其机理研究[D]. 北京. 中国科学院金属研究所,2012.