【作者】 檀玉；

【导师】 张胜寒；

【作者基本信息】 华北电力大学 ， 热能工程， 2012， 博士

【摘要】 核电站中采用Zn离子添加技术减少一回路材料的应力腐蚀破裂和职业辐照,其原理简单理解为Zn离子参与合金表面氧化膜中金属氧化物的生成,挤占氧化膜中部分金属空穴,高温水中添加Zn离子前后合金氧化膜的半导体性质改变并不明确。本文采用光电化学响应和交流阻抗(Mott-Schottky曲线)法分析了高温水中多种形式Zn离子添加对镍合金表面氧化膜的半导体性质的影响,结合氧化膜的电化学研究结果和表面形貌与成分分析,利用点缺陷模型讨论了高温水中Zn离子对镍合金氧化膜的半导体性质影响。并用上述实验方法进行了高温水中SUS316L不锈钢的实验,全面地分析高温水中Zn离子添加改变Fe基和Ni基合金表面氧化膜的半导体性质的机理及抑制腐蚀的原因。首先应用光电化学响应和Mott-Schottky曲线研究了纯Ni在500℃空气气氛下生成的氧化膜和在pH8.4中性缓冲溶液中阳极氧化生成钝化膜的半导体性质。其在中性溶液中生成钝化膜的光电化学响应表明,饨化膜由NiO内层和Ni(OH)2外层构成,其带隙宽度分别为2.8eV和1.6eV,其中,内层NiO的带隙宽度与纯Ni在高温空气气氛生成氧化膜的带隙宽度2.4eV相似。Mott-Schottky曲线表明纯Ni在pH8.4中性溶液中生成钝化膜的平带电位约0.40V,其在高温空气气氛生成氧化膜的平带电位约0.15V,前者的载流子浓度约是后者34倍。通过上述研究建立了纯Ni上钝化膜的电子能带结构模型,解释了其内层NiO和外层Ni(OH)2间同为p型半导体组成钝化膜的半导体性质。为后续镍合金和不锈钢的高温水实验研究创造基础条件。应用稳态光电流响应法分析了镍基合金在高温水中添加硫酸盐等形式Zn离子生成氧化膜的半导体性质,指出氧化膜中不同氧化相的特征带隙宽度分别为Fe2O32.2eV, Cr2O33.5eV, FexNi1-xCr2O44.1eV和ZnO3.2eV,在开路电压下,无Zn2+参与生成的氧化膜表现阴极光电流响应(p型半导体),有Zn离子参与生成的氧化膜表现阳极光电流响应(n型半导体)。Mott-Schottky曲线表明有Zn离子参与生成的氧化膜平带电位较负,相同极化电压下Csc-2(Csc空间电荷电容)值较大。采用恒电位仪和锁相放大器联用技术发展了暂态光电流响应分析方法,并应用于镍基合金和不锈钢在高温水中添加氧化锌(ZnO)形式Zn离子生成氧化膜的半导体性质分析,指出Zn离子取代氧化膜外层中部分Fe生成复杂Zn Fe、Ni和Cr氧化物,同时改变了氧化膜的半导体性质,使其在一定电位区间表现非典型的n型半导体响应。同时分析了氧化膜的暂态光电流响应的幅值与相角和外加电压间的关系,建立了采用相角判断氧化膜半导体类型的方法。结合金属表面氧化膜的点缺陷模型,分析了由Mott-Schottky曲线获得的平带电位和载流子浓度与氧化膜的稳定性(耐腐蚀性)的关系。采用表面分析技术研究了上述氧化膜的形貌和成分。SEM分析指出有Zn离子参与生成的氧化膜其表面氧化物颗粒较无Zn离子参与生成的小,较致密。XPS分析指出氧化膜表面和一定深度有Zn检出,其成0价和+2价形态,说明Zn离子与氧化膜中的其他氧化相共同作用生成了复杂氧化物。更多还原

【Abstract】 Stress corrosion cracking and occupational radiation can be retarded effectively by zinc injection to the primary circuit of nuclear power plant. For simple understanding, the Zn ion cooperated with the other metallic oxide in the oxide film on the alloy and was instead of metallic hole. It is unclear the changes of the semiconductor properties of oxide films on alloy in high temperature water with zinc addition. The photoelectrochemical and capacitance responses(Mott-Schottky plots) were employed to investigate the semiconductor properties of the oxide films on Ni-based alloys in high temperature water with various Znion addition. And also the electrochemical analysis, surface morphology and component analysis were adopted. The results of the Znion addition to high temperature water were discussed by point defect model. Also the same experiment was introduced to SUS316L stainless steel. The semiconductor properties of oxide films on Ni-based and Fe-based alloys in high temperature water with Zn addition were fully discussed.The semiconductor properties of the passive film formed on pure Ni by anodic passivation in pH8.4borate buffer solution and the oxide film on pure Ni by thermally grown in air at500℃were investigated by photoelectrochemical response and Mott-Schottky plots analysis. The photocurrent spectra of the passive film on pure Ni were derived into two peaks for inner NiO and outer Ni(OH)2layers, respectively. The band gap energy Eg for the inner NiO was2.8eV and Eg for outer Ni(OH)2was1.6eV, respectively. Eg2.8eV of the inner NiO of the passive film on pure Ni was close to that2.4eV of the thermally grown oxide of pure Ni, indicating that the inner NiO in the passive film is crystalline structure. The Mott-Schottky plots for both the passive film and the thermal oxide film on pure Ni demonstrated that the two films exhibited p-type semiconductors with different values of flat band potential:0.40V for the passive film and0.15V for the thermally grown NiO. An electronic energy band model of both p-type semiconductors of inner NiO and outer Ni(OH)2layers was proposed to explain the photocurrent and Mott-Schottky plots for the passive film on pure Ni.The steady photocurrent response was employed to investigate the oxide films formed on Incone1600with various sulfate zinc addition. The photocurrent of the oxide film was plotted as a function of photon energy, for separating into several parts which can be derived from Fe2O3with a band gap energy2.2eV, Cr2O33.5eV, FexNi1-xCr2O44.1eV besides ZnO3.2eV which was firstly recorded in the oxide films of Incone1600by photoelectrochemical responses. For steady photoelectrochemical responses, the oxide film formed with zinc addition exhibited anodic photocurrent(n type semiconductor) at open circle potential while the film without zinc exhibited cathodic photocurrent(p type semiconductor). Mott-Schottky plots indicated a negative movement of the flat band potential of the oxide film on Incone1600with zinc addition to the film without zinc. At the same potential, the higher CSC-2(CSC, space charge capacitance) indicated a more compact oxide film of Incone1600with zinc addition in the high temperature water.A transient state photocurrent response was developed by coupling technique of potentiostat and lock-in amplifier and was also employed to investigate the semiconductor properties of oxide films on Ni-base alloys and stainless steel in high temperature water with ZnO addition. A compact structure oxide with formula ZnyFexNi1-x-yCr2O4of the outer layer, besides the chromium enrichment of the inner layer, of the oxide film on Incone1600in high temperature water with ZnO addition was studied. The semiconductor properties of the oxide films on Incone1600in high temperature water with ZnO addition suggested an untypical n-type semiconductor at anodic polarization with a negative movement of the flat band potential of the oxide films without ZnO. The value and dephasing angle of the transient state photocurrent response in function of the applied potential were also discussed. The relationship of the stability of the oxide film and the flat band potential and carrier density of the oxide film from Mott-Schottky plots were discussed by point defect model.The surface morphology and components of the corrosion oxide layers in high temperature water with Zn addition were examined by scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS). The results revealed that smaller crystals on the alloys with Zn addition. And the Zn was detected on the surface and in the depth of the oxide film with both0valence and+2valence.更多还原