针铁矿和赤铁矿吸附As(V)的EXAFS研究

砷是一种有毒污染物,其在铁氧化物表面的吸附是影响其迁移转化行为的重要因素。针铁矿和赤铁矿是自然界中广泛存在的稳定氧化铁矿物,它们具有粒径小、比表面积大、活性基团多等特性,可用做吸附剂。在不同pH和不同铁砷摩尔比的实验条件下,用针铁矿和赤铁矿吸附五价砷As(V),结果表明:实验所用的两种吸附剂均呈现吸附量随铁砷摩尔比升高而降低的现象,而在酸性pH条件下的砷吸附量均大于其在碱性pH条件下的吸附量;在相同的实验条件下,针铁矿对砷的吸附量要大于赤铁矿对砷的吸附量。进一步通过扩展X射线吸收精细结构光谱(Extended X-ray Absorption Fine Structure Spectroscopy,EXAFS)观测砷在针铁矿和赤铁矿上吸附后形成的络合物的分子结构,结果显示:砷与针铁矿和赤铁矿中的铁氧八面体之间的配位数均接近1,不同样品中As-Fe键的长度范围为3.29～3.31?,表明As(V)在针铁矿和赤铁矿表面吸附后主要形成单齿单核络合物,且该结构与吸附p H和铁砷摩尔比无关。     

铀表面腐蚀初始阶段的理论模型

本文使用数值模拟方法讨论了铀表面腐蚀初始阶段的氧化物形成过程.这个阶段发生在从清洁的铀表面吸附反应气体后到整个表面被一层氧化物所覆盖的过程之间.对储存在含有腐蚀气体气氛中的铀和铀合金材料,准确了解铀最初开始反应到表面被氧化物完全覆盖的反应速率是非常重要的.本文对该氧化物形成的过程进行了数学推导,讨论了等温情况下的近似分析数学表达式,得到了动力学方程,并与实验结果进行比较,表明理论模型是合理的.     

双层辉光离子渗金属技术制备Al-Cr-Si氧化物阻氚涂层

本文采用双层辉光离子渗金属技术在316L不锈钢表面进行Al-Cr-Si共渗后氧化处理,制备致密的氧化物阻氚渗透涂层。用SEM、TEM和XRD分析制备涂层的组织结构,用划痕法和抗热震实验对其进行性能测试。结果表明,Cr、Si元素的掺入使涂层生成连续致密的Al2O3氧化膜;在外层富铝区,Al2O3和少量Fe、Cr的氧化物反应生成了尖晶石型复合氧化物Fe(AlCr)2O4。氧流量为0.01L/min时制得的氧化涂层的组织和性能最佳,其结合力达68N,热震实验后表面无裂纹出现。     

穆斯堡尔谱研究Fe_2(C_2O_4)_3/HY和Fe_2(C_2O_4)_3/HZSM-5在氢气中的热分解

以穆斯堡尔谱研究了Fe_2(C_2O_4)/HY和Fe(C_2O_4)_3/HZSM-5在氢气中的热分解。草酸铁(Ⅲ)在HY和HZSM-5沸石上不同的热分解方式主要是由于两种沸石的表面酸性不同。HY沸石的硅铝比较低,表面酸性较弱,草酸铁(Ⅲ)在其表面发生离解吸附,结果一部分Fe(Ⅲ)直接同表面羟基配位,这部分Fe(Ⅲ)具有较大的四极分裂值,且难以被还原;另一部分Fe(Ⅲ)受HY沸石表面作用较弱,其四极分裂值较小,240℃时被还原     

黄钾铁矾的制备及其对U(Ⅵ)的吸附

为了研究黄钾铁矾对溶液中U(Ⅵ)的吸附效果,采用一步水热法制备了黄钾铁矾,并利用X射线衍射(XRD)、拉曼光谱(Raman spectrum)、红外光谱(FTIR)和扫描电子显微镜(SEM)等技术表征了材料的理化特性。利用静态吸附实验研究了溶液pH值、离子强度、固液比和U(Ⅵ)初始浓度对吸附过程的影响。结果表明:溶液pH对于U(Ⅵ)的吸附产生较大的影响,而离子强度则对吸附过程没有影响,表明黄钾铁矾对U(Ⅵ)的吸附机理为内层表面络合。吸附在100 min内基本达平衡,且符合准二级动力学模型。吸附等温线符合Langmuir等温模型,表明U(Ⅵ)的吸附是单层吸附。在溶液的pH=7.0、298 K时,黄钾铁矾对U(Ⅵ)的最大吸附量为154 mg/g。最佳吸附条件为:固液比1.0 g/L、U(Ⅵ)初始浓度为0.42 mmol/L、298 K、pH=7.0,达到平衡时的吸附量为(76.0±1.4) mg/g(n=3),去除率达到了(88.0±1.3)%(n=3)。以上结果表明,黄钾铁矾可以作为含U(Ⅵ)废水处理的潜在吸附材料。     

Am(Ⅲ)在铁氧化物上的吸附行为

为了解放射性核素在可能作为高放废物固化体包装容器材料腐蚀产物上的吸附行为,以我国高放废物处置库预选场址--甘肃北山地区深部地下水为介质,研究了包装容器材料的主要组分铁的腐蚀产物Fe2O3, Fe3O4对Am(Ⅲ)的吸附,讨论了pH值、总CO2-3, SO2-4、腐殖酸、Am(Ⅲ)浓度等对吸附的影响,并就可能的吸附机理进行了探讨.实验结果表明,Am(Ⅲ)在铁氧化物上的吸附分配比随水相pH值增大而增大;地下水的化学组分是影响Am(Ⅲ)存在形态和吸附的关键,Am(Ⅲ)在Fe2O3和Fe3O4上的吸附机理为界面配合,可用Freundlich吸附等温式描述.     

离子注入碳对铀表面初始氧化行为影响的研究

用俄歇电子能谱(AES)分别对高真空室中铀样品及多能量叠加离子注入碳铀样品与氧气吸附及初始氧化过程进行了研究.结果表明,在高真空室中,清洁铀表面很容易吸附氧化,发生氧化反应,当O2暴露剂量为40 L时,清洁铀表面就会形成一层UO2;离子注入碳后铀表面的抗氧化能力增强.     

微陶材料对铀的吸附特性

采用多种方法对微陶材料进行了表征,分别采用静态法和动态法研究了溶液pH、吸附时间、铀初始浓度、吸附剂用量、解吸流速、吸附剂粒度等因素对微陶材料吸附铀的影响;探究了微陶材料对模拟放射性废水的处理能力。实验结果表明,扫描电镜显示微陶材料底部为层状结构,能谱显示其表面主要成分为铝元素,还有少量(质量分数6.00%)的铁元素;XRD结果显示微陶材料表面无明显Fe的衍射峰;红外光谱显示微陶材料对铀进行了吸附;当pH=5、吸附时间为1h、铀初始质量浓度为100μg/L、微陶材料用量为50mg时,微陶材料对铀的吸附率达到95%以上;动态法中流速和粒度对吸附影响较小;微陶材料对铀的吸附等温线符合Freundlich吸附等温模型;采用准二级反应动力学模型描述微陶材料对铀的吸附,吸附过程主要为化学吸附;微陶材料对模拟放射性废水中铀的吸附率均在90%以上,对锶、铯也有一定的吸附能力。     

放射性核素在矿物表面的吸附微观结构分析进展

放射性核素在矿物表面的吸附行为是影响其在环境中的浓度、迁移、转化及毒性的重要过程。本文简要介绍了放射性核素在吸附剂表面的吸附、沉淀、氧化还原反应的作用机理,针对放射性核素在矿物表面的微观吸附形态的研究中所使用的一些先进的实验分析方法,重点介绍了同步辐射X射线吸收精细结构（XAFS）技术、荧光分析以及理论计算等技术,并展望了放射性核素在矿物表面微观反应机制的研究趋势。     

Pu在铁及铁氧化物上的吸附行为研究

为了解放射性核素在可能作为高放废物固化体包装容器材料及其腐蚀产物上的吸附行为,研究了包装容器材料的主要组分铁及铁的腐蚀产物FeO,Fe2O3,Fe3O4对Pu的吸附行为,探讨了水相pH值（1．0～10．0）,CO3^2-离子浓度（4．0 mmol/L～0．1mol/L）等因素对吸附的影响。实验结果表明,Pu在铁及其氧化物上的吸附能力随水相pH值增大而增大;实验环境中氧浓度变化对Pu在铁及其氧化物上的吸附影响较小;CO3^2-浓度增大不利于Pu的吸附。     

Cellular automaton modeling on the corrosion/oxidation mechanism of steel in liquid metal environment

Corrosion and oxidation of structure material in liquid lead alloys, which have been strongly associated with the nuclear industry, are specific but important areas of corrosion in liquid environments. In high temperature liquid metal environment, the corrosion rate of stainless steels is controlled by the solid diffusion of iron along grain boundaries in the oxide layer and a duplex oxide layer is formed with the inner layer growing by infiltration of corrosive solution along oxide micropores and the outer layer growing by the diffusion of metal ions. To interpret the role of diffusion and reaction process in the process of oxidation, a cellular automaton model, which combines the surface growth and internal oxidation, was created to explain the oxidation mechanism of steels in high temperature corrosive liquid metal environment. In this model, three main processes, which include the corrosion of the substrate, the diffusion of iron species across the oxide layer and precipitation of iron on the oxide layer, are simulated. The diffusion process is simulated by random walk model. Mapping between present model and experimental data has been created. The gross features concerning the evolution of the involved process were explored.     

Dissolution of magnetite using an environmentally friendly chelant: an electrochemical impedance spectroscopy study

Ethylenediaminedisuccinic acid (EDDS), a biodegradable substitute for EDTA, was used as a chelant for dissolving magnetite and magnetite formed on iron metal surface. Dissolution was found to increase in presence of ferrous ions and depend on pH of solution, concentration of ferrous ion, EDDS concentration, applied cathodic potential and temperature. The impedance spectrum for the dissolution of magnetite film formed on iron exhibited two time constants. The first at high frequency range is ascribed to the reductive dissolution of magnetite. It is very crucial to carry out the dissolution process at the appropriate temperature to insure complete removal of oxide layer.     

Application of Zeolites to Remove Iodine from Dissolver Off-Gas, (I)

The oxidation behavior of Zr(Fe,Cr)₂ precipitates being present at the surface of Zircaloy-4 was examined with microprobe Auger electron analysis, focussing attention on the oxidation behavior of chromium and iron in the early stage of oxidation where the oxide film was coherent. Chromium formed a thin oxide layer at the top surface of the zirconium oxide film of precipitate and remained in a metallic state inside the oxide film. Iron was oxidized via dissolution in the matrix zirconium oxide near the top surface and remained in a metallic state inside the oxide film. Such variety of chemical state of chromium and iron with depth in the oxide film was attributed to the existence of oxygen potential gradient in the oxide film.     

The early stages of the oxidation of a 9% chromium steel em carbon dioxide studied by Auger electron spectroscopy

The early stages of the oxidation of 9% Cr steel in carbon dioxide at atmospheric pressure and 773 K have been studied by use of Auger electron spectroscopy. The surface of the sample was monitored throughout the oxidation process without changing the environment other than to evacuate the system for a short period so that the Auger spectrum could be recorded. Sulphur was found to be an important participant in the early stages of oxidation and an oxide film containing iron was formed. Chromium was not detected in this oxide, indicating that its presence in the alloy is not conducive to the formation of a protective Cr₂O₃ layer. The mechanism of oxidation was similar to that of pure iron under the same conditions.     

Effects of oxide and hydrogen on the behavior of Zircaloy-4 cladding during the loss of the coolant accident (LOCA)

Effects of surface oxide and absorbed hydrogen on the behavior of the loss of the coolant accident (LOCA) were investigated in this study. High temperature ballooning and thermal quench tests were performed for Zircaloy-4 cladding which had been prepared with up to 50 μm of oxide and 1000 ppm of hydrogen, respectively. In the high temperature ballooning test, the initially pressurized cladding was heated until a rupture. Threshold oxidation (ECR) of each condition was evaluated in the thermal quench test in which oxidized cladding at the LOCA temperature was quenched by water. Ring compression test was performed to assess the ductility of the quenched cladding The results showed that both the oxide and hydrogen affected the high temperature ballooning property due to the constraint of the α phase by the surface oxide as well as the expansion of the β phase by the absorbed hydrogen. In the quench test, the pre-oxide and absorbed hydrogen did not affect the high temperature oxidation whereas the threshold ECR decreased in the hydrogen charged cladding because the absorbed hydrogen increased the maximum oxygen solubility inside the residual β layer to reduce the cladding ductility.     

ESR Dosimetry of Teeth of Residents Close to Chernobyl Reactor Accident

Sorption behavior of uranium (VI) during crystallization of amorphous iron (A.Fe) minerals to crystalline iron (C.Fe) minerals have been investigated. Two different sorption conditions are applied for the experiments. One is the condition in which uranium is sorbed on A.Fe minerals before the crystallization (dynamic condition). The other is the condition in which uranium is sorbed on the A.Fe minerals and C.Fe minerals of goethite (static condition). Associations of uranium with the iron minerals are examined by a selective extraction test using a 1 M CH₃COOK solution at pH 7, 1 M CH₃COONa solution at pH 5 (Morgan's solution), and TAO solution (10.9g.l^?1 oxalic acid+l6.1g.l^?1 ammonium oxalate).

Under the static condition, the fraction of uranium desorbed by a 1 M CH₃COOK solution at pH 7 from A.Fe minerals is lower than that from goethite. And all of uranium are desorbed by the TAO solution from both A.Fe minerals and goethite. Contrary, under the dynamic condition, fractional uranium is remained after the TAO solution extraction. The fractional uranium remained after the TAO solution extraction from the iron minerals increases with increase in the crystallinity of the iron minerals. The concentrations of uranium in the solutions are less than 1%. These show that during the crystallization of amorphous to crystalline iron minerals most of uranium associated with the amorphous iron minerals is not released into the solution, and some fractional uranium move to be fixed to crystalline iron minerals.     

In situ study of the oxidation of Zircaloy-4 by ESEM

Zircaloy-4 has been oxidised in environmental scanning electron microscope (ESEM), at a temperature of 700 °C and the surface of the material has been observed during the oxidation, directly in the ESEM. The material has been subsequently analysed by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Several aspects of the oxidation were revealed in these experiments. Zircaloy-4 oxidises at a different rate depending on the crystallographic orientation of the grains at the surface. The iron and chromium in the secondary phase particles (SPP) diffuse to the surface and oxidise to produce a profile at the surface of the material. The in situ observations reveal no cracks at the surface during the oxidation. Subsequent examination of the surface (ex situ) by AFM reveals the presence of pores in the oxide. TEM examinations indicate the presence of weak internal planes in the oxide layer, inducing cracks parallel to the metal-oxide interface.     

红绿彩瓷之釉上彩的XAFS研究

红绿彩瓷是一种低温釉上彩瓷,从结构层次探讨其釉上红彩、绿彩、黄彩的呈色机理一直是古陶瓷研究的空白。采用X射线吸收精细结构(X-rayabsorption fine structure,XAFS)方法,测试分析红绿彩瓷中的红彩、绿彩和黄彩。结果表明,红彩中致色元素Fe主要为+3价,其局域结构与Fe2O3相近,最近邻配位为扭曲的八面体结构。透射电子显微分析证实其物相为氧化铁晶体。黄彩中致色元素Fe主要存在+2价和+3价,绿彩中致色元素Cu主要为+2价,两者均处于无序度较高的局域环境中,最近邻配位为O原子。     

水化学对Zr-4合金氧化膜形貌的影响

为了研究LiOH水溶液影响Zr-4合金耐腐蚀性能的机理,用扫描电子显微镜和扫描探针显微镜观察Zr-4合金样品在不同介质中腐蚀后氧化膜内外表面的形貌。实验结果表明：由于氧化过程体积膨胀,氧化膜中存在平行于界面的压应力。在压应力的作用下,氧化膜向外鼓起,并在垂直于平面的方向上产生张应力,导致氧化膜破裂,从而使腐蚀加速。LiOH水溶液浓度越高,这个过程越快。     

Investigation on the stability of water-soluble ZnO quantum dots in KB cells by X-ray fluorescence and absorption methods

The structural stability of water-soluble ZnO quantum dots (QDs) in oral epidermoid carcinoma (KB) cells was studied by the External Micro Proton Induced X-ray Emission (External Micro-PIXE) technique and the X-ray absorption fine structure (XAFS) measurement. The External Micro-PIXE and XAFS experiments were respectively performed at the JAEA and the Shanghai Synchrotron Radiation Facility. The elements’ distributions were detected by the External Micro-PIXE technique. The XAFS method was applied to obtain information about zinc (Zn) K-edge spectra. The fits of the XAFS data showed that the Zn-O bond structure of water-soluble ZnO QDs was stable after being absorbed by KB cells. Its local structural parameters were almost identical with those of the standard wurtzite structure. Water-soluble ZnO QDs had good structural stability in KB cells.