镍基铸造高温合金K52在900 ℃恒温氧化性能的研究

研究了镍基铸造高温合金K52在900 ℃和100 h下的氧化行为, 并与ЧC104-Bи合金进行了比较, 为K52合金的设计提供了实验基础与理论依据. 结果表明, 两种合金在900 ℃和100 h下的氧化动力学曲线均符合抛物线规律, 属于完全抗氧化级. X射线衍射、扫描电镜、电子探针元素面分布和能谱分析等实验表明, K52合金和ЧC104-Bи合金的氧化膜相似, 可分为三层: 外层以TiO2层为主, 性质疏松, 空隙较多, 没有形成连续氧化层; 中间层为连续、致密、平直的氧化物, 形成保护性氧化层, 以Cr2O3为主, 并含有少量尖晶石NiCr2O4及TiO2; 内层以Al2O3为主, 含有少量TiO2氧化物. K52合金的恒温抗氧化性能优于ЧC104-Bи合金.     

扫描电子显微镜在鹌鹑蛋壳表征中的应用

利用扫描电子显微镜对鹌鹑蛋蛋壳的横截面、内外表面进行观察,蛋壳由内向外分别是壳膜、乳突层、海绵层、垂直晶体层和角质层. 外表面分布有深褐色、浅黄色的不规则颜色斑点,深褐色区域比浅黄色区域的角质层厚,其差异来自于角质层. 对深褐色区域与浅黄色区域进行外表面能谱分析,深褐色区域的C、O和N元素含量相对高于浅黄色区域,浅黄色区域的Mg、P、S和Ca元素含量相对高于深褐色区域.     

纳米Y2O3对Ni-WC合金喷焊层组织和耐磨性的影响

通过在含35%WC的Ni基自熔合金粉末中添加微量的纳米Y2O3,研究纳米Y2O3对合金喷焊层组织、硬度和耐磨性影响规律及其作用机制.实验结果表明,添加适量的纳米Y2O3可细化合金喷焊层组织,提高合金喷焊层硬度和耐磨性,改善合金喷焊层和基体的结合状态,并且经一定温度的后续热处理,可进一步提高合金喷焊层硬度和耐磨性.     

电化学去合金化Pt(Pd)-Cu对氧的电催化还原活性的研究

应用电化学去合金法制备了表面覆盖有Pt(Pd)原子层的Pt(Pd)-Cu合金催化剂.研究该催化剂在0.1mol.L-1HClO4酸性溶液中对氧气电化学还原的催化活性,并采用同步辐射反常X-射线衍射法(Anomalous X-ray Diffraction,AXRD)和表面X-射线散射法(Surface X-ray Scattering,SXS)从原子尺度研究了去合金化后催化剂的结构.分析对比纳米颗粒、薄膜和单晶3种不同形式的去合金化Pt-Cu的结构和催化活性以及Pt-Cu和Pd-Cu两种不同合金薄膜的结构和催化活性.结果表明,表面应力是影响催化剂催化活性的关键因素,而应力大小则与去合金化后所形成的表面Pt(Pd)层的厚度相关,材料尺寸和组成元素等都影响表面Pt(Pd)层的厚度.提出可利用调控材料表面的应力来设计高催化活性的催化剂.     

电泳沉积技术在生物合金上的应用

电泳沉积(EPD)是目前广泛应用于增加医用金属合金生物相容性以及耐蚀性的一种简便的涂层技术.该技术能够在复杂形貌基体上形成可控厚度的膜层,因此可有效应用于增加不锈钢、钛合金、镁合金等医用金属合金的生物相容性.本文介绍了电泳沉积技术原理、优缺点以及影响因素,同时也对电泳沉积技术在不同合金上沉积不同的功能涂层进行了综述.     

包裹在碳纳米管内Cu-Fe合金纳米线偏聚结构及稳定性研究

采用分子动力学方法系统研究了包裹在刚性碳纳米管内的Cu-Fe二元合金纳米线经高温退火后的稳定结构.研究结果表明,所形成的合金纳米线具有圆柱形壳层结构且有明显的偏聚现象.其中Cu原子富集于靠近管壁的外层,而Fe原子则富集于靠近轴心的核层.偏聚程度与碳纳米管管径和合金组分显著相关,而与被包裹的金属原子数无明显相关性.管径越大,组分中Cu原子含量越高,则偏聚程度越显著.表明可通过调节合金中Cu原子含量获得最外壳层为纯Cu而内部为纯Fe或合金的"同心异质"结构纳米线.用平均原子势能对体系稳定性进行了描述,结果显示,碳纳米管管径越大,包裹在内的金属原子数目越多,Fe原子含量越高,体系稳定性越好.这种偏聚行为和稳定性随碳纳米管管径、合金组分及金属原子数的变化而变化,几乎不受碳纳米管长度和手性的影响.     

Sm2(Co,Cu,Fe,Zr)17合金铸锭的缺陷和成分分布研究

采用X射线荧光仪、扫描电子显微镜及X射线电子探针仪,通过对Sm2(Co,Cu,Fe,Zr)17合金铸锭沿轴向不同截面、孔洞区域和异常结晶区域进行微区形貌观察和成分分析,研究合金铸锭缺陷及缺陷形成的原因.元素的轴向分布情况为Co、Sm、Fe等自下而上稍有增加,Cu、Zr分布较均匀;而O则大量集中在中部.在孔洞壁表面的树枝状区域富含Sm和Cu,贫Co,含有一定量的O,凸起区域富集偏析大量的Sm和O;氧化夹杂物的形成是铸锭孔洞形成的主要原因;铸锭结晶异常部位呈柱状结晶,含有一定量的O,铸件凝固区域较窄导致的溶质再分配现象、冷却速度过快及氧化夹杂物的存在是铸锭结晶异常部位形成的主要原因.     

热碱处理对La-Mg-Ni系A2B7型储氢合金电极性能的影响

用真空感应熔炼和热处理制备了La0.64Gd0.2Mg0.16Ni3.1Co0.3Al0.1合金,利用SEM,EDS能谱分析、振动样品磁力计、XPS、ICP和电化学方法,研究了热碱处理时间(0~60 min)对合金颗粒表面的微观形貌、表面元素组成及状态、体相化学成分以及电化学性能的影响。研究表明:热碱处理使合金表面的Mg,Al,La和Ni元素发生不同程度的溶解析出或氧化,随处理时间增加,合金饱和磁化强度呈先增大后减小的趋势。当处理时间为15 min时,合金表面可形成较多的富Ni层,其饱和磁化强度达到最大值0.808 emu·g-1;当大于15 min时,随时间延长,富Ni层被氧化的倾向逐渐增大,同时表面形成稀土氧化物,导致合金饱和磁化强度逐渐减小。电化学性能测试表明:随热碱处理时间的增加,合金电极最大放电容量(Cmax)、循环稳定性(S100)及大电流放电特性(HRD900)均呈先增加后减小的规律。经15 min热碱处理的合金电极性能最佳,循环寿命S100由未处理时的83.67%提高到热碱处理后的93.09%。合金电极性能随热碱处理时间的变化规律与合金表面形成富镍层及其后续氧化倾向以及析出稀土氧化物关系密切。     

铝热还原法制备铝-稀土中间合金的研究

以混合稀土碳酸盐为原料,Al为还原剂,还原时间为2 h,在温度范围为1000～1200℃的冰晶石熔体中,分别制备了RE含量为2.11%～9.75%(质量分数)的Al-RE中间合金.研究发现,Al-RE合金中的RE含量与温度的关系可近似用公式y=-0.74673-0.02813X 3.07273×10-5X2描述;合金中存在着La,Ce,Pr,Nd和Pm等稀土元素.分析了还原温度对合金中稀土含量的影响,分析了[RE2O3]的活度、[Al2O3]的活度、Al-RE合金中的[RE]的活度及[Al]的活度对反应的影响;讨论了Al-RE中间合金形成的热力学及动力学条件,对Al-RE中间合金的形成机制进行了探讨.     

非晶态合金纳米管的制备及其催化性能研究进展

 在 Tween 系列非离子/阴离子混合型表面活性剂与过渡金属盐所形成的溶致液晶体系中加入 NaBH4, 制备了过渡金属 (M) 与 B 的非晶态合金纳米管 M-B (M = Fe, Co, Ni); 制备时若在含 Ni 盐溶液中添加第三种组分 (可为 P, Co 或 Cu 的化合物), 则还可得到相应的 NiPB, NiCoB 或 NiCuB 三元非晶态合金纳米管. 讨论了这类反应的机制, 指出层状液晶相模板的存在是获得纳米管的关键, 层中过渡金属离子被 NaBH4 还原的同时析出 H2, 导致层状液晶相解离并卷曲形成纳米管. 在这一基础上通过微调实验条件并添加适当的稳定剂, 可得到稳定的二元或三元过渡金属非晶态合金纳米管, 并可在一定范围内调控其管径. 在某些加氢反应中, 非晶态纳米管具有比相应的非晶态纳米颗粒更好的催化性能, 而且管径小的纳米管的催化性能比管径大的更好. 由于非晶具有与结晶材料迥异的特性, 非晶态合金纳米管可能具有独特的性能和应用前景.     

不同碱溶液表面处理对稀土镁镍基储氢合金的影响

采用相同浓度即6 mol·L^-1 LiOH、NaOH和KOH对稀土镁镍基储氢合金进行表面处理,研究了不同碱溶液和不同处理时间对合金表面形貌、组成和电极电化学性能的影响。研究表明,合金经6 mol·L^-1 NaOH溶液处理10 min后具有最好的综合电化学性能。但随着处理时间的延长,采用6 mol·L^-1 NaOH溶液处理的合金放电容量衰减明显,实验证明这是由合金表面稀土元素和Al元素的大量溶解进入碱溶液造成的。3种碱溶液比较,LiOH溶液能有效去除合金表面镁元素减少合金在碱溶液处理过程中的氧化,虽然形成的表面不利于H在合金表面的吸脱附,却能有效提高合金在碱溶液中的抗腐蚀能力,提高合金的循环稳定性。     

Surface analysis of nitride layers formed on Fe‐based alloys through plasma nitride process

Nitriding phenomena that occur on the surfaces of pure Fe and Fe? Cr alloy (16 wt% Cr) samples were investigated. An Ar + N₂ mixture‐gas glow‐discharge plasma was used so that surface nitriding could occur on a clean surface etched by Ar⁺ ion sputtering. In addition, the metal substrates were kept at a low temperature to suppress the diffusion of nitrogen. These plasma‐nitriding conditions enabled us to characterize the surface reaction between nitrogen radicals and the metal substrates. The emission characteristics of the band heads of the nitrogen molecule ion (N₂⁺) and nitrogen molecule from the glow‐discharge plasma suggest that the active nitrogen molecule is probably the major nitriding reactant. AES and angle‐resolved XPS were used to characterize the thickness of the nitride layer and the concentration of elements and chemical species in the nitride layer. The thickness of the nitride layer did not depend on the metal substrate type. An oxide layer with a thickness of a few nanometers was formed on the top of the nitride layer during the nitriding process. The oxide layer consisted of several species of N_x‐Fe_y‐O, NO⁺, and NO₂^?. In the Fe? Cr alloy sample, these oxide species could be reduced because chromium is preferentially nitrided. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of grain orientation on zinc enrichment and surface morphology of an Al?Zn alloy

Zinc is an important alloying element in the 7000 series aluminium alloys. It is also an element that may enrich near the alloy surface during treatments of aluminium alloys by processes such as electropolishing, alkaline anodic etching and alkaline etching. The enrichment may occur since the change in Gibbs free energy per equivalent for formation of ZnO is less negative than that for formation of Al₂O₃. The enriched alloying element is present in an alloy layer up to ～5 nm thick located immediately beneath the alloy/film interface. In the present study, the dependence of the enrichment of zinc on the grain orientation of the alloy is investigated for a solid solution Al‐1.1at.%Zn alloy. The enrichment of the zinc is developed by alkaline etching of the alloy. The grain orientation is determined by electron backscattering diffraction, with enrichments quantified on selected grains by Rutherford backscattering spectroscopy and medium energy ion scattering. The morphologies of the surfaces of the etched grains are characterised by scanning electron microscopy and atomic force microscopy. The findings reveal that the zinc enrichment ranges from 1.7 × 10¹⁵ atoms/cm² to 3.9 × 10¹⁵ atoms/cm², with the greatest enrichment occurring on a grain of (100) orientation, while differing surface topographical textures are developed on the various grains. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of the functionalizing of carbon nanotubes on the electrodeposited catalysts’ structure and catalytic properties

The structure and hydrophilic-hydrophobic properties of functionalized single-wall carbon nanotubes are studied by the standard porosimetry method. It is shown that the functionalized nanotubes have highly hydrophilic surface; at that the summary surface area measured “by octane” decreased, as a result of the functionalizing, due to the blocking of the nanotubes’ inner channels by the functional groups located at the nanotubes’ ends. The nanotubes’ capacitive properties are studied; their charging-discharging curves appeared being highly reversible, unlike those of other carbonaceous materials. Catalytic properties of the functionalized nanotubes are studied, with particular tendency toward their using as a carrier of platinum catalysts for the methanol oxidation and oxygen electroreduction reactions. When minor amounts (5–10 μg cm⁻²) of platinum or platinum-ruthenium alloy are deposited onto the nanotubes’ hydrophilic surface, uniform layer of the catalyst is formed, with specific surface area up to 150–300 m² g⁻¹; high current of the methanol oxidation or oxygen electroreduction is observed at these catalysts. When the catalyst deposit mass increased, its specific surface area decreased, as well as the specific current of the reactions occurring thereon. When the current is related to the electrochemically active unit surface, the catalytic activity is nearly the same both for different catalyst mass deposited onto the nanotubes and the same catalyst mass at different carbonaceous carriers.     

A Raman spectroscopy study of cerium oxide in a cerium–5 wt.% lanthanum alloy

This paper describes a study of a cerium–5 wt.% lanthanum (Ce–5 wt.% La) alloy using Raman spectroscopy and X-ray diffraction (XRD). Examination of the alloy microstructure by optical microscopy and Raman spectroscopy revealed the presence of inclusions which were identified as cerium oxide (CeO₂). The study also highlighted the need to avoid excessive laser power during acquisition of the Raman spectra as this appeared to cause the oxidation of the region being analysed where previously no cerium oxide peak had been detected. The propensity of cerium to oxidise in air results in the formation of a CeO₂ layer on the surface of the alloy. Raman spectroscopy of the oxide layer formed on the alloy after exposure to air for 21 days found that the Raman peak denoting cerium oxide was seen at between 5 and 7 cm⁻¹ lower than the value for CeO₂ (465 cm⁻¹). This is attributed to a combination of a sub-stoichiometric oxide layer and the presence of La in the alloy.     

3D aluminum/silver hierarchical nanostructure with large areas of dense hot spots for surface‐enhanced raman scattering

Plasmonic nanomaterials possessing large‐volume, high‐density hot spots with high field enhancement are highly desirable for ultrasensitive surface‐enhanced Raman scattering (SERS) sensing. However, many as‐prepared plasmonic nanomaterials are limited in available dense hot spots and in sample size, which greatly hinder their wide applications in SERS devices. Here, we develop a two‐step physical deposition protocol and successfully fabricate 3D hierarchical nanostructures with highly dense hot spots across a large scale (6 × 6 cm²). The nanopatterned aluminum film was first prepared by thermal evaporation process, which can provide 3D quasi‐periodic cloud‐like nanostructure arrays suitable for noble metal deposition; then a large number of silver nanoparticles with controllable shape and size were decorated onto the alumina layer surfaces by laser molecular beam epitaxy, which can realize large‐area accessible dense hot spots. The optimized 3D‐structured SERS substrate exhibits high‐quality detection performance with excellent reproducibility (13.1 and 17.1%), whose LOD of rhodamine 6G molecules was 10^?9 M. Furthermore, the as‐prepared 3D aluminum/silver SERS substrate was applied in detection of melamine with the concentration down to 10^?7 M and direct detection of melamine in infant formula solution with the concentration as low 10 mg/L. Such method to realize large‐area hierarchical nanostructures can greatly simplify the fabrication procedure for 3D SERS platforms, and should be of technological significance in mass production of SERS‐based sensors.     

Methodology for the qualitative screening of parallel arrays of potential Am ligands using a photographic film

A screening method for parallel Am³⁺ ligand libraries is presented. The method makes use of α-radiation in combination with a photographic film to detect the complexed Am³⁺. After screening and development of the film spots of varying intensities are obtained. The intensities of the spots correspond with the amount of complexed Am³⁺. This allows a fast discrimination between the Am³⁺ complexation efficiencies of ligands from large libraries. Depending on the exposure time of the film, activities as small as 5 Bq ²⁴¹Am can be detected. Using internal standards a semi-quantitative assessment can be performed.     

On the Complementary Photoluminescent and Electroluminescent Images of Poly(phenylenevinylene)‐Based Light‐Emitting Diodes with a Thin Active Layer

A clear complementary relationship between photoluminescent (PL) and electroluminescent (EL) images was observed for organic light‐emitting diodes (OLEDs) based on poly(phenylenevinylene) (PPV) and dye‐doped PPV. So‐called ‘black spots' (dark circular regions observed on the active area of running OLEDs) become bright ones, when the photoluminescence of the same area is excited. A very small thickness of the active layer (ca. 10 nm) was the crucial point to observe this anticorrelation between EL and PL. A substantial increase of the PL yield (‘anti‐burning' effect) was observed after strong light exposure (ca. 10 mJ/cm²) of the polymer covered by an aluminium layer. The same light exposure without aluminium protection resulted in complete photobleaching of the polymer. The presence of a thin insulating layer between the polymer and aluminium was proposed to be responsible for these effects. This layer prevents electron injection and PL quenching due to exciton dissociation at the metal‐polymer interface. The former effect leads to black spots in the EL image, the latter one gives rise to bright spots on the PL image situated on the same places. The intermediate layer can be also induced by light exposure. A very efficient energy transfer from the polymer to the dye and to the J‐aggregates of the dye was demonstrated in PPV/dye composite films.     

Determination of the Real Surface Area of Palladium Electrode

Four methods, including voltammetric measurement of double layer capacitance, surface oxides reduction, under potential deposition of Cu and carbon monoxide (CO) stripping have been applied to evaluate the real surface area of a polycrystalline Pd (pc-Pd) electrode. The results reveal that the second and third methods lead to consistent results with deviations below 5%. And from the determined double layer capacitance and CO stripping charge, it is deduced that the double layer capacity unit area is 23.1±0.4 μF/cm² and the saturated CO adlayer should be ca. 0.66 ML in order to ensure that the real surface area as determined isconsistent with the other two techniques. The applicability as well as the attentions when applying these techniques for the determination of the real surface area of pc-Pd electrodes have been discussed.     

Corrosion behaviour of mechanically polished AA7075‐T6 aluminium alloy

In the present study, the effects of mechanical polishing on the microstructure and corrosion behaviour of AA7075 aluminium alloy are investigated. It was found that a nano‐grained, near‐surface deformed layer, up to 400 nm thickness, is developed due to significant surface shear stress during mechanically polishing. Within the near‐surface deformed layer, the alloying elements have been redistributed and the microstructure of the alloy is modified; in particular, the normal MgZn₂ particles for T6 are absent. However, segregation bands, approximately 10‐nm thick, containing mainly zinc, are found at the grain boundaries within the near‐surface deformed layer. The presence of such segregation bands promoted localised corrosion along the grain boundaries within the near‐surface deformed layer due to microgalvanic action. During anodic polarisation of mechanically polished alloy in sodium chloride solution, two breakdown potentials were observed at ?750 mV and ?700 mV, respectively. The first breakdown potential is associated with an increased electrochemical activity of the near‐surface deformed layer, and the second breakdown potential is associated with typical pitting of the bulk alloy. Copyright © 2009 John Wiley & Sons, Ltd.