952 resultados para Fe-Rh alloy
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氧化还原液流电池是近十几年来发展起来的一种大容量的贮能电池,目前研究比较成熟功率,容量较大的是盐酸体系Fe/Cr氧化还原电池。但是对于该体系的铬负极,仍然存在着氢气的伴随发生和铬盐溶液的时效陈化问题,此外,作为隔膜的离子交换膜也不能满足电池的性能要求。本文用循环伏安法、恒电流法、紫外可见分光光度法、交流阻抗法研究了铬负极的性质和溶液的时效陈化问题;探讨了三价铬离子的电化学还原过程;组装了试验型氯化铵体系的Fe/Cr氧化还原液流电池,测试了电池的性能;为降低隔膜的离子选择性的要求,对Cr(III)/Cr(VI)电对的氧化还原反应进行了探讨。讨论了三价铬离子在银离子存在下氧化成铬酸盐的反应机理。用循环伏安法研究了金、银、铜、石墨等电极材料对Cr(III)/Cr(rIII)电对氧化还原可逆性和析氢速度的影响。金电极能催化Cr(III)/Cr(II)电对的氧化还原反应,在溶液中含有Pb~(2+)离子时,具有较高的氢过电位。银、铜电极在电位扫描过程中不断地进行溶解和沉积,电极性能不稳定,而石墨电极上Cr(III)/Cr(II)电对的可连性较差。因此选择金作工作电极。研究了电解液中加入Pb、In、Tl的作用,结果表明,同时添加Pb-In、Pb-Tl比添加Pb、Tl等单一添加剂更能有效地提高氢过电位。电子探针分析表明,Pb、In、Tl在金基底上是均匀分布的。文献上尚未见到在这一电池体系中应用上述复合添加物的报导。在盐酸溶液中,存在着如下平衡:[Cr(H_2O)_4Cl_2] Cl·2H_2O <-> [Cr(H_2O)_5Cl]Cl_2·H_2O<->[Cr(H_2O)_6]Cl_3利用各级络合物的稳定常数计算了不同浓度的Cr(III)离子溶液中,上述三种络合物的浓度。以循环伏安曲线上Cr(III)的还原峰值电流i_p对Cr(H_2O)_4Cl_2~+和Cr(H_2O)_5Cl~+的浓度和作图,得到通过原点的直线。恒电流法研究发现,电位-时间曲线相继在-550mv·vs·scE和-660mv·vs·scE出现二个电位平阶,其电量比与Cr(H_2O)_4Cl_2~+、Cr(H_2O)_5Cl~2+的浓度比相当。据此认为参加电化学反应的活性离子是Cr(H_2O)_5Cl~(2+)和Cr(H_2O)_4Cl_2~+。利用循环伏安法比较了盐酸、氯化铵、醋酸、醋酸铵作电解液时Cr~(3+)离子的反应活性。盐酸体系中氢气的伴发生极为严重。醋酸、醋酸铵体系析氢电流较小、Cr~(3+)离子的反应活性也不高。相对来说,氯化铵体系对Cr(III)/Cr(II)电对的氧化还原反应有较高的活性,而且氢的析出电流也较小。紫外可见分光光度法对盐酸。氯化铵作电解液时铬络离子稳定性的研究表明,在溶液久置过程中,铬络离子在氯化铵体系中比在盐酸体系中稳定。循环伏安法的研究也符合这一结论。由于氯化铵体系的优点,组装了以氯化铵为电解液的铁铬单体电池。当充、放电电流密度为20mA/cm~2时,库仑效率达99%,瓦时效率在60%以上,电池的开路电压可达1.18V。与以盐酸为电解液的电池相比,具有电池开路电压高、放氢量小库仑效率高等优点。由于溶液的酸度低,也延缓了溶液对电池壳体及其附件的腐蚀。看来,它是一种很有希望的电解液体系。为了降低电池对离子交换膜的离子选择性要求,一种有效的方法是采用全铬电池体系,即正负极活性物质分别为Cr(III)/Cr(VI)和Cr(III)/Cr(II)。本文在Pt、石墨、钛电极上在硫酸溶液中对Cr(III)/Cr(VI)电对的氧化还原过程进行了探讨。循环伏安法表明,Cr(III)的氧化与氧的发生同时进行,加入Pb~(2+), Co~(2+)离子使Cr(III)离子的氧化电位负移。加入Ag~+时,在循环伏安曲线上出现Cr(III)离子的氧化峄。表明Ag~+对Cr(III)的氧化过程有较好的催化作用。在Cr(III)离子浓度0.1m时,峰值电位φ_P与扫描速度的对数logV呈线性关系,2ψ_p/2logv=100mv;峰值电流i_p与扫描速度v成正比。浓度在0.07M以下时,峰电位与扫描速度无关,峰电流与扫描速度平方根成正比,表现为扩散控制的过程。银离子存在下,Pt电极上Cr(III)离子的氧化过程的交流阻抗谱图呈现二个半圆,可以认为电极过程包括中间吸附物的生成。
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自从1956年Blake等研究HDEHP萃取铀时发现协同效应以来,由于协同萃取具有可以显著地提高萃取效率,改变萃取选择性等优点,所以对协同萃取进行了大量研究工作,目前已广泛应用于核燃料稀有金属湿法冶金分离分析。但协同萃取研究领域十分广阔,新协萃体系,协萃机理和协萃配合物结构等许多方面还有待进一步研究。Fe~(3+)、Zn~(2+)和Cd~(2+)等过渡金属离子常与稀土离子在一起,成为高纯稀土产品的重要杂质元素,因此寻找Fe(III)、Zn(II)和Cd(II)与RE(III)的新协同萃取分离体系,不但具有理论意义,也有实际意义。本文研究了萃取分离中广泛使用的四种萑取剂,甲基膦酸二(1-甲基庚基)酯(P_(350), 以B表示)、仲碳伯胺N_(1923)(以RNH_2表示)、1-苯基-3-甲基-4-苯甲酰基吡唑酮-5(PMBP,以HL表示)和2-乙基基膦酸单(2-乙基已基)酯(P_(507),以HA表示)对盐酸介质中Fe(III)、Zn(II)、Cd(II)和Nd(III)等金属离子的协同萃取,得到了六个新协萃体系,并且对协萃机理和萃取平稀奇规律等进行了研究,得到了一些有意义的结果。
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本文分另研究了H[DEHP]从不同酸性介质中萃取稀土(III)(Sc、Y、Ho、Er、yb、Lu)及Fe(III)、Zn(II)的机理及性能。一、H[DEHP]从 H_2SO_4介质中萃取Sc(III)的机理 1. H[DEHP]萃取H_2SO_4及其机理 2. H[DEHP]萃取Sc(III)的机理,用斜率法和饱和法确定了H[DEHP]的正庚烷溶液从H_2SO_4溶液中萃取Sc_2(SO_4)_3的机理及萃合物组成。研究表明,H[DEHP]萃取Sc(III)在高、低两种酸度范围内存在着两种不同的萃取机理。二、H[DEHP]从HCl介质中萃取Ln(III)和Fe(III)的性能及H[DEHP]萃取Ln(III)的机理研究了H[DEHP]的正庚烷溶液从HCl介质中萃取稀土(III)(Sc、Y、Ho、Er、Yb、Lu)和Fe(III)的性能,得出H[DEHP]在相同条件下萃取以上各金属离子的顺序是:Sc(III)>Fe(III)>Lu(III)>Yb(III)>Er(III)>Y(III)>Ho(III), 并计算了各金属离子之间的分离因素(β)。文中还讨论了Sc(III)、Fe(III)、Lu(III)之间的分离以及重稀土离子间的萃取分离,同时与相同实验条件下HEH[EHP]的萃取性能进行了比较,为新的萃取体系提供了一些参数。三、H[DEHP]从不同介质中萃取Fe(III)的机理,研究了H[DEHP]的正率烷溶液从Hcl介质中和H[DEHP]的正庚烷溶液从H_2SO_4介质中萃取Fe(III)的平衡规律;用斜率法、饱和法以及IR和NMR谱等讨论了低酸度下的萃取机理。四、H[DEHP]萃取Zn(II)的机理,研究了H[DEHP]的正率烷溶液从Hcl介中萃取Zn(II)的平衡,利用斜率法、饱和法及SR、NMR谱等讨论了低Hcl浓度下的萃取机理。
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本文对YCl_3-KCl.NaCl熔体中Y在固体M_0,Ni和Fe电极上的电化学过程及用氯化的熔休电解制备Y_(mm)-Ni和Y_(mm)-Fe合金进行了系统研究。对电解时电解槽内熔体温度分布进行了测定,得出了电解制备Y_(mm)-Ni合金时槽内熔体温度分布图。结果表明,从阴极表面到电解槽内表面的温度递降不是均匀的,阴极附近出现一个高温区。随着边缘电解质温度的升高,阴极表面温度基本上平行地上升。电极表面温度超出边缘电解质温度随电解时阴极电流密度和电流强度的增大而增加,在一定范围内有很好的线性关系;当使用高阴极电流密度时,可高达近百度。
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钙钛石型复合氧化物由于具有许多独特的物理化学性质,如多种类型的磁性和导电性、对多种物理和化学因素的敏感性、高温下的稳定性和结构的明确易调性等长期以来一直受到固体物理、固体化学和催化科技工作者重视,本文第一部分详细总结了文献中有关这类氧化物的结构、电子状态、电磁性质、表面吸附性能、稳定性以及反应机理和催化性能等方面的重要结果。第二部分为催化剂的制备和表征方法。第三部分针对文献中研究较少的B位取代钙钛石型氧化物,系统研究了系列化合物LaM_yM'_(1-y)O_a (M, M' = Mn, Fe, Co)的固体物理化学性质和对NH3和CO氧化反应的催化性能,讨论了它们之间的关系。1. 催化剂的制备、晶体结构与光谱性质。2. LaM_yM'_(1-y)O_3(M、M' = Mn、Fe、Co)r的氧化还原性质和稳定性。3. 过渡金属离子的状态及其之间的相互作用。4. 催化剂中氧的形态。5. 氨氧化性能与固体物化性质之间的关系。6. 一氧化碳氧化与固体物化性质之间的关系。
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The second-harmonic generation (SHG) from Si1-xGex alloy films has been investigated by near-infrared femtosecond laser. Recognized by s-out polarized SHG intensity versus rotational angle of sample, the crystal symmetry of the fully strained Si0.83Ge0.17 alloy is found changed from the O-h to the C-2 point group due to the inhomogeneity of the strain. Calibrated by double crystal X-ray diffraction, the strain-induced chi((2)) is estimated at 5.7 x 10(-7) esu. According to the analysis on p-in/s-out SHG, the strain-relaxed Si0.10Ge0.90 alloy film is confirmed to be not fully relaxed, and the remaining strain is quantitatively determined to be around 0.1%.
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The band structure of the Zn1-xCdxSySe1-y quaternary alloy is calculated using the empirical pseudopotential method and the virtual crystal approximation. The alloy is found to be a direct-gap semiconductor for all x and y composition. Polynomial approximation is obtained for the energy gap as a function of the composition x and y. Electron and hole effective masses are also calculated along various symmetry axes for different compositions and the results agree fairly well with available experimental values.
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We present studies of alloy composition and layer thickness dependences of excitonic linewidths in InGaAs/GaAs strained-layer quantum wells grown by MBE, using both photoluminescence and optical absorption. It is observed that linewidths of exciton spectra increase with indium content and well size. Using the virtual crystal approximation, the experimental data are analyzed. The results obtained show that the alloy disorder is the dominant mechanism for line broadening at low temperature. In addition, it is found that the absorption spectra related to light hole transitions have varied from a peak to a step-like structure as temperature increases. This behavior can be understood by the indirect space transitions of light holes.
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Two thermostable levels E(0.31) and E(0.58) related to Rh in Si were observed using deep level transient spectroscopy and double correlation deep level transient spectroscopy techniques. By means of thermal annealing and electron irradiation, the microscopic natures of these levels were identified for the first time. The levels E(0.31) and E(0.58) arise from by the same impurity center but have different charge states. Their microstructures are not related to a pure substitutional Rh atom, but correspond to a complex. This result is compared to our self-consistent theoretical calculation.
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Thermally stimulated redistribution and precipitation of excess arsenic in Ge0.5Si0.5 alloy has been studied by X-ray photoelectron spectroscopy (XPS), cross sectional transmission electron microscopy (XTEM) and X-ray energy disperse spectrometry (EDS). Samples were prepared by the implantation of 6 X 10(6) As+ cm(-2) and 100 keV with subsequent thermal processing at 800 degrees C and 1000 degrees C for 1 h. The XPS depth profiles from the implanted samples before and after the thermal annealing indicate that there is marked redistribution of the elements in heavily arsenic-implanted Ge0.5Si0.5 alloys during the annealing, including: (1) diffusion of As from the implanted region to the surface; (2) aggregation of Ge in the vicinity of the surface. A high density of precipitates was observed near the surface which were by XTEM and EDS identified as an arsenide. It is suggested that most of the implanted As in Ge0.5Si0.5 alloy exists in the form of GeAs.
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Fe-N films were deposited on Si(100) and GaAs(100) substrates at room temperature by ion beam assisted deposition under various N/ Fe atomic arrival ratio, 0.09, 0.12, 0.15. The results of X-ray diffraction indicated that the film deposited at 0.12 of N/Fe arrival ratio contained a considerable fraction of the Fe16N2 phase which had grown predominantly in the [001] orientation. For the larger N/Fe arrival ratio, a martensite phase with 15 at.% nitrogen was obtained. It was found that a lower deposition temperature (<200 degrees C) was necessary for the formation of the Fe16N2 phase.
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Lattice matched Ga_(1-x)In_xAs_ySb_(1-y) quaternary alloy films for thermophotovoltaic cells were successfully grown on n-type GaSb substrates by liquid phase epitaxy. Mirror-like surfaces for the epitaxial layers were achieved and evaluated by atomic force microscopy. The composition of the Ga_(1-x)In_xAs_ySb_(1-y) layer was characterized by energy dispersive X-ray analysis with the result that x = 0.2, y = 0.17. The absorption edges of the Ga_(1-x)In_xAs_ySb_(1-y) films were determined to be 2. 256μm at room temperature by Fourier transform infrared transmission spectrum analysis, corresponding to an energy gap of 0.55eV. Hall measurements show that the highest obtained electron mobility in the undoped p-type samples is 512cm2~/(V·s) and the carrier density is 6. 1×10~(16)cm~(-3) at room temperature. Finally, GaInAsSb based thermophotovoltaic cells in different structures with quantum efficiency values of around 60% were fabricated and the spectrum response characteristics of the cells are discussed.
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Natural surface coatings sampled (NSCSs) from the surface of shingles and surficial sediments (SSs) in the Songhua River, China were employed to investigate the similarities and difference in fractions of heavy metals (Fe, Mn, Zn, Cu, Pb, and Cd) between NSCSs and SSs using the modified sequential extraction procedure (MSEP). The results show that the differences between NSCSs and SSs in Fe fractions were insignificant and Fe was dominantly present as residual phase (76.22% for NSCSs and 80.88% for SSs) and Fe-oxides phase (20.33% for NSCSs and 16.15% for SSs). Significant variation of Mn distribution patterns between NSCSs and SSs was observed with Mn in NSCSs mainly present in Mn-oxides phase (48.27%) and that in SSs present as residual phase (45.44%). Zn, Cu, Pb and Cd were found dominantly in residual fractions (>48%), and next in solid oxides/hydroxides for Zn, Pb and Cd and in easily oxidizable solids/compounds form for Cu, respectively. The heavy metal distribution pattern implied that Fe/Mn oxides both in NSCSs and SSs were more important sinks for binding and adsorption of Zn, Pb and Cd than organic matter (OM), and inversely, higher affinity of Cu to OM than Fe/Mn oxides in NSCSs and SSs was obtained. Meanwhile, it was found that the distributions of heavy metals in NSCSs and SSs were similar to each other and the pseudo-total concentrations of Zn, Cu, Pb and Cd in NSCSs were greater than those in SSs, highlighting the more importance for NSCSs than SSs in controlling behaviours of heavy metals in aquatic environments.