The contribution of electrochemical reactions to sulfur transfer from electrode to slag in electroslag remelting

In order to assess the contribution of electrochemical reactions to refining reactions, such as sulfur removal, in electroslag remelting, electrochemical experiments which simulate conditions at the electrode/slag, and liquid metal pool/slag interfaces have been carried out. Liquid copper electrodes and a CaO-Al₂O₃-CaF₂ electrolyte were used. The experimental technique involved chronopotentiometry at constant current. Sulfur reversion from slag to metal is shown to be a diffusion controlled, reversible electrochemical process involving two electrons. On the other hand sulfur transfer from metal to slag occurs both by the diffusion controlled electrochemical reaction and the direct exchange reaction. A hanging drop electrode system was used to simulate conditions at the electrode/slag interface. Further experiments on the hanging drop electrode with and without applied current showed that direct reaction was a minor contribution to sulfur removal. The results are compared to findings from industrial practice.     

Drug metabolism biosensors: electrochemical reactivities of cytochrome P450cam immobilised in synthetic vesicular systems

Biosensors containing cytochrome P450cam in a didodecyldimethylammonium bromide vesicular system were prepared by cross-linking onto a glassy carbon electrode (GCE) with glutaraldehyde in the presence of bovine serum albumin. Cyclic voltammetric responses of the sensor in air-free buffer solution showed that the sensor exhibited reversible electrochemistry due to direct electron exchange between the haem Fe(3+/2+) redox system and the GCE surface. In air-saturated solution containing camphor, the biosensor gave an irreversible electrocatalytic current which is compatible with the monooxygenation of the substrate. Steady state amperometric experiments with camphor, adamantanone and fenchone were performed with a biosensor prepared by cross-linking P450cam with glutaraldehyde onto a Pt disc electrode. The sensor was characterised by fast amperometric responses, attaining steady-state in about 20 s in a cobalt sepulchrate mediated electrochemical system. The kinetic parameters of the biosensor were analysed using the electrochemical Michaelis Menten equation. The estimated apparent Michaelis-Menten constant, Km, values for the biosensors were in the range of 1.41-3.9 mM.     

活性炭纤维负载CuO改性及其性能表征

以Cu(NO_3)_2溶液作为前躯体,采用浸渍–煅烧法对盐酸预处理后的活性炭纤维(activated carbon fiber,ACF)毡进行负载氧化铜化学改性,制备CuO/ACF电极材料。通过扫描电镜(SEM)、X射线光电子能谱仪(XPS)、比表面积及孔径分析仪以及傅立叶变换红外光谱仪(FTIR)对ACF及其负载CuO后的形貌与结构、元素组成、比表面积、孔径等进行观察与分析,并利用电化学工作站测试其电化学性能。结果表明:经过负载CuO化学改性的CuO/ACF电极材料,比表面积及孔容较改性前分别下降31.94%和33.95%,表面含氧基团增多,出现明显的Cu—O键,CuO/ACF电极材料中Cu元素的质量分数为13.7%;负载CuO后比电容升高17.95%,电吸附性能提高。CuO/ACF材料可作为电极材料用于去除废水中的无机盐离子。     

Reactor for the Oxidation of Galena in Ammonium Carbonate Solution

Anodic behaviour of galena in ammonium carbonate solution and products of anodic reaction resulting in passivation have been studied by electrochemical technologies including ring-disc electrode. The electrochemical dissolution parameters of sulfides have been measured using short circuit cells consisting of massive mineral electrodes. The effects of impurities in galena such as pyrite and pyrrhotite on converting it to lead carbonate have been examined. The conversion can be accelerated by the addition of a little cupric ion to the ammonium carbonate solution. A suitable reactor for the conversion is a propeller-agitated tank without baffles which has been confirmed in large scale experiments with 50 kg ore.     

Sb含量对Sn–Sb合金焊料电化学腐蚀行为的影响

为了评估Sn-Sb合金焊料的电化学可靠性，以Sn-xSb(x=0.5%,3%,5%,10%,质量百分数)合金为工作电极，Pt片为对电极，饱和甘汞电极（SCE，饱和KCl溶液）为参比电极，中性5% NaCl溶液为腐蚀溶液，采用电化学腐蚀试验方法，研究了Sb含量对Sn-Sb合金焊料的电化学腐蚀行为的影响。通过对合金样品的动电位极化曲线和电化学交流阻抗谱（EIS）的分析，得出Sn-Sb合金焊料耐腐蚀性下降的趋势为Sn-10Sb > Sn-5Sb > Sn-3Sb > Sn-0.5Sb。     

层层自组装纳米金/硫堇修饰玻碳电极测定亚硝酸根

研究了纳米金/硫堇多层膜修饰玻碳电极的制备以及亚硝酸根在该电极上的电化学行为。在稀硝酸溶液中,通过恒电位法将玻碳电极活化,使其表面产生-COH等含氧基,然后将其浸泡在硫堇溶液中,硫堇中的-NH2与玻碳电极表面的-COH基团发生席夫碱反应,将硫堇固定在电极上。最后将电极浸泡在纳米金溶液中,通过纳米金与硫堇的相互作用将纳米金修饰到电极表面,从而制得纳米金/硫堇多层膜修饰玻碳电极。实验结果表明,该修饰电极能显著促进亚硝酸根在电极表面的电化学过程,电化学响应信号与亚硝酸根的浓度在20×10-6~50×10-5 mol/L和50×10-5~20×10-3 mol/L范围内呈良好的线性关系,检出限为5×10-8 mol/L (S/N=3)。方法用于水样中亚硝酸根的测定,相对标准偏差为22%~32%,回收率在98%~104%范围。     

基于乙炔黑/壳聚糖膜修饰电极的阳极溶出伏安法测定水样中铅

利用阳极溶出伏安法详细研究了Pb2+在乙炔黑/壳聚糖膜修饰玻碳电极上的电化学行为,并对各种实验条件如支持电解质、溶液pH值、富集电位、富集时间等进行了优化。相对于裸玻碳电极,Pb2+离子在复合膜修饰电极上具有良好的电化学响应,Pb2+在pH 5.6的BR缓冲溶液中,在峰电位－0.51 V处出现一尖锐的阳极溶出峰。当富集电位为-1.20 V,富集时间为300 s时,Pb2+的溶出峰电流与其浓度在2×10-9～2×10-7 mol/L间和1×10-6～5×10-5 mol/L间呈良好的线性关系,检出限可达1×10-10 mol/L（S/N=3）。该修饰电极对铅离子的阳极溶出伏安检测还有一定的抗干扰能力,将用该修饰电极应用于实际水样中Pb2+的加标测定,结果与原子吸收光谱法测得结果相一致。     

直接甲醇燃料电池Pt／C催化剂对甲醇的电催化氧化研究

通过循环伏安法研究了Pt/C催化剂对甲醇的电催化氧化活性,详细地考察了甲醇浓度、温度、介质以及酸度等电化学体系因素对Pt/C催化剂活性的影响。结果表明,上述四个电化学体系因素对Pt/C催化剂活性存在着明显的影响。甲醇浓度和温度的增加可以显著降低工作电极内阻,增加电极反应速率,提高Pt/C催化剂活性。改善溶液介质和控制适宜的酸度有利于Pt/C催化剂活性的提高。在本实验条件下,其最佳的运行工艺参数为:溶液介质为二次去离子水,酸度为1.0 mol/L H2SO4。     

AZ31镁合金微区电偶腐蚀的数值研究

结合水平集函数方法及移动网格技术,利用有限元法模拟分析了离散型β相分布和连续型β相分布的AZ31镁合金在NaCl溶液中的腐蚀行为,通过解Nernst-Planck方程得到腐蚀过程中AZ31镁合金/NaCl界面的电势、氯离子及镁离子浓度分布,并通过扫描离子选择性电极实验验证了此模拟方法的可行性.模拟分析表明,当β相离散分布在α相周边时,在与β相相邻的α相区域腐蚀速率最快,形成腐蚀缩颈坑,坑内氯离子富集,进一步加速了α相的腐蚀,最终β相逐渐脱离合金进入溶液;当β相连续分布在α相周边时,α相不断被腐蚀,最终α相全部溶解而只剩β相,求解随即停止.扫描离子选择性电极实验结果表明此模拟模型可以对镁合金的电化学腐蚀进行较好预测和判断.      

La0.75Mg0.25Ni3.47Co0.2Al0.03储氢合金电极失效研究

采用中频感应真空熔炼制备La0.75Mg0.25Ni3.47Co0.2Al0.03合金,并借助电化学和气态循环实验、SEM、XPS等手段对合金电极失效的原因进行研究.结果表明,合金放电容量和吸氢容量的衰减在循环过程中均分为快速和缓慢两个阶段.随循环次数的增加,在电化学循环过程中,合金颗粒表面的氧化腐蚀产物逐渐增多,接触电阻和电荷传递电阻先降低后提高;在气态吸放氢过程中,合金颗粒裂纹逐渐增多,且开裂程度增大.La和Mg的氧化腐蚀损耗是导致合金放电容量衰减的主要原因,而合金颗粒粉化加剧了La、Mg的腐蚀,进一步恶化合金电极的稳定性.     

电化学法深度处理低浓度贵金属贫液的研究

以自制的煤基材料为电极,采用电化学法深度处理贵金属贫液,研究了电压、时间、pH值及温度等因素对各离子去除率的影响规律,采用扫描电镜及能谱（SEM-EDS）对反应后极板的表面形貌及负载物组成进行表征分析。实验结果表明,随着处理时间的延长,温度的增加,溶液中各离子的去除率逐渐增大,随着电压增大离子去除率表现为先升后降的趋势,在1.6 V时达到最佳,而pH值的升高不利于反应进行。选用原液pH值,在电压为1.6 V、溶液温度为50 ℃、处理时间为6 h的条件下,钯离子去除率为99.32%,铂离子去除率为97.13%,金与钌离子可视为完全去除。研究证实,采用电化学法可以对低浓度贵金属贫液进行深度处理并实现回收贵金属的目的,该电化学反应由电沉积和电吸附两方面共同作用,且前者占主导作用。     

黄原酸钾盐介质中黄铁矿的电化学行为Ⅱ:疏水性产物双黄药的吸附及其稳定性研究

利用恒电位和恒电流的电化学研究方法 ,研究了黄原酸钾溶液中黄铁矿表面的电化学行为。研究表明 ,随着pH值提高 ,电极表面的双黄药吸附层变薄 ;双黄药在黄铁矿电极表面的还原动力学方程式表明 ,高碱条件下 (pH=11.0) ,双黄药易于还原解离。     

Electrocatalytic surface for the oxidation of NADH and other anionic molecules of biological significance

A simple electrochemical treatment of a carbon fiber electrode surface has been found to dramatically improve the voltammetry of NADH and several other anionic molecules under steady-state and fast scan (100 V/s) conditions. The electrocatalytic surface is generated through the electrochemical oxidation of NADH on a carbon fiber electrode that exhibits product adsorption. The oxidative product is reacted with ascorbic acid at elevated temperatures to create a surface which has very little overpotential for the oxidation of dopamine and many metabolites such as NADH, DOPAC, uric acid, and ascorbate. The electrochemical properties of the modified surface were examined voltammetrically at both slow and fast scan rates. The surface shown in this paper shifts the oxidation overpotentials different magnitudes for each analyte tested, thus allowing discrimination between analytes of interest and their major interferences. Another benefit of this new electrocatalytic wave is that it decreases the limit of detection for NADH by approximately 1 order of magnitude. Therefore, this new carbon surface not only gives better discrimination between two analytes but also gives better detection limits for certain analytes of interest.     

Cathodic copper deposition at 65 °C in the absence and presence of Bi3+ and Sb3+ additives in acidified CuSO4 aqueous solutions

An electrochemical study by cyclic voltammetry and potentiostatic pulse method of the cathodic deposition of copper on polycrystalline copper electrode was carried out in acidic aqueous copper sulfate solution. Comparative electrochemical investigations were performed in electrolytes in the absence and presence of Bi³⁺ and Sb³⁺ ions. All experiments were performed at 65 °C. For bulk copper deposition, the results indicate that in the presence or absence of additive ions, the charge transfer at the Cu/Cu²⁺ electrode occurs in two consecutive one-electron steps, with Cu⁺ being formed as an intermediate. The addition of Bi³⁺ to the electrolyte retarded the copper deposition process, while the introduction of Sb³⁺ caused a depolarization effect. The kinetic studies in the potential range which characterizes the deposition of bismuth show that this reaction takes placevia a stepwise electron transfer mechanism. In the case of antimony-containing electrolyte, the cathodic reduction was found to proceedvia a two-electron transfer pathway. The presence of Sb³⁺ and Bi³⁺ in potentiostatic studies shows that the additive ions behave in a manner consistent with that observed by cyclic voltammetry. The nucleation and growth of bulk copper deposition appears to occurvia aninstantaneous three-dimensional (3-D) nucleation and growth mechanism. However, in the presence of Bi³⁺ or Sb³⁺, copper is deposited by aprogressive 3-D nucleation and growth pattern. X-ray photoelectron spectroscopic surface analyses revealed strong incorporation of both antimony and bismuth within the copper deposit.     

Antenatal and delivery risk factors simultaneously associated with neonatal death and cerebral palsy in preterm infants

Apomorphine is a powerful agonist of dopaminergic receptors which several years ago was introduced into the therapy of Parkinson's Disease. The pharmacological activity of apomorphine already appears significant at low doses. Unfortunately, the difficulty in determining the drug in plasma at low concentrations hampers the completion of accurate pharmacokinetic studies in humans. Considering the analogy of apomorphine with the molecular structure of catecholamines, the extraction of the drug from plasma was optimized by using adsorption on alumina, a technique widely used for noradrenaline and adrenaline analysis in clinical chemistry laboratories. This method proved particularly efficient and selective in apomorphine extraction from plasma prior to high-performance liquid chromatographic analysis. After pretreatment of 200 microliters of plasma sample with 40 mg of alumina and 10 microliters of tris buffer (pH 8.6), the drug was eluted with 200 microliters of an acidic-organic solution. One volume of the supernatant was mixed with two volumes of phosphate buffer (pH 3.6), and 100 microliters of the obtained mixture were injected into the HPLC system. The chromatograph was equipped with a C18 reversed-phase column and with an electrochemical coulometric detector fitted with a high-sensitivity cell (first electrode 0.00 volts, second electrode +0.35 volts). Sensitivity (20 pg of injected drug), precision (CV within assay and between assays of 3.7% and 5.6%, respectively) and accuracy were comparable to more complex analytical procedures. The miniaturisation of the entire sample pretreatment proved very advantageous for pharmacokinetics studies and, in principle, for therapeutic drug monitoring and toxicological investigations.     

Electrochemical cell with the reversible electrode–solid electrolyte or ionic melt interface in galvanodynamic and potentiodynamic operating modes

This work is aimed at studying the kinetics of the following two simultaneous processes: charging of the double electrical layer and the charge transfer at the reversible silver electrode–sulfate solid electrolyte or corresponding ionic melt interface in two operating modes of electrochemical cell, namely, galvanodynamic and potentiodynamic ones. The electrochemical kinetics has been studied by the method of operational impedance based on the Ohm law of interaction between Laplace transformed current, voltage, and complex resistance (impedance). Using appropriate mathematical calculations, analytical expressions are obtained for the current passing via a cell during linear potential scanning (potentiodynamic mode) as a function of time and for the interface potential as a function of time in the galvanodynamic mode (linear current scanning). The time dependence of the potential of the electrode–solid electrolyte or ionic melt interface is described by an exponential function in the potentiodynamic mode of the cell operation. An analysis and comparison of the results of the two independent electrochemical modes demonstrate that the behavior of the electrochemical cells containing a reversible metallic electrode, i.e., a solid electrolyte or the corresponding ionic melt, obeys the classical Randles–Ershler equivalent circuit. This statement can be proved by both the alternating current method (impedance method) and relaxation galvanodynamic and potentiodynamic methods (linear scanning of potential and current).     

Fabrication and characterization of glucose sensors based on a microarray H2O2 electrode

A glucose sensor was recently developed by modifying an immobilized GOD (glucose oxidase) membrane and coating Nafion diffusion limiting membrane over an amperometric H2O2 MAE (microarray electrode), which was fabricated by using standard planar processing. The chip of the sensor is 2.5 mm by 15. The MAE is composed of an Ag/AgCl RE (reference electrode), a Pt CE (counter electrode) and two sets of Pt WE (working electrode), each set consists of five bands. Silicon nitride was chosen as the top insulator. Six MAEs different in both width and length of the band were examined and the MAE with the narrowest width (10 microns) of bands exhibits the best electrochemical performances. The glucose sensor based on the MAE B1-2 presents a linear range of 0.5-40 mM glucose at 37 degrees C with a 1/15 M phosphate buffer solution (pH = 7.0) as supporting electrolyte. The sensitivity, background current, response time, CV (coefficient of variation) and long-term stability of the sensor are 7.1 +/- 0.5 nA/mM, 2 +/- 0.5 nA, 30 s, 3.4% and 6 days respectively.     

Effect of surface treatment on the structure and high-rate dischargeability properties of AB5-type hydrogen storage alloy

Surface-treated MmNi3.55Co0.75Mn0.4Al0.3 alloy as negative electrode material of nickel-metal hydride battery was employed to improve the high-rate dischargeability. Surface treatment was realized by dipping and stirring the alloy into a HCI aqueous solution with various concentrations at room temperature. The microstructure of the alloy before and after surface treatment was analyzed by X-ray dif-fraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties before and after surface treatment were compared, and the alloy treated in 0.025 mol/L HCI solution showed the optimal high-rate dischargeability.     

镉在嵌入式碳纳米管 铋膜玻碳电极上的电化学行为及电位溶出法测定研究

制备了一种新型嵌入式碳纳米管 铋复合膜玻璃碳电极,利用循环伏安法研究了Cd在电极上的电化学行为。 Cd在电极具有一个不可逆的氧化峰,Epa=0637 V（vs．SCE）,电极对Cd具有高灵敏的电化学响应。研究了影响Cd微分电位溶出的因素,获得的最佳条件是：富集电位为-11 V,Bi3+浓度为04 mg/L,pH 46 HAc NaAc缓冲溶液。通过同位镀铋、标准加入法进一步提高了分析的可靠性。在最佳条件下,峰高与Cd质量浓度在01～20 μg/L范围呈线性,检出限为02 μg/L。对实际样品进行测定,测定值与原子吸收光谱法的结果一致, RSD在31%～72%范围,回收率在92%～102%之间。     

Content effects in problem categorization and problem solving.

In many domains, the content of a problem (i.e., its surface cover story) provides useful clues as to the type of problem it is and to its solution. Five experiments examined this role of problem content on the problem solution and categorization of algebra word problems with experienced participants. In the first experiment, when problem content was atypical for the the problem's deep structure, people were worse at solving the problem. Differences were also detected in the problem solution where the problem's content was highly correlated with its deep structure versus problems where content was neutral to their deep structure. In the other experiments, problem categorization and determination of information relevance depended on how closely the problem's content matched its deep structure. These results suggest that content may be influential even for experienced problem solvers. The discussion examines the implications for problem schema access and application. (PsycINFO Database Record (c) 2010 APA, all rights reserved)