Amperometric detection of simple alcohols in aqueous solutions by application of a triple-pulse potential waveform at platinum electrodes

Application of a triple-pulse waveform is described for the anodic detection of methanol, ethanol, and ethylene glycol. The execution of the waveform incorporates the cleaning and reactivation of the platinum electrode, by alternate anodic and cathodic polarization, with measurement of the faradaic signal for the analyte at the reduced electrode surface. Some results for formic acid are also presented. The waveform is completed within approximately 2 s and the faradaic signal exhibits no decay with time as would be the case for amperometric detection at a constant applied potential. Calibration curves made by plotting —1/I vs. 1/C are linear. This is consistent with a reaction mechanism in which the analyte is adsorbed prior to anodic detection. The technique is applicable for detection in chromatographic and flow-injection systems.     

硫酸根离子对铁在弱碱性溶液中阳极溶解和钝化行为的影响

采用浸泡实验, 电化学测试和表面分析技术研究了硫酸根离子浓度对铁在稀碳酸氢钠溶液中开路状态和阳极极化行为的影响. 在无硫酸根离子及含有少量硫酸根离子的碳酸氢钠溶液中, 铁的开路电位约为(-0.225±0.005) V, 并呈现钝化状态, 其电化学阻抗很大, 腐蚀速率较低. 在含有较高浓度硫酸根离子的碳酸氢钠溶液中, 铁的开路电位为(-0.790±0.010) V并呈现活性溶解状态, 其电化学阻抗较小, 腐蚀速率较高, 同时阳极极化曲线上能观察到活化-钝化转变现象. 由于铁在含有较高浓度硫酸根离子的碳酸氢钠溶液中处于活化状态, 阳极极化曲线上存在数个电流峰. 足够高的硫酸根离子浓度会导致铁表面预先形成或转变而成的氧化膜失效. 相比于自然曝氧状态, 在除氧条件下较低的硫酸根离子浓度即可引起铁在碳酸氢钠溶液中由钝态向活性溶解态的转变.     

Kinetics of Active Dissolution of Hydrophilic Metals Allowing for Anodic Activation

The anodic activation of dissolution of the iron metals is due to the accelerated formation of excess sources of steps during an activating anodic pulse. This is shown on the basis of a model of spatial separation of dissolution and passivation, with allowance made for the formation of pairs of kinks on stationary steps. The formation of pairs of kinks is also the reason for the emergence of a nonpolarizability portion in steady-state current–voltage curves pertaining to anodic dissolution of iron in acid chloride solutions.     

Effect of specific adsorption of anions on the kinetics of the current relaxation after pulsed anodic activation of dissolution of hydrophilic metals

Based on the model of spatial separation of the dissolution and passivation of hydrophilic metals, the effect of strong specific adsorption of anions on the shape of curves for the relaxation of anodic current of metals in acid solutions after switching an anodic activation pulse off is considered by using iron as an example.     

炔氧甲基胺氨基三甲撑膦酸盐的缓蚀作用和阳极吸脱附行为研究

采用稳态极化曲线和交流阻抗测试技术研究了己基二炔氧甲基胺氨基三甲撑膦酸盐在盐酸介质中的缓蚀作用机理和阳极吸附行为。吸附等温式符合Ｆｒｅｕｎｄｌｉｃｈ等温式，随缓蚀剂的脱附，阻抗谱在低频区出现感抗弧，且随脱附的进行而增大。     

Comparison Between a Charge Transfer Process and an Electrocatalytic Process in Cyclic Voltammetry and Cyclic Voltcoulommetry. Application to the Oxidation of Ferrocyanide at a Ferrocene‐Monolayer Modified Gold Electrode

Ferrocyanide oxidation catalyzed by a ferrocene‐alkylthiolate monolayer at gold electrodes has been investigated by using cyclic voltammetry (CV) and cyclic voltcoulommetry (CVC). The voltammetric current‐potential curves obtained present a stationary sigmoidal feature which points out to a very high rate constant for the chemical step, whereas the charge‐potential curves do not reach an stationary behavior in any case. Simple expressions are presented for the characterization of the CV and CVC curves under Nernstian conditions for the charge transfer step. From these expressions, a value for the chemical rate constant 2.5×10⁴ M^?1 s^?1 has been easily obtained from an anodic plateau of the CV curves or from the linear anodic region of the CVC curves.     

用正电子湮没寿命谱法研究铝阳极氧化膜

退火纯铝(99.99%)在15%H_2SO_4中于不同电解条件下进行阳极氧化, 然后测其正电子湮没寿命谱, 寿命谱拟合为三个寿命成份, 指认第二寿命成分为e~+在氧化膜中的湮没。从I_2随电解条件的变化推知膜厚与槽压近似成正比, 在恒温和固定槽压条件下, 膜厚只能达到某极限值。根据τ_2的变化推断出, 使用较高槽压或延长电解时间均使膜的结晶度提高, 它诱发了裂缝或微洞的形成, 导致膜体松散。根据上述结论进一步分析提高膜机械性能的可能途径。     

不同类型GaAs上应用约束刻蚀剂层技术进行电化学微加工

应用约束刻蚀剂层技术(CELT)对GaAs进行电化学微加工. 研究了刻蚀溶液体系中各组成的浓度比例、GaAs类型、掺杂以及阳极腐蚀过程对GaAs刻蚀加工过程的影响. 循环伏安实验表明, Br-可以通过电化学反应生成Br2作为刻蚀剂, L-胱氨酸可作为有效的捕捉剂. CELT中刻蚀剂层被紧紧束缚于模板表面, 模板和工件之间的距离小于刻蚀剂层的厚度时, 刻蚀剂可以对GaAs进行加工. 利用表面具有微凸半球阵列的导电模板, 可以在不同类型GaAs上加工得到微孔阵列. 实验结果表明: 在相同刻蚀条件下, GaAs的加工分辨率与刻蚀体系中各组分的浓度比例有关, 刻蚀结构的尺寸随着刻蚀剂与捕捉剂浓度比的增加而增大; 在加工过程中, p-GaAs相对于n-GaAs和无掺杂GaAs受到阳极氧化过程的影响较为显著, p-GaAs表面易生成氧化物层, 影响电化学微加工过程. X射线光电子能谱(XPS)和极化曲线实验也证明了这一点.     

Application of anodic dissolution method for a study of electrocolored aluminum oxides

The anodic dissolution of color carrier of colored aluminum anodic oxide films (AOF) is studied before and after their coloring, using ac in various electrolytes containing Cu(II). The voltammetric polarization curves of anodic dissolution of colored AOF in 0.1 M H₂SO₄ depend on the amount of copper deposited in the pores and its oxidation state (Cu, Cu₂O, CuO). Analytical and X-ray diffraction examination of AOF prior to and after the anodic dissolution shows that the anodic dissolution method is inapplicable for the determination of the oxidation state of copper electrodeposited in AOF pores or the amount of copper oxides.     

Anodic film formation on osmium electrodes: Part II. Galvanostatic and potentiostatic measurements

The formation and reduction of anodic films on Os electrodes in 2 M HCl and HClO₄ solutions were studied by anodic and cathodic charging curves. The galvanostatic oxidation of Os in HClO₄ shows the formation of OsO₂ as an intermediate step to OsO₄ that goes in the solution. The cathodic charging curves at Os electrodes previously oxidized at constant potential reveal the anodic film to be made up of a reversibly desorbed oxygen layer and an oxide phase reduced irreversibly. Both layers increase with time under potentiostatic conditions following a logarithmic equation until a constant value is reached. At all times, the content of OsO₂ in the anodic film at high potentials is larger than that of chemisorbed oxygen.In HCl solutions only the reversible reduction of an oxygen layer is observed. The growth of this film also complies with a direct logarithmic law before attaining a limiting coverage. The charge involved in the reduction increases linearly with the potential at a given time of formation. The results are discussed in terms of a Temkin-type isotherm and a place-exchange mechanism.     

An EQCM study on the influence of saccharin on the corrosion properties of nanostructured cobalt and cobalt-iron alloy coatings

Nanostructured cobalt (Co) and cobalt-iron (CoFe) alloy coatings were electrodeposited from sulfate solutions in the presence and absence of saccharin. The effects of saccharin on the corrosion behavior of Co and CoFe alloy coatings were investigated using the electrochemical quartz crystal microbalance (EQCM) technique coupled with cyclic voltammetry (CV) measurements. Saccharin was added to the electrolyte as a grain refiner and brightener. Interestingly, opposite corrosion behaviors were found for all nanostructured coatings in 0.1 M H₂SO₄ and 0.1 M NaOH. The use of saccharin as an additive in the plating solution accelerated the anodic reaction for all deposits in acidic medium. The mass decreases while dissolution rate increased with higher saccharin concentration. Meanwhile, formation of a thick passive film on the Co electrode surface were enhanced while a hindering effect was observed for CoFe alloy coatings deposited in the presence of saccharin in alkaline solution. The anodic and cathodic curves obtained from potentiodynamic polarization experiments were also in agreement with the EQCM results.     

Graphene-modified electrode. Determination of hydrogen peroxide at high concentrations

A gold electrode partially coated by graphene multilayer is developed and tested with respect to high concentrations of hydrogen peroxide. The effective use of conventional electrode materials for the determination of such an analyte by anodic oxidation or cathodic reduction is prevented by the occurrence of adsorptions fouling the electrode surface. This prevents reliable and repeatable voltammetric curves for being recorded and serious problems arise in quantitative analysis via amperometry. The gold–graphene electrode is shown to be effective in quantitative evaluation, by cathodic reduction, of hydrogen peroxide at concentration levels that are of interest in an industrial. Acid, neutral, and basic pH values have been tested through correct adjustment of a Britton Robinson buffer. The experiments have been performed both by cyclic voltammetry and with amperometry at constant potential in unstirred solution. The latter technique has been employed in drawing a calibration linear plot. In particular, the performances of the developed electrode system have been compared with those of both pure gold and pure graphene electrode materials. The bi-component electrode was more sensitive; co-catalytic action by the combination of the two components is hypothesised. The system is stable over many potential cycles, as checked by surface-enhanced Raman spectra recorded over time.     

还原剂对多孔阳极氧化铝纳米孔道结构的影响

多孔阳极氧化铝(PAA)和多孔阳极氧化钛纳米管(PATNT)的结构调控近年来倍受关注. 在形成机理尚不清楚的情况下, 对PAA和PATNT的结构调控很难避免盲目性. 为验证“氧气气泡模具”可以形成纳米孔道这个新观点, 本文采用化学方法对PAA的结构进行调控, 成功地引入了一种还原剂来吸收纳米孔道中的氧气气泡. 在添加还原剂的草酸溶液中得到了一种特殊的阳极氧化铝膜. 研究了还原剂的含量对磷酸溶液中形成PAA孔道结构的影响, 结果表明随着还原剂含量的增加, PAA的孔道直径逐渐减小, 有序性降低. 对比了添加还原剂前后阳极氧化过程的电压-时间曲线的差异, 结果表明, 在含有还原剂溶液中制备的阳极氧化铝膜的导电性明显提高. 在密封的条件下, 还原剂能吸收掉孔道中的氧气, 使气泡模具效应消失, 得到完全的致密型氧化膜. 这些实验事实充分证明PAA中有序孔道的形成是氧气气泡模具效应的结果.     

稀土铈对铝合金LY12CZ微生物腐蚀行为的影响

采用紫外分光光度法（UVS）、最大可能数法（MPN）、循环阳极极化法、电化学阻抗谱（EIS）和表面荧光显微法（EFM）研究了不同含量稀土Ce³⁺离子对硫酸盐还原菌（SRB）生长及LY12CZ铝合金微生物腐蚀行为的影响.结果表明:低浓度的Ce³⁺离子能够促进SRB生长,而高浓度时则抑制其生长;循环阳极极化曲线表明,稀土Ce³⁺离子的加入使铝合金LY12CZ的点蚀敏感性降低;电化学阻抗谱表明,在纯培养基中,随稀土Ce³⁺离子浓度的增大,铝合金耐蚀性增大.而在接种1%SRB的培养基中,当Ce³⁺浓度为0.376 mg·L^-1时,生长旺盛的生物膜与Ce³⁺间产生协同作用,增加了基体铝合金耐腐蚀性能.随着Ce³⁺浓度的增加,SRB生长受到抑制,不能形成致密的生物膜.此时SRB的存在促进铝合金腐蚀,显著减弱Ce³⁺对基体铝合金的保护作用.     

钨酸盐对镁合金在3.5%NaCl介质中的缓蚀作用

研究钨酸钠对AZ61镁合金在3.5%NaC l腐蚀介质中的缓蚀作用.电化学阻抗谱(EIS)、Tafel极化曲线、扫描电子显微镜(SEM)等测试表明,钨酸钠缓蚀剂可有效抑制镁合金在NaC l介质中的腐蚀,当钨酸钠浓度为0.01 mol.L-1可达到较好的缓蚀效果,缓蚀效率达75.5%.钨酸钠可参与镁合金表面膜的形成,使表面膜更致密,从而抑制镁合金的腐蚀;其缓蚀作用属于阳极抑制型缓蚀机理.     

碳钢在NaHCO_3溶液中的阳极极化行为(英文)

研究碳钢在NaHCO3溶液中的阳极极化行为. 极化曲线测试表明,在 (0. 05 ~1. 0mol/L)NaHCO3浓度范围内,碳钢的阳极极化曲线都显示 2个电流峰和 2个钝化区,当HCO3-浓度低于 0. 1mol/L时,两电流峰相距很近,致使第 1个钝化区不易观察到. 而当HCO3-浓度>0. 1mol/L后,其第 1电流峰峰电流愈加上扬,而第 2电流峰峰电流反而下降. XPS分析表明,在较高电位下碳钢形成的表面膜,其外层主要成分为Fe2O3,而内层组成主要含Fe(Ⅱ)和Fe(Ⅲ)氧化物.     

Fabrication and characterization of 20 nm planar nanofluidic channels by glass-glass and glass-silicon bonding

We have characterized glass-glass and glass-Si bonding processes for the fabrication of wide, shallow nanofluidic channels with depths down to the nanometer scale. Nanochannels on glass or Si substrate are formed by reactive ion etching or a wet etching process, and are sealed with another flat substrate either by glass-glass fusion bonding (550 degrees C) or an anodic bonding process. We demonstrate that glass-glass nanofluidic channels as shallow as 25 nm with low aspect ratio of 0.0005 (depth to width) can be achieved with the developed glass-glass bonding technique. We also find that silicon-glass nanofluidic channels, as shallow as 20 nm with aspect ratio of 0.004, can be reliably obtained with the anodic bonding technique. The thickness uniformity of sealed nanofluidic channels is confirmed by cross-sectional SEM analysis after bonding. It is shown that there is no significant change in the depth of the nanofluidic channels due to anodic bonding and glass-glass fusion bonding processes.     

酸性化学镀镍磷合金的动力学机理

通过极化曲线研究了3种不同溶液（阴极液、阳极液和完整镀液）的电化学行为,测定了主盐、还原剂浓度以及镀液pH和体系温度对化学镀镍沉积速率的影响. 与直接在镁合金上化学镀镍并使用重量分析法得到的沉积速率相比较发现,完整镀液体系的极化曲线才能真实地反映化学镀镍的沉积过程,其过程不能简单视为由彼此完全独立毫无关联的阴阳极半反应构成. 根据Butler-Volmer公式,本化学镀液体系的化学镀镍过程属混合控制,其表观反应活化能为42.89 kJ·mol^-1.     

Electrogenerated chemiluminescence in mechanistic investigations of electroorganic reactions: Part II. Anodic dehydrogenation of 1,4-dihydropyridines

The anodic oxidation of fifteen 1,4-dihydropyridines in acetonitrile was investigated by electrogenerated chemiluminescence measurements at a rotating platinum disc electrode in the presence of some luminescent compounds D. The emission observed originates from the homogeneous electron transfer between the cation radicals of D and the free pyridiniumyl radicals formed in the dihydropyridine oxidation. It follows from the luminescence-potential curves that, in addition to the pyridiniumyl radicals, the dihydropyrindine cation radicals are also involved in the dehydrogenation process. Therefore, from the different oxidation pathways of dihydropyridines described in the literature an ECE mechanism is preferred in acetonitrile. The substituent effect on the oxidation reaction and on the anodic luminescence is discussed.     

Estimation of Corrosion Rate of STARBOND–CoS Cobalt–Chromium Alloy in the NaCl Solution

Russian Journal of Electrochemistry - The corrosion potential Ecorr of STARBOND–CoS alloy in the 0.5 M NaCl solution was measured for 100 h. The anodic and cathodic potentiodynamic curves...