Focused microwaves in electrochemical processes

The effects of high intensity microwave radiation in electrochemistry are summarized and discussed. In situ microwave activation of electrochemical processes has been introduced recently and is possible by placing a carefully designed electrochemical cell directly into a microwave cavity. Self-focusing of intense microwave radiation occurs into a region close to the electrode | solution (electrolyte) interface of a microelectrode placed into the electrochemical cell. The electrode diameter and the electrode material strongly affect the observed mass transport enhancement and temperature effects. Experiments have been conducted to determine the temperature at the electrode surface electrochemically and to quantify the rate of chemical processes which occur in the vicinity of the electrode under high intensity microwave conditions. The effects of microwaves in a wide range of solvent systems from aqueous solutions to organic solvents (DMSO, acetonitrile, DMF, formamide) and in an ionic liquid (BMIM⁺PF₆⁻) have been investigated. Considerable current and temperature enhancements are observed in all solvents and are explained based on the interaction of microwaves with the liquid (electrolyte) and the physical properties of the liquids or solutions.     

Oxygen permeation studies on alternative proton exchange membranes designed for elevated temperature operation

Kinetic and mass transport properties were investigated for the oxygen reduction reaction in Nafion 117 and a sulfonated poly (arylene ether sulfone) membrane (SPES-40, 40% sulfonated groups/repeat unit) under 1 atm oxygen pressure, 100% relative humidity in a temperature range of 303-343 K using a solid-state electrochemical cell. Kinetic parameters were obtained using slow-sweep voltammetry while mass transport parameters, the diffusion coefficient (D) and solubility (C), were obtained using chronoamperometry at a Pt (microelectrode)/proton exchange membrane (PEM) interface. Oxygen reduction kinetics was found to be similar for both Nafion® 117 and SPES-40 membrane at the Pt microelectrode interface. The temperature dependence of O₂ permeation parameters showed same trends for both the membranes studied, there was an increase in D and a concomitant decrease in C. Despite lower equivalent weight and hence higher water content SPES-40 exhibited relatively close values of D with Nafion® 117. The results are discussed in the context of their different microstructures. Values of C showed a closer relationship to water content and the percent volume of aqueous phase in the respective membranes. The values of overall oxygen permeability were significantly higher in Nafion® 117, with a higher positive slope in its variation with temperature.     

Local environment under simulated disbonded coating on steel pipelines in soil solution

Taking advantage of microelectrode technique, the local potential and pH in a crevice simulating disbonded coating on X70 pipeline steel were investigated as a function of cathodic protection (CP) in a near neutral pH soil bulk solution bubbled with 5% CO₂/N₂ gas. The experimental potential–pH (E–pH) diagrams were established for the steel in the crevice. Stress corrosion cracking (SCC) susceptibility of the steel in the local environment in the crevice was analyzed based on the experimental E–pH diagrams. The results showed that the local steel potential in the deep of the crevice was independent on CP potential applied at the opening. Due to the effect of the atmospheric CO₂, a near-neutral pH local environment promoting near-neutral pH SCC (also known as transgranular SCC, TGSCC) might be harbored in the crevice even with normal CP at the opening. During CP interruption, the steel potential decay and CO₂ absorption (pH decrease) might shift E–pH points into a susceptibility region of near-neutral pH SCC.     

An optimized process for fabrication of high-aspect-ratio photoresist-derived carbon microelectrode array on silicon substrate

An optimized process was developed for fabrication of high-aspect-ratio photoresist-derived carbon microelectrode array on silicon substrate. This process consisted of conventional photolithography, three-step linear pyrolyzing process and micromechanical interlocking. Comparing with previous two-step pyrolysis, three-step linear pyrolysis process can better preserve the geometry of microstructure during pyrolysis, and micromechanical interlocking was introduced to improve bonding strength between carbon microstructure and substrate. As a result, it can be achieved that high-aspect-ratio carbon microelectrode array remained upright and robustly with substrate. The experimental results confirmed that the optimized process is very effective, and the technology will be helpful for integration of 3-dimensional carbon-based devices in the fields of bioMEMS and electrochemical analysis.     

微电极法评估储氢合金的循环寿命

本文报告了一种方法评估储氢合金电极的循环寿命。使用储氢合金粉末微电极,适当地选择电位扫描范围和扫描速度,做循环伏安曲线,用氧化峰面积代表电极的放电量,可以测得放电量随时间的变化曲线,从而得到电极容量的衰减曲线。相对于常规寿命测试方法,本方法用时大大减少,且操作简便,结果准确。     

Construction of DNA-based logic gates on nanostructured microelectrodes

Electrochemical logical operations utilizing biological molecules (protein or DNA),which can be used in disease diagnostics and bio-computing,have attracted great research interest.However,the existing logic operations,being realized on macroscopic electrode,are not suitable for implantable logic devices.Here,we demonstrate DNA-based logic gates with electrochemical signal as output combined with gold flower microelectrodes.The designed logic gates are of fast response,enzyme-free,and micrometer scale.They perform well in either pure solution or complex matrices,such as fetal bovine serum,suggesting great potential for in vivo applications.     

Influence of Ag,Sb, Bi and Zn impurities on electrochemical and flotation behaviour of galena

The influences of Ag, Bi, Sb and Zn impurities on the electrochemical adsorption of butyl xanthate on a galena surface were investigated. The impurity-doped and pure galena samples were synthesised by chemical precipitation and tested by X-ray diffraction (XRD) analyses. The flotation results suggest that the Ag and Bi impurities can promote the flotation of galena, while the Zn and Sb inhibit it. Both the lead- and impurity-xanthate are observed on the galena surface by infrared spectra, which suggests that the impurities on galena surface also interact with xanthate. However, Ag-xanthate and Bi-xanthate at the galena surface doped Ag or Bi may need to be further verified. The cyclic voltammetric measurements on galena microelectrodes reveal two oxidation peaks for both the pure and impurity-doped PbS, while no obvious reduction peaks are observed. It is found that the presence of Ag and Bi enhances the oxidation of xanthate on the galena surface, while the Zn and Sb impurities inhibit the oxidation of xanthate on the galena surface. The amount of electrochemically adsorbed xanthate on the galena surface varies based on the type of impurity and has a positive correlation with the flotation recovery of galena.     

Novel method for fast determination of ultra trace amounts of timolol maleate by continuous cyclic voltammetry at Au microelectrode in flowing injection systems

A novel method for easy and fast detection of timolol maleate in flow-injection system has been introduced. It was used for analysis of timolol maleate in pure form as well as in its pharmaceutical formulations. The reported method is simple, precise, accurate, time saving and economic as compared to all previously reported methods. The best performance for measurement of timolol maleate was obtained at, pH 2.0, scans rate 300 V s⁻¹, accumulation potential −500 mV and delay time 0.6 s. The advantages of the proposed detection method are, (1) the removal of oxygen from the test solution is not required any more, (2) the detection limit of the method is sub-micromolar, (3) this method is fast enough for determination of the drug compound, in a wide variety of chromatographic techniques. The potential waveform consists of potential steps for cleaning, accumulation and potential ramp that were continuously applied on an Au disk microelectrode (with a radius of 12.5 μm). The detection limit of the method for timolol maleate was 1.58 ng ml⁻¹. The relative standard deviation of the method at 1.0 × 10⁻⁹ M was 2.3% for 20 runs.     

An Experimental Study on Electro Chemical Machining of Microelectrode

Puts forward a new method in machining microelectrode by electro chemical machining （ECM） and plastic deformed theory. The procedure of this method is to machine the microelectrode according to the basic rule of ECM theory at first. Then, with the change of ECM machining parameters, one of the microelectrode ends is exerted by a load. As a result, the elastic and plastic deformation is produced at the machining section and the microelectrode diameter is reduced. It has been proved that the proposed method can determine the optimum machining parameters to machine the microelectrode of Cu.     

微细电火花加工中微细电极的制作与检测技术研究

分析了微细电火花加工技术中各种微细电极制作方法的特点,提出了一种加工效率与尺寸精度相兼顾的微细电极在线制作方法.充分利用微细电火花加工机床的数控和接触感知功能,探索并提出了一种微细电极的在线检测方法,并对检测误差进行了分析.实验表明,该方法具有广泛的实用性.