关键词： Pulsed electrochemical micromachining   Electrical double layer   Inter-electrode gap   Numerical simulation   Finite Element Method  

摘要： Pulsed electrochemical micromachining is a metal dissolution process where the capacitive behaviour of the double layer enhances the confinement of the machining profile, when very short voltage pulses are applied. During the pulses, the dissolution is confined to electrode regions where the tool-workpiece gap is the smallest. The model used combines the potential distribution in the electrolyte with the load-unload behaviour of the double layer. The model is solved using the Finite Element Method. The pulse and double layer charging are the main focus and therefore no shape change is included in the model at this point. The influence of the double layer, pulse signal parameters and inter-electrode gap size on the dissolution current density (material removal depth), as a function of time, is investigated. An estimation of the double layer loading time is presented, as well as a quantification method for the metal removal confinement, by comparing the calculated error against an ideal removal profile. The influence of pulse characteristics on the dissolution process has also been studied. It was found that a strongly non-linear polarization in combination with nano-second pulses and a small gap size increases the confinement. All the simulation results were obtained on an axisymmetric case by considering several geometrical set-ups. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： Impurity segregation   Electrorefining   Ultrapure materials   Solar-grade silicon  

摘要： A theory for impurity segregation in electrochemical processes is formulated based on the Nernst equation, which forms the theoretical foundation for electrorefining. It is found that the current two-electrode configuration, while being widely used to purify metals, is incapable of producing ultrahigh purity. A three-electrode configuration is required, in which the potential applied to the anode or the cathode with respect to the reference electrode is the key to produce ultrapure materials. The theory is applied to electrorefining of metallurgical-grade silicon to produce solar-grade silicon. It is suggested that two-step electrorefining is required to remove all the impurities, in which the anode and cathode potentials are controlled in separate steps. The precise anode and cathode potentials for each step are determined from the impurity concentrations in metallurgical-grade silicon and the target impurity concentrations for solar-grade silicon. It is also found that low process temperatures promote effective electrorefining. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： Ion-exchange membranes   transport phenomenon   electro-membrane processes   in situ ion substitution   separation   water splitting  

摘要： Membrane-based separation processes are achieving a remarkable attention both in academics and industrial research due to the versatility and economic considerations. Ongoing challenges in water and wastewater treatment, food and biotechnology industries accelerating applications of electro-membrane processes. Intensified research on ion-exchange membranes (IEMs) based electro-membrane processes has been accomplished during recent years to produce potable water and downstream processes for biomolecules separation and recovery. The choice of proper membrane, design and operational optimization of the process are highly essential for successful commercialization of any process. Thus, the development of cost effective membranes by eco-friendly route is highly required for researchers working in the field of membrane development by electro-membrane-based processes. This review provides a brief summary of different preparative procedures for IEMs, transport phenomenon and their applications in electro-membrane separation processes. The most relevant studies have been discussed.

关键词： Scanning Kelvin probe (SKP)   Scanning electrochemical microscopy (SECM)   Oxygen reduction reaction (ORR)   Aluminum alloy   Corrosion  

摘要： An integrated SKP-SECM system was successfully optimised with respect to improved lateral resolution. An aluminum alloy was synthesised by solidification of a liquid melt of pure Al, Cu and Mg metal powders in order to visualize single S-phase intermetallic particles (IMPs) using a newly proposed "glass free" SKP-SECM tip. The obtained IMPs were randomly distributed in the solid solution matrix of the alloy and their average chemical composition was in agreement with that of S-phase IMPs in commercially available AA2024-T351 alloys. The S-phase IMPs were localized in the SKP mode of the SKP-SECM system. The increased electrochemical activity of the S-phase IMPs was visualized using the feedback mode of SECM and the in situ consumption of O-2 on the surface of a single S-phase IMP was visualized in the redox-competition mode of the SECM using the same tip. Thus, the local Volta potential difference obtained in the SKP mode could be overlaid with the local electrochemical activity for O-2 reduction. (c) 2012 Elsevier Ltd. All rights reserved.

关键词： Co-axial diamond wheel-tool array   Electrochemical co-deposition   RWEDM technique  

摘要： This study presents a novel hybrid technique for fabricating a multi-edged co-axial micro diamond wheel-tool array. The technique combines an electrochemical process with a RWEDM (Rotary Wire Electrical Discharge Machining) technique to precisely electroform a diamond wheel-blank and then produce a coaxial wheel-tool array. A duplex tank design, containing a mini-tank made of porous aluminium-dioxide material is developed for the electrochemical co-deposition of a nickel-based diamond matrix onto a cylindrical aluminium alloy substrate. Optimal conditions for the co-deposition are examined and tested in the production of the wheel-blank. A small RWEDM mechanism that uses permanent magnet tension braking to maintain wire tension and reduce wire vibration is also proposed. The RWEDM process is used for slicing, truing and dressing the grinding edges of the blank. Experimental findings and machining examples show that the proposed novel hybrid process can successfully fabricate a co-axial diamond wheel-tool with a grinding-edge array that has extremely thin high integrity cutting edges. (C) 2012 Elsevier B.V. All rights reserved.

关键词： Oxides   Sol-gel chemistry   X-ray diffraction   Microstructure   Electrochemical properties  

摘要： Lithium-ion battery cathode material Li1+xV3O8 was synthesized by a tartaric acid assisted sol-gel method and thermally treated at 350 degrees C, 450 degrees C and 550 degrees C for 3 h for the formation of Li1+xV3O8 phase. The synthesized samples were fully characterized by FTIR, TG/DTA, XRD and charge-discharge tests. Li1+xV3O8 material synthesized by tartaric acid assisted route, followed by heat treatment at 450 degrees C for 3 h shows best electro-chemical performance. It shows a high initial capacity of 249 mAh g(-1) and still reserves a discharge capacity of 260 mAh g(-1) after 50 cycles. Moreover, for all tartaric assisted products, no capacity decadence is observed in 50 cycles. The in situ X-ray measurements reveal a two-phase transition mechanism in the lithium intercalation/deintercalation process. During lithium extraction, the structure of the delithiated compound changes from Li4V3O8 (x > 3.1) to the original LiV3O8 phase (x < 1.4) via the coexistence state of these two phases (1.4 < x < 3.2). An obvious contraction, especially at Li(3)-Li(4) transition, along a axis and a slight expansion along b axis are also observed. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： Electric double layer capacitors   Solid polymer electrolytes   Electrospinning   Poly(acrylonitrile)   Compression molding  

摘要： The electrochemical characteristics of electric double layer capacitors composed of solid polymer electrolytes with different thicknesses were investigated. A solid polymer electrolyte membrane was fabricated using electrospun fibers through solvent-assisted or thermally induced compression molding. Through the solvent-assisted or thermally induced compression molding processes, the poly(acrylonitrile) (PAN) microfibers consolidated together by the interlocking of the fibers under compression. A solid polymer electrolyte membrane clearly exhibited a free-standing shape with a bending capability. The electrospun PAN non-woven fabric and electrolyte salt composites showed higher ionic conductivity (>10(-3) S cm(-1) at 298 K) and capacitance compared with the liquid organic electrolyte. The solid polymer electrolytes provided a 10.6% increase in the energy density, seemingly due to the decrease in the IR drop and increase in the capacitance. (C) 2012 Elsevier B.V. All rights reserved.

关键词： Ballast water   E. coli   Electrochemical disinfection   Kinetics modeling  

摘要： The invasion of biological organisms via ballast water has created threats to the environment and human health. In this study, a cost-effective electrochemical disinfection reactor was developed to inactivate Escherichia coli, one of the IMO-regulated indicator microbes, in simulated ballast water. The complete inactivation of E. coli could be achieved within a very short time (150, 120, or 60 s) with an energy consumption as low as 0.0090, 0.0074 or 0.0035 kWh/m(3) for ballast water containing E. coli at concentrations of 10(8), 10(7) and 10(6) CFU/100 mL, respectively. Electrochemical chlorination was the major disinfection mechanism in chloride-abundant electrolytes, whereas oxidants such as ozone and free radicals contributed to 20% of the disinfection efficiency in chloride-free electrolytes. Moreover, a disinfection kinetics model was successfully developed to describe the inactivation of E. coli. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： chemical mechanical polishing (CMP)   electrochemical-mechanical polishing (ECMP)   current-voltage (I-V)   linear sweep voltammetry (LSV)   electrolyte   Cu electrode  

摘要： We examine the correlation between process parameters and electrochemical surface state for electrochemical-mechanical polishing (ECMP) application of copper (Cu) in alkali-based NaNO3 and acid-based HNO3 electrolyte. First, the effects of electrolyte concentration on the electrochemical surface reaction of Cu electrode were evaluated from the current-voltage (I-V) curve obtained by linear sweep voltammetry (LSV) method. Second, we fundamentally studied the chemical states and element composition of the Cu surface according to the concentration of the electrolyte and the potential variation using scanning electron spectroscopy (SEM) and X-ray diffraction (XRD) patterns. The proposed mechanism and analyses were a good methodology in finding suitable electrochemical process parameter for ECMP application.

关键词： Process control  

摘要： This work deals with the electrochemical polymerization of pyrrole. The electrochemical polymerization process is evaluated in terms of polymer yield and conversion with respect to monomer and dopant concentrations, applied voltage, and polymerization temperature. An expression for predicting the system current as a function of the aforesaid process parameters has been developed. The system current and normalized system current have been found to be the determining factors for controlling the yield and conversion, respectively. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.050209jes] All rights reserved.