关键词： ECM   Two-phase Material   Process Simulation   42CrMo4  

摘要： The macroscopic shaping process in electrochemical machining can be forecasted within industrial manufacturing tolerances by means of numerical methods. However, the evolution of surface microstructure is rarely taken into account by existing models. With regard to the achievable surface integrity including surface roughness the microstructure is a crucial factor, especially for multi-phase materials. Therefore, this paper presents a new approach for modeling the anodic dissolution process for an alloy containing at least two phases. The model characterizes the electrochemical process with nonlinear electronic elements and will allow the forecast of the evolution of machined surfaces of two-phase materials.

关键词： Electric field   Fouling rate   Bound extracellular polymeric substances (bEPS)   Soluble microbial products (SMP)   Transparent exopolymeric particles (TEP)   Sludge hydrophobicity  

摘要： Membrane bioreactor (MBR) technology is becoming increasingly popular as wastewater treatment due to the unique advantages it offers. However, membrane fouling is being given a great deal of attention so as to improve the performance of this type of technology. Recent studies have proven that the application of electrochemical processes to MBR represents a promising technological approach for membrane fouling control. In this work, two intermittent voltage gradients of 1 and 3 V/cm were applied between two cylindrical perforated electrodes, immersed around a membrane module, at laboratory scale with the aim of investigating the treatment performance and membrane fouling formation. For comparison purposes, the reactor also operated as a conventional MBR. Mechanisms of nutrient removal were studied and membrane fouling formation evaluated in terms of transmembrane pressure variation over time and sludge relative hydrophobicity. Furthermore, the impact of electrochemical processes on transparent exopolymeric particles (TEP), proposed as a new membrane fouling precursor, was investigated in addition to conventional fouling precursors such as bound extracellular polymeric substances (bEPS) and soluble microbial products (SMP). All the results indicate that the integration of electrochemical processes into a MBR has the advantage of improving the treatment performance especially in terms of nutrient removal, with an enhancement of orthophosphate (PO4-P) and ammonia nitrogen (NH4-N) removal efficiencies up to 96.06 and 69.34 %, respectively. A reduction of membrane fouling was also observed with an increase of floc hydrophobicity to 71.72 %, a decrease of membrane fouling precursor concentrations, and, thus, of membrane fouling rates up to 54.33 %. The relationship found between TEP concentration and membrane fouling rate after the application of electrochemical processes confirms the applicability of this parameter as a new membrane fouling indicator.

关键词： Gear   Finishing   ECH   PECH   Honing  

摘要： Part 1 of this review discussed conventional gear surface finishing processes and their advantages and limitations, and introduced the electrochemical honing (ECH) process (and its extension of pulsed electrochemical honing (PECH)), to improve the surface characteristics of different types of gears, working principles, mechanism of material removal and equipment details. Part 2 gives a review of past work, and discusses effects of various process parameters on surface characteristics and finishing productivity (i.e. material removal rate), advantages and limitations, and its other applications. The objective of this review paper is to present ECH/PECH as one emerging alternative, economical, productive and sustainable gear finishing process.

关键词： Balance   Corrosion   Gravimetric Method   Hydrogen Evolution   Hydrogen Measurement  

摘要： A new method to measure the amount of hydrogen generated from the surface of an immersed electrode is presented in this work. The method consists of a mechanical balance with a horizontal arm attached to two hydrogen-collecting containers that are submerged in two independent electrochemical cells. One of the two cells (the test cell) contains the electrode of interest, generating an unknown amount of hydrogen, whereas the other cell (the measurement cell) contains an inert electrode that is used to evolve an amount of hydrogen equal to that generated in the test cell, such as the mechanical equilibrium between the sides of the balance is constantly maintained. Adequate electrical connections and circuitry ensures that, as hydrogen is evolved from the electrode of interest in the test cell, the displacement of the balance arms activates an electrical contact, which triggers the hydrogen evolution in the measuring cell. Once a sufficient amount of hydrogen is evolved from the measuring cell, the horizontal arm is displaced in the opposite direction and the electrical contact to the measuring cell is interrupted. The measurement of the current flowing through the measuring cell enables precise estimation of the amount of hydrogen generated in the test cell. (C) The Author(s) 2017. Published by ECS. All rights reserved.

关键词： silicon anode   poly(acrylic) acid neutralization   anode calendering   lithium ion battery  

摘要： Silicon is a promising anode active material for lithium ion batteries due to improvements to overcome the volume expansion problem and preserve the electrode structural integrity during the lithiation and delithiation processes. Significant studies have been performed to overcome this problem and make silicon available for commercial applications. In this study, we developed a facile and functional method to demonstrate the possibility of widespread usage of silicon anode. Here, two methods were investigated;neutralization of poly(acrylic) acid (PAA) and calendering process during electrode production. PAA without neutralization is commonly used in silicon based anodes. Calendering is a typical process for cathode preparation. However, it is not generally utilized for making silicon anodes. This study aims to show the effect of PAA neutralization and anode calendering on the electrochemical performance of cells in comparison to anodes prepared by conventional processes. Furthermore, a high mass loading is a critical step for the use of Si anode commercially. The electrode was successfully loaded in this study as 1 mg/cm(2). Electrochemical performance measurements showed that 1370 mAh/g specific capacity was achieved after neutralization of PAA and calendering of the electrode at the 100th cycle. Meanwhile, the calendered electrode prepared with PAA polymer showed a specific capacity of 511 mAh/g after 100 cycles. Traditionally, graphite is used as anode material in commercial batteries and theoretical specific capacity is 372 mAh/g. Our observations with quite high specific capacity achieved by the process applied in this study show an important promise for the use of silicon based anode materials in the future utilization of Li ion batteries. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： LiFePO4   Melt synthesis   Iron ore concentrate   Compositions   Impurities  

摘要： LiFePO4 was prepared from low-cost iron ore concentrate (containing 4.48 wt.% SiO2 and MgO, CaO and Al2O3 below 0.5 wt.% as contaminant) using a melt synthesis. X-ray diffraction (XRD) refinement associated with Mossbauer spectroscopy and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDX) analyses are used to track the location of Si in the material. It is shown that the iron content in the melt can be used as a means to control the doping rate of elements from iron ore concentrate (IOC) precursor according to the formula (Li1 - z A (z) )(Fe1 - y M (y) )(P1 - x Si (x) )O-4. Electrochemical behavior of the material is affected by the doping of LiFePO4. While capacity is decreased in doped material, the cycling stability is much improved. When dopants are out of LiFePO4 structure, capacity retention dramatically drops as well as capacity due to the gravimetric impact of impurity phases. A trade-off between high capacity and best cycling performance is necessary. For instance, slight lack of iron in the melt (6 % deficiency) leads to a capacity only 2 % lower than that of pure Fe2O3-based material for the same stoichiometry and fairly good capacity retention.

关键词： Mn3O4   Nanoparticles   Alkalinity-controlled synthesis   Pseudocapacitors  

摘要： Mn3O4 nanoparticles were prepared at 60 A degrees C in ethanol solution by a facile precipitation method. It was found that the particle size of the as-prepared Mn3O4 depended on the alkalinity of precipitants. Nanoparticles with average size of 6 nm were obtained by using morpholine as precipitant which had low alkalinity, while 10 nm particles were produced by using NaOH as precipitant. The former particles presented higher degree electrochemical double-layer capacitor-like behavior and higher electrochemical performance than the latter. This could be attributed to the effective faradaic reactions of particles, which originated from the low equivalent series resistance resulting from their smaller particle size. Mn3O4 nanoparticles were prepared in ethanol by a facile precipitation method using precipitants with different alkalinity. It was found that smaller particles (a) were generated by using precipitant with low alkalinity as compared with the one with higher alkalinity (b). As a result, the Mn3O4 nanoparticles presented a high-degree electrochemical double-layer capacitor-like behavior due to their low equivalent series resistance.

关键词： ion exchange membrane   electrochemical impedance spectroscopy   direct current method   diffusion boundary layer thickness   electrochemical properties  

摘要： Electrochemical impedance spectroscopy (EIS) and direct current method (DC) are two powerful techniques to investigate the electrochemical properties in ion exchange membrane transport processes. This work investigated the resistance of membrane systems obtained by EIS and DC with different solution velocity and temperature. Analysis of experimental data from EIS revealed that EIS can be used to analyze each sublayer of ion exchange membrane systems separately and quantitatively and that the resistance of interfacial layers was related to Donnan exclusion. The Bode plots of EIS data were corrected for ohmic resistance to determine the evident constant phase element (CPE) behavior in the data, and the effects of flow velocity and temperature on ohmic-resistance-corrected Bode plots were also analyzed. With the comparison of data obtained from EIS and DC, the sum of pure membrane resistance, diffusion boundary layer resistance and electrical double layer resistance determined by EIS equaled to the overall resistance of membrane systems determined by DC. The results confirmed the linear relationship between the overall conductivity of membrane systems from DC and the pure membrane conductivity from EIS. These results are of major importance for applications of ion exchange membranes in various electro-membrane processes and applications of EIS on characterization of membrane transport properties. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Ultrasonic vibrations   Electrochemical honing (ECH)   Bevel gears   Tooth finishing   MRR   EN8  

摘要： Electrochemical honing (ECH) is a novel variant of hybrid machining processes (HMPs). The key feature is that the distinct coupling of electrochemical machining (ECM) and honing provide a controlled functional surface generation and faster material removal rate in a single operation. In the present study, the influence of ultrasonic vibrations on process performance of ECH of bevel gears made of EN8 is investigated. An analysis of the process has been presented with suitable illustrations. Ultrasonic frequency and processing time were considered as the input variables while improvement in surface finish, material removal and geometrical accuracies were considered as the monitored output. The effectiveness of the process was investigated through experimental trials by conducting a comparison study between classical ECH and ultrasonic vibration-assisted ECH (UECH). The results confirm that improvements in surface roughness and martial removal rate are significantly higher than those obtained with classical ECH. The study further reveals that the scrubbing of the oxide layer is easier to be achieved and surface quality is obviously improved due to ultrasonic vibrations. The experimental results demonstrate that UECH gives 18.36 % improvement in average roughness, 9.31 % improvement in maximum roughness and 20 % improvement in material removal rate as compared with ECH.

关键词： Proton diffusion   Manganese dioxide cathode   Impedance   EMD   NMD  

摘要： The aim of the present work is the study of the performances of dry cells containing the electrolytic MnO2, natural MnO2, or a mixture of both. The two components have been characterized by chemical analysis. The continuous discharge tests done on the dry cells based on EMD present a discharge time largely greater than that of the pure NMD;however, the cells containing a mixture present intermediate values of the discharge time. The value of the diffusion coefficient estimated by the GITT or impedance spectroscopy shows that the H+ diffuses more quickly in the EMD variety that in the NMD one.