On the polarography of zinc in ethylenediamine medium

Polarography of zinc in ethylenediamine medium has been carried out. The equilibrium potentials have been determined by amalgam polarography. The standard rate constant for the electrode reaction and the stability constants of the complexes have been calculated.     

Amperometric titrations using the tubular graphite electrode. Development of an automatic technique

The tubular geometry of the electrode, by virtue of which the electrode can permit continuous analysis of electroactive solutions, has been made use of in developing an automatic technique for carrying out amperometric titrations, the tubular graphite electrode acting as an indicator electrode. A correlation, describing the time required for the completion of a particular titration in terms of relevant parameters such as the concentrations of the titrant and the titration solutions, volumetric flow rate of the titrant/titration solution and the total volume of the titration solution, has been derived theoretically and verified experimentally. Knowing the time required for the completion of a particular titration from the titration curve recorded automatically, the concentration of the titration solution can be easily calculated.     

Vibration optimization of an infinite circular AT-cut quartz resonator with ring electrodes

This paper presents the thickness-shear (TSh) vibration modes of an infinite circular AT-cut quartz resonator with ring electrodes. By application of 2D scalar differential equations derived by Tiersten and Smythe, we obtain the resonant frequencies and vibration amplitude distributions of thickness-shear modes in the resonator. The theoretical results have been verified in commercial FEM software COMSOL. Through numerical examples, we illustrate that the distribution of displacement fields in the center part of the ring electrode is adjustable. Furthermore, we optimize the size of the electrodes and the mass ratio of the electrode to the plate, in order to achieve a nearly uniform displacement distribution and mass sensitivity of the resonator. These results can be a theoretical guidance for design and optimization of sensors based on quartz resonators.     

Polarisation and polishing studies on copper in a Hull cell

In continuation of our previous work,^1–2 the effects of polishing time, sp. gr. of the electrolyte, addition of EDTA, electrolyte level, etc., on the position, size and shape of the variously polished bands obtained in a Hull cell have now been studied. I–V measurement when carried out showed that total cell voltage increases regularly with total cell current, thereby affording no explanation for the variously polished bands. However, with a specially designed probe electrode,³ it has been possible to study the current distribution as existing during polarisation at different points of the anode surface and thus offer some explanation for the appearance of variously polished bands which could not be interpreted earlier in terms of electrode potentials.     

Studies on the redoxokinetic effect: Preparation of reproducible electrode surfaces

An experimental technique has been developed for obtaining a reproducible platinum electrode surface for measurement of the redoxokinetic potential. The values for ψ for the platinum/ferrous sulphateferric sulphate-sulphuric acid system at room temperature are reported, at frequencies of the A.C. field within the range 50–250 cycles/second. The energy transfer coefficient has been calculated from the measurements of ψ. The effects of the circuit resistance, frequencies within the range 50–250 cycles/second and of temperature on the value of ψ have been studied and the results discussed in relation to the theory of the redoxokinetic effect.     

Electrochemical behaviour of zinc in alkaline solutions

The cathodic and anodic polarization of zinc in different concentrations of alkaline solutions has been studied under constant-current conditions. The changes of zinc electrode-potential with reference to a Hg/HgO/KOH system have been measured both in KOH and zincate solutions using a “Luggin” capillary and a specially designed cell, current being drawn from an electronic current stabilizer. Time-potential curves have been plotted and it is found that the anodic zinc passivates at a certain stage showing a sudden rise in potential by as much as 3–4 volts. Before the passivation, the main electrode reaction is the formation of Zn⁺⁺, while after the passivation it changes to gas evolution. No definite relationship as previously suggested by Muller, between the current density and the passivation time was found, perhaps due to migration and non-linear diffusion effects and other reasons discussed in the paper. It has been found that the behaviour of zinc differs in concentrated alkaline solutions (i.e., 0·5 N to 5 N) from that in dilute solutions (0·2 N to 0·01 N), in which case the open circuit rest-potential of zinc is indefinite and may vary by as much as 500–600 mV., while the maximum passivation jump in potential is about 2 volts only. Also the passivation and the decay of current on breaking the circuit are found to be slower than in the case of concentrated solutions. Colour changes of the zinc electrode, during the polarization, are also briefly described and discussed.     

Electrochemical behaviour of zinc in alkaline solutions

As the whole passivation phenomenon in the case of zinc is very quick and sudden and as it cannot be fully studied and followed by galvanostatic techniques alone, the constant over-potential technique has, for the first time, been applied to zinc and results reported. A special apparatus consisting of suitable oscillator, modulator, demodulator and a stable D.C. amplifier with a gain of 100,000 was used for the purposes and is described. Potential curves for equilibrium current rates, achieved on 0·1 V. and 25 mV. steps after 1 minute each, have been obtained in 6N, N, 0·1 N KOH and zincate solutions for the complete range of ?1·3 to about ?2·0 volts with reference to Hg/HgO/KOH reference electrode. It has been found that in the first truly active region, the main electrode reaction is the formation of zinc ions while after the passivation it changes to gas evolution. Potentiostatic techniques reveal intermediary stages, undisclosed by constant current methods, of pseudo-passivation and current-plateau regions in which the anodic layer thickens, controlled by the high field cation transport. These observations and explanations are further supported by plotting rate-time transients obtained by suddenly dropping the potentials from higher to lower values, when the rates were found to cut off. Some anomalies and sudden reversal of currents with increasing over-voltages, have also been fully discussed. The influence of other factors,e.g., concentration, stirring, sudden changes in over-voltages, presence of zincate, sulphate, etc., has also been considered. Studies such as these are found to throw considerable light on the electrochemical behaviour of zinc.     

结构参数对静电驱动微机械陀螺动态性能的影响

为研究结构参数对静电驱动微机械陀螺动态性能的影响,考虑支承刚度的三次非线性和静电力的分式非线性,基于两自由度动力学模型,利用谐波平衡法结合留数定理求解了系统的周期响应,得到了驱动电极的梳齿厚度、梳齿间隙以及检测电极的极板面积、极板间隙变化时电容变化量随驱动力频率和载体角速度的变化曲线,以及电容灵敏度和非线性度随这些参数的变化曲线。结果表明,检测电容变化量随驱动力频率的变化曲线会呈现明显的非线性特征,即第二个峰向右倾斜,从而引起跳跃现象。驱动电极的梳齿厚度、梳齿间隙和检测电极的极板间隙对检测电容变化量随载体角速度的变化影响较大,而检测电极的极板面积的影响很小。驱动电极梳齿厚度、梳齿间隙以及检测电极的极板面积对电容灵敏度和非线性度的影响基本上是线性的,但检测电极的极板间隙对电容灵敏度和非线性度的影响是非线性的。     

A desktop computer model of the arc,weld pool and workpiece in metal inert gas welding

A sophisticated computational model of metal inert gas arc welding of aluminium alloys is presented. The arc plasma, the wire electrode and the workpiece are included in the computational domain self-consistently. The flow in the arc plasma and in the weld pool are calculated in three dimensions using equations of computational fluid dynamics, modified to take into account plasma effects and coupled to electromagnetic equations. The formation of metal vapour from the wire electrode and workpiece is considered, as is the mixing of the wire electrode alloy with the workpiece alloy in the weld pool. A graphical user interface (GUI) has been developed, and the model runs on standard desktop or laptop computers.The computational model is described, and results are presented for lap-fillet weld geometry. The importance of including the arc in the computational domain is shown. The predictions of the model show good agreement with measurements of weld geometry and weld composition. The GUI is introduced, and the application of the model to predicting the thermal history of the workpiece, which is the input information that is required for predicting important weld properties such as residual stress and distortion and weld microstructure, is discussed. Initial predictions of residual stress and distortion of the workpiece are presented.     

Pull-in instability and free vibration of electrically actuated poly-SiGe graded micro-beams with a curved ground electrode

This paper investigates the pull-in instability and free vibration of functionally graded poly-SiGe micro-beams under combined electrostatic force, intermolecular force and axial residual stress, with an emphasis on the effects of ground electrode shape, position-dependent material composition, and geometrically nonlinear deformation of the micro-beam. The differential quadrature (DQ) method is employed to solve the nonlinear differential governing equations to obtain the pull-in voltage and vibration frequencies of the clamped poly-SiGe micro-beams. The present analysis is validated through direct comparisons with published experimental results and excellent agreement has been achieved. A parametric study is conducted to investigate the effects of material composition, ground electrode shape, axial residual stress and geometrical nonlinearity on the pull-in voltage and frequency characteristics.     

Effect of complexing agents on the disproportionation of uranium (V)

The effect of lactate, thiocyanate, sulphate, oxalic acid and fluoride on the disproportionation of uranium (V) formed at the dropping mercury electrode has been studied. The rate constants for the disproportionation reaction are calculated and the results are discussed on the basis of the stability of the complexes.     

Free energy relationship in some electron-transfer reactions

A linear logarithmic dependence of the standard rate constant on the apparent free energy of activation for the electrode process has been observed for the reduction of zinc in the presence of alanine, glycine, aspartic acid, glutamic acid, ammonia, ethylenediamine and tartrate. The value of the slope is close to the transfer coefficient of zinc in these media. For a homogeneous electron-exchange reaction, such as the disproportionation of uranium(V) in solution, a linear free energy relation has been observed.     

A polarographic study of methionine complexes of nickel and cobalt

A polarographic study of nickel and cobalt complexes of methionine has been carried out. In sodium perchlorate and tetramethyl-ammonium bromide (TMAB) media, catalytic hydrogen waves were observed owing to the lowering of hydrogen overvoltage on mercury by the adsorption of these complexes on the dropping electrode. The presence of tetrabutylammonium ion inhibits the catalytic activity.     

Design and simulation of a carbon nanotube-based adjustable nano-electromechanical shock switch

In this paper, design and simulation of a carbon nanotube-based nano-electromechanical shock switch is reported. The switch is represented by a carbon nanotube placed over a ground electrode. Response of the nano-switch based on nonlinear beam theory is studied using Galerkin’s method. Up to five mode shapes have been utilized to capture the response of system and results are validated by comparing with Molecular Dynamics (MD) simulation. Due to their high stiffness, CNTs cannot be actuated to pull-in (switch ON) state by conventional mechanical shocks in range of 10–1000 g under one-step voltage. Here, a multi-steps voltage modification is applied to enhance the actuation. Employing this method, a nano-switch with fixed geometry can be adjusted to be triggered by wide rang of mechanical shocks (10–1000 g).     

Boundary Homogenization of an Inverse Non-local Elliptic Boundary-Value Problem

In this paper, a mathematical analysis is given of an inversenon–local elliptic boundary–value problem for conductivityprospecting with a patched–electrode well-log instrument.As the electrode cells of the patched electrode system becomesmaller and smaller, the microscopic structure of the electrodesystem becomes increasingly complicated and themathematicalanalysis becomes much more difficult. Nevertheless, it is shownthat the electrode system can be homogenized macroscopically;that is, the solution of the inverse problem for the patchedelectrode system converges to the solution of the correspondinginverse problem for the original electrode system.     

The impact of multi-layered porosity distribution on the performance of a lithium ion battery

This study investigates the impact of a multi-layered porosity profile on the electrical and thermal performance of a lithium-ion battery. Consideration is given to key attributes of the battery, namely its specific power and energy and the temperature distribution that may generated throughout the cell under electrical load. The COMSOl Multiphysics software tool has been employed to develop a 3D electrochemical–thermal model of a commercially available 10 Ah lithium iron phosphate cell. Through an extensive simulation study, for a fixed value of active material, the impact of varying the porosity profile across both the thickness and height of the electrode has been studied. For each case study, the distribution of reaction current and the corresponding localised state of charge and temperature profile are quantified for a constant current discharge of 5C. Simulation results highlight that a multi-layered porosity distribution across the thickness of the electrode has the potential to yield superior battery performance compared to when the porosity is varied along the electrode height. Moreover, the total heat generation within the cathode may be reduced by up to 14% compared to a Reference Case, along with 0.33% and 0.44% improvement in the specific energy and power, respectively.     

The solution of unsteady coupled electromechanical problems for multilayered media

A rigorous formulation of the unsteady coupled electromechanical problem of the interaction of a massive electrode with a multilayered piezoelectric medium is given, and a general formulation of a method of solving it is proposed. As an example the problem for a massive strip electrode, which interacts with a single-layer, double-layer and triple-layer piezoelectric medium with unsteady loading is considered. The effect of the electroelastic properties of different materials (classes 6 mm of the hexagonal system) on the displacement of the electrode and the potential is pointed out.     

Polarography of potassium ethylxanthate,a titrant in amperometry

Polarograpbic studies of potassium ethylxanthate (RSH or xantbate) at the dropping mercury electrode (DME) reveal that the product of the anodic reaction is strongly adsorbed at the mercury drop as indicated by a prewave. The adsorbed film (0·15 mM to 1·0 mM xanthate solution) greatly affects the characteristics of the anodic wave of xanthate in aqueous medium. The current of main wave is proportional to the concentration of xanthate up to 2·5 mM in aqueous medium at DME. This electrode is used as an indicator electrode for amperometric titrations of metal ions with xanthate. Proper buffer composition and pH are developed for the accurate determination of metal ions. The combined use of the cathodic current of metal ions and the anodic current of xanthate under controlled pH conditions makes possible the amperometric titration of two metal ions in a mixture.     

Second-order kinetics for EC' reactions at a spherical microelectrode

A second-order (nonlinear) model is derived for steady-statekinetics of an EC' (catalytic electrochemical) reaction at aspherical microelectrode in the case where the electron transferprocess is followed by a homogeneous chemical reaction regeneratingthe electroactive species. An asymptotic analysis of the modelis performed, and the asymptotic results are compared with thosefrom a numerical solution of the full nonlinear model. It isshown that in the fast reaction limit, where the current atthe electrode takes its maximum possible value, the concentrationsof the reactants are controlled by diffusion both close to andfar from the electrode, with significant chemical activity occurringonly in a narrow zone standing off the electrode. Also, it isshown that an equation obtained from a different asymptoticlimit may be used to predict the limiting current at the microelectrodein all circumstances. The reasons for the surprising measureof agreement at the surface of the electrode are discussed,the predictions from the model of the limiting current are compared(favourably) with experimental results, and the model is comparedwith the standard pseudo-first-order model, which, althoughalso based on a linearization of the governing equations, hasa restricted range of validity.     

A new approach to the characterization of the nano-surface structure by using factor analysis

The study provides a new approach to explore the existence of a nanostructure on the benzoic acid-modified glassy carbon electrode (BA-GC) system by applying factor analysis with varimax rotation of factors. The infrared spectra (IR) spectra of the bare glassy carbon electrodes (GC) and the BA-GC electrode systems with benzoic acid-nanofilm (BA-FILM) were obtained by using 10 different surface modification experiments. The IR data of the bare GC, BA-GC and BA-FILM were categorized into three series corresponding to the GC, BA-GC and BA-FILM. The factor analysis method was separately applied to each group to extract the factor loadings. By making use of these loadings, the rotated factor loadings corresponding to the first two factors were computed to estimate the relationship among and within groups. The results provided by the factor analysis method indicate the existence of the BA-FILM on the BA modified glassy carbon electrode.