Determination des parametres cinetiques de l'electrodeposition du cuivre a haute densite de courant. Cas des solutions sulfuriques sans inhibiteur

Copper can be deposited at very high current density with an electrolyte flowing at high speed parallel to the electrodes. The cathodic diffusion limiting current density reaches 300 A dm^?2 at a flow speed of 2 ms^?1. The determination of the values of the kinetic constants which characterize copper deposit at high current density requires an adjustment of the electrochemical measuring methods. Copper reduction mechanisms at high current density are different depending on the main type of nucleation, two- or three-dimensional.     

High-rate electrochemical dissolution of Ni–Cu alloys in nitrate electrolyte

High-rate anodic dissolution of nickel, copper, and two alloys Ni30Cu70 and Ni65Cu32 in NaNO₃ solution was studied, using a flow-channel electrochemical cell. In all experiments, the initial interelectrode distance was 208 m and the electrolyte velocity was 15 m s^–1. The dependence of the current efficiency and surface brightening on the current density was determined. Voltage transients at various current densities were measured and voltammograms were constructed. Compared to nickel and copper, the alloys showed intermediate behaviour, especially at j > j ₁. The shape of the voltage transients and the occurrence of surface brightening were more suitable to detect the existence of a limiting current region than voltammograms, especially for Ni. Using the voltammograms and literature data, anodic and cathodic potentials and the voltage drop in the interelectrode gap at a given current density were estimated for j < j ₁.     

A computer simulation of continuous ion exchange membrane electrodialysis for desalination of saline water

A computer simulation program including the principle of ① mass transport, ② current density distribution, ③ energy consumption and ④ limiting current density is developed for predicting desalinating performance of a continuous (one-pass flow) electrodialysis process. In this simulation the following parameters are inputted; ① membrane characteristics such as overall transport number, overall solute permeability, overall electro-osmotic permeability, overall hydraulic permeability, direct current electric resistance etc. ② electrodialyzer specifications such as flow-pass thickness, flow-pass width and flow-pass length of a desalting cell etc. and ③ electrodialytic conditions such as current density, electrolyte concentration in a feeding solution, linear velocity in desalting cells, standard deviation of normal distribution of solution velocity ratio etc.In a practical-scale electrodialyzer, electrolyte concentration in a desalting cell is decreased along a flow-pass and it gives rise to electrolyte concentration distribution. It causes electric resistance distribution and current density distribution. Solution velocities in desalting cells vary between the cells, and give rise to solution velocity distribution. In this simulation, these distributions are taken into account assuming that the frequency distribution of solution velocity ratio is equated by the normal distribution. Further, the influences of electrodialyzer specifications and elctrodialysis conditions described above on the performances of an electrodialyzer (desalting ratio, current efficiency, electrolyte concentration at the outlets of desalting cells, cell voltage, energy consumption, electrolyte concentration distribution, current density distribution, and limiting current density) are predicted. The simulation model is developed on the basis of the experiments and its reasonability is supported by the performance of electrodialyzers operating in salt-manufacturing plants.     

Studies of three-dimensional electrodes in the FMO1-LC laboratory electrolyser

A FMO1-LC parallel plate, laboratory electrochemical reactor has been modified by the incorporation of stationary, flow-by, three-dimensional electrodes which fill an electrolyte compartment. The performance of several electrode configurations including stacked nets, stacked expanded metal grids and a metal foam (all nickel) is compared by (i) determining the limiting currents for a mass transport controlled reaction, the reduction of ferricyanide in 1 m KOH and (ii) measuring the limiting currents for a kinetically controlled reaction, the oxidation of alcohols in aqueous base. It is shown that the combination of the data may be used to estimate the mass transfer coefficient, _L, and the specific electrode area, A _e, separately. It is also confirmed that the use of three dimensional electrodes leads to an increase in cell current by a factor up to one hundred. Finally, it is also shown that the FM01-LC reactor fitted with a nickel foam anode allows a convenient laboratory conversion of alcohols to carboxylic acids; these reactions are of synthetic interest but their application has previously been restricted by the low rate of conversion at planar nickel anodes.Nomenclature A _e electrode area per unit electrode volume (m²m^–3) - c bulk concentration of reactant (mol m^–3) - E electrode potential vs SCE (V) - E _1/2 half wave potential (V) - F Faraday constant (96 485 C mol^–1) - I current (A) - IL limiting current (A) - j _L limiting current density (A m^–2) - _L mass transfer coefficient (m s^–1) - n number of electrons transferred - p empirical constant in Equation 2 - P pressure drop over reactor (Pa) - R resistance between the tip of the Luggin capillary and the electrode surface () - q velocity exponent in Equation 2 - (interstitial) linear flow rate of electrolyte (ms^–1) - V _e volume of electrode (m³)     

A computer simulation of batch ion exchange membrane electrodialysis for desalination of saline water

A computer simulation program is developed for predicting desalinating performance of a batch electrodialysis process. The program includes the principle of ① mass transport, ② current density distribution, ③ cell voltage, ④ mass balance/energy consumption and ⑤ limiting current density. In this simulation the following parameters are inputted; ① membrane characteristics such as overall transport number, overall solute permeability, overall electro-osmotic permeability, overall hydraulic permeability, direct current electric resistance etc., ② electrodialyzer specifications such as flow-pass thickness, flow-pass width and flow-pass length in a desalting cell etc. and ③ electrodialytic conditions such as voltage, electrolyte concentration in a feeding solution, linear velocity in desalting cells, standard deviation of normal distribution of solution velocity ratio etc.The following phenomena were computed and discussed; ① Changes of electrolyte concentration and current density with operation time. ② Influence of cell voltage on operation time (batch duration), water recovery and energy consumption. ③ Influence of volume of an electrolyte solution prepared at first on operation time. ④ Influence of cell voltage, electrolyte concentration and standard deviation of solution velocity ratio in desalting cells on limiting current density. ⑤ Energy consumption in a reverse osmosis process. ⑥ Excepting limiting current density, the performance of an electrodialyzer is never influenced by the standard deviation of normal distribution of solution velocity ratio in desalting cells. ⑦ Energy consumption in electrodialysis is less than that in reverse osmosis at feeding saline water concentration less than about 2000 mg/l.     

Material characterisation of electroplated nickel structures for microsystem technology

Nickel layers 15 μm thick were pulse plated from a commercially available sulphamate-based electrolyte on an evaporated gold substrate or an electroplated copper substrate. The gold layer showed a (111) crystalline preference orientation, whereas for the copper layer no texture was observed. The deposited nickel layer showed a (110) texture at a low mean current density of 2.5 mA/cm², whereas at a high mean current density of 20 mA/cm² a (100) texture was observed. The structure analysis was supported by SEM pictures of polished and etched cross sections. For the nickel layers deposited on the gold substrate the structure changed from a columnar structure at low mean current densities to a granular structure at high mean current densities, whereas for the layers deposited on copper a granular structure was observed even at low mean current densities.     

An electrochemical study of mass transfer in free convection at vertical arrays of horizontal cylinders

Rates of mass transfer between an electrolyte and vertical arrays of horizontal cylinders have been measured using the limiting current electrolytic technique. The system used was the deposition of copper at the test cathode cylinders from an acidified cupric sulphate solution. Various combinations of solution concentration, cylinder diameter, number of cylinders and cylinder spacing have been used, including experiments on single cylinders. Results for single cylinders have been correlated by the equation. Sh₀ = 0.56 (Sc Gr_m'd)^0.25 which agrees well with previous work on both heat and mass transfer. In arrays of cylinders the mass transfer rate, normalized with respect to a single cylinder, either decreased or increased with array position, depending on the particular combination of experimental variables. This behaviour has been explained in terms of the opposing effects of the interacting concentration and velocity fields between cylinders. The findings lend support to the suggestion of Marsters [1] that a position-based Grashof number in the range 10⁶ to 10⁷ determines the transition between a decrease and an increase in mass transfer up an array. The results are relevant to the modelling of tubular heat exchangers in free convection dominating conditions, and also illustrate the important effect of boundary layer carry-over in determining current distribution in multi-electrode electrochemical cells.     

Pressure dependence of limiting current density of sparking during electrochemical drilling

The cathodic current density used in electrochemical drilling can be increased only up to a certain value, above which current oscillations, sparking and acoustic phenomena appear, whereby the cathode can be damaged. The limiting current density for sparking, j _s, depends on the rate of flow and properties of the electrolyte and on the hydrostatic pressure. Values of j _s were measured for metal capillaries provided with external insulation in the turbulent flow regime in the range of Reynolds numbers from 2 300 up to 30 000 and at hydrostatic pressures ranging from 0.12 to 1.1 MPa. A simple heat generation model is proposed and the limiting current densities for sparking (868 experiments) are correlated with a criterion equation enabling the calculation of j _s.List of symbols c _pE specific heat of electrolyte (J kg^–1 K^–1) - d ₁ inner diameter of the cathode (m) - d ₂ outer diameter of the cathode (m) - I current (A) - I _s limiting current for sparking (A) - j current density (Am^–2) - j _s limiting current density for sparking (Am^–2) KT constant - K _T constant - L characteristic length (m) - N _u Nusselt number - p pressure (Pa) - p ₀ reference atmospheric pressure (Pa) - P exponent - P _r Prandtl number - q exponent - q heat flux (W m^–2) - R exponent - Re Reynolds number - _E linear electrolyte velocity (m s^–1) Greek symbols - heat transfer coefficient (W m^–2 K^–1) - temperature difference (K) - _E electrolyte conductivity (^–1 m^–1) - _E electrolyte thermal conductivity (Wm^–1 K^–1) - µ_E electrolyte viscosity (kgm^–1 s^–1) - _E electrolyte density (kg m^–3)     

A feasibility study of mercury deposition in a lead fluidized bed electrode

Following previous work on the recovery of copper from very dilute solutions using a copper fluidized bed electrode, the behaviour of a lead fluidized bed electrode (FBE) is described, for the recovery of mercury from chloride solutions, as typified by chlor-alkali plant effluent.Injection of known quantities of Hg(II) into the FBE catholyte and integration of the current vs time response followed by chemical analysis, allowed mean current efficiencies for mercury deposition to be determined as a function of:feeder electrode potential, Hg(II) concentration, flow rate, bed depth, particle size range, and reservoir volume. By judicious choice of these experimental variables, particularly by limiting bed depths to 20 mm, (potentiostatic) current efficiencies for Hg(II) deposition of 99% could be achieved.Nomenclature a cross sectional area of FBE cell (1.26×10^–3 m²) - A area per unit volume of FBE electrode (m^–1) - c(x) concentration at distancex from feeder electrode (mol m^–3) - c ₀ inlet concentration (mol m^–3) - c _XL outlet concentration (mol m^–3) - D diffusion coefficient (m²s^–1) - I current density (A m^–2) - L static bed length (mm) - t time (s) - T catholyte temperature (K) - u electrolyte superficial linear velocity (mm s^–1) - V electrolyte volume (m³) - XL expanded bed length (mm) - diffusion layer thickness (m) - characteristic length (u/DA) (m) - (lead) density (11.4×10⁶ g m^–3)     

Prediction of mass transport profiles in a laboratory filter-press electrolyser by computational fluid dynamics modelling

A commercial computational fluid dynamics code (Fluent) has been used to analyze the performance of a unit cell laboratory; the filter-press reactor (FM01-LC) operating with characteristic linear flow velocities between 0.024 m s⁻¹ and 0.110 m s⁻¹. The electrolyte flow through the reactor channel was numerically simulated using a finite volume approach to the solution of the Navier-Stokes equations. The flow patterns in the reactor were obtained and the mean linear electrolyte velocity was evaluated and substituted into a general mass transport correlation to calculate the mass transport coefficients. In the region of 150 < Re < 550, mass transport coefficients were obtained with a relative error between 5% and 29% respect to the experimental k_m values. The differences between theoretical and experimental values are discussed.     

Mass transport to reticulated vitreous carbon rotating cylinder electrodes

Mass transport to rotating cylinder electrodes (radius 0.5 cm and height 1.2 cm) fabricated from reticulated vitreous carbon (RVCRCE) was investigated using linear sweep voltammetry in a 0.5 m Na₂SO₄ + 1 mm CUSO₄ electrolyte at pH 2. At a fixed cupric ion concentration the limiting current was found to be dependent upon velocity to the power 0.55 to 0.71 depending upon the porosity grade of the carbon foam. The product of mass transport coefficient and specific electrode area, km A _e, was found to be approximately 0.51 s^–1 at 157 rad s^–1 (corresponding to 1500 rpm) for the 100 ppi material. The experimental data are compared to the predicted performance of a hydrodynamically smooth rotating disc electrode (RDE) and rotating cylinder electrode (RCS).Nomenclature A electrode area (cm²) - A _e active electrode area per unit volume (cm^–1) - C _B bulk copper concentration (mol cm^–3) - c ₀ concentration at t = 0 (mol cm^–3) - c _t concentration at time t (mol cm^–3) - D diffusion coefficient (cm²s^–1) - F Faraday constant (96 485 A s mol^–1) - h height of rotating cylinder electrode (cm) - I _L limiting current (A) - I _L,RDE limiting current at an RDE (A) - I _L,RCE limiting current at an RCE (A) - I _L,RVC limiting current at a rotating RVCRCE (A) - km mass transport coefficient (cm s^–1) - r radius of RCE (cm) - U electrolyte velocity (cm s^–1) - V reactor volume (cm ³) - V _e overall volume of electrode (cm ³) - x characteristic length (cm) - z number of electrons Greek symbols ratio of limiting current at an RVCRCE relative to an RDE of same diameter - ratio of limiting current at an RVCRCE relative to an RCE of same overall volume - thickness of the diffusion layer (cm) - electrolyte viscosity (cm²s^–1) - rotation speed (rads^–1 Dimensionless groups Re = U _/ Reynolds number - Sc = /D Schmidt number - Sh = k _m/D Sherwood number     

Geschwindigkeitsverteilung und Gasdruckschwankungen in querdurchströmten Behältern

In the process engineering industry tanks with large volumes from 250 to 1000 m³ are often required, which are flowed through by large gas volume flows up to 150 000 m³h^–1. The flow leads to a mean flow velocity from 0.347 – 1.0 m s^–1. The inflow and outflow of the gas have to be done by one or two inlet and outlet pipes with diameter sizes of 1.20 to 2.0 m. Nevertheless, with respect to the chemical or catalytic reaction, a constant flow velocity is required in the tank. This paper shows how gas distribution plates for crosswise flow tanks or catalysts with a differential cross section distribution can be calculated and designed for the flow‐through area, which nearly ensure a constant flow velocity without an increase of the flow resistance.     

Electrodeposition from a fluidized bed electrolyte. III. Electrodeposit structure

Copper electrodeposits grown from a fluidized bed electrolyte appear to be unaffected by mechanical action of the inert particles. Additions of thiourea to the electrolyte caused some improvement in levelling at lower current densities but, at the limiting value, additions of up to 10^?2 M gave no improvement. Micrographic evidence is presented to suggest that a simultaneous dissolution process may account for the transition from nodular to powder growths at the limiting current density.     

Conductive‐diamond electrochemical advanced oxidation of naproxen in aqueous solution: optimizing the process

BACKGROUND: Electrochemical advanced oxidation treatment using boron‐doped diamond (BDD) electrodes is a promising technology to treat small amounts of toxic and biorefractory pollutants in water. This process has been tested on the degradation of naproxen, a common pollutant drug present in surface waters. To optimize the process a series of experiments have been designed to study the interaction between four variables: pH (over the range 5–11); current (0–320 mA cm^?2); supporting Na₂SO₄ electrolyte concentration (0–0.375 mol L^?1); and solution flow rate (Q_v) between 3.64 and 10.8 cm³ min^?1. RESULTS: Among these variables the influence of current was the greatest, the second was the salt concentration, the third flow rate, and the fourth pH. An ANOVA test reported significance for seven of the fourteen variables involved and the degradation of naproxen was optimized using response surface methodology. CONCLUSIONS: Optimum conditions for naproxen removal (100%) were found to be pH = 10.70, Q_v = 4.10 cm³ min^?1, current density = 194 mA cm^?2 using a supporting electrolyte concentration of 0.392 mol L^?1. Copyright © 2010 Society of Chemical Industry     

Mass transfer enhancement by the counter-electrode gases in a new cell design involving a three-dimensional gauze electrode

Limiting currents and mass transfer coefficients were measured for the electrodeposition of copper from an acidified solution of copper sulphate at an array of closely packed screens stirred by oxygen. The oxygen evolved at a horizontal lead anode placed below the screen array. Variables studied were: oxygen discharge rate, electrolyte concentration and number of screens per array. For a single-screen electrode, oxygen discharge was found to increase the mass transfer coefficient according to the equation logK =a + 0.377 logV. The mass transfer coefficient was found to decrease slightly with increasing number of screens per array, the decrease becoming pronounced when the number of screens per array reached six. A new cell design involving an array of closely packed screens as a working electrode stirred by the counter-electrode gases is described and its merits and disadvantages are pointed out.List of symbols a constant - I limiting current (A) - Z number of electrons involved in the reaction - F the Faraday (96 500 C) - K mass transfer coefficient (cm s^–1) - C concentration of copper sulphate (mol l^–1) - V oxygen discharge rate (cm³cm^–2s^–1)     

Optimizing swirl in compact uniflow cyclones

This paper presents an experimental examination of the velocity field distribution in the separation chamber of a uniflow cyclone with closed particle outlet to evaluate the swirl characteristics in the vortex finder region based on stereoscopic particle image velocimetry. A cold flow model with a closed particle outlet was used to assess different angles of attack and core size ratios at typical Reynolds numbers for the separation of low loaded gas-solid flows. The focus of the study was on the relationship between swirl strength as well as performance data. At higher angles, the parabolic swirl strength distribution changed to a region with constant high acceleration of the particles in the separation zone. Integral and differential swirl numbers were correlated with the ratio of tangential to radial velocity and to the calculated cut size diameter. At low angles of attack, implying a strong redirection of flow perpendicular toward the main flow direction and small core size ratios, defined by the radial distance between hub and tip, the local differential swirl number can be more than twice as large as in the base configuration. Yet, the integral swirl number hardly changed. The velocity fields showed mean tangential to radial velocity ratios ranging from 0.73 to 6.85 at swirl vane angles of 15 ^° –60 ^° ; core size ratios between 0.125 and 0.625 at vortex finder diameter were measured and calculated cut size diameters between 10 and 90 μm were derived. This data provides the foundation for further validation studies and the development of new design criteria. © 2018 American Institute of Chemical Engineers AIChE J, 65: 766–776, 2019     

Modeling and Parametric Study of a Single Solid Oxide Fuel Cell by Finite Element Method

A 2D isothermal axisymmetric model of an anode‐supported solid oxide fuel cell has been developed. The model, which is based on finite element approach, comprises electronic and ionic charge balance, Butler–Volmer charge transfer kinetic, flow distribution and gas phase mass balance in both channels and porous electrodes. The model has been validated using available experimental data coming from a single anode‐supported cell comprising Ni–YSZ/YSZ/LSM–YSZ as anode, electrolyte and cathode, respectively. Hydrogen and steam were used as fuel inlet and air as an oxidant. The validation has been carried out at 1 atm, 1,500 ml min^–1 air flow rate and three different operating conditions of temperature and fuel flow rate: 1,073 K and 400 ml min^–1, 1,073 K and 500 ml min^–1, and 1,003 K and 400 ml min^–1. The polarization and power density versus current density curves show a good agreement with the experimental data. A parametric analysis has been carried out to highlight which parameters have main effect on the overall cell performance as measured by polarization curve, especially focusing on the influence of two geometrical characteristics, temperature and some effective material properties.     

Electrochemical Removal of Copper Ions from Aqueous Solutions Using a Modulated Current Method

The use of porous electrodes to remove toxic metals from industrial effluents has been recognized over the years due to its high mass transfer rates resulting in high current efficiencies (CE) and low energy consumption (EC), even at very low metal concentrations. This work addresses the effects of flow velocity and electric current on current efficiency and energy consumption of copper electrodeposition using reticulated vitreous carbon, aiming to optimize the CE and EC by using a modulated current method. First, it was found that a flow velocity of 0.246 m s^?1 maximizes the mass transfer coefficient (k_m). Applying this flow velocity and a modulated current, the electrodeposition process was investigated and compared with that carried out under galvanostatic mode. The results showed that using a current control there is a reduction of average EC due to the improvement of the average CE, but the operational time also increases when compared to that obtained using the galvanostatic mode.     

Ionic mass transfer rate of CuSO4 in electrodialysis

Ionic mass transfer rate of copper ion in the ion exchange membrane electrodialysis at limiting current density has been studied using a planar flow electrodialyzer consisted of a cation exchange membrane and an anion exchange membrane. Their effective area is 4 × 5 cm². The effects of flow rate, viscosity of electrodialysate solution and thickness of electrodialyzer to the ionic mass transfer rate have been studied. An empirical correlation equation (Nu)_exp. = 4.57 × Re^0.333 Sc^0.307 (de/L)^O.33 is obtained. It fitted well with the theoretical performance equation (NU)_theor.= 3.70 × (Re · Sc · de/L), which is derived from the Nernst-Planck Equation based on the assumption that mass transfer in the concentration boundary layer in the desalting compartment is controlling.     

The vertical distribution of current in a gas-evolving membrane cell

A one-dimensional numerical model to describe gas void fraction and current distribution in five model membrane cell configurations is described in this work. The five models describe ideal (equipotential), upright (top cathode/bottom anode), inverted, u- and n-type electrical connections with anodic chlorine and cathodic hydrogen evolution in each case. In all but the first case the finite resistances of the electrodes are taken into account. The effects of (a) different terminal arrangements, (b) different current densities, (c) different cell heights, (d) different compartment widths, and (e) different overvoltages, have been investigated. For each study the current distribution and anolyte and catholyte void fraction distribution is displayed. The resistive components of the cell voltages are also calculated; the calculated resistive voltage loss varies between extremes of 0.291 V for the ideal cell to 0.377 V for the inverted cell at 3 kA m^–2 and 0.25 m cell height with typical fixed values of other parameters.Nomenclature A cross-sectional area - d bubble diameter - void fraction - _m maximum void fraction - G gas volumetric flow rate - K ratio of conductivities of bubble-free and bubble-filled electrolyte - L liquid volumetric flow rate - electrolyte viscosity - R _AN,R _A resistances of anode, anolyte, membrane - R _M,R _C cathode and catholyte, respectively (see - R _CA resistive network scheme of Fig. 2) - _L, _G liquid and gas phase densities - u ₁ single bubble rise velocity - u _sw bubble swarm rise velocity Paper presented at the 2nd International Symposium on Electrolytic Bubbles organized jointly by the Electrochemical Technology Group of the Society of Chemical Industry and the Electrochemistry Group of the Royal Society of Chemistry and held at Imperial College, London, 31st May and 1st June 1988.