Application of porous flow through electrodes: IV. Hydrogen evolution on packed bed electrodes of iron spheres in flowing alkaline solutions

Packed bed electrodes of small iron spheres have been used for the electrolytic production of hydrogen from alkaline solutions at different temperatures under conditions of electrolyte flow. The effects of temperature, electrolyte type, concentration and flow rate on the polarization behavior of the electrode were evaluated and analyzed. It was shown that increases in the conductivity of the electrolyte or the operating temperature decreases the potential required to support the reaction. The generated gas bubbles disperse in the pore electrolyte, resulting in an increase in its resistivity and, subsequently, an increase in the potential. It was shown that some gas bubbles are trapped within the porous electrode. The implications of the trapped gas bubbles on the behaviour of the electrode are discussed.Nomenclature A geometrical cross-sectional area (cm²) - a empirical constant (cm³ C^–1) - b RT/F in volt, withR the gas constant,T the absolute temperature - E ₀ electrode potential at the entry face (V) - E _L electrode potential at the exit face (V) - F Faradays's constant - i ₀ exchange current density of the electrode reaction (A cm^–2) - i _L experimentally measured current density at the exist face (A cm^–2) - L bed thickness (cm) - q tortuosity - Q electrolyte volume flow rate (cm³ s^–1) - V electrolyte flow rate,V=Q/A (cm s^–1) - S specific surface area of the bed (cm^–1) - x position in the electrode - transfer coefficient - gas void fraction - ₀ polarization at the entry face (V) - _L polarization at the exit face (V) - porosity - pore electrolyte resistivity ( cm) - ₀ resistivity of the bubble-free pore electrolyte ( cm) - ₀ ^b resistivity of the bulk electrolyte ( cm)     

Effect of grain size on tribological behavior of hot-pressed boron carbide sliding against alumina balls

Boron carbide ceramics (B₄C) have extraordinary hardness and well-abrasive resistance, while the tribological behavior of ceramic materials is complicated, which are affected by microstructures, mechanical properties, and surface characteristics, and so on. In this paper, the effect of grain size on the mechanical properties especially the wear resistance of hot-pressed B₄C was investigated. The average coefficient of friction of the B₄C/Al₂O₃ friction pair ranges from .41 to .66. The sample with the minimum grain size possesses the lowest wear rate of about 2.15 × 10⁻⁶–7.66 × 10⁻⁶ mm³∙N⁻¹∙m⁻¹. The analysis of the wear rate (W_R) and grain size (G) indicates that the wear resistance (W_R⁻¹) and the reciprocal of the square root of grain size (G^−1/2) are in line with the Hall–Petch relation. Fracture and the resulting abrasive wear are the main wear mechanisms of B₄C in the dry sliding process. This success provides a theoretical basis and a design approach of microstructure to improve the tribological behavior of ceramic materials.     

The transient behaviour of a class of semicontinuous tank electrolysers

The transient behaviour and figures of merit of an isothermal electrolyser consisting of a perfectly mixed-flow compartment and a batch compartment separated by an ion-selective membrane are analysed by means of its governing balance equations solved on a microcomputer.Nomenclature c acid concentration - E conversion of the oxidized to the reduced species at the cathode - F Faraday's constant (96487 C mol^–1) - i current density - K cost of operation - k ₁,k ₂ cost coefficients (specific costs) - Q _s charge density; its sample regression - S _O initial slope of the conversion-time curve (Fig. 3) - t time - t _H transport (transference) number of hydronium ions - V magnitude of the imposed voltage - x ₁ ⁰ magnitude of the inlet concentration of the oxidized species - w acid concentration in the anolyte - lumped parameter, defined as 1+^k m ^A/Q _c - sample linear regression parameters (Table 5) - fractional concentration of the oxidized species defined as (concentration — surface concentration)/concentration - _c mean residence time defined asV _c /Q _c Special symbols MU arbitrary monetary unit - * steady-state The majority of symbols is defined in Table 1.     

Sliding wear of CaZrO3-MgO composites against ZrO2 and steel

The wear behaviour of a fine grained and dense CaZrO₃-MgO composite is presented. Un-lubricated Pin-on-disc tests at room temperature have been performed using 10 N as normal force and 0.10–0.15 ms^-1 as sliding rate and ZrO₂ and steel counterparts. The coefficient of friction versus the sliding distance and the specific wear, together with a complete microstructural analysis of the worn surfaces by field emission scanning electron microscopy is reported. The composite presents a wear resistance similar to other ceramics under ceramic/ceramic sliding contact and improved wear resistance in contact with steel.Initial wear is dominated by abrasion independently of the chemical nature of the counterpart. The second stage wear depends on the characteristics of the third body formed. Zirconia leads to a brittle particulate third body with little protective capability. Steel forms a strongly bonded and plastic cermet third body that protects the material limiting the level of further wear.     

Use of multiple regression analysis to develop equations for predicting Li-Al/iron sulphide cell performance

A multiple regression analysis was conducted to develop predictive equations for the specific energy and specific power of Li-Al/iron sulphide cells over a wide range of cell designs and operating variables. The intent was to make these equations as general as possible such that one set of equations would predict the performance of Li-Al/FeS or Li-Al/FeS₂ cells with bicell (one positive electrode and two facing negative electrodes) or multiplate cell configurations. Data from 33 cells were used in the analysis of specific energy, and 26 cells were used to develop the specific power equation. The calculated specific energy and specific power showed good agreement with the measured values for these cells. In general, the deviation between the calculated and measured values was within ±10%. A check of the predictive capability of these equations also showed good agreement. The specific energy and specific power calculated for 14 cells not used in the regression analysis deviated by ±10% from the measured values. These equations were used to identify the most likely cell designs to meet selected electric-vehicle battery performance goals. These designs were included in an experimental programme for further performance evaluation.Nomenclature A _e limiting electrode area (cm²) - AHREFF coulombic efficiency (%) - b _i constants in multiple regression equation - CCO cell charge cut-off voltage (V) - CF charge factor (1.0 for fully charged cell, 0.5 for cell 50% discharged, 0.05 for cell discharged to a cut-off of 0.9–l.0 V) - DCO cell discharge cut-off voltage (V) - FCCF fully charged correction factor (1.0 for fully charged cell, 0.05 for any state of discharge) - FSLMUL product of FSUBL and MUL (defined below) - FSUBL calculated utilization factor of the limiting electrode (%) - i _c charge current density (A cm^–2) - i _D discharge current density (A cm^–2) - MUL theoretical specific energy factor (W h kg^–1) - NSPTHC negative-to-positive capacity ratio - OCV cell open-circuit voltage (V) - OFFEUT factor related to LiCl composition in electrolyte (%) - PF power factor (W kg^–1) - POSPIN reciprocal of the number of positive electrode plates - PPXCYC product of the number of positive electrode plates in the cell and the number of deep discharge cycles - R ² correlation coefficient - ¯R _c average cell resistance () - SP calculated cell specific power (W kg^–1) - SPECYC calculated cell specific energy (W h kg^–1) - SPEBAS calculated cell specific energy early in life (W h kg^–1) - TEMPR temperature ratio - TSUBCR thickness ratio of counter electrode and electrode separator - VFSNEG volume fraction salt in the negative electrode - VFSPOS volume fraction salt in the positive electrode - VOLT1R discharge voltage factor - VOLT2R charge voltage factor - W cell weight (kg) - X _i independent variables in regression equation - dependent variable in regression equation     

Electroantennographic and coupled gas chromatographic-electroantennographic responses of the mediterranean fruit fly,Ceratitis capitata,to male-produced volatiles and mango odor

We have identified five compounds from the headspace of calling male Mediterranean fruit flies (medfly),Ceratitis capitata (Wiedemann), and three compounds from the headspace of ripe mango (Mangifera indica L). using coupled gas chromatographic-electroantennographic (GC-EAG) recordings, coupled gas chromatographic-mass spectrometric (GC-MS) analysis, and electroantennographic (EAG) assays of standards. The male-produced volatiles eliciting responses from female antennae were ethyl-(E)-3-octenoate, geranyl acetate, (E,E)--farnesene, linalool, and indole. An EAG dose-response test of linalool enantiomers and indole with female medfly antennae showed relatively strong EAG activities, but no significant difference between (R)-(-)-linalool and (S)-(+)-linalool. The three mango volatiles were identified as (1S)-(-)--pinene, ethyl octanoate, and-caryophyllene. In addition, a strong antennal response was recorded from a contaminant,-copaene, present in a commercial sample of-caryophyllene. The EAG response amplitudes from both male and female antennae to the above three mango volatiles were significantly greater than to a hexanol control. For both male and female medfly antennae, the greatest EAG responses were elicited by-caryophyllene followed by ethyl octanoate. The mean EAG responses of female antennae to-caryophyllene and (1S)-(-)--pinene were significantly greater than those of male antennae.     

Mass transfer to percolated porous materials in a small-scale cell operating by self-pumping

The paper deals with an experimental electrochemical study of mass transfer to porous nickel materials (felt, foams) in a small-scale laboratory cell functioning in a self-pumping mode. The liquid flow through a disc of the porous material is induced by the rotation of a solid circular disc. The cell is simple and is useful for laboratory studies of materials for porous electrodes and also for small-scale synthesis using such materials. The work examines separately the mass transfer to the rotating disc and to the porous disc. Empirical correlations of the experimental data are given.Nomenclature a _e specific surface area (per unit of total volume of electrode) (m^–1) - C ₀ entering concentration of ferricyanide ions (mol m^–3) - D molecular diffusion coefficient of ferricyanide (m² s^–1) - e thickness of the sheet of material (m) - F Faraday number (C mol^–1) - g acceleration due to gravity (m s^–2) - h distance between the discs (m) - I _L limiting current (A) - 736-1 mean mass transfer coefficient (m s^–1) - N roating velocity (rev min^–1) - Q _v volumetric electrolyte flow rate (m³ s^–1) - R radius of the solid disc (m) - R _c inner radius of the cell (m) - R _i radius of the porous disc (m) - Re _h Reynolds number based onh (=h²/) - Re _R Reynolds number based onR (=R²/) - S _c Schmidt number - Sh _h Sherwood number based onh (=k _d h/D) - Sh _r Sherwood number based onR (=k _d R/D) - mean electrolyte velocity (m s^–1) - V electrode volume (m³) - X conversion - electrolyte density (kg m^–3) - _e number of electrons in the electrochemical reaction - kinematic viscosity (m² s^–1) - angular velocity (s^–1) - ₀ minimum angular velocity (s^–1)     

Computer simulation of high-discharge-rate battery systems

Simulations were carried out for a proposed two-dimensional high-discharge-rate cell under load with an interelectrode gap of the order of 100 m. A finite difference program was written to solve the set of coupled, partial differential equations governing the behaviour of this system. Cell dimensions, cell loads, and kinetic parameters were varied to study the effects on voltage, current and specific energy. Trends in cell performance are noted, and suggestions are made for development of cells to meet specific design criteria. Modelling difficulties are discussed and suggestions are made for improvement.Nomenclature A surface area of unit cell (cm²) - A _k conductivity parameter (cm^{2 –1} mol^–1) - b Tafel slope (V) - c concentration (mol cm^–3) - c ₀ concentration of bulk electrolyte (mol cm^–3) - D diffusivity (cm² s^–1) - D _h lumped diffusion parameter (J s cm^–2 mol^–1) - D _s lumped diffusion coefficient (A cm² mol^–1) - E rest potential of electrode (V) - F Faraday constant (96 500 C mol^–1) - i current density (A cm^–2) - I total current for unit cell (A) - i ₀ exchange current density (A cm^–2) - N flux of charged species (mol cm² s^–1) - R gas constant (8.314 J mol^–1 K^–1) - R _ext resistance external to cell () - t time (s) - T temperature (K) - t ₀ transference number - u mobility (cm² mol J^–1 s^–1) - V volume of an element in the cell (cm³) - V _ext voltage external to cell (V) - z charge on an ion - _c concentration overpotential (V) - _s surface overpotential (V) - conductivity (^–1 cm^–1) - stoichiometric coefficient - electric potential in solution (V)     

The effect of the gas void distribution on the ohmic resistance during water electrolytes

Due to the presence of gas bubbles on the electrode surface and in the interelectrode gap during water electrolysis, the ohmic resistance in the cell increases. The main aim of this investigation is to obtain insight into the effect of the gas void distribution on the ohmic resistance in the electrolysis cell. The gas void distribution perpendicular to the electrode surface has been determined at various current densities, solution flow velocities and heights in the cell, taking high speed motion pictures. From these measurements it follows that two bubble layers can be distinguished. The current density distribution and the ohmic resistance in the electrolysis cell have been determined using a segmented nickel electrode. The current density decreases at increasing height in the cell. The effect is more pronounced at low solution flow velocities and high current densities. A new model to calculate the ohmic resistance in the cell is proposed.Nomenclature A _l electrolyte area (m²) - c constant (–) - d _wm distance between the working electrode and the diaphragm resp. the tip of the Luggin capillary (m) - E voltage of an operating cell (V) - f gas void fraction (–) - F Faraday constant (C/mol) - f ₀ gas void fraction at the electrode surface (–) - f _b gas void fraction in the bulk electrolyte (–) - h height from the bottom of the working electrode (m) - h _r reference height (= 1 cm) (m) - H total height of the electrode (m) - i current density (A m^–2) - i _av average current density (A m^–2) - i _r reference current density (= 1 kA m^–2) (A m^–2) - R resistance () - R specific resistance (_m) - R unit surface resistance (m²) - R ₁ resistance of the first bubble layer () - R ₂ resistance of the second bubble layer () - R _cell ohmic resistance in the cell () - R _b bubble radius (m) - s _l degree of screening by bubbles in the electrolyte (–) - _l liquid flow velocity (m s^–1) - _{1, r} reference liquid flow velocity (= l m s^–1) (m s^–1) - V _M molar gas volume (m³ mol^–1) - w width of the electrode (m) - x distance from the electrode surface (m) - thickness of the bubble layer adjacent to the electrode (m) - number of bubbles generated per unit surface area and unit time (m^–2 s^–1) Paper presented at the International Meeting on Electrolytic Bubbles organised by the Electrochemical Technology Group of the Society of Chemical Industry, and held at Imperial College, London, 13–14 September 1984.     

Meniscus shape and lateral wetting at the hanging meniscus rotating disc (HMRD) electrode

The hanging meniscus rotating disc (HMRD) electrode is a configuration in which a cylinder of the electrode material is used without an insulating mantle. We have recently shown that the hydrodynamic behaviour of the HMRD is similar to that of the conventional rotating disc electrode and that this configuration can also be used to study the kinetics of simple charge transfer reactions. In this paper experimental data on the change of meniscus shape upon meniscus height and rotation for different electrode materials are presented and analysed in relation to lateral wetting and stability.List of symbols A electrode area (cm²) - C ₀ ^* bulk concentration (mol cm^–3) - D ₀ diffusion coefficient (cm²s^–1) - f force on a cylinder supporting a hanging meniscus (dyn) - F Faraday (96 500 Cmol^–1) - g gravitational acceleration (cm s^–2) - h height (cm) - h _m meniscus height (cm) - h ₀ critical meniscus height (cm) - i total current (A) - i _L limiting current (A) - i _max kinetic current (A) - k proportionality constant (cm^–1) - K dimensionless constant - n number of electrons exchanged - R _eff effective radius of the electrode (cm) - R ₀ geometric radius of the electrode (cm) - V volume of the meniscus above the general level of the liquid surface (cm³) Greek letters ₀ thickness of hydrodynamic boundary layer (cm) - surface tension (dyn cm^–1) - kinematic viscosity (cm²s^–1) - density difference between the liquid and its surrounding fluid (gcm^–3) - _C normal contact angle - _L local contact angle 0_L + 90° - electrode rotation rate (s^–1)     

Estimation of current bypass in a bipolar electrode stack from current-potential curves

A simple method is proposed for the estimation of the current bypass from experimental current-potential (i-U) curves measured for a bipolar reactor and with a one-element cell of similar geometry. The model is valid only in the region where a lineari-U relation is obtained.Notation F Faraday constant (C mol^–1) - i _o electrical feed current density (A m^–2) - i _i current density in cellj (A m^–2) - I _o current (A) - N number of cells - P pressure (N m^–2) - R gas constant (J mol^–1 K^–1) - R _e slope of the linear part of thei-U relation for one element cell ( m²) - T temperature (K) - U _o intercept of the lineari-U relation withU axis for one element cell (V) - U ₁ potential difference for one element cell (V) - U _N potential difference for a bipolar electrode stack with N cells (V) - U _j potential difference for cellj in the stack (V) - V experimental gas flow rate (m³s^–1) - V _o theoretical gas flow rate given by Relation (7) (m³s^–1) - current bypass     

Resolution of Pheromonal Epoxydienes by Chiral HPLC, Stereochemistry of Separated Enantiomers, and Their Field Evaluation

Resolution of insect pheromonal cis-epoxydiene racemates derived from (Z,Z,Z)-3,6,9-trienes with a C₁₈–C₂₃ chain was examined utilizing chiral HPLC columns, and the result showed that a Chiralpak AS column was suitable to separate enantiomers of the 3,4-epoxides, and a Chiralpak AD column was indispensable for the resolution of the racemic 6,7- and 9,10-epoxides. The absolute configuration of the enantiomers of the 3,4- and 9,10-epoxides separated by HPLC was studied after methanolysis of their epoxy rings. Examination of the ¹H NMR data from esters of the methoxyalcohols produced by a modified Mosher's method with (S)- and (R)--methoxy--(trifluoromethyl)phenylacetic acid indicated that the dextrorotatory parent epoxides with a shorter R _t were 3S,4R and 9S,10R isomers and the levorotatory enantiomers having a longer R _t possessed 3R,4S and 9R,10S configuration. Field tests with both enantiomers of (Z,Z)-6,9-cis-3,4-epoxynonadecadiene separated by HPLC with the chiral column revealed new specific attraction of geometrid forest defoliators, Pachyerannis obliquaria, to the 3R,4S isomer and Zethenia albonotaria nesiotis to the 3S,4R isomer.     

Mass diffusion-controlled bubble behaviour in boiling and electrolysis and effect of bubbles on ohmic resistance

A survey is given of theoretical asymptotic bubble behaviour which is governed by heat or/and mass diffusion towards the bubble boundary. A model has been developed to describe the effect of turbulent forced flow on both bubble behaviour and ohmic resistance. A comparison with experimental results is also made.Nomenclature ga liquid thermal diffusivity (m² s^–1) - B width of electrode (m) - c liquid specific heat at constant pressure (J kg^–1 K^–1) - C ₀ initial supersaturation of dissolved gas at the bubble wall (kg m^–3) - d bubble density at electrode surface (m^–2) - D diffusion coefficient of dissolved gas (m² s^–1) - D _h –4S/Z, hydraulic diameter, withS being the cross-sectional area of the flow andZ being the wetted perimeter (m) - e base of natural logarithms, 2.718... - f local gas fraction - F Faraday constant (C kmol^–1) - G evaporated mass diffusion fraction - h height from bottom of the electrode (m) - h _w total heat transfer coefficient for electrode surface (J s^–1 m^–2 K^–1) - h _w,conv convective heat transfer coefficient for electrode surface (J s^–1 m^–2K^–1) - H total height of electrode (m) - i electric current density (A m^–2) - j, j ^* number - J modified Jakob number,C ₀/ ₂ - enthalpy of evaportion (J kg^–1) - m density of activated nuclei generating bubbles at electrode surface (m^–2) - n product of valency and number of equal ions forming one molecule; for hydrogenn=2, for oxygenn=4 - p pressure (N m^–2) - p excess pressure (N m^–2) - R gas constant (J kmol^–1 K^–1) - R ₁ bubble departure radius (m) - R ₀ equilibrium bubble radius (m) - R/R relative increase of ohmic resistance due to bubbles, R, in comparison to corresponding value,R, for pure electrolyte - Re Reynolds number,D _h/ - Sc Schmidt number,/D - Sh Sherwood number - t time (s) - T absolute temperature (K) - T increase in temperature of liquid at bubble boundary with respect to original liquid in binary mixture (K) - gu solution flow velocity (m s^–1) - x mass fraction of more volatile component in liquid at bubble boundary in binary mixture - x ₀ mass fraction of more volatile component in original liquid in binary mixture - y mass fraction of more volatile component in vapour of binary mixture - contact angle - local thickness of one phase velocity boundary layer (m) - _m local thickness of corresponding mass diffusion layer (m) - ^* local thickness of two-phase velocity boundary layer (m) - _o initial liquid superheating (K) - constant in Henry's law (m² s^–2) - liquid kinematic viscosity (m² s^–1) - ^* bubble frequency at nucleus (s^–1) - ₁ liquid mass density (kg m^–3) - ₂ gas/vapour mass density (kg m^–3) - surface tension (N m^–1) Paper presented at the International Meeting on Electrolytic Bubbles organized by the Electrochemical Technology Group of the Society of Chemical Industry, and held at Imperial College, London, 13–14 September 1984.     

The role of mass transfer in the electrolytic reduction of hexavalent chromium at gas evolving rotating cylinder electrodes

The rate of electrolytic reduction of hexavalent chromium from acidic solution at a hydrogen-evolving rotating cylinder lead cathode was studied under conditions of different current densities, Cr⁶⁺ concentrations and rotation speeds. The rate of the reaction was found to follow a first order rate equation. The specific reaction rate constant was found to increase with increasing rotation speed until a limiting value was reached with further increase in rotation speed. Mechanistic study of the reaction has shown that at relatively low rotation speeds the reduction of Cr⁶⁺ is partially diffusion controlled, at higher speeds the reaction becomes chemically controlled. The limiting specific reaction rate constant was related to the operating current density by the equationK=0.044i ^1.385. The current efficiency of Cr⁶⁺-reduction was measured as a function of current density, initial Cr⁶⁺ concentration and rotation speed. Possible practical applications are discussed.Nomenclature A electrode area (cm²) - a, b constants in Equations 5 and 13, respectively - C bulk concentration of Cr⁶⁺ at timet(M) - C _o initial concentration of Cr⁶⁺ (M) - C _i interfacial concentration of Cr⁶⁺ (M) - d cylinder diameter (cm) - D diffusivity of Cr⁶⁺ (cm² s^–1) - e _o standard electrode potential (V) - F Faraday's constant (96 487 C) - current consumed in hydrogen discharge (A) - i current density (A cm^–2) - I cell current (A) - K _l mass transfer coefficient (cm s^–1) - K _r mass transfer coefficient due to cylinder rotation (cm s^–1) - K _o natural convection mass transfer coefficient (cm s^–1) - K _g mass transfer coefficient due to hydrogen stirring (cm s^–1) - K ₂ specific reaction rate constant (cm s^–1) - K overall rate constant (cm s^–1) - m theoretical amount of Cr⁶⁺ reduced during electrolysis (g) - P gas pressure (atm) - R gas constant (atm cm³ mol^–1 K^–1) - T temperature (K) - t time (s) - V linear speed of the rotating cylinder (cm s^–1) - hydrogen discharge rate (cm³ cm^–2 s^–1) - V _s solution volume (cm³) - z electrochemical equivalent (g C^–1) - Z number of electrons involved in the reaction - Re Reynolds number (Vd/v) - Sh Sherwood number (K _r d/D) - Sc Schmidt number (v/D) - rotation speed (r.p.m.) - kinematic viscosity (cm² s^–1)     

Flow-through and flow-by porous electrodes of nickel foam. I. Material characterization

This paper deals with the characterization of three nickel foams for use as materials for flow-through or flow-by porous electrodes. Optical and scanning electron microscope observations were used to examine the pore size distribution. The overall, apparent electrical resistivity of the reticulated skeleton was measured. The BET method and the liquid permeametry method were used to determine the specific surface area, the values of which are compared with those known for other materials.Nomenclature a _e specific surface area (per unit of total volume) (m^–1) - a _s specific surface area (per unit of solid volume) (m^–1) - (a _e)_BET specific surface area determined by the BET method (m^–1) - (a _e)_Ergun specific surface area determined by pressure drop measurements (m^–1) - mean pore diameter (m) - mean pore diameter determined by optical microscopy (m) - mean pore diameter using Ergun equation (m) - e thickness of the skeleton element of the foam (m) - G grade of the foam (number of pores per inch) - P/H pressure drop per unit height of the foam (Pa m^–1) - r electrical resistivity ( m) - R _h hydraulic pore radius (m) - T tortuosity - mean liquid velocity (m s^–1) Greek symbols mean porosity - circularity factor - dynamic viscosity (kg m^–1 s^–1) - liquid density (kg m^–3) - pore diameter size dispersion     

Microstructure and tribological behavior of TiAlSiN coatings deposited by deep oscillation magnetron sputtering

Development of pulsed‐techniques aimed to generate highly ionized target species and high plasma density opens up a new way to tailor composition, structure, and properties of coatings. In this work, TiAlSiN coatings have been deposited at various negative substrate biases (V_s) using deep oscillation magnetron sputtering by sputtering a TiAlSi compound target in Ar/N₂ mixtures. The increase in V_s from ?30 to ?120 V resulted in a decrease in (111)‐preferred orientation and grain size, together with the increase in residual stress and rough morphology. The nc‐TiAlN/a‐Si₃N₄ nanocomposite structure was obtained in coatings. The highest hardness and Young's modulus reached 42.4 and 495 GPa at ?120 V, respectively. However, at ?60 V, the coatings with the highest H/E* and H³/E*² ratios of 0.095 and 0.332 exhibited excellent adhesion with above HF1 level, the lowest coefficient of friction (COF) of 0.35 and specific wear rate of 2.1 × 10^?7 mm³ N^?1 m^?1. Wear mechanism changed from the mixture of severe adhesive, oxidative and abrasive wear to mild oxidative wear to severe oxidative wear. TiAlSiN coatings with high hardness and H/E* and H³/E*² ratios exhibited the decrease in COF and wear rate due to refined grains in uniform distribution, which well promoted oxide layers formed on sliding contact surface.     

Electrolytic recovery of metals from waste waters with the ‘Swiss-roll’ cell

The Swiss-roll cell has been used for the removal of copper from dilute synthetic waste waters. Batch experiments have shown that in acidic solutions the copper concentration may be taken down to a concentration under 1 ppm. Without N₂-sparging the current efficiency at a concentration of 22 ppm Cu was 30%. The cell was also used to separate metals from mixtures found in pickling baths. Thus 99·9% copper was removed from a Cu/Zn sulphate solution with no detectable change in the Zn concentration. The deposited metal may be leached out chemically or stripped out by anodic polarization.List of symbols a specific cell cost ($ m^–2s^–1) - A electrode area (m²) - b integration constant (M) - c concentration (M) - c _o initial concentration (M) - c steady state concentration (M) - d thickness of cathode spacer (m) - d _h hydraulic diameter (m) - D diffusion coefficient (m²s^–1) - f friction factor - k mass transfer coefficient (m s^–1) - K flow rate independent cost per unit time ($ s^–1) - K _cell cost associated with cell per unit time ($ s^–1) - K _pump cost associated with pumping per unit time($ s^–1) - K _tot total cost per unit time ($ s^–1) - l breadth of electrode perpendicular to flow (m) - L length flow path across electrode (m) - p specific pumping cost [$(W s)^–1] - P pressure drop across cell (N m^–2) - (Re) Reynolds number - (Sc) Schmidt number - (Sh) Sherwood number - t time (s) - v electrolyte flow velocity (m s^–1) - V volume of electrolyte in batch experiment (m³) - [Y effluent through-put (m³ s^–1) - Z volume flow rate through cell (m³ s^–1) - porosity of cathode spacer This paper was presented at the 27th ISE-Meeting Zurich, September 6–11, 1976.     

Mass transfer and structure of asbestos and non-asbestos diaphragms for chlorine and caustic production

Models and equations describing aspects of diaphragm performance are discussed in view of recent experiences with non-asbestos diaphragms. Excellent control of wettability and, therefore, of the amount of gases inside the diaphragm, together with chemical resistance to the environment during electrolysis, was found to be an essential prerequisite to performances of non-asbestos diaphragms that are comparable to those of asbestos diaphragms. Equations, derived and supported by experimental evidence from previous work, are shown to describe and predict hydrodynamic permeability and ohmic voltage drop of diaphragms, even in cases where the amount of gases inside the diaphragm slowly increases during electrolysis. Current efficiency is observed to be only dependent to a slight extent on the effective electrolyte void fraction inside the diaphragm. Major effects that determine current efficiency at 2 kA m^–2 and 120 gl^–1 caustic are shown to be diaphragm thickness, pore diameter distribution and the number of interconnections between pores inside the diaphragm. A discussion on design of the structure of non-asbestos diaphragms is presented.Nomenclature B permeability coefficient (m²) - c _i,x concentration of ionic species i at position x (mol m^–3) - c _k concentration of hydroxyl ions in catholyte (mol m^–3) - CE current efficiency - d thickness of diaphragm (m) - thickness of layer (m) - D _i ionic diffusion coefficient of species i (m²s^–1) - D _e dispersion coefficient (m²s^–1) - electrolyte void fraction - E potential inside diaphragm (V) - F Faraday constant, 96487 (C mol^–1 of electrons) - F _j,i flux of ionic species i in the stagnant electrolyte inside small pores of layer j - H hydrostatic head (N m^–2) - i flux of current =j/F (mol m^–2s^–1) - j current density (A m^–2) - k _i,l constant representing diffusion in diaphragm (m²s^–1) - k ₂ constant representing migration in diaphragm (m^–1) - v _p hydraulic pore radius according to [15] (m) - N number of layers - N _j,i flux of ionic species i in layer j (mol m^–2s^–1) - P hydrodynamic permeability (m³ N^–1s^–1) - R gas constant, 8.3143 (J mol^–1 K^–1) - density of liquid (kg m^–3) - R ₀ electric resistivity of electrolyte (ohm m) - R _d electric resistivity of porous structure filled with electrolyte (ohm m) - R _m resistance of the diaphragm (ohm m²) - R _a resistance of anolyte layer (ohm m²) - R _e resistance of electrodes (ohm m²) - s specific surface of porous structure (m^–1) - s ₀ standard specific surface of solids in porous structure (m^–1) - tortuosity defined according toR _d/R ₀=/ - T absolute temperature (K) - u superficial liquid velocity (m s^–1) - U cell voltage (V) - dynamic viscosity (N s m^–2) - v kinematic viscosity (m²s^–1) - x diaphragm dimensional coordinate (m) - y radial coordinate inside pores (m) Paper presented at the meeting on Materials Problems and Material Sciences in Electrochemical Engineering Practice organised by the Working Party on Electrochemical Engineering of the European Federation of Chemical Engineers held at Maastricht, The Netherlands, September 17th and 18th 1987.     

Electromagnetic Field and Current Waves in a Conductor Compressed by a Shock Wave in a Magnetic Field

A physically correct and mathematically rigorous solution of the problem on the structure of an electromagnetic field formed when a shock wave enters a conducting half–space in a transverse magnetic field is obtained. It is shown that only physically grounded boundary conditions lead to a noncontrovercial pattern of the electromagnetic field and a system of currents in a conductor. The main parameters and characteristic times are found, which determine the structure of current waves in a metal. The solution in the uncompressed region is determined by the parameter R₁ = µ₀₁D²t and that in the compressed region by the parameter R₂ = µ₀₂(D—U)²t (₁ and ₂ are the electric conductivities of the uncompressed and compressed substance, respectively, µ₀ is the magnetic permeability of vacuum, D is the wave–front velocity, U is the mass velocity, and t is the time). The parameter for the compressed substance R ₂ coincides with the parameter obtained previously for the shock–wave dielectric—metal transition; the governing parameter for the uncompressed substance R ₁ is obtained for the first time. The asymptotic solutions of the problem for small and large times and the special case R ₁ = R ₂ considered help in understanding the physical meaning of the solution found.     

Mass transfer at the gas evolving inner electrode of a concentric cylindrical reactor

Mass transfer coefficients for an oxygen evolving vertical PbO₂ coated cylinder electrode were measured for the anodic oxidation of acidified ferrous sulphate above the limiting current. Variables studied included the ferrous sulphate concentration, the anode height, the oxygen discharge rate and the anode surface roughness. The mass transfer coefficient was found to increase with increasing O₂ discharge rate,V, and electrode height,h, according to the proportionality expressionK V ^0.34 h ^0.2. Surface roughness with a peak to valley height up to 2.6 mm was found to increase the rate of mass transfer by a modest amount which ranged from 33.3 to 50.8% depending on the degree of roughness and oxygen discharge rate. The present data, as well as previous data at vertical oxygen evolving electrodes where bubble coalescence is negligible, were correlated by the equationJ=7.63 (Re. Fr)^–0.12, whereJ is the mass transferJ factor (St. Sc ^0.66).Notation a ₁,a ₂ constants - A electrode area (cm²) - C concentration of Fe²⁺ (M) - d bubble diameter (cm) - D diffusivity (cm² s^–1) - e electrochemical equivalent (g C^–1) - F Faraday's constant - g acceleration due to gravity (cm s^–2) - h electrode height (cm) - I _Fe ²⁺ current consumed in Fe²⁺ oxidation A - I _{o 2} current consumed in O₂ evolution, A - K mass transfer coefficient (cm s^–1) - m amount of Fe²⁺ oxidized (g) - P gas pressure (atm) - p pitch of the threaded surface (cm) - Q volume of oxygen gas passing any point at the electrode surface (cm³ s^–1) - R gas constant (atm cm³ mol^–1 K^–1) - r peak-to-valley height of the threaded surface (cm) - t time of electrolysis (s) - T temperature (K) - solution viscosity (g cm^–1 s^–1) - V oxygen discharge velocity as defined by Equation 3 (cm s^–1) - Z number of electrons involved in the reaction - Sh Sherwood number (Kd/D) - Re Reynolds number (Vd/) - Sc Schmidt number (v/D) - J mass transferJ factor (St. Sc ^0.66) - St Stanton number (K/V) - Fr Froude number (V ²/dg) - Solution density, g cm^–3 - v Kinematic viscosity (cm² s^–1) - bubble geometrical parameter defined in [31] - fractional surface coverage - diffusion layer thickness (cm)