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Full-Text Articles in Chemical Engineering

A Mathematical Model Of An Electrochemical Capacitor With Double-Layer And Faradaic Processes, Chuan Lin, James A. Ritter, Branko N. Popov, Ralph E. White Jan 1999

A Mathematical Model Of An Electrochemical Capacitor With Double-Layer And Faradaic Processes, Chuan Lin, James A. Ritter, Branko N. Popov, Ralph E. White

Faculty Publications

A mathematical model of an electrochemical capacitor with hydrous ruthenium oxide (RuO2·xH2O) electrodes including both double-layer and surface faradaic processes is developed to predict the behavior of the capacitor under conditions of galvanostatic charge and discharge. The effect of RuO2·xH2O particle size is studied and shows that the smaller the particles the better the performance because of the increased surface area per unit volume or mass. The model also predicts that the faradaic process increases significantly the energy per unit volume of the capacitor for power densities of …

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Development Of Carbon-Metal Oxide Supercapacitors From Sol-Gel Derived Carbon-Ruthenium Xerogels, Chuan Lin, James A. Ritter, Branko N. Popov Jan 1999

Development Of Carbon-Metal Oxide Supercapacitors From Sol-Gel Derived Carbon-Ruthenium Xerogels, Chuan Lin, James A. Ritter, Branko N. Popov

Faculty Publications

Sol-gel derived high surface area carbon-ruthenium xerogels were prepared from carbonized resorcinol-formaldehyde resins containing an electrochemically active form of ruthenium oxide. The electrochemical capacitance of these materials increased with an increase in the ruthenium content indicating the presence of pseudocapacitance associated with the ruthenium oxide undergoing reversible faradaic redox reactions. A specific capacitance of 256 F/g (single electrode) was obtained from a carbon xerogel containing 14 wt % Ru, which corresponded to more than 50% utilization of the ruthenium. The double layer accounted for 40% of this capacitance. This material was also electrochemically stable, showing no change in a cyclic …

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A Mathematical Model For Electroless Copper Deposition On Planar Substrates, M. Ramasubramanian, Branko N. Popov, Ralph E. White, K. S. Chen Jan 1999

A Mathematical Model For Electroless Copper Deposition On Planar Substrates, M. Ramasubramanian, Branko N. Popov, Ralph E. White, K. S. Chen

Faculty Publications

A mathematical model for the electroless deposition of copper on a planar electrode is presented and used to make time-dependent predictions on the various quantities in the system. The model takes into account mass transport by diffusion and migration, Butler-Volmer kinetics at the electrode surface, and mixed potential theory. A finite difference approach is used to solve the equations, and the resultant model is used to predict the concentration profiles, potential response, and plating rate as a function of time and concentration of various reactive components.

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Mathematical Modeling Of Electrochemical Capacitors, Venkat Srinivasan, John W. Weidner Jan 1999

Mathematical Modeling Of Electrochemical Capacitors, Venkat Srinivasan, John W. Weidner

Faculty Publications

Analytic solutions to the mathematical model of an electrochemical capacitor (EC) are used to study cell performance under two types of operating conditions: (i) constant current and (ii) electrochemical impedance spectroscopy. The analytic solution under constant-current operation is used to investigate the relative importance of ionic resistance in the separator, and ionic and electronic resistances in the porous electrode in the design and operation of an EC. Model results are presented that show the trade-off between energy and power density, as the physical properties of the cell components are varied (e.g., electrode thickness). The analytic solution …

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Chromium Oxides And Lithiated Chromium Oxides. Promising Cathode Materials For Secondary Lithium Batteries, Pankaj Arora, Dong Zhang, Branko N. Popov, Ralph E. White Sep 1998

Chromium Oxides And Lithiated Chromium Oxides. Promising Cathode Materials For Secondary Lithium Batteries, Pankaj Arora, Dong Zhang, Branko N. Popov, Ralph E. White

Faculty Publications

Chromiumoxides and lithiated chromium oxides were synthesized by thermal decompositionof chromium trioxide (CrO3) at high temperatures and oxygen pressures.Synthesis temperature and pressure markedly affect the performance of thesecathode materials. Higher pressures lead to a higher O/Cr ratioand fewer impurities in the final product. These materials arestable intercalation hosts for lithium, and exhibit a higher capacitythan any of the prominent positive electrodes used in secondarylithium batteries. m-CrOx has a capacity of 255 mAh/g, while m-LiCrOxhas a capacity of 210 mAh/g, during the first discharge. Theaverage voltage of these cells is 3.0 V vs. Li/Li …

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Proton Diffusion In Nickel Hydroxide: Prediction Of Active Material Utilization, Sathya Motupally, Christopher C. Streinz, John W. Weidner Jan 1998

Proton Diffusion In Nickel Hydroxide: Prediction Of Active Material Utilization, Sathya Motupally, Christopher C. Streinz, John W. Weidner

Faculty Publications

Galvanostatic charge and discharge experiments reveal that the active material in nickel electrodes cannot be fully accessed at high currents or for thick films. It has been proposed that the utilization of the active material is controlled by the diffusion rate of protons through the film. This hypothesis is supported by the good agreement between mathematical simulations of material utilization and experimental data over a range of charge and discharge currents and film thicknesses. Furthermore, the fraction of material utilized is larger on charge than on discharge. The asymmetry on charge and discharge is due to a diffusion coefficient that …

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Chromium Oxides And Lithiated Chromium Oxides. Promising Cathode Materials For Secondary Lithium Batteries, Pankaj Arora, Dong Zhang, Branko N. Popov, Ralph E. White Jan 1998

Chromium Oxides And Lithiated Chromium Oxides. Promising Cathode Materials For Secondary Lithium Batteries, Pankaj Arora, Dong Zhang, Branko N. Popov, Ralph E. White

Faculty Publications

Chromium oxides and lithiated chromium oxides were synthesized by thermal decomposition of chromium trioxide (CrO3) at high temperatures and oxygen pressures. Synthesis temperature and pressure markedly affect the performance of these cathode materials. Higher pressures lead to a higher O/Cr ratio and fewer impurities in the final product. These materials are stable intercalation hosts for lithium, and exhibit a higher capacity than any of the prominent positive electrodes used in secondary lithium batteries. m-CrOx has a capacity of 255 mAh/g, while m-LiCrOx has a capacity of 210 mAh/g, during the first discharge. The average …

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Electrochemical Investigations Of Cobalt-Doped Limn2O4 As Cathode Material For Lithium-Ion Batteries, P. Arora, Branko Popov, Ralph E. White Jan 1998

Electrochemical Investigations Of Cobalt-Doped Limn2O4 As Cathode Material For Lithium-Ion Batteries, P. Arora, Branko Popov, Ralph E. White

Faculty Publications

A wide range (y = 0.05–0.33) of Co-doped LiCoyMn2–yO4 spinels were synthesized and electrochemically characterized. These Co-doped spinels showed improved specific capacity and capacity retention over pure spinels. Electrochemical impedance spectroscopy and the linear polarization resistance technique were used to determine the transport and electrochemical kinetic parameters of Co-doped spinels. The presence of Co in the spinel inhibits the passivation process occurring on the surface of the cathode. Also, Co increases the exchange current density and facilitates the charge-transfer reaction of the active material. The lower self-discharge observed for Co-doped spinels was attributed …

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Characterization Of Hydrogen Permeation Through Zinc-Nickel Alloys Under Corroding Conditions: Mathematical Model And Experimental Study, M. Ramasubramanian, Branko N. Popov, Ralph E. White Jan 1998

Characterization Of Hydrogen Permeation Through Zinc-Nickel Alloys Under Corroding Conditions: Mathematical Model And Experimental Study, M. Ramasubramanian, Branko N. Popov, Ralph E. White

Faculty Publications

A mathematical model was developed for the characterization of hydrogen permeation into metals and alloys under corroding conditions. The model requires a knowledge of the corrosion rate of the given metal or alloy in solutions of various H+ concentrations. It provides quantitative values of rate constants of the hydrogen discharge, recombination, and adsorption reactions. This model can serve as a diagnostic criterion for determining the effectiveness of various metals and alloys as hydrogen permeation inhibitors and can be used for evaluation of hydrogen entry inhibition efficiency. Experiments were carried out to study the effectiveness of thin layers of electrodeposited …

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Characterization Of Sol-Gel-Derived Cobalt Oxide Xerogels As Electrochemical Capacitors, Chuan Lin, James A. Ritter, Branko N. Popov Jan 1998

Characterization Of Sol-Gel-Derived Cobalt Oxide Xerogels As Electrochemical Capacitors, Chuan Lin, James A. Ritter, Branko N. Popov

Faculty Publications

Very fine cobalt oxide xerogel powders were prepared using a unique solution chemistry associated with the sol-gel process. The effect of thermal treatment on the surface area, pore volume, crystallinity, particle structure, and corresponding electrochemical properties of the resulting xerogels was investigated and found to have significant effects on all of these properties. The xerogel remained amorphous as Co(OH)2 up to 160°C, and exhibited maxima in both the surface area and pore volume at this temperature. With an increase in the temperature above 200°C, both the surface area and pore volume decreased sharply, because the amorphous Co(OH)2 decomposed …

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Studies On Electroless Cobalt Coatings For Microencapsulation Of Hydrogen Storage Alloys, Bala S. Haran, Branko N. Popov, Ralph E. White Jan 1998

Studies On Electroless Cobalt Coatings For Microencapsulation Of Hydrogen Storage Alloys, Bala S. Haran, Branko N. Popov, Ralph E. White

Faculty Publications

LaNi4.27Sn0.24 alloy was microencapsulated with cobalt by electroless deposition from an alkaline hypophosphite bath. Discharge curves of the encapsulated alloy indicate an additional contribution to the capacity arising from the cobalt on the surface. Studies on cobalt thin films reveal the presence of adsorbed hydrogen in cobalt. The amount of hydrogen adsorbed was observed to increase with time of cathodic polarization and to reach a maximum. Polarization techniques have been used to characterize the cobalt-plated alloy as a function of state of charge. The equilibrium potential of the microencapsulated electrode at low hydrogen concentration is determined by …

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Theoretical Analysis Of Metal Hydride Electrodes: Studies On Equilibrium Potential And Exchange Current Density, Bala S. Haran, Branko N. Popov, Ralph E. White Jan 1998

Theoretical Analysis Of Metal Hydride Electrodes: Studies On Equilibrium Potential And Exchange Current Density, Bala S. Haran, Branko N. Popov, Ralph E. White

Faculty Publications

A theoretical model for the metal hydride electrode has been developed assuming that hydrogen diffusion in the alloy and charge-transfer at the surface control the discharge process. Theoretical equations for the dependence of equilibrium potential and exchange current density on the surface hydrogen concentration have been derived. These parameters have been used to correlate experimental data with the theoretical electrode discharge model. Analysis of both the experimental and theoretical discharge curves reveals a potential plateau determined by the magnitude of the interactions between the hydrogen in the alloy and the unhydrided metal. Neglecting these hydrogen-metal site interactions results in simulations …

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The Role Of Oxygen At The Second Discharge Plateau Of Nickel Hydroxide, Sathya Motupally, Mukul Jain, Venkat Srinivasan, John W. Weidner Jan 1998

The Role Of Oxygen At The Second Discharge Plateau Of Nickel Hydroxide, Sathya Motupally, Mukul Jain, Venkat Srinivasan, John W. Weidner

Faculty Publications

It was shown that the appearance of a secondary discharge plateau approximately 400 mV below the primary plateau can result from the reduction of oxygen. During the galvanostatic discharge of planar nickel-hydroxide films at room temperature and in 3 weight percent KOH solutions, the second discharge plateau was observed only in the presence of dissolved oxygen in the electrolyte. When the solution was deoxygenated, no residual capacity could be extracted from the films even at low discharge rates or from overcharged films. In addition, the duration of the second plateau is inversely proportional to the square of the discharge current, …

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Steady-State Modeling Of A Parallel-Plate Electrochemical Fluorination Reactor, Kamal Jha, Gerald L. Bauer, John W. Weidner Jan 1998

Steady-State Modeling Of A Parallel-Plate Electrochemical Fluorination Reactor, Kamal Jha, Gerald L. Bauer, John W. Weidner

Faculty Publications

A steady-state mathematical model of a parallel-plate reactor was developed for studying the electrochemical fluorination of organic compounds dissolved in anhydrous hydrogen fluoride. The model incorporates two-phase flow with differential material, energy, and pressure balances. Profiles of temperature, pressure, vapor volume fraction, and current density in the reactor are presented at two inlet temperatures to provide insight into the operation of the reactor. The effects of the inlet temperature, feed flow rate, and cell current on the cell pack voltage and current efficiency of the reactor are presented to determine problematic operating regions for the reactor. Optimum operating currents based …

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The Effect Of Particle Size On The Discharge Performance Of A Nickel-Metal Hydride Cell, Jussi M. Heikonen, Harry J. Ploehn, Ralph E. White Jan 1998

The Effect Of Particle Size On The Discharge Performance Of A Nickel-Metal Hydride Cell, Jussi M. Heikonen, Harry J. Ploehn, Ralph E. White

Faculty Publications

We investigate the effect of particle size on the discharge performance of a nickel-metal hydride cell with a mathematical model. Electrodes with uniform as well as with nonuniform particle sizes are studied. With uniform particle size, the dependence of the particle-to-particle resistance on the particle size is taken into account. The optimal particle size depends on the discharge rate. Moreover, we show that under certain conditions it is advantageous to use a nonuniform particle size. In general, the higher the discharge current density, the more the particle size affects the electrode performance.

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Measurement Of Thin Liquid Film Drainage Using A Novel High-Speed Impedance Analyzer, Kevin O. Hool, Robert C. Saunders, Harry J. Ploehn Jan 1998

Measurement Of Thin Liquid Film Drainage Using A Novel High-Speed Impedance Analyzer, Kevin O. Hool, Robert C. Saunders, Harry J. Ploehn

Faculty Publications

This work describes the design and implementation of a new instrument, called the thin film impedance analyzer, which measures the rate of drainage of thin oil films. The instrument forms an oil film by elevating a planar oil–water interface into a water drop hanging from a stainless steel capillary tube immersed in the oil. The instrument measures the magnitude of the impedance of the matter between the capillary tube and a screen electrode immersed in the lower water phase. Under appropriate conditions, the capacitance of the oil film dominates the impedance. The instrument records the increase in the magnitude of …

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Ellipsometric And Raman Spectroscopic Study Of Thermally Formed Films On Titanium, E. Hristova, Lj. Arsov, Branko N. Popov, Ralph E. White Jan 1997

Ellipsometric And Raman Spectroscopic Study Of Thermally Formed Films On Titanium, E. Hristova, Lj. Arsov, Branko N. Popov, Ralph E. White

Faculty Publications

Thermal films on titanium surfaces were formed by heating titanium samples in air at atmospheric pressure. The optical constants, thickness, and structure of the formed films at various temperatures and times of heating were investigated by ellipsometry and Raman spectroscopy. The complex index of refraction and the thickness of generated films were determined by comparing the experimental loci and obtained by ellipsometric measurements with theoretical computed vs. curves. It was found that the thickness in homogeneity and porosity of formed films increase with increasing temperature and the duration of the thermal treatment. Beyond a certain critical temperature, the appearance of …

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The Effects Of Organic Compounds On Inhibition Of Hydrogen Permeation Through A Mild Steel Membrane, H. A. Duarte, D. M. See, Branko N. Popov, Ralph E. White Jan 1997

The Effects Of Organic Compounds On Inhibition Of Hydrogen Permeation Through A Mild Steel Membrane, H. A. Duarte, D. M. See, Branko N. Popov, Ralph E. White

Faculty Publications

The effectiveness of 5-(4-pyridyl)-2,7-nonadiene, and 1 phenyl-2-propyn-ol (PP) on inhibition of the hydrogen evolution reaction on a 1010 steel membrane and on the degree of hydrogen ingress into the membrane was determined. Hydrogen evolution rates and permeation currents were monitored as a function of time at different applied potentials. In the presence of 0.5 g/liter PP in the electrolyte, the hydrogen discharge and permeation current density were inhibited by 98 and95%, respectively.

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Electrowinning Of Nonnoble Metals With Simultaneous Hydrogen Evolution At Flow-Through Porous Electrodes Iii. Time Effects, Mahmoud M. Saleh, John W Weidner, Bahgat E. El-Anadouli, Badr G. Ateya Jan 1997

Electrowinning Of Nonnoble Metals With Simultaneous Hydrogen Evolution At Flow-Through Porous Electrodes Iii. Time Effects, Mahmoud M. Saleh, John W Weidner, Bahgat E. El-Anadouli, Badr G. Ateya

Faculty Publications

The electrowinning of zinc from a recirculating alkaline zincate solution at a flow-through porous electrode was investigated. Experimental results were obtained to test the predictions of a mathematical model. The effects of electrolyte flow rate, cell current, and electrode thickness on the concentration-time relations and coulombic efficiency-time relations were studied. The experimental results show that the highest recovery rate was obtained at both high flow rates and cell currents. There is, however, a practical limit for increasing both the cell current and the electrolyte flow rate. Reasonable agreement between the model predictions and experimental results was obtained. A case study …

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An Electrochemical Route For Making Porous Nickel Oxide Electrochemical Capacitors, Venkat Srinivasan, John W. Weidner Jan 1997

An Electrochemical Route For Making Porous Nickel Oxide Electrochemical Capacitors, Venkat Srinivasan, John W. Weidner

Faculty Publications

Porous nickel oxide films were prepared by electrochemically precipitating nickel hydroxide and heating the hydroxide in air at 300°C. The resulting nickel oxide films behave as an electrochemical capacitor with a specific capacitance of 59 F/g electrode material. These nickel oxide films maintain high utilization at high rates of discharge (i.e., high power density) and have excellent cycle life. Porous cobalt oxide films were also synthesized. Although the specific capacitances of these films are approximately one-fifth that of the nickel oxide films, the results demonstrate the versatility of fabricating a wide range of porous metal oxide films using …

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Molecular-Level Modeling Of The Viscoelasticity Of Crosslinked Polymers: Effect Of Time And Temperature, Philip P. Simon, Harry J. Ploehn Jan 1997

Molecular-Level Modeling Of The Viscoelasticity Of Crosslinked Polymers: Effect Of Time And Temperature, Philip P. Simon, Harry J. Ploehn

Faculty Publications

We present a new molecular-level picture of chain dynamics for describing the viscoelasticity of crosslinked polymers. The associated mathematical model consists of a time-dependent momentum balance on a representative polymer segment in the crosslinked network, plus phenomenological expressions for forces acting on the segments. These include a cohesive force that accounts for intermolecular attraction, an entropic force describing the thermodynamics governing chain conformations, and a frictional force that captures the temperature dependence of relative chain motion. We treat the case of oscillatory uniaxial deformation. Solution of the model equations in the frequency domain yields the dynamic moduli as functions of …

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Anodic Oxidation Of Ethylenediaminetetraacetic Acid On Platinum Electrode In Alkaline Medium, S. N. R. Pakalapati, Branko N. Popov, Ralph E. White Jan 1996

Anodic Oxidation Of Ethylenediaminetetraacetic Acid On Platinum Electrode In Alkaline Medium, S. N. R. Pakalapati, Branko N. Popov, Ralph E. White

Faculty Publications

The anodic oxidation of ethylenediaminetetraacetic acid (EDTA) was studied in alkaline medium on a smooth platinum electrode. Bulk electrolysis indicated that stable organic intermediates (formaldehyde and glyoxal) are formed during the oxidation of EDTA and that complete oxidation to CO2 can be achieved. The proposed pathway suggests that the acetate groups in EDTA are initially oxidized, generating formaldehyde and ethylenediamine. The rest potential of EDTA (0.066 to 0.164 V vs. Hg/HgO) was observed to be higher than for other organic species. In alkaline medium, very little EDTA oxidation was found to occur on bare platinum. Limiting-current behavior due to …

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The Effects Of Multiple Electroplated Zinc Layers On The Inhibition Of Hydrogen Permeation Through An Iron Membrane, D. H. Coleman, G. Zheng, Branko N. Popov, Ralph E. White Jan 1996

The Effects Of Multiple Electroplated Zinc Layers On The Inhibition Of Hydrogen Permeation Through An Iron Membrane, D. H. Coleman, G. Zheng, Branko N. Popov, Ralph E. White

Faculty Publications

The Devanathan-Stachurski permeation technique was used to investigate the rate of hydrogen permeation through an iron membrane with consecutively electroplated zinc layers. Hydrogen evolution rates and hydrogen permeation rates were followed as functions of time at different applied potentials. Hydrogen evolution and permeation decreased with each successive zinc layer until finally reaching an average decrease of 93 and 96%, respectively, as compared with bare iron. Hydrogen surface coverage, exchange current density, absorption-adsorption reaction constant, and hydrogen recombination constant were estimated on bare iron and on zinc-plated iron. It was found that the decrease in the permeation rate of hydrogen through …

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Anomalous Codeposition Of Fe-Ni Alloys And Fe-Ni-Sio2 Composites Under Potentiostatic Conditions, M. Ramasubramanian, S. N. Popova, Branko N. Popov, Ralph E. White, K. M. Yin Jan 1996

Anomalous Codeposition Of Fe-Ni Alloys And Fe-Ni-Sio2 Composites Under Potentiostatic Conditions, M. Ramasubramanian, S. N. Popova, Branko N. Popov, Ralph E. White, K. M. Yin

Faculty Publications

A mathematical model has been developed to describe the electrodeposition of Fe-Ni alloys and Fe-Ni-SiO2 composites under potentiostatic conditions. This model can be used to predict the polarization behavior, partial current densities, and alloy composition of each of the components as a function of the applied potential. Fe-Ni-SiO2 samples were deposited on platinum rotating disk electrodes from sulfate electrolytes under potentiostatic conditions, and the results obtained were compared to the model. The model predictions were found to agree well with the experimental observations for the Fe-Ni and Fe-Ni-SiO2 systems.

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Determination Of Transport And Electrochemical Kinetic Parameters Of Bare And Copper-Coated Lani4.27Sn0.24 Electrodes In Alkaline Solution, G. Zheng, Branko N. Popov, Ralph E. White Jan 1996

Determination Of Transport And Electrochemical Kinetic Parameters Of Bare And Copper-Coated Lani4.27Sn0.24 Electrodes In Alkaline Solution, G. Zheng, Branko N. Popov, Ralph E. White

Faculty Publications

Electrochemical properties of bare and copper-coated LaNi4.27Sn0.24 electrodes were investigated in alkaline solution. The exchange current density, polarization resistance, and equilibrium potential were determined as functions of the state of charge in the electrodes. The symmetry factors for bare and copper-coated electrodes were estimated to be 0.53 and 0.52, respectively. By using a constant current discharge technique, the hydrogen diffusion coefficient in bare and coated LaNi4.27Sn0.24 was estimated to be 6.75 × 10–11 cm2/s.

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Application Of Porous Electrode Theory On Metal Hydride Electrodes In Alkaline Solution, G. Zheng, Branko N. Popov, Ralph E. White Jan 1996

Application Of Porous Electrode Theory On Metal Hydride Electrodes In Alkaline Solution, G. Zheng, Branko N. Popov, Ralph E. White

Faculty Publications

Porous electrode theory was applied to estimate the exchange current density, the polarization resistance, and symmetry factor for LaNi4.27Sn0.24 hydride electrode in alkaline solution. The exchange current density, polarization resistance, and symmetry factor were determined from polarization curves which were obtained at low overpotentials.

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A Model For The Galvanostatic Deposition Of Nickel Hydroxide, Mahesh Murthy, Gowri S. Nagarajan, John W. Weidner, John W. Van Zee Jan 1996

A Model For The Galvanostatic Deposition Of Nickel Hydroxide, Mahesh Murthy, Gowri S. Nagarajan, John W. Weidner, John W. Van Zee

Faculty Publications

A mathematical model is presented for the galvanostatic deposition of Ni(OH)2 films in stagnant Ni(NO3)2 solutions. The objective is to quantify the anomalous deposition behavior reported previously in which the utilization of the electrochemically generated OH– species decreased drastically as the concentration of Ni(NO3)2 increased beyond 0.1 M. For example as the Ni(NO3)2 concentration increased from 0.1 to 2.0 M, the deposition rate decreased by a factor of ten at 2.5 mA/cm2. At this high ratio of concentration to current density, a comparison with Faraday's …

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Analysis Of Transient Hydrogen Uptake By Metal Alloy Particles, Wenlin Zhang, Supramaniam Srinivasan, Harry J. Ploehn Jan 1996

Analysis Of Transient Hydrogen Uptake By Metal Alloy Particles, Wenlin Zhang, Supramaniam Srinivasan, Harry J. Ploehn

Faculty Publications

This paper describes a new approach to solving the equations comprising the shrinking core model for diffusion and reaction of a chemical species in a solid spherical particle. The reactant adsorbs on the particle surface, diffuses into the particle's interior, and reacts with the particle to form a solid product. The shrinking core model assumes a fast reaction rate compared to reactant diffusion so that the reaction is localized in the interfacial zone between the unreacted solid core and the surrounding shell of reacted product. Analytical solutions of the governing conservation equations usually invoke the pseudo-steady state (PSS) approximation which …

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Hydrogen-Atom Direct-Entry Mechanism Into Metal Membranes, G. Zheng, Branko N. Popov, Ralph E. White Jan 1995

Hydrogen-Atom Direct-Entry Mechanism Into Metal Membranes, G. Zheng, Branko N. Popov, Ralph E. White

Faculty Publications

The hydrogen-atom direct-entry mechanism is used to explain why the steady-state hydrogen permeation current density through a metal membrane is directly proportional to the cathodic current density, ic, and is independent of the membrane thickness when ic is small.

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Electrowinning Of Non-Noble Metals With Simultaneous Hydrogen Evolution At Flow-Through Porous Electrodes Ii. Experimental, Mahmoud M. Saleh, John W. Weidner, Bahgat E. Ei-Anadouli, Badr G. Ateya Jan 1995

Electrowinning Of Non-Noble Metals With Simultaneous Hydrogen Evolution At Flow-Through Porous Electrodes Ii. Experimental, Mahmoud M. Saleh, John W. Weidner, Bahgat E. Ei-Anadouli, Badr G. Ateya

Faculty Publications

This paper presents an interpretation of the experimental results obtained on the electrowinning of zinc at a flow-through porous electrode in light of a mathematical model which was presented in Part I. The process is accompanied by simultaneous hydrogen evolution within the electrode, which increases the pore electrolyte resistivity and decreases the coulombic efficiency. We measured polarization curves, coulombic efficiencies, and current distributions under various conditions of zincate concentrations, flow rates, cell current, and electrode thickness. Reasonable agreement between the measured and predicted current distributions was obtained only under conditions of high electrolyte flow rates, low cell currents, and thinner …

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