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Faculty Publications

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Articles 841 - 870 of 914

Full-Text Articles in Chemical Engineering

In Situ Degradation Of Polyhalogenated Aromatic Hydrocarbons By Electrochemically Generated Superoxide Ions, E. E. Kalu, Ralph E. White Jan 1991

In Situ Degradation Of Polyhalogenated Aromatic Hydrocarbons By Electrochemically Generated Superoxide Ions, E. E. Kalu, Ralph E. White

Faculty Publications

The reduction of dioxygen in aprotic media yields superoxide ions which react with polyhalogenated aromatic hydrocarbons by nucleophilic substitution. The degradation of hexachlorobenzene to bicarbonates and chlorides using in situ generated superoxide ions was carried out at room temperature in a flow cell system equipped with a gas fed, porous electrode. The effects of current, electrolyte flow, and aprotic media on the extent of degradation of hexachlorobenzene are presented.

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A Mathematical Model Of A Hydrogen/Oxygen Alkaline Fuel Cell, Michael C. Kimble, Ralph E. White Jan 1991

A Mathematical Model Of A Hydrogen/Oxygen Alkaline Fuel Cell, Michael C. Kimble, Ralph E. White

Faculty Publications

A mathematical model of a hydrogen/oxygen alkaline fuel cell is presented that can be used to predict polarization behavior under various potential loads. The model describes the phenomena occurring in the solid, liquid, and gaseous phases of the anode, separator, and cathode regions, assuming a macrohomogeneous, three-phase porous electrode structure. The model calculates the spatial variation of the partial pressures of oxygen, hydrogen, and water vapor, dissolved oxygen and hydrogen concentrations, electrolyte concentration, and the solid- and solution-phase potential drops. By developing a complete model of the alkaline fuel cell, the interaction of the various transport and kinetic resistances can …

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Mathematical Modeling Of A Nickel-Cadmium Battery: Effects Of Intercalation And Oxygen Reactions, Deyuan Fan, Ralph E. White Jan 1991

Mathematical Modeling Of A Nickel-Cadmium Battery: Effects Of Intercalation And Oxygen Reactions, Deyuan Fan, Ralph E. White

Faculty Publications

Extensions are presented for a previously published (1) mathematical model of a nickel-cadmium (Ni-Cd) cell. These extensions consist of intercalation thermodynamics for the nickel electrode and oxygen generation and reduction reactions during charge and overcharge. The simulated results indicate that intercalation may be important in the nickel electrode and that including the oxygen reactions provides a means of predicting the efficiency of the cell on charge and discharge.

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Effect Of Ohmic, Mass-Transfer, And Kinetic Resistances On Linear-Sweep Voltammetry In A Cylindrical-Pore Electrode, John W. Weidner, Peter S. Fedkiw Jan 1991

Effect Of Ohmic, Mass-Transfer, And Kinetic Resistances On Linear-Sweep Voltammetry In A Cylindrical-Pore Electrode, John W. Weidner, Peter S. Fedkiw

Faculty Publications

Extracting quantitative kinetic information from linear-sweep voltammograms (LSV) on porous electrodes is more difficult than on planar electrodes since the electrode surface is not uniformly accessible to the bulk supply of reactant or the counterelectrode. We present here a means to account for the effect of ohmic, mass-transfer, and kinetic resistances on LSV by modeling a pore in a porous matrix as a cylindrical-pore electrode, and solving the mass and charge conservation equations in the context of this geometry for the simply redox reaction O + ne– <=> R where both O and R are soluble species. Both analytical …

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A Simple Model For A Zinc/Bromine Flow Cell And Associated Storage Tanks, G. D. Simpson, Ralph E. White Jan 1990

A Simple Model For A Zinc/Bromine Flow Cell And Associated Storage Tanks, G. D. Simpson, Ralph E. White

Faculty Publications

A simple model for a parallel plate, zinc/bromine flow cell and associated storage tanks is presented and used to make time-dependent predictions for various quantities in the system. The model is based on a previously published algebraic model of the cell at steady-state and time-dependent, first-order differential equations for the storage tanks. The Butler-Volmer equation is used for the electrochemical reactions, and the homogeneous reaction between bromine and bromide is included. The model predictions indicate that the charging operation of a zinc/bromine battery can be significantly improved by using a storage tank with a larger residence time for the bromine …

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Mathematical Modeling Of An H2s Removal Electrolyzer, Z. Mao, P. Adanuvor, Ralph E. White Jan 1990

Mathematical Modeling Of An H2s Removal Electrolyzer, Z. Mao, P. Adanuvor, Ralph E. White

Faculty Publications

A mathematical model is presented for a high temperature H2S electrolyzer. It is shown that the maximum current in this type of a cell is determined entirely by the transport rate of sulfide ions through the separator. It is suggested that this model could be used to determine the feasibility of various designs for this electrolyzer.

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Electrochemical Behavior Of Graphite And Ni-Cr Electrodes In Sodium Polysulfide In The Absence And Presence Of Hydrogen Sulfide, Z. Mao, Ralph E. White, B. Dandapani, A. Anani, S. Srinivasan, A. J. Appleby Jan 1990

Electrochemical Behavior Of Graphite And Ni-Cr Electrodes In Sodium Polysulfide In The Absence And Presence Of Hydrogen Sulfide, Z. Mao, Ralph E. White, B. Dandapani, A. Anani, S. Srinivasan, A. J. Appleby

Faculty Publications

The electrochemical behavior of graphite and Ni-Cr electrodes in sodium tetrasulfide melt has been investigated using voltammetric, chronoamperometric, and chronopotentiometric techniques in the presence and absence of hydrogen sulfide. Two continuous phases, namely, Na2S2 and Na2S, are apparently formed at different potentials during the cathodic polarization. The blocking effect by these layers was much less significant on the Ni-Cr electrode than on graphite. The presence of H2S did not appear to influence the electrode reactions, but it significantly reduced the rate of formation of the continuous phases (Na2S2 or Na …

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A Computer Simulation Of The Oxygen Reduction Reaction In Carbonate Melts, P. K. Adanuvor, Ralph E. White, A. J. Appleby Jan 1990

A Computer Simulation Of The Oxygen Reduction Reaction In Carbonate Melts, P. K. Adanuvor, Ralph E. White, A. J. Appleby

Faculty Publications

A computer simulation of the oxygen reduction reaction in various carbonate melts has been carried out under steady-state conditions on the basis of a proposed kinetic model which takes into consideration the autocatalytic reaction involving oxygen and other reducible oxygen species in the melt, and the neutralization of oxide ions by dissolved carbon dioxide. A simulation of the presence of (physically) dissolved oxygen, in the diffusion layer region of the melt, corresponding to the possible situation in porous electrodes, causes a significant enhancement in the polarization curves, particularly in the mass-transfer control region. On the other hand, high levels of …

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Estimation Of The Diffusion Coefficient And Solubility For A Gas Diffusing Through A Membrane, Michael C. Kimble, Ralph E. White, Yu-Min Tsou, R. Neal Beaver Jan 1990

Estimation Of The Diffusion Coefficient And Solubility For A Gas Diffusing Through A Membrane, Michael C. Kimble, Ralph E. White, Yu-Min Tsou, R. Neal Beaver

Faculty Publications

Analysis of the data obtained by the electrochemical monitoring technique for diffusion of a gas through a membrane is considered. It is shown that combining a numerical method with a nonlinear parameter estimation technique provides a means to determine values for the diffusion coefficient and the solubility of the diffusing gas. It is shown that better accuracy can be obtained for the diffusion coefficient and solubility of this gas by using the method presented and all experimental data rather than only part of the data, as has often been done in the past.

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Predicted Secondary Current Distributions For Linear Kinetics In A Modified Three-Dimensional Hull Cell, F. A. Jagush, Ralph E. White, William E. Ryan Jan 1990

Predicted Secondary Current Distributions For Linear Kinetics In A Modified Three-Dimensional Hull Cell, F. A. Jagush, Ralph E. White, William E. Ryan

Faculty Publications

Current density distribution is an important consideration
for those involved in designing electrochemical systems
and electroplating systems in particular. Although it
is important, the common practice in industry is to use
trial and error to determine designs that optimize current
density distributions in electroplating. The purpose of this
paper is to illustrate the use of the finite element method
(FEM) to predict three-dimensional current density distributions.

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Mathematical Model Of A Lithium/Polypyrrole Cell, Taewhan Yeu, Ralph E. White Jan 1990

Mathematical Model Of A Lithium/Polypyrrole Cell, Taewhan Yeu, Ralph E. White

Faculty Publications

A mathematical model to simulate the charge/discharge behavior of a lithium/lithium perchlorate-propylene carbonate/polypyrrole(Li/LiClO4-PC/PPy) secondary battery cell is presented. The model can be used to gain a better understanding of the behavior of this cell and to provide guidance toward the design of new secondary batteries which utilize an electronically conductive polymer such as polypyrrole (PPy) as the cathode. The model includes the capability of handling charge and discharge behavior and is used to study the effect of various design parameters on the performance of the cell.

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Three-Dimensional Current Distributions In A Bipolar, Chlor-Alkali Membrane Cell, Ralph E. White, F. Jagush, H. S. Burney Jan 1990

Three-Dimensional Current Distributions In A Bipolar, Chlor-Alkali Membrane Cell, Ralph E. White, F. Jagush, H. S. Burney

Faculty Publications

The current distributions in a stack of bipolar, membrane
chlor-alkali cells are important design considerations
(1). The degree of nonuniformity of the current distribution
is important to know because highly nonuniform
current distributions could cause, among other things, severe
damage to the membrane in a cell stack (2).

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Electrochemical Production Of Hydrogen And Sulfur By Low-Temperature Decomposition Of Hydrogen Sulfide In An Aqueous Alkaline Solution, A. A. Anani, Z. Mao, Ralph E. White, S. Srinivasan, A. J. Appleby Jan 1990

Electrochemical Production Of Hydrogen And Sulfur By Low-Temperature Decomposition Of Hydrogen Sulfide In An Aqueous Alkaline Solution, A. A. Anani, Z. Mao, Ralph E. White, S. Srinivasan, A. J. Appleby

Faculty Publications

Electrolysis of hydrogen sulfide to its constituents in a solution containing equimolar concentrations of NaOH and NaHS has been carried out at 80°C. In a double-compartment cell employing Nafion membrane as a separator, both crystalline elemental sulfur and high-purity hydrogen have been produced at high current efficiencies. Only minimal, if any, passivation of the anode by sulfur product was observed. According to solution composition, electrolysis could result in gas evolution at the anode, passivation of the anode by sulfur deposition, or oxidation of sulfide (S2–) or polysulfide (S) to sulfur oxyanions. However, in an optimized solution, electrolysis gave …

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The Effects Of Separator Design On The Discharge Performance Of A Starved Lead-Acid Cell, T. V. Nguyen, Ralph E. White, Hiram Gu Jan 1990

The Effects Of Separator Design On The Discharge Performance Of A Starved Lead-Acid Cell, T. V. Nguyen, Ralph E. White, Hiram Gu

Faculty Publications

A mathematical model of a starved lead-acid cell has been developed to study the dynamic behavior of the cell during discharge. Concentrated binary electrolyte theory and a volume-averaging technique were used to model the transport of electrolyte. The model can be used to predict cell voltage and profile of: acid concentration, overpotential, porosity, reaction rate, and electrode capacity, as functions of time. The effects of separator thickness and its porosity were examined with respect to cold-cranking amperage and reserve capacity of the battery. The separator was found to be a significant factor governing performance.

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Molecular Dynamics Simulation Of Real-Fluid Mutual Diffusion Coefficients With The Lennard-Jones Potential Model, Richard L. Rowley, J. M. Stoker Sep 1989

Molecular Dynamics Simulation Of Real-Fluid Mutual Diffusion Coefficients With The Lennard-Jones Potential Model, Richard L. Rowley, J. M. Stoker

Faculty Publications

Mutual diffusion coefficients for selected alkanes in carbon tetrachloride were calculated using molecular dynamics and Lennard-Jones (LJ) potentials. Use of effective spherical LJ parameters is desirable when possible for two reasons: (i) computer time is saved due to the simplicity of the model and (ii) the number of parameters in the model is kept to a minimum. Results of this study indicate that mutual diffusivity is particularly sensitive to the molecular size cross parameter, σ12, and that the commonly used Lorentz–Berthelot rules are inadequate for mixtures in which the component structures differ significantly. Good agreement between simulated and experimental mutual …

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Oxygen Reduction In A Proton Exchange Membrane Test Cell, S. J. Ridge, Ralph E. White, Y. Tsou, R. N. Beaver, G. A. Eisman Jan 1989

Oxygen Reduction In A Proton Exchange Membrane Test Cell, S. J. Ridge, Ralph E. White, Y. Tsou, R. N. Beaver, G. A. Eisman

Faculty Publications

Oxygen reduction in a gas-fed porous electrode attached to a proton exchange membrane is discussed. Experimental data and a mathematical model are presented for the test cell used. Various membrane and electrode assemblies were tested at different levels of platinum loading and Teflon® content. The model accounts for the diffusion and reaction of oxygen and the diffusion and reaction of hydrogen ions. Sulfuric acid was placed above the membrane in the test cell reservoir to provide a source of protons for the reduction of oxygen at the cathode. Based upon model predictions, it is shown that the transport of the …

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An Algebraic Model For A Zinc/Bromine Flow Cell, G. D. Simpson, Ralph E. White Jan 1989

An Algebraic Model For A Zinc/Bromine Flow Cell, G. D. Simpson, Ralph E. White

Faculty Publications

An algebraic model for a parallel plate, zinc/bromine flow cell is presented and used to predict various performance quantities, which are compared to those predicted by using previously published differential equation models. The results presented compare well with previous work. The model is based on the concept of using well-mixed zones and linear concentration and potential profiles for the diffusion layers and the separator. The Butler-Volmer equation is used for the electrochemical reactions, and the homogeneous reaction between bromine and bromide is included.

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A Comparison Of Newman's Numerical Technique And Deboor's Algorithm, D. A. Curtis, T. I. Evans, Ralph E. White Jan 1989

A Comparison Of Newman's Numerical Technique And Deboor's Algorithm, D. A. Curtis, T. I. Evans, Ralph E. White

Faculty Publications

No abstract provided.

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Estimation Of Electrode Kinetic Parameters Of The Lithium/Thionyl Chloride Cell Using A Mathematical Model, T. I. Evans, Ralph E. White Jan 1989

Estimation Of Electrode Kinetic Parameters Of The Lithium/Thionyl Chloride Cell Using A Mathematical Model, T. I. Evans, Ralph E. White

Faculty Publications

A one-dimensional mathematical model for the lithium/thionyl chloride primary cell is used in conjunction with a parameter estimation technique, in order to estimate the electrode kinetic parameters of this electrochemical system. The electrode kinetic parameters include the anodic transfer coefficient and exchange current density of the lithium oxidation, a,1 and i0,1,ref; the cathodic transfer coefficient and the effective exchange current density of the thionyl chloride reduction, c,4 and a0i0,4,ref, and a morphology parameter, . The parameter estimation is performed on simulated data first in order to gain confidence in the method. Data reported in …

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A Mathematical Model Of A Lithium/Thionyl Chloride Primary Cell, T. I. Evans, T. V. Nguyen, Ralph E. White Jan 1989

A Mathematical Model Of A Lithium/Thionyl Chloride Primary Cell, T. I. Evans, T. V. Nguyen, Ralph E. White

Faculty Publications

A one-dimensional mathematical model for the lithium/thionyl chloride primary cell has been developed to investigate methods of improving its performance and safety. The model includes many of the components of a typical lithium/thionyl chloride cell such as the porous lithium chloride film which forms on the lithium anode surface. The governing equations are formulated from fundamental conservation laws using porous electrode theory and concentrated solution theory. The model is used to predict one-dimensional, time dependent profiles of concentration, porosity, current, and potentialas well as cell temperature and voltage. When a certain discharge rate is required, the model can be used …

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A Thermal Analysis Of A Spirally Wound Battery Using A Simple Mathematical Model, T. I. Evans, Ralph E. White Jan 1989

A Thermal Analysis Of A Spirally Wound Battery Using A Simple Mathematical Model, T. I. Evans, Ralph E. White

Faculty Publications

A two-dimensional thermal model for spirally wound batteries has been developed. The governing equation of the model is the energy balance. Convective and insulated boundary conditions are used, and the equations are solved using a finite element code called TOPAZ2D. The finite element mesh is generated using a preprocessor to TOPAZ2D called MAZE. The model is used to estimate temperature profiles within a spirally wound D-size cell. The model is applied to the lithium/thionyl chloride cell because of the thermal management problems that this cell exhibits. Simplified one-dimensional models are presented that can be used to predict best and worst …

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Electrochemical Production And Corrosion Testing Of Amorphous Ni-P, Jose L. Carbajal, Ralph E. White Jan 1988

Electrochemical Production And Corrosion Testing Of Amorphous Ni-P, Jose L. Carbajal, Ralph E. White

Faculty Publications

Ni-P alloys were prepared by electrodeposition under different conditions on a rotating disk electrode. A variety of alloys were prepared ranging from Ni-15P to Ni-25P. An indirect reduction of species in solution involving several steps appears to be favored over the direct reduction at the electrode based on the low P content in the alloy. Energy dispersion x-ray microanalysis was used to determine composition of the alloy. Transmission electron microscopy and x-ray diffraction corroborated the amorphous nature of the structure. The physical and chemical homogeneity of the metallic glasses produced electrochemically is substantiated by the absence of electrochemical localized attack. …

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Oxygen Reduction On Silver In 6.5 Molar Caustic Soda Solution, Prosper K. Adanuvor, Ralph E. White Jan 1988

Oxygen Reduction On Silver In 6.5 Molar Caustic Soda Solution, Prosper K. Adanuvor, Ralph E. White

Faculty Publications

No abstract provided.

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A Two-Dimensional Mathematical Model Of A Porous Lead Dioxide Electrode In A Lead-Acid Cell, E. C. Dimpault-Darcy, T. V. Nguyen, Ralph E. White Jan 1988

A Two-Dimensional Mathematical Model Of A Porous Lead Dioxide Electrode In A Lead-Acid Cell, E. C. Dimpault-Darcy, T. V. Nguyen, Ralph E. White

Faculty Publications

A two-dimensional mathematical model is presented for a lead dioxide electrode in a lead-acid cell. It is used to simulate the time dependent behavior of the electrode during discharge. The model contains six dependent variables: the concentration of the acid electrolyte, the porosity, the electrical potentials of the solid and solution phases, and the two directional components of the current density in the electrolyte. The effect of the electrode grid was included by varying the conductivity of the solid. Parameters such as electrode conductivity, electrode dimensions, and temperature are investigated to understand their effects on electrode discharge performance.

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Secondary Current Distributions Using Topaz2d And Linear Kinetics, E. C. Dimpault-Darcy, Ralph E. White Jan 1988

Secondary Current Distributions Using Topaz2d And Linear Kinetics, E. C. Dimpault-Darcy, Ralph E. White

Faculty Publications

Secondary current density distributions are of interest
to cell designers. The purpose of this note is to illustrate
how to use an existing numerical method to determine
these distributions for cells that contain conducting and
nonconducting bodies between the main anode and cathode.

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Analysis Of Electrokinetic Data By Parameter Estimation And Model Discrimination Techniques, Prosper K. Adanuvor, Ralph E. White Jan 1988

Analysis Of Electrokinetic Data By Parameter Estimation And Model Discrimination Techniques, Prosper K. Adanuvor, Ralph E. White

Faculty Publications

An alternative approach to classical methods of electrochemical data analysis is presented. This alternative method is based on nonlinear parameter estimation and model discrimination techniques. The method is used to obtain the relevant kinetic and transport parameters and to elucidate the kinetic mechanism of O2 reduction at carbon and silver electrodes in alkaline electrolytes.

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A Mathematical Model For Predicting Cyclic Voltammograms Of Electronically Conductive Polypyrrole, Taewhan Yeu, Trung V. Nguyen, Ralph E. White Jan 1988

A Mathematical Model For Predicting Cyclic Voltammograms Of Electronically Conductive Polypyrrole, Taewhan Yeu, Trung V. Nguyen, Ralph E. White

Faculty Publications

Polypyrrole is an attractive polymer for use as a high energy density secondary battery because of its potential as an inexpensive, lightweight, and noncorrosive electrode material. A mathematical model to simulate cyclic voltammograms for polypyrrole is presented here. The model is for a conductive porous electrode film on a rotating disk electrode (RDE) and is used to predict the spatial and time dependence of concentration, overpotential, and stored charge profiles within a polypyrrole film. The model includes both faradaic and capacitive charge components in the total current density expression.

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Predicting Shunt Currents In Stacks Of Bipolar Plate Cells With Conducting Manifolds, H. S. Burney, Ralph E. White Jan 1988

Predicting Shunt Currents In Stacks Of Bipolar Plate Cells With Conducting Manifolds, H. S. Burney, Ralph E. White

Faculty Publications

A method is presented for predicting shunt currents in stacks of bipolar plate cells with conducting manifolds. The method is based on the requirement that the potential drop through the solution in a manifold be large enough to force current to leave the solution and to enter the conducting manifold. The current that leaves the solution in the manifold enters the conducting manifold at the anode end of the stack and returns to the solution at the cathode end. This could cause catastrophic failure of a manifold.

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Oxygen Reduction On Silver In 6.5m Caustic Soda Solution, Prosper K. Adanuvor, Ralph E. White Jan 1988

Oxygen Reduction On Silver In 6.5m Caustic Soda Solution, Prosper K. Adanuvor, Ralph E. White

Faculty Publications

The cathodic reduction of oxygen in 6.5M membrane-grade caustic soda solution has been studied experimentally at a silver rotating disk electrode at 25°C. The results can be approximated by the parallel mechanism for oxygen reduction with catalytic decomposition of peroxide. Further analysis of this mechanism indicates that the sequential process with catalytic decomposition of peroxide predominates over the direct 4e– process. Direct application of the sequential mechanism to the data indicates that the latter mechanism with catalytic decomposition of peroxide much more accurately reflects the experimental results. The relevant kinetic parameters are calculated on the basis of …

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A Mathematical Model For The Electrodeposition Of Alloys On A Rotating Disk Electrode, Shiuan Chen, Ken-Ming Yin, Ralph E. White Jan 1988

A Mathematical Model For The Electrodeposition Of Alloys On A Rotating Disk Electrode, Shiuan Chen, Ken-Ming Yin, Ralph E. White

Faculty Publications

A general multiple electrode reaction model for electrodeposition of alloys on a rotating disk electrode is presented. Included in the model are mass transport equations with the effect of ionic migration, Butler-Volmer kinetic rate expressions, and the mole fractions of the individual components in the solid state. The model shows that the effect of ionic migration is important and that plating variables such as applied potential, pH, and bulk concentration can be included. Two examples (Ni-P and Ru-Ni-P) are used to illustrate the predictions of the model.

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