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Articles 181 - 210 of 247
Full-Text Articles in Chemical Engineering
Calorimetric Determination Of The Thermoneutral Potential Of Li/Bcx And Li/Socl2 Cells, E. E. Kalu, Ralph E. White, E. C. Darcy
Calorimetric Determination Of The Thermoneutral Potential Of Li/Bcx And Li/Socl2 Cells, E. E. Kalu, Ralph E. White, E. C. Darcy
Faculty Publications
Through a continuous recording of the cell voltage, heat flow, and current, the effective thermoneutral potential, Eetpof Li/BCX and Li/SOCl2 cells were determined in the temperature range, 0–60°C. The depth of discharge (DOD), temperature (T), and cell type (cell chemistry) affect the effective thermoneutral potential. The effective thermoneutral potential, Eetp differs from the classical thermoneutral potential of a cell because it takes into account the heat flow due to non-faradaic processes. The average effective thermoneutral potential at 25°C (determined by selecting the most constant region of Eetp vs. time of discharge) was 4.0 …
Comparing Electrochemical Impedance Spectroscopy Methods For Estimating The Degree Of Delamination Of Organic Coatings On Steel, S. A. Mccluney, S. N. Popova, Branko N. Popov, Ralph E. White, R. B. Griffin
Comparing Electrochemical Impedance Spectroscopy Methods For Estimating The Degree Of Delamination Of Organic Coatings On Steel, S. A. Mccluney, S. N. Popova, Branko N. Popov, Ralph E. White, R. B. Griffin
Faculty Publications
Electrochemical impedance spectroscopy (EIS) was used to evaluate the degree of delamination of the epoxy primer Uniprime ED-41 electrocoated on phosphate-treated cold-rolled steel in 3.5% NaCl exposed to air. Specimens with coating thicknesses of 20.3 and 20.8 µm and surface areas of 78.5 cm2 were used. Coating parameters were obtained using a circuit-analog model. The area of delamination was estimated using several EIS parameters, including the pore resistance and the break point frequency. These values were compared to the corroded area determined visually. All methods considered exhibited a strong correlation over some or all of the range of …
Reduction Of Chromium (Vi) When Solar Selective Black Chromium Is Deposited In The Presence Of Organic Additive, Branko N. Popov, Ralph E. White, D. Slavkov, Z. Koneska
Reduction Of Chromium (Vi) When Solar Selective Black Chromium Is Deposited In The Presence Of Organic Additive, Branko N. Popov, Ralph E. White, D. Slavkov, Z. Koneska
Faculty Publications
Electrochemical dc methods were used to study the reduction of chromium (VI) in the presence of organic additives. It is shown that F–, thiourea, and citric acid are essential to enable deposition of black chrome from concentrated chromic acid solutions. A new formulation of the plating bath is defined. The optimum operating conditions under which spectrally selective surface of black chrome is deposited have been determined.
Measurements Of The Fundamental Thermodynamic Parameters Of Li/Bcx And Li/Socl2 Cells, E. E. Kalu, Ralph E. White, E. C. Darcy
Measurements Of The Fundamental Thermodynamic Parameters Of Li/Bcx And Li/Socl2 Cells, E. E. Kalu, Ralph E. White, E. C. Darcy
Faculty Publications
The thermodynamic data needed to estimate the heat generation characteristics of Li/BCX and Li/SOCl2 cells were determined using two experimental techniques, equilibrium or reversible cell discharge and measurement of open circuitpotential as a function of temperature. The results obtained showed that the reversible cell potential (Er), the temperature dependence of the reversible cell potential (dEr/dT) and thermoneutral potential (Eh) of the BCX cell were respectively, Er,25oc = 3.74 V, dEr/dT = –0.857 ± 0.198 mV/K and Eh = 3.994 …
A Mathematical Model Of A Cuo/Cu Vaporvolt Cell, Makoto Kawanami, Trung V. Nguyen, Ralph E. White
A Mathematical Model Of A Cuo/Cu Vaporvolt Cell, Makoto Kawanami, Trung V. Nguyen, Ralph E. White
Faculty Publications
A new battery named "Vaporvolt"b cell is in the early stage of its development. A mathematical model of a CuO/CuVaporvolt cell is presented that can be used to predict the potential and the transport behavior of the cell during discharge.A sensitivity analysis of the various transport and electrokinetic parameters indicates which parameters have the mostinfluence on the predicted energy and power density of the Vaporvolt cell. This information can be used to decide whichparameters should be optimized or determined more accurately through further modeling or experimental studies. Theoptimal thicknesses of electrodes and separator, the concentration of the electrolyte, and …
A Mathematical Model Of A Sealed Nickel-Cadmium Battery, Deyuan Fan, Ralph E. White
A Mathematical Model Of A Sealed Nickel-Cadmium Battery, Deyuan Fan, Ralph E. White
Faculty Publications
A mathematical model for the charge and discharge of a sealed nickel-cadmium (Ni-Cd) battery is presented. The model is used to study the effect of transport properties of the electrolyte and kinetic parameters of the electrode reactions on the cell performance during the charge and discharge period. The model can also be used to demonstrate the changes of cell performance during cycling. Some comparisons between model predictions and experimental results indicate that the model predictions appear to fit the experimental data well. Sensitivity analyses illustrate that the sealed nickel-cadmium battery operates under activation control. It is also shown theoretically that …
Electrode Kinetics Of Oxygen Reduction In Lithium Carbonate Melt: Use Of Impedance Analysis And Cyclic Voltammetric Techniques To Determine The Effects Of Partial Pressure Of Oxygen, Bhasker B. Davé, Ralph E. White, Supramanian Srinivasan, A. John Appleby
Electrode Kinetics Of Oxygen Reduction In Lithium Carbonate Melt: Use Of Impedance Analysis And Cyclic Voltammetric Techniques To Determine The Effects Of Partial Pressure Of Oxygen, Bhasker B. Davé, Ralph E. White, Supramanian Srinivasan, A. John Appleby
Faculty Publications
The effects of the partial pressure of oxygen and temperature on the oxygen reduction on a submerged gold electrode in a lithium carbonate melt were investigated using cyclic voltammetry and impedance analysis. The values for the mass-transfer parameters, DCO, obtained from cyclic voltammetry and impedance analysis were in good agreement. The reaction orders for oxygen at 800°C were calculated to be about 0.3 for the exchange current density and 0.5 for the product DCO; these values are consistent with the mechanism proposed in the literature for oxygen reduction in Li2CO3 melt.
Modification Of Newman's Band(J) Subroutine To Multi-Region Systems Containing Interior Boundaries: Mband, D. Fan, Ralph E. White
Modification Of Newman's Band(J) Subroutine To Multi-Region Systems Containing Interior Boundaries: Mband, D. Fan, Ralph E. White
Faculty Publications
Newman's BAND(J) subroutine, which has been used widely to solve models of various electrochemical systems, is extended to solve a system of coupled, ordinary differential equations with interior boundary conditions. A set of coupled, linear ordinary differential equations is used to demonstrate the solution procedure. The results show that the extended technique has the same accuracy as that of using pentadiagonal BAND(J), but the execution speed is about five times faster than that of pentadiagonal BAND(J). Using sparse matrix solver Y12MAF to solve the same set of equations takes even longer time than pentadiagonal BAND(J).
A Mathematical Model Of Electrochemical Reactions Coupled With Homogeneous Chemical Reactions, Ken-Ming Yen, Taewhan Yeu, Ralph E. White
A Mathematical Model Of Electrochemical Reactions Coupled With Homogeneous Chemical Reactions, Ken-Ming Yen, Taewhan Yeu, Ralph E. White
Faculty Publications
The zinc/bromine (Zn/Br2) flow battery has received considerable
attention in recent years [e.g., (2-4)]. Although it
is agreed that the solution chemistry is important in the
system, most of the work that has been done is concentrated
on the design variables. In this note the basic mass
transfer-solution and surface kinetics are studied to furnish
a better understanding of the system.
Current Distribution In A Horizon® Lead-Acid Battery During Discharge, Z. Mao, Ralph E. White, B. Jay
Current Distribution In A Horizon® Lead-Acid Battery During Discharge, Z. Mao, Ralph E. White, B. Jay
Faculty Publications
A simple mathematical model is presented and used to analyze the potential and current distributions in a HORIZON® sealed lead-acid battery. It was found that an increase in the thickness of an electrode would not enhance the discharge rate of that electrode; instead, it causes the transfer current distribution to be less uniform in the electrode. Also, the ohmic drop across the separator would decrease with a decrease in the thickness of the separator more rapidly when the thickness is small than when it is large. In addition, it was found that efficient high-capacity, high-rate electrodes must consider the electrode …
Impedance Analysis For Oxygen Reduction In A Lithium Carbonate Melt, Bhasker B. Davé, Ralph E. White, Supramaniam Srinivasan, A. John Appleby
Impedance Analysis For Oxygen Reduction In A Lithium Carbonate Melt, Bhasker B. Davé, Ralph E. White, Supramaniam Srinivasan, A. John Appleby
Faculty Publications
Oxygen reduction on a smooth gold electrode in a pure lithium carbonate melt was investigated by electrochemical impedance spectroscopy and cyclic voltammetry. The impedance data were analyzed using the Randles-Ershler equivalent circuit to determine parameters such as the charge-transfer resistance, Warburg coefficient, double-layer capacity, and uncompensated electrolyte resistance. The parameters estimated by complex plane plots and a complex nonlinear least squares method are in good agreement. Cyclic voltammetric measurements showed that oxygen reduction in a lithium carbonate melt is very rapid. A mass transfer parameter, DC0, estimated by the cyclic voltammetry concurred withthat calculated by the electrochemical …
Electrochemical Characterization Of Electronically Conductive Polypyrrole On Cyclic Voltammograms, Taewhan Yeu, Ken-Ming Yin, Jose Carbajal, Ralph E. White
Electrochemical Characterization Of Electronically Conductive Polypyrrole On Cyclic Voltammograms, Taewhan Yeu, Ken-Ming Yin, Jose Carbajal, Ralph E. White
Faculty Publications
Experimental and theoretical cyclic voltammograms for electronically conducting polypyrrole film are obtained from the identical conditions and compared to each other to characterize electrochemical behavior of the polymer. A comparison of the simulated and experimental cyclic yoltammograms shows quantitative agreement. The profiles of the dependent variables show that the switching process is governed by the availability of the counter ion to the polypyrrole electrode and the amount of electroactive sites. Sensitivity analysis shows that the double layer effects have more influence in the cyclic voltammograms than the electrokinetic effects.
A Modified Electrochemical Process For The Decomposition Of Hydrogen Sulfide In An Aqueous Alkaline Solution, Z. Mao, A. Anani, Ralph E. White, S. Srinivasan, A. J. Appleby
A Modified Electrochemical Process For The Decomposition Of Hydrogen Sulfide In An Aqueous Alkaline Solution, Z. Mao, A. Anani, Ralph E. White, S. Srinivasan, A. J. Appleby
Faculty Publications
An electrochemical process for the decomposition of hydrogen sulfide into its constituents in an aqueous alkaline solution is presented. It essentially consists of presaturation of an alkaline scrubber solution with H2S. Thereafter, partial neutralization of the presaturated solution provides not only the necessary mass balance for electrolysis, but also creates the optimum conditions under which passivation of the anode, as well as side chemical and electrochemical reactions, are minimized. Finally, the electrolysis stage of the process leads to precipitation of crystalline sulfur at the anode and evolution of hydrogen at the cathode. Regeneration of the alkaline solution via …
A Mathematical Model Of The Self-Discharge Of A Ni-H2 Battery, Z. Mao, Ralph E. White
A Mathematical Model Of The Self-Discharge Of A Ni-H2 Battery, Z. Mao, Ralph E. White
Faculty Publications
A simple mathematical model is presented and used to characterize the self-discharge of a nickel oxyhydroxide(NiOOH) electrode in a hydrogen environment. This model includes diffusion of dissolved hydrogen in an electrolyte film which covers a flooded electrode, electrochemical oxidation of hydrogen, reduction of nickel oxyhydroxide, and changes of surface area and of porosity of the electrode during the self-discharge process. Although the self-discharge process is complicated, the predictions of the model are consistent with experimental results reported in the literature, which include linear relationships between the logarithm of hydrogen pressure and time and between the logarithm of the capacity remaining …
In Situ Degradation Of Polyhalogenated Aromatic Hydrocarbons By Electrochemically Generated Superoxide Ions, E. E. Kalu, Ralph E. White
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.
A Mathematical Model Of A Hydrogen/Oxygen Alkaline Fuel Cell, Michael C. Kimble, Ralph E. White
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 …
Mathematical Modeling Of A Nickel-Cadmium Battery: Effects Of Intercalation And Oxygen Reactions, Deyuan Fan, Ralph E. White
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.
Effect Of Ohmic, Mass-Transfer, And Kinetic Resistances On Linear-Sweep Voltammetry In A Cylindrical-Pore Electrode, John W. Weidner, Peter S. Fedkiw
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 …=>
A Simple Model For A Zinc/Bromine Flow Cell And Associated Storage Tanks, G. D. Simpson, Ralph E. White
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 …
Mathematical Modeling Of An H2s Removal Electrolyzer, Z. Mao, P. Adanuvor, Ralph E. White
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.
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
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 …
A Computer Simulation Of The Oxygen Reduction Reaction In Carbonate Melts, P. K. Adanuvor, Ralph E. White, A. J. Appleby
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 …
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
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.
Predicted Secondary Current Distributions For Linear Kinetics In A Modified Three-Dimensional Hull Cell, F. A. Jagush, Ralph E. White, William E. Ryan
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.
Mathematical Model Of A Lithium/Polypyrrole Cell, Taewhan Yeu, Ralph E. White
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.
Three-Dimensional Current Distributions In A Bipolar, Chlor-Alkali Membrane Cell, Ralph E. White, F. Jagush, H. S. Burney
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).
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
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 …
The Effects Of Separator Design On The Discharge Performance Of A Starved Lead-Acid Cell, T. V. Nguyen, Ralph E. White, Hiram Gu
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.
Oxygen Reduction In A Proton Exchange Membrane Test Cell, S. J. Ridge, Ralph E. White, Y. Tsou, R. N. Beaver, G. A. Eisman
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 …
An Algebraic Model For A Zinc/Bromine Flow Cell, G. D. Simpson, Ralph E. White
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.