Engineering Commons^™

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.

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 …

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).

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 …

In Situ Infrared Evidence For The Electrochemical Incorporation Of Hydrogen Into Si And Ge, K. C. Mandal, F. Ozanam, J.-N. Chazalviel

Faculty Publications

No abstract provided.

On The Electrochemical Etching Of Tips For Scanning Tunneling Microscopy, Nancy Burnham, J. Ibe, P. Bey Jr., S. Brandow, R. Brizzolara, D. Dilella, K. Lee, C. K. Marrian, R. Colton

Nancy A. Burnham

The sharpness of tips used in scanning tunneling microscopy(STM) is one factor which affects the resolution of the STM image. In this paper, we report on a direct‐current (dc) drop‐off electrochemicaletching procedure used to sharpen tips for STM. The shape of the tip is dependent on the meniscus which surrounds the wire at the air–electrolyte interface. The sharpness of the tip is related to the tensile strength of the wire and how quickly the electrochemical reaction can be stopped once the wire breaks. We have found that the cutoff time of the etch circuit has a significant effect on the …

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.

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.

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 i_0,1,ref; the cathodic transfer coefficient and the effective exchange current density of the thionyl chloride reduction, _c,4 and a⁰i_0,4,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 …

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.

Modeling The Rotating Disk Electrode For Studying The Kinetics Of Electrochemical Reactions, P K. Adanuvor, Ralph E. White, S E. Lorimer

Faculty Publications

A general mathematical model for studying the kinetics of electrochemical reactions at a rotating disk electrode under steady-state potentiostatic conditions is presented. The model, apart from predicting the net and partial current densities at given values of the applied potential, the ohmic potential drop, and the concentration and potential profiles in the solution, also accounts for homogeneous reactions of any order in the solution and noncharge transfer reactions at the electrode surface. The versatility of the model is demonstrated by the application of the model to a variety of complex reaction schemes.

Simple Models For Diaphragm-Type Chlorine/Caustic Cells I. Dynamic Behavior, John Van Zee, Ralph E. White, A T. Watson

Faculty Publications

A simple model of the dynamic behavior of a diaphragm-type chlorine/caustic cell is presented. The model is based upon measurable diaphragm properties and the mass transfer of hydroxyl ion through the diaphragm. The anolyte is modeled simply as a region in which the OH^– ion concentration is fixed, the diaphragm is modeled as a plug-flow reactor with an electrochemical reaction occurring at the catholyte/diaphragm interface where the cathode is placed, and the catholyte is modeled as a completely stirred flow reactor. Analytical integration of the governing equations for thesemodels yields two mathematical expressions: one for the concentration distribution of …

Simple Models For Diaphragm-Type Chlorine/Caustic Cells Ii. Effect Of Acidic Anolyte On Steady-State Caustic Yield, John Van Zee, Ralph E. White

Faculty Publications

A simple steady-state model of a diaphragm-type chlorine/caustic cell in which the diaphragm is divided into two regions by a homogeneous acid-base reaction is presented. The location of the reaction affects significantly the caustic yield and effluent concentration. The model is used to predict the location of this reaction as a function of the operating variables, the physical constants, and three measurable properties of the diaphragm. These measurable properties are the MacMullin number or resistivity ratio of electrolyte-filled diaphragm relative to the electrolyte, the Darcy's law diaphragmpermeability, and the diaphragm thickness. The model is used to predict a maximum in …

Prediction Of The Current Density At An Electrode At Which Multiple Electrode Reactions Occur Under Potentiostatic Control, Ralph E. White, S. E. Lorimer, R. Darby

Faculty Publications

It is often desirable to be able to predict the total current density at an electrode when multiple electrochemical reactions occur there under potentiostatic control. It is also sometimes desirable to include the effect of ionic migration within the diffusion layer upon the predicted total (1) and partial current densities (2). A procedure for doing this can be illustrated by considering the rotating disk electrode (RDE) system and the associated potential distribution near the RDE as shown in Fig. 1 and 2.

Electrochemical Reduction Of Molybdenum(Vi) Compounds In Molten Lithium Chloride-Potassium Chloride Eutectic, Branko N. Popov, H. A. Laitinen

Faculty Publications

Molybdenum (VI) oxide reacts with molten LiCl-KCl eutectic at 450° to form MoO₂CI₂, which probably is present as an anion MoO₂Cl₄⁼, and pyromolybdate, Mo₂O₇⁼. Both of these species are electrochemically reduced to MoO₂, which can be reoxidized to MoO₂Cl₂ by current reversal. A second reduction step, observed whether MoO₃ or Mo₂O₇²⁻ is added to the melt, can be attributed to the reduction of MoO₄⁻⁻, formed as a secondary reaction product in the first …

Electrochemical Reduction Of Chromate In The Presence Of Nickel Chloride In Molten Lithium Chloride-Potassium Chloride Eutectic, Branko N. Popov, H. A. Laitinen

Faculty Publications

Chronopotentiometry of chromate in the presence of NiCl₂ in molten LiCl-KCl eutectic reveals a diffusion controlled, three electron reduction step. In the presence of excess NiCl₂, chromate is reduced at −0.35V vs. Pt(II)/Pt reference electrode and the electroactive species responsible for the chrono-potentiometric wave is estimated to have a diffusion coefficient of 1.06 · 10⁻⁵ cm² sec⁻¹ at 450°C. The stoichiometry of the reduction product depends mainly on the temperature at which the deposit is formed. At 500°C the deposit approaches the composition LiNi₂CrO₄. X-ray powder diffraction shows the deposit …

Electrolytic Refining Of Copper By The Series System, Jerome Yopps

Bachelors Theses and Reports, 1928 - 1970

The purpose of this thesis investigation was to determine the characteristics of the series system of electrolytic refining of copper.

Electrodeposition Of Cellulose And Carboxy-Methylcellulose, Charles Edward Driesens Jr.

Theses

The previous work done by Frank Cozzarelli on the eleotrodeposition of cellulose from a sodium zincate-urea-cellulose system has been verified, except that zinc was found to deposit on the cathode at all voltages and current densities within the range of the optimum conditions for deposition. The optimum conditions are: voltage - 1.10 to 1.28 volts; current density 0.13 to 1.10 amperes/square foot; electrode material - copper. Current efficiencies range from 0.80 to 5.53%.

A chelate-like complex formed from the sodium zincate and urea which couples with the cellulose has been proposed as a possible explaination of the mechanism governing the …

The Theory Of Alloy Deposition And The Effect Of A Rotating Cathode Upon Such Deposition, With Special Attention To The Possibility Of Depositing Sterling Silver, Kenneth J. Stodden

Bachelors Theses and Reports, 1928 - 1970

In the past few years a great deal of atten­tion has been given to the electrodeposition of alloys. For the main part, this investigation has been of scien­tific interest only; but in a few instances, such work has attained commercial importance.