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 dissolved CO2 in the melt reduce the current density in the mass-transfer control region by reducing the concentration of active dioxygen ions, but enhance it considerably in the kinetic limiting (CO2 neutralization) region. High rates of the autocatalytic and neutralization reactions display the same effects on the polarization curves as dissolved O2 and CO2, respectively, but to a lesser degree. Comparison of the simulated polarization curves in various carbonate melts indicates that Li-rich melts show the best kinetic performance. On the contrary, the highest limiting currents are observed in K- or Na-rich melts. Variation of the cation composition in Li/K carbonate melts indicates that melts of high Li-content should give better kinetic performance.

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.

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 im- proved by using a storage tank with a larger residence time for the bromine side of the system.

A galvanostatic pulse plating model is presented for the electrodeposition of an alloy on a rotating disk electrode. This model is used to simulate the electrodeposition of nickel/chrome alloys. The mass transport equations used in the model include the effects of diffusion, migration and convection; and the electrode kinetics are described by the Butler‐Volmer equation. It is predicted that the effect of ionic migration is significant and therefore should be included in models of pulse plating. Copyright © 1990 American Institute of Chemical Engineers

Summary Using dimensionles variables in the governing and boundary condition equations, the dimensionless option of TOPAZ3D can be used to predict current density distributions in electroplating systems. This was illustrated by determining the curent density distributions in a modified Hull Cell.

The underlying principles and structure of an easy-to-use solver for two-point boundary-value problems described by sets of nonlinear ordinary differential equations is presented. The solution approach is based on the finite difference approximations for the derivatives. The Newton-Raphson iterative scheme with analytical Jacobians is used for solving the resulting large-scale nonlinear set of algebraic equations. Part 1 of the paper presents an in-depth analysis of the general problem and the solution method which results in a split of the overall problem into two distinct parts, a pure mathematical analytical part, which does not depend on the chosen numerical solution method, and a numerical part, which implements all the details of the numerical procedure. The prototype implementation, presented in Part 2, is based on this separation. It makes use of different programs which are specialized for solving particular subproblems identified in the analysis. An algebraic manipulator is used to aid in generating the Jacobians analytically and a matrix-oriented environment is used to implement the numerical matrix operations. The resulting package requires only the essential information from the user, namely the model equations and the solution domain variables as well as initial guesses of the solution. The package is a prototype that can be used to solve second-order problems based on three-point polynomial approximations of the derivatives. © 1990.

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 potential as well as cell temperature and voltage. When a certain discharge rate is required, the model can be used to determine the design criteria and operating variables which yield high cell capacities. Model predictions can be used to establish operational and design limits within which the thermal runaway problem, inherent in these cells, can be avoided.