Publications

The objective of this investigation was to study the growth of thick passivating layers on the Li anode in Li/BCX (Li/SOCl 2 +BrCl) cells which were stored for a period of 3 years. Impedance spectroscopy and equivalent circuit models were used to determine characterizing parameters for these cells. The equivalent circuit used for virgin cells includes a faradic contribution and diffusion of the electroactive species. the equivalent circuit for batteries stored 1 or 2 years includes the impedance of a metal/ passive film interface, the resistance of the film, and the impedance of the passivating film/electrolyte interface. The equivalent circuit used for batteries stored for 3 years accounts for cathodic contributions in the overall impedance spectrum.

Effects of partial pressure of CO2 and temperature on O reduction kinetics on a Au electrode in a Li2CO3 melt were examined using electrochem. impedance spectroscopic (EIS) and linear sweep voltammetric techniques. The impedance spectra were analyzed by a complex nonlinear least squares method, using the Randles-Ershler equivalent circuit model, to determine the electrode-kinetic and the mass-transfer parameters, such as the charge-transfer resistance and the Warburg coefficient The cyclic voltammetric measurements indicated that the O reduction process in the Li2CO3 melt is reversible up to 200 mV/s. The D01/2C0 values determined by cyclic voltammetry agreed well with those estimated by the EIS method. The reaction. order with respect to CO2 and the activation energy for the exchange c.d. are -0.52 and 132 kJ/mol, resp. Also, the reaction. order with respect to CO2 and the activation energy for D01/2C0 were calculated to be -0.8 and 185 kJ/mol, resp.

A first principle mathematical model of the formation of calcareous deposits on a cathodically protected steel rotating disk electrode in seawater is presented. The model includes equations which transport phenomena, electrochemical reactions, precipitation reactions, and a homogeneous reaction involved in the formation of calcareous deposits on an electrode surface. Predicted concentration profiles show that a high concentration of OH- ions on the electrode surface leads to the formation of calcareous deposits. The calcareous deposits contain mostly CaCO3, but the initial deposits are predicted to contain more Mg(OH)2 than CaCO3. The predicted calcareous deposits on the electrode surface reduce the active surface area available for the electrochemical reactions, which results in a decrease in the cathodic current density. The predicted current density as a function of time during the formation of deposits agrees qualitatively with experimental data.

A mathematical model is presented for a Li/TiS2 cell under galvanostatic discharge. This model has been used to illustrate the importance of considering the effect of the separator on the material utilization of a porous TiS2 electrode in a Li/TiS2 cell. The model predictions show that a porous TiS2 electrode in a cell with a thin separator would deliver much more capacity than the electrode would in a large volume of electrolyte and that the material utilization of the TiS2 electrode increases with a decrease in the separator thickness. © 1993.

This article presents an approach to fault diagnosis of chemical processes at steadystate operation by using artificial neural networks. The conventional back‐propagation network is enhanced by adding a number of functional units to the input layer. This technique considerably extends a network s capability for representing complex nonlinear relations and makes it possible to simultaneously diagnose multiple faults and their corresponding levels in a chemical process. A simulation study of a heptane‐to‐toluene process at steady‐state operation shows successful results for the proposed approach. Copyright © 1993 American Institute of Chemical Engineers

Electrochemical impedance spectroscopy (EIS) has been used to study the solute uptake for epoxy/phenolic (E/p) and epoxy/amine (E/a) thick-coated mild steel samples immersed for 160 days in 3.5 weight percent NaCl solution exposed to air. Samples with thicknesses of approximately 200$μ$m with an exposed surface area of 22.6 cm 2 were used to follow solute saturation of the organic coating. Good agreement was obtained between the calculated and measured coating capacitance when, according to the diffusion equation, the coating capacitance was plotted against exposure time. © 1993, The Electrochemical Society, Inc. All rights reserved.

Proper water and heat management are essential for obtaining high-power-density performance at high energy efficiency for proton-exchange-membrane fuel cells. A water and heat management model was developed and used to investigate the effectiveness of various humidification designs. The model accounts for water transport across the membrane by electro-osmosis and diffusion, heat transfer from the solid phase to the gas phase and latent heat associated with water evaporation and condensation in the flow channels. Results from the model showed that at high current densities (\textgreater1 A/ cm2) ohmic loss in the membrane accounts for a large fraction of the voltage loss in the cell and back diffusion of water from the cathode side of the membrane is insufficient to keep the membrane hydrated (i.e., conductive)

A thermal analysis of Li/BCX and high rate Li/SOCl2 cells is presented. The thermal model developed was used to study the effect of ambient temperature of discharge (0-40°C) on Li/BCX cells discharged at the same rate. The model predictions show that ambient temperature of discharge was critical in thermal management of the cell. For forced convection cooled cells, the model predicted that ambient temperature near room temperature (25°C) was required to achieve the lowest maximum temperature rise in the cell. Inclusion of the effects of reaction products to the model predictions showed that a constant composition assumption may be misleading. Heat transfer through the spiral constituted a smaller fraction of the total heat dissipation from the cell. In a comparison of the thermal performance of high rate Li/SOCl2 cell with Li/BCX cell, the model predicted a higher temperature rise in the Li/SOCl2 cell (assuming the temperature rise behaves linearly with discharge current) if both cells were discharged at the same rate.

A semi-analytical solution technique is presented for solving linear partial differential equations. The technique is based on analytically solving the equations that result from discretizing the spatial coordinates of a partial differential equation. Two examples are presented to illustrate the proced and the savings in computation time relative to a method of lines numerical solution. © 1992.