Publications

A mathematical model for a nickel/hydrogen cell is developed to investigate the dynamic performance of the cell s charge and discharge processes. Concentrated solution theory and the volume averaging technique are used to character-ize the transport phenomena of the electrolyte and other species in the porous electrode and separator. Other physical fun-damentals, such as Ohm s law, are employed to describe the electrical and other physical processes in the cell. The model is designed to predict the distribution of electrolyte, hydrogen, and oxygen concentrations within the cell, hydrogen and oxygen pressure, potential, current density, electrochemical reaction rates, and state of charge. The model can be used to evaluate the influences of all the physical, design, and operation parameters on the behavior of a nickel-hydrogen cell. The model simulations show excellent agreement with experimental data for charge and discharge operations. The model simulations show the formation of a secondary discharge plateau by the end of discharge. This plateau is caused by oxygen reduction at the nickel electrode. It is the first model that predicts this feature, which is a characteristic of the nickel electrode. The model simulations also show the existence of an optimum charge rate that maximizes the charge effi-ciency, which can be used for the implementation of optimal operating conditions.

Corrosion rate studies were carried out on carbon steel rebar samples under different pH conditions and in the presence and absence of chloride ions in solution. Known amounts of calcium nitrite was added as an inhibitor and the mechanism of inhibition was studied by tracking both the thermodynamic and kinetic properties of the system. The studies indicate that there is a competition of a corrosion and a passivation reaction, and the resulting open circuit potential depends on the relative strength of the corroding and passivating environments.

Electrochemical and transport properties of La0.65Ce0.35Ni3.55Co0.75Mn 0.4Al0.3 electrode were investigated in alkaline solution. The exchange current density, polarization resistance and the symmetry factor were determined from polarization curves obtained at low overpotentials. The symmetry factor was estimated to be 0.55 ± 0.01 and is independent of the state of charge. The equilibrium potential of the electrode was found to depend upon the hydrogen content in the alloy. The constant current discharge technique was used to determine the hydrogen diffusion coefficient in the alloy. The estimated value of D̄/a2 at 0.1 C discharge rate was 1.39 × 10-4s-1. © 1996 Chapman & Hall.

A mathematical model has been developed to describe the electrodeposition of Fe-Ni alloys and Fe-Ni-SiO 2 composites under potentiostatic conditions. This model can be used to predict the polarization behavior, partial current densities, and alloy composition of each of the components as a function of the applied potential. Fe-Ni-SiO 2 samples were deposited on platinum rotating disk electrodes from sulfate electrolytes under potentiostatic conditions, and the results obtained were compared to the model. The model predictions were found to agree well with the experimental observations for the Fe-Ni and Fe-Ni-SiO 2 systems.

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The use of a hydrogen gas-fed anode and an acid anolyte in an electrochemical cell used to destroy nitrate is demonstrated. A mixed Na 2SO 4/H 2SO 4 anolyte is shown to favor nitrate cell performance and the generation of a higher hydroxide ion concentration in the catholyte. The suggested scheme is an apparent method of sodium sulfate disposal and a possible means through which ammonia (to ammonium sulfate, fertilizer) and hydrogen gas could be recycled through the anode side of the reactor. This could result in a substantial savings in the operation of a nitrate destruction cell.

A semianalytical technique is presented using Maple to solve coupled nonlinear partial differential equations (PDEs). The technique is based on analytically solving the equations resulting from discretizing the spatial coordinate of the PDEs and using quasilinearization with Newton s method to treat nonlinear terms.

A method is presented for determining a set of independent half-cell equations. The difference between half-cell equations and half-cell reactions is discussed. The method is applied to two electrochemical examples: electrodeposition/electro-oxidation of copper and electrochemical reduction and oxidation of nitrate and nitrite in a caustic solution.

Hydrogen surface coverage, exchange current density, absorption-adsorption reaction constant, and hydrogen recombination constant were estimated on bare iron and on zinc and nickel-zinc plated iron. Hydrogen evolution and permeation decreased with each successive zinc layer until finally reaching an average decrease of 93% and 96%, respectively, as compared with bare iron. It was found that the decrease in the permeation rate of hydrogen through the iron membrane was due: (i) to the decrease of hydrogen discharge rate and (ii) to the suppression of hydrogen absorption and adsorption on the deposited zinc layers. The kinetic parameters obtained from the model, along with the observation that permeation was decreased even when the cathodic current was the same (at a given cathodic potential), indicated that the decrease in permeation when zinc-nickel is plated compared to bare iron is due to a decrease in the absorption of atomic hydrogen (shown by a decrease in absorption-adsorption constant, k ). The kinetic parameters obtained from the model, along with the observation that permeation was decreased even when the cathodic current was the same (at a given cathodic potential), indicated that the decrease in permeation when zinc-nickel is plated compared to bare iron is due to a decrease in the absorption of atomic hydrogen

The dynamic mechanical properties of a uniaxial continuous carbon fiber-thermoplastic composite were found to degrade significantly when subjected to anodic and cathodic currents in the presence of seawater. The composite tested was made of PAN-based graphite fibers (50 vol%) in Du Pont s J-2 thermoplastic resin (nylonbased). The shear storage modulus, G′, and the shear loss modulus, G", of the composite were measured by subjecting a rod-shaped sample to small amplitude torsional oscillations. The moduli remained constant over time when the sample was in air and when it was submerged in seawater in the absence of applied currents. Both moduli decreased to ∼45% of their initial values when a constant anodic current of density 0.414 $μ$A/cm2 was applied for 2 h. A cathodic current of the same density and duration caused the moduli to decrease to ∼63% of their initial values. The moduli remained at these low levels after the current had been turned off. Inspection, under a scanning electron microscope, of the sample exposed to the anodic current revealed numerous cracks in the polymer matrix. In the sample exposed to the cathodic current, the fibers separated from the matrix of the composite.