Publications

A new electrokinetic technology has been developed for in-situ decontamination of hexavalent chromium in sand. Imposition of a constant potential gradient across the soil matrix through a graphite cathode and iron anode resulted in successful migration of chromate towards the anode. The hexavalent chromium ions are reduced to the harmless trivalent form by chemical reaction with the anodic electrochemical dissolution product, Fe2+. The alkaline front generated at the cathode due to water reduction flushes across the cell and favors faster transport of chromate by enhancing its conductivity. The acidic front generated due to water oxidation at the anode remains adjacent at the electrode-sand interface due to its consumption by the corrosion reaction with iron. The lower production rate of H+ is also due to the competing anodic dissolution reaction. The low pH at the anodic region favors the reduction of hexavalent chromium to its trivalent state. The experimental results are compared with a theoretical model developed from first principles. The water electrolysis reactions at both electrodes, the sorption processes in sand and the water hydrolysis reaction have been included in the model. Concentration profiles for the movement of ionic species under a potential field were simulated for different times. The model predicts the sweep of the alkaline front across the cell due to the transport of OH- ions. Comparison of the chromate concentration profiles with experimental data after 28 days of electrolysis shows good agreement. The potassium cations are positively charged and remained at the cathode where they had been placed initially. The good agreement between the model and the data demonstrates that the analysis is likely to be an accurate estimation of the physical situation, within the limits of the assumptions made.

The effect of temperature on the performance of a LaNi4.76Sn0.24 metal hydride electrode was investigated in the temperature range of 0 to 50°C. The electrode showed a maximum discharge capacity at 25°C. The total resistance increases with a decrease of temperature from 50°C to 0°C. The apparent activation enthalpies at different states of charge were determined by evaluating the polarization resistance at different temperatures. It was found that the apparent activation enthalpy is an indicator of the relative reaction rate of the charge-transfer reaction and hydrogen absorption.

A mathematical model is presented for the chloride induced corrosion of reinforcing steel bars (rebars) in concrete. The time for the chloride concentration level to exceed the threshold limit to initiate corrosion on the rebars was calculated using first principles. The model is characterized by the time dependent surface concentration due to adsorption at the surface of the concrete. Although the entire adsorption and diffusion process is complicated, the predictions of the model are consistent with experimental results. The simplifying assumption of a constant diffusion coefficient does not affect the model predictions. A finite difference model was used to study the effect of water and oxygen on chloride diffusivity in concrete. © 1997 Elsevier Science Ltd. All rights reserved.

The specific conductivity of concentrated solutions of potassium hydroxide was measured over a temperature range of -15 to 100°C for concentrations of 15 to 45 mass %. An empirical correlation relating temperature, mass % KOH, and specific conductivity was made with a correlation coefficient of 0.9995. Using experimental density data from Akerlof and Bender, the correlation was extended to relate temperature, molarity, and conductivity.

The effectiveness of 5-(4-pyridyl)-2,7-nonadiene, and 1 phenyl-2-propyn-ol (PP) on inhibition of the hydrogen evolution reaction on a 1010 steel membrane and on the degree of hydrogen ingress into the membrane was determined. Hydrogen evolution rates and permeation currents were monitored as a function of time at different applied potentials. In the presence of 0.5 g/liter PP in the electrolyte, the hydrogen discharge and permeation current density were inhibited by 98 and 95%, respectively.

Thermal films on titanium surfaces were formed by heating titanium samples in air at atmospheric pressure. The optical constants, thickness, and structure of the formed films at various temperatures and times of heating were investigated by ellipsometry and Raman spectroscopy. The complex index of refraction and the thickness of generated films were determined by comparing the experimental loci $Δ$ and $\Psi$ obtained by ellipsometric measurements with theoretical computed $Δ$ vs. $\Psi$ curves. It was found that the thickness inhomogeneity and porosity of formed films increase with increasing temperature and the duration of the thermal treatment. Beyond a certain critical temperature, the appearance of some Raman bands and changes in their intensities indicated that the film transformed from amorphous to microcrystalline and crystalline structure.

Fuel cells are electrochemical devices that convert the chemical energy of a reaction directly into electrical energy. Among the several types of fuel cell, Proton Exchange Membrane Fuel Cell (PEMFC) is a suitable choice for distributed energy sources. In this paper, a mathematical model of 750W PEMFC is developed. This model describes the behaviour of PEMFC under steady-state and transient conditions. Novel feature of this model is integration of all possible dynamic equations like dynamics of the charge equations like dynamics of the charge double layer capacitance, lumped fuel cell body dynamics and anode and cathode channel dynamics into a single model. The VI characteristic of PEMFC is obtained for different values of input parameters. The transient response of the PEMFC model over short and long-time periods is analyzed. Finally, the behaviour of the PEM fuel cell model under a resistive load

General governing equations for a porous electrode containing three phases (liquid, solid, and gas) are developed using the volume-averaging technique. These equations include the mass transfer in each phase, ohmic drop in the liquid and solid phases, and the equations resulting from applying the principle of conservation of charge. The electrolyte is considered to be a concentrated binary solution.

Galvanostatic pulse and pulse reverse techniques have been used to study the plating of zinc-nickel alloys in the presence of nonyl phenyl polyethylene oxide. The effects of average current density, rotation speed of disc electrode and the presence of nonyl phenyl polyethylene oxide in the electrolyte on deposition of zinc-nickel alloys were evaluated. Zinc-nickel plating bath solution chemistry was studied by determining the equilibrium concentrations at various pH levels. It was found that the alloy composition was determined by solution equilibria, mass transfer of the electroactive species within the diffusion layer and by the surface coverage of nonyl phenyl polyethylene oxide.

A new in-situ technique was developed for hexavalent chromium removal from sand. Imposition of constant potential gradient across the soil matrix through a graphite cathode and iron anode resulted in successful migration of chromate towards the anode. The hexavalent chromium ions are reduced to harmless trivalent form by chemical reaction with the anodic dissolution product, Fe2+.