Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemistry

Supervisor

Dr. Jungsook Clara Wren

Abstract

This thesis presents work on the mechanism and kinetics of the surface film reactions involving the conversion of aqueous species on solid surfaces, and specifically, the reactions of iodide and bromide on silver oxide on silver substrate. These reactions provide a method of immobilizing unwanted halides and are particularly suited to control of hazardous radioactive iodine. Potential applications of this research include nuclear reactor safety and post-accident radioiodine management, and the safe production and use of the medical isotope 131I.

The aqueous-solid conversion of reaction Ag2O with X-(aq) to form AgX on a Ag substrate can occur via one of three main reaction pathways. The first pathway is a chemical reaction that occurs at the oxide/solution interface. This is a molecule-molecule interaction that does not involve charge transfer. A second, electrochemical (galvanic coupling) reaction pathway is possible where the reduction of Ag2O to Ag is coupled to the oxidation of Ag to AgX. Lastly, conversion can proceed via a dissolution pathway where Ag+(aq) released from Ag2O dissolution reacts with X-(aq) in solution and AgX precipitates on the Ag surface. The fastest reaction path will determine the nature of the AgX film that is formed. From the perspective of immobilizing the halide ion, the dissolution pathway would be least effective. We are interested in understanding how the system thermodynamics and mass transport properties affect the relative pathway rates.

The kinetics of the Ag/Ag2O/X-(aq) solid-liquid interfacial reactions were studied using a range of electrochemical techniques. Different electrochemical measurements provided chemical kinetic information. The diffusion-limited and surface reaction-limited components of the total reaction rate were separated by measuring the reaction time as a function of the electrode rotation rate. Linear polarization and potentiostatic polarization were used to probe the rate of the galvanic coupling reaction.

These studies concluded that the reaction of iodide with silver oxide proceeds mainly via the chemical reaction pathway, while the corresponding reaction of bromide proceeds via a combination of the galvanic coupling and the dissolution reaction pathways.


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