Thesis (Ph. D.)--University of Rochester. Dept. of Chemistry, 2016.
The interaction of tritium with aluminum, copper, stainless steel, and gold plated substrates was studied using a low-pressure, argon plasma, as well as thermal desorption spectroscopy. These experimental methods allowed the influence of modifying metal surfaces on the absorption and adsorption of tritium to be measured. Stainless steel surfaces were modified by mechanical polishing, electropolishing, selective oxidation pre-treatments, and gold plating. The only surface modification performed on aluminum and copper samples was gold plating.
Use of the low-pressure plasma constitutes a novel approach to studying tritium migration and to measuring the quantity of adsorbed tritium. The migration of tritium was inferred from experiments, where a metal sample was exposed to a pulsed plasma. In such a method, tritium migration to the surface in between each pulse influences the quantity of tritium removed during subsequent plasma pulses. The results of these measurements indicated that the mechanism for tritium migration to the surface was limited by diffusion out of the underlying metal lattice. The measured rate of tritium migration to the surface does not appear to depend strongly on the metal type or surface modification.
Thermal desorption experiments were used to measure the influence of modifying metal surfaces on the total absorption of tritium. Thermal desorption involves heating samples to high temperatures for protracted periods of time, in order to remove all tritium contained within the metal lattice. These measurements indicated that modifying a metal surface significantly influences the total absorption of tritium during room temperature (25°C) exposures.
Finally, a quantitative tritium migration model (QTRIMM) was developed in this work to describe the transport of the isotope through metal lattices. Additionally, QTRIMM includes a condition that relates the tritium concentrations adsorbed to the surface to the concentrations within the metal lattice. This model represents a major step forward in describing the migration of tritium through metal substrates, as many previous transport models have not included a condition for tritium adsorption. As demonstrated in this study, QTRIMM describes the measured data reasonably well.
