Date of Award
Doctor of Philosophy (PhD)
Materials Science and Engineering
The interaction between hydrogen isotopes and irradiation defects in nickel is studied using Gas-phase Permeation and Thermal Desorption Analysis techniques. The work was motivated by the need for the understanding and control of tritium diffusion and trapping in structural materials of the first generation of D-T fusion reactors, as well as by the need for minimizing helium "ash" in the plasma. Major attention was given to the study of relationships between helium defect configuration and deuterium diffusion and trapping behavior.
Permeation results show that crystalline defects such as dislocation loops produce no measurable effect on deuterium permeation in the temperature range of 373 K - 573 K, whereas helium defects decrease the apparent diffusivity and, sometimes, the permeability of deuterium by several orders of magnitude, indicating a strong trapping effect for hydrogen isotopes. Thermal treatments at elevated temperatures of samples pre-implanted with helium ions resulted in a newly observed abnormal aging history dependence on deuterium diffusion and permeation behavior. The basic aspects of this abnormal behavior were examined and analyzed.
Thermal desorption technique was used to obtain additional information on helium trapping mechanisms: for examples, the effective binding energies of deuterium to helium defects consist of a distribution of values and are in the range of 0.4 - 0.6 eV with higher values observed when helium bubbles formed; the trapping efficiency decreases from> 1 to < 0.3 when the helium fluence increases from 1x10¹⁵ to 4x10¹⁷/cm²; thermal treatments of these samples resulted in a decrease in the trapping efficiency that was also dependent on the initial helium fluences. An interesting phenomenon, "H" enhancement of helium release, was observed and analyzed using the Hydrogen-Assisted Cracking model.
Shi, San-Qiang, "Permeation and Thermal Desorption Studies of Deuterium Diffusion and Trapping in Ion-Implanted Nickel" (1991). Open Access Dissertations and Theses. Paper 3589.