Abstract:

Nuclear energy conversion methods can be employed to meet growing energy needs, both terrestrially and in space. To accommodate increasing demands, a robust synthesis method is required for the fabrication of materials involved. Internal gelation is a sol-gel technique that can address the dust-formation issue associated with powder processing methods, and additionally offers benefits such as the fabrication of high purity products and the production of a versatile microspherical feedstock. However, the process is limited to metals that hydrolyze and precipitate at a pH below ~6-7. This dissertation explores applying internal gelation to the synthesis of γ-LiAlO2 as a tritium breeder blanket material for fusion energy applications and Nd2O3 as a surrogate for americium oxide radioisotope power system fuel.

Past work on γ-LiAlO2 synthesis via internal gelation found the final product to be lithium deficient. Complementary analytical techniques (e.g., XRD, FTIR, NMR) are utilized to determine the reaction pathway throughout the gelation process. These analyses identify the formation of a lithium-aluminum layered double hydroxide intermediate, which limits lithium content leading to lithium loss during synthesis. This work further explores infiltering as an alternative method of lithium introduction to overcome the stoichiometric limitations by providing an alternate reaction pathway and facilitate fabrication of pure γ-LiAlO2.

Neodymium does not form a gel via the typical internal gelation process due to its high pH of hydrolysis and precipitation. For the synthesis of Nd2O3, this work investigates the use of organic acids as complexing agents to produce gels without requiring neodymium hydrolysis. Introduction of citric acid as a reagent is found to produce robust neodymium citrate gels that yield high quality Nd2O3 microspheres upon heat treatment. Various analytical techniques (e.g., UV/Vis, TGA/DSC, SEM) are utilized to determine the chemistry of the citrate-modified internal gelation process and characterize the properties of the final Nd2O3 microspheres. In addition to initial properties of synthesized spheres, the stability of the Nd2O3 microspheres upon storage in ambient conditions is also assessed. While citric acid is the complexing agent primarily assessed, the use of other organic acids is also explored and mandelic acid was found to successfully form gel samples.

This research contributes to the fundamental understanding of the internal gelation process, primarily in support of the fabrication of nuclear energy relevant materials. While the work presented in this dissertation focuses upon the synthesis of γ-LiAlO2 and Nd2O3, these results pave the way for applying internal gelation to a wider variety of metals through exploring modifications to the technique.