Chemistry PhD Final Defense – Natalie Yaw

About the event

Speaker: Natalie Yaw

Group: Dr. Xiaofeng Guo

Title: DRIVERS OF STABILITY IN SOLID SOLUTION NUCLEAR CERAMICS AND CRITICAL METAL MINERALS

Abstract:

Nuclear ceramics, including minerals, fuels, and wasteforms, are an important class of materials which incorporate large, diverse fractions of actinides (An) and lanthanides (Ln). Studying how these mixing elements combine to (de)stabilize crystalline phases enables a deep understanding of how composition can influence structure and long-term behavior, allowing the intentional design of homogeneous materials or separations processes. This talk covers several recent studies which combine advanced structural and thermodynamic characterization to describe mixing behavior in solid solution nuclear ceramics and critical metal minerals. First, the thermal oxidation of uranium mononitride, an advanced ceramic fuel, is studied in-situ and anomalous thermal expansion is identified. Next, U-Th-Ce mixing is described in brannerite (UTi2O6) wasteforms using machine learning assisted experimental calorimetry, with both oxygen defects and cation-cation interactions identified as stabilizing features. Finally, Ln-F mineral formation under hydrothermal conditions is recreated in the laboratory, revealing the fractionation of light from heavy rare earth elements is driven by a combination of crystal strain and solution conditions.