Abstract
Non-ideal thermodynamics of solid solutions can greatly impact materials degradation behavior. We have investigated an actinide silicate solid solution system (USiO4–ThSiO4), demonstrating that thermodynamic non-ideality follows a distinctive, atomic-scale disordering process, which is usually considered as a random distribution. Neutron total scattering implemented by pair distribution function analysis confirmed a random distribution model for U and Th in first three coordination shells; however, a machine-learning algorithm suggested heterogeneous U and Th clusters at nanoscale (~2 nm). The local disorder and nanosized heterogeneous is an example of the non-ideality of mixing that has an electronic origin. Partial covalency from the U/Th 5f–O 2p hybridization promotes electron transfer during mixing and leads to local polyhedral distortions. The electronic origin accounts for the strong non-ideality in thermodynamic parameters that extends the stability field of the actinide silicates in nature and under typical nuclear waste repository conditions.
| Original language | English |
|---|---|
| Article number | 34 |
| Journal | npj Materials Degradation |
| Volume | 5 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 2021 |
Funding
This work was supported by the institutional funds from the Department of Chemistry and New Faculty Seed Grant from ORAP at Washington State University. Funding for E.T.N. and J.M. was provided by the Department of Energy (DOE) Waste Treatment & Immobilization Plant (WTP) Federal Project Office under the direction of Dr. Albert A. Kruger, contract numbers DE-EM0002904 and DE-EM0003207. Funding for J.S.M.C. was provided by DOE Office of Nuclear Energy, Nuclear Energy University Programs, award # DE-NE0008689. Research presented in this article was also supported by the Laboratory Directed Research and Development (LDRD) program of Los Alamos National Laboratory (LANL) under project number 20180007 DR (to H.X.). LANL, an affirmative action/equal opportunity employer, is managed by Triad National Security, LLC, for the National Nuclear Security Administration of the U.S. DOE under contract 89233218CNA000001. A portion of this research used resources at the Spallation Neutron Source, the Oak Ridge National Laboratory, was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. DE-AC05-00OR22725. We also acknowledge the support from Alexandra Navrotsky Institute for Experimental Thermodynamics and the WSU-PNNL Nuclear Science and Technology Institute. We thank Dr. Francisco Espinosa for discussion and Mr. Ke (Edward) Zhao for help with visualization.
| Funders | Funder number |
|---|---|
| Alexandra Navrotsky Institute for Experimental Thermodynamics | |
| Department of Chemistry | |
| ORAP | |
| Scientific User Facilities Division | |
| WSU-PNNL Nuclear Science and Technology Institute | |
| U.S. Department of Energy | DE-AC05-00OR22725, DE-EM0003207, DE-EM0002904 |
| Office of Nuclear Energy | |
| Basic Energy Sciences | |
| National Nuclear Security Administration | 89233218CNA000001 |
| Oak Ridge National Laboratory | |
| Nuclear Energy University Program | DE-NE0008689 |
| Laboratory Directed Research and Development | |
| Washington State University | |
| Los Alamos National Laboratory | 20180007 |
