Atomistic Thermodynamics of Water over Actinide Oxide  Surfaces: Implications on Stabilities and Morphologies

Authors: Niveen W. Assaf, Ibukun Oluwoye, Ali Marashdeh and Ali Elrashidi

DOI: https://doi.org/10.48103/jjeci8202025

JORDANIAN JOURNAL OF ENGINEERING AND CHEMICAL INDUSTRIES (JJECI)

Pages: : 214-226

Highlights

• Stability of water over actinide oxides was revealed.
• Dissociative adsorption is predominant on (100) and (110) surfaces.
• (111) surfaces were found to have a stable mixed water layer.
• Nanoparticles will adopt octahedral and truncated-octahedral shapes in moist media.
• The study provides insights into corrosion and catalysis.

 

Abstract

The surface free energy diagrams of water adsorption on the low-index surfaces of UO₂ and PuO₂ were calculated using the ab initio atomistic thermodynamics technique. The phase diagrams of both UO₂(100) and PuO₂(100) surfaces show that the dissociative H-OH adsorption of water exhibits higher stability for all applied coverages. Chemical potential, with PuO₂(100) stabilizing hydroxylated structures at lower chemical potentials than UO₂(100). On the (110) surfaces, dissociative adsorption is also preferred, but with reduced reactivity compared to (100); UO₂(110) supports hydroxylation at lower chemical potentials than PuO₂(110), indicating a greater tendency for early-stage protonation. On the closed-packed (111) surfaces, the stability diagrams revealed that only a mixed monolayer containing both molecular and dissociated water becomes stable, and only under more humid or elevated temperature conditions. The mixed adsorption phase on PuO₂(111) becomes stable at a lower chemical potential relative to UO₂(111), indicating slightly higher reactivity. The equilibrium morphology of UO₂ and PuO₂ nanoparticles in humid environments were predicted using the Wulff construction. The results showed that the (111) facets dominate across the full range of water chemical potentials, yielding octahedral nanoparticles. For PuO₂, a transition to truncated octahedral was observed  eV due to the emergence of (110) facets. These findings clarify the role of thermodynamic and kinetic variables affecting water interactions with actinide oxides, pertinent to corrosion, catalysis, and the performance of nuclear materials.

Paper type: Research Paper.

Keywords: uranium dioxide, plutonium dioxide, adsorption; DFT, wulff construction, stability, thermodynamic.

 Citation: Assaf, N., W., Oluwoye, I., Marashdeh, A., and Elrashidi, A. “Atomistic thermodynamics of water over actinide oxide  surfaces: implications on stabilities and morphologies” Jordanian Journal of Engineering and Chemical Industries, Vol. 8, No.2, pp:214-226 (2025).