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Grain growth and pore coarsening in dense nano‐crystalline UO 2+ x fuel pellets
Author(s) -
Yao Tiankai,
Mo Kun,
Yun Di,
Nanda Sonal,
Yacout Abedellatif M.,
Lian Jie
Publication year - 2017
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.14780
Subject(s) - grain growth , materials science , sintering , grain boundary , grain boundary diffusion coefficient , activation energy , pellets , annealing (glass) , grain size , microstructure , stoichiometry , chemical engineering , mineralogy , metallurgy , composite material , chemistry , engineering
Dense nano‐sized UO 2+ x pellets are synthesized by spark plasma sintering with controlled stoichiometries (UO 2.03 and UO 2.11 ) and grain sizes (~100 nm), and subsequently isothermally annealed to study their effects on grain growth kinetics and microstructure stability. The grain growth kinetics is determined and analyzed focusing on the interaction between grain boundary migration, pore growth, and coalescence. Grains grow much bigger in nano‐sized UO 2.11 than UO 2.03 upon thermal annealing, consistent with the fact that hyper‐stoichiometric UO 2+ x is beneficial for sintering due to enhanced U ion diffusion from excessive O ion interstitials. The activation energies of the grain growth for UO 2.03 and UO 2.11 are determined as ~1.0 and ~2.0 eV, respectively. As compared with the micrometer‐sized UO 2 in which volumetric diffusion dominates the grain coarsening with an activation energy of ~3.0 eV, the enhanced grain growth kinetics in nano‐sized UO 2+ x suggests that grain boundary diffusion controls grain growth. The higher activation energy of more hyper‐stoichiometric nano‐sized UO 2.11 may be attributed to the excessive O interstitials pinning grain boundary migration.