Supercritical hydrothermal synthesis of UO2+x: stoichiometry, crystal shape and size, and homogeneity observed using23Na-NMR spectroscopy of (U, Na)O2+x

Chihiro Tabata, Kenji Shirasaki, Ayaki Sunaga, Hironori Sakai, Dexin Li, Mariko Konaka, Tomoo Yamamura

Research output: Contribution to journalArticlepeer-review


The hydrothermal synthesis of pure uranium dioxide under supercritical water (SCW) conditions was investigated using a starting material composed of a uranyl(vi) nitrate solution at 450 °C. The synthesis was conducted using an autoclave method for 30 min and yielded UO2+xparticles with nonstoichiometries, shapes, and sizes depending on additives such as ethanol, ammonium carbonate, guanidine carbonate, and several aldehydes. The nonstoichiometry,i.e., the value ofxin UO2+x, varied from 0.03 with ethanol to 0.20 with a combination of ethanol and guanidine carbonate. The crystallite size was the largest (57 nm) with ethanol and methanol, and the smallest (37 nm) with propionaldehyde. Additionally, the morphology of the UO2+xparticles was modified from a spherical shape with a diameter of 0.20 μm to a rectangular parallelepiped shape with a size of 2.25 μm × 0.50 μm. The23Na-NMR spectra of the Na-doped UO2+xsamples indicated high homogeneities in the products prepared using SCW hydrothermal synthesis. The SCW hydrothermal synthesis may be a promising method for producing homogeneous UO2+xand its solid solutions with well-defined nonstoichiometries (x), shapes, and sizes.

Original languageEnglish
Pages (from-to)8660-8672
Number of pages13
Issue number48
Publication statusPublished - 2021 Dec 28

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics


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