The plutonium-oxygen phase diagram in the 25-900 [degrees]C range: Non-existence of the PuO sub(1.515) phase

Evaluation of data for phases formed in the Pu-O system at temperatures below 900 [degrees]C shows that the observed oxides are not at equilibrium. Results are consistent with coexistence of a hexagonal solid solution (hex-PuO sub(1.5+z), [< or =, slant] z [< or =, slant] 0.010) and a cubic ph...

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Bibliographic Details
Published in:Journal of nuclear materials 2015-03, Vol.458, p.275-280
Main Authors: Haschke, John M, Dinh, Long N, McLean, William II
Format: Article
Language:English
Subjects:
Eutectic decomposition
Nuclear engineering
Oxides
Peritectic reactions
Phase diagrams
Plutonium
Solid solutions
Transformations
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Summary:Evaluation of data for phases formed in the Pu-O system at temperatures below 900 [degrees]C shows that the observed oxides are not at equilibrium. Results are consistent with coexistence of a hexagonal solid solution (hex-PuO sub(1.5+z), [< or =, slant] z [< or =, slant] 0.010) and a cubic phase (cub-PuO sub(1.60)) in equilibrium at 800 [degrees]C, but fail to confirm that the O/Pu ratio of the body-centered-cubic (bcc) oxide formed near the sesquioxide composition is 1.515 (1.52) or that bcc-PuO sub(1.515) is formed by the peritectic reaction of hex-PuO sub(1.510) with cub-PuO sub(1.60). Stable Pu(IV)/Pu(III) ratios observed for products of the Pu-H sub(2)O reaction correspond to members of the Pu sub(n)O sub(2n-2) homologous series, but a product is not formed at O/Pu = 1.515. Metastable bcc-PuO sub(1.50) (n = 4) and stable hex-PuO sub(1.5+z) coexist below 285 [degrees]C, the point at which reversible eutectic decomposition of cubic PuO sub(1.60) (n = 5) produces a non-equilibrium mixture of bcc-PuO sub(1.50) and sub-stoichiometric dioxide (PuO sub(2-y)). Transformation of bcc-PuO sub(1.50) to stable hex-PuO sub(1.50) and reactions of the hexagonal oxide to form higher-composition cubic phases are kinetically hindered. An alternative diagram describing non-equilibrium chemical behavior of the Pu-O system is presented.
ISSN:0022-3115
DOI:10.1016/j.jnucmat.2014.12.106