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Phase Behavior Studies on Neptunium Oxide–Zirconium Oxide and Neptunium Oxide–Calcia‐Stabilized Zirconia Systems
Author(s) -
Sali Sanjay K.,
Kulkarni Narendra K.,
Phal Dilip G.,
Aggarwal Suresh K.,
Venugopal Venkatarama
Publication year - 2010
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/j.1551-2916.2010.03825.x
Subject(s) - neptunium , fluorite , cubic zirconia , zirconium , tetragonal crystal system , actinide , phase (matter) , chemistry , inorganic chemistry , solid solution , materials science , oxide , nuclear chemistry , metallurgy , ceramic , organic chemistry
Phase relations in the systems NpO 2 –ZrO 2 and CaO‐stabilized zirconia–NpO 2 were studied for the suitability of immobilization of minor actinide neptunium in crystalline zirconia‐based waste forms. Phase studies of NpO 2 –ZrO 2 system were studied for the first time. The solid‐state reaction between NpO 2 and ZrO 2 in air at 1400°C showed the formation of Zr y N p 1‐ y O 2 type of phases having single‐phase fluorite, single‐phase tetragonal, and a mixture of fluorite and tetragonal solid solutions for zirconium concentration ranges 0< y ≤0.3, 0.8≤ y ≤0.95, and 0.3< y <0.8, respectively. Np 2 Zr 2 O 7 could not be prepared in contrast to reported trans‐plutonium pyrochlores. In the CaO‐stabilized zirconia–NpO 2 system, two fluorite‐types, zirconium‐rich and neptunium‐rich regions were observed. Forty mole% of NpO 2 can be incorporated in calcia‐stabilized zirconia forming fluorite‐type zirconium‐rich solid solution. The cubic unit cell parameter a varied linearly with neptunium concentration as: a (Å) = 5.135 + 0.309 (1− y ).