Behavior and Removal of Impurity Sulphate in Sol-Gel Process for ThO₂ and (Th, U)O₂ Microsphere Fabrication

抄録

The behavior of impurity sulphate, fed from source Th(NO₃)₄, in a sol-gel process for fabricating (Th, U)O₂ microspheres is studied. In sols, almost all the sulphates are adsorbed on colloid particles regardless of U content U/M (M : Th+U). However, the sulphate in gel-microspheres is easily washed out for U/M higher than 10 mol/0, while not for lower U/M ; especially, the sulphate in ThO₂ gel-microspheres is difficult to be removed even by long-time washing. The sulphur remaining in the gel-microspheres is able to be removed out by heating in air or steam at 1, 000°C for 3 h ; as for ThO2, slight residue is found but not after 1, 300°C heating. On the other hand, heating them in Ar-4%H₂ atmosphere, even at 1, 500°C, allows most of the sulphur to remain as an unidentified M-O-S compound ; during the heating, the sulphur is gradually released by the reaction with H₂ to form H₂S.
The study finds optimum conditions for removal of the impurity sulphate in the sol-gel process.