Phase stability and effects of sintering atmosphere on the crystalline structure of Np-doped yttria-stabilized zirconia (YSZ) were evaluated in comparison with those same properties and conditions for Ce-doped YSZ. Different sintering atmospheres for Ce-doped YSZ led to differences in phase formation through reduction of the dopant from Ce 4؉ to Ce 3؉ . On the other hand, YSZ specimens containing up to 40 mol% Np formed only a fluorite-structure phase regardless of sintering atmosphere. Yttria-stabilized zirconia thus seems to accommodate Np within a wide range of concentrations and to have excellent phase stability under both oxidizing and reducing atmospheres.
The sorption behavior of Cs and Sr ions on natural clay minerals such as sand, bentonite and loam, and mixtures of bentonite-sand and -loam was studied under static condition.It was found that the distribution ratio of Sr ion on bentonite and loam are influenced by H ion concentration of solution, along with the concentration of ion of interest. The obtained results revealed that the distribution ratio of ion on the clay mixture can be expressed in terms of distribution ratio of each constituent of the mixed sorbent, provided that the corrections for pH and sorbed ion concentration of solution are made.
Sorption of Np (V) ion on a tuffaceous loam was studied under static and flowing conditions. The obtained results revealed that the distribution ratio of Np ion was influenced by pH and Ca ion concentration of the solution, probably because of the change in surface charge of loam with pH and of the coprecipitation due to the formation of calcium carbonate. The Np ion flowing down the column of the sorbent showed a breakthrough curve which enabled one to calculate the distribution ratio and the dispersion coefficient of the ion in the clay using the model for the process limited by the one-dimensional dispersion.
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