Self-propagating synthesis of Y2-xNdxTi2O7 pyrochlores using CuO as the oxidant and its characterizations as waste form

Abstract

In this study, Y2Ti2O7 pyrochlore waste forms were rapidly prepared by self-propagating high-temperature synthesis plus quick pressing (SHS/QP) using CuO as the oxidant and Ti as the reductant. As the surrogate of trivalent actinides, Nd was introduced to substitute the Y site with nominal formulation of Y2-xNdxTi2O7. Highly densified Nd-bearing Y2Ti2O7 pyrochlore waste forms were readily synthesized within 5 min from this process. The pyrochlore phase was generated as the exclusive ceramic phase within x ≤ 1.0, while higher Nd2O3 incorporation (x > 1.0) results in impurity phases. Phase separation can be detected in the ceramic matrix, which is actually composed of Nd-rich and Y-rich pyrochlore solid-solutions. The representatively selected waste form (Nd0.5) demonstrates promising aqueous durability as the 42 days normalized leaching rates of Cu, Y and Nd are measured to be 4.67 × 10−2, 4.42 × 10−5 and 3.17 × 10−5 g m-2 d-1.