Phase evolution and aqueous durability of nano-grained Gd2HfxZr2-xO7 ceramics for nuclear-waste immobilization

Nanograin Gd 2 Hf x Zr 2- x O 7 (GHZO, 0.0 ≤  x  ≤ 2.0) ceramic was first designed for use as a matrix for immobilizing radionuclides. • The optimal hafnium content ( x Hf ) in GHZO (0.0 ≤  x  ≤ 2.0) ceramic was studied and revealed. • Hf-doping can significantly improve the mechanical properties and aqueous corrosion resistance of Gd 2 Zr 2 O 7 material. • The study provides new guidance for the design of HLW curing material with high-performance and environmentally friendliness. A series of novel nanograined Gd₂Hf ₓ Zr₂₋ ₓ O₇ (GHZO, 0.0 ≤  x  ≤ 2.0) ceramic samples, designed for nuclear-waste immobilization, were successfully fabricated in this study. The microstructural features, phase evolution, and aqueous corrosion resistance of these samples were thoroughly studied. Results indicated that the GHZO samples (0.0 ≤  x  ≤ 2.0) crystallized into a pyrochlore-type structure. As the Hf proportion ( x Hf ) increased from 0.0 to 2.0, the average grain sizes of the GHZO samples remained relatively stable, ranging from 260 to 280 nm. Their relative densities also remained between 95 % and 96 %. The hardness of the GHZO-1.0 sample reached 21.08 GPa, which was significantly higher than that of the GZO (7.91 GPa) and GHO (10.61 GPa) samples. The leaching rates ( LR ) of Zr and Hf in the GHZO-1.0 sample were 1.0 × 10⁻⁷ and 6.8 × 10⁻⁸ g·m⁻²·d⁻¹, respectively, after 42 days of leaching. These values were notably lower than the Zr leaching rate of the GZO sample (8.0 × 10⁻⁷ g·m⁻²·d⁻¹) and Hf leaching rate of the GHO sample (2.9 × 10⁻⁷ g·m⁻²·d⁻¹). This enhanced aqueous durability could be attributed to the higher configurational mixing entropy and lattice distortion. A series of novel nanograin Gd 2 Hf x Zr 2- x O 7 (GHZO, 0.0 ≤  x  ≤ 2.0) ceramic samples designed as a nuclear waste forms, were successfully fabricated. The microstructure features, phase transition behavior, and aqueous corrosion resistance were systematically investigated. After 42 days test, the normalized release rates of Zr and Hf elements in the GHZO-1.0 specimen were 1.0 × 10 −7 and 6.8 × 10 −8 g ·m −2 ·d −1 , respectively, much lower than the LR Zr of GZO specimen (8.0 × 10 −7 g ·m −2 ·d −1 ) and LR Hf of GHO specimen (2.9 × 10 −7 g ·m −2 ·d −1 ) owing to the increase of mixed entropy and lattice distortion, exhibiting excellent aqueous durability. The study provides new guidance for the design of HLW curing material with high-performance and environmentally friendly. Download: Download high-res image (393KB) Download: Download full-size image