Chemical durability of Gd2Zr2O7 transparent ceramics under different pH conditions

To study the influence of acidic and alkaline environments on the leaching behavior of Gd2Zr2O7 immobilization matrix in deep geological landfills, and to directly reflect the change of leaching behavior on its appearance, the chemical durability of Gd2Zr2O7 transparent ceramics was investigated in different pH environments in this study. The leaching results demonstrate that the normalized leaching rates in acidic environments are higher than those in alkaline and neutral environments. The transmittance of the leached transparent ceramics in the visible range decreases slightly at pH ≤ 9.0, and the macroscopic color of all samples fades after leaching. The leaching behavior leads to lattice contraction and increment of surface roughness, but it exhibits no significant effect on the surface elemental distribution. In conclusion, Gd2Zr2O7 transparent ceramics show excellent chemical durability in a weak alkaline environment, and the leaching behavior causes the discoloration of Gd2Zr2O7 transparent ceramics.

Study of The Effect of TiO2 Addition On The Crystalline Phases, Structure and Chemical Durability of a Nuclear Glass Ceramic

This study focused on the effect of TiO 2 addition on the crystallines phases’ formation, structure and chemical durability of a nuclear glass ceramic constituted by an aluminosilicate glass in the system: SiO2-Al2O3-CaO-MgO-ZrO2-TiO2 . The materials with four contents of TiO2 , ranging from 4.11 to 7.11 wt.%, are synthesized by a discontinuous method,. For the whole of materials, X-ray diffraction analysis allow identifying an aluminosilicate belonging to pyroxenes silicates family as a main phase, powelite and calzirtite. Both SEM and DTAanalyses confirmed these results. The materials FTIR analysis reveals the glass ceramics complex chemical composition. MCC1 and MCC2 tests, performed on selected glass ceramic materials, indicate that the materials with 4.11 and 5.11 wt.% TiO2 are the most durable against Si, Al, Mg and Ce elements release, in MCC2 test; The results make conclusions valuable on the selection of such glass ceramics as candidate for the disposal of high-level waste.

Aqueous alteration of silicate glass: state of knowledge and perspectives

The question of silicate glass chemical durability is at the heart of many industrial and environmental issues, with certain glasses, such as bioglasses, needing to transform rapidly, while others, like nuclear glasses, extremely slowly. Due to the wide diversity of the chemical composition for these types of materials and their metastability—no thermodynamic equilibrium can be reached between glass and solution—the evaluation of chemical durability remains a scientific challenge. In this article, we review the current state of knowledge on glass alteration mechanisms and kinetics, and point to some perspectives for glasses for which no direct experimental validation is currently possible. Thanks to the development of novel techniques and international collaborations, a better understanding of the mechanisms involved has been achieved. Mechanistic models have been developed at some specific scales, although holistic models still need further development to link the various scales and perform reliable predictions.