A low-temperature molten salt synthesis strategy of Eu2Ti2O7 ceramic enabling ultra-durable glass-ceramic waste forms

The conventional solid-phase sintering method for the preparation of Ln2Ti2O7 ceramics using oxides as reactants generally requires higher temperature, larger pressure, and greater energy consumption. In this paper, we synthesize a Eu2Ti2O7 ceramic powder in relatively low-temperature molten salt (KCl-NaCl) using Eu2O3 powder and TiO2 powder as reactants at 1000 °C. The results of XRD, SEM, and element mapping indicate that the product have high phase purity, good crystal morphology and uniform chemical composition. Moreover, Eu2Ti2O7-based glass-ceramics are obtained by sintering with different contents of borosilicate glass. The SEM images of glass-ceramic show that almost no obvious defects or voids are found on the surface of the samples. The values of water absorption for all glass-ceramic waste forms are less than 0.5%. With the increase of ceramic embedding rate, the hardness of the glass-ceramics first increases and then decreases, while the density gradually increases. When the embedding rate increased to 30 wt.%, the hardness of glass-ceramic reaches a maximum of 19.53 GPa. The glass-ceramic waste form embedded with 30% Eu2Ti2O7 exhibits very stable chemical durability with a low leaching rate of 1.42×10-8 g·m-2·d-1 at 90 °C even after 28 days.