Phase evolution and chemical stability of the Nd2O3-ZrO2-SiO2 system synthesized by a novel hydrothermal-assisted sol-gel process

Abstract

A hydrothermal-assisted sol-gel process, a novel method of combining both advantages of sol-gel and hydrothermal processes, was developed to synthesize dense Nd-doped ZrSiO4 ceramics with high Nd (surrogate for trivalent actinides) loading at low sintering temperature (1723 K) and short time (6 h). The evolutions of phase and microstructure of the obtained ceramics with the varying composition, sintering temperature and pH value were investigated. The chemical durability of the ceramics was also evaluated. The results show that the properties of ceramics strongly depend on sintering temperature and pH value. The acidic condition is beneficial to phase formation and densification of ZrSiO4 ceramics. It was found that the maximum immobilization capacity of Nd in the single-phase ZrSiO4 ceramics is highly dependent upon the synthesis method and sintering temperature. With decreasing sintering temperature, the maximum immobilization capacity increases. And the immobilization capacity of Nd in ZrSiO4 ceramics was found to be enhanced by the hydrothermal-assisted sol-gel method. Furthermore, the normalized release rate of Nd in Nd-doped ZrSiO4 ceramics decreases with increasing time and remains almost unchanged (∼10−4 g m-2 d-1) after 28 days, and the fractional release of Nd in all samples is about ∼10−5 wt%, exhibiting high chemical stability.