Synthesis and characterization of rare-earth doped aluminium phosphate glasses

Sodium aluminium phosphate (NAP) glass is a potential candidate for the immobilization of minor actinides (MA). The composition of the NAP glass 38Na2O–30Al2O3–32P2O5 (mol %) was found to be the optimal choice, through experimental trials and specimens of this glass containing 1, 5, 10 and 15 wt% of the rare-earths (Ce, Pr, Nd and Gd-as surrogates for MA) were prepared by the melt quench technique. All these samples were X-ray amorphous, and were found to contain (PO4)−2 Q1 and (PO4)−1 Q2 units. Both Al2O3 and rare-earths were found to modify the structure of the phosphate glass significantly. Al2O3 plausibly acts as a network former at higher concentrations. The melting point, glass transition temperature, viscosity, Angell thermal stability and glass forming ability of these glasses increase with the concentration of the dopants, while their fragility decreased. Absolute values of the heat capacity of these glasses (Cp) as well as the attendant change in the heat capacity during the glass transition ΔCp showed an increase up to 5 wt % doping and a decrease subsequently when the concentration of the dopants were increased up to 15 wt%. Glasses containing 10 and 15 wt% dopants show sharper crystallization peaks while the crystallization is less pronounced in the rest of the glass samples. The rare-earth cations improve the strength of the glass when doped up to 5 wt%, beyond which the rigidity of the structure begins to fall. The networking due to complexation diminishes and leads to weaker chains resulting in the glasses with higher concentration of the rare-earths modifiers. These first results on the dependence of the structure and thermal properties of the NAP glass 38Na2O–30Al2O3–32P2O5 (mol%) doped with rare-earth reported here show that this glass could serve as a suitable matrix for immobilizing rare earths and minor actinides.