DTA/TGA/DSC and densification data for iron phosphate glasses having natural UO2.67 or surrogate Bi2O3 added

Abstract

A new set of iron-uranium phosphate glasses containing (1–20) UO2.67. (10–20) Fe2O3. (55–68) P2O5 (mass/%) were melted adequately. They were tested for glassy matrices to immobilize hazardous wastes such as radioactive ones. Likewise, new compositions had uranium oxide replaced with Bi2O3. Differential Thermal Analysis (DTA), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and dilatometry measurements allowed us to study the thermal properties. TGA runs on phosphate glasses containing Fe and U oxides indicated that on heating the glasses, up to TS (dilatometric softening point), the Fe2+ ions oxidized irreversibly to Fe3+ ions which can increase the thermal stability of the glasses by delaying (or even avoiding) crystallization. The densification behavior, applied to pressed powder pellets of ground glasses, from controlled heating rate (CHR) runs (Δl/lo versus T/K), shows relative sample length change versus temperature during heating, provided further thermal data like densification details as well as definition of ranges of creep stability. Various DTA, DSC methods allowed estimating the activation energy for crystallization of these kind of glasses. In addition, separate crystallization treatments for a particular composition provided samples suitable to study the shape and content of crystals with the Scanning Electron Microscope (SEM)/Energy-Dispersive X-ray Spectroscopy (EDS) technique. Thus, a new family of iron-phosphate glasses having Na2O, Al2O3 added (RR6—RR62—RR63) is presented and discussed here and compared to various glasses (like PFeOx and PFeUOx) previously developed at the Bariloche Atomic Center, Argentina (CAB) for radioactive waste immobilization. Activation energies depicted roughly similar values for viscous flow densification of glasses melted with controlled amounts of UO2 for the earlier compositions as well as for the new formulations.