Preparation method and thermal properties of samarium and europium-doped alumino-phosphate glasses

摘要

The present work investigates alumino-phosphate glasses from Li_2O-BaO-Al_2O_3-La_2O_3-P_2O_5 system containing Sm~(3+) and Eu~(3+) ions, prepared by two different ways: a wet raw materials mixing route followed by evaporation and melt-quenching, and by remelting of shards. The linear thermal expansion coefficient measured by dilatometry is identical for both rare-earth-doped phosphate glasses. Comparatively to undoped phosphate glass the linear thermal expansion coefficient increases with 2× 10~(-7) K~(-1) when dopants are added. The characteristic temperatures very slowly decrease but can be considered constant with atomic weight, atomic number and f electrons number of the doping ions in the case of T_g (vitreous transition temperature) and T_(sr) (high annealing temperature) but slowly increase in the case of T_(ir) (low annealing temperature-strain point) and very slowly increase, being practically constant in the case of T_D (dilatometric softening temperature). Comparatively to undoped phosphate glass the characteristic temperatures of Sm and Eu-doped glasses present lower values. The higher values of electrical conductance for both doped glasses, comparatively to usual soda-lime-silicate glass, indicate a slightly reduced stability against water. The viscosity measurements, showed a quasi-linear variation with temperature the mean square deviation (R~2) being ranged between 0.872% and 0.996%. The viscosity of doped glasses comparatively to the undoped one is lower at the same temperature. Thermogravimetric analysis did not show notable mass change for any of doped samples. DSC curves for both rare-earth-doped phosphate glasses, as bulk and powdered samples, showed T_g values in the range 435-450℃ Bulk samples exhibited a very weak exothermic peak at about 685℃, while powdered samples showed two weak exothermic peaks at about 555℃ and 685℃ due to devitrification of the glasses. Using designed melting and annealing programs, the doped glasses were improved regarding bubbles and cords content and strain elimination.