Structural characterization of-high-zirconia borosilicate glasses using Raman spectroscopy

Polarized Raman spectra were obtained for a collection of borosilicate glas ses that have been developed as candidate compositions for the immobilizati on of wastes generated from the reprocessing of Zircaloy-clad spent nuclear fuel. Raman spectra were obtained for borosilicate glasses with zirconia c ompositions as high as 21 wt%, as well as for crystalline ZrO2 (baddeleyite ) and crystalline ZrSiO4 (zircon). As zirconia content in the glass is incr eased, two trends in the spectra indicate that the partially polymerized si licate tetrahedral network becomes more depolymerized: one, the polarized m id frequency envelope near 450 cm(-1), assigned to Si-O-Si symmetrical bend modes, decreases in area; and two. the higher frequency band assigned to S i-O stretch in Q(2) units (silicate chains) increases in area, while band a reas decrease for modes assigned to Si-O stretch in more polymerized Q(3) a nd Q(4) units (silicate sheets and cages). These trends take place whether the glass composition is relatively simple or considerably more complex. As zirconia concentrations in the glass increase beyond 15 wt%, a series of s harp lines are observed in the spectra from baddeleyite crystals. and to a minor extent Zn-Cr spinel phases, superimposed on broad features from the g lass matrix. A low intensity, broad band near 1400 cm(-1) in the glass spec tra is probably due to B-O stretch modes within BO3 units. (C) 2000 Elsevie r Science B.V. All rights reserved.