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The effect of starting material purity and reactive atmosphere on six ftuorozirconate glass compositions was examined. Compositions made with low purity starting materials showed a high degree of surface crystallization with absorption bands, tails, or shoulders present in the UV-Vis spectra. A shoulder located off theIR cutoff was also present in all low purity glass compositions. The high purity compositions exhibited sharp UV and IR cutoffs at ,...., 210 nm (47,600 em-•) and 7575 nm (1320 cm-1 ), respectively. T g and Tx values were determined for each composition using a DSC. There appeared to be no correlation between material purity and the value of glass formability index (Tx-Tg).

Two ZrF 4 -BaF 2 -LaF 3 -AIF 3 (ZBLA) and four ZrF,-BaF 2 -YF 3 -AIF 3 (ZBY A) glasses were immersed in a buffered base at 25°C for several days. They were then examined using an IR spectrophotometer in order to determine the effect on the optical properties, and a microhardness tester for surface degradation. The ZrF • content in these compositions ranged from 44 mol% to 57 mol%. IR analysis showed that the amount of hydroxyl and H 2 0 penetration was dependent upon the concentration of ZrF, in the glass. The IR characteristics of ZBYA-1, which contained 44 mol% ZrF 4 , did not appear to be affected by the aqueous environment, while ZBLA-20, which contained 57 mol% ZrF 4 , showed the presence of a large amount of hydroxyl and H 2 0. The base immersion did not appear to strongly affect the microhardness of the compositions.