Influence of water on the physical properties of fluoride glass

Several physical properties of ZBLAN glass, including their characteristic transformation temperatures, density, refractive index and ultrasonic velocity, were studied as a function of their residual water content. A series of samples with OH concentrations up to ∼ 0.0043 mol dm −3 was prepared. The OH content was determined for the partially hydrated glasses from FTIR measurements, using a known molar extinction coefficient value for the 2.9 μm band, assigned to fundamental OH stretching vibrations in Zr OH species. Molecular H 2 O was not found at the present levels of water concentration. The preliminary results obtained indicate that an increase in the OH concentration causes a decrease of the density and refractive index values, similar to what has been observed in v-SiO 2 , as opposed to the case of silicate glasses. This behavior was not expected, since ZBLAN glass has a complex structure closer to that of modified silicates than to v-SiO 2 . The effect of the OH concentration on the other physical properties was generally found to coincide with known trends for silicate glasses.