Dingwell, Donald B.; Knoche, Ruth; Webb, Sharon L.
A volume temperature relationship for liquid GeO2 and some geophysically relevant derived parameters for network liquids.
In: Physics and Chemistry of Minerals, Vol. 19, No. 7: pp. 445-453
The thermal expansivity of liquid GeO2 at temperatures just above the glass transition has been obtained using a combination of scanning calorimetry and dilatometry. The calorimetric and dilatometric curves of c p and dV/dT are normalized to the temperature derivative of fictive temperature versus temperature using the method of Webb et al. (1992). This normalization, based on the equivalence of relaxation parameters for volume and enthalpy, allows the completion of the dilatometric trace across the glass transition to yield liquid expansivity and volume. The values of liquid volume and expansivity obtained in this study are combined with high temperature densitometry determinations of the liquid volume of GeO2 by Sekiya et al. (1980) to yield a temperature-volume relation for GeO2 melt from 660 to 1400 °C. Liquid GeO2 shows a strongly temperature-dependent liquid molar expansivity, decreasing from 20.27 × 10–4 cm3 mol–1°C–1 to 1.97 × 10–4cm3 mol–1 °C–1 with increasing temperature. The coefficient of volume thermal expansion ( v ) decreases from 76.33 × 10–6 °C–1 to 2.46 × 10–6 °C–1 with increasing temperature. A qualitatively similar volume-temperature relationship, with v decreasing from 335 × 10–6 °C–1 to 33 × 10–6 °C–1 with increasing temperature, has been observed previously in liquid B2O3. The determination of the glass transition temperature, liquid volume, liquid and glassy expansivities and heat capacities in this study, combined with compressibility data for glassy and liquid GeO2 from the literature (Soga 1969; Kurkjian et al. 1972; Scarfe et al. 1987) allows the calculation of the Prigogine-Defay ratio (), c p -c v and the thermal Grüneisen parameter ( th) for GeO2. From available data on liquid SiO2 it is concluded that liquid GeO2 is not a good analog for the low pressure properties of liquid SiO2.