Determination of silicate liquid thermal expansivity using dilatometry and calorimetry
b'A method for the determination of relaxed silicate liquid molar volume and expansivity at temperatures\\njust above the glass transition is discussed. The method involves the comparison of heat capacity and molar\\nexpansivity in the glass transition region. Glassy and liquid heat-capacity data are obtained using differential\\nscanning calorimetry, and glassy thermal expansion data are obtained using scanning dilatometry. The molar\\nexpansivity of the liquid is calculated by a fictive temperature normalization of the relaxation behavior of both\\nthe heat capacity and the molar expansivity in the glass transition region, with the normalized heat capacity curve\\nbeing used to extend the dilatometric data into the liquid temperature range. This comparison is based upon the\\nassumed equivalence of the parameters describing the relaxation of volume and enthalpy.\\nThe molar expansivity of relaxed sodium trisilicate (Na2Si3O7) has been determined in this manner at temperatures\\nabove the glass transition temperature. This low-temperature determination of liquid molar expansivity has\\nbeen tested against high-temperature liquid expansivity data obtained from high temperature Pt double bob Archimedean\\nbuoyancy measurements. The low-temperature molar expansivity (26.43\\xb10.83xl0~4 cm3 mole"l\\u03b2C_1\\nat 540\\xb0C) determined in this manner agrees within error with the high-temperature molar expansivity\\n(23.29\\xb11.39xl0~4 cm3 mole^\\xbaC1 at 1400\\xb0C). This dilatometric/calorimetric method of liquid molar expansivity\\ndetermination greatly increases the temperature range accessible for thermal expansion measurements. A\\nweighted linear fit to the combined low and high temperature volume data gives a molar expansivity of\\n23.0010.25x10^ cm3 mole^\\xbaC"1. The volume-temperature relationship thus derived reproduces the measured\\nvolumes from both dilatometry and densitometry with a RMSD value of 0.033 cm3 mole"1 or 0.14%. This\\nrepresents a substantial increase in precision, which is especially important for liquids whose high liquidus\\ntemperatures restrict the temperature range accessible to liquid volume determinations.'