SUPERCOOLED DIOPSIDE MELT: CONFIRMATION OF TEMPERATURE-DEPENDENT EXPANSIVITY USING CONTAINER-BASED DILATOMETRY

Abstract

The expansivity of supercooled diopside liquid has been determined using techniques of container-based dilatometry. Two thermal strategies have been employed, one in which the sample is brought to volumetric equilibrium by long-duration dwells at low temperatures (817 °C) and one in which scanning dilatometry of the sample has been performed at somewhat higher temperatures (890-913 °C). The results of both experiments yield a supercooled liquid expansivity for diopside liquid in the temperature range of 817-913 °C of 84.4 ± 2.8 × 10-4 cm3/mol K. The expansivity is 65% higher than that obtained for diopside melt obtained at superliquidus temperatures using the double bob Archimedean method. Combined fitting of the new low temperature, volume-temperature data from the present study and the superliquidus data from the literature has been performed. The combined fit yields the following equations for the volume-temperature relationship of diopside liquid (T=temperature in °C):<formula form="DISPLAY"><![IGNORE[$$\hskip -.3mm\eqalign{\hbox{Specific volume} \ (\hbox{cm}^3\! / \hbox{mol }\hbox{K}) & = 31.73\pm 0.16\times 10^{-2} \cr & \quad+ 59.64 \pm 3.1 \times 10^{-6} T \cr & \quad-11.23 \pm 1.29 \times 10^{-9} T^{2}} \fleqno{}$$]]></formula><formula form="DISPLAY"><![IGNORE[$$\hskip -1.1\eqalign{\hbox{Molar volume} \ (\hbox{cm}^3\! / \hbox{mol }\hbox{K})& = 69.40 \pm 0.46 + 12.40 \pm 0.82 \times 10^{-3} T \cr & \quad-2.37 \pm 0.34 \times 10^{-6} T^{2}}$$]]></formula> The standard error of the fit using both equations reproduces the volume-temperature data for diopside liquid within experimental error. This result reconciles the disparate values of expansivity measured at low temperatures in the supercooled state and at superliquidus temperatures and confirms the temperature-dependence of the expansivity of diopside liquid. Comparison with previous low temperature estimates of melt volume and expansivity are discussed in light of these new results.