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This run features an aqueous solution that is approximately 15.5 wt.% Na2SO4. Initially, the pressure was about 56 MPa. 05/10/19 09:33:56: The run starts around T = 293 K with all liquid. The sample is gradually cooled and the volume decreases due to thermal contraction. 05/10/19 14:18:44: Upon supercooling to 286 K, crystals (presumably mirabilite) rapidly grow from the bottom of the image. (Gravity points down.) Although the mirabilite is denser than the original solution, the remaining water-rich solution is less dense, leading to a slight overall increase in volume. 05/10/19 14:43:44: With additional cooling, the crystals continue to grow. 05/10/19 18:35:44: After further cooling, over 10 degrees below the eutectic temperature, the system finally freezes and the screen goes dark as the tiny ice crystals scatter the light. Since this is in the Ice Ih regime, the volume increases significantly, and the pressure increases as well. 05/10/19 19:06:44: With the system frozen solid, the material in the tubing connecting the pressure cell to the volume and pressure sensors is also frozen, and those sensors no longer accurately track conditions inside the cell. 05/10/20 02:37:44: Start warming the sample. Some material begins melting. 05/10/20 14:07:44: As melting continues, it becomes clear that the crystals are floating upward, as would be expected for Ice Ih crystals that are less dense than the surrounding fluid. Since the volume sensor is not moving significantly, we conclude that the connecting tubing may still be mostly frozen, and that the pressure inside the vessel is likely still higher than indicated reading of 66.8 MPa.o 05/10/21 01:51:44: As the mirabilite crystals in the window continue to dissolve, the volume starts dropping dramatically, consistent with eutectic melting commencing throughout the sample. Although we did not do it in this run, in other runs, we were able to reverse the warming during this transition, and get crystals to regrow again. 05/10/21 05:03:44: Continuing to warm up simply starts dissolving the mirabilite until the liquidus point is reached. The volume here is slightly higher than the volume upon cooling, likely because the warming is occurring at a relatively rapid rate. 05/10/22 14:51:44: Cooling down momentarily shows that the crystals will regrow. 05/10/24 11:19:44: Past the liquidus point, the sample is now all liquid, and further warming increases the volume, due to thermal expansion. 05/10/25 00:41:05: A final cooling merely retraces the warming curve for the liquid. No crystals regrow, indicating that the system is all liquid.
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