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This run features an aqueous solution that is approximately 15.5 wt.% Na2SO4. Initially, the pressure was about 235 MPa. 11/09/08 13:46:34: This run starts around T = 287 K and p = 235 MPa with some leftover crystals from an earlier run. The system is first warmed to dissolve everything and then cooled. 11/09/08 19:46:51: After supercooling to 281.6 K, mirabilite crystals grow. They continue to grow somewhat upon further cooling until flash freezing occurs at 238.6 K, Even though the pressure of 232.5 MPa is well above the Ice Ih/Ice III transition, the initial volume increases considerably here, indicating the formation of a low-density ice phase, presumably metastable Ice Ih. Further cooling results in little change. 11/09/10 02:01:51; Gradual warming leads to a reversible melting transition around 245 K. 11/09/14 15:52:51: To see whether this metastable phase persists at even higher temperatures, the pressure is gradually increased and the sample is slowly warmed up. Since the sample is frozen solid, the increase of the pressure on the outside is not necessarily fully communicated to the sample in the pressure cell. 11/09/14 19:55:51: Eventually, the material in the connecting tubing softens enough that the pressure inside the cell also increases and the volume decreases. This yields a change to a denser phase of ice. This phase is put through several freeze/melt cycles before eventually the whole system is warmed up and the original mirabilite crystals dissolve.
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