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Figure 10
(a) Melting temperature of pure α-DL-menthol and β-DL-menthol compressed and recrystallized in the DAC chamber: the black squares mark the onset of melting of the crystal filling the volume of the chamber, and the red squares mark the melting completion, according to the microscopic observation of the sample, as exemplified for the heating run of the sample at the starting pressure 0.48 GPa in (b). The increased temperature for the full melting (red squares) compared with that at the start (black squares) results from the pressure–temperature interdependence for the isochoric process: the larger portion of the sample is molten, the higher pressure is in the DAC chamber. Due to the thermal expansion of the sample, the pressure measurements at 296 K plotted in (a) are lower than the actual values for which the melting onset, and even more so the melting completion, took place. In the DAC chamber several small irregular ruby chips are placed close to the gasket walls for the ruby-fluorescence pressure measurements.

IUCrJ
Volume 10| Part 3| May 2023| Pages 341-351
ISSN: 2052-2525
https://doi.org/10.1107/S2052252523002452