Solidification and loss of hydrostaticity in liquid media used for pressure measurements

TL;DR

This study investigates how nine different liquid pressure media solidify under pressure up to 2.3 GPa, affecting hydrostatic conditions crucial for accurate pressure measurements in high-pressure experiments.

Contribution

It provides the first systematic pressure-temperature data for these media, establishing the hydrostatic limit and freezing pressures using electrical resistivity measurements.

Findings

Identified the solidification pressures for nine media.

Mapped the temperature-pressure phase boundary separating liquid and solid phases.

Provided practical guidelines for maintaining hydrostatic conditions in experiments.

Abstract

We carried out a study of the pressure dependence of the solidification temperature in nine pressure transmitting media that are liquid at ambient temperature, under pressures up to 2.3 GPa. These fluids are: 1:1 isopentane/n-pentane, 4:6 light mineral oil/n-pentane, 1:1 isoamyl alcohol/n-pentane, 4:1 methanol/ethanol, 1:1 FC72/FC84 (Fluorinert), Daphne 7373, isopentane, and Dow Corning PMX silicone oils 200 and 60,000 cst. We relied on the sensitivity of the electrical resistivity of Ba(Fe1-xRux)2As2 single crystals to the freezing of the pressure media, and cross-checked with corresponding anomalies observed in the resistance of the manganin coil that served as the ambient temperature resistive manometer. In addition to establishing the Temperature-Pressure line separating the liquid (hydrostatic) and frozen (non-hydrostatic) phases, these data permit rough estimates of the freezing pressure of these media at ambient temperature. This pressure establishes the extreme limit for the medium to be considered hydrostatic. For higher applied pressures the medium has to be treated as non-hydrostatic.