All-optical method to directly measure the pressure–volume–temperature equation of state of fluids in the diamond anvil cell

Proctor, J. E.; Robertson, C. E. A.; Jones, L. J.; Phillips, J.; Watson, K.; Dabburi, Y.; Moss, B.

Abstract

We have developed a new all-optical method to directly measure the pressure–volume–temperature (PVT) equation of state (EOS) of fluids and transparent solids in the diamond anvil high pressure cell by measuring the volume of the sample chamber. Our method combines confocal microscopy and white light interference with a new analysis method, which exploits the mutual dependence of sample density and refractive index: Experimentally, the refractive index determines the measured sample chamber thickness (and therefore the measured sample volume/density), yet the sample density is by far the dominant factor in determining the variation in the refractive index with pressure. Our analysis method allows us to obtain a set of values for the density and refractive index, which are mutually consistent and agree with the experimental data within error. We have conducted proof-of-concept experiments on a variety of samples (H2O, CH4, C2H6, C3H8, KCl, and NaCl) at ambient temperature and at high temperatures up to just above 500 K. Our proof-of-concept data demonstrate that our method is able to reproduce known fluid and solid EOS within error. Furthermore, we demonstrate that our method allows us to directly and routinely measure the PVT EOS of simple fluids at GPa pressures up to, at least, 514 K (the highest temperature reached in our study). A reasonable estimation of the known sources of error in our volume determinations indicates that the error is currently ±2.7% at high temperature and that it is feasible to reduce it to ca. ±1% in future work.

Citation

Proctor, J. E., Robertson, C. E. A., Jones, L. J., Phillips, J., Watson, K., Dabburi, Y., & Moss, B. (2024). All-optical method to directly measure the pressure–volume–temperature equation of state of fluids in the diamond anvil cell. Physics of Fluids, 36(8), 087145. https://doi.org/10.1063/5.0220503

• Journal Article Type: Article
• Acceptance Date: Aug 1, 2024
• Online Publication Date: Aug 20, 2024
• Publication Date: Aug 20, 2024
• Deposit Date: Aug 28, 2024
• Publicly Available Date: Aug 30, 2024
• Journal: Physics of Fluids
• Print ISSN: 1070-6631
• Electronic ISSN: 1089-7666
• Publisher: AIP Publishing
• Peer Reviewed: Peer Reviewed
• Volume: 36
• Issue: 8
• Pages: 087145
• DOI: https://doi.org/10.1063/5.0220503
• Additional Information: This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Proctor, J. E., Robertson, C. E. A., Jones, L. J., Phillips, J., Watson, K., Dabburi, Y., & Moss, B. (2024). All-optical method to directly measure the pressure–volume–temperature equation of state of fluids in the diamond anvil cell. Physics of Fluids, 36(8), 087145 and may be found at https://doi.org/10.1063/5.0220503