How to determine the equations of state of hot fluids at GigaPascal pressures
| Dates: | 20 March 2024 |
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| Times: | 12:00 - 13:00 |
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| What is it: | Seminar |
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| Organiser: | Photon Science Institute |
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| Who is it for: | University staff, Current University students |
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| Speaker: | Dr. John Proctor |
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Join us for this PSI seminar with guest speaker Dr John Proctor. The pressure-volume-temperature equations of state (PVT EOS) of solids are measured routinely using synchrotron X-ray diffraction on samples confined in diamond anvil high pressure cells combined with resistive or laser heating up to pressures above 100 GPa. However, the density (and therefore EOS) of fluids cannot be determined from diffraction data. Instead, the density is an important input parameter in the analysis of these data 1. Routine measurement of the PVT EOS of fluids above room temperature has only been performed so far up to about 0.1 GPa using piston-cylinder devices that enable direct measurement of the volume. However, the simple fluids that comprise the outer layers of the gas giant planets and their moons do not solidify until pressures of 5 – 10 GPa at high temperature.
The following approaches to rectify this problem have been attempted by others: (a) Extrapolation of data from lower pressures or temperatures (b) Numerical integration of sound speed data obtained using Brillouin scattering and © All-optical Measurement of the entire sample chamber volume.
In my talk I will outline why none of these approaches have provided satisfactory results to date, leading to a critical lack of PVT EOS data in the literature on the simple fluids that comprise the outer layers of the gas giant planets and their moons. I will then go on to outline our recent experimental and theoretical research into this topic at the University of Salford. Theoretically, we have constructed a new physical model 2 to describe fluids which allows equation of state data to be fitted using equations that are obtained from first principles (i.e. the laws of physics) 3 rather than from empirical models. Thus it is feasible that these equations may provide the correct results when extrapolated to pressures and temperatures at which real experimental data do not yet exist.
Experimentally, we have focussed on approach ©. The existing method for this measurement in the scientific literature uses a method 4 that does not work above room temperature. I will outline a new method which can solve this problem and present our proof-of-concept data that demonstrate how direct all-optical measurement of sample chamber volume and hence fluid PVT EOS is feasible in the diamond anvil cell above 300 K. Finally, I will outline how the combination of our new method with approach (b) (Brillouin spectroscopy) and with X-ray or neutron diffraction data can in future allow reliable experimental determination of a range of fluid properties above 300 K in addition to the PVT EOS.
Speaker
Dr. John Proctor
Organisation: University of Salford
Biography: Dr John Proctor is a senior lecturer in physics at the University of Salford. His research concerns the behaviour of matter at extreme pressures and temperatures. Some highlights are the first study of graphene at high pressure (2009), stabilization of boron carbide using silicon-doping (2014), the hydrogenation of graphene using high pressure and temperature (2015) and experimental measurements of the Frenkel line separating the supercritical fluid state into liquid-like and gas-like regions (2017 onwards). He has written two textbooks: An Introduction to Graphene and Carbon Nanotubes (2017) and The Liquid and Supercritical Fluid States of Matter (2020).
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