Marc Cassiède

Impedance analysis for characterizing the influence of hydrostatic pressure on piezoelectric quartz crystal sensors

The effect of hydrostatic pressure on the electrical behavior of quartz crystal resonators vibrating in the megahertz range is investigated by impedance analysis. The responses in frequency and dissipation of five AT-cut polished quartz crystals immersed in helium gas are analyzed and compared from conductance spectra around the resonance on several overtones. A model is then proposed to correlate the variations in frequency and dissipation with pressure and to explain the particular behavior observed on the fundamental harmonic mode.

Viscosity measurements of liquids under pressure by using the quartz crystal resonators.

A quartz crystal viscometer has been developed for measuring viscosity in liquids under pressure. It employs an AT-cut quartz crystal resonator of fundamental frequency 3 MHz inserted in a variable-volume vessel designed for working up to 80 MPa. Viscosity is determined by two methods from resonance frequency and bandwidth measurements along up to eight different overtones. The resonance frequency allows an absolute measurement of the viscosity but leads to an accuracy limited to 5% whereas the bandwidth technique which works in a relative way provides an accuracy of 2%. The techniques were tested by carrying out measurements in two pure compounds: heptane and toluene. Measurement results demonstrate the feasibility of the technique in this viscosity range. The apparatus was also used to determine the viscosity of n-decane with dissolved methane. The results obtained with these mixtures reveal the applicability of the apparatus for reservoir fluids study.

Electrical behavior of a quartz crystal resonator immersed in a pressurized fluid (gas or liquid)

A network analyzer connected to a high pressure vessel was used to measure the conductance spectrum in a wide range of frequency (1–250 MHz) of an AT-cut quartz crystal resonator of nominal frequency 3 and 5 MHz totally immersed in a fluid under pressure ranging from atmospheric pressure to 80 MPa. Measurements carried out with several gases (methane, nitrogen, argon, carbon dioxide) and various hydrocarbon liquids (toluene, heptane, nonane, decane, dodecane) show that quartz resonators correctly work when they are fully immersed in pressurized fluids whatever the state gas or liquid and whatever the pressure. At constant pressure, both shifts in frequency and bandwidth follow a regular behavior versus overtone number in a domain limited in the lower range by the influence of the circle edge boundary conditions and by the interference with the anharmonic modes in the upper range. In this working domain, experimental observations were well represented by a model that takes into account the effects of hydro...

A quartz crystal microbalance technique to study wax crystallization in the presence of gas

A quartz crystal microbalance (QCM) was designed to measure the melting temperature in the presence of gas under high pressure. The capacity of the experimental technique to determine the liquid–solid as well as the solid–solid transitions was first tested by measuring the phase transition temperatures of several pure n-alkanes from n-C19 to n-C30 under atmospheric pressure and by comparing the results with literature data. Then, the wax disappearance conditions were determined for linear alkanes from n-C20 to n-C22 in the presence of carbon dioxide under pressure. The resulting solid–liquid–vapour three-phase equilibrium curves correctly match those obtained in earlier studies.

Electrical characterization of a quartz crystal in high pressure CO2 by impedance analysis

The quartz crystal microbalance (QCM) is a very accurate sensor for measuring small changes of mass of thin films spread on the quartz surface. Under certain conditions, the resonance frequency of a quartz crystal can be used for monitoring the mass change caused by solvent adsorption or dissolution inside a film. However, when a quartz crystal is immersed in a high-pressure non-inert gas, various effects such as pressure, viscosity, roughness on the surface of the quartz crystal, adsorption of gas or even gas film formation slipping at the solid–gas interface can influence the resonance frequency of the quartz crystal and consequently complicate the relation between mass and frequency changes. In order to determine experimentally such effects in contact with carbon dioxide in the neighborhood of the critical conditions, the resonance curve of a quartz crystal under gas pressure was examined with a network analyzer which is able to determine both resonance frequency and half-band-half-width on several overtones.