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.