Quartz contact with liquid

Quartz crystals have a characteristic oscillation frequency which varies according to their mass. Although crystal wafers have been used as mass sensors in vacuum and gas-phase experiments for many years, it is only recently that they have been employed in contact with liquids or solutions. Quartz crystal wafers can be used as electrodes by depositing a thin film of electrode material on the exposed surface, and interfacial mass changes can then be monitored. It is then known as the electrochemical QCM or EQCM. It is a direct, but non-selective, probe of mass transport. 

Since the early work of Kanazawa [1] and Bruckenstein in 1985 [2], quartz crystal resonators have been used for more than 12 years in contact with liquids to assess changes in mass during electrochemical surface processes. Extensive use of the electrochemical quartz crystal microbalance (EQCM) has been done in the study of electrode processes with change of mass simultaneous to charge transfer. 

Mason [46] first observed that the viscoelastic properties of a fluid in contact with quartz crystals can affect the resonant properties. However, Mason s work had been forgotten and for a long time there have not been studies of piezoelectric acoustic wave devices in contact with liquids until Nomura and Okuhara [15] found an empirical expression that described the changes in the quartz resonant frequency as a function of the liquid density, its viscosity and the conductivity in which the crystal was immersed. Shortly after the empirical observations of Nomura were described in terms of physical models by Kanazawa [1] and Bruckenstein [2] who derived the equation that describes the changes in resonant frequency of a loss-less quartz crystal in contact with an infinite, non conductive and perfectly Newtonian fluid ... 

Kanazawa KK, Gordon JG (1985) Frequency of a quartz microbalance in contact with liquid. Anal Chem 57 1770-1771... 

Kanazawa, K. Gordon, J. G., The oscillation frequency of a quartz resonator in contact with liquid. Anal. Chem. Acta 1985, 175, 99-105... 

Liquid Entrainment. Because of its shear-horizontal surface particle displacement (in the plane of the device surface), the SH-APM propagates in contact with liquids without excessive attenuation. The inplane oscillation of the quartz surface contacting the liquid does lead, however, to entrainment of a thin layer of liquid near the interface Ql). This viscous coupling of liquid to the APM has two effects (1) to alter the propagation characteristics (velocity and attenuation) of the APM, and (2) to alter the transduction efficiency for excitation and detection of APMs. By confining the liquid to the region between transducers, propagation effects are measured without the influence of transduction effects this is necessary even if the side of the device opposite the transducers is used for measurement. 

As mentioned above the acoustic disturbances generated in the sample are detected by some kind of pressure sensor. In contact with liquid or solid samples these are piezoelectric devices such as lead zirco-nate titanate (PZT), LiNb03 or quartz crystals with a typical responsivity R in the range of up to V bafi or thin polyvinylidene-difluoride (PVF2 or PVDF)-foils with lower responsivity. These sensors offer fast response times and are thus ideally adapted for pulsed photoacoustics. 

There is a great interest in the nature of the interface between water and silicate minerals (see for example Davis and Hayes (1986)). Much of the chemical activity in soils, sediments and porous rocks occurs at such an interface. Experimentally, it is very difficult to examine this interface because it is such a small part of the liquid-solid system. Hydrated smectites and vermiculites have water between all of the silicate layers and therefore the percentage of the sample which is interface is enormously larger than the interface between, for example, a grsin of quartz in contact with liquid water. Another way to look at this is that the surface are of a quartz sand is probably much less than 1 m gram while a typical smectite has a surface area of as much as 800 m /gram. For these, and other reasons, intercalated clays have been extensively studied. 

Apparatus. The preparations may be carried out in quartz or Teflon vessels. A bottle of 30-ml. capacity and internal diameter 2.5 cm., provided with a standard-taper quartz joint, for attachment to a vacuum system is satisfactory. A small copper, nickel, Monel, or Kel-F funnel is needed to facilitate addition of liquid bromine trifluoride. Excess bromine trifluoride removed on the vacuum line must be collected in a quartz or Kel-F trap. Silicone or Kel-F vacuum grease must be employed in those parts of the vacuum system likely to come into contact with bromine trifluoride vapor. Vacuum grease should be applied to the cone of the quartz bottle only after... 

More recently the treatment was extended to piezoelectric devices in contact with viscoelastic media (i.e., liquids and polymers). It was then realised that if the deposited mass was not rigidly coupled to the oscillating quartz crystal, separation of inertial mass and energy losses was not possible with the measurement of the resonant frequency alone. Quartz crystal impedance in the acoustic frequencies was introduced in order to study mass and viscoelastic changes and a full electrical characterization of the crystal behaviour near resonance was employed. 

For a Newtonian liquid in contact with the quartz crystal, additional... 

Example 3.4 Calculate the liquid decay length S, motional resistance Rz, and change in series resonant frequency Af, caused by placing water in contact with one face of a 5 MHz TSM resonator having C =5 pF. For quartz [23] 7.74 X 10 , p, = 2.65... 

Quartz Crystal Operating in Contact with a Liquid. 120... 

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