WHh a continuum electromechanical model, the electrical admittance has been derived for an AT-cut quartz crystal microbalance (QCM) simultaneously loaded by a surface mass layer and a contacting Newtonian liquid. This admittance expression Is used to derive a lumped-element equivalent circuit model that describes the near-resonance electrical characteristics of the QCM under these loading conditions. The resulting model Is a modified Butterworth-Van Dyke equivalent circuit, having circuit elements that are explicitly related to physical properties of the quartz, perturbing mass layer, and contacting liquid. The effects of mass and liquid loading on the fundamental and third harmonic resonances are predicted from the model and compared with experimental Impedance analyzer measurements. Surface mass accumulation causes a simple translation In frequency of the resonance peak, while Increasing the density-viscosity product of the contacting solution causes both a translation and a damping of the resonance peak. With the model, changes In surface mass can be differentiated from changes In solution properties.

Impedance analysis of thickness-shear mode quartz crystal resonators in contact with linear viscoelastic media Rev. Sci. Instrum. 69, 2375 (1998); 10.1063/1.1148963 Frequency-temperature relations of thicknessshear and flexural vibrations of contoured quartz resonators

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A new application for surface complexation modeling is described. These models, which describe chemical equilibria among aqueous and adsorbed species, have typically been used for predicting groundwater transport of contaminants by modeling the natural adsorbents as various metal oxides. Our experiments suggest that this type of modeling can also explain stainless steel surface contamination and decontamination mechanisms.Stainless steel transportation casks, when submerged in a spent fuel storage pool at nuclear power stations, can become contaminated with radionuclides such as 137 Cs, 134 Cs, and 60Co.Subsequent release or desorption of these contaminants under varying environmental conditions occasionally results in the phenomenon known as "cask weeping." We have postulated that contaminants in the storage pool adsorb onto the hydrous metal oxide surface of the passivated stainless steel and are subsequently released (by conversion from a fixed to a removable form) during transportation, due to varying environmental factors, such as humidity, road salt, dirt, and acid rain. It is well known that 304 stainless steel has a chromium enriched passive surface layer; thus its adsorption behavior should be similar to that of a mixed chromium / iron oxide. To help us interpret our studies of reversible binding of dissolved metals on stainless steel surfaces, we have studied the adsorption of Co+ 2 on Cr 2 0 3 . The data are interpreted using electrostatic surface complexation models. The FITEQL computer program was used to obtain the model binding constants and site densities from the experimental data. The MINTEQA2 computer speciation model was used, with the fitted constants, in an attempt to validate this approach.