Quartz dielectric constant

Fig. 4.3. Typical normalized piezoelectric current-versus-time responses are compared for x-cut quartz, z-cut lithium niobate, and y-cut lithium niobate. The y-cut response is distorted in time due to propagation of both longitudinal and shear components. In the other crystals, the increases of current in time can be described with finite strain, dielectric constant change, and electromechanical coupling as predicted by theory (after Davison and Graham [79D01]).

For SiC>2, we have only considered sources for silica suspensions which were non-porous, such as Ludox (39), pyrogenic silica (40), heat-treated BDH silica (22), or ground quartz (41). The data from these sources at 0.1M concentration has been collected in Figure 7. The data of the various researchers is quite consistent, in spite of the differences in origin of the suspensions, and the different electrolytes used. The slope of the points above pH 7 shows that the adsorption capacitance for cations is very large for both sodium and potassium ions, around 200 pF/cm2. Such a capacitance corresponds to a distance of 0.25.X, when using the dielectric constant of immobilized water molecules. The equilibrium constant for adsorption is low, however, since both KNa+ and Kk+ lie between 0.1 and 0.01 dms/mol. A possible interpretation of these results is as follows there is little specific attraction between SiC>2 and alkali cations,... 

Fe solutions have been aerated at pH 7.2 in the presence of various minerals and rocks including quartz and basalt (Posey Dowty et al., 1986). The major product in all cases except that of quartz (goethite) was lepidocrocite. These authors also noted that lowering the dielectric constant of the solvent (by replacing water with a mixture of water and dioxane) promoted goethite over lepidocrocite. Poorly crystalline lepidocrocite was also the sole product when Fe was oxidized at pH 7 and RT in the presence of bacteria (Bacillus suhtilis Escherichia coli) (Chatellier et al. 2001) (see also chap. 17). 

Experimental volatility studies of M04 (M = Ru, Os and Hs) were performed in a chromatography column with a pure quartz surface [10], For these highly symmetric molecules having no dipole moments, the interaction should be of a pure van der Waals type. With the use of a model of the molecule-slab interaction and the relation between the dielectric constant of... 

A solvothermal process is one in which a material is either recrystallized or chemically synthesized from solution in a sealed container above ambient temperature and pressure. The recrystallization process was discussed in Section 1.5.1. In the present chapter we consider synthesis. The first solvothermal syntheses were carried out by Robert Wilhelm Bunsen (1811-1899) in 1839 at the University of Marburg. Bunsen grew barium carbonate and strontium carbonate at temperatures above 200°C and pressures above 100 bar (Laudise, 1987). In 1845, C. E. Shafhautl observed tiny quartz crystals upon transformation of freshly precipitated silicic acid in a Papin s digester or pressure cooker (Rabenau, 1985). Often, the name solvothermal is replaced with a term to more closely refer to the solvent used. For example, solvothermal becomes hydrothermal if an aqueous solution is used as the solvent, or ammothermal if ammonia is used. In extreme cases, solvothermal synthesis takes place at or over the supercritical point of the solvent. But in most cases, the pressures and temperatures are in the subcritical realm, where the physical properties of the solvent (e.g., density, viscosity, dielectric constant) can be controlled as a function of temperature and pressure. By far, most syntheses have taken place in the subcritical realm of water. Therefore, we focus our discussion of the materials synthesis on the hydrothermal process. 

In the strict sense, the dielectric constant for the bulk particles as measured here may be incorrect as applied to a hydrated surface environment which has undergone substantial changes in electrical properties upon addition of water. Levine ( ), for example, uses a value of 10 for the dielectric constant of a solvated quartz surface when the actual capacitor plate value for the solid is only 4.3. The effect of a variation in the value for the solid dielectric constant on the pH-dependence of adsorption, however, is minimal, requiring only a very small change in the value of the fitting parameter AGJ in order to produce the same results. For this reason, our use of the measured value of 16.4 for the solid should suffice, producing little error as compared to estimating a value for the solvated solid. 

Using the result obtained by Bull and Gortner [J. Phys, Chem, 36, 111 (1932)], that SIP for the streaming of 2 X 10 N sodium chloride through a diaphragm of quartz particles is about 25 millivolts per cm. of mercury pressure, calculate the approximate specific surface conductance of the solution used. Compare the result with the normal value for sodium chloride at the same concentration. The viscosity and dielectric constant of the solution may be assumed to be the same as for water, and the zeta-potential may be taken as 0.05 volt. (Care should be exercised in the matter of units, use being made of the conversion factors in Table I.)... 

In order to measure the effect of temperature on dielectric constants at constant density, we have first to determine the equation of state of the gases and vapours under investigation. This is done as follows the vapour being investigated is led into the gas-holder at a density which in the first instance is selected arbitrarily, and the quartz manometer then enables us to find the pressure at various temperatures when the density is kept at this constant value. 

The measured enthalpies of adsorption of alkanes into zeolites are very large, and can be calculated from this formula [13]. The dielectric constants for the open networks formed by the aluminium silicate frameworks of zeolites can be related to the known and measured dielectric and optical properties of bulk quartz. The calculation assiunes that the zeolite framework tessellates a hyperbolic surface as described in Chapter 2. The polarisabilities of different adsorbate alkanes are also known. When the calculations are carried out for a whole range of alkanes as adsorbate molecules and for different zeolites (with differing pore structure and size) the agreement between measured and predicted heats of adsorption is excellent (cf. Fig. 3.2). The results depend... 

Zeolite membranes and films have been employed to modify the surface of conventional chemical electrodes, or to conform different types of zeolite-based physical sensors [49]. In quartz crystal microbalances, zeolites are used to sense ethanol, NO, SO2 and water. Cantilever-based sensors can also be fabricated with zeolites as humidity sensors. The modification of the dielectric constant of zeolites by gas adsorption is also used in zeolite-coated interdigitaled capacitors for sensing n-butane, NH3, NO and CO. Finally, zeolite films can be used as barriers (for ethanol, alkanes,...) for increasing the selectivity of both semiconductor gas sensors (e.g. to CO, NO2, H2) and optical chemical sensors. 

The early applications of the piezoelectric crystal detectors were limited to the measurement in the gas phase, because of the common impression that stable oscillation cannot be obtained in the liquid phase. However, recent advances in PZ research have shown that quartz crystals can oscillate in contact with solution, and several studies have been reported addressing the theoretical aspects of the oscillating frequency of piezoelectric crystals in solution. Nomura and Okuhara (92) demonstrated that the frequency change of a crystal immersed in an organic solvent depends on the density and viscosity of the solvent, and was not affected by the dielectric constant ... 

What about the detection behavior of QCM if applied in solutions that is, does the deposited material have viscoelastic properties In 1981 Nomura and lijima first reported the QCM measurement in liquid medium. Since then much effort has been devoted to measuring QCM in solution. It appears that the frequency of quartz changes with the density, viscosity, conductivity, and dielectric constants of the solution studied. In addition the roughness of deposition materiaP and the nature of the electrode " used on the quartz s surface can affect the frequency of QCM. The Sauerbrey expression in (14.1) is therefore modified... 

The thickness of the substrate supporting the TPS is application dependent but is typically between 0.002 inches to 0.020 inches. Good substrate materials have a fairly low dielectric constant and loss tangent. Typical substrate materials include glass/epoxy (such as FR4), glass/PTFE, quartz/polyimide, quartz/cyanate-ester, as well as kapton or mylar film. 

---