Dense-phase 6 INDEX

The results for the TEA--water mixtures at atmospheric pressure are shown in Figure 6. These are for TEA mole fractions of x 0.05 and 0.59. The LOST is 18.2 at x - 0.09. We also obtained a very similar data set at the latter mole fraction, but we omitted it for clarity. For contrast and comparison, a data set for pure water is shown. These mixture results again show a sharp rise in heat transfer coefficient as condensate first appeared. In fact, the appearance was remarkably similar to the n-decane--C02 results for x - 0.973 discussed above, but the visibility of the phase separation was enhanced by the presence of a fine emulsion at the phase interface and the absence of strong refractive index gradients characteristic of the supercritical systems. This permitted the structure of the interface to be seen more clearly. In Figure 7 we show photographs that typify the appearance of the two phases. In all cases observed here, both in supercritical vapor--liquid and in liquid--liquid systems, the dense phase appears to wet the cylinder surface regardless of composition. 

If there is no chemical reaction but mass exchange between phases, such as evaporation, subfimation, and condensation, we can replace the reaction rate with certain mass exchange rate tm, and similarly define the heterogeneity index for structure-dependent mass transfer. For example, assume that the concentration of transferred species at particle surface is saturated further, the diffusion rate from the particles to the gas in the dense phase is equal to that from the gas in the dense phase to the gas in the dilute phase and we get... 

In internal reflection spectroscopy (IRS), the spectrum is obtained with the sample in optical contact with another material (e.g. a prism) and the beam is passed through the prism onto the sample. The prism is optically denser than the sample, the incoming light forms a standing wave pattern at the interface within the dense prism medium whereas in the sample (with the lower refractive index), the amplitude of the electric field falls off exponentially with the distance from the phase boundary. When the sample exhibits absorbance, the reflectance measured is given by ... 

No carbon was recorded for the D-treated film. The O/Si composition ratio was found to be 2.08 and is attributed to the extent of condensation as the organic phase has been removed completely. Based on the amount of Si for sample D and assuming a density of 2.3 g cm3 for amorphous SiC>2, the top layer would correspond to a thickness of 154 nm, if a dense layer is assumed. As the actual layer thickness is 458 nm, this would imply a porosity of 66%. Here a considerable discrepancy with the porosity obtained from ellipsometry is evident. In this respect it should be noted that the RBS measurement was done more to the edge of the sample than ellisometry, where the thickness is smaller than in the centre. Further, the refractive index determined with ellipsometry is very accurate. However, the relation of porosity with refractive index depends on the model used. 

The examination of surface properties of three low-index surfaces of Pt3Ni(/j/ 0 has also been pursued recently by a combination of low-energy electron diffraction (FEED) and LEIS [23]. As summarized in Fig. 3.2, the PtjNi(l 11) surface exhibits a (1 X 1) FEED pattern (Fig. 3.2d) the atomically less dense PtjNi(lOO) surface shows a clear (1 x 5) reconstruction pattern (the so-called hex phase) in both the... 

The present Collection serves as a source of reference patterns for pure zeolite phases. The data will be helpful in establishing the structural purity of experimental phases and in indexing their diffraction patterns. The data will also aid in the determination of changes in the lattice parameters with changing composition, assessing preferred orientation effects, background evaluation, and line broadening. We have also included diffraction patterns of several common dense silicate phases to facilitate their detection in mixed phase syntheses. 

As it was introduced in Sect. 29.2.3, neutrons of sufficiently long wavelength can bring about optical phenomena when encountering boundaries of condensed phases they, as waves, interact with the continuous potential represented by densely packed atoms. Reflection does occur (although only for very small incident angles, due to the very nearly unity value of the refractive index of most materials for neutrons), which can be exploited for studying Uquid (and solid) surfaces (and interfaces) by neutron reflectometry. 

In internal reflection, at angles of incidence larger than the critical angle, electromagnetic radiation is totally reflected (attenuated total reflectance, ATR. see Section 16.2.2.4 and Fig. 5). This special ca.se is very important in analysis for two approaches. First, simple transportation of radiation within the fiber (or a waveguide). Second, in total reflection, an evane.scent field appears in which the electrical field vector decays exponentially in the optically less dense medium. Every change within the medium with lower refractive index influences the field vector coupled to the field in the optically denser medium. Therefore, the totally reflected radiation contains information about effects on the other side of the phase boundary (the medium with lower refractive index) [20], [144]. Various principles to interogate this effect are known and used in evanescent field sensors. 

Table 16.2. Shape parameters (equations (16.1) and (16.4)) and approximate swelling exponents s and s, cf. equation (16.8)) for known lyotropic mesophases. The (variable) constants /i and depend on the specific symmetry of the phase ( /i is the homogeneity index, ideal equal to 3/4 (cf. Table 16.1) / is the interstitial packing fraction for dense sphere and circle packings, equal to unity for ideal homogeneous packings)...

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