Dispersed Phase Identification

Conductivity can be used to distinguish O/W from W/O emulsions, since the conductivity is very high when the aqueous phase is continuous and conductivity is very low when oil is the continuous phase. 

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Local composition is very useful supplementary information that can be obtained in many of the transmission electron microscopes (TEM). The two main methods to measure local composition are electron energy loss spectrometry (EELS), which is a topic of a separate paper in this volume (Mayer 2004) and x-ray emission spectrometry, which is named EDS or EDX after the energy dispersive spectrometer, because this type of x-ray detection became ubiquitous in the TEM. Present paper introduces this latter method, which measures the X-rays produced by the fast electrons of the TEM, bombarding the sample, to determine the local composition. As an independent topic, information content and usage of the popular X-ray powder dififaction database is also introduced here. Combination of information from these two sources results in an efficient phase identification. Identification of known phases is contrasted to solving unknown stmctures, the latter being the topic of the largest fiaction of this school. 

The most obvious choice to determine phases that may be present in the molybdena catalyst is XRD. Matching of diffraction lines obtained for the catalyst with those of pure bulk compounds gives unequivocal identification of phases present. This is one of the few techniques that yields positive results. The absence of matching diffraction lines, however, is not proof that the phase in question is not present in the catalyst. The XRD technique is limited to particle sizes of above approximately 40 A for oxides or sulfides, lower sized particles giving no discernible pattern over that of the broad alumina pattern. Thus, the presence of a highly dispersed phase, either as small crystallites or as a surface compound of several layers thickness will not be detected. Also, if the phase is highly disordered (amorphous), a sharp pattern will not be obtained, although some broad structure above that of the alumina may be detected. It is a moot point as to whether such a case is considered as a separate phase or a perturbation of the alumina structure. Ratnasamy et al. (11) have examined their CoMo/Al catalyst from the latter point of view, with particular emphasis on the effect of calcination temperature. 

Most powder diffraction databases only serve angular dispersive X-ray diffraction. Energy dispersive X-ray diffraction data can be transformed into an angular dispersive equivalent that can then be used in conventional search-match software. Users of neutron diffraction data are currently limited to performing phase identification using a list of crystal structures imported into a Rietveld program. It is wise to first run samples destined for neutron diffraction sample in a powder XRD prior to confirm phase purity, and to use calculated patterns to assist in phase identification of possible undesired phases due to ancillary equipment or sample environment. 

The further progress can be related to the development of alloys of Ti-B-Si-X system. Preliminary study of these alloys has shown an availability of some additional early unknown phase. In addition to typical lamellar borides visible in structure of the alloys is extremely disperse phase having boron and silicon in its composition. Electron microscopy image of this phase is shown in Figure 4. Structural identification of this silicoboride is not completed yet, however it is already possible to note appreciable increase of stiffness of the alloys at simultaneous presence of boron and silicon (Table ) ... 

For any process, the lack of accurate process measurements limits the successful implementation of model identification and control. Crystallizers are dispersed-phase systems, and the shortcomings of on-line measurement techniques for these types of systems are particularly evident. 

The penetration of siliceous species in the porous support is investigated by means of energy dispersive X-ray. Phase identification and determination of any preferred orientation is performed by using X-ray diffraction. 

The effective-medium approach is valid only for the random-dispersion structure including the cases in which phase B disperses in matrix phase A and phase A conversely disperses in matrix phase B. However, for the percolationlike structure, in which the identification of dispersion phase and matrix phase is difficult to determine, the effective-medium theory cannot be used directly. To deal with such a transition area, a newly developed type of fuzzy logic [19, 20] may be useful for describing the complex microstructure and thermophysical properties. 

If the problem is the identification of a specific thermal event, the substitution of one of the system components may be very effective, as shown in Fig. 18, where the DSC spectra of a H20-hexadecane and a D20-hexadecane microemulsion are presented. In the latter case, the aim was to ascertain that the 263 K thermal event was unambiguously due to the dispersed phase, whether water or heavy water [24]. 

The second feature is the identification of a measuring system for the quantification of the flame-retardant effectiveness of clay as a dispersed phase in polymers. The cone calorimeter is an excellent tool for this purpose [3]. An additional device referred to as a simulated solid rocket motor (SSRM) will be introduced. The SSRM is designed to evaluate polymer composite flame retardancy at extreme conditions. 

For spin-f nuclei, dipolar interactions may be modulated by intramolecular (DF, reorientation etc.) and/or intermolecular (TD) processes. In general, the intra- and inter-molecular processes can produce quite different Tj frequency dispersion curves. In practice, NMR field cycling experiments are often needed to extend the frequency domain from those employed in conventional spectrometers to a lower frequency range (i.e., the kHz regime) for unambiguous separation (and identification) of different relaxation mechanisms. The proton spin relaxation by anisotropic TD in various mesophases has been considered by Zumer and Vilfan.131 133,159 In the nematic phase, Zumer and Vilfan found the following expression for T ... 

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