Other phases

Silica is an abundant component of phosphorite deposits, found as both authigenic silica (later crystallized to quartz) and detrital quartz. Interbeds of chert and phosphorite 

Finally, organic matter is a significant component of phosphorites. These organic phases have been of interest because phosphorites have been shown to be effective sources for hydrocarbon development (Maughan 1980). Organics have also been of interest to those studying the residency of trace elements in phosphorites, such as the interest in Se in the Phosphoria Formation, which will be discussed later. 

In the nematic phase the typical temperature dependence of dielectric constants and e are given in Fig. 2.4. Similar temperature curves are observed in the chiral nematic phase. The only difference comes from a specific definition of the main dielectric constants in the chiral nematic phase the components e h and e h are taken into consideration, denoting the dielectric properties parallel and perpendicular to the helical axis 

Dielectric properties of the smectic phase could be illustrated using the series of 4,4 -di-n-alkylazoxybenzene 

The results are reproduced in Fig. 2.6 [15]. It can be seen that with a drop in temperature the difference e, — e decreases even in the nematic phase. The change in sign of the anisotropy of the molar susceptibility occurs either in the smectic A phase (homologues with n = 7 and 8) or in the nematic phase (n = 6) near the transition point to smectic A. The dielectric anisotropy decreases both because of the decrease in s, and the increase in e . The effect clearly indicates the presence of the short-range smectic order even in the nematic phase. The decrease in and the increase in e , due to the short-range smectic order in the nematic phase (and the long-range order in smectic A), occurs as a consequence of correlation in 

FIGURE 2.6. The dielectric permittivities of three homologues of 4,4 -n-alkyla-oxybenzene (n = 6,7,8), all having an Sa phase [15]. 

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It is important to note that, in this example, as in real seeond-order transitions, the eiirves for the two-phase region eaimot be extended beyond the transition to do so would imply that one had more than 100% of one phase and less than 0% of the other phase. Indeed it seems to be a quite general feature of all known seeond-order transitions (although it does not seem to be a themiodynamie requirement) that some aspeet of the system ehanges gradually until it beeomes eomplete at the transition point. 

Consider simulating a system m the canonical ensemble, close to a first-order phase transition. In one phase, is essentially a Gaussian centred around a value j, while in the other phase tlie peak is around Ejj. 

One can define a phase that is given as an integral over the log of the amplitude modulus and is therefore an observable and is gauge invariant. This phase [which is unique, at least in the cases for which Eq. (9) holds] differs from other phases, those that are, for example, a constant, the dynamic phase or a gauge-transformation induced phase, by its satisfying the analyticity requirements laid out in Section I.C.3. 

There are two independent coordinates that define the plane of a loop. If the loop is phase inverting, one of these coordinates must be phase inverting, the other, phase preserving. Out of the infinite number of possible candidates, a convenient choice are reaction coordinates (Section I). Any one of the three reaction coordinates connecting two of the anchors can be used for the... 

Figure 29, The effect of the phase-preserving component of the degenerate 2 distorting mode, It may be regarded as a major component of the reaction coordinate that leads to the A] structure (going left, one phase of the mode). Going right, the other phase of the same vibration, the B2 state is formed. (A type-V structure is also obtained along the same coordinate).

In a simple liquid-liquid extraction the solute is partitioned between two immiscible phases. In most cases one of the phases is aqueous, and the other phase is an organic solvent such as diethyl ether or chloroform. Because the phases are immiscible, they form two layers, with the denser phase on the bottom. The solute is initially present in one phase, but after extraction it is present in both phases. The efficiency of a liquid-liquid extraction is determined by the equilibrium constant for the solute s partitioning between the two phases. Extraction efficiency is also influenced by any secondary reactions involving the solute. Examples of secondary reactions include acid-base and complexation equilibria. 

In the hexapole, one phase of the RF field is applied to three evenly spaced rods and the other phase to the remaining triplet of rods. 

In three-phase systems the top phase, T, is an oleic phase, the middle phase, Af, is a microemulsion, and the bottom phase, B, is an aqueous phase. Microemulsions that occur ia equiUbrium with oae or two other phases are sometimes called "limiting microemulsions," because they occur at the limits of the siagle-phase regioa. 

The bulk stmcture of the catalyticaHy active phase is not completely known and is under debate in the Hterature (125,131—133). The central point of controversy is whether (Valone or in combination with other phases is the most catalyticaHy active for the conversion of butane to maleic anhydride. The heart of this issue concerns the role of stmctural disorder in the bulk and how it arises in the catalyst (125,134,135). Most researchers agree that the catalysts with the highest activity and selectivity ate composed mainly of (Vthat exhibits a clustered or distorted platelet morphology (125). It is also generaHy acknowledged that during operation of the catalyst, the bulk oxidation state of the vanadium in the catalyst remains very close to the +4 valence state (125). 

Multiphase Reactors. The overwhelming majority of industrial reactors are multiphase reactors. Some important reactor configurations are illustrated in Figures 3 and 4. The names presented are often employed, but are not the only ones used. The presence of more than one phase, whether or not it is flowing, confounds analyses of reactors and increases the multiplicity of reactor configurations. Gases, Hquids, and soHds each flow in characteristic fashions, either dispersed in other phases or separately. Flow patterns in these reactors are complex and phases rarely exhibit idealized plug-flow or weU-stirred flow behavior. 

In addition to the three principal polymorphs of siUca, three high pressure phases have been prepared keatite [17679-64-0] coesite, and stishovite. The pressure—temperature diagram in Figure 5 shows the approximate stabiUty relationships of coesite, quart2, tridymite, and cristobaUte. A number of other phases, eg, siUca O, siUca X, sihcaUte, and a cubic form derived from the mineral melanophlogite, have been identified (9), along with a stmcturaHy unique fibrous form, siUca W. 

As mentioned above, uranium trioxide exists in six weU-defined modifications with colors ranging from yeUow to brick-red. Of these phases, the y-phase has been found to be the most stable, however, other phases, especially a and 3, are also frequently used and studied. The stmcture of the a-modification is based on sheets of hexagons, whereas the 3-, y-, and 8-modifications contain an infinite framework. AH of these topologies have been fliUy described (105,106). They are a-brown, hexagonal 3-orange, monoclinic y-yeUow, rhombic 5-red, cubic S-brick red, triclinic and Tj-rhombic. 

Phases Formed in Pordand Cements. Most clinker compounds take up small amounts of other components to form soHd solutions (11). Best known of these phases is the C S soHd solution called aHte. Phases that may occur Hi Portiand cement clinker are given Hi Table 1. In addition, a variety of minor phases may occur Hi Portiand cement clinker when certain minor elements are present Hi quantities above that which can be dissolved Hi other phases. Under reducHig conditions Hi the kiln, reduced phases, such as ferrous oxide [1345-25-17, FeO, and calcium sulfide [20548-54-3] CaS, maybe formed. 

Other Phases in Portland and Special Cements. In cements free lime, CaO, and periclase, MgO, hydrate to the hydroxides. The in situ reactions of larger particles of these phases can be rather slow and may not occur until the cement has hardened. These reactions then can cause deleterious expansions and even dismption of the concrete and the quantities of free CaO and MgO have to be limited. The soundness of the cement can be tested by the autoclave expansion test of Portiand cement ASTM C151 (24). 

Emulsification is essential for the development of all types of skin- and hair-care preparations and a variety of makeup products. Emulsions (qv) are fine dispersions of one Hquid or semisoHd ia a second Hquid (the contiauous phase) with which the first substance is not miscible. Generally, one of the phases is water and the other phase is an oily substance oil-ia-water emulsions are identified as o/w water-ia-oil emulsions as w/o. When oil and water are mixed by shaking or stirring ia the absence of a surface-active agent, the two phases separate rapidly to minimize the iaterfacial energy. Maintenance of the dispersion of small droplets of the internal phase, a requirement for emulsification, is practical only by including at least one surface-active emulsifier ia the oil-and-water blend. 

Transfer of material between phases is important in most separation processes in which two phases are involved. When one phase is pure, mass transfer in the pure phase is not involved. For example, when a pure liqmd is being evaporated into a gas, only the gas-phase mass transfer need be calculated. Occasionally, mass transfer in one of the two phases may be neglec ted even though pure components are not involved. This will be the case when the resistance to mass transfer is much larger in one phase than in the other. Understanding the nature and magnitudes of these resistances is one of the keys to performing reliable mass transfer. In this section, mass transfer between gas and liquid phases will be discussed. The principles are easily applied to the other phases. 

Liquid-liquid fractionation, or fractional extraction (Fig. 15-6), is a sophisticated scheme for nearly complete separation of one solute from a second solute by liquid-liquid extraclion. Two immiscible liquids travel countercurrently through a contaclor, with the solutes being fed near the center of the contactor. The ratio of immiscible-liquid flow rates is operated so that one of the phases preferentially moves the first solute to one end of the contactor and the other phase moves the second solute to the opposite end of the contactor. Another way to describe the operation is that a primaiy solvent S preferentially extracts, or strips, the first solute from the feed F and a wash solvent... 

Evaluation forms, MOC packages, audits, procedure changes, and test results are reviewed. (Feeds back to other phases.)... 

It is recommended to test eacli phase to ground separately with the other phases also grounded. This is because the insulation resistance of a complete winding to ground does not provide a check of the insulation condition between the windings. 

Some users/consultants, however, are of the opinion that by this method the other phases are not subjected to the same severity. Accordingly, they prefer to consider the phase that is subjected to the least fault current as the base. Accordingly, the test duration should be adjusted for this phase. In the above case, the minimum severity has occurred in phase R, with only 39.6 kA. According to this philosophy the test duration should be enhanced to... 

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