Phase intermediate

Phases with noncubic structures were first identified by X-ray scattering from aqueous soap mixtures [68, 69] and anhydrous soap melts in a series of papers by Luzzati and Skoulios [69-73]. In the first of these papers [68] the term intermediate was applied to a rectangular structure found in aqueous mixtures of potassium and sodium oleates and potassium laurate and pal-mitate. The structures found in the anhydrous soaps were reinterpreted as intermediate, tetragonal, rhombohedral, and ribbon structures in the paper by Luzzati and coworkers [74] in 1968. It was not until the early eighties that interest in these unusual phase structures was rekindled. 

Ribbon phases have been the most comprehensively studied of the intermediate phases. They occur when the surfactant molecules aggregate to form long flat ribbons with an aspect ratio of about 0.5 located on two dimensional lattices of oblique, rectangular (primitive or centred), or hexagonal symmetry. Ribbon phases were first proposed by Luzzati [68,69] in aqueous sur- 

The first identification of intermediate mesh phase structures was by Luzzati [74] from the measurements by Spegt and Skoulios [70-73] in anhydrous soap melts. It was not until the work of Kekicheff and others [62, 76-81] on sodium dodecyl sulfate (SDS)/water and on lithium perfluoroocta- 

Many intermediate phase regions are bounded by lamellar phases which contain water filled defects the nonuniform curvature is retained although there is no longer any ordering of the defects within the bilayer and there are no correlations between the bilayers. These defected lamellar phases may also be regarded as random mesh phases. They have been seen in the SDS/water 

Hyde et al. [97, 98] have considered the origin of intermediate phases in detail. All intermediate phase structures are characterized by nonuniform interfacial curvature. The forces between the polar head groups and those between the lipidic alkyl chains tend to impose a certain value for the interfacial curvature. This curvature may not be compatible with the molecular length. The 

Even in its mean-field version, rigidity theory contains some obvious limitations that can be detected by the simple inspection of (11.1). 

Cd-Te phase diagram. The line compound at 50 At% is CdTe. (Reprinted from Massalski, T.B., Handbook cf Binary Alloy Phase Diagrams, ASM, 1990. Reprinted with permission of ASM International. All rights reserved.) 

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Trilead tetroxide, Pb304, red lead and other intermediate phases, e.g. Pb70i, and Pb203 are formed by heating PbO or Pb02- Uses... 

Although hydration under hydrothermal conditions may be rapid, metastable iatermediate phases tend to form, and final equiUbria may not be reached for months at 100—200°C, or weeks at even higher temperatures. Hence, the temperatures of formation given ia Table 6 iadicate the conditions under saturated steam pressure that may be expected to yield appreciable quantities of the compound, although it may not be the most stable phase at the given temperature. The compounds are Hsted ia order of decreasiag basicity, or lime/siHca ratio. Reaction mixtures having ratios C S = 1 yield xonotHte at 150—400°C. Intermediate phases of C—S—H (I), C—S—H (II), and crystalline tobermorite ate formed ia succession. Tobermorite (1.13 nm) appears to persist indefinitely under hydrothermal conditions at 110—140°C it is a principal part of the biader ia many autoclaved cement—silica and lime—silica products. 

Kaolin most commonly originates by the alteration of feldspar or other aluminum siHcates via an intermediate solution phase (97,98) usuaHy by surface weathering (26,99) or by rising warm (hydrothermal) waters. A mica, or hydrated alumina soHd may form as an intermediate phase during the alteration from parent material to kaolin minerals. 

The reaction of metals with gas mixtures such as CO/CO2 and SO2/O2 can lead to products in which the reaction of the oxygen potential in the gas mixture to form tire metal oxides is accompanied by the formation of carbon solutions or carbides in tire hrst case, and sulphide or sulphates in the second mixture. Since the most importairt aspects of this subject relate to tire performairce of materials in high temperature service, tire reactions are refeiTed to as hot corrosion reactions. These reactions frequendy result in the formation of a liquid as an intermediate phase, but are included here because dre solid products are usually rate-determining in dre coiTosion reactions. 

Fig. 3.6. (a) The copper-nickel diagram is a good deal simpler than the lead-tin one, largely because copper and nickel are completely soluble in one another in the solid state. (b) The copper-zinc diagram is much more involved than the lead-tin one, largely because there are extra (intermediate) phases in between the end (terminal] phases. However, it is still an assembly of single-phase and two-phase fields. 

Most alloy systems are more complicated than the lead-tin system, and show intermediate phases compounds which form between components, like CuAlj, or AljNi, or FojC. Their melting points are, usually, lowered by alloying also, so that eutectics can form between CuAlj and A1 (for example), or between AljNi and Al. The eutectic point is always the apex of the more or less shallow V formed by the liquidus lines. 

The sequence just outlined provides a salutary lesson in the nature of explanation in materials science. At first the process was a pure mystery. Then the relationship to the shape of the solid-solubility curve was uncovered that was a partial explanation. Next it was found that the microstructural process that leads to age-hardening involves a succession of intermediate phases, none of them in equilibrium (a very common situation in materials science as we now know). An understanding of how these intermediate phases interact with dislocations was a further stage in explanation. Then came an nnderstanding of the shape of the GP zones (planar in some alloys, globniar in others). Next, the kinetics of the hardening needed to be... 

The second type of mass-exchange units is the differential (or continuous) contactor. In this category, the two phases flow through the exchanger in continuous contact throughout without intermediate phase separation and recontacting. Examples of differential contactors include packed columns (Fig. 2.6), spray towers (Fig. 2.7), and mechanically agitated units (Fig. 2.8). 

Table 14.15 Intermediate phases formed by ordering of defects in the praseodymium-oxygen system...

Oxides of the actinides are refractory materials and, in fact, Th02 has the highest mp (3390°C) of any oxide. They have been extensively studied because of their importance as nuclear fuels. However, they are exceedingly complicated because of the prevalence of polymorphism, nonstoichiometry and intermediate phases. The simple stoichiometries quoted in Table 31.5 should therefore be regarded as idealized compositions. 

PET fibers in final form are semi-crystalline polymeric objects of an axial orientation of structural elements, characterized by the rotational symmetry of their location in relation to the geometrical axis of the fiber. The semi-crystalline character manifests itself in the occurrence of three qualitatively different polymeric phases crystalline phase, intermediate phase (the so-called mes-ophase), and amorphous phase. When considering the fine structure, attention should be paid to its three fundamental aspects morphological structure, in other words, super- or suprastructure microstructure and preferred orientation. 

The mesomorphous phase, also called an intermediate phase or a mesophase, is formed by molecules occurring in surface layers of the crystallites. It can be assumed that the mesophase is made up largely by regularly adjacent reentry folds. However, it cannot be excluded that the mesophase is also composed of some irregular chain folds, which are characterized by a long length and run near the crystal face in the direction perpendicular to the microfibril axis. 

Although the above results again point towards a relation between the preeursing distortions and the martensite shuffles, detailed analysis of the neutron seattering data in the temperature region elose to Ms indieate that an intermediate phase may exist with an effective 6-layer periodieity. In this view the ISD modulations eould rather be preeursors to this intermediate phase than to the final martensite strueture. 

By way of example, the Cu-Zn phase diagram shown in Fig. 20.42 exhibits a number of different intermediate phases (j8, 7, 6, etc.) and a number of peritectic reactions and a eutectoid reaction. In many instances it is not necessary to consider a complete phase diagram. Thus Fig. 20.43 illustrates the Al-rich end of the Al-Cu phase diagram and is used below in a discussion... 

Phase composition changes as a function of temperature are similar to these that were observed for the lithium-containing system (see Fig. 21), except that individual stable ammonium-cobalt-oxyfluoroniobate occurs prior to the formation of CoNbOF5 (Fig.21, curve 4). It is assumed that the composition of this intermediate phase, formed at 330-350°C, is (NH CoNbOFy [129]. Complete removal of ammonium occurs at about 400°C (Fig. 21, curve 5) and leads to the formation of CoNbOFs. The compound is defined as practically isotropic rose-colored ciystals with a refractive index of N = 1.500. The... 

Delmas and co-workers have proposed the existence of an intermediate phase between a- and / -Ni(OH)2 [48]. This phase consist of interleaved a and ft material and can be formed on ageing of a - Ni(OH)2. Recent Raman results confirm the existence of such a phase [49]. 

Measurements were also made of the potential-composition behavior, as well as the chemical diffusion coefficient, and its composition dependence, in each of the intermediate phases in the Li-Sn system at 415 °C [39]. 

The generation of an intermediate phase during melting under isometric conditions of orientationally crystallized polyethylene has also been observed56 at temperatures exceeding the melting temperature of ECC. The authors suppose that the mesophase... 

A study of the effect of the mesophase layer on the thermomechanical behaviour and the transfer mechanism of loads between phases of composites will be presented in this study. Suitable theoretical models shall be presented, where the mesophase is taken into consideration as an additional intermediate phase. To a first approximation the mesophase material is considered as a homogeneous isotropic one, while, in further approximations, more sophisticated models have been developed, in which the mesophase material is considered as an inhomogeneous material with progressively varying properties between inclusions and matrix. Thus, improvements of the basic Hashin-Rosen models have been incorporated, making the new models more flexible and suitable to describe the real behaviour of composites. 

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