Phase structure relationship

P. Sakya, J. M. Seddon, R. H. Templer, R. J. Mirkin, G. J. T. Tiddy. Micellar cubic phases and their structural relationships the nonionic surfactant system Ci2EOi2/water. Langmuir 75 3706-3714, 1997. 

In each of the composition diagrams in Fig. 14.2, the numbers represent a series of reactions run at a defined composition and temperature. These are isometric sulfur slices through three-dimensional K/P/RE/S quaternary phase diagrams. As just one example of what we have studied. Table 14.1 identifies the compositions at each point and the resulting phase(s). We have rigorously studied how phase formation is dependent upon the compositions of reactions for the rare-earth elements Y, Eu, and La and we have also discovered key structural relationships between the rare-earth elements, indicating a significant dependence on rare-earth and alkali-metal size for sulfides and selenides. 

Figure 11 The structural relationship between the metastable phases Cs2Te 3 and Cs4Te2 on the reaction pathway to Cs3Te22...

General characteristics of alloys such as those presented in Fig. 3.3 have been discussed by Fassler and Hoffmann (1999) in a paper dedicated to valence compounds at the border of intermetallics (alkali and alkaline earth metal stannides and plumbides) . Examples showing gradual transition from valence compounds to intermetallic phases and new possibilities for structural mechanisms and bonding for Sn and Pb have been discussed. Structural relationships with Zintl phases (see Chapter 4) containing discrete and linked polyhedra have been considered. See 3.12 for a few remarks on the relationships between liquid and amorphous glassy alloys. 

It has already been noticed (see 3.9.4) that according to the mentioned concepts several ternary compounds may be considered as the result of a sort of structural interaction between binary compounds. As a consequence some regular trend could also be predicted for their occurrence in their phase diagrams and in the description (and perhaps modelling) of their thermodynamic properties. A few details about this type of structural relationships will be considered in the following and, in this introduction, examples of blocks of simple structural types and of their combination in more complex types will be described. 

The second type of transformation, the reconstructive transformation involves dis-solution/reprecipitation the initial phase breaks down completely (dissolves) and the new phase precipitates from solution (for a review see Blesa Matijevic, 1989). There is, therefore, no structural relationship between the precursor and the product. In contrast to the solid-state transformation, the reconstructive process is... 

The transformation of ferrihydrite to hematite by dry heating involves a combination of dehydration/dehydroxylation and rearrangement processes leading to a gradual structural ordering within the ferrihydrite particles in the direction of the hematite structure. This transformation may or may not be facilitated by the postulated structural relationship between the two phases. EXAFS studies have shown, for example, that some face sharing between FeOg octahedra, characteristic of hematite, also exists in 6-line ferrihydrite (see chap. 2). 

Aqueous Solubility. Solubility of a chemical in water can be calculated rigorously from equilibrium thermodynamic equations. Because activity coefficient data are often not available from the literature or direct experiments, models such as UNIFAC can be used for structure—activity estimations (24). Phase-equilibrium relationships can then be applied to predict miscibility. Simplified calculations are possible for low miscibility, however, when there is a high degree of miscibility, the phase-equilibrium relationships must be solved rigorously. 

LoJacono et al. (108) also utilized X-ray diffraction methods to study the structural and phase transformations which occurred in the Bi-Fe-Mo oxide system. They detected two ternary compounds containing bismuth, molybdenum, and iron. One of the compounds formed when the atomic ratio Bi/Fe/Mo = 1 1 1 the other formed when the atomic ratio Bi/Fe/Mo = 3 1 2. The X-ray data indicated a close structural relationship of the bismuth iron molybdate compounds with the scheelite structure of a-phase bismuth molybdate. Moreover, their structures were similar to compound X. The structure of the Bi/Fe/Mo = 3 1 2 compound was identical to the compound reported by Sleight and Jeitschko (107). The authors proposed that the structures of both of the compounds could be viewed as resulting from the substitution of Fe3+ in the a-phase lattice. In the Bi/Fe/Mo = 1 1 1 compound, 1 Mo6+ ion is replaced by 2 Fe3+ ions one Fe3+ ion occupies a Mo6+ site the other Fe3+ ion occupies one of the vacant bismuth sites. In the Bi/Fe/Mo = 3 1 2 compound, the Fe3+ ion replaces one Mo6+ ion while the additional Bi3+ ion occupies one of the vacant bismuth sites. 

Phase Structure as Revealed from the Mobility of the Solvent. The phase structure of the sPP crystal in the gel form, which was elucidated by the line-decomposition analysis of the DD/MAS 13C NMR spectrum, will reflect on the mobility of the solvent in the gel. The mobility of the solvent can be examined by the longitudinal relaxation of resonance lines assigned to the carbons of the solvent. Figure 31 shows the longitudinal relaxation for the line at 130 ppm of the o-dichlorobenzene. The open circles indicate the data of the pure solvent and the closed ones those of the solvent in the gel. As can be seen, the relaxation of the pure solvent evolves exponentially with a Tic of 3.0 s, whereas that of the solvent in the gel evolves nonexponentially. This indicates that there are some solvent molecules in the gel that differ in their mobility. We assume here that the longitudinal relaxation of each component of the solvent evolves exponentially. Then the longitudinal relaxation of the total solvent follows the relationship ... 

The study of the phase structure of semicrystalline polymers, particularly that of the interfacial region, is of foremost importance, since it has an intimate relationship with the macroscopic properties of polymers. Many techniques have been used to study this problem. To determine the mass fraction of each phase of the three-phase structure, such techniques as H broad-line NMR or Raman... 

Figure 3. Families of carbon matenals The top line indicates the connectivity followed by the parent carbon matenals representing according to present knowledge all allolrope phases of carbon The range of matenals in the center of the figure compnses carbons with distinct structural and chemical properties Whether these are distinct phases or metastable phase mixture is not clear The arrows mark structural relationships between the matenals The lower lines indicate the shape of the basic structural units and their organization in the solid state...

Energetics of overgrowth formation. When a second solid phase forms on a solid support by adsorption or reaction from the vapor phase, often sufficiently strong structural relationships exist between the two layers to consider the film as an overgrowth of the support. 

Interface between two liquid solvents — Two liquid solvents can be miscible (e.g., water and ethanol) partially miscible (e.g., water and propylene carbonate), or immiscible (e.g., water and nitrobenzene). Mutual miscibility of the two solvents is connected with the energy of interaction between the solvent molecules, which also determines the width of the phase boundary where the composition varies (Figure) [i]. Molecular dynamic simulation [ii], neutron reflection [iii], vibrational sum frequency spectroscopy [iv], and synchrotron X-ray reflectivity [v] studies have demonstrated that the width of the boundary between two immiscible solvents comprises a contribution from thermally excited capillary waves and intrinsic interfacial structure. Computer calculations and experimental data support the view that the interface between two solvents of very low miscibility is molecularly sharp but with rough protrusions of one solvent into the other (capillary waves), while increasing solvent miscibility leads to the formation of a mixed solvent layer (Figure). In the presence of an electrolyte in both solvent phases, an electrical potential difference can be established at the interface. In the case of two electrolytes with different but constant composition and dissolved in the same solvent, a liquid junction potential is temporarily formed. Equilibrium partition of ions at the - interface between two immiscible electrolyte solutions gives rise to the ion transfer potential, or to the distribution potential, which can be described by the equivalent two-phase Nernst relationship. See also - ion transfer at liquid-liquid interfaces. 

G65 Grudemo, A., Strength-structure relationships of cement paste materials. Part I. Methods and bctsic data for studying phase composition and microstructure (CBI Research, 6 77), 101 pp., Swedish Cemcnl and Concrete Research Institute, Stockholm (1977) also private communication quoted by L.-O. Nilsson in Report TVBM-1003, Division of Building Materials, University of Lund, Sweden (1980). 

Both of the pentoxides, but especially Nb205, have complex structural relationships.3 They are built of M06 octahedra sharing edges and corners, but this can be (and is) done in an almost unlimited number of ways. The Ta205 phase exists with an excess of Ta atoms from Ta025 to nearly Ta02. 

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