Phase diagram studies

The unary phase diagram is seldom used in solid state syntheses. However, the unary diagram forms the basis for the phase diagrams of multicomponent systems. Since there are no composition variables, the only externally controllable variables in a unary system are simply the temperature and pressure. For this 

Bivariant behavior, for which both temperature and pressure are allowed to vary independently, fixes two degrees of freedom and restricts the system to a single phase. This is represented on the phase diagram as an open area. Since there is only one component, there may only be single areas for the liquid and vapor phases, but several areas corresponding to solids of different crystal structure may exist. 

Univariant equilibrium for which there is one degree of freedom, represents the equilibrium between two co-existing phases. Since there is only one degree of freedom, choosing a value for one external variable, e.g. temperature, determines the remaining variable in a dependent manner, and the locus of points represented on the phase diagram for univariant behavior must lie on a line or curve. Thus the curves on the unary phase diagram represent solid-liquid, solid-vapor, solid-solid, and liquid-vapor equilibrium. 

Invariant behavior occurs at the intersection of three univariant curves. This intersection defines a point at which three phases are in equilibrium. At these so called triple or invariant points, there are no degrees of freedom and both temperature and pressure assume fixed values. 

Because there is an added term, the composition, binary systems are inherently more complex than unary systems. In order to completely represent the phase diagram of a binary system a three dimensional pressure-temperature-composition (P-T-x) diagram can be constructed. However, it is a more common 

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J. Zhao and S. V. Olesik, Phase diagram studies of methanol-CHFj and methanol-FI20-CF1F3 mixtures. Fluid Phase Equilib. 154 261-284 (1999). 

Phase diagram studies of the magnesium-al uminum-zinc system have shown that there exists a ternary phase, which has been given the name A phase or T phase (Egar, 1913 Koster Wolf, 1936 Koster ... 

Spectroscopic and phase-diagram studies suggest complex formation between tetrachloromethane and chloroform with alkylbenzene donors, and... 

The information available on aqueous polymer blends is qualitative in nature because of the lack of a suitable theory to interpret the experimental observations. Mixed gels can be comprised of an interpenetrating network, a coupled network (as discussed above), or a phase-separated network [2]. The latter is the most common as the blends have a tendency to form two phases during gelation. In such cases the miscibility and thermodynamic stability have to be empirically investigated and proper conditions for miscible blends identified. This involves a phase diagram study as is described in [3]. 

Peck DH, Miller M, and Hilpert K. Phase diagram study in the Ca0-Cr203-La203 system in air and under low oxygen partial pressure. Solid State Ionics 1999 123,47-57. 

Contradictions and disagreements may therefore be found in the literature. In the tables included in this chapter, intended to describe the reference stable behaviour, attention has been especially dedicated to the results of phase diagram studies. 

A number of publications have appeared recently on super-lattice complexes which have enhanced conductivity, eg. "nazirpsio NaaPOif 2Zr02 2Si02 whose conductivity at room temperature is of the same order as that of an aqueous salt solution. Most of the super-lattices are unstable thermodynamically, and can be expected to collapse under chemical attack by the anodic and cathodic reactants. However, there may exist some thermodynamically stable structures, and the search should concentrate on the complicated phase-diagram studies of selected quatemarys. 

X-Ray Identification and Characterization of Components in Phase Diagram Studies... 

Tc as a function of, 241 penetration depth, 683 phase diagram study to identify, 476-83... 

The alkylamine hydrate inclusion compounds form a large variety of structures. Phase diagram studies at the end of the last century [7651 (see Tkble 21.3), and an extensive series of phase diagram studies carried out between 1970 and 1981 [798], showed that aliphatic amines form a large variety of hydrates. Relatively few of these have been studied by X-ray crystal structure analysis and none by neutron diffraction [433, 799]. These hydrates differ from the gas hydrates and the alkyl ammonium salt hydrates in that there appear to be no definite structural types into which several hydrates can be classified. Hitherto, a different crystal structure has been observed for every alkylamine hydrate studied. In this respect, they resemble low hydrated crystals. 

Phase diagrams provide the thermodynamic foundation for all alloy work by presenting the equilibrium constitution of alloys. Systematic phase diagram studies were first initiated about 100 years ago, when the thermodynamic foundations of phase diagrams were being established an additional... 

In the vanadium-nitrogen system, the phases /3-V2N and 5-VNi x have cph and fee struetures, respeetively. Carlsson et have reviewed the V-N system and reinvestigated the vanadium-rieh portion. Compiled data and results of a phase diagram study based on diffusion eouples have been used to eonstruet the phase diagram shown in Figure 7. 

From phase diagram studies on the pseudobinary Se-(SeCl4 -b 4AICI3) system, the compounds Se4(AlCl4)2 and Se8(AlCl4)2 have been identified. " " Se8(AlCLi)2 alone was prepared from a stoichiometric mixtme of Se, SeCLi, and AICI3... 

The heat of melting is calculated from the phase diagram studies of... 

Sanghvi SP, Naim JG. Phase diagram studies for microencapsulation of pharmaceuticals using cellulose acetate trimellitate. ] Pharm Sci 1991 80 394-398. 

In many of these studies the structure of the middle phase is not established, but it is clearly immiscible in water or oil and its electrical conductivity is closer to water than oil. Phase diagram studies of oil-water-emulsifier systems Ekwall, (5), indicate that surfactant-rich phases immiscible in oil or wa"ter have rodshaped or lamellar micelles with some degree of optical anisotropy or flow birefringence, and these phases have much greater elec-rical conductivity than oil. Figure 1 illustrates that the middle phase composition varies smoothly from a water-rich composition to an oil-rich composition as the emulsifier partition changes from mostly water-soluble to mostly oil-soluble. If lamellar structures are present the relative thickness of oleophilic and hydrophilic layers must vary smoothly from the water-rich compositions to the oil-rich compositions. 

Apparently a detailed investigation of the K20-A1203 system has not been conducted or reported since the phase relations between these two compounds have not been published in a phase diagram. Studies of this system have most likely been limited due to experimental difficulties associated with the high temperatures required for melting. In addition, the hygroscopic nature of compositions in the K20-A1203 system precludes the collection of reliable data. 

From a phase diagram study of the system Se-Br, Bom et al. [79BOR/KN1] identified an intermediate phase of composition Sc2Br2 with a melting point at 278 K. No thermodynamic data have been found for this compound. 

The phase diagram studies by Serezhkina et al. show that the stable solid phase in contact with water at 298.15 K is U02Se04-4H20. The solubility is ... 

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