Binary-phase materials

W. G. Moffatt, The Handbook of Binary Phase Diagrams, General Electric Co., Schenectady, NY, 1977. Lxxiseleaf system in three volumes with regular updating. Contains excellent index to material contained in refs. 1-3. 

The polarity values of binary acetonitrile/water and methanol/water mobile phases used in RPLC were measured and compared with methylene selectivity (acH2) for both traditional siliceous bonded phases and for a polystyrene-divinylbenzene resin reversed-phase material [82], The variation in methylene selectivity for both was found to correlate best with percent organic solvent in methanol/water mixtures, whereas the polarity value provided the best correlation in acetonitrile/water mixtures. The polymeric resin column was found to provide higher methylene selectivity than the siliceous-bonded phase at all concentrations of organic solvent. 

These reactions were applied to the preparation of macrocycles containing pyridine and other heterocycles as shown in Scheme 12 [84JCS(P1)1833]. The starting material for this synthesis is 2,6-dichloropy-ridine which was converted to 2-chloro-6-methylthiopyridine quantitatively when the reaction was carried out under a liquid-liquid binary phase... 

Some progress along these lines has recently been made90) in a comparative study of some of the principal formulae quoted by Barrer 88). Most of these refer to binary composite materials consisting of phase A dispersed in microparticulate form in a continuous matrix of B. In the study in question 90), attention was first drawn to the upper and lower bounds of Eqs. (28) and (29) already mentioned, in place of the more... 

In 1989, Liu and Cohen performed theoretical calculations to investigate the structural and physical properties of P-C3N4, a metastable binary phase of carbon and nitrogen.It was predicted that this material possesses low compressibility with bulk... 

QSRR Eqs. (11.15) and (11.16) clearly demonstrate that the organic modifier of binary aqueous eluents used in reversed-phase liquid chromatography also modifies the stationary phase. The hydrocarbon brush on the silica matrix adsorbs the modifier and gets to some extent its properties 117]. QSRR enables differences in the mechanism of reversed-phase retention in individual HPLC. systems employing the. same stationary phase material, are characterized in a numerical manner. 

For the morphological analysis of the binary blends (materials DZ and NZ), the samples were cryofractured in liquid nitrogen and the rubber phase was dissolved after exposure at 140°C for 6 hours to xylene vapour. After the chemical treatment, the surfaces were gold-sputtered for SEM observation. 

Figure 27. Binary phase diagram of the //alkane system C23H48—C25H52. Phases denoted with capital letters R, O, and M refer, respectively, to rotator, orthorhombic and monoclinic (from ref 157 by permission of Materials Research Society).

In most cases such binary phases are not of importance for the production of alloys, because they exhibit completely different physical properties in comparison to the materials of the solid solution regions (higher hardness, brittleness, etc.) which are in use as alloys. A typical example are a-phase inclusions in powder metallurgically produced W-lORe alloy, which lead to a pronounced embrittlement They are die consequence of improper mixing of the two components prior to the sintering process. Re-enriched areas cannot be completely equalized by difiusion during sintering. 

Figure 20.3. Comparison of the predicted Young s moduli of binary multiphase materials with morphologies best described by the aligned lamellar fiber-reinforced matrix model (Equation 20.1), the blend percolation model (Equation 20.2), and Davies model for materials with fully interpenetrating co-continuous phases (Equation 20.3). The filler Young s modulus in Equation 20.1 was assumed to be 100 times that of the matrix, and calculations were performed at Af=10, At-=100 and Af=l()00 to compare the effects of discrete filler particles with differing levels of anisotropy. It was assumed that E(hard phase)=100, pc=0.156 and (3=1.8 in Equation 20.2. For...

The factors determining the particular structure adopted hy an intermetallic compound or, indeed, whether such a compound exists at all as a single-phase material, have been the subject of much discussion for a considerable period of time. The Hume-Rothery rules for electron compound formation will he very familiar and are related physically to the size of the Fermi sphere in the appropriate Brillouin zone. For example, electron compounds are expected for valence electron concentrations of , fj and l for the bcc, y-brass and cph structures, respectively. The interplay of other factors such as the atomic size, solubility and crystal structure of the components on the formation of intermetallic compounds has been considered in considerable detail by many workers, including Yao (1962), who suggested that transition metal binary systems could be classified into groups according to an excess energy dE expressed as... 

Binary phases. Specific heat measurements of ThPt between 1.5 and 40 K performed by Luengo et al. (1976) indicate no transition. The material is probably paramagnetic down to 1.5 K. Also the temperature dependence of the electrical resistivity measured by the same authors up to 300 K, shown in the inset of fig. 3.1, is regularly linear with no anomaly. The electronic specific heat coefficient y = 3.5 mJ/mol K2 indicates that 5f states (and also 5d states) are absent at Ev. 

Chemical reactions involving precipitation of elemental (metals) or binary phases (metal oxides, nitrides, chalco-genides, etc.) are relatively straightforward. The process becomes more complicated in the simultaneous precipitation of various components from the reaction mixture this is especially challenging when several stable compositions exist in a multi-component system. The products of room-temperature precipitation reactions are usually amorphous, and calcination or annealing steps are inevitable to obtain a defined material. Since the nature of the amorphous intermediates is difficult to determine by experimental techniques, any inhomogeneity with respect to the elemental distribution shows up, in the form of constituent segregation and secondary products, in the final material. 

A phase diagram is a map that indicates the areas of stability of the various phases as a function of external conditions (temperature and pressure). Pure materials, such as mercury, helium, water, and methyl alcohol are considered one-component systems and they have unary phase diagrams. The equilibrium phases in two-component systems are presented in binary phase diagrams. Because many important materials consist of three, four, and more components, many attempts have been made to deduce their multicomponent phase diagrams. However, the vast majority of systems with three or more components are very complex, and no overall maps of the phase relationships have been worked out. 

The reactions at the Au or Al interface on a-Si H exhibited different properties from those reported on crystalline Si, and the result is displayed most dramatically in Fig. 17 (Tsai et al, 1982). Here, laige ( l-/im) inclusions are observed that have been determined to be crystalline Si. The lateral extent indicates dendritic growth, which resulted from Si dififiision through the Au. Similar effects are observed for Al deposited on a-Si H. In both cases, evidence of atomic interdifftision was noted before the Si crystallization. These reactions occurred at temperatures of200-250° C, which is well below the crystallization temperature of a-Si H or the lowest eutectic in the binary phase diagram of the respective materials. Although the lai e crystalline Si inclusions are not observed for similar structures on crystalline Si,... 

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