Solid phases, stable

Fig. 7.2 Fe-O phase diagram showing the principal solid phases stable on iron and wide stoichiometry limits of FeO (after White )...

Because bismuth has several well-characterized solid, crystalline phases, it is used to calibrate instruments employed in high-pressure studies. The following phase diagram for bismuth shows the liquid phase and five different solid phases stable... 

It is well known that liquids are characterized by a local order that is often close to one of the solid phases stable at the same density [1,2]. The existence of a well-defined local order is fundamental to understand liquid liquid transitions (LLTs), that is, the first-order transitions between two liquid phases different from each other in the local atomic arrangement and thermodynamic properties. Although an LLT can be possibly expected for multiatomic liquids, only quite recently it has been demonstrated that such transitions also exist for single component, isotropic liquids such as phosphorus [3,4], which polymerizes at high pressures and... 

Unlike melting and the solid-solid phase transitions discussed in the next section, these phase changes are not reversible processes they occur because the crystal stmcture of the nanocrystal is metastable. For example, titania made in the nanophase always adopts the anatase stmcture. At higher temperatures the material spontaneously transfonns to the mtile bulk stable phase [211, 212 and 213]. The role of grain size in these metastable-stable transitions is not well established the issue is complicated by the fact that the transition is accompanied by grain growth which clouds the inteiyDretation of size-dependent data [214, 215 and 216]. In situ TEM studies, however, indicate that the surface chemistry of the nanocrystals play a cmcial role in the transition temperatures [217, 218]. 

In accordance with these data, ionic associates (lA) can be precipitated at phosphate concentrations more than 10 M. Below this concentration stabile supersaturated solutions of lA are formed. Colour of lA appeal s immediately after mixing of the solutions and remains constant during several hours. There is a new band in spectmm at 570-590 nm. Appearance of color is caused by formation of stable solid phase in the solution. 

In recent years the solid-phase hydrosilylation reaction was successfully employed for synthesis of hydrolytically stable surface chemical compounds with Si-C bonds. Of special interest is application of this method for attachment of functional olefins, in particular of acrolein and some chiral ligands. Such matrices can be used for subsequent immobilization of a wide range of amine-containing organic reagents and in chiral chromatography. 

H2/Pd-C, EtOH, 20°. < -Bromobenzyl carbonates have been developed for use in solid-phase peptide synthesis. An aryl o-bromobenzyl carbonate is stable to acidic cleavage (CF3CO2H) of a /-butyl carbamate a benzyl carbonate is cleaved. 

The iron-carbon solid alloy which results from the solidification of non blastfurnace metal is saturated with carbon at the metal-slag temperature of about 2000 K, which is subsequendy refined by the oxidation of carbon to produce steel containing less than 1 wt% carbon, die level depending on the application. The first solid phases to separate from liquid steel at the eutectic temperature, 1408 K, are the (f.c.c) y-phase Austenite together with cementite, Fe3C, which has an orthorhombic sttiicture, and not die dieniiodynamically stable carbon phase which is to be expected from die equilibrium diagram. Cementite is thermodynamically unstable with respect to decomposition to h on and carbon from room temperature up to 1130 K... 

At 183°C. The liquid composition has reached the eutectic point (the bottom of the V). This is the lowest temperature at which liquid is stable. At this temperature all the remaining liquid transforms to two solid phases a tin-rich a phase, composition Xpb= 1.45% and a lead-rich (3 phase, composition Xpi, = 71%. This reaction ... 

A nitrophenylsulfenate, cleaved by nucleophiles under very mild conditions, was developed as protection for a hydroxyl group during solid-phase nucleotide synthesis. The sulfenate ester is stable to the acidic hydrolysis of acetonides. ... 

X-ray diffraction studies show that solid N2O5 consists of an ionic array of linear NO2+ (N-O 115.4 pm) and planar NO3 (N-O 124 pm). In the gase phase and in solution (CCI4, CHCI3, OPCI3) the compound is molecular the structure is not well established but may be O2N-O-NO2 with a central N-O-N angle close to 180°. The molecular form can also be obtained in the solid phase by rapidly quenching the gas to — 180°, but it rapidly reverts to the more stable ionic form... 

Br20 a dark-brown solid moderately stable at —60° (mp —17.5° with decomposition), prepared by reaction of Bt2 vapour on HgO (cf. CI2O p. 846) or better, by low-temperature vacuum decomposition of BrOa. The molecule has C2v symmetry in both the solid and vapour phase with Br-O 185 1pm and angle BrOBr 112 2° as determined by EXAFS (extended X-ray absorption fine structure). It oxidizes I2 to I2O5, benzene to 1,4-quinone, and yields OBr in alkaline solution. 

The solid is the more dense phase (Figure 9.7a). The solid-liquid equilibrium line is inclined to the right, shifting away from the y-axis as it rises. At higher pressures, the solid becomes stable at temperatures above the normal melting point In other words, the melting point is raised by an increase in pressure. This behavior is shown by most substances. 

Figure 8.9 is the phase diagram for Sn, a system that shows (solid + solid) phase transitions." Solid II is the form of tin stable at ambient conditions, and it is the shiny, metallic element that we are used to observing. Line ab is the melting line for solid II. Points on this line represent the values of p and T for which... 

At a temperature such that the solid phase is stable AF is necessarily positive and the stable crystal has infinite thickness. However, any crystal which has AG < 0 will be stable compared with the liquid, so that a crystal of finite thickness may be metastable if there is a free energy barrier to the formation of an infinite crystal. AG < 0 if ... 

Another family of polyols is the filled polyols.llb There are several types, but die polymer polyols are die most common. These are standard polyether polyols in which have been polymerized styrene, acrylonitrile, or a copolymer thereof. The resultant colloidal dispersions of micrometer-size particles are phase stable and usually contain 20-50% solids by weight. The primary application for these polyols is in dexible foams where the polymer filler serves to increase foam hardness and load-bearing capacity. Other filled polyol types diat have been developed and used commercially (mainly to compete with die preeminent polymer polyols) include the polyurea-based PEID (polyhamstoff dispersion) polyols and the urethane-based PIPA (poly isocyanate polyaddition) polyols. 

Figure 8.30a shows how the molar Gibbs free energies of the liquid and solid phases of a pure solvent vary with temperature. The solid is the more stable phase... 

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