Phase composition solid solution

Tin oxide-based materials are potent oxidation and isomerization catalysts. Their bulk and surface properties, as well as their presumed mechanism in oxidation catalysis, have been reviewed (53j. Considerable uncertainty remains concerning the phase compositions, solid-solution range, and the redox behavior (Sn / Sn" vs. Sb WSb ) of these materials. Structural investigations have so far concentrated on the use of " Sn and Sb Mossbauer spectroscopy. Surprisingly, no " Sn solid-state NMR studies have appeared to date on this system, although it was recently demonstrated that isotropic " Sn chemical shifts and chemical shift anisotropies give characteristic fingerprints of the various tin coordination environments in Sn(IV) oxide compounds [54]. In situ C NMR has been used to study the double bond shift of 1-butene to t /.s-2-butene, and the subsequent cis-trans isomerization over tin antimony oxide catalysts [55 j. 

If we look at the mechanistic and crystallographic aspects of the operation of polycomponent electrodes, we see that the incorporation of electroactive species such as lithium into a crystalline electrode can occur in two basic ways. In the examples discussed above, and in which complete equilibrium is assumed, the introduction of the guest species can either involve a simple change in the composition of an existing phase by solid solution, or it can result in the formation of new phases with different crystal structures from that of the initial host material. When the identity and/or amounts of phases present in the electrode change, the process is described as a reconstitution reaction. That is, the microstructure is reconstituted. 

As the amount of Fe is increased, the (111) peak shifts to smaller d-spacings, reflecting a contraction of the lattice. The (111) peak positions in Fig. 11.5 show a continuous shift from pure Pt to pure Fe. The Pt-Fe XRD patterns are consistent with a single-phase, substitutional solid solution (disordered alloy) over the entire compositional range. In contrast, Fig. 11.6 clearly displays diffraction from inter-metallic compounds of lower symmetry. Post-deposition annealing has resulted in an ordering of the Pt and Fe atoms, the effect of which is the crystallization of an ordered metal alloy of lower symmetry than 100% Pt. In essence, the applied vacuum deposition method is ideally suited for the preparation of multi-component,... 

Polythermal projections of the liquidus discussed in section 4.3.2. do not provide information on the compositions of solid phases if solid solutions or non-stoichiometric compounds are formed at equilibrium. For providing this information, the method of isothermal section is particularly useful. The following figure represents a simple ternary eutectic system with terminal solid solutions formed. 

Consider 40,000 lb/h (18,150 kg/h) of a 25 wt % MgS04 solution being fed at 200°F (366 K) to an evaporative crystallizer that boils off water at a rate of 15,000 lb/h (6800 kg/h). The crystallizer is operated at 130°F (327 K) under vacuum conditions. Determine the solid-phase composition, solid-phase production rate, and solid-phase yield. Also calculate the required energy addition rate for the process. 

With Th carbides, two carbohydride phases, ThjCHj and ThjCH, are obtained by heating the carbide in Hj gas at 0.1 MPa and 850°C. Pressure-composition isotherms show that these are definite phases, not solid solutions. The ThjCHj is hexagonal and the ThjCH monoclinic (probably distorted hexagonal). These are stable compounds extrapolation of the pressure-composition-temperature data to RT indicates dissociation pressures of ca. 10 and 10 Pa, respectively. However, the hexagonal ThjCHj transforms to a cubic phase at 380°C. 

Examples of synergistic effects are now very numerous in catalysis. We shall restrict ourselves to metallic oxide-type catalysts for selective (amm)oxidation and oxidative dehydrogenation of hydrocarbons, and to supported metals, in the case of the three-way catalysts for abatement of automotive pollutants. A complementary example can be found with Ziegler-Natta polymerization of ethylene on transition metal chlorides [1]. To our opinion, an actual synergistic effect can be claimed only when the following conditions are filled (i), when the catalytic system is, thermodynamically speaking, biphasic (or multiphasic), (ii), when the catalytic properties are drastically enhanced for a particular composition, while they are (comparatively) poor for each single component. Therefore, neither promotors in solid solution in the main phase nor solid solutions themselves are directly concerned. Multicomponent catalysts, as the well known multimetallic molybdates used in ammoxidation of propene to acrylonitrile [2, 3], and supported oxide-type catalysts [4-10], provide the most numerous cases to be considered. Supported monolayer catalysts now widely used in selective oxidation can be considered as the limit of a two-phase system. 

It has already been pointed out that when the gas is absorbed by the solid component without formation of a compound, the system is bivariant. There will therefore be no breaks in the pressure-composition curve. Continued addition of the vapour phase will lead to a continuous change in the composition of the solid phase (a solid solution), and to a continuous increase of the pressure. Similarly, withdrawal of the gaseous product of dissociation will lead to a continuous change in the composition of the solid phase and diminution... 

Temperature. Solid phase. Composition of solution m grams of salt per loo grams of water. ... 

At high temperatures, the liquid phase is a homogeneous mixture of the two atom types, lead and tin. However, the mismatch in the sizes of the lead and tin atoms prevents the formation of a complete homogeneous solid solution in the crystalline state. Instead, partial solid solutions occur at each end of the phase range, close in composition to the parent phases. The solid solutions, also referred to a terminal solid solutions, are normally called a, which is found on the lead-rich side of the diagram, and j3, found on the tin-rich side. These solid solutions adopt the crystal structure of the parent phases. Thus, the a phase has the same crystal... 

In addition, the following nonstoichiometric phases, usually solid solutions (of variabie composition), have also been obtained, and are also disordered ... 

Three types of crystallization reactions that may occur during devitrification can be classified, depending on their chemical compositions (Koster Herold, 1981 Lu, 1996) polymorphous, eutectic and primary crystallization. Fig. 2 shows a hypothetical free energy diagram to illustrate the crystallization reactions during crystallization. This schematic is essentially a representation of the variation of free energy with the chemical compositions of the amorphous phase and various crystalline phases (in this case, two crystalline phases, a solid solution a and a compound p, are included) at a chosen annealing temperature. 

Representative XRD patterns of CuSn deposits obtained in the solution containing PEG-40000 are shown in Figure 9.38. It is evident that the phase composition strongly depends on potential with an increase in negative potential, the quantity of the a-CuSn fee phase (supersaturated solid solution of tin in copper) decreases while the quantity of hep increases. 

An example of phase composition is shown in Figure 9.39. The deposits obtained in the PEG-free solution present a mixture of pure copper, a-CuSn phase (supersaturated solid solution of tin in copper) and hep phase. The content of pure Cu decreases with PEG molecular mass (except PEG-40000), but the a-CuSn phase prevails in all cases. The tendency was observed according to which the luster characteristics of coatings improve when the content of hep phase decreases. For... 

Composites which form Single Phase Oxide Solid Solutions. 379... 

While few examples of this phenomenon exist and little work has been done in this area, it is possible to affect the oxidation behavior of materials which form a single phase oxide solid solution. For example, upon oxidation, a HfC/ZrC composite would form a solution of Hf02/Zr02. Use of this type of composite, and choosing the HfC to ZrC ratio might be useful to control the monoclinic to tetragonal transformation temperature of the resulting scale or other properties of the matrix or scale. 

Vegard s law In phases in which there is a range of composition of solid solution then the cell dimensions vary linearly with the molar proportions of the constituents. The (aw is rarely followed exactly. 

System in which the solid phases consist of the pure components and the components are completely miscible in the liquid phase. We may now conveniently consider the general case of a system in which the two components A and B are completely miscible in the liquid state and the solid phases consist of the pure components. The equilibrium diagram is shown in Fig. 1,12, 1. Here the points A and B are the melting points of the pure components A and B respectively. If the freezing points of a series of liquid mixtures, varying in composition from pure A to pure B, are determined, the two curves represented by AC and BC will be obtained. The curve AC expresses the compositions of solutions which are in equilibrium, at different temperatures, with the solid component A, and, likewise, the curve BC denotes the compositions... 

The general case of two compounds forming a continuous series of solid solutions may now be considered. The components are completely miscible in the sohd state and also in the hquid state. Three different types of curves are known. The most important is that in which the freezing points (or melting points) of all mixtures lie between the freezing points (or melting points) of the pure components. The equilibrium diagram is shown in Fig. 7, 76, 1. The hquidus curve portrays the composition of the hquid phase in equihbrium with sohd, the composition of... 

---