Solid solutions continuous

Solutions and glasses do not follow the third law. If a solid solution continues to persist on cooling a sample to the lowest possible temperature, then at this temperature the molecules of the several components are distributed in some fashion in the same crystal lattice. Under such conditions all of the molecules of the substance could not attain the same quantum state on further cooling to 0 K in the sense of the required extrapolation. Only if the solid solution was separated into the pure components would the value of zero be obtained for the entropy function at 0 K. If the molecules of the components were randomly distributed in the crystal lattice, as in an ideal solution, then the entropy of the substance at absolute zero would be equal to the ideal entropy of mixing, so... 

Solid Solutions. EQ3/6 includes provision for dealing with solid solutions, both as "reactant" and "product" phases. Both ideal and non-ideal solid solution models have been incorporated. The compositions of "product" solid solutions continually readjust to remain in equilibrium with the changing fluid composition. In the "flow-through" open system mode, "product" solid solutions are removed from the reacting system as they form, resulting in zoning... 

A solid solution with x(ZrF4) = 0.24 appears at 855 °C. The solid solution continues to form, and its ZrF4 content increases until it reaches x(ZrF4) = 0.40 and 820 °C. At that temperature, the entire sample is solid. 

The main alloying elements of Al materials are Cu, Si, Mg, and Zn while Mn, Fe, Cr, and Ti are frequently present in small quantities, either as impurities or additives. Ni, Co, Ag, Li, Sn, Pb, and Bi are added to produce special alloys. Be, B, Na, Sr, and Sb may be added as important trace elements. All of these elements affect the structure and thus the properties of an alloy. The compositions of the more important aluminium materials are discussed below, using the relevant phase diagram. All alloying components are completely soluble in liquid aluminium if the temperature is sufficiently high. However, these elements have only limited solubility in solid solution. Continuous solid solubil-... 

Siher(Il) oxide, AgO, is a black solid, Ag Ag 02, obtained by anodic or persulphate oxidation of an AgNOs solution. Continued anodic oxidation gives impure Ag203. Argentates, e.g. K.AgO, containing silver(I) are known. 

System in which the two components form a continuous series of solid solutions. In all the preceding examples the individual components (A or B or A By) form separate crystals when solidifying from the melt. There are, however, a number of examples of the separation of a homogeneous solid solution of A and B (or A and A By, etc.). 

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... 

Two other types of equilibrium curves are occasionally encountered with the system of two components forming a continuous series of solid solutions. These are shown in Figs. 1,16, 3 and 1,16, 4. In the former the freezing or melting curve passes through a minimum (examples p-chloroiodobenzene, m.p. 57° - p-dichlorobenzene, m.p. 53° naphtha-... 

Drop 1 g. of sodium into 10 ml. of ethyl alcohol in a small flask provided with a small water condenser heat the mixture until all the sodium has dissolved. Cool, and add 1 g. of the ester and 0-5 ml. of water. Frequently the sodium salt of the acid will be deposited either at once or after boiling for a few minutes. If this occurs, filter oflF the solid at once, wash it with a little absolute ethyl alcohol (or absolute methylated spirit), and convert it into the p-bromophenacyl ester, p-nitro-benzyl ester or S-benzyl-tso-thiuronium salt (for experimental details, see Section 111,85). If no solid separates, continue the boiling for 30-60 minutes, boil oflF the alcohol, allow to cool, render the product just neutral to phenolphthalein with dilute sulphuric or hydrochloric acid, convert the sodium salt present in solution into a crystalline derivative (Section 111,85), and determine its melting point. 

Table 1 fists many metal borides and their observed melting points. Most metals form mote than one boride phase and borides often form a continuous series of solid solutions with one another at elevated temperatures thus close composition control is necessary to achieve particular properties. The relatively small size of boron atoms facilitates diffusion. 

The difference in stability between FeO and NiO is not as large as that between iron and copper oxides, and so the preferential oxidation of iron is not so marked in pentlandite. Furthermore, the nickel and iron monoxides form a continuous series of solid solutions, and so a small amount of nickel is always removed into die oxide phase (Table 9.2). 

Tellurium has only one crystalline form and this is composed of a network of spiral chains similar to those in hexagonal Se (Fig. 16.1c and d). Although the intra-chain Te-Te distance of 284 pm and the c dimension of the crystal (593 pm) are both substantially greater than for Scjt (as expected), nevertheless the closest interatomic distance between chains is almost identical for the 2 elements (Te Te 350 pm). Accordingly the elements form a continuous range of solid solutions in which there is a random... 

Tantalum-Molybdenum Schumb, Radtke and Bever studied the corrosion resistance of tantalum-molybdenum alloys that form a continuous series of solid solutions. The results of tests of up to 500 hours duration (Table 5.26) indicate the corrosion resistance of the alloy to be substantially that of tantalum, provided its concentration exceeds 50%. 

It must be noted that the values of Dq and E are influenced by the concentration of the solute metal and also by the presence of alloying elements in the solvent. It has also been shown that the diffusion coefficient for a given solute is in inverse proportion to the melting point of the solvent. D is least for metals forming continuous series of solid solutions and for self-diffusion. 

The points R have to be on a straight line terminating in the composition of the methanol hydroquinone clathrate (A) in equilibrium with a-hydroquinone at 25°C. The point B roughly corresponds to the composition of the clathrate obtained by Palin and Powell24 when crystallizing hydroquinone from methanol points between A and B form a continuous range of solid solutions in equilibrium with liquid phases whose compositions lie on the curve CE. It is found that the equilibrium clathrate has a composition corresponding to y — 0.474 at 25°C. 

Two product barrier layers are formed and the continuation of reaction requires that A is transported across CB and C across AD, assuming that the (usually smaller) cations are the mobile species. The interface reactions involved and the mechanisms of ion migration are similar to those already described for other systems. (It is also possible that solid solutions will be formed.) As Welch [111] has pointed out, reaction between solids, however complex they may be, can (usually) be resolved into a series of interactions between two phases. In complicated processes an increased number of phases, interfaces, and migrant entities must be characterized and this requires an appropriate increase in the number of variables measured, with all the attendant difficulties and limitations. However, the careful selection of components of the reactant mixture (e.g. the use of a common ion) or the imaginative design of reactant disposition can sometimes result in a significant simplification of the problems of interpretation, as is seen in some of the examples cited below. 

In a saturated solution, any solid solute present still continues to dissolve, but the rate at which it dissolves exactly matches the rate at which the solute returns to the solid (Fig. 8.17). In a saturated solution, the dissolved and undissolved solute are in dynamic equilibrium with each other. 

Knowledge of phase diagrams is not only a prerequisite for efficient crystal-growth, but also provides information on the formation of solid solutions, in which, for example, physical properties may change continuously. The numerous publications concerning Group VA systems are summarized in Tables XXV-XXVII, together with the respective references and the most important information. Abbreviations used... 

Calcium is miscible with Sr in the liquid and in all the solid bcc, hep and fee allotropic forms (Fig. 1). Barium exhibits no hep or fee forms, however, so that solid solubility between the close-packed structures of Ca and Sr, and the bcc structure of Ba is restricted in the Ca-Ba and also in the Sr-Ba systems. A continuous series of solid solutions is only achieved in Ca-Ba and Sr-Ba for the high-T bcc modifications. In Ca-Ba, the solid solutions are separated by a narrow heterogeneous field between 32 and 36 mol% Ba in Sr-Ba this occurs between 24 and 30 mol% Ba (Fig. 1). 

Figure 8.14 Emission spectra at 298 l< of [Au(C6F40CtoH2i)-(CNCgH4C6H40CgHi3)] (excitation 344 nm) in the solid state (continuous line) and in CH2CI2 solution (dashed line). (Reproduced from Ref [32] by permission.).

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