Solid solutions discontinuous

Decomposition rates of (Ni,Co) mellitates [1110] increase with increase in nickel content. The a—time curves for the pure components and the mixed mellitates were deceleratory throughout and there was no discontinuity in shape with changes in composition. Rates of decomposition of the solid solutions were appreciably greater than those expected from the decomposition of the individual components present (Fig. 19). The values of E determined for the initial stages of the decomposition of mixtures were close to that found for the nickel salt (184 kJ mole 1) and in the latter stages tended to increase towards that for cobalt mellitate (251 kJ mole-1). Values of A showed a systematic decrease with increase in cobalt content. 

The remainder of the book treats discontinuous transformations. Nucleation, which is necessary for the production of a new phase, is treated in Chapter 19. The growth of new phases under diffusion- and interface-limited conditions is treated in Chapter 20. Concurrent nucleation and growth is treated in Chapter 21. Specific examples of discontinuous transformations are discussed in detail these include solidification (Chapter 22), precipitation from solid solution (Chapter 23), and martensite formation (Chapter 24). 

The transition metal hydrides exhibit such wide variations from stoichiometric compositions that they have often been considered interstitial solid solutions of hydrogen in the metal. This implies that the metal lattice has the same structure in the hydride phase as in the pure metal. That this is not the case can be seen in Table I, where of 28 hydrides formed by direct reaction of metal and hydrogen, only three (Ce, Ac, Pd) do not change structure on hydride formation. Even in these three cases, there is a large discontinuous increase in lattice parameter. The change in structure on addition of hydrogen plus the high heats of formation (20 to 50 kcal. per mole) (27) indicates that the transition metal hydrides should be considered definite chemical compounds rather than interstitial solid solutions,... 

We think there is another phase of the blende type near ZnS, under the region of the wurtzite solid solution, with a two-phase region between them. Nevertheless, some observations permit us to consider the possibility of this blende phase as being not a continuous solid solution, but a discontinuous series of definite compounds of similar compositions, each having a narrow homogeneity range. We are continuing this study. 

In sediments and the maflc portion of the subducted crust, all of the reactions involving hydrous phases and carbonates involve solid solutions whose compositions depend on the bulk composition, in addition to pressure and temperature. Different bulk compositions cause different phase compositions and thus cause reactions to shift in P-T space, i.e., to start shallower or deeper. In peridotites, amphibole and to some extent chlorite are controlled by continuous and discontinuous reactions however, the other volumetrically important hydrous phases (e.g., brucite, serpentine, talc, and phase A ) in altered harzburgites display a relatively restricted compositional range, at least compared to those present in mafic eclogites. As a result, breakdown reactions of hydrous phases in harzburgites are dominated (in a first approximation) by discontinuous reactions, and take place over a restricted depth range of only a few kilometers. 

Solid solutions can be classified by two methods. According to the extent of miscibility of the two components, they may be classified as continuous or discontinuous. In continuous solid solutions, the two components are miscible in the solid state in all proportions. Typical phase diagrams of continuous and discontinuous solid solutions are shown in Figs. 2 and 3, respectively. Discontinuous solid solutions exist at extremes of composition. In general, some solid-state solubility can be expected for all two-component systems. 

Fig. 3 A typical phase diagram of a discontinuous solid solution for a binary system A and B a and P are regions of solid solution formation.

Most chemical reactions that occur in natural waters take place at phase discontinuities, that is, at atmosphere-hydrosphere and lithosphere-hydrosphere interfaces. In this chapter the discussion deals primarily with the solid-solution interface. This is still a very broad topic. 

During charging and discharging, the overall composition of the Li-Al alloy electrode changes into a two-phase region limited on one side by a saturated solid solution of Li in A1 (a phase) and on the other side by the p phase of Li-Al alloy. These processes are accompanied by a first order phase transition, clearly indicated by the discontinuity of the AE relation (Fig. 3.56) and typical 3D nucleation and... 

One can apply the relations of Palmer et al. (1997) to the solid solution data of Martin and Lagache (1975) along the two substitutional joins that exhibit transitions, namely Ki jcCSjcAlSi206 and Rbi.jcCSjcAlSi206. In this analysis, the spontaneous strain is dependent not on temperature but on the concentration of the dopant Cs. This treatment demonstrates that Stot, Sa, and Se (and not the squares of these values) are linear with composition (Fig. 5). In addition, both the volumetric and the ferroelastic strains appear to be discontinuous at the critical compositions, which occur at = 0.67 for K-Cs leucite and xcs = 0.45 for Rb-Cs leucite. Consequently, the behavior of the compositionally induced transition in leucite is... 

There was an increase in the rate of decomposition of cobalt-nickel mixed mellitates [111] with increase in the proportion of nickel present. Values of measured during the early stages of reaction were close to that characteristic of nickel melhtate (184 kJ mol" ), but in the later period of reaction increased towards the value found for the cobalt salt (250 kJ mol ). No discontinuous change in kinetic behaviour was apparent and it was concluded that reaction proceeded in a solid solution. 

The effect of rhenium on the properties of refractory metals has been a research topic of discontinuous relevance since its discovery in the 1950 s [1, 2], Several works have been devoted to the mechanical property enhancement seen in VIb group transition metals when solid solution alloyed with rhenium [3-12], In the 1970 s the works of... 

This case corresponds to that of the partial miscibility of liquids. The solid component A can dissolve the component B until the concentration of the latter in the solid solution has reached a certain value. Addition of a further amount of B will not alter the composition of the solid solution, but there will be formed a second solid phase consisting of a solution of A in B. At this point the four phases, solid solution containing excess of A, solid solution containing excess of B, liquid solution, vapour, can coexist this will therefore be an invariant point. The temperature concentration curves will therefore no longer be continuous, but will exhibit a break or discontinuity at the point at which the invariant system is formed. ... 

With solutions the problem is similar to that with gases here again—except in the case of solid solutions, the specific heats of which can obviously be measured down to temperatures as low as desired—we are not, in general, in a position to prevent separation, and hence a discontinuity, on intense cooling. 

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