Composites solid solutions compared

Hence, the decision to use a heated substrate with simultaneous evaporation of the component metals as an aid to homogenization requires consideration of whether or not it might have an adverse effect, i.e., causing preferential nucleation of one component, which interdiffusion may not be able to remedy. It was believed (60) that in preparing Pd-Rh alloys by simultaneous deposition on a substrate at 400°C, rhodium nucleated preferentially and that crystallites grew by the addition of palladium (and rhodium) atoms. The diffusion of palladium atoms into this kernel formed a phase with 88 =t 5% Rh (phase II). The outer shell of the crystallite, phase I, was in effect a solid solution deficient in rhodium compared with the overall film composition, and the Rh content of phase I therefore increased as the Rh flux was increased. 

Although nearly identical solid-aqueous solution compositions are observed in recrystallization from two directions under conditions of total constant composition, this alone is insufficient proof of the establishment of equilibrium. In order to test for equilibrium, the solid solution activity coefficients must be determined and used to compare observed solid and aqueous solution compositions with the appropriate values expected at equilibrium. 

This permits provisional calculation of the compositional dependence of the equilibrium constant and determination of provisional values of the solid phase activity coefficients (discussed below). The equilibrium constant and activity coefficients are termed provisional because it is not possible to determine if stoichiometric saturation has been established without independent knowledge of the compositional dependence of the equilibrium constant, such as would be provided from independent thermodynamic measurements. Using the provisional activity coefficient data we may compare the observed solid solution-aqueous solution compositions with those calculated at equilibrium. Agreement between the calculated and observed values confirms, within the experimental data uncertainties, the establishment of equilibrium. The true solid solution thermodynamic properties are then defined to be equal to the provisional values. 

Composite-pulse decoupling schemes like WALTZ [36, 37], DIPSI [38], or GARP [39], which are used in solution-state NMR, have failed to offer any significant improvements in the solid state compared to CW decoupling. The residual line width in CW-decoupled spectra is dominated by a cross term between the chemical-shielding tensor of the protons and the heteronuclear dipolar-coupling tensor [40, 41]. 

Optical spectra showed a gradual shift of the onset with composition, as expected for a true solid solution. Additionally, the refractive index (and therefore the dielectric constant) increased gradually as the Se content increased, mirroring the larger dielectric constant of CdSe compared with CdS. 

We wish here to obtain the thermodynamic equations defining the liquidus surface of a solid solution, (At BB)2, ). It is assumed that the A and atoms occupy the sites of one sublattice of the structure and the C atoms the sites of a second sublattice. For the specific systems considered here Sb and play the role of C in the general formula above. It is also assumed that the composition variable is confined to values near unity so that the site fractions of atomic point defects is always small compared to unity. This apparently is the case for the solid solutions in the two systems considered. Then it can be shown theoretically (Brebrick, 1979), as well as experimentally for (Hgj CdJ2-yTe)l(s) (Schwartz et al, 1981 Tung et al., 1981b), that the sum of the chemical potentials of A and C and that of and C in the solid are independent of the composition variable y ... 

During the growth of solid solutions (e. g., pseudobinary alloys and doped compounds), the melt composition at the interface can be a function of time, a situation that results in a natural composition gradient in the growth direction. Heteroepitaxy, the growth of an epitaxial film with a composition different from that of the substrate, is more difficult compared with other... 

Feldspar Unlike enstatite and forsterite, feldspar is present in most meteorites. The meteoritic feldspars are dominated by plagioclase which are those feldspar compositions in the continuous solid solution series ranging from albite (NaAlSi308) to anorthite (CaAl2Si2C>8) compositions near the ends of this series are most common. The earliest CL studies of feldspar were prompted by the lunar program about 1970 and a series of papers compared the CL of lunar, meteoritic and doped synthetic plagioclase. Later observations were made for anorthite in the carbonaceous chondrites. 

The relations are comparatively simple within the Fe-Cu-W-S quaternary system78. The 700 °C isotherm is shown in Fig. 28, from which the high-temperature equilibria can easily be deduced. Since tungsten does not form ternary or quaternary sulfides, the phase relations of the Fe—Cu—S ternary system dominate and influence the whole tetrahedron. Tungsten is stable only with the very metal-rich portions of the pyrrhotite solid solution ( FeS composition) and of the chalcocite-bornite mixed-crystal row, as a result of its lower affinity to sulfur. Tungstenite (WS2) can... 

Solid materials, even at elevated temperatures, may not often achieve thermodynamic equilibrium due to the slowness of mass transport in solid state. Metastable equilibria (well known for glasses) may then be established. This makes it possible to prepare metastable solid solutions in wider compositional ranges if compared to thermodynamic equilibrium, by using various synthesis techniques at relatively low temperatures. 

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. 

As a point of reference for the following discussion. Figure 8 shows the range of solid solution for high-temperature (nonclay mineral) chlorites. This range can serve as a guide to compare the compositions of chlorite and chloritelike green clays. 

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