Intermetallic compounds thermodynamics

Equilibrium vapor pressures were measured in this study by means of a mass spectrometer/target collection apparatus. Analysis of the temperature dependence of the pressure of each intermetallic yielded heats and entropies of sublimation. Combination of these measured values with corresponding parameters for sublimation of elemental Pu enabled calculation of thermodynamic properties of formation of each condensed phase. Previ ly reported results on the subornation of the PuRu phase and the Pu-Pt and Pu-Ru systems are correlated with current research on the PuOs and Pulr compounds. Thermodynamic properties determined for these Pu-intermetallics are compared to analogous parameters of other actinide compounds in order to establish bonding trends and to test theoretical predictions. 

Only two processes for the manufacture of Be are of industrial importance (i). the thermal reduction of BeF2 using Mg, and (ii) the electrolysis of BeCl2 in a molten chloride electrolyte. Direct reduction of the oxide is ineffective because of its thermodynamic stability only Ca reduces BeO to the metal unfortunately, Ca cannot be used since it forms a stable intermetallic compound with Be, BejjCa. 

Ellner, M. and Predel, B. (1995) Bond characterization from thermodynamic properties. In Intermetallic Compounds. Principles and Practice, eds. Westbrook, J.H. and Fleischer, R.L. (John Wiley Sons Ltd., Chichester), Vol. 1, p. 91. 

Griessen, R. and Riesterer, T. (1988) Heat of formation models, in Hydrogen in Intermetallic Compounds I Electronic, Thermodynamic and Crystallographic Properties, Preparation, Vol. 63 (ed. L. Schlapbach), Springer Series Topics... 

Most metals of practical importance are actually mixtures of two or more metals. Recall from Section 1.1.3 that these intimate mixtures of metals are called alloys, and when the bond between the metals is partially ionic, they are termed intermetallics. For the purposes of this chapter, and especially this section, we will not need to distinguish between an intermetallic and an alloy, except to note that when a compound is indicated on a phase diagram (e.g., CuAb), it indicates an intermetallic compound. We are concerned only with the thermodynamics that describe the intimate mixing of two species under equilibrium conditions. The factors affecting how two metal atoms mix has already been described in Section 1.1.3. Recall that the solubility of one element in another depends on the relative atomic radii, the electronegativity difference between the two elements, the similarity in crystal structures, and the valencies of the two elements. Thermodynamics does not yet allow us to translate these properties of atoms directly into free energies, but these factors are what contribute to the free energy of... 

Lebedev, V.A., Pyatkov, V.I., Ushenin, S.N., 1983. Thermodynamic properties and phase composition of the alloys of the La-Sb system. In IV All-Union Conference on the Crystal Chemistry of Intermetallic Compounds, Abstracts, Lvov, p. 206. 

No indication of the presence of the NiBi intermetallic compound was found. The reasons for its absence from the Ni-Bi couple will be discussed in the next chapters. Here, it suffices to underline that those are of kinetic rather than of thermodynamic nature. 

Flanagan, T.B., Oates, W.A. (1992) Thermodynamics of Intermetallic Compound - Hydrogen Systems. In Intermetallic Compound - Hydrogen , Berlin, Springer V.l, 49-85. 

Here, AH(A-B) is the partial molar net adsorption enthalpy associated with the transformation of 1 mol of the pure metal A in its standard state into the state of zero coverage on the surface of the electrode material B, ASVjbr is the difference in the vibrational entropies in the above states, n is the number of electrons involved in the electrode process, F the Faraday constant, and Am the surface of 1 mol of A as a mono layer on the electrode metal B [70]. For the calculation of the thermodynamic functions in (12), a number of models were used in [70] and calculations were performed for Ni-, Cu-, Pd-, Ag-, Pt-, and Au-electrodes and the micro components Hg, Tl, Pb, Bi, and Po, confirming the decisive influence of the choice of the electrode material on the deposition potential. For Pd and Pt, particularly large, positive values of E5o% were calculated, larger than the standard electrode potentials tabulated for these elements. This makes these electrode materials the prime choice for practical applications. An application of the same model to the superheavy elements still needs to be done, but one can anticipate that the preference for Pd and Pt will persist. The latter are metals in which, due to the formation of the metallic bond, almost or completely filled d orbitals are broken up, such that these metals tend in an extreme way towards the formation of intermetallic compounds with sp-metals. The perspective is to make use of the Pd or Pt in form of a tape on which the tracer activities are electrodeposited and the deposition zone is subsequently stepped between pairs of Si detectors for a-spectroscopy and SF measurements. 

At temperatures on the order of 200°C, where diffusion of the metal atoms becomes significant, the latter reaction tends to begin and results in a loss of reversible capacity (i.e., irreversible Eq. 4 tends to predominate over reversible Eq. 3). Although most of the intermetallic compounds tend to be thermodynamically unstable relative to disproportionation, their actual tendency to do so varies markedly from system to system. 

In some cases, empirical rules can also relate thermodynamic properties to crystal structures. One of the best-known cases is in the AB5 systems where the equilibrium pressure is linearly correlated to the cell volume. As the cell volume increases, the equilibrium plateau pressure decreases, following a InPn law [64]. However, some exceptions exist to this rule such as in LaPts where electronic effects make the smaller unit cell more stable [65[. Nevertheless, generally, for intermetallic compounds the stability of the hydride increases with the size of the interstices [66]. A limitation of this empirical rule is that comparison between different types of intermetallics is impossible. For example, the stabilities of AB2 alloys cannot be compared with those of AB5 alloys [43]. 

For oxide electrocrystallization, the last condition is the most strenuous, sine many oxides are insulating non-stoichiometric compounds, however, are sufficient conductive. When two (or more) substances are codeposited, certain specific feature of the crystallization can be expressed for both cathodic and anodic processes on th basis of the thermodynamics of binary (or more complex) systems. If stabl multicomponent phases exist, then it is their deposition (not the deposition of mixture of simpler products) that preferentially proceeds in a certain potential regioi In such cases, intermetallic compounds are deposited in cathodic processes, and th deposition of mixed oxides takes place in anodic processes. These products ca represent both chemical compounds and solid solutions. 

It is important to understand the thermodynamic basis of the phase diagram to which an alloy belongs. A congruently melting intermetallic compound (e.g., UAlj in Fig. 1) may melt above or below the mp of its end members. A solid intermetallic phase... 

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