Metallic Solutions and Intermetallic Compounds

The Li-In phase diagram has been exhaustively re-examined by Alexander et al., using thermal and X-ray diffraction analysis. The work has confirmed the liquidus data of Grube and Wolf and delineated the solid-state relationships. Eleven new phases (Table 2), together with the previously known Liln phase (which extends from ca. 46 to between 55 and 63 mol % Li, depending on temperature), have been observed. The discovery of new phases, of which only five are stable at room temperature, has removed the apparent anomaly between the Li-In and the Li-Ga and Li-Tl systems. The solid solubility of Li in In is low (ca. 1.5 mol % Li at 432 K) and that of In in Li is very small.  

Intennetallic phases of the Li-Pd and Li-Pt systems have been synthesized 

Bronger, B. Nacken, and K. Ploog, J. Less-Common Metals, 1975, 43, 143. 

Phase Space group Structure type alnm c/nm Ref. 

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Krebs, H., M. Haucke, and H. Weyand Atomic Distribution in Liquid Bi, SnSb and InSb. Aufsatz im Buch The Phys.-Chemistry of Metallic Solutions and Intermetallic Compounds. National Phys. Lab. Symp. No. 9. London Her Majesty s Stationery Office 1959. 

A. Schneider and G. Heymer, Phenomena Accompanying Solid-Liquid Transformations of Metals and Alloys, in The Physical Chemistry of Metallic Solutions and Intermetallic Compounds (Symposium No. 9, Natl. Phys. Laboratory), Her Majesty s Stationery Office, London, 1959, pp. 4A.P2-4A.P18. 

Ian landelli. A. The Physical Chemistry of Metallic Solutions and Intermetallic Compounds,... 

No v2 Nowotny, H., Holub, F., Wittmann,A. The Physical Chemistry of Metallic Solutions and Intermetallic Compounds, London, H.M.S.O., 1959, p.3E. 

Many metals, alloys and intermetallic compounds (Me) react reversibly with gaseous H2 to form a metal hydride, MeHx, at practical temperatures and pressures. This simple reaction, neglecting the solid solution phase, may be written as ... 

Superconductivity has been found in metallic elements and intermetallic compounds and within their solid-solution-range. But, superconductivity has not been found in an alloy with an arbitrary composition. 

Open metals, OH Ordered solid solution, 78, 80, 82 — solutions and intermetallic compounds, 80... 

The various classes of metallic phases that may be encountered in crystalline alloys include substantially pure elements, solid solutions of one element in another and intermetallic compounds. In crystalline form, alloys are subject to the same type of defects as pure metals. Crystalline alloys may consist of a solid solution of one or more elements (solutes) in the major (base) component, or they may contain more than one phase. That is, adjacent grains may have slightly or extremely different compositions and be of identical or disparate crystallographic types. Often, there is one predominant phase, known as the matrix, and other secondary phases, called precipitates. The presence of these kinds of inhomogeneities often results in the alloy having radically different mechanical properties and chemical reactivities from the pure constituent elements. (Noel)5... 

Early work on pure metals, solid-solution alloys, and intermetallic compounds has been reviewed by Azaroff and Pease (9). Some of the very best X-ray absorption X-edge spectra for 3d transition metals were reported in 1939 by Beeman and Friedman (24), who applied band theory for their interpretation. Up to the early 1960s X-ray band spectra of metals were mainly explained in terms of a density of states multiplied by a transition probability. 

Solid solutions can form in metals if the atoms of which they are composed.are similar also, compounds can form. In such cases, expressions for the excess Gibbs energy of solid mixtures should contain a strain or mechanical energy term (which results from distorting the crystal structure to accommodate an atom of different size), a valence or coiilombic term to account for the difference in charge between the solute atom and the atoms of the host crystal, the noncoulombic interactions of the type we considered in discussing molecular fluids in Sec. 9.5, and perhaps a chemical reaction term to account for compound formation. Alloys, amalgams, and intermetallic compounds can occur in solids these more complicated situations will not be considered here. 

Alloys are manufactured by combining the component elements in the molten state followed by cooling. If the melt is quenched (cooled rapidly), the distribution of the two types of metal atoms in the solid solution will be random the element in excess is termed the solvent, and the minor component is the solute. Slow cooling may result in a more ordered distribution of the solute atoms. The subject of alloys is not simple, and we shall introduce it only by considering the classes of substitutional and interstitial alloys, and intermetallic compounds. 

In the discussion of the bond valence method two important problems are skirted. The first, currently a topic of lively debate, is the problem of deciding whether two atoms that are in close proximity in a structure are in fact bonded together. The second is the problem of determining, a priori, the valence of an atom. These problems are circumvented by avoiding situations where their solution is not obvious . The treatment of the bond valence method owes much to the work of Brown [1,2] but also contains some new results. It complements an earlier account [3] of new methods of describing structures. Historically the concept of bond valence derives from the Pauling [4] bond number as applied to metals and intermetallic compounds and subsequently applied to oxides by Bystrom and Wilhelmi [5]. 

Runnals [85] patented a method for making americium-aluminum alloys in which a mixture of aluminum metal and an americium halide is heated in a vacuum of 10 torr at 700-1200°C until the americium is reduced and alloyed. Homogeneous ameridum-aluminum alloys suitable for irradiation of americium can be prepared by reaction of aluminum, Am02, and NajAlF (cryolite) at 1100-1200°C [86]. d-Plutonium and jS-americium form a continuous series of fee solid solutions that are stable at room temperature in the composition range from about 6 to 80 at % americium [294]. Other alloys and intermetallic compounds are listed in Table 8.3. 

The reduction of molecular oxygen that is supplied either directly from containers or in a diluted form as air constitutes the reaction at the cathode in fuel cells. The use of air is preferable for economic reasons. Platinum metals and alloys of platinum metals are electrocatalysts for acid and alkaline electrolytes. Silver, silver alloys, nickel, carbon, and intermetallic compounds represent less expensive electrocatalysts for the oxygen electrode in alkaline solutions. In contrast to the hydrogen electrode, the overvoltage of the oxygen electrode is large at temperatures below 100 °C when a reasonable current is drawn. 

A series of Be-Pt intermetallic compounds arc prepared during the electrodeposition of Be on Pt from a solution of BeCl2 in an equimol NaCl-KCl mixture at 710°C. X-Ray diffraction of the electrode surface shows the presence of BePt, BcjPt. Electrolytic methods are also used to extract single crystals of Be,V from alloys prepared by arc melting Be and the transition metal in the proportion 15 1. 

Two metals that are chemically related and that have atoms of nearly the same size form disordered alloys with each other. Silver and gold, both crystallizing with cubic closest-packing, have atoms of nearly equal size (radii 144.4 and 144.2 pm). They form solid solutions (mixed crystals) of arbitrary composition in which the silver and the gold atoms randomly occupy the positions of the sphere packing. Related metals, especially from the same group of the periodic table, generally form solid solutions which have any composition if their atomic radii do not differ by more than approximately 15% for example Mo +W, K + Rb, K + Cs, but not Na + Cs. If the elements are less similar, there may be a limited miscibility as in the case of, for example, Zn in Cu (amount-of-substance fraction of Zn maximally 38.4%) and Cu in Zn (maximally 2.3% Cu) copper and zinc additionally form intermetallic compounds (cf. Section 15.4). 

The electrodeposition of alloys at potentials positive of the reversible potential of the less noble species has been observed in several binary alloy systems. This shift in the deposition potential of the less noble species has been attributed to the decrease in free energy accompanying the formation of solid solutions and/or intermetallic compounds [61, 62], Co-deposition of this type is often called underpotential alloy deposition to distinguish it from the classical phenomenon of underpotential deposition (UPD) of monolayers onto metal surfaces [63],... 

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