Alkali metals intermetallic compounds with

The alkali metals do not form intermetallic compounds with the transition metals. Both Na and Li dissolve only ppm quantities of most transition metals, although the solubilities are greater in Li. Nickel is very soluble in Li (900 ppm at 600°C), but no intermetallic compound forms. Intermetallic compound formation is, however, observed between Li and the noble metals Rh, Ir, Pd and Pt, so this section concentrates on the preparation of these compounds. 

Intermetallic and Semiconducting Compounds. Indium forms intermetallic compounds with a great many metals and combinations of metals including alkali metals, magnesium, the iron group, rare earths, and precious metals such as the platinum group. Carbon-free indium-based... 

Carbon dispersed in liquid alkali metals is hydrided by the reaction with dissolved hydrogen or hydrides to evolve methane. Some reactions of non-metals dissolved in the molten metals are important for the compatibility of materials with the alkali metals. Transition metals are almost insoluble in molten alkali metals. Their solubilities can be considerably raised by dissolved non-metals. Several metals of the fourth and fifth group form one or more intermetallic compounds with alkali metals. 

Sodium is the alkali metal, the chemical properties of which are best established in the molten state. Lithium chemistry has been improved during the last decade due to the interest of the fusion reactor technology. Nevertheless, several chemical properties are still unknown. Potassium and the heavy alkali metals still require research work concerning the solutions of their compounds with non-metals, as well as on the solu-bihty of metallic elements. The solubility of transition elements may range at the same level as in sodium. The degree of solubility of the elements of the fourth and fifth groups and the formation of intermetallic compounds with them are not well known. Further research may detect some new aspects, which may help to improve the application of liquid alkali metals in modem technology and chemistry. 

Me Me + -I- ze . When no metal compounds are formed with mercury, the value of Eg is close to or equals zero [1]. Compounds of the alkali metals and the alkaline earths with mercury have the best-defined composition, while copper and zinc do not form any intermetallic compounds with mercury. The compositions of many intermetallic compounds are variable. In diluted amalgams, the compounds are dissociated to various degrees. 

Pu forms intermetallic compounds with intermediate solid solutions with most metallic elements. However, simple eutectic mixtures are usually made with the group Va and Via metals, and very little solubility in either the liquid or solid state is exhibited by alkali and alkaline earth metals. 

Intermetallic compounds are generally prepared by simply heating the elements in the correct molar proportion at or just below the liquidus temperature specified in the phase diagram. The major experimental problems associated with these methods are first, attack of the container material by the alkali metal or the intermetallic compound in the molten state second, the temperature chosen must be such as to attain true homogeneity of the intermetallic compound. 

A review about the Zintl phases has been published by Sevov (2002) from the introduction of this publication we quote a few remarks. It was preliminary observed that the number of Zintl phases has increased many-fold since Zintl s time and that the definition of a Zintl phase has never been very exact often compounds that include non-metals have been considered in this family. The paper by Sevov is mainly dedicated to clearly intermetallic Zintl phases (that is phases containing main group metals, semi-metals or semiconductors only). Attention has therefore been dedicated to compounds of alkali metals with the elements of the 13th, 14th and 15th groups (without B, Al, C, N and P). To this end the following definitions and statements have been considered. 

Phase diagrams of alkali metal alloys. The pattern of the intermetallic reactivity of these metals is shown in Fig. 5.6, where the compound formation capability with the different elements is summarized. 

According to Hachenberg and Brauer , the maximum yield for metals, 5, is usually between 0.6 and 1.7. The maximum yield for insulators and semiconductors cover a much wider range 1 < 5 < 20. At the lower limit of this range we have the well-known semiconductive elements Ge, Si, Se and also compound semiconductors such as CujO and PbS. Substances with high yields include intermetallic compounds, alkali halides, alkali oxides, and alkali earth oxides. 

Bismuthides. Many intermetallic compounds of bismuth with alkali metals and alkaline earth metals have the expected formulas M3Bi and M3Bi2, respectively. These compounds are not salt ike but have high coordination numbers, interatomic distances similar to those found in metals, and metallic electrical conductivities. They dissolve to some extent in molten salts (eg, NaCl—Nal) to form solutions that have been interpreted from cryoscopic data as containing some Bi3 . Both the alkali and alkaline earth metals form another series of alloylike bismuth compounds that become superconducting at low temperatures (Table 1). The MBi compounds are particulady noteworthy as having extremely short bond distances between the alkali metal atoms. 

Rare earth oxides are useful for partial oxidation of natural gas to ethane and ethylene. Samarium oxide doped with alkali metal halides is the most effective catalyst for producing predominantly ethylene. In syngas chemistry, addition of rare earths has proven to be useful to catalyst activity and selectivity. Formerly thorium oxide was used in the Fisher-Tropsch process. Recently ruthenium supported on rare earth oxides was found selective for lower olefin production. Also praseodymium-iron/alumina catalysts produce hydrocarbons in the middle distillate range. Further unusual catalytic properties have been found for lanthanide intermetallics like CeCo2, CeNi2, ThNis- Rare earth compounds (Ce, La) are effective promoters in alcohol synthesis, steam reforming of hydrocarbons, alcohol carbonylation and selective oxidation of olefins. 

Bismuth with a formal oxidation state of -3 is found in solid-state phases MsBi (M = alkali metal) and M)Bi2 (M = alkaline-earth metal). The compoundNasBi is metallic. Less reduced intermetallic phases with the alkali metals and alkaline-earth metals are also known. Examples inclnde MBi (M = Li, Na), MBi2 (M = K, Rb, Cs), and M Bk (M = Mg, Ca, Sr, Ba). The compounds M Bis (M = Ca, Sr, or Ba) superconduct at low temperatures. Some of these intermetallic phases have been extracted with amine solvents to yield anionic bismuth clusters in solntion (see Section 2.8.2). 

The hydrides formed in reaction (a) may be classified as (1) saline or ionic hydrides, (2) metallic hydrides and (3) covalent hydrides. The saline hydrides include the hydrides of the alkali and alkaline-earth metals, except BeHj, which is covalent. Transition metals form binary compounds with hydrogen that are classified as metallic hydrides including rare-earth and actinide hydrides. Intermetallic compound hydrides, such as TiFeHj and LaNijH, may be thought of as pseudobinary metallic hydrides. 

Alloys and intermetallics of Pb and the alkali metals except Er, find interest, especially the Pb-Na system for the industrial synthesis of alkyllead antiknock compounds. The Pb—Li system, e.g., the Lii7Pbg3 eutectic may be used as a liquid breeder in the thermonuclear fission reactor ". The tendency for compound formation with the alkali metals decreases from Li to Os. ... 

Properties Gray, ductile, highly reactive metal. D 6.78, mp 795C, bp 3257C. Attacked by dilute and concentrated mineral acids and by alkalies. Readily oxidizes in moist air at room temperature. It has four allotropic forms. It is the second most reactive rare-earth metal. Cerium forms alloys with other lanthanides (see misch metal) it also forms a nonmetal with hydrogen, as well as carbides and intermetallic compounds. Decomposes water. 

At present a large variety of solid compounds are called Zintl phases. The name Zintl phase was introduced by Laves According to Laves, Zintl phases are those intermetallic compounds which crystallize in typical non-metal crystal structures. For these compounds one expects an ionic contribution to the chemical bond. This definition has been extended to a large number of solid compounds formed by alkali or alkaline earth metals with metallic or semimetallic elements of the fourth, fifth and partly third group of the Periodic Table for which common structural and bonding properties have been found. The crystal structures and chemical properties of these compounds have been studied extensively . ... 

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