Binary alloys alkali metals

The binary alloy is pyrophoric and may ignite in contact with water, as do other alkali metal germanides. 

Figure 5.6. Compound formation capability in the binary alloys of alkali metals. The different elements, the binary combinations of which with Li, Na, K, Rb, Cs are considered, are identified by their positions in the Periodic Table. No rehable data have been found about the stable equilibrium phases in the Na-P and Cs-As systems compound formation is, however, probable.

Table 5.6. A selection of formulae and structure types of intermediate phases in the alkali metal binary alloys (CNE coordination number around the A alkali metal).

Hetero-atomic clusters, moreover, may be derived from the binary structures mainly through the introduction of late transition or earlier post-transition elements. Examples of ternary alloys containing such structures are the alkali metal salts of centred clusters In10Me10 (Me = Ni, Pd, Pt), Tl12 Me12- (Me = Mg, Zn, Cd, Hg), etc. The crystal structure of the phase Na T Cdi x)27 (0.24 < x < 0.33)... 

Selenides, tellurides andpolonides. Se, Te and Po react easily with most metals and non-metals to form binary compounds (selenides and tellurides are common mineral forms of these elements). Non-stoichiometry is frequently observed in the compounds with the transition elements many of these compounds may be described as metallic alloys. The compounds of the metals of the first two groups may be considered the salts of the acids H2Se, H2Te, etc. The alkali metal selenides... 

The synthesis of M Cgo (M = Na, n = 2, 3 M = K, n = 3) has been achieved by the reaction of solid Cjq with solid MH or MBH4 [116]. The advantage of these reactions is the easier handling of small quantities of MH or MBH4 compared with alkali metals. As a source for alkali metals, binary alloys of the type CsM (M = Hg, Tl, Bi) can also be used [109]. However, the heavy metals partly co-intercalate into the Cgo lattice [115, 117]. 

One informative means of organizing a discussion of binary alkah metal compounds is by group in the periodic table. The overview provided below begins with binary alloys formed with other alkali metals and ends with binary compounds formed with halogens. The focus is primarily on second row elements. More detailed discussions can be found in the books concerning inorganic chemistry [26, 27]. 

Selenides. Selenium forms compounds with most elements. Binary compounds of selenium with 58 metals and 8 nonmetals, and alloys with three other elements have been described (55). Most of the selenides can be prepared by a direct reaction. This reaction varies from very vigorous with alkali metals to sluggish and requiring high temperature with hydrogen. 

CARBIDES. A binary solid compound of carbon and another element. The most familiar carbides are those of calcium, tungsten, silicon, boron, and iron (cemcntitc) Two factors have an important bearing on the properties of carbides (1) the difference in electronegativity between carbon and the second elemenl. and (2) whether the second element is a transition metal. Saltlike carbides of alkali metals are obtained by reaction with acetylene. Those ohlained from silver, copper, and mercury sails are explosive. See also Carbon and Iron Metals, Alloys, and Steels. 

Some interesting effects associated to the presence of well-defined structural units appear on a broad class of binary alloys formed by mixing an alkali metal (Li, Na, K, Rb, Cs) with a tetravalent metal like Sn or Pb. Due to the large difference in electronegativities it is normally assumed that one electron is transferred from the alkali to the tetravalent atom. As the Sn- or Pb-anions are isoelectronic with the P and As atoms, which in the gas phase form tetrahedral molecules P4 and AS4, in the same way the anions group in the crystal compounds forming (Sn4)4- and (Pb4)4- tetrahedra, separated by the alkali cations. This building principle was developed by Zintl in the early thirties [1], and the presence of such tetrahedra has been detected in the equiatomic solid compounds of Pb and Sn with Na, K, Rb and Cs, but not with Li [2, 3, 4]. In this paper we focus on alkali-lead alloys. 

Following the development of sponge-metal nickel catalysts by alkali leaching of Ni-Al alloys by Raney, other alloy systems were considered. These include iron [4], cobalt [5], copper [6], platinum [7], ruthenium [8], and palladium [9]. Small amounts of a third metal such as chromium [10], molybdenum [11], or zinc [12] have been added to the binary alloy to promote catalyst activity. The two most common skeletal metal catalysts currently in use are nickel and copper in unpromoted or promoted forms. Skeletal copper is less active and more selective than skeletal nickel in hydrogenation reactions. It also finds use in the selective hydrolysis of nitriles [13]. This chapter is therefore mainly concerned with the preparation, properties and applications of promoted and unpromoted skeletal nickel and skeletal copper catalysts which are produced by the selective leaching of aluminum from binary or ternary alloys. 

Germanium, tin, and lead give alloy-type binaries of the alkali metals of variable stoichiometry, but when dissolved in ammonia with the alkali metals they produce colored Zintl-type anions see Zintl Compounds) in solution which can be... 

The main new phenomenon described in this Chapter is the formation of binary and ternary surface alloys between A1 and the elements Na, K, Rb, and possibly Cs, that are immiscible in bulk Al. The ability of A1 to form surface alloys with alkali metals is explained by DFT calculations in terms of the low energy required for formation of a vacancy in a close-packed Al surface, and the large binding energy of alkali atoms in this vacancy. 

A wide open series of solid solution systems, such as ionic alkali halides KCl j jBr binary and pseudobinary metallic or semiconducting alloys Ag—Cu AI—-Cu... 

Sodium is miscible with the alkali metals below it in the periodic table (i.e., K, Rb, and Cs), and it forms a eutectic alloy with potassium (Na22 wt.% K78 wt.%) commercially known as NaK, which melts at -10°C. The eutectics formed in the Na-Rb and Na-Cs binary systems melt respectively at -4.5°C and -30°C. Sodium is the minor component with potassium and cesium of the ternary alloy Na-K-Cs. The composition of this ternary alloy is 3 wt.% Na, 24 wt.% K, and 73 wt.% Cs. This fluid is the lowest melting liquid alloy yet isolated, melting at -78°C. Sodium colors the flame of a Bunsen gas burner with a characteristic yellow color owing to the highly intense D line of its atomic spectra (589 nm). Sodium is ordinarily quite reactive with air, and its chemical reactivity is a function of the moisture content of air. 

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