Intermetallic compounds, element

Intermetallic Compounds. Numerous intermetalhc galhum—transition element compounds have been reported (17). The principal compounds ate hsted in Table 4 (18—23). There ate probably several Cs and Rb compounds however, none is well known. 

The intermetallic compounds with Group 16 (VIA) elements including CdS, CdSe, and CdTe have interesting semiconductor properties for photoconductors, photovoltaic cells, and ir windows. Cadmium sulfide is widely used as a phosphor in television tubes. 

Solution hardening is not confined to 5000 series aluminium alloys. The other alloy series all have elements dissolved in solid solution and they are all solution strengthened to some degree. But most aluminium alloys owe their strength to fine precipitates of intermetallic compounds, and solution strengthening is not dominant... 

Of the elements normally present in tin-rich alloys, lead forms a simple eutectic system with a eutectic composition at 63% Sn, and copper and antimony have a small solid solubility and form the intermetallic compounds Cu Sn, and SbSn respectively. ... 

In the papers referred to above it is pointed out that the mechanical properties of the transition elements and the distances between atoms in metals and intermetallic compounds are well accounted for by these considerations. In the following sections of the present paper a discussion is given of the number of valence electrons by the Brillouin polyhedron method, and it is shown that the calculations for the filled-zone alloys such as the 7-alloys provide further support for the new system of metallic valences. 

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. 

Several preparative methods do not use elemental mixtures. Group IIA-Pt intermetallic compounds have been prepared by reacting platinum metal with the group-IIA oxide under hydrogen or ammonia at 900-1200 C. Beryllium metal reacts with neptunium fluoride under vacuum at 1100-1200°C to form BC 3Np. 

The need for better performing and secure anodic materials in lithium-ion batteries compared with those based on carbon, has boosted research in various domains. Lithium/post-transition element (Al, Si, Sn, Sb...) binary systems have been widely investigated. Owing to the numerous intermetallic compounds that... 

The geometric principles for the packing of spheres do not only apply to pure elements. As might be expected, the sphere packings discussed in the preceding chapter are also frequently encountered when similar atoms are combined, especially among the numerous alloys and intermetallic compounds. Furthermore, the same principles also apply to many compounds consisting of elements which differ widely. 

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). 

It is very difficult to cool pure metals and other pure elements fast enough to form glasses. However, metallic alloys can often be converted into glasses, particularly if they contain a mixture of small and large atoms such as iron and boron, or they are multi-component mixtures of metals that crystallize into more than one intermetallic compound (i.e., eutectic compositions). Thus, covalent chemical interactions of the atoms are important because they stabilize liquids and thereby inhibit crystallization. 

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