Alloy and Intermetallic

In this chapter, the terms alloy and intermetallic a.re used to denote multicomponent systems composed of metals. In some quarters, the two terms denote extrema in the continuum of multicomponent systems, where the chemical identity of an atom occupying any given site is either random (alloy) or fixed (intermetallic). In this sense, QCs and approximants are more similar to intermetallics than to alloys. 

The use of hyphens to separate names of elements, as in Al-Pd-Mn, indicates that constituent elements are named without regard to stoichiometry. On the other hand, when stoichiometry is specified, the hyphens are omitted and subscripts are added to denote atomic percents, as in Al7QPd2oMnio. If there are no hyphens and no subscripts, the implied stoichiometry is 1 1, as in NiAl. 

The prefix i denotes an icosahedral quasicrystalline phase, as in i-Al-Pd-Mn. The prefix d denotes a decagonal quasicrystalline phase, as in d-Al-Ni-Co. 

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M X the explosive black nitride T1 3N is known, and the azides T1 N3 and T1 [T1 (N3)4] the phosphides TI3P, TIP3 and TIP5 have been reported but are not well characterized. With As, Sb and Bi thallium forms alloys and intermetallic compounds TI3X, Tl7Bi2 and TlBi2. 

Diffusion in Ordered Alloys and Intermetallic Compounds ed. by B. Fultz et al. TMS Publication, Warrendale, PA (1993), 79-90. 

The present chapter deals with the CVD of metals and some metal alloys and intermetallics. The metals are listed alphabetically. The range of applications is extensive as many of these materials play an important part in the fabrication of integrated circuits and other semiconductor devices in optoelectronic and optical applications, in corrosion protection, and in the design of structural parts. These applications are reviewed in greater depth in Chs. 13 to 19. 

Typically, Be-containing alloys and intermetallic phases have been prepared in beryllia or alumina crucibles Mg-containing products have been synthesized in graphite, magnesia or alumina crucibles. Alloys and compounds containing Ca, Sr and Ba have been synthesized in alumina , boron nitride, zircon, molybdenum, iron , or steel crucibles. Both zircon and molybdenum are satisfactory only for alloys with low group-IIA metal content and are replaced by boron nitride and iron, respectively, for group-IIA metal-rich systems . Crucibles are sealed in silica, quartz, iron or steel vessels, usually under either vacuum or purified inert cover gas in a few cases, the samples were melted under a halide flux . 

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. 

P.N. Ross, "Oxygen Reduction on Supported Pt Alloys and Intermetallic Compounds in Phosphoric Acid," Final Report, EM-1553, prepared under Contract 1200-5 for the Electric Power Research Institute, Palo Alto, CA, September 1980. 

A. Pebler, E.A. Gulbransen, Thermochemical and structural aspects of the reaction of hydrogen with alloys and intermetallic compounds of zirconium, Electrochem. Techn. 4 (1966) 211-215. 

Calcium combines with a number of metals at elevated temperatures forming alloys and intermetallic compounds. 

It is shown that the semi-empirical model of Miedema and v.d. Woude [66], which was developed for predicting the I.S. changes of Mossbauer nuclei in alloys and intermetallic compounds, gives a remarkably good prediction of the observed I.S. values for the surface sites [67]. 

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 ... 

Mg-Al alloys and intermetallics have been the focus of many investigations motivated by the interest in these materials due to their industrial use in the manufacture of lightweight components. Mg NMR spectra of Mg-rich alloys are similar to Mg metal. The alloy Mg-6wt% A1 was studied by Bastow and Smith, ° who reported a slight shift of the resonance compared to that foimd in pure Mg metal (/ 16ppm upheld) and a... 

The second type of impurity, substitution of a lattice atom with an impurity atom, allows us to enter the world of alloys and intermetallics. Let us diverge slightly for a moment to discuss how control of substitutional impurities can lead to some useful materials, and then we will conclude our description of point defects. An alloy, by definition, is a metallic solid or liquid formed from an intimate combination of two or more elements. By intimate combination, we mean either a liquid or solid solution. In the instance where the solid is crystalline, some of the impurity atoms, usually defined as the minority constituent, occupy sites in the lattice that would normally be occupied by the majority constituent. Alloys need not be crystalline, however. If a liquid alloy is quenched rapidly enough, an amorphous metal can result. The solid material is still an alloy, since the elements are in intimate combination, but there is no crystalline order and hence no substitutional impurities. To aid in our description of substitutional impurities, we will limit the current description to crystalline alloys, but keep in mind that amorphous alloys exist as well. 

We made a distinction between alloys and intermetallics in Chapter 1, indicating that intermetallics are more like componnds than alloys (which are more like mixmres), even thongh both contain two or more metallic components. Nonetheless, both are composed entirely of metallic elements, and a discnssion of the formation of either would be appropriate here. We focus on the formation of an intermetaUic, TLAls, to illustrate how kinetic parameters can be obtained from experimental observations. 

Calcium is an excellent reducing agent and is widely used for this purpose. At elevated temperatures it reacts with the oxides or halides of almost all metallic elements to form the corresponding metal. It also combines with many metals forming a wide range of alloys and intermetallic compounds. Among the phase systems that have been better characterized are those with Ag, Al, Au, Bi, Cd, Co, Cu, Hg, Li, Na, Ni, Pb, Sb, Si, Sn, Tl, Zn, and the other Group 2 (HA) metals (13). 

It is rather unfortunate that only a very limited amount of information on europium alloys and intermetallic compounds is available in the literature. In the following pages an attempt has been made to collect the available data on alloys containing europium. 

The CAS registry lists 5037 aluminum-containing compounds exclusive of alloys and intermetallics. 

V. V. Boldyrev, Interaction of Alloys and Intermetallic Compounds obtained by Mechanochemical method with hydrogen, Russian Chem. Rev., 1998, 67 (1), 69. 

These catalysts are composed of one or several metallic active components, deposited on a high surface area support, whose purpose is the dispersion of the catalytically active component or components and their stabilization [23-27], The most important metallic catalysts are transition metals, since they possess a relatively high reactivity, exhibit different oxidation states, and have different crystalline structures. In this regard, highly dispersed transition clusters of metals, such as Fe, Ru, Pt, Pd, Ni, Ag, Cu, W, Mn, and Cr and some alloys, and intermetallic compounds, such as Pt-Ir, Pt-Re, and Pt-Sn, normally dispersed on high surface area supports are applied as catalysts. 

Metals frequently used as catalysts are Fe, Ru, Pt, Pd, Ni, Ag, Cu, W, Mn, and Cr and some of their alloys and intermetallic compounds, such as Pt-Ir, Pt-Re, and Pt-Sn [5], These metals are applied as catalysts because of their ability to chemisorb atoms, given an important function of these metals is to atomize molecules, such as H2, 02, N2, and CO, and supply the produced atoms to other reactants and reaction intermediates [3], The heat of chemisorption in transition metals increases from right to left in the periodic table. Consequently, since the catalytic activity of metallic catalysts is connected with their ability to chemisorb atoms, the catalytic activity should increase from right to left [4], A Balandin volcano plot (see Figure 2.7) [3] indicates apeak of maximum catalytic activity for metals located in the middle of the periodic table. This effect occurs because of the action of two competing effects. On the one hand, the increase of the catalytic activity with the heat of chemisorption, and on the other the increase of the time of residence of a molecule on the surface because of the increase of the adsorption energy, decrease the catalytic activity since the desorption of these molecules is necessary to liberate the active sites and continue the catalytic process. As a result of the action of both effects, the catalytic activity has a peak (see Figure 2.7). 

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