Gold intermetallic

Figure4.11 Comparison of experimental dissociation energies of gold intermetallic compounds with those of copper and silver from mass spectroscopic measurements by Cingerich and coworkers [18, 159, 173, 176] arranged in group order according to the periodic table.

Recently, a new failure mode has been found in the accelerated testing of high temperature storage It shows an increase in the resistance of the bonding pad, or in severe cases disconnection, when a device is stored at high temperatures around 200 C. It is due to the formation of an aluminum-gold intermetallic compound Its formation seems to be accelerated by free bromine or chlorine it may be... 

A survey of gold intermetallic chemistry, R. Ferro, A. Saccone, D. Maccib, and S. Delfino, Gold Bulletin, 2003, 36(2), 39. 

The superconducting properties of gold intermetallics have been reviewed by Khan and Raub [4], although no intermetallic compound of gold has yet been found to exhibit sufficient superconductivity to make it industrially interesting. 

Selenium occurs in the slimes as intermetallic compounds such as copper silver selenide [12040-91 -4], CuAgSe disilver selenide [1302-09-6], Ag2Se and Cu2 Se [20405-64-5], where x < 1. The primary purpose of slimes treatment is the recovery of the precious metals gold, silver, platinum, palladium, and rhodium. The recovery of selenium is a secondary concern. Because of the complexity and variabiUty of slimes composition throughout the world, a number of processes have been developed to recover both the precious metals and selenium. More recently, the emphasis has switched to the development of processes which result in early recovery of the higher value precious metals. Selenium and tellurium are released in the later stages. Processes in use at the primary copper refineries are described in detail elsewhere (25—44). 

An interesting intermetallic gold compound is CsAu, where Au is bound to the most electropositive metal Cs (Xcs = 1-2). As a result we obtain an ionic bonding situation for the semiconductor Cs Au and not a metallic bond as one expects (two metals do not necessarily form a metallic bond ). Figure 4.12 nicely shows that the HOMO consists mainly of Au(6s) with much smaller Cs(6s) and Au(dn) participation, while the LUMO is mainly Cs(6s). Saue and co-workers calculated relativistic... 

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). 

Bis[2-(diphenylphosphino)phenyl]phenylphosphine (TP) is a very inflexible ligand with a rigid backbone and gives the trinuclear complex [Au3Cl3(TP)] (452), that has a compact unsymmetrical structure in the solid state which is retained in solution owing to the fixation of the gold atoms through intermetallic contacts.2651... 

Electrodes of this sort have many different chemical properties from pure mercury electrodes, because of the formation of a gold or platinum amalgam [18]. Normally, a drop is suspended just prior to an experiment, so this problem will be of no serious consequence. Nevertheless, since the solubility of these noble metals in mercury is about 0.05 M at room temperature [19], the concentration of gold or platinum in mercury may be quite significant on a longer time scale. In such cases, gold or platinum may form intermetallic compounds with several metals that are electrodeposited into the mercury [18]. 

As described above, among the several closed-shell metal ions that form luminescent supramolecular entities with gold, thallium(I) forms the most numerous examples. While aurophilic attractions can be considered the upper extreme of the metallophilic interactions (with values up to 46 kJ mol-1), intermetallic contacts involving T1(I) centers appear as the weakest ones (even <20 kJ mol-1),46 which is explained by the enhancement of the Au---Au interactions and the weakening of the Van der Waals attractions between the s2 metal atoms produced by the relativistic effects.47 Nevertheless, the complexes in which this interaction appears are surprisingly stable, with additional electrostatic, packing forces, or the ligand architecture, responsible for this fact. 

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