Gold and platinum

There is a general relationship between metal price and terrestrial concentration. Metals present at relatively high concentrations, in the earth s cmst, such as iron and aluminum, are the least expensive rare metals such as gold and platinum are the most valuable. This situation has existed for gold and silver valuation for centuries. The amount of silver in the earth s cmst is approximately 20 times that of gold, and the historical price ratio for gold and silver varied between 10 and 16 for over 3000 years. Since 1970 that price ratio has been strongly affected by market forces and investor speculation. 

Noble metals such as gold and platinum are not appreciably affected by pH, as shown in Fig. 28-2c,... 

Experimental values for tire sputtering efficiency tend to show lower values of a for elements, such as aluminium and mngsten which form stable oxides, compared with the metals such as gold and platinum which do not under normal experimental conditions. This is probably due to the presence of a surface oxide, since industrial sources of argon, which are used as a source of ions for example, usually contain at least 1 ppm of oxygen, which is more than enough to oxidize aluminium and tungsten. 

Passivity is the loss of chemical reactivity of certain metals and alloys under specific environmental conditions. In other words, certain metals (e.g., iron, nickel, chromium, titanium, etc.) become relatively inert and act as noble metals (e.g., gold and platinum). Figure 4-420 shows the behavior of a metal immersed in an air-free acid solution with an oxidizing power corresponding to point A... 

In the vast majority of cases at elevated temperatures, the answer to the first question is no. With the exception of gold and platinum, which are generally too expensive for large-scale industrial use, are in short supply and do not... 

A technologically important effect of the lanthanide contraction is the high density of the Period 6 elements (Fig. 16.5). The atomic radii of these elements are comparable to those of the Period 5 elements, but their atomic masses are about twice as large so more mass is packed into the same volume. A block of iridium, for example, contains about as many atoms as a block of rhodium of the same volume. However, each iridium atom is nearly twice as heavy as a rhodium atom, and so the density of the sample is nearly twice as great. In fact, iridium is one of the two densest elements its neighbor osmium is the other. Another effect of the contraction is the low reactivity—the nobility —of gold and platinum. Because their valence electrons are relatively close to the nucleus, they are tightly bound and not readily available for chemical reactions. 

Metals that are soft acids, such as gold and platinum, have low affinities for hard oxygen atoms, so they are not affected by O2 in the atmosphere. Consequently, these metals, including Ru, Rh, Pd, Os, Ir, Pt, and Au, are found in the crust of the Earth in their elemental form. 

These P-CD/adamantyl pseudorotaxane-terminated dendrimers can be used as nanoreactors in the preparation of gold and platinum nanoparticles in water... 

Thiols are known to be excellent hgands for the stabilization of gold and platinum nanoparticles. In this respect, we did not observe any Iluxional behavior [31,52] in solution NMR experiments for thiols coordinated to the surface of noble metal particles (Fig. 8). However, in the case of rutheniiun, we foimd the slow catalytic formation of alkyl disulfides [31]. After exclud-... 

Fig. 2.12 Silver, gold and platinum complexes with monodentate NHC ligands as catalysts for the diboration of alkenes and alkynes...

Theileis, V. and Bross, H. (2000) Relativistic modified augmented plane wave method and its application to the electronic structure of gold and platinum. Physical Review B - Condensed Matter, 62, 13338-13346. 

Bergsoe, P. (1937), The Metallurgy and Technology of Gold and Platinum among pre-Columbian Indians (transl. F. C. Reynolds), Copenhagen. 

Wu C, Mosher BP, Zeng T (2006) Rapid synthesis of gold and platinum nanoparticles using metal displacement reduction with sonomechanical assistance. Chem Mater 18 2925-2928... 

Nadagouda, M.N. and Varma., R.S. (2006) Green and controlled synthesis of gold and platinum nanomaterials using vitamin B2 density-assisted self-assembly of nanospheres, wires and rods. Green Chemistry. 8 516-518. 

The interdiffusion of gold and platinum is much slower than that of copper and nickel, and films formed by successive evaporation of the component metals were not brought to equilibrium by sintering at 200°C. Films formed by simultaneous evaporation were equilibrated by sintering... 

Some second- and third-row transition metals are, for good reason, known as precious metals. These include silver, palladium, rhodium, iridium, osmium, gold, and platinum. As this is written, gold is over 900 per ounce and silver is over 15 per ounce. Some of the other metals such as rhodium, osmium, and rhenium are also extremely expensive. Most of the second- and third-row transition metals are found as minor constituents in ores of other metals. Consequendy, we will not enumerate the sources, minerals, or the processes by which these metals are obtained. Some of their most important properties are shown in Table 11.3. 

The mixture containing one volume of concentrated HN03 and three volumes of concentrated HC1 is known as aqua regia, and it will dissolve even gold and platinum. 

Moebius An electrolytic process for removing gold and platinum from silver. The crude metal, known as Dore, is used as the anode. The cathodes are of silver or stainless steel. The electrolyte is a diluted solution of silver nitrate and nitric acid. Gold and other metals collect as anode slimes. Invented in Mexico by B. Moebius, first operated there in 1884, and subsequently widely operated in Germany and the United States. See also Balbach, Thum, Wohlwill. 

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