To gold

Figure Bl.19.36. Image of the frictional force distribution of a pattern consisting of areas of CH -tenuinated and areas of COOH-tenninated molecules attached to gold-coated silicon. The tip was also fiinctionalized in (a) with CH3 species and in (b) with COOH species. The bright regions correspond to the higher friction force, which in (a) is observed on the CH areas and in (b) on the COOH areas. (Taken from [187], figure 3.)...

This is attributed to the different nature of the bonding of sulphur to silver as compared to gold and the slightly different packing density. The coherence length detennined with He atom diffraction was found to be 12 mn [162]. 

This ion is very easily reduced to gold, and hence alkaline solutions of chloraurates(III) (often wrongly called gold chloride ) are used with a reducing agent to prepare colloidal gold. 

Gold compounds are all easily reduced in alkaline solution to metallic gold which may occur in colloidal form and so be red, blue or intermediate colours. Reduction to gold, followed by weighing of ihe metal precipitated, may be used in quantiiaiive analysis. 

Jets for continuous filament textile yam are typically 1 cm diameter gold—platinum ahoy stmctures with 20—500 holes of 50—200 p.m diameter. Tire yam jets are also 1 cm in diameter but typicahy use 1000—2000 holes to give the required balance of filament and yam denier. Staple fiber jets can have as many as 70,000 holes and can be made from a single dome of ahoy or from clusters of the smaller textile or tire yam jets. The precious metal ahoy is one of the few materials that can resist the harsh chemical environment of a rayon machine and yet be ductile enough to be perforated with precision. Glass jets have been used for filament production, and tantalum metal is a low cost but less durable alternative to gold—platinum. 

Halides. Gold(III) chloride [13453-07-1] can be prepared directiy from the elements at 200°C (167). It exists as the chlotine-bridged dimer, Au2Clg ia both the soHd and gas phases under an atmospheric pressure of chlorine at temperatures below 254°C. Above this temperature ia a chlorine atmosphere or at lower temperatures ia an iaert atmosphere, it decomposes first to AuCl [10294-29-8] and then to gold. The monochloride is only metastable at room temperature and slowly disproportionates to gold(0) and gold(III) chloride. The disproportionation is much more rapid ia water both for AuCl and the complex chloride, [AuCy, formed by iateraction with metal chlorides ia solution. 

Metallic Powders. These are usually either aluminum or bronze flakes and vary ia shades from silver to gold, depending on the composition of the metal used. The silver powders can also be toned with organic pigments to produce golds or copper shades usiag transparent yellow or red pigments. 

Ruthenium and osmium have hep crystal stmetures. These metals have properties similar to the refractory metals, ie, they are hard, britde, and have relatively poor oxidation resistance (see Refractories). Platinum and palladium have fee stmetures and properties akin to gold, ie, they are soft, ductile, and have excellent resistance to oxidation and high temperature corrosion. 

Electronic Applications. The PGMs have a number of important and diverse appHcations in the electronics industry (30). The most widely used are palladium and mthenium. Palladium or palladium—silver thick-film pastes are used in multilayer ceramic capacitors and conductor inks for hybrid integrated circuits (qv). In multilayer ceramic capacitors, the termination electrodes are silver or a silver-rich Pd—Ag alloy. The internal electrodes use a palladium-rich Pd—Ag alloy. Palladium salts are increasingly used to plate edge connectors and lead frames of semiconductors (qv), as a cost-effective alternative to gold. In 1994, 45% of total mthenium demand was for use in mthenium oxide resistor pastes (see Electrical connectors). 

Oxygen Reactivity. Silver is second only to gold as the element having the weakest interaction with oxygen, providing silver with its superior sparking and combustion resistance. Silver must be oxidized chemically or electrolyticaHy to form AggO. Thermodynamically, silver exists only in the... 

Titanium-Based Casting and Wrought Alloys. Titanium-based alloys offer an attractive alternative to gold alloys and to the base-metal alloys that contain nickel or chromium. On a volume basis the cost of titanium is roughly comparable to that of the chromium-containing alloys, but the price of titanium tends to be more stable because its ores are abundant and widely distributed (see Titaniumand titanium alloys). 

To paraphrase an old fable, Midas asked the gods that everything he touched might be turned to gold. His request was granted. His food turned to gold the moment he touched it, and he had to ask the gods to take their favor back. 

For gold, by contrast, - -3 is the element s best-known oxidation state and Au is often compared with the isoelectronic Pt (p. 1161). The usual route to gold(III) chemistry is by dissolving the metal in aqua regia, or the compound AU2CI6 in cone HCl, after which evaporation yields yellow chloroauric acid, HAUCI4.4H2O, from which numerous salts of the square-planar ion [AuCLj]" can be obtained. 

Hodges, R. J. The Corrosion Resistance of Gold and Base Metal Alloys , in Alternatives to Gold Alloys in Dentistry (Ed.) T. M. Valega, Sr., DHEW Publication No. (NIH) 77-1227 106-138 (1987)... 

The development of new alloys in new fields for example the development of molybdenum and tungsten with iron, cobalt or nickel for coating of dies and nozzles, or the development of palladium-nickel alloy as an alternative to gold for connectors. 

For ruthenium, electrolytes based on ruthenium sulphamate or nitrosyl-sulphamate have been described, but the most useful solutions currently available are based on the anionic complex (H2 0 Cl4 Ru N Ru-Cl4-OH2) . The latter solutions operate with relatively high cathode efficiency to furnish bright deposits up to a thickness of about 0-005 0 mm, which are similar in physical characteristics to electrodeposited rhodium and have shown promise in applications for which the latter more costly metal is commonly employed. Particularly interesting is the potential application of ruthenium as an alternative to gold or rhodium plating on the contact members of sealed-reed relay switches. 

A number of thiourea complexes of silver have shown the tendency to bind up to four ligands, in contrast to gold. Thus Agtu2X (X = Cl, NCS) have essentially 3-coordinate silver (one distant fourth atom) Agtu3C104 is a 4-coordinate dimer (Figure 4.12) [58]. 

While tertiary phosphines and arsines tend to reduce gold(III) to gold(I), the reverse reactions can be used synthetically [126] ... 

Au(diphos)2 and Au(diars)2 can be oxidized to gold(III) species [127]. These tend to add halide ions so that Au(diars)2lJ has a distorted octahedral structure with very weakly bound iodides (section 4.12.5). 

Chemical and physical effects are manyfold [193]. The contraction leads to gold forming shorter and stronger covalent bonds and is likely to be... 

Alkene complexes Alkynyl complexes Ammine complexes Aqueous chemistry Arsine complexes Auranofin Auride ion Aurophilicity Binary compounds Bond lengths acetylacetonate complex alkyls and aryls ammine complexes carboxylates cyanide complexes dialkyl sulphide complexes dithiocarbamates to gold... 

A gene gun is a device to introduce DNA into cells in vivo. The DNA is attached to gold particles, which are introduced under high velocity into the target tissue. 

Tolerance to gold usually decreases with age. The older adult must be carefully monitored when receiving gold therapy. 

The turnover frequency (TOP) based on surface-exposed atoms significantly increases with a decrease in the diameter of the gold particle from 5 nm [66]. This feature is unique to gold, because other noble metals usually show TOFs that decrease or remain the same with a decrease in the diameter [7]. The decrease in particle size gives rise to an increase in corner or edge and perimeter of NPs and change in electronic structure however, the origin of size effects on catalytic activity for CO oxidation is not clear. 

Fig. 35 TEM image of peptide fibres coated with streptavidin-gold nanoparticles, (a, b) Peptides with biotin directly attached (using SAF-pl-biotin) particles are 10 nm, (c) Peptide fibre with biotinylated anti-FLAG antibody attached that was then bound to gold-labelled streptavidin particles are 5 nm. Reprinted with permission from Ryadnov and Woolfson [76]. Copyright 2004 American Chemical Society...

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