Gold series

Other active methylene compounds also react with both palladium(ll) <2002POL2653> and gold(m) <1997JOM243> to produce metallacyclobutane complexes (Scheme 34). The gold complex is not sufficiently stable for isolation. In these reactions, the silver oxide functions both as a base and a reagent for halide abstraction. In the gold series, 1,1,3,3-tetracyanopropane is also a competent pro-nucleophile <1999JOM219>. 

The very small volume in which the solutes elute requires that the extra-column volumes are reduced to prevent extra-column dilution and band broadening. This means that the volume of the flow cell should be less than that used with conventional 5 fim particle size colunms, thus causing a loss in mass detectability. The recent development of wide-bore 3 jum particle size columns (Zorbax Gold Series),... 

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Metallic gold, which is found free in nature, has always been valued for its nobility, i.e. its resistance to chemical attack. This property is to be expected from its position in the electrochemical series. It... 

These elements formed Group IIB of Mendeleef s original periodic table. As we have seen in Chapter 13, zinc does not show very marked transition-metaf characteristics. The other two elements in this group, cadmium and mercury, lie at the ends of the second and third transition series (Y-Cd, La-Hg) and, although they resemble zinc in some respects in showing a predominantly - - 2 oxidation state, they also show rather more transition-metal characteristics. Additionally, mercury has characteristics, some of which relate it quite closely to its immediate predecessors in the third transition series, platinum and gold, and some of which are decidedly peculiar to mercury. 

Betts Electrolytic Process. The Betts process starts with lead bullion, which may carry tin, silver, gold, bismuth, copper, antimony, arsenic, selenium, teUurium, and other impurities, but should contain at least 90% lead (6,7). If more than 0.01% tin is present, it is usually removed from the bullion first by means of a tin-drossing operation (see Tin AND TIN ALLOYS, detinning). The lead bullion is cast as plates or anodes, and numerous anodes are set in parallel in each electrolytic ceU. Between the anodes, thin sheets of pure lead are hung from conductor bars to form the cathodes. Several ceUs are connected in series. 

Other Metals. Metals such as the austenitic series. Types 301—347, and the ferritic series. Types 409—446, of stainless steels may be enameled, as well as a number of other alloys (17). The metal preparation usually consists of degreasiag and grit blasting. Copper, gold, and silver are also enameled. These metals are usually prepared for appHcation by degreasiag. Copper is pickled usiag either a nitric acid [7697-37-2] or a sulfuric acid [7664-93-9] solution, followed by a dilute nitric acid dip. Silver may be pickled in hot dilute sulfuric acid followed by a dip in a nitric acid solution (18). 

A series of force-distance curves for various materials pairs examined (gold/ nickel, diamond/graphite, diamond/diamond) are shown in Fig. 4 [39]. For an indentation, the unloading slope (dF/dr) of the force-displacement curve is a measure of the contact stiffness and can be used to determine the modulus if the contact area (A) is known using a variant of Eq. 3 below. 

Gold-copper alloys exhibit exceptional resistance to corrosion, and have very low vapour pressures. Gold-nickel alloys, with similar low vapour pressure, are somewhat stronger than gold-copper at high temperatures. Both series of alloys are widely employed in vacuum systems. 

The hardness of such coatings may reach a maximum of about 400 Hy as compared with approximately 50 Hy for a soft gold deposit. A series of corrosion studies in industrial and marine atmospheres by Baker" has indicated that the protective value of hard gold coatings is comparable with that of the pure metal, and that a thickness of only 0-002 5 mm gives good protection to copper base alloys during exposure for six months. 

But even the value of the second coefficient b2 is less determined. In different theoretical papers the values from 4.4 to 14.1 are encountered, though, probably, the most reliable value for spherical particles was given by Gut — Gold b2 = 14.1. As regards the higher terms of the series, they are still less determined. 

The series M(PP)C1 (PP = 2,ll-bis(diphenylphosphinomethyl)benzo[c]-phenanthrene M = Cu, Ag, Au) is interesting in showing group trends (Table 4.7) where the silver and copper complexes have trigonal coordination and the gold member is linear [50]. 

Values of the single-bond radii for the metals of the series silver to tin and gold to lead are also given in table 6, as calculated by equations (10c) and (11c) for the pure valence states A, B, C and D and for certain intermediate valencies, corresponding to resonance among these states. 

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