Metal migration

Metal migration, especially silver migration, may be quickly tested by applying adrop of deionized water across two closely spaced silver or silver-filled conductors while a DC potential of 2-10 volts is applied. Catastrophie bridging and shorting ofthe conductors lines is visible at low magnification. The onset of migration is also indicated by the decrease in insulation resistance between the lines. 

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The above value for R = H corresponds to an intermolecular process, either assisted by the solvent (in solution) or by other NH-pyrazole molecules (in solution and in the solid state) while metal migrations are probably intramolecular (the bigger the metal, the easier) and those of COR correspond (for R = NHR ) to a dissociation-recombination mechanism. Minkin [quoted in 96MI(15)339] suggests that a tautomeric process should... 

Other peculiarities have occurred. As an example of a potential problem that can occur is when a silicone release agent is used when injection molding electrical connectors, etc. It can behave like the metal migration just reviewed. 

DOtz KH, Wenzel B, Jahr HC (2004) Chromium-Templated Benzannulation and Hapto-tropic Metal Migration. 248 63-103... 

The branched polymers produced by the Ni(II) and Pd(II) a-diimine catalysts shown in Fig. 3 set them apart from the common early transition metal systems. The Pd catalysts, for example, are able to afford hyperbranched polymer from a feedstock of pure ethylene, a monomer which, on its own, offers no predisposition toward branch formation. Polymer branches result from metal migration along the chain due to the facile nature of late metals to perform [3-hydride elimination and reinsertion reactions. This process is similar to the early mechanism proposed by Fink briefly mentioned above [18], and is discussed in more detail below. The chain walking mechanism obviously has dramatic effects on the microstructure, or topology, of the polymer. Since P-hydride elimination is less favored in the Ni(II) catalysts compared to the Pd(II) catalysts, the former system affords polymer with a low to moderate density of short-chain branches, mostly methyl groups. 

Early NMR work by Roberts and coworkers51-53 showed that allyl Grignard reagents (16) are of the a type in which the metal migrates rapidly from one terminus to the other. This result was confirmed by more recent high resolution 13C NMR work of Schlosser and Stahle54. 

Heavy metals in the environment, especially their accumulation in soils, is a serious environmental problem which the whole world faces (Du et al. 2005). The farmland soils are an important media of the ecological cycle of Cadmium, and its harm to human health can t be neglected (Wu et al. 2004). Heavy metal migration, transformation and toxicity to plants in soil are directly influenced by the quantity proportions of various forms (Zhu et al. 2002). The toxicity of water-extractable and adsorbed and exchangeable metals are the greatest, and residual metals is the lowest (Liu etal. 2002). Different forms have different bioavailability thus their influences on the environment and human health are different. It is critical to have a good understanding of Cadmium forms in soil. This paper describes the Cadmium forms in the acid soils of eastern China. 

The amount of organic matters not only determines the nutrition of the soils, but also form complex compound with heavy metals to influence metal migration and bioavailability (Liu et al. 2002). From table 1, we can found that extractable Cd contents, especially occluded Cd onto Fe-Mn oxides and organically bounded Cd has a prominent positive correlation with organic matters (a =0.05,n =30, F =0.361), (Fig. 2). Organic matters are one of the major factors which influence Cd... 

Heavy Metal Migration in Biogeochemical Food Webs... 

The excessive amounts of nitrogen and phosphorus as well as heavy metals migrate with water fluxes and enter into surface waters. This is accompanied by eutrophication of surface water bodies. 

Alkenyl and alkynyl Fischer carbene complexes reacted with pyrrole imine 108 to give, through a 1,2- and 1,3-metal migration, respectively, indolizine derivatives at a different level of unsaturation (Scheme 29) <1999JA3065>. 

Metal migration from one face to the other ( envelope flip ). 896... 

Metal migration about a tr-complexed polyene ligand... 

Metal migration about a jt-complexedpolyene ligand ( ring-whizzing )... 

The crystal structure of (ij4-cyclooctatetraene)(hexamethylbenzene)ruthenium (16) indicates bonding as a tetrahapto ligand60. For this complex and similar iron-, ruthenium- and osmium-(ij4-cyclooctatetraene)(arene) complexes, their XH and 13C NMR spectra exhibit only a single signal for the cyclooctatetraene ligand at temperatures as low as —145 °C. Using this temperature, the barrier-to-metal migration is estimated to be <6.6 kcal mol 1. 

Migration of the metal along the polyene chain in (l,l- 2-l,3,5-hexatriene)CoCp occurs with an activation energy of 25.6 kcalmoT 1 (equation 15)136b. This barrier is ca 5-8 kcal mol 1 lower than that for metal migration in (triene)- or (tetraene)Fe(CO)3 complexes (see Section IV.E.l.d). 

Evidence of 25-m of Vertical Metal Migration Over the High-Grade Perseverance Zinc Ore Body, Matagami, Quebec... 

Chromium-Templated Benzannulation and Haptotropic Metal Migration... 

The adhesion of noble metals to the insulating substrates is generally poor. In order to overcome this problem, a thin layer (10-50nm) of adhesive metal (Cr, Ti, W) is deposited under the noble metal. Often this adhesive metal migrates through the noble metal and forms an oxide layer that significantly alters its surface... 

Inter-ring metal migrations, dynamic NMR studies, 1, 412 Intracyclic germanium-carbon bond formation large rings, 3, 706 small rings, 3, 703 Intramolecular Alder-ene reactions with metals, 10, 576 with palladium, 10, 568 with rhodium, 10, 575 with ruthenium, 10, 572 with transition metal catalysts, 10, 568 Intramolecular allylations, in cyclizations, with indium compounds, 9, 679... 

Metal migrations, around rings, dynamic NMR studies, 1, 411 Metal nitrides, synthesis, 12, 53... 

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