Chromium migration

Davis A, Olsen RL (1995) The geochemistry of chromium migration and remediation in the subsurface. Ground Water 33 759-768... 

Chromium migration 356 to 357 was observed on heating the 2-methylindole in which = dioxolanyl. Stereoselectivity was assisted by the... 

When the Cr content is established, we may calculate the content of all other chromium migration forms using equations of p. 6. With analytical concentration of chromium of 10 mole-T we have ... 

Moreover, the equation system of pp. 6 and 8 provides an opportunity to calculate and construct a correlation graph of relative concentrations for various chromium migration forms vs. pH (Figure 3.4). Such graph is the Bjerrum diagram. In a case of limited number of interacting components it is easily constructed using Excel. 

Figure 3.4 Bjerrum diagram for chromium migration forms in pure water.

Setting the functional values of all boxmdaries in needed intervals, we may start direct construction of Eh(pe)-pH diagram using commands Line in Insert panel of Excel. So constructed diagram Eh(pe)-pH of chromium migration forms in pure water is shown in Figure 3.7. 

Figure 3.7 Eh-pH diagram of chromium migration forms in pure water under standard conditions. This chart is constructed without the chromium concentration. Field pH and Eh lack of migration forms is outlined by solid lines.

The replacement of traditional ceramic intercoimects with metallic components to create SOFC stacks offers significant improvements in SOFC performance along with reduced cost. However, understanding the degradation processes in terms of corrosion and chromium migration is critical for developing cost effective SOFCs. Raman spectroscopy is particularly sensitive to the relevant oxides and corrosion processes. 

To avoid these problems, Sulzer has used metal interconnects in their small-scale residential SOFC heat and power unit [29]. The alloy is largely chromium, with 5 wt% iron and 1 wt% yttria to give dispersion strengthening, made by Plansee AG in Austria. This alloy has almost the same expansion coefficient as YSZ and has the benefit of improved strength and toughness when compared with lanthanum chromite. But it requires coating to prevent chromium migration and is also expensive at the present time. 

An electrocyclic ring closure then leads to a cyclohexadienone complex 7, which upon migration of a proton, yields the chromium tricarbonyl-hydroquinone complex 3. 

The fact that the pH values of the pure metals were lower than the theoretical values was attributed to the formation of hydroxy-chloro complexes of the metal and to the high chloride ion concentration in the pit, and the results highlight the very pronounced decrease in pH that can occur in an occluded cell, particularly when the alloy contains high concentrations of chromium and molybdenum. They also showed that migration of chloride ions into the solution in the pit can result in a 7-12-fold increase in concentration, and that the potential in the pit is in the active region. 

Seven-membered carbocycles are also available from the reaction of alkenylcarbene complexes of chromium and lithium enolates derived from methyl vinyl ketones [79b] (Scheme 65). In this case, the reaction is initiated by the 1,2-addition of the enolate to the carbene complex. Cyclisation induced by a [1,2]-migration of the pentacarbonylchromium group and subsequent elimination of the metal fragment followed by hydrolysis leads to the final cyclo-heptenone derivatives (Scheme 65). 

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

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