Chromium vaporization

Focusing on reactions using the Fluid Matrix Technique, we have studied the interaction of chromium vapor with 2 at 200 K (13). The resulting film was found to contain metal complexes encapsulated within the polymer in which the isocyanide group adopts a well-defined octahedral arrangement around the chromium center, i.e. a species of type Cr(CN-[P])g. Since characterization of this metal complex within the polymer is not trivial we shall develop the analysis in a little detail. 

Thermally Activated Processes - Any detrimental thermally activated processes can be affected beneficially such as chromium vaporization, elemental interdiffusion and migration, metallic corrosion affects and some ceramic aging affects. 

Similar results were obtained with erbium, dysprosium, and chromium vapors (104, 115). However, on deuterolysis, most transition metal cocondensates afforded mainly unlabeled propene with only two traces of propane and hexanes (104, 107, 110). The differing reactions of metal vapors with propene were interpreted in terms of a change in the [Pg.60]

These reactions may proceed through an M(C5H6)2 intermediate, but in the absence of isolated or trapped intermediates there is no compelling evidence that this is so. Chromium vapor-C5H6 condensates liberate H2 only on warming, and, in this case, it has been possible to isolate a complex by trapping with carbon monoxide ... 

Pure bis(alkylbenzene)chromium complexes are best prepared by the chromium vapor route as there is no rearrangement of the alkylbenzene that often accompanies the Fischer synthesis for these compounds. However, the yield of bis(alkylbenzene)chromium compounds are not high, rarely more than 20% polymeric materials accompany the desired product (32, 83, 84). 

By condensing chromium atoms, PFS, and arenes, numerous complexes of type Cr(arene)(PF3)3 have been made. Such complexes may be formed even when the corresponding bisarenechromium cannot be prepared from chromium vapor (see following sections for examples). 

Vanadium or chromium vapors, condensed with the appropriate arenes, form M(C6H5C1)2, M(C8H5F)2, M(C8H4F2)2, and M(C8H5CF3)2. Chromium forms Cr[C8H4(CF3)2]2 and Cr(C8H4Cl2)2, but the corresponding vanadium compounds are not obtained from vanadium vapor. 

Methyl benzoate, anisole, and diphenyl ether each give sandwich compounds with chromium vapor, although in rather low yield (32, 55, 110). Chromium appears to attack alkyl ethers and this deoxygenation probably competes with complexation with the aromatic oxygen compounds. No simple product has been isolated from chromium atoms and aniline, but bis(7V,7V-dimethylaniline)chromium has been prepared (32). The behavior of molybdenum and tungsten vapors closely resembles that of chromium in reactions with oxygen- and nitrogen-substituted arenes (113). 

Hexamethylborazene, chromium vapor, and PF3 together give a low yield of Cr(7)6-B3N3Me6)(PF3)3. Attempts to isolate a bisborazenechrom-ium complex were not successful (55). 

In the gas phase, the co-condensation of chromium vapors with azines and subsequent cooling (77 K) led to the first 7r-complexes of pyridine (44, in the presence of PF3) [75AG(E)273] and (45) (76JA1044). The gas-phase synthesis was utilized to prepare the parent bis(pyridine) sandwich species (46) (88CB1983). An attempt to prepare the -complex of pyridine was... 

Stanislowski, et al. (2007), Reduction of Chromium Vaporization from SOFC Interconnectors by Highly Effective Coatings , J. Power Sources, 164, 578-589. 

Evaporation and condensation of chromium vapor from the interconnect onto the air electrode are considered critical mechanisms of performance degradation in an SOFC. While no details of similar effect have been reported for the electrolysis stacks, such a mechanism is likely to be operative, leading to performance degradation. This is another area that requires attention to address and mitigate the problem in order to achieve long-term stable operation of SOFC stacks. Much of the work in this area is being conducted for SOFC applications. 

So far no > -complex with benzocyclopropene (1) as a ligand has been reported. The reaction of 1 with chromium vapor in the gas phase gives only starting material with a slightly higher toluene content than before and polymeric material. ... 

When chromium vapor is diffused into salts or when Cr + impurities are irradiated, Cr+ species are trapped and are readily detected by ESR. 

Chromium. Molybdenum. Tungsten. Cocondensation of PH3 with chromium vapor at 60 K leads to the formation of a PH3 complex of Cr [78]. Chromium powder with PH3 forms phosphides of different composition at 700 to 950 C. The reaction at 850 C yields CrP, whereas at 950 C only the lowest phosphide, CrgP, is obtained the latter dissociates at 10OO C to give Cr [79]. Gaseous PH3 is inert in the presence of metallic Mo on an AI2O3 support at about 350 C [80]. The reaction of PH3 with W at 850 C gives WP [81]. 

Hilpert, K., Das, D., Miller, M., Peck, D.H., and Weiss, R. (1996) Chromium vapor species over solid oxide fuel cell interconnect materials and their potential for degradation processes. J. Electrochem. Soc., 143 (11), 3642-3647. 

Stanislowski M, Wessel E, Hipert K, Markus T, Singheiser L (2007) Chromium vaporization from high-temperature alloys 1. Chromia-forming steels... 

Reduction of chromium vaporization frran SOFC interconnectors by highly effective coatings. J Power Sources 164 578-589... 

When the operating temperature is about 1000°C, interconnects need to be made of ceramic materials. Although excellent performances of fuel cells based on ceramic interconnects have been proved, costs are still a relevant restriction. At reduced temperature, the use of less expensive materials, like for instance stainless steel, is possible. Several organizations are currently investigating the interaction of different metals with the electrodes (De Jonghe et al. 2004, Zahid et al. 2004, Pedersen et al. 2004). The two main issues to overcome are the oxidation of the metal when in contact with air at the cathode side and the interaction of the chromium vapors with the cathode. 

---