Aluminum halide environments

Fig. 7.42 Pitting potential of 99.99 wt% aluminum in several halide environments. All environments are pH = 11 except as indicated for pH = 6. Redrawn from Ref 60...

Reduction of ZrIV in ZrX4-Al2X6 (X = Cl, Br or I) melts, with either zirconium or aluminum metal, yields soluble blue species. These species were not isolated, but they have been formulated as Zr(X2AlX2)3 complexes on the basis of their electronic spectra. Absorption bands at 17 400 (X = C1), 16 000 (X = Br) and 14 000 cm-1 (X = I) may be assigned to the 2t -2es transition of Zr111 in an octahedral environment of halide ions. The solid zirconium(III) halides exhibit ligand-field bands at closely similar frequencies.32... 

Corrosion can also occur by a direct chemical reaction of a metal with its environment such as the formation of a volatile oxide or compounds, the dissolution of metals in fused metal halides. The reaction of molybdenum with oxygen and the reaction of iron or aluminum with chlorine are typical examples of metal/gas chemical reactions. In these reactions, the metal surface stays film-free and there is no transport of electrical charge.1 Fontana and Staehle2 have stated that corrosion should include the reaction of metals, glasses, ionic solids, polymeric solids and composites with environments that embrace liquid metals, gases, aqueous and other nonaqueous solutions. 

Of course, these compounds are also dimeric, containing electron-deficient bonds with the aluminum atoms in four-coordinate tetrahedral environments. It is significant that the AI-X-AI angle in alkylaluminum halides is considerably widened from that observed in Me6Al2 (75°) to -90°. 

The first step in equation 14 involves the exchange of the halide groups attached to the metal atom with the alkyl groups bound to one or more aluminum atoms. In equations 8-10, it is assumed that the metallocene is introduced into the reactor as a dialkyl complex, or that it has been converted into such form by a halide-exchange process involving an alkylating agent in the polymerization environment. 

Solutions of aluminum salts in alcohols have been widely studied using H, and Al spectroscopy. " The early Al results are consistent with the Al " cation being in an octahedral environment but the proton and carbon spectra suggest that the coordination number is less than six in the halide solutions and is six or a little less in the perchlorate solutions. The existence of ion pairing in AICI3 solution is thus postulated though there is a difference between the views of this taken by the Russian group, who seem to prefer solvent separated ion pairs and the other workers who... 

Halide ions (Cl, Br, and I ) have the greatest effects in accelerating attack (Fig. 13). Chloride is the most important halide ion because it is a natural constituent of marine environments and is present in other environments as a contaminant. Because it acceierates SCC, Cr is the principai component of enviromnents used in acceierated iaboratory tests to determine sus-ceptibiiity of aluminum alloys to this type of attack. 

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