Intermolecular exchange in a triarylborane-phosphine complex: a multinuclear magnetic resonance study

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Abstract
A novel procedure is described for incorporating layers of alumina, contaminated with species derived from the electrolyte, e.g. molybdenum species, within anodic films, for application in the study of mobility and growth mechanisms of anodic barrier films on aluminium. Use of these mobile tracers shows that anodic alumina, developed at a high current efficiency, forms at the metal/film and film/electrolyte interfaces with no significant formation within the film bulk. The outward mobility of incorporated molybdenum species, the tracer, was found to be unchanged throughout the film regions. Indeed, the movements of the various species during anodizing are fully accounted for by use of their usual transport numbers. Occasional anomalous behaviour is observed locally during film growth at and in the vicinity of flaws, probably owing to local current concentration at the flaw site, and when chromium-containing layers are used as tracers. In the latter situation, voids and cracks are revealed in the contaminated alumina, possibly arising from the development of a crystalline alumina containing incorporated chromium species.