Observing Oxidation Kinetics On an Aluminium Alloy Surface

Metal oxides, in contrast to most metals, are well known to be easily distinguished by their characteristic Raman spectra; their presence can be detected on a scale of micrometers with a Raman microprobe. Often, the various oxides of a particular metallic ion have significantly different Raman spectra, with even the degree of hydration of the ligated cation generating a tell-tale vibrational fingerprint. Thus, the diverse oxide forms of a variety of metals, including, for example, iron, nickel, lead, titanium, zirconium, molybdenum, copper, and vanadium, can be distinguished by a fast and non-destructive spectroscopic measurement. In practice, this allows the scientist or engineer to delineate the kinetics of oxidation of any of these species, observing where and when successive species are formed during the oxidation of a raw metal. For example, steel rust exhibits layers of several oxides of iron, including hematite, lepodocrocite, goethite,and magnetite, with the layer thicknesses and ordering dependent upon the composition of the steel, the conditions of the environment, and the duration of exposure.