Abstract
Specimens of polycrystalline nickel have been annealed at ∼700°C and oxidised in situ within a scanning Auger microscope. Auger spectroscopy has been used to monitor the chemical composition of the free surface, and real time secondary electron imaging used to observe the specimen surface. A novel segregation effect has been recorded whereby sulphur emerges on to the free surface via emergent grain boundaries in the form of sulphurous bands, displacing the established oxide overlayer. The kinetics of the broadening of these bands depends on the tenacity of the oxide which, in turn, depends on the levels of sulphur present on the specimen surface before oxidation. Qualitative mechanisms are proposed for the observed effects.
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