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Several mechanism-related aspects of the corrosion of zirconium alloys have been investigated using different examination techniques. The microstructure of different types of oxide layers was analyzed by transmission electron microscopy (TEM). Uniform oxide mainly consists of m-ZrO2 and a smaller fraction of t-ZrO2 with columnar grains and some amount of equiaxed crystallites. Nodular oxides show a high open porosity and the grain shape tends to the equiaxed type. A fine network of pores along grain boundaries was found in oxides grown in water containing lithium. An enrichment of lithium within such oxides could be found by glow discharge optical spectroscopy (GD-OES) depth profiling. In all oxides, a compact, void-free oxide layer was observed at the metal/oxide interface. Compressive stresses within the oxide layer measured by an X-ray diffraction technique were significantly higher compared to previously published values. Electrical potential measurements on oxide scales showed the influence of the intermetallic precipitates on the potential drop across the oxide. In long-time corrosion tests of Zircaloy with varying temperatures, memory effects caused by the cyclic formation of barrier layers could be observed. It was concluded that the corrosion mechanism of zirconium-based alloys is a barrier-layer controlled process. The protective properties of this barrier layer determine the overall corrosion resistance of zirconium alloys.

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The initial stages of zirconium oxide formation on Zircaloy after water (H2O) and oxygen (O2) exposures have been investigated in situ using photoelectron spectroscopy and X-ray-absorption spectroscopy. The reactivity of the zirconium alloy with O2 at room temperature is about 1000 times higher than for H2O. Up to 100 L (1 L = 1 Langmuir unit = 1 ∙ 10-6 mbar ∙ s) H2O exposure, the reactivity of the zirconium alloy at 450°C is comparable to the room temperature reaction. At higher H2O exposure, a sharp increase in the reaction rate for the high-temperature oxidation is observed. From the energy position of the Zr 3d photo emission line and their oxygen-induced chemical shifts, one can directly follow the formation of the oxide films. Two different substoichiometric oxides were found during reaction with water. Suboxide (1) is located at the zirconium/zirconium-oxide interface. Subsequently, a Suboxide (2) is concluded from the chemical shift of the zirconium photoelectrons. After an oxide thickness of 2 nm, the stoichiometric ZrO2 phase is not yet developed.