Millimetre UO2 single crystals were cut and oriented at JRC Karlsruhe. The orientation of each face of the parallelepiped single crystals was determined with Laue diffraction and the corresponding surface area by geometric measurements. Then, the (111), (100), (110) faces of each single crystal were polished to optical grade and characterized by XRD in order to confirm the surface orientation. The dissolution of the three single crystals was achieved in nitric acid media under dynamic conditions, at room temperature. Two dissolution regimes were observed for all samples. The normalized dissolution rate measured in the first step was not influenced by the crystallographic orientation of the faces. However, during the second step, (110) oriented faces were found to dissolve 4 times faster than the (100) faces. One explanation could involve the atomic composition of each oriented surface in the fluorite-type structure

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

The high temperature oxidation behaviour of cast superalloys strengthened by carbides has been studied as a function of their grain fineness and their dendritic orientation near the surface. These microstructural features have both a significant influence on the oxidation kinetics. The effect depends on the nature of the base metal of the superalloy, on the overall chemical composition or on the types of carbides.