Corinne Legros

Oxygen Diffusion in Alumina. Application to Synthetic and Thermally Grown Al2O3

S. Chevalier, B. Lesage, C. Legros, G. Borchardt, G. Strehl, M. Kilo Laboratoire de Recherches sur la Reactivite des Solides, CNRS UMR 5613, Universite de Bourgogne, F-21078 Dijon, France Laboratoire d’Etudes des Materiaux Hors Equilibre, CNRS UMR 8647, Universite Paris XI, F-91405 Orsay, France. Institut fur Metallurgie, TU Clausthal, Robert Koch Strasse 42, D38678 Clausthal-Zellerfeld, Germany. * sebastien.chevalier@u-bourgogne.fr

Diffusion Study of Cerium and Gadolinium in Single- and Polycrystalline Yttria-Stabilized Zirconia

Yttria-stabilized zirconia (YSZ) ceramic is considered as an attractive matrix for nuclear applications, such as inert matrix for the destruction of excess plutonium or good host material for nuclear waste storage. Some actinide elements in high-level radioactive wastes can be simulated by cerium as tetravalent actinide, and gadolinium as trivalent actinide or neutron absorber. The present work is focused on the diffusion study of Ce and Gd in YSZ single crystal and high density polycrystals. A thin film of Ce or Gd was deposited either by spin-coating method or by physical vapour deposition on the surface of polished samples. The diffusion experiments were performed from 1173 to 1673 K under air. The Ce or Gd diffusion profiles were determined by secondary ion mass spectrometry. The experiments led to the determination of effective diffusion coefficient, Deff, bulk and grain boundary diffusion coefficients, DB and DGB. The dependence of these diffusion coefficients on temperature is described by means of Arrhenius equations and the diffusivity is compared with literature.

Lanthanide Diffusion in Single Crystalline and Polycrystalline Pure or Yttrium Doped Alpha-Alumina

In order to bring a contribution to cationic diffusion in alpha-alumina, results on diffusion of 14 lanthanides and Y are presented. Samples are either single crystals with a known orientation or polycrystals with various grain-sizes elaborated from Y-doped alumina powders (100 ppm or 1000 ppm) or from pure alumina powder. After pre-heating in air at the diffusion temperature, small drops of a solution containing these elements are deposited at the surface of the sample. After the diffusion treatment (1200°C, 48 h or 1300°C, 21h), the diffusion profiles are obtained by a CAMECA IMS 4F SIMS device. The isotopes which are taken in account are: 45Sc, 89Y, 139La, 140Ce, 141Pr, 146Nd, 147Sm, 153Eu, 158Gd, 159Tb, 163Dy, 165Ho, 166Er, 169Tm, 174Yb and 175Lu which are the most suitable for this analysis. At first, it can be observed that the diffusion profiles are quite the same for all lanthanides. Diffusion profiles obtained for single crystals allow to calculate the lattice diffusion coefficients, which are necessary to determine the diffusion coefficients values in grain boundaries. Lattice and grain-boundary diffusion coefficients values are compared with cationic diffusion coefficients determined earlier.

Phase Transformation and Densification of Nanostructured Alumina. Effect of Seeding and Doping

By following the densification kinetics of nanocrystalline g alumina and corresponding microstructural evolution we showed that the diffusive transformation gamma-alpha involves several processes such as nucleation of alpha phase, rearrangement of gamma crystallite at alpha seed and grain surfaces, formation of porous alpha alumina monocrystalline colonies. Results concerning the effects of seeding and doping elements on the transformation-densification behaviour of the same g-alumina raw powder batch are also presented. Doping elements seem to have no influence on nucleation rate but could modify the redistribution rate of the ions during the transformation by short range diffusion of doping elements.