Papers by Author: Martin Kilo

Abstract: Oxygen uptake and oxygen diffusion in Mayenite (Ca12Al14O33) were investigated using the stable tracer 18O2. Mayenite contains one intrinsic, highly mobile oxygen anion. It was shown that for high temperatures (above 700 °C), the diffusion goes through a interstitialcy mechanism, where the interstitial oxygen anion knocks out a lattice oxygen anion. The activation enthalpy for this process is around 0.9 eV, suggesting that the ionic migration is very fast.

Abstract: 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.