3D characterization of He bubbles in aged palladium tritide by electron tomography

Session

PSA.4 - Batteries & Materials for Energy Conversion

Authors

Eric Leroy (3), Bérengère Evin (1), Walid Baaziz (2), Mathieu Segard (1), Sylvain Challet (1), Ovidiu Ersen (2), Michel Latroche (3), Valérie Paul-Boncour (3), Arnaud Fabre (1)

Affiliations

1. CEA Valduc, F-21120
2. Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS, UMR 7504
3. Université Paris-Est Créteil, CNRS, ICMPE (UMR 7182)

Keywords

Electron tomography, helium, palladium, tritiade aging

Abstract text

Palladium and its alloys are used for the storage of hydrogen isotopes as they form reversible metal hydrides at low equilibrium pressure and room temperature, ensuring safe practical storage. Tritium storage, the radioactive isotope of hydrogen, is unique in that the decay of tritium in helium-3 is responsible for the gradual modification of most of the properties of metal tritides, 

Helium-3 remains trapped in the material as nanoscale bubbles, up to a critical level beyond which helium is massively released in the gas phase from the material. During this last stage, the helium-3 pressure can increase drastically that of the storage container, which determines its sizing to ensure safety. It is therefore fundamental to understand and predict the behaviour of helium-3 bubbles during aging. Several parameters must be determined to model the process. These include the spatial distribution and size of the bubbles. In this study, we present the first 3D results obtained for this type of materials.

The 3D characterization of the cavities formed in palladium after different aging time was studied by STEM HAADF electron tomography. As the size of the bubbles is nanometric (diameters range between 1 to 3 nm), the use of a corrected probe microscope was mandatory. After the acquisition of tilt series of images, the reconstructed volumes were calculated and segmented. 

These experiments have allowed the achieving of the 3D spatial distribution of the cavities and the extraction of significant features like bubble size distribution and the first neighbourhood distances between He bubbles. These results are confronted with simulations of the aging process and found in good agreement with the calculated values.