In situ dilatometry measurements of MgH2 compacted disks
Résumé
In situ dilatometry measurements were performed in order to characterize the progressive swelling which is observed upon cycling on compacted disks made of ball-milled MgH2. Each sample was submitted to 200 hydrogen cycles at 310 C, under 0.1 MPa for desorption and 1 MPa for absorption. These measurements clearly show a dilatation on absorption and a contraction on desorption especially in the radial direction. However, at the end of the desorption, the initial position is not recovered and a ''cumulate displacement'' is observed which increases progressively up to about 30 cycles where a stabilisation of the phenomenon is achieved. The introduction of Natural Expanded Graphite (NEG) appears very efficient to limit the radial expansion, with a maximal amplitude three times lower than without NEG and a radial stress equivalent to an applied pressure of 3.4 MPa.