Spark plasma sintering of UO2 nanopowders: Pressure, heating rate and current effects
Alexandre Margueret, Luca Balice, Karin Popa, Michael Holzhäuser, Emanuele De Bona, Walter Bonani, A. Bulgheroni, Fabienne Audubert, Marco Cologna
Abstract
We analysed with different methods the densification of UO2 nanopowders in SPS under constant heating rate (CHR) and isothermal sintering conditions. The apparent activation energy of densification in SPS (75 kJ/mol with CHR method) is significantly smaller than in conventional sintering. It is shown that this is likely not an effect of the applied current. We also observed a threshold stress at 64 MPa for the transition from pressure-insensitive sintering (stress exponent n≈0) to pressure-assisted sintering, suggesting that the contribution of the capillary stresses in such nanopowders is comparable with the typical stress applied in SPS.