Spark plasma sintering of UO2 nanopowders: Pressure, heating rate and current effects

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 approximate to 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.

Automated summary

We analyzed the densification of UO2 nanopowders in SPS under different conditions and found that the apparent activation energy of densification in SPS is smaller than that in conventional sintering. We also observed a threshold stress for the transition from pressure-insensitive sintering to pressure-assisted sintering.