Combining in situ HT-ESEM observations and dilatometry: An original and fast way to the sintering map of ThO2

The sintering of ThO2 pellets prepared from the initial precipitation of thorium oxalate was investigated by the means of HT-ESEM observations and dilatometric measurements. On the one hand, the use of environmental microscope allowed the in situ observation of the pellet behaviour during heat treatments between 1250 °C and 1400 °C. Subsequent image analysis led to the determination of local (i.e. at the grain scale) and global (i.e. at the pellet scale) kinetic parameters. Particularly, the average grain size was plotted versus the holding time for the three considered temperatures. On the other hand, analogous experiments were performed by dilatometry and led to monitor both linear shrinkage and density of the samples. On this basis, the combination of the two sets of data allowed us to establish for the first time a sintering map for ThO2. This latter clearly evidenced two different zones driven by densification (d ≤ 92%) then by grain growth (d ≥ 92%) which can be used efficiently to monitor the final microstructure of sintered thorium oxide.