The fracture microstructures of the CSP-CS specimens after sintering at 1400 °C for 2 h and 48 h are indicated by the FE-SEM images in Fig. 9. It can be seen that the densification was enhanced with increasing amount of yttrium nitrate and further enhanced when the sintering time was increased to 48 h. In particular, hardly any pores are observed in the 20YN specimen which is highly densified after sintering at 1400 °C for 48 h.