Sintering temperature has a moderat

Sintering temperature has a moderate effect on the relative density of the cold-sintered D5 composites (see the black curve in Fig. 2(b)). However, its effect on the relative density of HA seems noticeable (the red curve in Fig. 2(b)) and could be divided into three stages. In stage S1 (T ≤ 90 ◦C), the composition in the cold-sintered composites was HA/ DCPD (the relative density of pure DCPD samples was ~98%). The calculated relative density of the HA component was only ~63%, which is equivalent to the value of pure HA after CSP (D0 in Fig. 2(a)), suggesting that the DCPD before decomposition should have a negligible effect on the densification of HA. In stage S2 (90–100 ◦C), DCPD decomposed into DCPA, releasing considerable amount of water molecules, and the relative density of the HA component dramatically increased, indicating that the released water molecules should play a significant role in the densification of HA. In stage S3 (≥100 ◦C), the composition in the cold-sintered composites was HA/DCPA. The relative density of the composites reached ~85% and that of HA was estimated to be ~80% when the sintering temperature was 100 ◦C, and then their relative densities increased slightly with increasing temperature.