**3.6 S.E.M characterization of sintered samples**

The microstructure of the sintered specimens was observed by scanning electronic microscopy (SEM). **Figure 13** shows the S.E.M micrographs of the Alumina (Al2O3) reinforced with the Tricalcium phosphate (TCP) with different additives amounts sintered at 1600°C for 1 hour. This technique helps to investigate the porosity and the texture of any biomaterial. These micrographs show the coalescence between alumina grains produced with all the percentages of added TCP (**Figure 13(a–f)**).

These micrographs show the difference between fracture surface of Alumina, Alumina 10 wt.% TCP and Alumina 50 wt.% TCP samples (**Figure 13(a–f)**). The SEM micrographs of the pure Alumina sintered without TCP show an intergranular porosity (**Figure 13a** and **b**). The significant improvement of the characteristics of the Al2O3–10 wt.% TCP samples can be explaining by a coalescence between Alumina grains produced with all the percentages of added TCP. In addition, the formed spherical pores demonstrate that a liquid phase was formed a 1600°C (**Figure 13c** and **d**). For this composition, one notices also the absence of micro-cracking and the reduction of the sizes of the pores that achieves higher

**Figure 12.** *Fracture toughness (KIC) as function of the percentage of TCP.*

**Figure 13.**

*SEM micrographs of different bioceramic composites sintered at 1600°C for 1 h: (a) and (b) Al2O3, (c) and (d) Al2O3–10 wt.% TCP, (e) and (f) Al2O3–50 wt.% TCP.*

densities and decrease the grain size. For this reason, the Alumina-10 wt.% TCP composite presents excellent mechanical properties.

The strength started to decrease with higher percentage of TCP (20, 40, and 50 wt.%). A particular relation between grain size and mechanical strength in sintered alumina-TCP composites was found.
