Glassy pocket

Fig. 9. Observation by BF and DF of a glassy pocket in a mullite ceramics and CBED pattern of this very small glass zone showing the amorphous halo...

As for the room temperature mechanical properties, hardness, fracture toughness and Young s modulus do not seem to be substantially dependent on the sintering additive. On the other hand, strength directly follows the microstructural features in terms of grain size, residual glassy pockets, amorphous grain boundaries, etc. 

Strength was instead strongly influenced by the microstmcture, i.e. secondary phases, residual glassy phases and mean grain size. TCM and ZBT had the highest room temperature flexural strength, 900 and 840 MPa, respectively, probably owing to the presence of discrete amonnt of silica-based pockets which healed small 170... 

---