Thermo-mechanical and microstructural characterization of geopolymers with α-Al ₂O ₃ particle filler

Geopolymers with different content of α-Al ₂O ₃ particle filler were prepared. The thermo-mechanical and microstructural characterization of the obtained geopolymers were systematically studied by flexural strength and thermal shrinkage measurements, TG-DTA (thermogravimetry and differential thermal analysis), XRD (X-ray diffractometry), and SEM (scanning electron microscopy). The results show that the addition of α-Al ₂O ₃ particle filler not only increases the onset crystalline temperature but also reduces the crystalline velocity of the geopolymers. The thermal shrinkage of the geopolymers increases with increasing heat treatment temperatures due to the water loss and densification. The flexural strength of the geopolymers increases with the increase of heat treatment temperatures from RT to 1200 °C, and shows a sharp increase in the range from 600 °C to 800 °C due to crystallization and solidification. The increase in content of α-Al ₂O ₃ particle filler can clearly reduce the thermal shrinkage and maintain a higher porosity at high temperatures. However, it has no distinct influence on the flexural strength after heat treatment. This is mainly attributed to the higher thermal resistance and strength of α-Al ₂O ₃.