Effect of preliminary heat treatment of alumina on the thermal-shock resistance and strength of corundum ceramics

Conclusions

The firing temperature of the starting alumina is one of the important factors influencing the formation of the microstructure of corundum materials and determines the properties of the ceramics. At low alumina firing temperatures (1400°C) the structure of the specimens is finely crystalline. An increase in the firing temperature (to 1600–1750°C) causes an increase in the crystal sizes.

The finely crystalline structure ensures a high strength in corundum materials, while the coarsely crystalline structure reduces it.

The high thermal-shock resistance of specimens is determined by the formation of regular, random orientation, and close contacting crystals of corundum. An important role in this case, apparently, is played by the structure of the crystals. The thermal-shock resistance of the materials is favored by a combination of starting materials having different firing temperatures, namely, aluminas fired at 1750 and 1600°C.