Four mixtures of kaolinite clay and feldspar (Western-Cameroon) were prepared and sintered at 1200 °C for 2 h at the heating rate of 5 °C/min, 10 °C/min, 15 °C/min and 20 °C/min. The main new crystalline phase was mullite associated with quartz, anatase and cristobalite for all heating rates. By increasing the feldspar content, both the amounts of mullite and of glassy phase increase which promotes the densification of the samples. Heating rate has less influence on the formation of new mineral phases, while this process is sensitive to flux content. Both heating rate and flux content have an effect on the microstructure of the fired bodies as well as technological properties. The specimens with 30% feldspar content sintered at 1200 °C from 5 °C/min to 20 °C/min exhibited water absorption values <10% and bending strength >12 MPa. These materials are suitable as wall tiles. Thus, these samples can be sintered at a heating rate of 20 °C/min instead of 5 °C/min which leads to a saving in firing time and in energy.
Njoya, D., Tadjuidje, F. S., Ndzana, E. J. A., Pountouonchi, A., Tessier-Doyen, N., & Lecomte-Nana, G. (2017). Effect of flux content and heating rate on the microstructure and technological properties of Mayouom (Western-Cameroon) kaolinite clay based ceramics. Journal of Asian Ceramic Societies, 5(4), 422–426. https://doi.org/10.1016/j.jascer.2017.09.004