Preparation of Mullite- and Zircon-Based Ceramics Using Kaolinite and Zirconium Oxide: A Sintering Study

The interactions between zirconia (ZrO2) powder and three Algerian hydrated kaolinitic clays were studied at high temperatures. The analysis by X‐ray diffraction of the prepared products allowed to follow the different phase developments during heat treatment and to identify the parameters controlling the zirconia conversion into zircon (ZrSiO4). It was found that ZrSiO4 formation, occurring at temperatures above 1150°C, is enhanced by the presence, in the clays, of fusing impurities such as K, Fe, Ca, and Mn, and by a decrease in zirconia particle size. A reactional mechanism, involving zirconia, a flux, and cristobalite is proposed. Moreover, the effect of zirconia additions on sintering was studied. It was also found that the increase in the porosity ratio of the final products for zirconia levels above 20 wt% was governed by a decrease in the flux amount, due to its lower clay content. Finally, it was shown that ceramics obtained by sintering at 1400°C for 2 h of a mixture of 38 wt% of fine zirconia powder and 62 wt% of the more reactive clay were mainly constituted of zircon and mullite.