Advanced mullite ceramics from cost-effective kaolin

ABSTRACT This study presents a wet processing route for the production of dense mullite ceramics intended for advanced, high-value-added applications, using kaolin -a low-cost raw material-. An aqueous suspension milling system that combined both dispersion and attrition milling enabled the production of homogeneous mixtures of kaolin and alumina at the individual particle level. This processing route demonstrated good reproducibility under the processing conditions investigated in this study. The resulting dense mullite compacts achieved relative densities in the range of 94–96%, depending on the drying route. A mechanical study was conducted at 25 °C, 800 °C, and 1100 °C, which showed flexural strengths at room temperature of 205–238 MPa and values increasing to approximately 300 MPa at 1100 °C, thus remaining competitive with the values reported for commercial high-purity synthetic mullite powders. Furthermore, the permittivity and loss tangent values were similar to those obtained for pure mullite (ε r = 8.4, tan δ = 4×10 -4 , respectively). These results open up the possibility of using these materials as electrical components. Therefore, the proposed low-cost processing route reveals a wide range of applications for mullite compacts in many processes that require operation in an oxidizing atmosphere in the range of 25 °C to 1100 °C.