Processing of mullite-glass ceramics using simplex-centroid design: Densification process dominated by liquid-phase sintering

Mullite is one of the preferred aluminosilicates for both traditional and advanced ceramics. This paper reports the use of simplex-centroid mixture design to prepare mullite-glass ceramics by reactive sintering. The phase composition and technological properties of formulations containing kaolinitic clay, kaolin waste and alumina were investigated after sintering at 1400 degrees C. The sintering behavior was assessed by dilatometry. Microstructural analysis indicated the crystalline phases mullite, residual quartz, cristobalite, and a-alumina. A glassy phase was also identified as a matrix embedding mullite grains (as seen by X-ray diffractometry and scanning electron microscopy). In kaolin waste-rich formulations, a liquid phase sintering mechanism favored the densification process and the mechanical resistance. Highly significant statistical models allow correlating the concentrations of raw materials with linear firing shrinkage, water absorption and apparent porosity. Overall results stand out for the potential of using kaolin waste in the preparation of mullite-glass ceramics. (C) 2020 SECV. Published by Elsevier Espana, S.L.U.