Mullite compacts obtained by colloidal filtration of alumina powders dispersed in colloidal silica suspensions

This work deals with the manufacture of mullite-matrix composites by a colloidal filtration route. A variation of the transient viscous sintering process is studied in which submicrometer sized alumina particles are dispersed in a nanosize colloidal silica suspension. High solids loading suspensions (45 and 50 vol.%) are prepared by ultrasonic mixing and dispersed with citric acid. Rheological optimisation allows to obtain low viscosities and to reduce thixotropy and ageing effects. Specimens are obtained by slip casting and sintered to 1550 °C/2 h by using different heating cycles, the best results being obtained with a plateau after the maximum rate of sintering where reaction occurs.