Effect of mechanical activation on the rheology and casting performance of kaolin/talc/alumina suspensions for manufacturing dense cordierite bodies

Previous work studied the rheological behaviour of 40 vol.% slips of kaolin/talc/alumina mixtures with relative weight ratios of 40/43.8/16.2 for manufacturing cordierite foams. However, the manufacture of the corresponding dense bodies makes it necessary to reduce the starting particle sizes through intensive ball milling. The rheological behaviour and the slip casting performance of both milled and unmilled slips have been studied. Milling did not significantly change the rheological behaviour but served to improve the casting performance. Sintering tests and XRD analysis demonstrated that at 1250 °C some reflections of sapphirine, spinel, mullite and cristobalite can still be detected, as well as coarse quartz particles, but at 1280 °C and above the cordierite phase is practically the only phase detected whereas in the unmilled powder the coarse silica was detected even at 1350 °C. In contrast with unmilled slips, where a large porosity is always observed, milled slips lead to highly dense structures without remaining pores, as a consequence of the activation of the raw materials.