Influence of the deagglomeration procedure on aqueous dispersion, slip casting and sintering of Si3N4-based ceramics

The influence of the deagglomeration procedure on the rheological behaviour of Si3N4-based aqueous suspensions, the slip casting performance and the final properties after sintering were investigated. Ball milling and planetary milling performed deagglomeration of powders. The experimental results showed that the time required to obtain the same degree of deagglomeration was considerably shorter in the case of planetary milling. The decrease in viscosity during the milling procedure enabled well dispersed and relatively high-concentrated (55-vol.%), suspensions to be obtained by adding successive 5-vol.% increments of solids to an initial 45-vol.% suspension. The time required to achieve complete deagglomeration of the starting suspension or after adding each 5-vol.% solidsʹ increments was of 4 h for planetary mill and varied from 24 to 48 h for ball mill, with increasing solids loading, reaching total deagglomeration times of 12 and 96 h, respectively. The results have shown that, for a given solids volume fraction, both the degree of deagglomeration and the time required to achieve it, i.e. the duration of the contact between the powders and the dispersing aqueous solution, are key factors for achieving dense and homogeneous green microstructures, and for improving the densification behaviour and final properties of sintered bodies.