In situ characterization of spinel nanoceramic suspensions

In this study, an approach to characterize ceramic colloidal suspensions has been developed, based on vitrification of aqueous ceramic suspensions and microstructural characterization using cryogenic-temperature scanning electron microscopy (cryo-SEM), augmented by conventional rheological measurements. The flocculation phenomenon in as-milled and aged Mg-spinel (MgAl ₂O ₄) aqueous suspensions was characterized. A microstructure based on hard particle agglomerates separated by long-chain deflocculant molecules was directly observed, and correlated to the rheological properties of the suspension. Several levels of flocculation were detected as a function of suspension preparation conditions. Although suspensions at solid-loading levels appropriate for ceramic processing cannot be characterized using conventional particle size measurement techniques, cryo-SEM can be used to measure characteristic sizes, and to distinguish between agglomerated and flocculated particles, opening a new approach for optimizing solid-loading conditions for slip casting in terms of viscosity and green density.