Control of the viscous behavior of highly concentrated mullite suspensions for robocasting

Aqueous-mullite suspensions stabilized with an organic polyelectrolyte dispersant were characterized in terms of settling and rheological behaviors at solids concentrations as high as 60 vol.% (within 3 vol.% of the maximum consolidated density). The suspensions were cast into parts by a solid freeform fabrication technique termed robocasting and qualitatively characterized in terms of build behavior. Sedimentation and viscometry data were interpreted in view of knowledge of the interparticle forces. Through control of suspension pH and counter-ion addition, pseudoplastic mullite suspensions were created for use in the robocasting process. The suspensions were robocast at 52 vol.% solids and dried to yield a consolidated density of 55 vol.%. After firing to 1650 °C, robocast parts were greater than 96% dense.