Stress-density Variations in Alumina Sediments: Effects of Polymer Chemistry

INTRODUCTION Achieving spatially uniform and hierarchically structured microstructures during the shape-forming of colloidal ceramics depends largely on (t) the magnitude of the effective stresses (i.e., stresses that are supported by the particulate network) and (ii) plastic properties, which in turn are significantly altered by processing parameters affecting interparticle friction and adhesion. To quantify the effects of processing parameters on consolidation, we present a novel approach for analyzing sediments by gamma-ray densitometry and a fluid mechanics model. This method enables us to correlate processing parameters with spatial variations of the packing density and the local effective stress. These correlations are difficult to achieve by traditional techniques (e.g., rheometry, sedimentation kinetics modeling, soil mechanics tests), especially for the low stresses (< 1000 Pa) that are typically encountered in sediments. Aside from being destructive to samples, these techniques also tend to measure volume-averaged properties, and as a result they usually fall short of describing localized consolidation phenomena. Significant variations in plasticity can arise through modification of interparticle forces by changing the chemistry of surface-adsorbed polymers or ions. In the present study, we address the question of how to design surface-adsorbed polysiloxanes to enhance particle rearrangement into densely packed structures. Polysiloxanes are excellent lubricants (e.g., silicon oil) due to the low rotational energy of the Si-O-Si bonds comprising the polymer backbone. These inorganic polymers are also available with a broad range of chemical structures that can pyrolyze to various inorganic silicon-based compounds under appropriate conditions. 2 This research is part of a larger program examining the use of polymeric additives that may form useful inorganic phases within the pores of a ceramic compact upon pyrolysis. 3