Executive Summary
Although compaction has been the object of considerable study, questions remain about compaction. These questions exist due to the difficulties with obtaining in-situ information about powder rearrangement/breakage during compaction. In general, compaction work has primarily studied stress-strain curves. Depending upon the relative density and the change of density with pressure, one tries to infer the mechanism(s) of compaction.
In this work, we address the development of in-situ techniques to tlrobe comtlaction mechanisms. Instead of simply measuring density variation and attempting to infer compaction mechanisms, we employ scattering to study compaction. In order to demonstrate the utility of these in-situ techniques, we have; 1) performed preliminary experiments to demonstrate the sensitivity of the technique to a dilute second phase (sensitive to l-5% depending upon the powder size, morphology, and electron density), 2) used compaction with ex- situ scattering to demonstrate how compaction mechanisms can be directly observed and 3) employed fluids with electron density matched to that of the solid phase (or one powder if a mixture) to selectively study the second powder. In one example, we studied changes of a silica compact as it was compacted isostatically or by drying capillary pressure. By assessing the variation in the scattering intensity associated with different length scales as well as the change in the hydraulic radius with pressure/density, pores around the agglomerates were observed to disappear due to agglomerate breakage and compaction. This result could not have been obtained by simply measuring the stress-strain of the compact as is normally done in compaction studies. For another example, dibromomethane was impreganted into a silica-titania mixture and scattering was performed. This shows that contrast matching and small-angle x-ray scattering may be employed to selectively “illuminate” a few hard aggiomerates of a second material type during compaction.