Assembly of Ceramic Particles in Aqueous Suspensions Induced by High-Frequency AC Electric Field

Ceramic materials processed using colloidal methods have been the focus of a great deal of research aimed at tailoring the final structure and microstructure of the finished ceramic sample. To this end, various external field effects have been investigated to modify the suspension microstructure without manipulating the ceramic particles directly. In a previous work in the field of ice templating it has been shown that AC electric fields are able to produce microstructural changes in ice templated ceramics that have significantly improved the final mechanical properties. However, the mechanisms for this process are still not well understood in ceramics. To better understand the mechanisms that are present in colloidal processing of ceramics using AC field, this thesis investigates the role of high frequency alternating current (AC) electric field in the assembly of alumina and barium titanate particles in aqueous media. Field-particle interactions were in situ investigated via optical microscope for coarse and fine alumina as well as fine barium titanate powder particles in very dilute suspensions. In the first half of the work with both coarse and fine alumina particles, AC field-induced assembly led to the formation of chains aligned in the field direction. Chain length increased with both field strength and field duration. Chain formation was attributed to mutual dielectrophoretic (DEP) interaction forces. Threshold field strength for chain formation suggested stronger interactions for finer particles. In the second half of the work, fine alumina and fine barium titanate powders of similar size were compared to study the effect of the particle type on the formation of chains. The inter-chain distance was also measured suggesting that the particle type had a strong effect on how the chain structure developed. The effect of frequency on chain formation showed that decreasing the frequency of the AC field resulted in fluid motion that impeded the formation of chains. Darvan-C dispersant was added to the medium of the solution improving the formation of chains for both alumina and barium titanate. SEM images were used to confirm these findings by preserving the chains using a binder