Papers by Author: S. Wildhack

Abstract: Aqueous freeze casting is an alternative wet shaping technique where water-based ceramic suspensions containing a cryoprotectant are cast in molds, frozen and dried. The method can be applied to various ceramic systems depending mainly on the ability to produce high solid loading in aqueous ceramic slurries. Against this background, aqueous aluminum nitride (AlN) suspensions were developed for the application in freeze casting. The results show that the applied process additives are most effective not only in chemically protecting AlN against hydrolysis but also in obtaining colloidally stable slurries with solid loadings in excess of 50 vol.-%. After optimization of the viscosity, the freeze cast green samples exhibit homogeneous microstructures without cracks and warpage. Besides, the systematic control of the freezing step and the solid loading allow the preparation of sintered samples with defined density.

Abstract: In the present contribution, the electrophoretic deposition (EPD) of nanocrystalline SiC powders will be discussed. In order to avoid the electrolysis of water during deposition as well as oxygen uptake of the nanocrystalline SiC by hydrolysis reactions, nonaqueous solvents were tested including ethanol and diethyl formamide. The solvents were compared regarding their effect on particle size distributions and sedimentation tests. Auxiliary information on the surface conditions as a function of the acidity of the suspension was drawn from aqueous zeta-potential measurements. The influence of dispersants, binders and the type of powder on the suspension properties was studied, and EPD was performed. For promising solvent-dispersant systems, the film thickness, current and deposition time at a given voltage were monitored during EPD.