Freeze Casting of Aluminium Nitride
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.
S. Wildhack and F. Aldinger, "Freeze Casting of Aluminium Nitride", Advances in Science and Technology, Vol. 45, pp. 407-412, 2006