Gel casting of high strength ceramics

University essay from Chalmers tekniska högskola/Institutionen för material- och tillverkningsteknik

Abstract: Gelcasting is a new ceramic forming technology for making complex-shaped ceramic products with high performance. The processes used in gelcasting are similar to processes often used in conventional ceramic forming process. However, when new high performance materials are introduced with the aim to improve the strength, defects such as air bubbles or agglomerates that can be found in many traditional ceramic materials are no longer be allowed since this would reduce the performance and reliability of the final ceramic products. The aim of this thesis project was to find an appropriate recipe of the ceramic suspension meanwhile improving the process of gelcasting and obtaining ceramic products with excellent mechanical behavior.To achieve this specified target, alumina and zirconia powders were studied in the following experiments which included rheological measurement of viscosity and storage modulus measurement for ceramic suspensions and drying shrinkage measurement of cast materials. The binder was burned out and the density was measured for ceramic materials sintered at different temperatures. The mechanical strength of sintered materials with high density was evaluated and the microstructure of fracture surfaces of ceramic samples was studied.Through rheological measurement, a good balance between fluidity and solid content of ceramic suspension was found. For alumina suspensions a solid content of 55vol% was selected and for zirconia solid contents of 46, 48 and 50vol% were studied. A monomer was dissolved in the suspension and an initiator was added to facilitate the polymerization of the monomer when the temperature was increased to around 70oC. The failure analysis of the fractured bending bars showed that the defects that caused the failure were not air bubbles but agglomerates. As a result, in future research for ceramic gelcasting with the intention to improve the mechanical strength, the suggestion is to use an appropriate recipe for the ceramic suspension and focus on elimination of granules and agglomerates from the suspension