The use of colloidal and surface chemistry for processing nanosized ceramic powders

Abstract

Surface and colloidal chemistry have been applied to the synthesis and processing of nanoscale ceramic powders. Redispersable oxides, e.g. ZrO2 and Y2O3/ZrO2 with particle sizes less than 20 nm have been prepared by the microemulsion technique as well as by thermodynamically controlled growth reaction in the presence of surface active compounds. By surface modification with short-chained organic molecules which provided short-range steric repulsive forces, nano-scale boehmite and TiN could be processed to high green density compacts. Due to the small particle size of TiN (40nm) and homogeneous green microstructure, nearly full density (>98%) was achieved below 1300°C with negelctable grain growth. The system SiC/B4C/C has been investigated for the improvement of the carbon black distribution within the green specimens prepared by casting techniques and electrohporesis, respectively. For slip casting it was found that nano-scale carbon black can be directly deposited on the surface on the SiC-particles which leads to significantly improved processing and properties of the sintered material (Tb>600 MPa, HV05=31 GPa). An excellent sintering aid distribution within the green parts was achieved by electrophoresis after careful adjustment of the electrophoretic velocity of the different components by surface modification with a polymeric base.