Preparation Of Submillimeter ZrO₂ Microbeads By Gelcasting

Submillimeter zirconia microbeads have wide applications due to their excellent mechanical properties. However, the preparation method has a profoundly effect on their properties. Researchers have paid more attention to the gelcasting process, which is a kind of technology combining traditional ceramic forming process and organic polymerization. Ceramic microbeads with good properties can be obtained by this process.In this dissertation, the preparation of zirconia slurry with high-stability and low-viscosity and the process of producing submillimeter zirconia microbeads by gelcasting were studied.According to the Zeta potential analysis and the results of sedimentation test, the dispersant ammonium citrate(AC) could make the Zr O2 powder homogenously dispersed and stable in water, especially when the p H value was between 10 and 11. Conducted on the slurry rheology analysis, it was found that the viscosity of the slurry with 75 wt% Zr O2 solid content dropped to 101 m Pa?s under the 100 s-1 shearing rate when the dispersant AC had added up to 0.5 ~ 0.6 wt%. After ball milling for 120 min, the plastic viscosity of the slurry was 632 m Pa?s. Rheology curve of the mixed slurry indicated that the Bingham Model could be applied to this slurry. When the slurry mixed with the initiator ammonium persulfate(APS), using the interval ball milling method could efficiently keep the slurry temperature lower than 30oC which prevented the thermal initiation. The plastic viscosity and the yield stress increased to 954 m Pa?s and 27.43 Pa, respectively. In order to met the requirement of gelcasting process, the mixed slurry should be kept under low temperature, seal and vibration or magnetic stirring condition.On the basis of the micro-fluidisation and reversed phase suspension, the monodisperse submillimeter Zr O2 gel-microbeads were prepared by controlling the proportion of catalyst N-N-N’-N’ tetramethyl-ethylenediamine(TEMED) and temperature of the liquid paraffin during the gelcasting forming process. When the ratio of TEMED to the liquid paraffin was 1:150, and temperature of the liquid paraffin was 35oC, more Zr O2 microbeads were obtained. After polishing in water for 100 min, the surface of green body became more smooth. The glue removing temperature range was 250oC to 480oC and the sintering temperature was 1350oC with shrinkage of 24.9%. The SEM analysis of inner Zr O2 microbeads showed that the fully densification was achieved for the microbeads free of defects, and the average grain size of zirconia was about 300 nm.