Preparation Of Fused Silica Ceramic With Slip Casting

Solar energy is largely developed as a well-potential and green energy all over the world, which drives the development of polysilicon used for the conversion of solar energy. Silica ceramic is applied as crucible in the polysilicon production because it don't react with silicon and has good properties including low thermal expansion coefficient, low thermal conductivity, and good thermal stability. In order to meet the need that the size of polysilicon film is enlarging, the size of silica ceramic crucible will be increasing respectively. Therefore, it puts forward higher requirement to the technology of silica ceramic crucible.Slip casting is a traditional manufacturing approach of silica ceramic crucible, and it possesses the advantage of low cost as well as low pollution. However, there is also a disadvantage that the strength of green body with slip casting is low, which makes it impossible to produce large size silica ceramic crucible.The effects of milling, pH value, dispersant and solid volume on the silica slurries were studied in this paper, and silica slurries which were fitted for slip casting with high solid volume and low viscosity were prepared by optimizing the process parameters. Besides, with the technology of second milling, the strength of green body was enhanced by adjusting the particle size distribution.It was showed by the experiment that silica slurry with the viscosity of 114mPa.S and solid content of 63vol% could be obtained in terms of these processes including a certain particle size distribution of the agate balls and nylon cans, dispersant for the lactic acid, lactic acid dosage of 0.1-0.5wt%, milling time of 5h and stirring time of 24h after milling. It was an effective approach to increase the strength of green body by adjusting the particle size distribution of slurries. It was adapted in this work by mixing two different size distribution of silica to adjust particle size distribution. The median diameter ratio of coarse and fine silica particle was 8.3, when the mixing ratio of two particles was 80:20, it formed an effective close packing between particles in the whole system, and the strength of green body could be almost doubled. Therefore, the problem of low green body strength with slip casting was solved. In addition, it was also proved from the experiment that Funk-Dinger ideal particle model can well reflect the packing degree of particles in a system.Furthermore, it was found that stirring could reduce the viscosity of the slurry because it could promote the generation of silica particle surface potential. Meanwhile, the mechanism of lactic acid stabilized silica slurry was proposed in this paper. It was evident that the adsorption of lactic acid on silica particle surface was due to the existence of hydrogen bond. The Infrared spectrum indicated that there was a certain amount of hydroxyl on silica particle surface, so the hydrogen atoms from the carboxyl of lactic acid molecules and the oxygen atoms from the hydroxyls on the surface of could form hydrogen bond. In this way, lactic acid molecules were combined on the surface of silica particles, and the other side of the molecule chains could emerge steric effect to stabilize silica slurries.