【作者】 严小平；

【导师】 吴建青；

【作者基本信息】 华南理工大学 ， 材料学， 2010， 硕士

【摘要】 太阳能作为开发前景最好的绿色能源被世界各国重视和大力推广,导致用于太阳能转换的多晶硅的用量急剧增加。石英陶瓷由于不会与硅发生化学反应,且具备低热膨胀系数、低热导率和优异的热稳定性而被应用于生产多晶硅的坩埚,为了适应多晶硅片的规格不断增大的需求,石英陶瓷坩埚的尺寸必须随之增大,从而对石英陶瓷的制造技术提出了更高的要求。注浆成形是石英陶瓷坩埚常用的成形方法之一,具有低成本和低污染等优点。但是生坯强度低制约了大尺寸石英陶瓷坩埚的发展。本文研究了球磨、pH值、分散剂和固相含量对石英陶瓷浆体的影响,通过优化工艺参数,制备出适合注浆成形的高固含量和低粘度的稳定石英浆体。并且通过二次加料球磨,调整浆料的颗粒级配提高石英陶瓷生坯强度。研究表明,采用乳酸为分散剂,其加入量为0.1-0.5 wt%,熔融石英固含量为63 vol%时,以一定颗粒级配的玛瑙球为研磨介质球磨5 h后,再搅拌24 h,制备的石英浆体粘度为114mPa.S,符合注浆成形的要求。通过调整浆体的颗粒级配,使颗粒之间能够形成有效紧密堆积,是非常有效提高坯体强度的方法。本课题通过混合两种不同粒径的石英颗粒来调整颗粒分布,粗细颗粒中位径比为8.3,当粗细颗粒混合比为80:20时,体系达到最紧密堆积,生坯强度提高1倍,解决了注浆成形生坯强度低的问题。同时研究也发现Funk-Dinger理想颗粒函数能够很好地反映颗粒间的堆积紧密程度。此外,本研究发现搅拌有利于降低浆体粘度,这与搅拌能够促进颗粒表面电位的生成有关。并且同时提出了乳酸稳定石英浆体的机理,红外光谱分析表明二氧化硅颗粒表面存在一定量的羟基,石英浆体对乳酸的吸附是由于氢键的作用,颗粒表面的羟基与乳酸分子中羧基中的氢离子形成氢键,从而吸附乳酸分子在二氧化硅颗粒表面周围,乳酸的另一端分子链之间产生的空间位阻作用使石英浆体稳定。更多还原

【Abstract】 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.更多还原