| Summary: | 碩士 === 國立中央大學 === 機械工程學系 === 105 === The Kyropoulos method (KY) is the most common crystal growth method used in the industrial manufacturing large size crystal, because the crystal with this method has lower temperature gradient, and therefore it is more suitable for the larger size crystal growth. It is not easy to observe the complete process of crystal growth directly because of the design of KY furnace. Moreover, experimental measurement will spend a lot of time and money, so this study uses COMSOL Multiphysics which is the finite element software based on the theories of thermal and fluid dynamics. With this software, we tried to simulate the whole process of sapphire crystal growth, and analysis the phenomenon of crystal growth.
The results show that with the growth of crystal, the maximum thermal stress can be divided into three stages: crown stage, body stage and tail stage. At crown stage, the maximum thermal stress increases as the length of crystal increases. And at body stage, the maximum thermal stress decreases as the length of crystal increases. The last stage, because the crystal is closer to the bottom of the crucible, so at tail stage, the maximum thermal stress increases as the length of crystal increase.
By adjusting the speed of different heater power, it can be found that if the heater power decreases faster, the crystal crown shape will be flat, and the maximum thermal stress will be larger. On the other hand, if the heating power decreases slower, the crystal crown shape will be relatively steep, and thermal stress will be relatively smaller.
The study also explored the effect of the different furnace structures, such as different size thermal shield and different crucible shape, which also effect the quality of crystal .
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