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Zhang J.,Jiangnan University | Ni Y.,Jiangnan University | Liu Q.-Q.,Jiangnan University | Ma W.-C.,Uonone Optoelectronics Technology Co. | Li L.-C.,Jiangsu Huasheng Tianlong Photoelectric Co.
Rengong Jingti Xuebao/Journal of Synthetic Crystals | Year: 2015

Numerical simulation of the temperature field in three-dimensional temperature gradient (3DGF) single crystal furnace by the finite element analysis method found that near the melt-crystal interface existed a large temperature gradient, which easily lead to crystal cracking; through improving crucible inner wall taper, adjusting the bottom heat shield structure and selecting the appropriate cooling program, good experimental results were achieved. The results show that a suitable temperature gradient and temperature programs can shorten the growth cycle and improve the quality of the crystal in the 3DGF sapphire crystal growth process. ©, 2015, Rengong Jingti Xuebao/Journal of Synthetic Crystals. All right reserved. Source


Ma W.,Xian Jiaotong University | Ma W.,Uonone Optoelectronics Technology Co. | Liu L.,Xian Jiaotong University
Kuei Suan Jen Hsueh Pao/Journal of the Chinese Ceramic Society | Year: 2016

For an industrial-scale sapphire furnace of heat exchanger method, a two-dimensional global model of heat transfer was established. The internal radiation heat transfer of crystal was simulated by discrete ordinate method. The effect of absorption coefficient on the temperature and thermal stress distributions in the sapphire crystal was investigated. The numerical results indicate that under the effect of the internal radiation, the region with great axial temperature gradient and thermal stress is located at the bottom of the crystal in a range of 1 cm from the bottom surface of the crystal. The maximal axial temperature gradient and stress firstly increase and then decrease with the increase of the crystal absorption coefficient from 1.9 m-1 to 1900 m-1. © 2016, Editorial Department of Journal of the Chinese Ceramic Society. All right reserved. Source


Wu M.,Xian Jiaotong University | Zhao W.,Xian Jiaotong University | Liu L.,Xian Jiaotong University | Yang Y.,Xian Jiaotong University | And 3 more authors.
Journal of Crystal Growth | Year: 2014

A crucible cover is designed in a furnace for growing sapphire crystals by heat exchanger method. Global simulations of heat transfer are carried out to investigate its effects on the thermal field and melt flow in the crucible during the growth of sapphire crystal. It is found that the crucible cover has significant effect on the thermal field in the melt. When the crucible cover is installed, the radial temperature gradient in the melt at the melt-crystal interface decreases while the axial temperature gradient increases. The melt flow is weakened accordingly. The melt-crystal interface becomes flatter and the thermal stress in the crystal is reduced with the installed crucible cover. It can be therefore concluded that use of a crucible cover is favorable for crystal growth. © 2014 Elsevier B.V. Source


Ma W.,Uonone Optoelectronics Technology Co. | Ma W.,Xian Jiaotong University | Zhao L.,Harbin Institute of Technology | Ding G.,Uonone Optoelectronics Technology Co. | And 4 more authors.
International Journal of Heat and Mass Transfer | Year: 2014

We developed a transient global model to study the heat transfer in sapphire crystal growth by heat exchanger method (HEM). Internal radiation in the semi-transparent sapphire was modeled with a rigorous discrete ordinate model and phase change was calculated based on a fixed-grid method in our simulations. The evolutions of thermal field, melt flow and melt-crystal (m-c) interface shape were predicted during the whole crystal growth process. Simulation results show that a U-shape distribution of axial temperature gradient appears along the centerline of the sapphire crystal and melt, respectively, due to the effect of internal radiation. The m-c interface is severely curved near the crucible wall and relatively flat at the central region with an increasing convexity when crystal grows. The sapphire melt flow is in a laminar state dominated by the thermal buoyancy force. The high growth rate at the final stage of the solidification process resulted in bubbles at the top layer of the grown crystal. The formation mechanism of the grain boundaries at the crystal periphery was discussed. The numerical simulation results show a good agreement with the experiment data. The developed global model herein provides important information to improve the growth process of sapphire crystal by the HEM technique. © 2014 Elsevier Ltd. All rights reserved. Source

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