The Experts below are selected from a list of 59973 Experts worldwide ranked by ideXlab platform
Lijun Liu - One of the best experts on this subject based on the ideXlab platform.
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optimization of the melt crystal Interface Shape and oxygen concentration during the czochralski silicon crystal growth process using an artificial neural network and a genetic algorithm
Journal of Crystal Growth, 2020Co-Authors: Yifan Dang, Lijun LiuAbstract:Abstract The melt/crystal Interface Shape and oxygen concentration during the Czochralski silicon crystal growth process significantly influence the crystal quality. In this paper, an optimization system with the combination of an artificial neural network and a genetic algorithm is proposed to optimize the growth parameters during the growth process. Flattening the melt/crystal Interface and reducing the oxygen concentration along the Interface were chosen as the optimization targets. Two important growth parameters, the crystal rotation rate and crucible rotation rate, were chosen as optimization variables. First, a global heat and mass transfer model was developed to simulate the crystal growth process and then tested with experimental data. The verified heat and mass transfer model was then used to train an artificial neural network with the aim of rapidly assessing the complex nonlinear dependence of the Interface Shape and oxygen concentration on the growth parameters. The trained neural network combined with a genetic algorithm was then used to obtain the optimal growth parameters. Both deflection of the melt/crystal Interface and the oxygen concentration along the Interface decreased after optimization. Finally, the optimal growth parameters were checked in the heat and mass transfer model to evaluate the performance of the optimization system. The proposed method will also be useful for optimization of other crystal growth processes.
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improved seeded directional solidification process for producing high efficiency multi crystalline silicon ingots for solar cells
Solar Energy Materials and Solar Cells, 2014Co-Authors: Wenhan Zhao, Xueqin Liang, Jun Zhang, Lijun LiuAbstract:Abstract We proposed an improved process design for the industrial mc-Si seeded directional solidification process to produce high-quality multi-crystalline silicon ingots for high-efficiency solar cells. A transient global model of heat transfer was employed to investigate the effects of the process design parameters on the melt–crystal Interface Shape, thermal field, and thermal stress distribution in the solidified silicon ingot during the solidification process. Ingot casting experiments were carried out and the solar cell performance was measured. The results show that the melt–crystal Interface Shape in the improved process design remains convex during almost the whole solidification process, and the thermal stress level at the bottom of the solidified ingots is significantly lower than in the original process design. Based on the experimental results, the quality of grown silicon ingots and the conversion efficiency of solar cells were analyzed. The shadow region present in the silicon ingot produced with the original process design disappears and the morphology of the ingot is improved with a more homogeneous distribution of grain orientation using the improved process design. The average yield rate of the solidified silicon ingot is 8.18% higher with the improved process design. The average conversion efficiency of solar cells is higher with the improved process design (17.59%) than with the original process design (17.48%).
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effects of argon flow on melt convection and Interface Shape in a directional solidification process for an industrial size solar silicon ingot
Journal of Crystal Growth, 2012Co-Authors: Lijun Liu, Xin Liu, Yunfeng Zhang, Jingfeng XiongAbstract:Abstract We carried out global simulations of heat transfer to investigate the argon flow effect on the melt convection and melt–crystal (m–c) Interface Shape at different stages of an industrial directional solidification (DS) process for the multi-crystalline silicon (mc-Si) ingot. We found that the convective heat transfer at the melt free surface due to the argon flow significantly changed the temperature distribution in the upper layer of the silicon melt. The shear stress caused by the argon flow along the melt free surface increases with an increase in argon flow rate. The melt flow pattern under the central area of the free surface changes accordingly. The argon flow has little impact on the m–c Interface Shape at the early stage of the DS process. At the middle stage, the m–c Interface Shape is mainly influenced by the pattern and intensity of the melt convection, which are modified by the argon flow. It is less convex to the melt with a larger argon flow rate. However, the m–c Interface is more convex to the melt with an increase in argon flow rate at the final stage of the DS process, because it is then directly affected by the cooling effect of the gas flow.
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numerical investigation of the influence of material property of a crucible on Interface Shape in a unidirectional solidification process
Crystal Growth & Design, 2009Co-Authors: Hiroaki Miyazawa, Lijun Liu, Koichi KakimotoAbstract:We carried out calculations to investigate the influence of thermal conductivity of the wall of a crucible on melt−crystal Interface Shape using three-dimensional global analyses. It was found that thermal conductivity of the wall of a crucible has significant influence on the melt−crystal Interface Shape due to modification of the amount of outgoing heat flux through the wall of a crucible. The results indicate that we should control not only heater power, growth velocity, and melt flow but also thermophysical properties of the wall of a crucible in order to reduce deformation of the melt−crystal Interface.
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study on thermal stress in a silicon ingot during a unidirectional solidification process
Journal of Crystal Growth, 2008Co-Authors: X J Chen, Lijun Liu, Satoshi Nakano, Koichi KakimotoAbstract:Abstract A transient global model was used to obtain the solution of a thermal field within the entire furnace during a unidirectional solidification process for photovoltaics. The melt–solid Interface Shape was obtained by a dynamic Interface tracking method. The thermal stress distribution in the silicon ingot was solved using the displacement-based thermo-elastic stress model. Furthermore, several different melt–solid Interface Shapes were obtained by using different growth velocities, and then the thermal stresses for different solidification times were compared. The simulation results suggested that the crucible constraint should be reduced and a longer solidification time should be used for growing a silicon ingot with low thermal stress and low dislocation density.
Yves Fautrelle - One of the best experts on this subject based on the ideXlab platform.
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thermoelectric magnetohydrodynamic flows and their induced change of solid liquid Interface Shape in static magnetic field assisted directional solidification
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2016Co-Authors: Yves Fautrelle, Jiang Wang, Guillaume Reinhart, Henri Nguyenthi, Hanlin Liao, Yunbo ZhongAbstract:Applying static magnetic field can produce flows (thermoelectric magnetohydrodynamic flows, TEMHDF) in the melt by interacting with the thermoelectric currents (TEC) during solidification of metals. A physical model was proposed to interpret how these TEC appear at the solid–liquid Interface and verified by a corresponding simulation. The influences of TEMHDF on solidification were investigated through both ex-situ experiments and n situ observations by means of synchrotron X-ray radiography. The 3D numerical simulations of TEMHDF were performed for these two cases, respectively, and suggested that both the change of Interface Shape with different transverse static magnetic fields demonstrated by the ex-situ experiments and the real time observed Interface Shape varying under a 0.08 T transverse static magnetic field could attribute to the TEMHDF advanced solid–liquid Interface in the static magnetic field-assisted directional solidification. The TEMHDF produced by an axial static magnetic field were also computed along with the Interface change predicted based on which is good in line with the published experimental results. This study of TEMHDF and their impacts on the solid–liquid Interface Shape provides a method to tailor the structure during directional solidification using static magnetic field.
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modification of liquid solid Interface Shape in directionally solidifying al cu alloys by a transverse magnetic field
Journal of Materials Science, 2013Co-Authors: Jiang Wang, Yves Fautrelle, Henri Nguyenthi, Zhongming Ren, Nathalie Mangelincknoel, Georges Salloum Abou Jaoude, Yunbo ZhongAbstract:Al-0.85wt%Cu and Al-2.5wt%Cu alloys were directionally solidified under different transverse magnetic field (TMF) intensities to investigate the influence of TMF on the liquid/solid Interface Shape with respect to the various length scales appearing (planar, cellular, and dendritic Interfaces). Results show that planar and cellular Interfaces tilt to one side and then level off with increasing TMF although the dendritic Interface appears not to behave in this manner. In situ synchrotron X-ray imaging was applied during directional solidification of the Al-4wt%Cu alloy under a 0.08T TMF, revealing leveling of the initially sloped Interface. Solute redistribution, caused by thermoelectric magnetic convection (TEMC), responds to the changes in the Interface Shape. Because different typical length scales should be used in estimating the velocity of TEMC for planar, cellular, and dendritic Interfaces, the maximum velocity of the convection ahead of the Interface is obtained under different TMF intensities; correspondingly, leveling of the Interface’s degree of slop varies with TMF.
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Effects of Thermoelectric Magnetic Convection on the Solidification Structure During Directional Solidification under Lower Transverse Magnetic Field
Metallurgical and Materials Transactions A, 2011Co-Authors: Zhongming Ren, Annie Gagnoud, Olga Budebkova, Yves FautrelleAbstract:This work investigated the thermoelectric magnetic convection (TEMC) during directional solidification under a transverse magnetic field numerically and experimentally. Numerical results show that the TEMC will form in liquid near the liquid/solid Interface and in the dendritic network. The value of the TEMC mainly depends on the crucible diameter, the temperature gradient, and the magnetic field intensity. The value of the TEMC increases as the crucible diameter and the temperature gradient are increased. The value of the TEMC on the sample scale increases to a maximum when the magnetic field is of the order of 0.1 T, and then decreases as the magnetic field still increases. However, the value of the TEMC on the cell/dendrite scale continues to increase with the increase of the magnetic field intensity when the applied magnetic field is less then 1 T. Two alloys are solidified directionally in the vertical configuration under a transverse magnetic field, and results show that the application of a lower transverse magnetic field (B < 1 T) modified the liquid/solid Interface Shape and the cellular/dendritic array significantly. Indeed, it was observed that, along with the refinement of the cell/dendrite, the magnetic field caused the deformation of the liquid/solid Interfaces and the extensive segregations (i.e., channel and freckle) in the mushy zone. Comparison of the numerical and experimental results shows that the modification amplitude of the liquid/solid Interface and the cellular/dendritic morphology is in good agreement with the value of the TEMC at the liquid/solid Interface and in the dendritic network. This implies that changes of the Interface Shape and the cellular/dendritic morphology should be attributed, respectively, to the TEMC on the sample and the cell/dendrite scales.
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investigation of thermoelectric magnetic convection and its effect on solidification structure during directional solidification under a low axial magnetic field
Acta Materialia, 2009Co-Authors: Annie Gagnoud, Yves Fautrelle, Zhongming Ren, Rene MoreauAbstract:Abstract Thermoelectric magnetic convection (TEMC) at the scale of both the sample (L = 3 mm) and the cell/dendrite (L = 100 μm) was numerically and experimentally examined during the directional solidification of Al–Cu alloy under an axial magnetic field ( B ⩽ 1 T ). Numerical results show that TEMC on the sample scale increases to a maximum when B is of the order of 0.1 T, and then decreases as B increases further. However, at the cellular/dendritic scale, TEMC continues to increase with increasing magnetic field intensity up to a field of 1 T. Experimental results show that application of the magnetic field caused changes in the macroscopic Interface Shape and the cellular/dendritic morphology (i.e. formation of a protruding Interface, decrease in the cellular spacing, and a cellular–dendritic transition). Changes in the macroscopic Interface Shape and the cellular/dendritic morphology under the magnetic field are in good agreement with the computed velocities of TEMC at the scales of the macroscopic Interface and cell/dendrite, respectively. This means that changes in the Interface Shape and the cellular morphology under a lower magnetic field should be attributed respectively to TEMC on the sample scale and the cell/dendrite scale. Further, by investigating the effect of TEMC on the cellular morphology, it has been proved experimentally that the convection will reduce the cellular spacing and cause a cellular–dendritic transition.
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influence of thermoelectric effects on the solid liquid Interface Shape and cellular morphology in the mushy zone during the directional solidification of al cu alloys under a magnetic field
Acta Materialia, 2007Co-Authors: Xi Li, Yves FautrelleAbstract:Abstract In this work thermoelectromagnetic convection (TEMC) is evaluated at different scales and the result shows that the effect of TEMC is different for different scales. To validate this analysis, Al–Cu hypoeutectic alloys were solidified directionally under a magnetic field, and both the Interface Shape and cellular morphology in the mushy zone investigated. The experimental results show that a weak magnetic field ( B ⩽ 0.5 T) has a significant affect on the cellular liquid–solid Interface and the cellular morphology. This is attributed to the TEMC caused by the interaction between the field and the thermoelectric (TE) current, which is consistent with the analysis. Under a higher magnetic field, the field causes the cells to break and makes the liquid–solid Interface uneven; these effects are attributed to the magnetic force and the TE torque.
Koichi Kakimoto - One of the best experts on this subject based on the ideXlab platform.
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3d numerical study of the asymmetric phenomenon in 200 mm floating zone silicon crystal growth
Journal of Crystal Growth, 2020Co-Authors: Xue Feng Han, Satoshi Nakano, Xin Liu, H Harada, Yoshiji Miyamura, Koichi KakimotoAbstract:Abstract In this paper, we propose a three-dimensional model for a 200 mm floating zone silicon crystal growth process to investigate the fluid flow and solid–liquid Interface. To study the effect of high-frequency (HF) electromagnetic (EM) heating on the melt flow and Interface Shape, HF-EM and heat transfer calculations were conducted in three dimensions. Through comparison of EM and Marangoni forces, EM force was found to have a larger effect than Marangoni force on the free surface flow. By considering 3D Marangoni and EM forces at the free surface, a more accurate melt flow distribution has been obtained. Moreover, the results showed that local growth rate became more inhomogeneous when the rotation speed of the crystal was increased. However, a more homogeneous three-phase line could be obtained with a high rotational crystal speed.
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numerical investigation of the influence of material property of a crucible on Interface Shape in a unidirectional solidification process
Crystal Growth & Design, 2009Co-Authors: Hiroaki Miyazawa, Lijun Liu, Koichi KakimotoAbstract:We carried out calculations to investigate the influence of thermal conductivity of the wall of a crucible on melt−crystal Interface Shape using three-dimensional global analyses. It was found that thermal conductivity of the wall of a crucible has significant influence on the melt−crystal Interface Shape due to modification of the amount of outgoing heat flux through the wall of a crucible. The results indicate that we should control not only heater power, growth velocity, and melt flow but also thermophysical properties of the wall of a crucible in order to reduce deformation of the melt−crystal Interface.
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study on thermal stress in a silicon ingot during a unidirectional solidification process
Journal of Crystal Growth, 2008Co-Authors: X J Chen, Lijun Liu, Satoshi Nakano, Koichi KakimotoAbstract:Abstract A transient global model was used to obtain the solution of a thermal field within the entire furnace during a unidirectional solidification process for photovoltaics. The melt–solid Interface Shape was obtained by a dynamic Interface tracking method. The thermal stress distribution in the silicon ingot was solved using the displacement-based thermo-elastic stress model. Furthermore, several different melt–solid Interface Shapes were obtained by using different growth velocities, and then the thermal stresses for different solidification times were compared. The simulation results suggested that the crucible constraint should be reduced and a longer solidification time should be used for growing a silicon ingot with low thermal stress and low dislocation density.
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numerical analysis of influence of crucible Shape on Interface Shape in a unidirectional solidification process
Journal of Crystal Growth, 2008Co-Authors: Hiroaki Miyazawa, Lijun Liu, Koichi KakimotoAbstract:Abstract We carried out calculations to investigate the melt–crystal (m–c) Interface Shape with cylindrical and square crucibles and the influence of crucible Shape on m–c Interface Shape using two-dimensional and three-dimensional global analyses. It was found that maximum deformation of the m–c Interface occurs near the corner of the square crucible because outgoing heat flux, which has a significant influence on the m–c Interface Shape, has three-dimensionality. It was also found that Shape and dimensions of the crucible have significant influence on the amount of outgoing heat flux. The results indicate that we should control not only heater power, growth ratio and melt flow but also Shape and dimensions of crucibles in order to reduce deformation of the m–c Interface.
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numerical analysis of the influence of tilt of crucibles on Interface Shape and fields of temperature and velocity in the unidirectional solidification process
Journal of Crystal Growth, 2008Co-Authors: Hiroaki Miyazawa, Lijun Liu, Sho Hisamatsu, Koichi KakimotoAbstract:Abstract We carried out calculations to investigate the influence of tilt of crucibles on the melt–crystal Interface Shape and fields of temperature and velocity of the melt and/or crystal by three-dimensional global and melt–crystal analyses. It was found that flow velocity was larger in the case of a fixed boundary condition of edge of the Interface than that in the case of a relaxed condition. Furthermore, deflection of the Interface with a fixed boundary condition was smaller than that without the fixed boundary condition. These results indicate that we should use three-dimensional global analysis with a relaxed boundary condition to investigate the influence of tilt of crucibles on the Interface Shape and flow velocity.
Yunbo Zhong - One of the best experts on this subject based on the ideXlab platform.
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thermoelectric magnetohydrodynamic flows and their induced change of solid liquid Interface Shape in static magnetic field assisted directional solidification
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2016Co-Authors: Yves Fautrelle, Jiang Wang, Guillaume Reinhart, Henri Nguyenthi, Hanlin Liao, Yunbo ZhongAbstract:Applying static magnetic field can produce flows (thermoelectric magnetohydrodynamic flows, TEMHDF) in the melt by interacting with the thermoelectric currents (TEC) during solidification of metals. A physical model was proposed to interpret how these TEC appear at the solid–liquid Interface and verified by a corresponding simulation. The influences of TEMHDF on solidification were investigated through both ex-situ experiments and n situ observations by means of synchrotron X-ray radiography. The 3D numerical simulations of TEMHDF were performed for these two cases, respectively, and suggested that both the change of Interface Shape with different transverse static magnetic fields demonstrated by the ex-situ experiments and the real time observed Interface Shape varying under a 0.08 T transverse static magnetic field could attribute to the TEMHDF advanced solid–liquid Interface in the static magnetic field-assisted directional solidification. The TEMHDF produced by an axial static magnetic field were also computed along with the Interface change predicted based on which is good in line with the published experimental results. This study of TEMHDF and their impacts on the solid–liquid Interface Shape provides a method to tailor the structure during directional solidification using static magnetic field.
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modification of liquid solid Interface Shape in directionally solidifying al cu alloys by a transverse magnetic field
Journal of Materials Science, 2013Co-Authors: Jiang Wang, Yves Fautrelle, Henri Nguyenthi, Zhongming Ren, Nathalie Mangelincknoel, Georges Salloum Abou Jaoude, Yunbo ZhongAbstract:Al-0.85wt%Cu and Al-2.5wt%Cu alloys were directionally solidified under different transverse magnetic field (TMF) intensities to investigate the influence of TMF on the liquid/solid Interface Shape with respect to the various length scales appearing (planar, cellular, and dendritic Interfaces). Results show that planar and cellular Interfaces tilt to one side and then level off with increasing TMF although the dendritic Interface appears not to behave in this manner. In situ synchrotron X-ray imaging was applied during directional solidification of the Al-4wt%Cu alloy under a 0.08T TMF, revealing leveling of the initially sloped Interface. Solute redistribution, caused by thermoelectric magnetic convection (TEMC), responds to the changes in the Interface Shape. Because different typical length scales should be used in estimating the velocity of TEMC for planar, cellular, and dendritic Interfaces, the maximum velocity of the convection ahead of the Interface is obtained under different TMF intensities; correspondingly, leveling of the Interface’s degree of slop varies with TMF.
Zhongming Ren - One of the best experts on this subject based on the ideXlab platform.
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modification of liquid solid Interface Shape in directionally solidifying al cu alloys by a transverse magnetic field
Journal of Materials Science, 2013Co-Authors: Jiang Wang, Yves Fautrelle, Henri Nguyenthi, Zhongming Ren, Nathalie Mangelincknoel, Georges Salloum Abou Jaoude, Yunbo ZhongAbstract:Al-0.85wt%Cu and Al-2.5wt%Cu alloys were directionally solidified under different transverse magnetic field (TMF) intensities to investigate the influence of TMF on the liquid/solid Interface Shape with respect to the various length scales appearing (planar, cellular, and dendritic Interfaces). Results show that planar and cellular Interfaces tilt to one side and then level off with increasing TMF although the dendritic Interface appears not to behave in this manner. In situ synchrotron X-ray imaging was applied during directional solidification of the Al-4wt%Cu alloy under a 0.08T TMF, revealing leveling of the initially sloped Interface. Solute redistribution, caused by thermoelectric magnetic convection (TEMC), responds to the changes in the Interface Shape. Because different typical length scales should be used in estimating the velocity of TEMC for planar, cellular, and dendritic Interfaces, the maximum velocity of the convection ahead of the Interface is obtained under different TMF intensities; correspondingly, leveling of the Interface’s degree of slop varies with TMF.
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Effects of Thermoelectric Magnetic Convection on the Solidification Structure During Directional Solidification under Lower Transverse Magnetic Field
Metallurgical and Materials Transactions A, 2011Co-Authors: Zhongming Ren, Annie Gagnoud, Olga Budebkova, Yves FautrelleAbstract:This work investigated the thermoelectric magnetic convection (TEMC) during directional solidification under a transverse magnetic field numerically and experimentally. Numerical results show that the TEMC will form in liquid near the liquid/solid Interface and in the dendritic network. The value of the TEMC mainly depends on the crucible diameter, the temperature gradient, and the magnetic field intensity. The value of the TEMC increases as the crucible diameter and the temperature gradient are increased. The value of the TEMC on the sample scale increases to a maximum when the magnetic field is of the order of 0.1 T, and then decreases as the magnetic field still increases. However, the value of the TEMC on the cell/dendrite scale continues to increase with the increase of the magnetic field intensity when the applied magnetic field is less then 1 T. Two alloys are solidified directionally in the vertical configuration under a transverse magnetic field, and results show that the application of a lower transverse magnetic field (B < 1 T) modified the liquid/solid Interface Shape and the cellular/dendritic array significantly. Indeed, it was observed that, along with the refinement of the cell/dendrite, the magnetic field caused the deformation of the liquid/solid Interfaces and the extensive segregations (i.e., channel and freckle) in the mushy zone. Comparison of the numerical and experimental results shows that the modification amplitude of the liquid/solid Interface and the cellular/dendritic morphology is in good agreement with the value of the TEMC at the liquid/solid Interface and in the dendritic network. This implies that changes of the Interface Shape and the cellular/dendritic morphology should be attributed, respectively, to the TEMC on the sample and the cell/dendrite scales.
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investigation of thermoelectric magnetic convection and its effect on solidification structure during directional solidification under a low axial magnetic field
Acta Materialia, 2009Co-Authors: Annie Gagnoud, Yves Fautrelle, Zhongming Ren, Rene MoreauAbstract:Abstract Thermoelectric magnetic convection (TEMC) at the scale of both the sample (L = 3 mm) and the cell/dendrite (L = 100 μm) was numerically and experimentally examined during the directional solidification of Al–Cu alloy under an axial magnetic field ( B ⩽ 1 T ). Numerical results show that TEMC on the sample scale increases to a maximum when B is of the order of 0.1 T, and then decreases as B increases further. However, at the cellular/dendritic scale, TEMC continues to increase with increasing magnetic field intensity up to a field of 1 T. Experimental results show that application of the magnetic field caused changes in the macroscopic Interface Shape and the cellular/dendritic morphology (i.e. formation of a protruding Interface, decrease in the cellular spacing, and a cellular–dendritic transition). Changes in the macroscopic Interface Shape and the cellular/dendritic morphology under the magnetic field are in good agreement with the computed velocities of TEMC at the scales of the macroscopic Interface and cell/dendrite, respectively. This means that changes in the Interface Shape and the cellular morphology under a lower magnetic field should be attributed respectively to TEMC on the sample scale and the cell/dendrite scale. Further, by investigating the effect of TEMC on the cellular morphology, it has been proved experimentally that the convection will reduce the cellular spacing and cause a cellular–dendritic transition.