Unidirectional Solidification of Solar Grade Silicon and lmpurities and Themal Stress Control of the Cast

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It is known that the quality of the silicon ingot made by the casting method is greatly influenced by the residual stress which exists in the material after solidification. However, the correct measuring method for the residual stress and the evaluating method of the result has not been established enough. The object of this research is to examine the measurement of the residual stress and the relation between the generation situation and the casting process in detail by international cooperation. Silicon was continuously cast with a equipment device that was installed in the Institute of Industrial Science, The University of Tokyo. Samples were made with different casting conditions and the residual stress of these silicon ingots were measured by mean of the neutron diffraction in the Canadian National Atomic Energy Research Institute, Chalk River, Canada. Because of the larger size of the crystal grains in the continuous cast silicon ingots, the measurement of the amount of the strai … More n was difficult with the conventional technique. New measurement technique was developed on the Canadian side, in which isotropy was given with rotating the sample while the neutron diffraction was measuring and was applied to the silicon ingot The model for the estimation of the residual stress of the silicon after continuous cast was developed on The University of Tokyo side. With this model, based on the heat conduction equation and the heat of coagulation, the analysis was done with actual process condition as the boundary condition. This result was compared with the experimental result mentioned above and discussed. In addition, for the shortening the calculation time and further establishment of general calculation technique, new version of the analytical approximation method is developing When the new version is completed, it will be possible to apply it for the online process monitoring of the manufacturing of the silicon continuous cast ingot Furthermore, a larger scale equipment were completed, that was not only the scale improvement of the smaller electron-beam equipment, but a number of improvements were made. By the large scaled electron-beam dissolution equipment, which has two electron beams generators and a large size water-cooled copper hearth, the experiments of silicon refining was performed. The experimental result was success of making 30kg class large-scale silicon ingots Less