Numerical Simulation Of Sapphire Crystal Growth By The Kyropoulos Method

Recently, sapphire crystals had been widely used in a variety of modern high-techapplications as the combination of desirable optical properties, mechanical and electricalproperties and thermal properties.In this paper, using CGSim numerical simulation software to established a mathematicalphysical model of sapphire crystal growth process. Through the coupling calculation oftemperature field and velocity field during the crystal growth, the thermal field structureand the influent of the process parameters on the sapphire crystal growth process can beinvestigated to discuss the conditions of thermodynamics and kinetics and importanttechnical parameters that suitable for the large size sapphire crystal growth.This work changed the inner molybdenum thermal shields into tungsten shields. Theresults show that the heat preservation effect in the furnace becomes better and the axistemperature gradient of internal crystal and the crystal surface temperature gradientdecreased, which can decrease the stress of the crystal, then reduce the probability of theupper crystal craze. The input power becomes lower at the early growth stage afterimproved.Proposed an special crucible in this article. The results show that when the crucible shapeis round for the outer wall and inverted conical for the inner wall, the maximum velocityand the temperature gradient in the melt are the smallest and the convexity is the lowest.The inverted conical crucible may reduce the occurrence of remelting phenomena andreduce the decline rate of convexity at the last growth stage, which indicates that thiscrucible shape has advantages for the heat transfer during the sapphire crystal growthprocess and can get better growth behavior than cylindrical and round crucible.Simulated and analyzed the effect of different necking diameter on thermal field ofsapphire crystal by using of the CGSim software. It was found that the heat flux densitydecreased with the reduce of necking diameter, so were the axial and radial temperaturegradients of crystal at the necking-shouldering stage. All of these can decrease the thermalstress, dislocation and low-angle grain boundaries and improved the quality of the crystaleffectively. The actual products validated the simulation results of our experiments.