The Optimization Analysis Of The Internal Structure Of The Kyropoulos Sapphire Single Crystal Furnace

In recent years,artificially-grown sapphire is becoming more and more popularized.Kyropoulos method is one of the most widely-used important methods.This paper uses numerical simulation software to carry out simulation analysis on the growth of sapphire by adoption of Kyropoulos method and respectively changes the inside diameter and position of heater and the material&shape of thermal insulation screen so as to analyze the impact of its change on temperature field and provide theoretical guidance for the optimization of the internal structure of monocrystal furnace body.The stages for crystal growth and temperature field are simulated.The simulation results show that:the crystal temperature presents the distribution characteristics of being lower in the upper part&higher in the lower part and being lower in the center&higher in the margin;the internal temperature variation of crystal is relatively smooth and the temperature gradient is smaller while the gradient of crystal edge temperature is larger;and the isotherm in crystal shows the shape of convex interface.It alters the inside diameter and position of the heater to analysis their effects on temperature field.The simulation results show that:with the increase of the inside diameter D of the heater,the radial temperature in crystal will firstly rise and then drop and the temperature gradient as well as the amount of deformation on solid-liquid interface will increase but it will produce no obvious effect on axial temperature;and when the heater moves in the axial direction,with the increase of the height of the heater L,the overall temperature in crystal will rise as a whole(more obvious in radial direction)and the axial temperature gradient and radial temperature gradient will both decrease.Based on the above-mentioned theoretical analysis,in the actual production,the inner diameter of the heater should be appropriately increased and the actual height of the heater should be properly reduced.The influence of adoption of thermal insulation screen in different materials and different shapes is analyzed.Three kinds of common thermal insulation screen materials including tungsten&molybdenum,graphite and zirconia are selected to compare their advantages and disadvantages in aspects like thermal insulation performance,influence on crystal temperature and impact on the solid-liquid interface of crystal;the effects of thermal insulation screen on the temperature distribution in the furnace and the amount of deformation of solid-liquid interface in two kinds of common shapes including layered shape and block shape are compared.The simulation results show that:zirconia has the best heat preservation performance while graphite has the worst heat preservation performance;the crystal temperature distribution by selecting tungsten&molybdenum thermal insulation screen and zirconia thermal insulation screen is relatively close to each other and their temperature is greater than that of graphite thermal insulation screen;and in the process of starting with the diameter increase of the pulling of single crystal and realizing the equal diameter,the corresponding solid-liquid interface of zirconia material is the most gentle and the solid-liquid interface of graphite has the largest amount of deformation.At the time of using block-shape thermal insulation screen,the overall crystal temperature is higher than that when using layered-shape thermal insulation screen.The amount of deformation of solid-liquid interface when using block-shape thermal insulation screen is relatively gentle.Based on the above-mentioned theoretical analysis,in the actual production,it is more recommended that the thermal insulation screen in zirconia material shall be adopted and the block-shape thermal insulation screen shall be used in the circumstance the actual conditions permit.