Investigation Of Simulation Analysis And Its Application For The Growth Of Large Size Sapphire With Sapmac Method

Sapphire crystal has excellent optical performance, thermal performance and chemical stability. It also has high strength, large hardness and can withstand erosion, etc. It is fit for working under severe conditions. So it is widely used in many fields of national defense and civilian industry.SAPMAC method can reduce the disturbance of temperature field and temperature gradient inside the crystal, anneal in in-situ location and make growing cycle short. But the problems that crystal diameter is hard to control, voids are easy to form inside the crystal and crystal can crack easily need to be resolved. Jobs in several aspects are developed in this thesis.Principles SAPMAC, reasons for the introduction of sapphire crystal defect and its controlling measure were researched from two aspects of theory and experiment. Results showed that under the condition of keeping H/DC <1, controlling the melt flow regime and the formation of cooled center can be achieved by regulating TI, TAd, and TRd. The key controlling factor of crystal growth is to regulate the transportation process of heat in the crystal growth system which can be achieved by increasing the heat dissipation and lowering heat supply of system. There are defects such as dislocations, mosaic structures, color centers, inclusions and cracks in the sapphire crystal with SAPMAC method. The reasons for the introduction of them were two factors that were material conditions and technological conditions. Material conditions showed mainly at the aspect of the precision of crystal growth equipments, harmful impurity and the quality of seed crystal. Technological conditions showed mainly at the aspect of the distribution of temperature field, the shape and stability of solid-liquid interface, growth rate and cooling rate.Mathematical physical model which reflect crystal growth with SAPMAC method was established. FEM was applied to solve the model. Temperature distribution, temperature gradient and convexity ratio of solid-liquid interface were taken as evaluating indicator to predict the effect of technological parameter to crystal growth and carry out design of temperature field of crystal growth and process. Results showed that growth velocity decreased gradually and temperature gradient in crystal/melt and the convexity ratio of solid-liquid interface increased followed by the increase of heat dissipation ability of the thermal exchanger. Crystal growth velocity increased gradually followed by the decrease of heating temperature. When heating temperature was closer to crystallization temperature, rate of change of crystal growth velocity was more drastic, temperature gradient and the convexity ratio of solid-liquid interface decreased. Appropriate axial and radial additional temperature gradient attached by the crystal growth thermal system could provide bigger regulating space for crystal growth velocity. According to the specific design of the temperature field, crystal seeding and Shoulder-expanding stages were controlled by regulating heat dissipation ability of the thermal exchanger and Iso-diameter and Tailing process stages were controlled by lowered heating temperature. Crystal growth process was controlled by stages.Anion coordination polyhedron growth unit theory mode was used to discuss the crystal habit of sapphire crystal. The selecting principle of crystalline growth direction was researched from crystal habit, lattice structure and crystal brittleness of sapphire crystal. Results showed that the growth velocity of every surface of sapphire crystal with melt method the relationship of V_{0001}{11-23}{01-12}{11-20}{01-10}. That a[11-20] or r[01-12] was chosen for the growth direction was feasible for the sapphire crystal with SAPMAC method.According to the characteristics of crystal growth process with SAPMAC method, thermodynamics performance of crystal material and the influence of its anisotropy to the quality of crystal growth were researched. Results showed that smaller thermal conductivity can reduce the temperature gradient and interface convexity ratio effectively when solid phase and liquid phase has the same conductivities and bigger thermal conductivity is convenient to improving crystal growth velocity. When solid phase and liquid phase has different conductivities, bigger thermal conductivity of solid phase is convenient to lower the temperature gradient inside the crystal and smaller thermal conductivity of liquid phase is convenient to increasing the temperature gradient inside the melt. When the thermal conductivity of the crystal is anisotropic, bigger axial conductivity and smaller radial conductivity are convenient to improving crystal growth velocity and keeping growth interface stable while bigger radial conductivity is convenient to keeping the subconvex growth interface. Thermal stress is in direct proportion to coefficient of thermal expansion in the crystal and increases followed by the increase of the coefficient of thermal expansion. The influence of radial coefficient of thermal expansion is more remarkable for the anisotropic crystalline material.According to the characteristics of crystal growth process with SAPMAC method, size effect of crystal growth process and distribution of temperature field was researched. Results showed that crystal growth was harder to control when the crystal diameter is bigger and the quality of the crystal was hard to be guaranteed. To grow the crystal with bigger diameter, selection of processes, confirmation of parameters and control precision and stability of equipments need develop further. Design of the temperature field should regulate in the direction of increasing axial additional temperature gradient and reducing radial additional temperature gradient.The modified design of the temperature field and optimized process engineering were applied to conduct the experiment of crystal growth. The experiment showed that the diameter of the sapphire crystal was 220²40mm, the weight of it is 26.5²8.5kg, its structure was integral without any obvious defect and its infrared transmission spectrum was well. Results of the experiment validated the theories and simulation results which were presented in the thesis.