Thermal insulation structure with adjustable cold core for growth of sapphire single crystals by virtue of kyropoulos method

Abstract

The invention provides a thermal insulation structure with an adjustable cold core for growth of sapphire single crystals by virtue of a kyropoulos method. A metal sheet made from tungsten or molybdenum is taken as a heat shield, wherein the heat shield comprises a horizontal type heat shield and a vertical type heat shield, and a gap between the shields is supported by adopting molybdenum bars at vertical intervals; a space between a stainless steel drum and the vertical type heat shield is divided into an inner layer filling region and an outer layer filling region by virtue of molybdenum plates and cylinders at intervals, the inner layer filling region is filled with zirconium oxide (ZrO2) hollow bubble shells, the outer layer filling region is divided into multiple vertical cubicle structures by adopting vertical molybdenum plates at intervals, and multiple cubicles form a symmetry structure taking the axis of a cylinder as the center; according to a cold core offset direction of an upper furnace, ZrO2 bubble shells are filled in the cubicles at one side of the offset direction or molybdenum slats with the same width of the cubicles are inserted in the cubicles, and a thermal insulation effect of the side of the offset direction is enhanced, so that the cold core moves toward the reverse direction of the offset direction, the effect that the cold core is arranged at a central position of a crucible is guaranteed, radial uniform distribution of a thermal filed in a furnace is improved, and the effects of seeding conveniently, reducing thermal stress inside crystals and preventing the crystals from adhering onto a boiler can be achieved.

Description

technical field [0001] The invention provides a thermal insulation structure with adjustable radial temperature field in a crystal growth furnace, in particular to a sapphire (α-Al 2 o 3 single crystal) high temperature heat insulation structure. Background technique [0002] α-Al 2 o 3 Single crystal, also known as sapphire, is a simple coordination oxide crystal. Sapphire single crystal has excellent optical and mechanical properties, stable chemical properties, and is widely used in infrared military devices, satellite space technology, and high-intensity laser window materials; its unique lattice structure and good thermal stability make sapphire Single crystal has become an ideal substrate material for GaN light-emitting diodes. [0003] The melting temperature of sapphire crystal is about 2050°C. The Kyropoulos method is one of the most important sapphire growth methods at present. A large number of thermal insulation heat shields are needed in the sapphire crys...

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Problems solved by technology

[0004]However, general heat shield materials are easily deformed at high temperature, which will cause the entire radial temperature gradient to change, and the cold core position 17 to shift, such as As shown in Figure 3, the cold core refers to convective convergence after melting in the crystal raw material furnace The center is the cold spot of the radial temperature field in the furnace. Generally speaking, for a thermal insulation structure with a uniform radial temperature field distribution and a symmetrical center, the cold center position 17 should be at the exact center of the crucible 8

The deviation of the cooling center position from the axis will increase the difficulty of seeding and increase the internal thermal stress of the crystal 18. At the same time, it will cause the crystal to grow too fast on one side and stick to the pot, and even cause the crystal to crack. After the heat preservation thermal field structure is grown in 5-8 furnaces, the deformation of the thermal field will affect the distribution of the thermal field in the furnace and is no longer suitable for growing crystals. Therefore, we need to design a heat preservation thermal field structure that can compensate and adjust the radial temperature field

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