阅读说明：本技术 一种大截面溴化钾晶体的生长方法 (Growth method of large-section potassium bromide crystal ) 是由 李永涛 张学建 郭立 刘卉昇 王红宇 刘明坤 张小伟 盖亮宇 刘景和 于 2020-03-18 设计创作，主要内容包括：本发明提出的一种大截面溴化钾晶体的生长方法,属于碱金属卤化物型光学晶体生长工艺领域,该生长方法是采用提拉法在大气环境下生长大截面溴化钾晶体的方法,包括籽晶的制备、块料压制、石英坩埚底部温度补偿和提拉法生长晶体步骤。该方法可以获得直径300mm以上的大截面高质量的溴化钾晶体毛坯。所获得的晶体测试表明：该溴化钾晶体在红外波段具有低于3％的吸收,溴化钾是典型的碱金属卤化物离子晶体,透过波段宽0.3μm～34μm,透过率高95％,广泛应用于激光器窗口材料。(The invention provides a growth method of a large-section potassium bromide crystal, belonging to the field of alkali metal halide type optical crystal growth process. The method can obtain the potassium bromide crystal blank with large section and high quality and the diameter of more than 300 mm. The crystal test obtained shows that: the potassium bromide crystal has absorption lower than 3% in an infrared band, is a typical alkali metal halide ion crystal, has a transmission band width of 0.3-34 mu m and a transmittance of 95%, and is widely applied to laser window materials.)

1. A method for growing large-section potassium bromide crystals is characterized by comprising the following steps:

step one, seed crystal preparation: taking a crystal blank cut along a potassium bromide cleavage plane as a seed crystal, wherein the seed crystal is in the shape of a cone, the diameter of the seed crystal is 50-55 mm, the height of the seed crystal is 50-60 mm, and the cleavage plane is a <100> crystal plane;

step two, pressing block materials: powder potassium bromide with the purity of 99.90 percent is used as an initial raw material, the raw material is purified and dried, the raw material is pressed into a block material sheet, and the block material sheet is sintered for 24 hours at the temperature of 300 ℃ to obtain a block;

thirdly, placing the seed crystal obtained in the first step into a seed crystal groove at the bottom end of a seed crystal rod, fixing the seed crystal in a seed crystal chuck, placing the material block obtained in the second step into a quartz crucible with a constant temperature field heater arranged at the bottom, wherein the constant temperature field heater at the bottom of the quartz crucible is 10cm away from the bottom of the quartz crucible, covering a quartz plate above the pulling furnace after adjusting the concentricity of the temperature field at the bottom of the quartz crucible, the pulling furnace and the seed crystal rod, setting a temperature-raising program, raising the temperature from the room temperature of 30 ℃ to 750 ℃ at the temperature-raising rate of 5 ℃/h, and keeping the temperature for 2 h;

and step four, growing the single crystal by adopting a Czochralski method process to obtain the large-section potassium bromide crystal with the diameter of more than 300 mm.

2. The method for growing the large-section potassium bromide crystal according to claim 1, wherein the Czochralski process comprises the following steps:

(1) putting the pressed and molded lump material into a quartz crucible, then putting the quartz crucible filled with the lump material into a pulling furnace, adjusting the concentricity of a temperature field at the bottom of the quartz crucible, the pulling furnace and a seed rod, then covering a quartz plate above the pulling furnace, setting a temperature-rising program, rising the temperature from the room temperature of 30 ℃ to 750 ℃ at a temperature-rising rate of 5 ℃/h, and keeping the temperature for 2 h;

(2) starting the pulling furnace to enable a heating system in a hearth of the pulling furnace to work, keeping the temperature for 2 hours after the temperature reaches 750 ℃, slowly dropping seed crystals when lump materials in a quartz crucible are completely melted and a melt liquid flow line is clear and stable, and performing a necking process after the seed crystals are contacted with the surface of the melt to reduce the diameter of the seed crystals by 8-10 mm;

(3) adjusting the temperature, starting crystal growth, wherein the seed crystal direction is <100>, and the crystal growth process comprises the following steps:

① shouldering, wherein the temperature reduction rate is 1 ℃/h, the pulling rate is 0.6 mm/h-0.8 mm/h, the crystal rotation rate is 8 r/min-10 r/min, the shouldering angle is controlled at 35-45 degrees, and the temperature is kept for 3h when the size of the shouldered part of the crystal is consistent with the target size;

② growing in equal diameter, wherein the temperature reduction rate, the pulling rate and the rotating speed are kept unchanged in the equal diameter growing process, the temperature reduction rate is 0.5 ℃/h, the pulling rate is 0.8 mm/h-1.2 mm/h, and the rotating speed is 6 r/min-8 r/min;

③ ending, namely, entering an ending stage when the crystal grows to a certain length, wherein the ending and shouldering processes are just opposite, adjusting the temperature reduction procedure to be a temperature rise procedure, adjusting the temperature rise rate to be 5 ℃/h, continuing for 2h, and finally reducing the pulling speed and the rotating speed to be 0 to finish the crystal growth;

④ and cooling and annealing to obtain the large-section potassium bromide crystal with the diameter of more than 300 mm.

3. The method for growing a large-section potassium bromide crystal according to claim 1 or 2, wherein: the block has a diameter of 380mm and a thickness of 5 mm.

4. The method for growing a large-section potassium bromide crystal according to claim 1 or 2, wherein: the quartz crucible is of an integrated structure consisting of a crucible wall part and a crucible bottom part, the crucible wall part is of a cylindrical barrel shape, the diameter is 400mm, the height is 150mm, the crucible bottom part is of a segment shape, and the height is 50 mm.

5. The method for growing a large-section potassium bromide crystal according to claim 1 or 2, wherein: the hearth of the lifting furnace is cylindrical, the diameter of the hearth is 500mm, the height of the hearth is 800mm, and the thickness of the hearth is 20 mm.

6. The method for growing a large-section potassium bromide crystal according to claim 2, wherein: in the Czochralski process: the melt is overheated and kept for more than 2 hours, and then the pulling growth process is carried out.

7. The method for growing the large-section potassium bromide crystal according to claim 2, wherein the temperature-reducing annealing in step ④ is carried out by keeping the temperature at 680 ℃ for 72 hours and then reducing the temperature to room temperature at a rate of less than 30 ℃ per hour.

Technical Field

The invention relates to a growth method of a large-section crystal, in particular to a growth method of a large-section potassium bromide crystal, belonging to the technical field of growth of alkali metal halide type optical crystals.

Background

The alkali metal halide crystal is a special material due to its excellent comprehensive properties, and has wide and important application in laser and infrared photoelectronic technology. At present, crystal technologists internationally have conducted a great deal of scientific research work on the research and application of alkali metal halide melt quasicrystal kinetic theory, solid lattice kinetic theory, crystal growth thermodynamics and kinetics, and the like.

The development of optoelectronic materials has stimulated interest in alkali metal halide, especially potassium bromide crystals, as optical materials, which has led to the development of alkali halide crystals for materials such as neutron monochromators, infrared prisms, infrared transmitters, laser windows, optical storage, etc. At present, a potassium bromide crystal infrared window material is widely applied to optical components which can transmit ultraviolet rays, visible light and infrared rays, an infrared window is arranged on electrical shells such as a high-voltage switch cabinet, a metal armored cabinet and an urban ring main unit, and a thermal infrared imager can realize infrared thermal imagery in the cabinet body through the infrared window, so that the purpose of live detection is realized. The high-quality infrared window of the infrared thermal imager helps the safety production of large enterprises for manufacturing power generation, power supply, electricity and power equipment, and greatly saves the production cost of the enterprises. In addition, the method has wide application in nuclear reactors, molten salt batteries, chemical preparation, energy storage, fast ion solid electrolyte ceramics and the like, and the important application greatly promotes the research of alkali metal halide crystals.

Disclosure of Invention

The invention aims to provide a method for growing a large-section potassium bromide crystal, which can obtain a large-section high-quality potassium bromide single crystal blank with the diameter of more than 300mm and ensure that the absorptivity of the potassium bromide single crystal blank in an infrared band is lower than 3%.

In order to achieve the purpose, the invention adopts the following technical scheme: a method for growing large-section potassium bromide crystals is characterized by comprising the following steps:

step one, seed crystal preparation: taking a crystal blank cut along a potassium bromide cleavage plane as a seed crystal, wherein the seed crystal is in the shape of a cone, the diameter of the seed crystal is 50-55 mm, the height of the seed crystal is 50-60 mm, and the cleavage plane is a <100> crystal plane;

step two, pressing block materials: powder potassium bromide with the purity of 99.90 percent is used as an initial raw material, the raw material is purified and dried, the raw material is pressed into a block material sheet, and the block material sheet is sintered for 24 hours at the temperature of 300 ℃ to obtain a block;

thirdly, placing the seed crystal obtained in the first step into a seed crystal groove at the bottom end of a seed crystal rod, fixing the seed crystal in a seed crystal chuck, placing the material block obtained in the second step into a quartz crucible with a constant temperature field heater arranged at the bottom, wherein the constant temperature field heater at the bottom of the quartz crucible is 10cm away from the bottom of the quartz crucible, covering a quartz plate above the pulling furnace after adjusting the concentricity of the temperature field at the bottom of the quartz crucible, the pulling furnace and the seed crystal rod, setting a temperature-raising program, raising the temperature from the room temperature of 30 ℃ to 750 ℃ at the temperature-raising rate of 5 ℃/h, and keeping the temperature for 2 h;

and step four, growing the single crystal by adopting a Czochralski method process to obtain the large-section potassium bromide crystal with the diameter of more than 300 mm.

Further, the Czochralski process comprises the following steps:

(1) putting the pressed and molded lump material into a quartz crucible, then putting the quartz crucible filled with the lump material into a pulling furnace, adjusting the concentricity of a temperature field at the bottom of the quartz crucible, the pulling furnace and a seed rod, then covering a quartz plate above the pulling furnace, setting a temperature-rising program, rising the temperature from the room temperature of 30 ℃ to 750 ℃ at a temperature-rising rate of 5 ℃/h, and keeping the temperature for 2 h;

(2) starting the pulling furnace to enable a heating system in a hearth of the pulling furnace to work, keeping the temperature for 2 hours after the temperature reaches 750 ℃, slowly dropping seed crystals when lump materials in a quartz crucible are completely melted and a melt liquid flow line is clear and stable, and performing a necking process after the seed crystals are contacted with the surface of the melt to reduce the diameter of the seed crystals by 8-10 mm;

(3) adjusting the temperature, starting crystal growth, wherein the seed crystal direction is <100>, and the crystal growth process comprises the following steps:

① shouldering, wherein the temperature reduction rate is 1 ℃/h, the pulling rate is 0.6 mm/h-0.8 mm/h, the crystal rotation rate is 8 r/min-10 r/min, the shouldering angle is controlled at 35-45 degrees, and the temperature is kept for 3h when the size of the shouldered part of the crystal is consistent with the target size;

② growing in equal diameter, wherein the temperature reduction rate, the pulling rate and the rotating speed are kept unchanged in the equal diameter growing process, the temperature reduction rate is 0.5 ℃/h, the pulling rate is 0.8 mm/h-1.2 mm/h, and the rotating speed is 6 r/min-8 r/min;

③ ending, namely, entering an ending stage when the crystal grows to a certain length, wherein the ending and shouldering processes are just opposite, adjusting the temperature reduction procedure to be a temperature rise procedure, adjusting the temperature rise rate to be 5 ℃/h, continuing for 2h, and finally reducing the pulling speed and the rotating speed to be 0 to finish the crystal growth;

④ and cooling and annealing to obtain the large-section potassium bromide crystal with the diameter of more than 300 mm.

Preferably, the block has a diameter of 380mm and a thickness of 5 mm.

Preferably, the quartz crucible is an integrated structure consisting of a crucible wall and a crucible bottom, the crucible wall is cylindrical and cylindrical, the diameter of the crucible wall is 400mm, the height of the crucible wall is 150mm, and the crucible bottom is in a segment shape and the height of the crucible bottom is 50 mm.

Preferably, the hearth of the pulling furnace is cylindrical, the diameter of the hearth is 500mm, the height of the hearth is 800mm, and the thickness of the hearth is 20 mm.

Preferably, in the czochralski process: the melt is overheated and kept for more than 2 hours, and then the pulling growth process is carried out.

Preferably, the temperature-reducing annealing process in step ④ is performed by keeping the temperature at 680 ℃ for 72 hours and then reducing the temperature to room temperature at a rate of less than 30 ℃ per hour.

Through the design scheme, the invention can bring the following beneficial effects: the large-section potassium bromide crystal prepared by the growth method of the large-section potassium bromide crystal provided by the invention is measured, the size reaches 300mm in diameter and 100mm in thickness, the crystal is cut into crystal pieces, after optical polishing, the infrared spectrum performance of the crystal is tested at room temperature, and an infrared spectrometer is adopted to test the infrared spectrum, so that the crystal has no obvious absorption peak in an infrared band and the absorption rate is lower than 3%.

Detailed Description

In order to more clearly illustrate the invention, the invention is further described below in connection with preferred embodiments. As will be appreciated by those skilled in the art. The following detailed description is illustrative rather than limiting in nature and is not intended to limit the scope of the invention. Well-known methods and procedures have not been described in detail so as not to obscure the present invention.