Crystalline ruby growth by the crucible lowering method

Abstract

This application discloses a crucible lowering method for ruby ​​crystal growth, comprising the following steps: weighing the raw material and calculating its melting point; placing the uniformly mixed raw material into a crucible containing a seed crystal; heating to melt the raw material; raising the crucible to a preset height; and lowering the crucible while simultaneously initiating a programmed cooling process. The programmed cooling process is as follows: Stage 1: rate 55℃ / h, decreasing the temperature by 600-650℃ from the raw material's melting point; Stage 2: rate 83℃ / h, decreasing the temperature by 330℃; Stage 3: rate 55℃ / h, decreasing the temperature by 350℃; Stage 4: rate 44℃ / h, decreasing the temperature by 160℃; Stage 5: rate 90℃ / h, maintaining the temperature at room temperature; and removing the crystal from the furnace 8 hours after the cooling stages end. This method produces ruby ​​crystal rods with a diameter of 70-100mm, resulting in a breakage rate of less than 5%, effectively reducing the breakage rate and improving the quality of the finished product.

Description

Technical Field

[0001] This application relates to the technical field of ruby ​​growth, and in particular to a crucible lowering method for growing ruby ​​crystals. Background Technology

[0002] Ruby is a gemstone variety of corundum (α-Al2O3) that exhibits its red color due to the substitution of Al3⁺ sites by trace amounts of Cr³⁺ ions. The artificial ruby ​​crystals obtained through growth can meet the needs of various fields such as jewelry, laser technology, precision instruments, and aerospace.

[0003] Existing growth methods include flame fusion, hydrothermal, Czochralski, crucible descent, and flux methods. The crucible descent method, also known as the Bridgman process, involves placing a crucible containing the raw material in a furnace with a temperature gradient. The crucible slowly descends through the molten zone, cooling and crystallizing first at the bottom, with the crystal growing gradually from bottom to top. The main drawbacks of this method are that the crystal is in direct contact with the crucible wall, making it susceptible to contamination by the crucible material. Furthermore, the difference in thermal expansion coefficients during cooling generates significant internal stress in the crystal rod, leading to a higher rate of crystal rod breakage in subsequent stages and affecting the product yield.

[0004] The information disclosed in the background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] This application addresses the aforementioned technical problem by providing a crucible lowering method for ruby ​​crystal growth. When the diameter of the ruby ​​crystal rod produced by this method is 70~100mm, the breakage rate is less than 5%, effectively reducing the breakage rate of the crystal rod and improving the quality of the finished product.

[0006] This application provides a crucible lowering method for ruby ​​crystal growth, including the following steps: After weighing the raw materials, calculate their melting point. Place the evenly mixed raw materials into a crucible containing seed crystals. Heat the materials to melt them, then raise the crucible to a preset height and lower it. Simultaneously, begin the programmed cooling process as the crucible descends. The cooling process is as follows: First stage: rate 55℃ / h, starting from the melting point of the raw material, the temperature drops by 600~650℃, and then the second stage begins; Second stage: Rate 83℃ / h, then decrease to 330℃ before proceeding to the third stage; Third stage: Rate 55℃ / h, then decrease to 350℃ before proceeding to the fourth stage; Fourth stage: Rate 44℃ / h, decrease 160℃ and then proceed to the fifth stage; Fifth stage: Rate 90℃ / h, maintain at room temperature after cooling, and remove from the furnace 8 hours after the cooling stage ends.

[0007] Preferably, the raw materials used are composed of high-purity alumina and chromium oxide.

[0008] Preferably, the amount of chromium oxide added is 0.3% of the mass of high-purity alumina.

[0009] Preferably, during the melting stage, after argon gas is introduced into the crystal furnace to form a protective atmosphere, the resulting gas pressure is -0.06 MPa.

[0010] Preferably, the melting stage includes: heating at 250℃ / h, and cyclically observing the changes in the polycrystalline alumina material inside the furnace through an observation window. When the corner of the material melts, the observation frequency is increased; when the material is half-melted, the heating rate is changed to 10℃ / h until the liquid material is completely melted and there are no solid material protrusions on the top surface of the liquid material; then the heating rate is changed to 5℃ / h to heat to above 2050℃ and held at that temperature for 8 hours.

[0011] Preferably, during the heat preservation stage, the temperature distribution inside the heating furnace is adjusted so that the surface temperature of the melt is 1% lower than the melting point of the raw material.

[0012] Preferably, the crucible lifting operation is performed during the heat preservation stage of melting the raw material.

[0013] Preferably, the crucible lifting operation involves raising the crucible to a calculated specified height using a lifting system, and then lowering it to cool it down after the holding time has been reached.

[0014] Preferably, the descent and cooling operation includes: the lifting system lowers the crucible by 200 mm at a rate of 100 mm / h, and after 2 hours, the scale is slowly lowered to 1600 mm at a rate of 12 mm / h. During the descent of the crucible scale, the heating rate is simultaneously changed to 2℃ / h, and this continues until the cooling stage ends.

[0015] The beneficial effects that this application can produce include: 1) Avoid internal stress accumulation and improve yield; This method effectively eliminates the internal stress accumulation formed inside the crystal rod during the cooling process by controlling the crucible descent rate and the cooling rate, while coordinating the cooling rate below 1000℃, thereby improving the product yield and reducing the proportion of crystal rod breakage or internal cracks.

[0016] 2) Control the contamination of the crystal rod by impurities on the crucible wall; This method effectively prevents the depth of material transfer from the crucible into the crystal rod by controlling the crucible descent rate and cooling rate, while keeping the melt temperature below 1% of the raw material's melting point during the melting and holding stage. Locally diffused material can be removed by subsequent grinding, thus preventing the diffusion of elements contained in the crucible into the crystal rod and causing the crystal rod to be scrapped. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to embodiments, but this does not limit the present invention in any way. Any modifications or improvements made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0018] Unless otherwise specified, all materials and instruments used in the following embodiments were obtained through commercial channels; and all detection methods used are existing methods unless otherwise specified. Example

[0019] 1. The raw materials used are: 0.3% chromium oxide by mass of high-purity alumina (Al2O3) are added to high-purity alumina (Al2O3). The theoretical melting point of the raw materials used is calculated. 2. After placing the seed crystal in the crucible, add the uniformly mixed raw material, then place the crucible into the furnace. When the furnace pressure reaches -0.06 MPa, increase the temperature at 250℃ / h, and continuously observe the changes in the polycrystalline alumina material inside the furnace through the observation window. When the material is partially melted, increase the observation frequency. When the material is partially melted, change the heating rate to 10℃ / h until the liquid material is completely melted and there are no solid material protrusions on the top surface of the liquid material. Then, change the heating rate to 5℃ / h and heat the material above its melting point, then hold the temperature for 8 hours to ensure complete melting.

[0020] 3. While maintaining the temperature, raise the crucible to the calculated specified height (total crucible height - 210mm = lifting height) using the lifting system. After the holding time is reached, lower the crucible to lower it for cooling. During the holding stage, adjust the temperature distribution inside the furnace to ensure that the surface temperature of the melt is 1% lower than the melting point of the raw material. This ensures stable crystal growth while preventing impurities inside the crucible from precipitating and dissolving into the crystal rod.

[0021] 4. The lifting system lowers the crucible by 200mm at a rate of 100mm / h. After 2 hours, the scale is slowly lowered to 1600mm at a rate of 12mm / h. During the lowering process of the crucible scale, the heating rate is changed to 2℃ / h and continues until the cooling stage ends.

[0022] As the crucible descends, the following cooling parameters are set: First stage: Rate 55℃ / h, the second stage begins after the temperature drops by 600~650℃ from the melting point of the raw material. Second stage: Rate 83℃ / h, then decrease to 330℃ before proceeding to the third stage; Third stage: Rate 55℃ / h, then decrease to 350℃ before proceeding to the fourth stage; Fourth stage: Rate 44℃ / h, decrease 160℃ and then proceed to the fifth stage; Fifth stage: Rate 90℃ / h, maintain at room temperature after cooling, and remove from the furnace 8 hours after the cooling stage ends.

[0023] The resulting ruby ​​crystal rods have a diameter of 70-100 mm. This temperature-controlled cooling method effectively reduces internal stress accumulation in the resulting crystal rods, increasing the yield. After adopting this method, the rate of crystal rod breakage and cracking is less than 5%, effectively increasing production output.

[0024] Method for detecting the depth of element doping on the surface of a crystal rod: Place the obtained crystal rod on a grinding machine to grind the outer wall. Each grinding depth is 0.5 mm. Collect the powder material obtained from each grinding. After a single sampling, clean the powder in the sampling area of ​​the grinding machine, and then perform further grinding.

[0025] The obtained samples were analyzed using laser ablation-inductively coupled plasma mass spectrometry (ICP-MS) to determine the content of impurity elements. When the content of an element was below 10 ppm, it was determined that the crystal sample at that depth was free of crucible material doping contamination. Common impurity elements included: molybdenum (Mo) in molybdenum (Mo) crucibles; tungsten (W) in tungsten (W) crucibles; carbon in graphite crucibles; and silicon in quartz crucibles.

[0026] The doping depth of the method provided in this application is only about 1 mm, which means that the method can effectively control the contamination caused by the diffusion of impurity elements from the inner wall of the crucible to the crystal rod in the descent method, reduce the thickness of the crystal rod that needs to be discarded due to cleaning the contamination layer, increase the yield, and reduce the scrap rate.

[0027] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A crucible lowering method for growing ruby ​​crystals, characterized in that, Includes the following steps: After weighing the raw materials, calculate their melting point. Place the evenly mixed raw materials into a crucible containing seed crystals. Heat the materials to melt them, then raise the crucible to a preset height and lower it. Simultaneously, begin the programmed cooling process as the crucible descends. The cooling process is as follows: First stage: rate 55℃ / h, starting from the melting point of the raw material, the temperature drops by 600~650℃, and then the second stage begins; Second stage: Rate 83℃ / h, then decrease to 330℃ before proceeding to the third stage; Third stage: Rate 55℃ / h, then decrease to 350℃ before proceeding to the fourth stage; Fourth stage: Rate 44℃ / h, decrease 160℃ and then proceed to the fifth stage; Fifth stage: Rate 90℃ / h, maintain at room temperature after cooling, and remove from the furnace 8 hours after the cooling stage ends.

2. The crucible lowering method for ruby ​​crystal growth according to claim 1, characterized in that, The raw materials used are composed of high-purity alumina and chromium oxide.

3. The crucible lowering method for ruby ​​crystal growth according to claim 2, characterized in that, The amount of chromium oxide added is 0.3% of the mass of high-purity alumina.

4. The crucible lowering method for ruby ​​crystal growth according to claim 1, characterized in that, During the melting stage, after argon gas is introduced into the crystal furnace to create a protective atmosphere, the resulting gas pressure is -0.06 MPa.

5. The crucible lowering method for ruby ​​crystal growth according to claim 1, characterized in that, The melting stage includes: heating at 250℃ / h, and continuously observing the changes in the polycrystalline alumina material inside the furnace through an observation window. When the corner of the material melts, the observation frequency is increased. When the material is half-melted, the heating rate is changed to 10℃ / h until the liquid material is completely melted and there are no solid material protrusions on the top surface of the liquid material. Then, the heating rate is changed to 5℃ / h to heat to above 2050℃ and held at that temperature for 8 hours.

6. The crucible lowering method for ruby ​​crystal growth according to claim 5, characterized in that, During the heat preservation stage, the temperature distribution inside the heating furnace is adjusted so that the surface temperature of the melt is 1% lower than the melting point of the raw material.

7. The crucible lowering method for ruby ​​crystal growth according to claim 5, characterized in that, The crucible is lifted during the heat preservation stage of melting raw materials.

8. The crucible lowering method for ruby ​​crystal growth according to claim 7, characterized in that, The crucible lifting operation involves raising the crucible to a calculated and specified height using a lifting system, and then lowering it to cool it down after the holding time has been reached.

9. The crucible lowering method for ruby ​​crystal growth according to claim 8, characterized in that, The descent and cooling operation includes: the lifting system lowers the crucible by 200 mm at a rate of 100 mm / h, and after 2 hours, the scale is slowly lowered to 1600 mm at a rate of 12 mm / h. During the descent of the crucible scale, the heating rate is simultaneously changed to 2℃ / h, and this continues until the cooling stage ends.