A method for melting a quartz crucible with ultra-low micro-bubbles

Abstract

The application discloses a melting method of an ultralow micro-bubble quartz crucible, which comprises the following steps: obtaining spherical synthetic quartz sand with a preset particle size range; stacking the quartz sand into a gradient accumulation structure with gradually decreasing particle size from the bottom layer to the inner surface, and fixing the quartz sand through centrifugal force and electrostatic adsorption; starting an electrode arc; entering a low-speed heating stage to remove adsorbed gas; entering a transparent layer melting stage, using the power provided by the first power surge to provide energy impact, so that the fine particles on the inner surface are rapidly melted and spread to form a uniform liquid film; entering a high-temperature maintaining stage, using the power provided by the second power surge to promote the interface fusion of quartz particles; entering a continuous heat preservation stage, and suddenly reducing the power to make the melt begin to cool down under controlled conditions; stopping melting and protecting the gas flow, demolding, cooling to room temperature, and obtaining the ultralow micro-bubble quartz crucible. The method can effectively inhibit the density of micro-bubbles in the micro-transparent layer, improve the purity, density and smoothness of the inner surface of the crucible, and make the crucible have higher crystal yield.

Description

Technical Field

[0001] This invention belongs to the field of quartz crucible manufacturing technology, and in particular relates to a melting method for an ultra-low microbubble quartz crucible. Background Technology

[0002] Quartz crucibles, as crucial auxiliary materials in crystal pulling, directly impact the performance and yield of subsequent products, making them indispensable equipment in the photovoltaic and semiconductor industries. During crystal pulling, the quartz crucible serves as the key container holding the high-temperature silicon molten metal, and its quality is a decisive factor affecting the success rate and purity of crystal growth. The crucible must remain in continuous high-temperature environments exceeding 1400°C for extended periods, requiring prolonged contact with the highly reactive silicon molten metal; therefore, extremely high requirements are placed on its purity, temperature resistance, and structural stability.

[0003] In existing technologies, quartz crucibles are typically made from high-purity natural quartz sand using an electric arc melting process. Centrifugal force is used to spread the quartz sand evenly within a mold, and a vacuum is applied to form a crucible blank. This blank is then melted by a high-temperature electric arc generated by a graphite electrode. After cooling, a crucible with a double-layered composite structure is formed. This structure usually consists of an outer, opaque bubble layer and an inner, transparent layer. The outer bubble layer helps to uniformly conduct heat, providing a stable thermal field for the molten silicon, while the inner transparent layer is in direct contact with the molten silicon. Its density and purity are crucial for ensuring the stability of the crystal growth interface.

[0004] However, existing quartz crucible preparation technologies still face many problems, among which the bubble problem is a core aspect affecting the quality of single-crystal silicon growth. During crystal pulling, if microbubbles exist in the transparent layer of the crucible, as the crucible continues to contact the molten silicon, the microbubbles in the transparent layer closer to the molten silicon will gradually expand, rupture, and release gas and quartz particles into the silicon melt. This not only disrupts the thermal convection state of the melt but may also cause dislocations or microdefects in the growing crystal, and in severe cases, even cause crystal edge breakage, resulting in economic losses.

[0005] The formation of microbubbles in the transparent layer mainly involves two aspects: raw materials and processes. The limitations of the purity and physical properties of quartz sand raw materials are as follows: ① The purification process of natural quartz sand is complex. Its impurities are divided into inclusion impurities and lattice impurities. Among them, impurities existing in the SiO2 lattice are difficult to completely remove by ordinary purification processes. After a series of impurity removal methods, the content of impurity elements is relatively fixed. If further purification is required, it is expensive and the effect is minimal. ② Existing quartz sand (whether natural or synthetic) is uneven in terms of particle size, morphology (both are flaky structures), and particle size distribution, resulting in low bulk density. It is easy to form voids during the crucible forming stage. These voids are difficult to remove during the subsequent melting process, eventually forming micron-sized bubbles. ③ The residual trace metal impurities in natural quartz sand will also exacerbate the formation of bubbles under high temperature volatilization. In the existing crucible forming and melting process, if synthetic quartz sand is used, the melting point of synthetic quartz sand is higher than that of natural quartz sand. Therefore, using the existing curing process parameters will result in uneven heating, which may form voids inside the quartz sand or cause inconsistent melting of raw materials. This will lead to an increase in bubbles in the transparent layer of the crucible, ultimately leaving bubble defects in the finished product and reducing the yield of the crucible. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a melting method for ultra-low microbubble quartz crucibles, which can effectively suppress the density of microbubbles in the microtransparent layer, improve the purity, density, and smoothness of the crucible's inner surface, and produce high-quality quartz crucibles with higher crystal yield per unit volume.

[0007] The present invention provides a method for melting an ultra-low microbubble quartz crucible, comprising:

[0008] Obtain spherical synthetic quartz sand with a preset particle size range;

[0009] The spherical synthetic quartz sand is stacked into a gradient stacking structure with the particle size gradually decreasing from the bottom layer to the inner surface, and fixed by centrifugal force and electrostatic adsorption of the mold rotation;

[0010] Electrode arc initiation is performed during the first preset period;

[0011] In the second preset period, a low-speed heating stage is entered to remove adsorbed gases;

[0012] In the third preset period, the transparent layer melting stage begins. The first surge in power provides an energy impact, causing the fine particles on the inner surface to melt and spread rapidly, forming a uniform liquid film.

[0013] In the fourth preset period, the high temperature holding stage is entered, and the second surge in power is used to promote the fusion of the quartz particle interface.

[0014] In the fifth preset period, the continuous heat preservation stage is entered, the power drops sharply, and the melt begins to cool under controlled conditions to release thermal stress;

[0015] Once the preset charge is reached, melting and protective gas flow are stopped, the material is demolded, and cooled to room temperature to obtain an ultra-low microbubble quartz crucible.

[0016] Preferably, in the above-mentioned melting method for ultra-low microbubble quartz crucibles, the preset particle size range of the spherical synthetic quartz sand is 50 micrometers to 200 micrometers, the raw material purity is 5N, and the spheroidization rate of the quartz sand is ≥95%.

[0017] Preferably, in the above-mentioned melting method for ultra-low microbubble quartz crucibles, the gradient stacking structure includes large particles with a diameter of 150 to 200 micrometers at the bottom layer, transitional particles with a diameter of 100 to 150 micrometers in the middle layer, and fine particles with a diameter of 50 to 100 micrometers on the inner surface, and each layer of different types of synthetic quartz sand is leveled with a molding rod after being added.

[0018] Preferably, in the above-mentioned melting method for ultra-low microbubble quartz crucibles, the graphite electrode column in the melting system is made of isostatically pressed high-purity graphite with a diameter of 60μm to 80μm and an ash content of <10ppm. The melting power supply is an IGBT frequency converter with a maximum output power of 4000kW to 5000kW.

[0019] Preferably, in the above-mentioned melting method for ultra-low microbubble quartz crucibles, the step of initiating electrode arcing during the first preset period includes:

[0020] During the first 100 kWh period, the electrode spacing was increased from 5 mm to 10 mm, the electrode power was increased from 0 to 1000 kW, and the height of the electrodes and water plate was kept constant while vacuuming was performed.

[0021] Preferably, in the above-mentioned melting method for ultra-low microbubble quartz crucibles, the step of entering a low-speed heating stage during the second preset period to remove adsorbed gases includes:

[0022] Between 100 and 300 degrees Celsius, the power gradually increases from 1000 kW to 1500 kW, with a heating rate of 1 kW / s. The electrode spacing is reduced from 10 mm to 3 mm to concentrate the arc energy and uniformly preheat the inner surface of the crucible. The electrodes remain in place, and the water plate is raised from 100 mm away from the mold to 250 mm away from the mold and maintained thereafter to achieve cooling and protection of the outer layer of the crucible. The power is maintained at 1500 kW for 10 to 15 minutes, while vacuuming continues.

[0023] Preferably, in the above-mentioned melting method for ultra-low microbubble quartz crucibles, the step of entering the transparent layer melting stage in the third preset period, using a first surge of power to provide an energy impact, causing the fine particles on the inner surface to rapidly melt and spread, forming a uniform liquid film, includes:

[0024] Between 300 and 450 kWh, the power surged from 1500 kW to 1700 kW. The opening and position of the electrodes, as well as the position of the water plate, remained unchanged. Vacuuming continued to efficiently extract the dissolved gas and tiny bubbles from the quartz melt.

[0025] Preferably, in the above-mentioned melting method for ultra-low microbubble quartz crucibles, the step of entering a high-temperature holding stage in the fourth preset period and using a second surge in power to promote the fusion of quartz particle interfaces includes:

[0026] Between 450 and 550 kWh, the power surges from 1700 kW to 2700 kW, vacuuming stops, the electrode spacing increases from 3 mm to 7 mm, and the electrode position decreases from 250 mm to -50 mm from the top of the mold to ensure the bottom quartz sand is completely melted. The height of the water plate decreases from 250 mm to 150 mm to enhance cooling of the bottom of the mold. This process is maintained for 2 to 5 minutes.

[0027] Preferably, in the above-mentioned melting method for ultra-low microbubble quartz crucibles, the step of entering a continuous holding stage in the fifth preset period, allowing the power to drop sharply, and causing the melt to begin cooling under controlled conditions to release thermal stress includes:

[0028] Between 500 kWh and 700 kWh, the power drops sharply from 2700 kW to 1600 kW, the electrode spacing increases from 7 mm to 8 mm, the electrode position increases from -50 mm to 60 mm from the top of the mold, the height of the water plate decreases from 150 mm to 0 mm, the holding time is 6 to 10 minutes, and argon gas is introduced for protection at a flow rate of 0.3 L / min to 0.7 L / min.

[0029] Preferably, in the above-mentioned melting method for ultra-low microbubble quartz crucibles, after the preset charge is reached, melting and protective gas flow are stopped, the melting carriage is removed from the melting furnace for demolding, and cooled to room temperature.

[0030] As described above, the melting method for the ultra-low microbubble quartz crucible provided by the present invention includes: obtaining spherical synthetic quartz sand with a preset particle size range; stacking the spherical synthetic quartz sand into a gradient stacking structure with particle size gradually decreasing from the bottom layer to the inner surface, and fixing it by centrifugal force and electrostatic adsorption of mold rotation; performing electrode arc initiation in a first preset period; entering a low-speed heating stage in a second preset period to remove adsorbed gases; entering a transparent layer melting stage in a third preset period, using a first surge in power to provide energy impact, causing the fine particles on the inner surface to melt rapidly and spread, forming a uniform liquid film; entering a high-temperature holding stage in a fourth preset period, using a second surge in power to promote the fusion of quartz particle interfaces; and entering a continuous heat preservation stage in a fifth preset period, allowing the power to drop sharply. The melt is cooled under controlled conditions to release thermal stress. After reaching the preset charge, melting and protective gas flow are stopped, the material is demolded, and cooled to room temperature to obtain an ultra-low microbubble quartz crucible. It can be seen that using this type of spherical synthetic quartz sand can reduce the filling porosity, which can reduce gas encapsulation and thus effectively reduce the density of microbubbles in the transparent layer of the crucible. Moreover, it has a larger specific surface area, which can promote heat conduction. Quartz sand has high contact thermal conductivity, uniform heating, and better melting consistency. It can form a thin, dense, high-strength, and smooth transparent layer. Furthermore, different melting stages are adjusted for this type of quartz sand to ensure the stability and controllability of the melting process, thereby improving the purity, density, and smoothness of the inner surface of the crucible and producing high-quality quartz crucibles with higher crystal yield. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of an embodiment of a melting method for an ultra-low microbubble quartz crucible provided by the present invention;

[0033] Figure 2 This is a schematic diagram of the melting system used in this application. Detailed Implementation

[0034] The core of this invention is to provide a melting method for ultra-low microbubble quartz crucibles, which can effectively suppress the density of microbubbles in the microtransparent layer, improve the purity, density and smoothness of the inner surface of the crucible, and produce high-quality quartz crucibles with higher crystal yield. The quartz crucibles produced can be applied to the fields of photovoltaic and semiconductor materials.

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] An embodiment of the melting method for an ultra-low microbubble quartz crucible provided by the present invention is as follows: Figure 1 As shown, Figure 1 This is a schematic diagram of an embodiment of a melting method for an ultra-low microbubble quartz crucible provided by the present invention. The method may include the following steps:

[0037] S1: Obtain spherical synthetic quartz sand with a preset particle size range;

[0038] It should be noted that this embodiment uses spherical synthetic quartz sand instead of the irregularly shaped natural quartz sand used in the prior art. Natural quartz sand is mainly characterized by an irregular, flaky structure. When irregularly shaped quartz sand particles accumulate, they interlock and connect with each other, forming an arched structure that prevents the upper particles from falling further and filling the gaps, thus leaving a large number of voids in the overall material layer. This embodiment uses spherical synthetic quartz sand, which reduces the porosity of the quartz sand filling. In a specific example, the preset shape of this spherical synthetic quartz sand... The particle size range can be from 50 micrometers to 200 micrometers, the raw material purity is 5N, and the spheroidization rate of quartz sand is ≥95%. Such a spherical shape can achieve a more compact filling, greatly reducing porosity, thereby reducing gas encapsulation and ultimately reducing the number of microbubbles in the transparent layer of the crucible. Moreover, it has a larger specific surface area, which can promote heat conduction, resulting in higher contact heat conduction efficiency, more uniform heating, and better melting consistency. It can form a thin, dense, high-strength, and smooth transparent layer, thereby improving the purity of the crucible and the yield of crystals in subsequent crystal pulling.

[0039] S2: Spherical synthetic quartz sand is stacked into a gradient stacking structure with particle size gradually decreasing from the bottom layer to the inner surface, and fixed by centrifugal force and electrostatic adsorption of mold rotation;

[0040] It should be noted that this step uses a raw material processing system, in which the spherical synthetic quartz sand adopts a gradient stacking structure. This gradient stacking structure can include large particles with a diameter of 150 to 200 micrometers at the bottom, transitional particles with a diameter of 100 to 150 micrometers in the middle layer, and fine particles with a diameter of 50 to 100 micrometers on the inner surface. After each layer of different types of synthetic quartz sand is applied, it is leveled with a forming rod. Each layer of quartz sand is fixed by the centrifugal force of the rotating mold and electrostatic adsorption. Since the quartz sand is all spherical, the quartz sand particles can be tightly pushed together (porosity <30%), reducing gas encapsulation. At the same time, the larger specific surface area can promote heat conduction. Quartz sand has high contact thermal conductivity, uniform heating, and better melting consistency, which can form a thin, dense, high-strength, smooth, and transparent layer.

[0041] S3: Electrode arc initiation is performed during the first preset period;

[0042] It should be noted that this example uses a 37-inch crucible for melting, but the actual process is not limited to this size. From this step onwards, a melting system and a process control system are required. (Refer to...) Figure 2 , Figure 2This is a schematic diagram of the melting system used in this application. The melting system consists of a double-layer water-cooled copper mold 1, a liftable graphite electrode column 2, and a liftable water plate 3. The diagram also shows the distance A between the electrode column and the upper end of the mold, and the distance B between the water plate and the mold. The total lifting stroke of the graphite electrode column is between -300mm and 300mm, and the stroke of the liftable water plate is between -100mm and 300mm. The graphite electrode column in this melting system can be isostatically pressed high-purity graphite with a diameter of 60μm to 80μm and an ash content <10ppm. The melting power supply uses an IGBT frequency converter with a maximum output power of 4000kW to 5000kW. Its advantage is that it can achieve rapid and precise power regulation through power electronics technology. The process control system can integrate a PLC module, which can accurately adjust the height of the electrode and water plate (accuracy ±0.1mm) and the melting power (adjustment rate 10kW / s) in real time. Because synthetic quartz sand has a higher melting point than natural quartz sand, the electrode height, opening, melting time, and melting power must be adjusted accordingly during the melting process to ensure the stability and controllability of the high-purity material. Specifically, the melting control system records the electricity consumption. During crucible melting, electricity consumption is generally used as the basis for determining whether to proceed to the next stage of the melting process. The first preset period involves increasing the electrode spacing from 5 mm to 10 mm and raising the electrode power from 0 to 1000 kW for approximately 5 minutes during the first 100 kWh of electricity. In the initial melting stage, increasing the electrode spacing reduces the current surge at the moment of arc initiation, minimizing quartz particle splashing caused by excessive local energy. Furthermore, maintaining the electrode and water plate heights while performing vacuum extraction removes residual air from the three-layer gradient structure before the quartz sand softens, laying the foundation for the subsequent densification process.

[0043] S4: In the second preset period, enter the low-speed heating stage to remove adsorbed gas;

[0044] It should be noted that this step may specifically include: between 100°C and 300°C, taking advantage of the high melting point and strong gas adsorption of synthetic quartz sand, a low-speed heating is adopted to give the adsorbed gas and air between particles sufficient time to escape, avoiding premature melting and sealing of the surface due to excessive heating. At this time, the power is gradually increased from 1000kW to 1500kW, the heating rate is 1kW / s, and the electrode spacing is reduced from 10mm to 3mm to concentrate the arc energy and uniformly preheat the inner surface of the crucible. The electrodes are kept in place, and the water plate is raised from 100mm away from the mold to 250mm away from the mold and maintained to achieve cooling and protection of the outer layer of the crucible, i.e., the bubble layer. The power is maintained at 1500kW for 10 to 15 minutes, preferably 10 minutes, while continuing to maintain vacuum.

[0045] S5: In the third preset period, the transparent layer melting stage is entered. The first surge in power provides an energy impact, causing the fine particles on the inner surface to melt and spread rapidly, forming a uniform liquid film.

[0046] Specifically, this step may include: increasing the power from 1500kW to 1700kW between 300°C and 450°C. It should be noted that the melting point of synthetic quartz sand is higher than that of natural sand, so it is necessary to quickly cross the melting energy threshold. The power surge provides sufficient energy impact to rapidly melt and spread the spherical fine particles (50-100μm) on the inner surface to form a uniform liquid film. The opening and position of the electrodes and the position of the water plate remain unchanged. Continue to maintain vacuum to efficiently extract the dissolved gas and microbubbles in the quartz melt. This step lasts for approximately 5 minutes in total.

[0047] S6: In the fourth preset period, the high temperature holding stage is entered, and the second surge in power is used to promote the fusion of the quartz particle interface.

[0048] Specifically, this step may include: increasing the power from 1700kW to 2700kW between 450°C and 550°C to provide sufficient energy to fully fuse the interfaces between the three-layer gradient structures. The tight packing of spherical synthetic quartz sand is transformed into a boundless monolithic structure at this stage, eliminating interlayer bonding lines. Vacuuming is stopped to prevent excessive volatilization of the quartz sand melt at extreme temperatures. The electrode spacing is increased from 3mm to 7mm, and the electrode position is reduced from 250mm from the top of the mold to -50mm to ensure that heat can be transferred to the bottom of the crucible, allowing the bottom quartz sand to melt completely and preventing the bottom raw material or transparent layer from being too thin. The height of the water plate is reduced from 250mm to 150mm to enhance cooling of the bottom of the mold. The holding time is 2 to 5 minutes.

[0049] S7: In the fifth preset period, enter the continuous heat preservation stage, so that the power drops sharply, and the melt begins to cool under controlled conditions to release thermal stress;

[0050] Specifically, this step may include: reducing the power from 2700kW to 1600kW between 500°C and 700°C to allow the melt to begin cooling under controlled conditions, releasing the thermal stress generated by the rapid expansion at high temperatures, and preventing microcracks from appearing after the crucible cools; increasing the electrode spacing from 7mm to 8mm and increasing the electrode position from -50mm to 60mm from the top of the mold to prevent premature cooling and shrinkage at the top, ensuring the roundness and dimensional accuracy of the crucible opening; reducing the height of the water plate from 150mm to 0mm to allow the entire crucible to cool uniformly for 6 to 10 minutes, preferably 6 minutes; and simultaneously introducing an argon protective gas flow at a rate of 0.3L / min to 0.7L / min, preferably 0.5L / min, to prevent air backflow contamination and to remove any remaining residual bubbles, further improving the purity of the inner surface.

[0051] S8: After reaching the preset charge, stop melting and protective gas flow, demold, and cool to room temperature to obtain an ultra-low microbubble quartz crucible.

[0052] In a specific example, once the preset charge is reached, melting and protective gas flow are stopped, the melting carriage is removed from the melting furnace for demolding, and cooled to room temperature, thus obtaining an ultra-low microbubble quartz crucible, which is then subjected to subsequent related processing.

[0053] As described above, the embodiment of the melting method for the ultra-low microbubble quartz crucible provided by the present invention includes: obtaining spherical synthetic quartz sand with a preset particle size range; stacking the spherical synthetic quartz sand into a gradient stacking structure with particle size gradually decreasing from the bottom layer to the inner surface, and fixing it by centrifugal force and electrostatic adsorption of mold rotation; performing electrode arc initiation in a first preset period; entering a low-speed heating stage in a second preset period to remove adsorbed gas; entering a transparent layer melting stage in a third preset period, using the first surge in power to provide energy impact, causing the fine particles on the inner surface to melt rapidly and spread, forming a uniform liquid film; entering a high-temperature holding stage in a fourth preset period, using the second surge in power to promote the fusion of quartz particle interfaces; and entering a continuous heat preservation stage in a fifth preset period, allowing the power to... The sudden drop in temperature causes the melt to begin cooling under controlled conditions, releasing thermal stress. Once the preset charge is reached, melting and protective gas flow are stopped, the melt is demolded, and cooled to room temperature to obtain an ultra-low microbubble quartz crucible. It is evident that using this type of spherical synthetic quartz sand can reduce the filling porosity, which reduces gas encapsulation and effectively reduces the density of microbubbles in the transparent layer of the crucible. Moreover, it has a larger specific surface area, which promotes heat conduction. Quartz sand has high contact thermal conductivity, uniform heating, and better melting consistency, forming a thin, dense, high-strength, and smooth transparent layer. Furthermore, adjustments have been made for this type of quartz sand at different melting stages to ensure stability and controllability during the melting process, thereby improving the purity, density, and smoothness of the inner surface of the crucible and producing high-quality quartz crucibles with higher crystal yield.

[0054] In the above-mentioned scheme of this application, spherical synthetic quartz sand is used as the sole raw material to replace traditional flaky natural quartz sand. The purity of the spherical sand reaches 5N grade (99.999%), the spheroidization rate is ≥95%, and the particle size distribution is within the range of 50-200μm. Leveraging the advantages of the thermal deposition and thermal conductivity of spherical synthetic quartz, gas encapsulation is reduced from the source, and the uniformity of heating is significantly improved. While the mold is rotating, a gradient sand-laying process is used, laying spherical synthetic quartz sand layer by layer according to the particle size order. After each layer is laid, a forming rod is used to smooth the surface. Large particles provide structural strength, fine particles ensure a dense and smooth inner wall, and transitional particles eliminate interlayer interfaces, achieving a smooth transition from the skeleton to the surface. After the sand is applied, the mold carriage enters the melting furnace, employing a five-stage dynamic melting process specifically designed for synthetic quartz sand. The precise implementation of these five stages relies on the hardware of the melting system. The melting power supply uses an IGBT frequency converter with a maximum power of 4000kW and a power adjustment rate of 10kW / s to meet the dynamic requirements of rapid rises and falls. The electrode material is high-purity graphite electrodes formed by isostatic pressing, with an ash content of <10ppm and a diameter of 80mm, ensuring structural stability and extremely low impurities at high temperatures. The control system uses an integrated PLC module to perform real-time closed-loop control of electrode lifting (total stroke ±300mm) and water plate lifting (stroke -100~300mm), achieving a control accuracy of ±0.1mm. After reaching the designated power level (700 kWh), the melting system and protective airflow are shut off, and the mold carriage automatically exits the melting furnace. After natural cooling to room temperature, it is demolded and further processed to obtain a high-quality quartz crucible with a dense and smooth inner wall, a low number of microbubbles in the transparent layer, and high single-crystal yield.

[0055] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for melting an ultra-low microbubble quartz crucible, characterized in that, include: Obtain spherical synthetic quartz sand with a preset particle size range; The spherical synthetic quartz sand is stacked into a gradient stacking structure with the particle size gradually decreasing from the bottom layer to the inner surface, and fixed by centrifugal force and electrostatic adsorption of the mold rotation; Electrode arc initiation is performed during the first preset period; In the second preset period, a low-speed heating stage is entered to remove adsorbed gases; In the third preset period, the transparent layer melting stage begins. The first surge in power provides an energy impact, causing the fine particles on the inner surface to melt and spread rapidly, forming a uniform liquid film. In the fourth preset period, the high temperature holding stage is entered, and the second surge in power is used to promote the fusion of the quartz particle interface. In the fifth preset period, the continuous heat preservation stage is entered, the power drops sharply, and the melt begins to cool under controlled conditions to release thermal stress; Once the preset charge is reached, melting and protective gas flow are stopped, the material is demolded, and cooled to room temperature to obtain an ultra-low microbubble quartz crucible.

2. The melting method for the ultra-low microbubble quartz crucible according to claim 1, characterized in that, The preset particle size range of the spherical synthetic quartz sand is 50 micrometers to 200 micrometers, the raw material purity is 5N, and the spheroidization rate of the quartz sand is ≥95%.

3. The method for melting the ultra-low microbubble quartz crucible according to claim 2, characterized in that, The gradient stacking structure includes large particles with a diameter of 150 to 200 micrometers at the bottom layer, transitional particles with a diameter of 100 to 150 micrometers in the middle layer, and fine particles with a diameter of 50 to 100 micrometers on the inner surface. Each layer of different types of synthetic quartz sand is leveled with a molding rod after being added.

4. The method for melting the ultra-low microbubble quartz crucible according to claim 3, characterized in that, The graphite electrode columns used in the melting system are high-purity graphite formed by isostatic pressing, with a diameter of 60μm to 80μm and an ash content of <10ppm. The melting power supply adopts an IGBT frequency converter power supply with a maximum output power of 4000kW to 5000kW.

5. The method for melting the ultra-low microbubble quartz crucible according to claim 4, characterized in that, The process of initiating electrode arcing during the first preset period includes: During the first 100 kWh period, the electrode spacing was increased from 5 mm to 10 mm, the electrode power was increased from 0 to 1000 kW, and the height of the electrodes and water plate was kept constant while vacuuming was performed.

6. The method for melting the ultra-low microbubble quartz crucible according to claim 5, characterized in that, During the second preset period, the low-speed heating stage is entered to remove adsorbed gases, including: Between 100 and 300 degrees Celsius, the power gradually increases from 1000 kW to 1500 kW, with a heating rate of 1 kW / s. The electrode spacing is reduced from 10 mm to 3 mm to concentrate the arc energy and uniformly preheat the inner surface of the crucible. The electrodes remain in place, and the water plate is raised from 100 mm away from the mold to 250 mm away from the mold and maintained thereafter to achieve cooling and protection of the outer layer of the crucible. The power is maintained at 1500 kW for 10 to 15 minutes, while vacuuming continues.

7. The method for melting the ultra-low microbubble quartz crucible according to claim 6, characterized in that, In the third preset period, the transparent layer melting stage is entered. An energy impact is provided by a first surge in power, causing the fine particles on the inner surface to rapidly melt and spread, forming a uniform liquid film. This includes: Between 300 and 450 kWh, the power surged from 1500 kW to 1700 kW. The opening and position of the electrodes, as well as the position of the water plate, remained unchanged. Vacuuming continued to efficiently extract the dissolved gas and tiny bubbles from the quartz melt.

8. The method for melting the ultra-low microbubble quartz crucible according to claim 7, characterized in that, The process of entering a high-temperature holding phase during the fourth preset period, and utilizing a second surge in power to promote the fusion of quartz particle interfaces, includes: Between 450 and 550 kWh, the power surges from 1700 kW to 2700 kW, vacuuming stops, the electrode spacing increases from 3 mm to 7 mm, and the electrode position decreases from 250 mm to -50 mm from the top of the mold to ensure the bottom quartz sand is completely melted. The height of the water plate decreases from 250 mm to 150 mm to enhance cooling of the bottom of the mold. This process is maintained for 2 to 5 minutes.

9. The method for melting the ultra-low microbubble quartz crucible according to claim 8, characterized in that, In the fifth preset period, the continuous heat preservation stage is entered, causing a sudden drop in power, allowing the melt to begin cooling under controlled conditions and releasing thermal stress, including: Between 500 kWh and 700 kWh, the power drops sharply from 2700 kW to 1600 kW, the electrode spacing increases from 7 mm to 8 mm, the electrode position increases from -50 mm to 60 mm from the top of the mold, the height of the water plate decreases from 150 mm to 0 mm, the holding time is 6 to 10 minutes, and argon gas is introduced for protection at a flow rate of 0.3 L / min to 0.7 L / min.

10. The method for melting the ultra-low microbubble quartz crucible according to claim 9, characterized in that, Once the preset charge is reached, melting and protective gas flow are stopped, the melting trolley is removed from the melting furnace for demolding, and cooled to room temperature.

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