Quartz glass high-temperature melting vacuum die-casting welding purification method

Abstract

The invention relates to the technical field of quartz glass purification, in particular to a quartz glass high-temperature melting vacuum die-casting welding purification method. The method comprises the following steps: stacking multiple layers of quartz glass sheets or quartz glass blocks into an expected product form, exhausting air in a hearth of a high-temperature furnace and gaps of the quartz glass blocks by utilizing high vacuum of equipment, and respectively carrying out constant high temperature and high pressure at multiple temperatures of 1400 DEG C or above so as to obtain the high-temperature high-pressure quartz glass. The softened quartz glass is extruded for a long time by increasing the pressure step by step through the pressure head, and volatile impurities overflowing from the quartz glass sheet are pumped and discharged in a vacuum manner, so that the original multi-layer or multiple quartz glass blocks are fused into a single quartz glass product in an expected form; the purity and the density of the high-purity quartz glass can be further improved, and the application performance of the product is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of quartz glass purification, in particular to a quartz glass high-temperature melting vacuum die-casting welding purification method. Background Art

[0002] Quartz glass is an industrial glass composed of high-purity quartz with high-purity quartz sand as the basic raw material. Its silicon dioxide content is generally above 99.99%. The SiO2 content of quartz glass products used in high-tech fields such as semiconductors, high-end optics, aerospace, and military industry is generally above 99.999%.

[0003] For example, CN111393022B discloses a method for preparing high-purity, low-hydroxyl quartz glass raw material. The method uses high-purity quartz sand, fused quartz glass, or recycled quartz glass products as the initial raw material. After sanding, the raw material is subjected to a dehydroxylation treatment under a high-temperature, high-vacuum environment to produce high-purity, low-hydroxyl quartz glass raw material. The resulting quartz glass raw material sand powder exhibits high purity, high transparency, low hydroxyl content, and is bubble-free.

[0004] However, the high-purity quartz sand used as the raw material for quartz glass inevitably contains a certain amount of volatile impurities. During the production process, these volatile impurities can easily cause structural defects in the quartz glass due to the high viscosity of the quartz glass melt. Furthermore, while the production technology for quartz glass sheets with specifications under 400 mm and thicknesses under 15 mm is very mature, large-scale, high-purity quartz glass products require long, uniform deposition times (several days to weeks), which can easily lead to microstructural inhomogeneities due to temperature fluctuations. For example, the temperature gradient within the furnace must be maintained at ≤1°C / cm during the melting process, otherwise thermal stress cracks may occur. When the thickness exceeds 20 mm, the difference in cooling rates between molten layers increases, easily forming internal defects (such as bubbles or gas lines). This directly leads to the extreme difficulty of manufacturing large-scale, high-purity quartz glass products with specifications over 1000 mm and thicknesses over 30 mm. Summary of the Invention

[0005] The object of the present invention is to provide a method for purifying quartz glass by high-temperature melting, vacuum die-casting and welding, so as to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides a method for purifying quartz glass by high-temperature melting, vacuum die-casting, welding, and the like, comprising the following steps:

[0007] Step S1: After cleaning and drying, multiple small-sized quartz glass sheets or blocks are stacked vertically in the center of a high-temperature furnace. The stacked products have the same design size and shape as the target product. Graphite stoppers of matching specifications are then used to fix and position the stacked products.

[0008] Step S2: setting the temperature rise program of the high-temperature die-casting furnace to a target temperature range of 1400-1750°C and starting the segmented gradient temperature rise control;

[0009] The high-temperature die-casting furnace is equipped with a vacuum pump. During the heating process of the high-temperature die-casting furnace, the residual gas inside the furnace, the gas trapped in the gap between the quartz glass layers, and the volatile impurities generated by the thermal decomposition of the material are simultaneously extracted;

[0010] Step S3: installing the pressure head and setting the maximum pressure of the die-casting machine. After the temperature of the high-temperature die-casting furnace reaches the set target temperature, directly starting the die-casting machine in the high-temperature die-casting furnace to perform multiple high-temperature melt die-casting operations.

[0011] Step S4: After completing the high-temperature melt die-casting, change the set temperature of the high-temperature die-casting furnace to the annealing temperature, turn off the heating and naturally cool it to the annealing temperature, maintain it in the annealing temperature range for 6-12 hours, and naturally cool it to below 550°C. Open the furnace door and take out the target product.

[0012] As a further improvement of the present technical solution, in step S1, the small-sized quartz glass sheet or quartz glass block refers to a quartz glass block with a maximum dimension in any direction not exceeding 600 mm and a dimension in the thickness direction not exceeding 20 mm.

[0013] As a further improvement of the present technical solution, in step S1, the graphite limiter is a hollow cylindrical or hollow square column structure as a whole, and its main body is divided into two open and closed halves along the axial direction, and the closed state is fixed by a locking device. The outer wall of the cylinder is evenly distributed with fine air vents for air extraction, and the inner cavity surface is coated with a release coating to ensure that the product can be smoothly separated from the limiter after molding.

[0014] As a further improvement of the present technical solution, in step S2, the vacuum pump is one of a rotary vane mechanical vacuum pump, a Roots pump, an oil diffusion pump or a turbomolecular pump.

[0015] As a further improvement of the present technical solution, in step S2, the temperature control accuracy of the high-temperature die-casting furnace is ±10°C.

[0016] As a further improvement of this technical solution, in step S2, the working vacuum range of the vacuum pump is set to 10 -1 -10 -8 pa.

[0017] As a further improvement of the present technical solution, in step S3, the indenter is one of a square indenter, a circular indenter, an annular indenter, an outer circle inner square indenter, or an outer square inner circle indenter, with a diameter or side length of 300-1000 mm.

[0018] As a further improvement of the present technical solution, in step S3, the multiple high-temperature melt die-casting by the die-casting machine includes the following stages:

[0019] The first stage: Set the maximum working pressure of the die-casting machine to 1000-4000MPa. When the temperature of the high-temperature die-casting furnace reaches 1400-1500℃, start the die-casting machine. After the pressure rises to the set maximum value, maintain the constant temperature and pressure for 30-60 minutes, and then suspend the die-casting operation.

[0020] The second stage: Set the maximum working pressure of the die-casting machine to 2000-6000MPa. When the high-temperature die-casting furnace continues to heat up to 1500-1550℃, start the die-casting machine. After the pressure rises to the set maximum value, maintain the constant temperature and pressure for 60-120 minutes, and then suspend the die-casting operation.

[0021] The third stage: Set the maximum working pressure of the die-casting machine to 2500-8000MPa. When the high-temperature die-casting furnace continues to heat up to 1600-1650℃, start the die-casting machine. After the pressure rises to the set maximum value, maintain the constant temperature and pressure for 120-180 minutes, and then suspend the die-casting operation.

[0022] The fourth stage: Set the maximum working pressure of the die-casting machine to 3000-10000MPa, and start the die-casting machine when the high-temperature die-casting furnace continues to heat up to 1700-1750℃. After the pressure rises to the set maximum value, maintain the constant temperature and pressure state for 180-300 minutes, and then shut down the die-casting machine.

[0023] As a further improvement of the present technical solution, in step S4, the annealing temperature is 1100-1300°C.

[0024] In the present invention, multiple layers of quartz glass sheets or blocks are stacked into the desired product form. The air in the high-temperature furnace hearth and the gaps between the quartz glass blocks is removed using a high vacuum pump. The softened quartz glass is then pressed for a long time at temperatures above 1400 degrees Celsius, at constant high temperatures and high pressures, with a pressing head applying progressively higher pressures. Simultaneously, volatile impurities released from the quartz glass sheets are vacuum-expelled. This not only allows the original multiple layers or blocks of quartz glass to be fused into a single quartz glass product of the desired form, but also further improves the purity and density of the high-purity quartz glass.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] In this quartz glass high-temperature melting vacuum die-casting welding purification method, multiple small-sized high-purity quartz glass sheets or blocks are stacked in a specially designed high-temperature furnace to the size and shape of the desired target product. High vacuum is then used to exhaust air in the furnace and between the quartz sheets, as well as volatile impurities such as hydroxyl groups and microbubbles that escape from the quartz glass at high temperatures, thereby improving the purity and density of the high-purity quartz glass.

[0027] After reaching the softening temperature of the quartz glass, the softened quartz glass is squeezed for extended periods of time at temperatures exceeding 1400°C, maintained at both high and high pressures. Simultaneously, volatile impurities escaping from the quartz glass sheets are vacuum-extracted. This die-casting method not only allows multiple small-sized quartz glass sheets to be stacked together into larger products, but more importantly, it further increases the purity and density of the high-purity quartz glass, significantly improving the product's performance. This allows for the production of large-scale, high-quality, quality-controlled quartz glass devices using stable and reliable process equipment at a lower cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the overall structure of the present invention. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0030] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0031] Because the high-purity quartz sand used as the raw material for quartz glass inevitably contains a certain amount of volatile impurities, and during the production process, due to the high viscosity of the quartz glass melt, these volatile impurities can easily cause structural defects in the quartz glass. Currently, the production technology for quartz glass sheets with specifications below 400 mm and thicknesses below 15 mm is very mature, with costs more than ten times lower and more stable and controllable quality. However, large-scale, high-purity quartz glass products require long, uniform deposition times (several days to weeks), which can easily lead to microstructural inhomogeneities due to temperature fluctuations. For example, the temperature gradient within the furnace must be maintained at ≤1°C / cm during the melting process, otherwise thermal stress cracks will occur. When the thickness exceeds 20 mm, the difference in cooling rate between molten layers increases, which can easily form internal defects (such as bubbles or microcracks). This directly leads to the extremely high difficulty of manufacturing large-scale, high-purity quartz glass products with specifications exceeding 1000 mm and thicknesses exceeding 30 mm.

[0032] Therefore, see Figure 1 As shown, the purpose of the present invention is to provide a quartz glass high-temperature melting vacuum die-casting welding purification method, comprising the following steps:

[0033] Step S1: After cleaning and drying, multiple small-sized quartz glass sheets or blocks are stacked vertically in the center of a specially designed high-temperature furnace to form a product having the same design size and shape as the target product. The stacked products are then secured and positioned using graphite stoppers of matching specifications. Small-sized quartz glass sheets or blocks refer to quartz glass blocks with a maximum dimension of no more than 600 mm in any direction and a thickness dimension of no more than 20 mm.

[0034] The graphite limiter has an overall hollow cylindrical structure. Its main body is divided into two halves along the axial direction, and the closed state is fixed by a locking device. The outer wall of the cylinder is evenly distributed with fine air vents for air extraction, and the inner cavity surface is coated with a release coating to ensure that the product can be smoothly separated from the limiter after molding.

[0035] Step S2: Set the temperature rise program of the high-temperature die-casting furnace to the target temperature range of 1400-1750℃, and start the segmented gradient temperature rise control. In order to improve product quality and accurately control the furnace temperature and furnace temperature uniformity, the temperature control accuracy of the high-temperature die-casting furnace is required to be ±10℃.

[0036] The vacuum pump is connected to the system. The vacuum pump can be a rotary vane mechanical vacuum pump, a roots pump, an oil diffusion pump or a turbomolecular pump. The working vacuum range of the vacuum pump is set to 10 -1 -10 -8 pa, during the heating process of the high-temperature die-casting furnace, the residual gas inside the furnace, the gas trapped in the gap between the quartz glass layers, and the volatile impurities (including Si-O oligomers, Cl- compounds, etc.) generated by the thermal decomposition of the material are simultaneously removed;

[0037] Step S3: Install a pressing head (one of a square pressing head, a circular pressing head, an annular pressing head, an outer circle inner square pressing head, or an outer square inner circle pressing head with a pressing head diameter or side length of less than 1000 mm) and set the maximum pressure of the die-casting machine. After the furnace temperature of the high-temperature die-casting furnace reaches the set target temperature, directly start the die-casting machine in the high-temperature die-casting furnace to perform multiple high-temperature melt die-casting. The multiple high-temperature melt die-casting of the die-casting machine includes the following stages:

[0038] The first stage: Set the maximum working pressure of the die-casting machine to 1000-4000MPa. When the temperature of the high-temperature die-casting furnace reaches the set target temperature, that is, 1400-1500℃, start the die-casting machine. After the pressure rises to the set maximum value, maintain the constant temperature and pressure state for 30-60 minutes, and then suspend the die-casting operation;

[0039] The second stage: Set the maximum working pressure of the die-casting machine to 2000-6000MPa. When the high-temperature die-casting furnace continues to heat up to 1500-1550℃, start the die-casting machine. After the pressure rises to the set maximum value, maintain the constant temperature and pressure for 60-120 minutes, and then suspend the die-casting operation.

[0040] The third stage: Set the maximum working pressure of the die-casting machine to 2500-8000MPa. When the high-temperature die-casting furnace continues to heat up to 1600-1650℃, start the die-casting machine. After the pressure rises to the set maximum value, maintain the constant temperature and pressure for 120-180 minutes, and then suspend the die-casting operation.

[0041] The fourth stage: Set the maximum working pressure of the die-casting machine to 3000-10000MPa, start the die-casting machine when the high-temperature die-casting furnace continues to heat up to 1700-1750℃, maintain constant temperature and pressure for 180-300 minutes after the pressure rises to the set maximum value, and then turn off the die-casting machine.

[0042] Step S4: In order to improve the strength of the target product, after completing the high-temperature melt die-casting, it is necessary to naturally cool down to the annealing temperature and perform constant temperature annealing to release the stress of the quartz glass caused by die-casting welding. Therefore, after completing the high-temperature melt die-casting, the set furnace temperature of the high-temperature die-casting furnace is changed to the annealing temperature, the heating is turned off and the temperature is naturally cooled to the annealing temperature, maintained in the annealing temperature range for 6-12 hours, and naturally cooled to below 550°C. The furnace door is opened and the target product is taken out. It is worth noting that the annealing temperature is 1100-1300°C.

[0043] The following specific examples are used to further illustrate the quartz glass high-temperature melting vacuum die-casting welding purification method provided by the present invention.

[0044] Example 1

[0045] Step S1: Using 100 high-purity quartz glass discs with a diameter of 300 mm and a thickness of 5 mm as the substrate, the quartz glass discs were cleaned and dried, and then stacked vertically in the center of the high-temperature furnace to form a cylindrical building block with a diameter of 300 mm and a height of 500 mm. The periphery was fixed with graphite stoppers of appropriate size.

[0046] Step S2: Set the furnace temperature to 1400℃, start the high temperature die casting furnace to heat up, connect the rotary vane mechanical vacuum pump, and set the vacuum degree to 10 -1 During the heating process of the high-temperature furnace, vacuum extraction is used to exhaust the air in the furnace and the gaps between small-sized quartz pieces, as well as the volatile impurities that overflow from the quartz glass pieces at high temperatures.

[0047] Step S3: Install a circular indenter with a diameter of 300 mm. After the temperature of the high-temperature die-casting furnace reaches the set target temperature, directly start the die-casting machine in the high-temperature die-casting furnace to perform multiple high-temperature melt die-casting. The multiple high-temperature melt die-casting of the die-casting machine includes the following stages:

[0048] The first stage: Set the maximum pressure of the die-casting machine to 1000Mpa. After the furnace temperature reaches 1400℃, start the die-casting machine. After reaching the set pressure, keep the temperature and pressure constant for 30 minutes, and then suspend the die-casting operation.

[0049] The second stage: Set the furnace temperature to 1500°C, start the high-temperature die-casting furnace to increase the temperature, set the maximum pressure of the die-casting machine to 2000 MPa, and start the die-casting machine after the furnace temperature reaches 1500°C. After reaching the set pressure, maintain constant temperature and pressure for 60 minutes, and then suspend the die-casting operation.

[0050] Stage 3: Set the furnace temperature to 1600°C and start the high-temperature die-casting furnace to increase the temperature. Set the maximum pressure of the die-casting machine to 2500 MPa. After the furnace temperature reaches 1600°C, start the die-casting machine. After reaching the set pressure, maintain constant temperature and pressure for 120 minutes, and then suspend the die-casting operation.

[0051] Stage 4: Set the furnace temperature to 1700°C and start the high-temperature die-casting furnace to increase the temperature. Set the maximum pressure of the die-casting machine to 3000 MPa. After the furnace temperature reaches 1700°C, start the die-casting machine. After reaching the set pressure, maintain constant temperature and pressure for 240 minutes, then shut down the die-casting machine.

[0052] Step S4: Change the set furnace temperature to 1300°C, cool it down naturally to 1300°C, and keep the temperature constant for 6 hours; turn off the heating, cool it down naturally to below 550°C, then open the furnace door and take out the target product.

[0053] Comparative Example 1: Comparative example 1: The current mainstream process for manufacturing quartz glass cylinders of the same specifications with a diameter of 300 mm and a height of 500 mm in this industry is the oxyhydrogen flame fusion deposition method (commonly known as ingot beating). The main quality parameters of the high-quality second-grade quartz ingot (first-grade quartz ingot products are rarely seen) made by this process are listed in Table 1.

[0054] Table 1 Comparison of product parameters of secondary quartz ingot and Example 1

[0055]

[0056]

[0057] As can be seen from Table 1, the product of Example 1 is significantly superior in all major quality indicators compared to the secondary quartz ingots of the same specifications on the market. In particular, the hydroxyl content and the total amount of metallic impurities are significantly reduced, which improves the quality level by one grade.

[0058] Example 2

[0059] Step S1: Using 400 square high-purity quartz glass sheets with a side length of 300 mm and a thickness of 12 mm as the substrate, the quartz sheets were cleaned and dried, and then stacked vertically in the center of the high-temperature furnace hearth, with 4 sheets per layer, for a total of 100 layers, to form a square columnar block with a side length of 600 mm and a height of 1200 mm. The perimeter of the block was fixed with graphite stoppers of appropriate size.

[0060] Step S2: Set the furnace temperature to 1450℃, start the high temperature die casting furnace to heat up, connect the Roots pump, and set the vacuum degree to 10 -2 During the heating process of the high-temperature furnace, high vacuum is used to exhaust the air in the furnace and the gaps between small-sized quartz pieces, as well as the volatile impurities that overflow from the quartz glass pieces at high temperatures.

[0061] Step S3: Install a square indenter with a side length of 600 mm. After the temperature of the high-temperature die-casting furnace reaches the set target temperature, directly start the die-casting machine in the high-temperature die-casting furnace to perform multiple high-temperature melt die-casting. The multiple high-temperature melt die-casting of the die-casting machine includes the following stages:

[0062] Stage 1: Set the maximum pressure of the die-casting machine to 2000 MPa. After the furnace temperature reaches 1450°C, start the die-casting machine. After reaching the set pressure, maintain constant temperature and pressure for 60 minutes, then suspend the die-casting operation.

[0063] Phase 2: Set the furnace temperature to 1550°C, start the high-temperature die-casting furnace, and set the maximum pressure of the die-casting machine to 3000 MPa. After the furnace temperature reaches 1550°C, start the die-casting machine. After reaching the set pressure, maintain constant temperature and pressure for 120 minutes, and then suspend the die-casting operation.

[0064] Stage 3: Set the furnace temperature to 1650°C, start the high-temperature die-casting furnace, and set the maximum pressure of the die-casting machine to 4000 MPa. After the furnace temperature reaches 1650°C, start the die-casting machine. After reaching the set pressure, maintain constant temperature and pressure for 180 minutes, and then suspend the die-casting operation.

[0065] Stage 4: Set the furnace temperature to 1750°C, start the high-temperature die-casting furnace to heat up, set the maximum pressure of the die-casting machine to 5000 MPa, and start the die-casting machine after the furnace temperature reaches 1750°C. After reaching the set pressure, maintain constant temperature and pressure for 300 minutes, and then shut down the die-casting machine.

[0066] Step S4: Change the set furnace temperature to 1200°C, cool it down naturally to 1200°C, and keep the temperature constant for 12 hours; turn off the heating, cool it down naturally to below 550°C, then open the furnace door and take out the target product.

[0067] Comparative Example 2: The main quality parameters of the substrate used in this example, i.e., a square high-purity quartz glass sheet with a side length of 300 mm and a thickness of 12 mm, are listed in Table 2.

[0068] Table 2 Comparison of quartz glass sheet and product parameters of Example 2

[0069]

[0070] As shown in Table 2, the product of Example 2 has significantly improved major quality indicators compared to the quartz glass substrate before high-temperature die-casting. In particular, the hydroxyl content has significantly decreased, improving the quality by one grade.

[0071] Example 3

[0072] Step S1: Using 320 fan-shaped high-purity quartz glass sheets with an outer diameter of 700 mm, an inner diameter of 300 mm, and a thickness of 15 mm as a substrate, the quartz sheets are cleaned and dried. In the center of a high-temperature furnace, a single layer of four fan-shaped quartz glass sheets is formed into a quartz ring with an outer diameter of 700 mm and an inner diameter of 300 mm. 80 layers are stacked vertically to form a quartz tube with an outer diameter of 700 mm, an inner diameter of 300 mm, and a height of 1200 mm. A release-coated graphite column with a diameter of 299 mm and a height of 1195 mm is inserted into the inner hole of the quartz tube. The outer periphery of the quartz tube is secured with graphite stoppers of appropriate size.

[0073] Step S2: Set the furnace temperature to 1500℃, start the high temperature die casting furnace to heat up, connect the oil diffusion pump, and set the vacuum degree to 10 -5 During the heating process of the high-temperature furnace, high vacuum is used to exhaust the air in the furnace and the gaps between small-sized quartz pieces, as well as the volatile impurities that overflow from the quartz glass pieces at high temperatures.

[0074] Step S3: Install an annular indenter with an outer diameter of 700 mm and an inner diameter of 300 mm. After the temperature of the high-temperature die-casting furnace reaches the set target temperature, directly start the die-casting machine in the high-temperature die-casting furnace to perform multiple high-temperature melt die-casting. The multiple high-temperature melt die-casting of the die-casting machine includes the following stages:

[0075] Stage 1: Set the maximum pressure of the die-casting machine to 3000 MPa. After the furnace temperature reaches 1500°C, start the die-casting machine. After reaching the set pressure, maintain constant temperature and pressure for 60 minutes, and then suspend the die-casting operation.

[0076] Phase 2: Set the furnace temperature to 1550°C, start the high-temperature die-casting furnace, and set the maximum pressure of the die-casting machine to 5000 MPa. After the furnace temperature reaches 1550°C, start the die-casting machine. After reaching the set pressure, maintain constant temperature and pressure for 90 minutes, and then suspend the die-casting operation.

[0077] Stage 3: Set the furnace temperature to 1650°C, start the high-temperature die-casting furnace, and set the maximum pressure of the die-casting machine to 7000 MPa. After the furnace temperature reaches 1650°C, start the die-casting machine. After reaching the set pressure, maintain constant temperature and pressure for 120 minutes, and then suspend the die-casting operation.

[0078] Stage 4: Set the furnace temperature to 1700°C, start the high-temperature die-casting furnace to heat up, set the maximum pressure of the die-casting machine to 9000 MPa, and start the die-casting machine after the furnace temperature reaches 1700°C. After reaching the set pressure, maintain constant temperature and pressure for 180 minutes, and then shut down the die-casting machine.

[0079] Step S4: Change the set furnace temperature to 1260°C, cool it down naturally to 1260°C, and keep the temperature constant for 10 hours; turn off the heating, cool it down naturally to below 550°C, then open the furnace door and take out the target product.

[0080] Comparative Example 3: The main quality parameters of the substrate used in this example, i.e., a sector-shaped high-purity quartz glass sheet with an outer diameter of 700 mm, an inner diameter of 300 mm, and a thickness of 15 mm, are tabulated in Table 3.

[0081] Table 3 Comparison of quartz glass sheet and product parameters of Example 3

[0082]

[0083]

[0084] As shown in Table 3, the product of Example 3 has significantly improved major quality indicators compared to the quartz glass substrate before high-temperature die-casting. In particular, the hydroxyl content has significantly decreased, improving the quality by one grade.

[0085] Example 4

[0086] Step S1: Using 200 fan-shaped high-purity quartz glass sheets with an outer diameter of 800 mm, an inner hole side length of 400 mm, and a thickness of 20 mm as a substrate, the quartz sheets are cleaned and dried. In the center of a high-temperature furnace, a single layer of four fan-shaped quartz glass sheets is formed into a special-shaped quartz ring with an outer diameter of 800 mm and an inner hole side length of 400 mm. 50 layers are stacked vertically to form a quartz tube with an outer diameter of 800 mm, an inner hole side length of 400 mm, and a height of 1000 mm. A graphite square column coated with a release agent with a side length of 399 mm and a height of 990 mm is inserted into the inner hole of the quartz tube. The outer periphery of the quartz tube is secured with a hollow cylindrical graphite stopper with an inner hole diameter of 800 mm.

[0087] Step S2: Set the furnace temperature to 1500℃, start the high temperature die casting furnace to heat up, connect the turbo molecular pump, and set the vacuum degree to 10 -8 During the heating process of the high-temperature furnace, high vacuum is used to exhaust the air in the furnace and the gaps between small-sized quartz pieces, as well as the volatile impurities that overflow from the quartz glass pieces at high temperatures.

[0088] Step S3: Install a square die with an outer diameter of 800 mm and an inner hole length of 400 mm. After the temperature of the high-temperature die-casting furnace reaches the set target temperature, directly start the die-casting machine in the high-temperature die-casting furnace to perform multiple high-temperature melt die-casting. The multiple high-temperature melt die-casting of the die-casting machine includes the following stages:

[0089] Stage 1: Set the maximum pressure of the die-casting machine to 4000 MPa. After the furnace temperature reaches 1500°C, start the die-casting machine. After reaching the set pressure, maintain constant temperature and pressure for 60 minutes, and then suspend the die-casting operation.

[0090] The second stage: Set the furnace temperature to 1550℃, start the high-temperature die-casting furnace to heat up, set the maximum pressure of the die-casting machine to 6000Mpa, and start the die-casting machine after the furnace temperature reaches 1550℃. After reaching the set pressure, keep the temperature and pressure constant for 90 minutes, and then suspend the die-casting operation;

[0091] The third stage: Set the furnace temperature to 1650°C, start the high-temperature die-casting furnace to heat up, set the maximum pressure of the die-casting machine to 8000Mpa, and start the die-casting machine after the furnace temperature reaches 1650°C. After reaching the set pressure, maintain constant temperature and pressure for 120 minutes, and then suspend the die-casting operation;

[0092] Stage 4: Set the furnace temperature to 1700°C, start the high-temperature die-casting furnace to heat up, set the maximum pressure of the die-casting machine to 10,000 MPa, and start the die-casting machine after the furnace temperature reaches 1700°C. After reaching the set pressure, maintain constant temperature and pressure for 180 minutes, and then shut down the die-casting machine.

[0093] Step S4: Change the set furnace temperature to 1100°C, cool it down naturally to 1100°C, and keep the temperature constant for 10 hours; turn off the heating, cool it down naturally to below 550°C, then open the furnace door and take out the target product.

[0094] Comparative Example 4: The main quality parameters of the substrate used in this example, i.e., a sector-shaped high-purity quartz glass sheet with an outer diameter of 800 mm, an inner hole side length of 400 mm, and a thickness of 20 mm, are tabulated in Table 4.

[0095] Table 4 Comparison of product parameters of quartz glass sheet and Example 4

[0096]

[0097] As can be seen from Table 4, the product of this embodiment has significantly improved in all major quality indicators compared to the quartz glass substrate before high-temperature die-casting. In particular, the hydroxyl content has decreased by nearly three times, improving by two quality grades.

[0098] Additional notes:

[0099] 1. The density is determined by the "balance-cylinder method". Specifically, the mass of the quartz glass sheet is directly measured using an electronic balance. The quartz glass sheet is then immersed in water and the volume of the quartz glass sheet is indirectly obtained by displacing the volume of the water. The density of the quartz glass sheet can then be obtained (density = mass / volume).

[0100] 2. The transmittance is measured using the "spectral transmission method". Specifically, a quartz glass sheet is processed into a flat sheet sample with a specification of 10mm×10mm (thickness of 2mm), and then soaked in anhydrous ethanol for 10 minutes to remove organic pollutants; the surface is then wiped unidirectionally with a dust-free cloth to avoid scratches. After drying, it is placed in a dust-free environment for standby use. The spectrophotometer is turned on and preheated for 30 minutes to stabilize the light source. After baseline calibration (no sample is placed, the air background is scanned (or a reference white board is placed), and the baseline is recorded), the sample is fixed in the sample holder, ensuring that the light path is perpendicular to the incident surface. The wavelength range is set to 200-300nm, 400-700nm, and 700-2500nm. The instrument automatically measures the transmitted light intensity. The transmittance calculation formula is as follows:

[0101]

[0102] Where λ is the wavelength, T(λ) is the transmittance at the corresponding wavelength, I0 is the incident light intensity, and I is the light intensity after passing through the sample;

[0103] 3. The hydroxyl content is determined according to GB / T 12442-90 Test method for hydroxyl content in quartz glass. The absorption spectrum of quartz glass is measured by Fourier transform infrared spectrometer, and then the hydroxyl content is calculated. Specifically, the quartz glass sheet is cut and ground into 25mm × 12mm mirror polished sheet samples with a thickness difference of ≤ 0.05mm. The sample is ultrasonically cleaned with anhydrous ethanol and dried to avoid contamination. A Fourier transform infrared spectrometer (such as Nicolet 6700 or FTIR-650) is used with a resolution of 4cm. -1 , the number of scans was 32, and the wavenumber range was 400–4000 cm -1 Then, turn on the machine and preheat for 30 minutes. Scan the air background or reference white plate to obtain the baseline spectrum. Place the sample vertically in the light path and set the scan to obtain the absorption spectrum. Position it at 3663cm -1 The sample is then flipped over and rescanned, and the average value is taken twice to reduce the error. The calculation formula is as follows:

[0104]

[0105] Where C is the hydroxyl content (ppm), d is the sample thickness, is the absorbance value, I0 is the distance from the baseline to the zero line (transmittance = 0) at 2.73 μm (mm), and I is the distance from the absorption peak to the zero line at 2.73 μm (mm);

[0106] 4. The method for measuring the content of metallic impurity elements is: JY / T0567-2020 "General Rules for Inductively Coupled Plasma Atomic Emission Spectrometry". Specifically, hydrofluoric acid and nitric acid are mixed in a volume ratio of 3:1. The quartz glass piece is digested under high pressure at 220°C and 6 MPa for 8-12 hours until the digestion solution is evaporated to dryness. The volume is then made up to 25 mL with 1% nitric acid. After matrix matching calibration, a gradient (0-100 μg / L) is prepared with a standard solution containing a Si matrix to simulate the sample matrix. Y or Sc (50 μg / L) is then added to correct the signal drift. The whole process is blank + spiked recovery sample + standard substance (such as NIST SRM 612). The pipeline is flushed with ultrapure water for ≥3 minutes before sampling on the machine. Each sample is measured 3 times and the average value is taken. The calculation formula is as follows:

[0107]

[0108] Where C 仪器 is the concentration measured by the instrument (μg / L), V is the constant volume (mL), and m is the sample mass (g);

[0109] The methods in the supplementary description are all existing technologies, and this solution uses the above methods to perform corresponding operations.

[0110] In the present invention, multiple small-sized high-purity quartz glass sheets or blocks are stacked in a specially designed high-temperature furnace to the desired size and shape of the target product. High vacuum is then used to evacuate the air from the furnace chamber and the gaps between the small quartz sheets. Key points: after reaching the softening temperature of the quartz glass, the softened quartz glass is pressed by a pressing head at temperatures exceeding 1400°C, at constant high temperatures and high pressures for extended periods of time. Simultaneously, volatile impurities released from the quartz glass sheets are vacuum-extracted. This die-casting method not only allows the stacked small quartz glass sheets to be fused into a larger product, but more importantly, further increases the purity and density of the high-purity quartz glass, significantly enhancing the product's performance. This enables the production of large-sized, high-quality, and quality-controlled quartz glass devices using stable and reliable process equipment at a relatively low cost.

[0111] Specifically, the principle of the present invention is that the stress-softening starting temperature of high-purity quartz glass is 1100°C and its melting point is 1713°C. When the temperature reaches near its melting point, multiple small-sized high-purity quartz glass sheets can be easily die-cast and welded together under the action of external force. After being kept at a high temperature of 1100-1300°C for several hours to release the stress, they can be transformed into a stable large-sized quartz glass material or device.

[0112] High-purity quartz glass in a highly softened or molten state can slowly expel volatile impurities such as hydroxyl groups and microbubbles under constant high temperature and high pressure.

[0113] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A quartz glass high temperature melting vacuum die casting welding purification method, characterized in that: The following steps are involved: Step S1: After cleaning and drying, multiple small-sized quartz glass sheets or blocks are stacked vertically in the center of a high-temperature furnace. The stacked products have the same design size and shape as the target product. Graphite stoppers of matching specifications are then used to fix and position the stacked products. Step S2: setting the temperature rise program of the high-temperature die-casting furnace to a target temperature range of 1400-1750°C and starting the segmented gradient temperature rise control; The high-temperature die-casting furnace is equipped with a vacuum pump. During the heating process of the high-temperature die-casting furnace, the residual gas inside the furnace, the gas trapped in the gap between the quartz glass layers, and the volatile impurities generated by the thermal decomposition of the material are simultaneously extracted; Step S3: installing the pressure head and setting the maximum pressure of the die-casting machine. After the temperature of the high-temperature die-casting furnace reaches the set target temperature, directly starting the die-casting machine in the high-temperature die-casting furnace to perform multiple high-temperature melt die-casting operations. Step S4: After completing the high-temperature melt die-casting, change the set temperature of the high-temperature die-casting furnace to the annealing temperature, turn off the heating and naturally cool it to the annealing temperature, maintain it in the annealing temperature range for 6-12 hours, and naturally cool it to below 550°C. Open the furnace door and take out the target product.

2. The quartz glass high-temperature melting vacuum die-casting welding purification method according to claim 1, characterized in that: In step S1, the small-sized quartz glass sheet or quartz glass block refers to a quartz glass block with a maximum dimension in any direction not exceeding 600 mm and a dimension in the thickness direction not exceeding 20 mm.

3. The quartz glass high-temperature melting vacuum die-casting welding purification method according to claim 1, characterized in that: In step S1, the graphite limiter is in the shape of a hollow cylinder or a hollow square column as a whole, and its main body is divided into two halves along the axial direction, and the closed state is fixed by a locking device. The outer wall of the cylinder is evenly distributed with fine air vents for air extraction, and the inner cavity surface is coated with a release coating.

4. The quartz glass high-temperature melting vacuum die-casting welding purification method according to claim 1, characterized in that: In step S2, the vacuum pump is one of a rotary vane mechanical vacuum pump, a Roots pump, an oil diffusion pump or a turbomolecular pump.

5. The quartz glass high-temperature melting vacuum die-casting welding purification method according to claim 1, characterized in that: In step S2, the temperature of the high-temperature die-casting furnace is controlled with an accuracy of ±10°C.

6. The quartz glass high-temperature melting vacuum die-casting welding purification method according to claim 1, characterized in that: In step S2, the vacuum pump is set to operate within a vacuum range of 10 -1 -10 -8 pa.

7. The quartz glass high-temperature melting vacuum die-casting welding purification method according to claim 1, characterized in that: In step S3, the diameter or side length of the indenter is 300-1000 mm, and the indenter is selected from the group consisting of a circular indenter, a square indenter, an annular indenter, an outer circle inner square indenter, or an outer square inner circle indenter.

8. The quartz glass high-temperature melting vacuum die-casting welding purification method according to claim 1, characterized in that: In step S3, the multiple high-temperature melt die-casting by the die-casting machine includes the following stages: The first stage: Set the maximum working pressure of the die-casting machine to 1000-4000MPa. When the temperature of the high-temperature die-casting furnace reaches 1400-1500℃, start the die-casting machine. After the pressure rises to the set maximum value, maintain the constant temperature and pressure for 30-60 minutes, and then suspend the die-casting operation. The second stage: Set the maximum working pressure of the die-casting machine to 2000-6000MPa. When the high-temperature die-casting furnace continues to heat up to 1500-1550℃, start the die-casting machine. After the pressure rises to the set maximum value, maintain the constant temperature and pressure for 60-120 minutes, and then suspend the die-casting operation. The third stage: Set the maximum working pressure of the die-casting machine to 2500-8000MPa. When the high-temperature die-casting furnace continues to heat up to 1600-1650℃, start the die-casting machine. After the pressure rises to the set maximum value, maintain the constant temperature and pressure for 120-180 minutes, and then suspend the die-casting operation. The fourth stage: Set the maximum working pressure of the die-casting machine to 3000-10000MPa, and start the die-casting machine when the high-temperature die-casting furnace continues to heat up to 1700-1750℃. After the pressure rises to the set maximum value, maintain the constant temperature and pressure state for 180-300 minutes, and then shut down the die-casting machine.

9. The quartz glass high-temperature melting vacuum die-casting welding purification method according to claim 1, characterized in that: In step S4, the annealing temperature is 1100-1300°C.

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