Preparation method of quartz glass

Abstract

The invention belongs to the technical field of quartz glass, and particularly relates to a preparation method of quartz glass. The method comprises the following steps: filling quartz sand into a graphite mold, melting under a vacuum condition, heating to a first temperature, carrying out first heat preservation treatment, cooling to a second temperature after the first heat preservation treatment is finished, and carrying out second heat preservation treatment; after the second heat preservation treatment is finished, groove sinking treatment is carried out in the inert gas atmosphere, and the groove sinking treatment comprises the steps of heating to a third temperature and carrying out third heat preservation treatment; and after the third heat preservation treatment is finished, cooling to obtain the quartz glass. According to the invention, the quartz sand is processed into the quartz glass through a founding and groove sinking one-step method, so that the problems of complicated production process, high equipment cost, influenced product quality and unstable performance of the traditional method are solved.

Description

Technical Field

[0001] This invention belongs to the field of quartz glass technology, and specifically relates to a method for preparing quartz glass. Background Technology

[0002] Quartz glass has excellent physical and chemical properties, such as high temperature resistance, corrosion resistance, and high light transmittance, and is widely used in semiconductors, optical communications, optical instruments and other fields. At present, the preparation of quartz glass usually requires melting first, melting raw materials such as quartz sand into a glassy state, and then performing a sinking treatment to further improve its performance. However, the traditional melting and sinking treatment are carried out in separate steps, and the quartz glass after melting needs to be transferred to the sinking equipment, which will bring several problems: (1) During the melting process, due to the adsorption of gas by raw materials, crucible contamination or improper control of the melting atmosphere, bubbles are easily formed in the glass melt, and subsequent bubble elimination treatment is required, resulting in a long process flow, and multiple heat treatments may introduce new stress defects. (2) Energy consumption is seriously wasted. After melting, the glass needs to be cooled to room temperature and then heated to the sinking treatment temperature. Repeated heating leads to increased energy consumption and a longer production cycle. (3) Poor process compatibility. The step-by-step treatment makes it difficult to control the impurity spots, crystallization, and failure of sidewall vitrification generated in the glass melt during the melting stage, which may bring more problems to the subsequent sinking and affect product quality. (4) The precision of temperature control and processing time in traditional methods is insufficient, which leads to unstable performance of quartz glass.

[0003] Previous studies have explored methods for directly preparing quartz glass from quartz sand, but these methods all have certain drawbacks. For example, the method described in "A Method for Manufacturing High-Purity Opaque Quartz Glass" involves drying quartz sand and sintering it into quartz glass, but this method is only suitable for opaque quartz glass and cannot meet the requirements for optical transparency. Another method described in "A Method for Preparing Quartz Glass" involves heating quartz sand to a semi-molten state, spraying it with an oxyhydrogen flame to form a porous quartz body, and then sintering it into glass after dehydration. This method simplifies the process, but the oxyhydrogen flame temperature needs to be maintained above 2000℃, and the spraying equipment needs to be resistant to high-temperature corrosion, resulting in high maintenance costs. Furthermore, micron-sized air bubbles may still remain after dehydration of the porous quartz body, requiring additional annealing treatment. The "Plasma Melting Quartz Cylindrical Billet Forming System" uses a DC non-transfer plasma torch to generate temperatures above 2500℃, directly melting quartz sand and forming it into cylindrical billets. This method can rapidly melt quartz sand and has a short forming cycle, but the equipment investment is high: the cost of the plasma torch and its supporting power system is about 10 times that of a traditional electric furnace, making it unsuitable for large-scale, mass industrial production. Furthermore, fluctuations in the plasma airflow can easily lead to uneven melting, affecting the properties of the quartz glass. The "Method for Manufacturing Quartz Glass Using a Sol-Gel Process" mixes quartz sand powder with dispersants and polymer monomers to form a sol, which is then injected into a mold and gelled. Quartz glass is then prepared through low-temperature drying and sintering. This method lowers the sintering temperature by 300-500℃ compared to the traditional melting method, reducing energy consumption. However, sol aging, gelation, and drying take several days to weeks, resulting in low efficiency for industrial mass production. Additionally, residual organic monomers may introduce carbon impurities, reacting with other substances and affecting the purity of the quartz glass. The "Low Absorption High Uniformity Continuous Melting Quartz Glass Products and Their Production Process" describes a method where quartz sand is heated and melted in a continuous melting furnace, and then directly formed and discharged on a mandrel. This method connects the molybdenum ring and the molybdenum rod, simplifying the heating system and reducing maintenance complexity. However, the continuous melting furnace needs to maintain a high temperature environment above 2000℃, and the exhaust pipe design may increase heat loss, resulting in high overall energy consumption. Secondly, the product size is limited because the mandrel forming method has low freedom of geometry for the product, making it difficult to manufacture complex structures (such as irregularly shaped parts). The method for preparing low-expansion quartz glass using recycled materials involves crushing CVD quartz glass waste, followed by ball milling, ultrasonic mixing, slip casting, and cold isostatic pressing to obtain a green blank. Finally, a three-stage vacuum sintering process (holding at 1400℃ for 2 hours → holding at 1700℃ for 3 hours → holding at 1800℃ for 5 hours) is used to eliminate air bubbles. This method transforms CVD tailings into a product with stable low-expansion properties. However, the raw materials are only suitable for CVD waste with high purity (purity > 99.999%). Secondly, the production cycle is long: from crushing (8 hours), ball milling (12 hours) to sintering (20 hours), the efficiency is lower than the continuous production mode of continuous melting furnace. Moreover, the equipment investment is high: it requires an ultrasonic mixing tank (pressure resistance 1 MPa) and cold isostatic pressing equipment (pressure ≥ 100 MPa).

[0004] Considering the current problems with the step-by-step melting and sinking processes, as well as the shortcomings in the one-step preparation of quartz sand into quartz glass products, existing technologies cannot yet achieve a method that completes melting and sinking processes in one step while simultaneously improving production efficiency and product quality. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing quartz glass. The method provided by this invention uses quartz sand as raw material and processes it into quartz glass in one step through melting and sinking. This method solves the problems of complex production processes, high equipment costs, product quality issues, and unstable performance associated with traditional methods.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing quartz glass, comprising the following steps: Quartz sand is loaded into a graphite mold and melted under vacuum conditions. The melting process includes heating to a first temperature and holding it for a first heat treatment, where the first temperature is ≥ the softening point temperature of quartz glass. After the first heat treatment, the temperature is lowered to a second temperature and held for a second heat treatment, where the second temperature is ≥ 1200℃. After the second heat treatment, a sinking process is performed in an inert gas atmosphere at a pressure of 0.1~1 bar. The sinking process includes heating to a third temperature and holding it for a third heat treatment. After the third heat treatment, the quartz glass is cooled to obtain the quartz glass. The cooling process includes a temperature-controlled cooling stage, where the final temperature of the temperature-controlled cooling stage is ≤ 800℃ and the cooling rate of the temperature-controlled cooling stage is ≤ 10℃ / min.

[0007] Preferably, the vacuum degree of the melting process is ≤10Pa, the heating rate of the melting process is 2~10℃ / min, the first temperature is 1600~1730℃, the first holding time is 30~60min, the cooling rate of the melting process is 2~5℃ / min, the second temperature is 1200~1400℃, and the second holding time is 30~60min.

[0008] Preferably, the heating process of melting includes a first heating stage and a second heating stage, wherein the heating rate of the first heating stage is 5~10℃ / min, the end temperature of the first heating stage is 1000~1050℃, and the heating rate of the second heating stage is 2~5℃ / min.

[0009] Preferably, the inert gas includes nitrogen and / or argon, the heating rate of the trough settling treatment is 2~5℃ / min, the third temperature is 1800~2000℃, and the third heat preservation treatment time is 2~4h.

[0010] Preferably, the cooling rate during the temperature control cooling stage is 2~10℃ / min.

[0011] Preferably, the temperature control cooling stage includes sequentially performing a first stage of cooling, a second stage of cooling, and a third stage of cooling. The cooling rate of the first stage is 2~3℃ / min, and the final temperature of the first stage of cooling is 1600~1650℃. The cooling rate of the second stage is 4~5℃ / min, and the final temperature of the second stage of cooling is 1200~1250℃. The cooling rate of the third stage of cooling is 2~3℃ / min.

[0012] Preferably, the cooling further includes a pressure relief stage, wherein the temperature of the pressure relief stage is ≤50°C.

[0013] Preferably, the purity of the quartz sand is ≥99.995%. Before being loaded into the graphite mold, the quartz sand is further subjected to pretreatment, which includes acid washing, drying and sieving in sequence. The acid solution used for acid washing is hydrofluoric acid solution, the mass content of HF in the hydrofluoric acid solution is 10~20%, and the acid washing time is 5~24h.

[0014] Preferably, the apparatus used in the preparation method includes: The furnace shell includes an air inlet and an air outlet; a support plate with load-bearing columns on the inner bottom surface of the furnace shell; a support plate on the support plate with load-bearing columns; graphite hard felt on the inner sidewall, inner top surface, and upper surface of the support plate of the furnace shell; a heating element on the surface of the graphite hard felt; graphite load-bearing columns on the support plate, the height of which is greater than the total thickness of the graphite hard felt and the heating element on the support plate; a support frame on the graphite load-bearing columns; and a graphite crucible mold on the support frame, the inner bottom surface and sidewalls of which are provided with a heat insulation layer having a porous structure. A gas storage tank, which is connected to the air inlet of the furnace shell; A vacuum unit is connected to the gas outlet of the furnace shell.

[0015] Preferably, the material of the insulation layer includes one or more of ceramic fiber, mineral wool and graphite felt; the ash content of the insulation layer is ≤20ppm.

[0016] This invention provides a method for preparing quartz glass, which completes the melting and settling of quartz sand in one step. First, the temperature is raised to the softening point of quartz glass to vitrify the quartz sand, causing it to soften and flow, conforming to the shape of a graphite mold. Then, an inert gas is introduced and the temperature is raised to the settling temperature to complete the settling process. The preparation method provided by this invention effectively improves efficiency and avoids impurities and contamination caused by quartz glass transfer. Compared with existing technologies, this invention has the following advantages: Efficiency improvement: Melting and sinking are integrated into one step, which greatly shortens the production cycle, reduces energy consumption, and the processing time of a single furnace can be controlled within 24 hours.

[0017] Better stress: Gradual cooling is used in the cooling stage of the sinking stage, which helps to eliminate the internal stress of the quartz glass, and the stress can reach ≤2nm / cm.

[0018] Higher purity: The melting and sinking processes are done in one step, eliminating impurities introduced during the transfer process; after melting, the quartz glass is free from defects such as crystallization adhering to the wall and pulverization.

[0019] Furthermore, the present invention provides an apparatus for use in the aforementioned preparation method. The insulating layer has a porous structure, which facilitates the removal of quartz sand and internal gases from the quartz glass during the melting and settling processes, ensuring the final product meets the requirements for Class 1 bubble removal. Moreover, the use of the insulating layer as a buffer layer significantly reduces the frequency of mold damage and extends the service life of the graphite mold. The combination of a graphite mold and a porous insulating layer in this invention also prevents impurities from penetrating the glass and avoids excessive glass stress. Furthermore, the porous structure of the insulating layer helps to remove quartz sand and internal bubbles from the quartz glass, thereby obtaining high-performance quartz glass.

[0020] In summary, the preparation method provided by this invention shortens the production cycle, reduces energy consumption and costs, and has significant economic and social benefits. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the device structure used in this invention; Figure 2 This is a melting-sinking temperature curve diagram in this invention; Figure 3 This is a graph showing the melting-sinking pressure curve in this invention; In the diagram: 1-furnace shell; 2-graphite hard felt; 3-heating element; 4-support plate load-bearing column; 5-support plate; 6-graphite load-bearing column; 7-bearing frame; 21-quartz sand; 22-insulation layer; 23-graphite crucible mold; 31-gas storage tank; 32-gas flow controller; 41-vacuum group; 42-vacuum exhaust pipe; 51-infrared thermometer; 61-pressure relief pipe. Detailed Implementation

[0022] This invention provides a method for preparing quartz glass, comprising the following steps: Quartz sand is loaded into a graphite mold and melted under vacuum conditions. The melting process includes heating to a first temperature and holding it for a first heat treatment, where the first temperature is ≥ the softening point temperature of quartz glass. After the first heat treatment, the temperature is lowered to a second temperature and held for a second heat treatment, where the second temperature is ≥ 1200℃. After the second heat treatment, a sinking process is performed in an inert gas atmosphere at a pressure of 0.1~1 bar. The sinking process includes heating to a third temperature and holding it for a third heat treatment. After the third heat treatment, the quartz glass is cooled to obtain the quartz glass. The cooling process includes a temperature-controlled cooling stage, where the final temperature of the temperature-controlled cooling stage is ≤ 800℃ and the cooling rate of the temperature-controlled cooling stage is ≤ 10℃ / min.

[0023] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0024] In this invention, the graphite mold is a graphite crucible mold, and the ash content of the graphite mold is preferably <5ppm. This invention uses a high-purity graphite mold, which can prevent impurities from the mold itself from penetrating into the glass during processing and affecting product quality.

[0025] In this invention, the purity of the quartz sand is preferably ≥99.995%. Before the quartz sand is loaded into the graphite mold, the invention preferably further includes pretreatment of the quartz sand, which includes acid washing, drying, and sieving in sequence. The acid solution used for acid washing is a hydrofluoric acid solution, and the HF content in the hydrofluoric acid solution is preferably 10-20% by mass. The acid washing time is preferably 5-24 hours. This invention preferably removes impurities and contaminants from the surface of the quartz sand through acid washing to ensure that the vitrification and settling of the quartz sand are not affected by impurities. This invention does not have special requirements for the specific implementation of the drying method. The sieving ensures uniform particle size, which is beneficial to product performance indicators. The mesh size of the quartz sand after sieving can be 40-80 mesh.

[0026] In this invention, the vacuum degree of the melting process is preferably ≤10 Pa. The heating rate of the melting process is preferably 2~10℃ / min. The heating process of the melting process preferably includes a first heating stage and a second heating stage. The heating rate of the first heating stage is preferably 5~10℃ / min. The final temperature of the first heating stage is preferably 1000~1050℃, and the invention uses the first heating stage for preheating. The heating rate of the second heating stage is preferably 2~5℃ / min.

[0027] In this invention, the first temperature is preferably 1600~1730℃. The first heat treatment time is preferably 30~60 min. The cooling rate of the melting process is preferably 2~5℃ / min. The second temperature is preferably 1200~1400℃. The second heat treatment time is preferably 30~60 min.

[0028] In this invention, during the melting process, the heating rate is controlled at 2~10℃ / min, and the first temperature is 1600~1730℃. This first temperature ensures that the quartz sand reaches its softening point and gradually vitrifies. The first holding time is 30~60min to ensure complete melting.

[0029] In this invention, the inert gas preferably includes nitrogen and / or argon. The pressure of the sump treatment is 0.1~1 bar, preferably 0.5~1 bar. The pressure of the sump is preferably adjusted by introducing an inert gas. The flow rate of the inert gas is preferably 5~10 L / min. The flow rate of the inert gas is adjusted according to the size of the furnace and the loading of quartz glass.

[0030] In this invention, the heating rate of the sump treatment is preferably 2~5℃ / min. The third temperature is preferably 1800~2000℃. The duration of the third heat preservation treatment is preferably 2~4h.

[0031] In this invention, the cooling rate of the temperature-controlled cooling stage is preferably 2~10℃ / min. The temperature-controlled cooling stage preferably includes a first stage of cooling, a second stage of cooling, and a third stage of cooling sequentially. The cooling rate of the first stage is preferably 2~3℃ / min. The endpoint temperature of the first stage of cooling is preferably 1600~1650℃. The cooling rate of the second stage is preferably 4~5℃ / min. The endpoint temperature of the second stage of cooling is preferably 1200~1250℃. The cooling rate of the third stage is preferably 2~3℃ / min. The endpoint temperature of the third stage of cooling is preferably 800℃. The cooling process preferably also includes a natural cooling stage following the temperature-controlled cooling stage.

[0032] In this invention, the cooling preferably further includes a pressure relief stage, wherein the temperature of the pressure relief stage is preferably ≤50°C, and in the embodiment it can be 50°C.

[0033] In the cooling process, this invention employs a temperature-controlled cooling stage. By controlling the cooling rate of the temperature-controlled cooling stage to 2~10℃ / min, a slow cooling rate is ensured to help eliminate internal stress in the quartz glass, guaranteeing the dimensional stability and mechanical properties of the product. When the cooling rate exceeds the limit specified in this invention, an excessively fast cooling rate may cause residual stress inside the product, affecting product quality.

[0034] In this invention, when the furnace temperature drops below 50°C, the quartz glass is considered to have essentially cooled. At this point, the pressure relief valve is opened, allowing the furnace pressure to gradually return to atmospheric pressure. Then, the furnace door is opened, the formed quartz glass product is removed, and the product is inspected.

[0035] In this invention, the apparatus used in the preparation method preferably includes: The furnace shell includes an air inlet and an air outlet; a support plate with load-bearing columns on the inner bottom surface of the furnace shell; a support plate on the support plate with load-bearing columns; graphite hard felt on the inner sidewall, inner top surface, and upper surface of the support plate of the furnace shell; a heating element on the surface of the graphite hard felt; graphite load-bearing columns on the support plate, the height of which is greater than the total thickness of the graphite hard felt and the heating element on the support plate; a support frame on the graphite load-bearing columns; and a graphite crucible mold on the support frame, the inner bottom surface and sidewalls of which are provided with a heat insulation layer having a porous structure. A gas storage tank, which is connected to the air inlet of the furnace shell; A vacuum unit is connected to the gas outlet of the furnace shell.

[0036] The structural schematic diagram of the device provided by the present invention is shown below. Figure 1 As shown below, in conjunction with Figure 1 The apparatus provided by the present invention will be described in detail.

[0037] The device provided by this invention includes a furnace shell 1. In this invention, the furnace shell 1 is the load-bearing component of the entire device, and is preferably made of a high-temperature resistant and high-strength material. In an embodiment of this invention, the material of the furnace shell 1 can be stainless steel.

[0038] In this invention, the furnace shell 1 is provided with an air inlet and an air outlet.

[0039] In this invention, the furnace shell 1 must ensure good sealing performance to meet the requirements of a vacuum or specific atmosphere environment. Preferably, the air inlet and outlet of the furnace shell 1 are equipped with sealing strips to ensure a stable internal environment during vacuuming or gas introduction.

[0040] In this invention, the furnace shell 1 is preferably also provided with a sealing door.

[0041] The device provided by the present invention includes a support plate bearing column 4 disposed on the bottom surface of the furnace shell; a support plate 5 is disposed on the support plate bearing column 4.

[0042] The device provided by this invention includes a graphite rigid felt 2 disposed on the inner sidewall, inner top surface, and upper surface of the support plate 5 of the furnace shell 1; and a heating element 3 disposed on the surface of the graphite rigid felt 2. In this invention, the graphite rigid felt serves as a graphite insulation layer and heat insulation layer of the device to reduce heat loss and improve energy utilization efficiency.

[0043] In this invention, the heating element 3 is responsible for providing the high-temperature environment required for dehydroxylation and trough molding.

[0044] In this invention, the heating element 3 preferably employs resistance heating. The heating element 3 is preferably a graphite heating element.

[0045] In this invention, the heating element 3 preferably comprises multiple heating element units that are separated from each other. The multiple heating element units are independently disposed on the surface of the graphite felt. The multiple heating element units are connected in parallel, and each heating element unit has an independent heating power control system. The multiple heating element units can independently control the temperature of different areas within the furnace shell 1 to ensure temperature uniformity within the furnace.

[0046] In this invention, multiple heating element units of the heating element 3 are respectively disposed on the inner top surface region, the inner side wall region, and the upper surface of the graphite hard felt 2 located on the upper surface of the support plate 5 of the furnace shell 1. This invention controls the temperature deviation inside the furnace shell 1 within ±8℃ by adjusting the heating power of the heating elements in each region.

[0047] The device provided by this invention also includes a graphite support column 6 on the support plate 5, the height of which is greater than the total thickness of the graphite felt and heating element on the support plate; a support frame 7 is provided on the graphite support column 6; and a graphite crucible mold 23 is provided on the support frame 7. The graphite crucible mold 23 contains quartz sand 21.

[0048] In this invention, the graphite crucible mold 23 is a key component in shaping the quartz glass. The graphite crucible mold 23 is used because graphite possesses excellent high-temperature resistance, chemical stability, and a low coefficient of thermal expansion. The shape of the graphite crucible mold 23 is designed according to the desired shape of the quartz glass product, such as a flat shape or a curved shape. Preferably, the surface of the graphite crucible mold 23 undergoes fine processing to ensure a smooth surface finish, ensuring that the quartz glass can smoothly conform to the graphite crucible mold 23 during the sink forming process, resulting in a high-precision molded product.

[0049] The device provided by this invention includes a heat insulation layer 22. The heat insulation layer 22 is provided on the inner bottom surface and side walls of the graphite crucible mold, and the heat insulation layer 22 has a porous structure. In this invention, the material of the heat insulation layer 22 preferably includes one or more of ceramic fiber, mineral wool, and graphite felt. The ash content of the heat insulation layer 22 is ≤20ppm. The heat insulation layer 22 facilitates the discharge of internal gases from the quartz sand and quartz glass, preventing the formation of bubbles, and also reduces stress caused by differences in expansion coefficients, preventing mold cracking.

[0050] The device provided by this invention includes a gas storage tank 31. The gas inlet of the furnace shell 1 is connected to the gas storage tank 31. In this invention, the gas storage tank 31 is preferably connected to the gas inlet of the furnace shell 1 via an inlet pipe. A gas flow controller 32 is preferably installed on the inlet pipe.

[0051] In this invention, the gas storage tank 31 and the gas flow controller 32 are used to control the pressure of the inert gas inside the furnace shell 1. The inert gas is introduced into the furnace shell 1 through the gas inlet pipe, and then discharged through the vacuum assembly 42 along the vacuum exhaust pipe 41. This invention ensures that the gas pressure inside the furnace is within the set range according to the inert gas flow rate set by the process.

[0052] The device provided by the present invention includes a vacuum assembly 41. The gas outlet of the furnace shell 1 is connected to the vacuum assembly 41. In the present invention, the vacuum assembly 41 is preferably connected to the gas outlet of the furnace shell 1 through a vacuum exhaust pipe 42.

[0053] In this invention, the vacuum assembly 41 is used to create vacuum conditions for melting.

[0054] In this invention, the vacuum unit 41 is composed of vacuum pumps, preferably multi-stage combination pumps such as rotary vane pumps and Roots pumps. The rotary vane pump first performs primary evacuation to reduce the pressure inside the furnace to a certain level, and then the Roots pump takes over to further reduce the pressure.

[0055] In this invention, the vacuum exhaust pipe 42 is preferably made of stainless steel, which has good airtightness and corrosion resistance.

[0056] In this invention, the vacuum assembly 41 preferably includes a vacuum valve. The vacuum valve used in the vacuum assembly 41 is used to control the inlet and outlet of gas and to adjust the vacuum level. This invention enables the vacuum level inside the furnace to reach below 10 Pa through the vacuum assembly 41.

[0057] The apparatus used in the simultaneous dehydroxylation and sintering treatment method for quartz glass provided by the present invention includes an infrared thermometer 51. The infrared thermometer 51 is installed on the furnace shell 1 and is used to detect the temperature inside the furnace shell 1.

[0058] The apparatus used in the simultaneous dehydroxylation and sintering treatment method for quartz glass provided by the present invention includes an in-furnace pressure relief pipe 61. The in-furnace pressure relief pipe 61 is connected to the furnace shell 1 and is used to discharge the gas inside the furnace shell 1.

[0059] The preferred method for preparing the quartz glass using the above-described apparatus according to the present invention includes: In the raw material pretreatment stage, the quartz sand is acid-washed to remove surface impurities and contaminants, ensuring that the vitrification and settling of the quartz sand are not affected by impurities. It is then dried and sieved to ensure uniform particle size and a purity ≥99.995%.

[0060] During the melting stage, pretreated quartz sand is placed into the graphite crucible mold 23, the furnace door is closed, and the vacuum unit 41 is activated to gradually reduce the furnace pressure until the set vacuum level of 10 Pa or less is reached. Once the furnace vacuum level is below 10 Pa, the heating program is initiated to heat the heating element 3, raising the furnace temperature at a certain rate, typically controlled at 2-10 °C / min. For example, the temperature is first raised to 1000 °C at a rate of 10 °C / min for initial preheating, and then raised to above the softening point of quartz glass at a rate of 5 °C / min, typically 1600-1730 °C. During the heating process, the present invention uses a temperature control system to monitor and adjust the temperature of each area within the furnace in real time to ensure temperature uniformity. The vacuum unit 41 continuously evacuates the furnace, maintaining the vacuum level below 10 Pa until the vacuum holding stage begins, typically lasting 30-60 minutes. After the heat preservation is completed, vacuum cooling begins, with the temperature decreasing to 1200~1400℃ at a rate of 5℃ / min, and then maintained for 30~60 minutes. After the heat preservation is completed, the settling stage begins.

[0061] During the settling stage, after vacuum insulation, the vacuum unit 41 is first shut off, and then gas is introduced into the furnace through the gas flow controller 32 to raise the furnace pressure to the set processing pressure. The gas supply system is then shut off. Nitrogen or argon can be used, and the set processing pressure is 0.1~1 bar. Once the pressure reaches the set value, the temperature continues to rise at a rate of 5℃ / min to the settling high temperature, typically 1800~2000℃, and is held for 2~4 hours. After the holding period, the quartz sand has completed its settling and begins the gradient cooling stage. Temperature control is applied to the furnace at a controlled rate, typically 2~10℃ / min. For example, the temperature is reduced to 1600℃ at a rate of 2℃ / min, to 1200℃ at a rate of 4℃ / min, and to 800℃ at a rate of 2℃ / min. Temperature control is then stopped, and natural cooling begins.

[0062] During the room temperature depressurization stage, when the furnace temperature drops below 50°C, the quartz glass can be considered to have essentially cooled. At this point, the depressurization valve inside the furnace is opened, allowing the furnace pressure to gradually return to atmospheric pressure. Once atmospheric pressure is reached, the furnace door is opened, and the formed quartz glass product is removed. The product undergoes quality inspection, including checks on appearance, dimensional accuracy, and other indicators.

[0063] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0064] Example 1 First, prepare two portions of pretreated quartz sand. One portion is processed in a step-by-step manner as a comparison: first, it is melted into quartz glass using CVD (chemical vapor deposition), then processed and cut into three quartz glass pieces of the same size, and then subjected to tank settling. The other portion is divided into three smaller portions, each of which undergoes a one-step process of melting and tank settling, ultimately becoming three quartz glass pieces.

[0065] (1) Step-by-step processing The following are test data for three methods that first use CVD melting and then immersion in a vat to produce quartz glass. The immersion process is similar to the "one-step melting and immersion" method, and aims to achieve high efficiency and low energy consumption in production. ① Place the high-purity graphite crucible on the support frame, then place the high-purity insulation layer, add the pre-cut quartz glass, and then load it into the furnace. ② Close the furnace door and start the vacuum system until the vacuum level drops below 10 Pa. ③ Start the heating program, first raising the temperature to 1000℃ at a rate of 10℃ / min; then raising it to 1300℃ at a rate of 5℃ / min. Subsequently, open the nitrogen gas flow control system to purge the furnace with 0.2 bar of nitrogen, while simultaneously raising the temperature to 1900℃ at a rate of 5℃ / min. Hold this temperature for 2 hours, then allow it to cool naturally. When the furnace temperature drops to 50℃, open the pressure relief valve, then open the furnace door, remove the quartz glass product, and inspect it.

[0066] See Table 1 for specific data: Table 1. Data of quartz glass samples prepared by CVD melting followed by trough settling.

[0067] (2) Melting and sinking in one step Melting and sinking are processed in one step. Figure 1 The apparatus shown is used to perform the operation. Figure 2 The melting-sinking temperature change curve shown is obtained by using... Figure 3 The curve showing the change in melting-sinking pressure is shown.

[0068] ① Place the high-purity graphite crucible on the support frame, then place the high-purity insulation layer, pour in quartz sand and spread it evenly, then load it into the furnace. ② Close the furnace door, start the vacuum system, and wait until the vacuum level is below 10 Pa. ③ Begin the melting process, start the heating program, first raise the temperature to 1000℃ at a rate of 10℃ / min; then raise it to 1650℃ at a rate of 5℃ / min, and hold for 30 min; then lower the temperature to 1300℃ at a rate of 5℃ / min, and hold for 30 min. ④ After the holding period, begin the settling process, turn on the nitrogen gas flow control system to purge the furnace with 0.2 bar of nitrogen, and simultaneously raise the temperature to 1900℃ at a rate of 5℃ / min, hold for 2 h, then lower the temperature to 1600℃ at a rate of 2℃ / min, lower it to 1200℃ at a rate of 4℃ / min, and lower it to 800℃ at a rate of 2℃ / min, then allow it to cool naturally. Once the furnace temperature drops to 50°C, open the pressure relief valve, then open the furnace door, remove the quartz glass product, and inspect it.

[0069] Table 2 shows the test data for three types of quartz glass that undergo a one-step melting and sinking process: Table 2 Test data of quartz glass processed by melting and sinking in one step.

[0070] As shown in Tables 1 and 2, compared with the step-by-step processing, the quartz glass processed by simultaneous melting and sinking has higher purity because it avoids the transfer of impurities from the quartz glass. Secondly, the heat treatment time of simultaneous processing is longer, and the quartz glass undergoes two softening and vitrification processes, resulting in better uniformity. Overall, the quartz glass processed by simultaneous processing has better performance, higher efficiency, and lower energy consumption.

[0071] As can be seen from the above embodiments, the quartz glass preparation method provided by the present invention completes melting and sinking in the same sinking furnace in one step, avoiding the problems of impurity introduction and low efficiency caused by transferring quartz glass in traditional step-by-step processing. Simultaneously, by precisely controlling the heating rate and temperature, and introducing inert gas, the present invention ensures the quartz sand is fully melted and processed at a suitable sinking temperature, effectively removing bubbles and impurities from the quartz glass and improving its density and performance. The present invention combines a high-purity graphite mold with graphite felt to prevent impurities from the mold itself from penetrating into the glass. The porous structure of the high-purity insulation layer helps to expel internal gases from the quartz sand during the melting stage and the quartz glass during the sinking stage, and also acts as a stress buffer during the cooling process, while preventing mold cracking. The present invention employs gradient cooling; the slow cooling rate helps to eliminate internal stress in the quartz glass, ensuring the dimensional stability and mechanical properties of the product, resulting in lower glass stress and fewer streaks.

[0072] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing quartz glass, characterized in that, Includes the following steps: Quartz sand is loaded into a graphite mold and melted under vacuum conditions. The melting process includes heating to a first temperature and holding it for a first heat treatment, where the first temperature is ≥ the softening point temperature of quartz glass. After the first heat treatment, the temperature is lowered to a second temperature and held for a second heat treatment, where the second temperature is ≥ 1200℃. After the second heat treatment, a sinking process is performed in an inert gas atmosphere at a pressure of 0.1~1 bar. The sinking process includes heating to a third temperature and holding it for a third heat treatment. After the third heat treatment, the quartz glass is cooled to obtain the quartz glass. The cooling process includes a temperature-controlled cooling stage, where the final temperature of the temperature-controlled cooling stage is ≤ 800℃ and the cooling rate of the temperature-controlled cooling stage is ≤ 10℃ / min.

2. The preparation method according to claim 1, characterized in that, The vacuum degree of the melting process is ≤10Pa, the heating rate of the melting process is 2~10℃ / min, the first temperature is 1600~1730℃, the first holding time is 30~60min, the cooling rate of the melting process is 2~5℃ / min, the second temperature is 1200~1400℃, and the second holding time is 30~60min.

3. The preparation method according to claim 1 or 2, characterized in that, The melting heating process includes a first heating stage and a second heating stage. The heating rate of the first heating stage is 5~10℃ / min, the final temperature of the first heating stage is 1000~1050℃, and the heating rate of the second heating stage is 2~5℃ / min.

4. The preparation method according to claim 1, characterized in that, The inert gas includes nitrogen and / or argon, the heating rate of the trough settling treatment is 2~5℃ / min, the third temperature is 1800~2000℃, and the third heat preservation treatment time is 2~4h.

5. The preparation method according to claim 1, characterized in that, The cooling rate during the temperature-controlled cooling stage is 2~10℃ / min.

6. The preparation method according to claim 1, 4, or 5, characterized in that, The temperature control cooling stage includes sequentially performing a first stage of cooling, a second stage of cooling, and a third stage of cooling. The cooling rate of the first stage is 2~3℃ / min, and the final temperature of the first stage of cooling is 1600~1650℃. The cooling rate of the second stage is 4~5℃ / min, and the final temperature of the second stage of cooling is 1200~1250℃. The cooling rate of the third stage of cooling is 2~3℃ / min.

7. The preparation method according to claim 1, characterized in that, The cooling process also includes a pressure relief phase, wherein the temperature during the pressure relief phase is ≤50°C.

8. The preparation method according to claim 1, characterized in that, The quartz sand has a purity of ≥99.995%. Before being loaded into the graphite mold, the quartz sand is further subjected to pretreatment, which includes acid washing, drying and sieving in sequence. The acid solution used for acid washing is hydrofluoric acid solution, and the mass content of HF in the hydrofluoric acid solution is 10~20%. The acid washing time is 5~24h.

9. The preparation method according to claim 1, characterized in that, The apparatus used in the preparation method includes: The furnace shell includes an air inlet and an air outlet; a support plate with load-bearing columns on the inner bottom surface of the furnace shell; a support plate on the support plate with load-bearing columns; graphite hard felt on the inner sidewall, inner top surface, and upper surface of the support plate of the furnace shell; a heating element on the surface of the graphite hard felt; graphite load-bearing columns on the support plate, the height of which is greater than the total thickness of the graphite hard felt and the heating element on the support plate; a support frame on the graphite load-bearing columns; and a graphite crucible mold on the support frame, the inner bottom surface and sidewalls of which are provided with a heat insulation layer having a porous structure. A gas storage tank, which is connected to the air inlet of the furnace shell; A vacuum assembly is connected to the gas outlet of the furnace shell.

10. The preparation method according to claim 9, characterized in that, The insulation layer is made of one or more of ceramic fiber, mineral wool, and graphite felt; the ash content of the insulation layer is ≤20ppm.

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