Preparation method of high-purity transparent quartz glass

Abstract

The invention discloses a preparation method of high-purity transparent quartz glass, which comprises the following steps: putting a quartz blank into a crucible, placing induction heating elements on the upper side and the lower side of the quartz blank, and filling the side surface of the quartz blank with a heat conduction material; and putting the crucible into a vacuum induction heating furnace, and sintering to obtain the high-purity transparent quartz glass. According to the invention, the large-size quartz glass with high transparency, extremely low bubble content and low hydroxyl content can be prepared, and the problems of long time consumption and large raw material loss of the high-purity transparent quartz glass fired by the existing production mode are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-purity transparent quartz glass manufacturing, and specifically relates to a preparation method of high-purity transparent quartz glass with a short firing time and low cost. Background Art

[0002] Due to a series of superior optical, mechanical, thermal properties and excellent biocompatibility, high-purity transparent quartz glass has become an extremely important semiconductor, optical and biological material. The photomask substrates, quartz tubes, quartz rods, etc. made of transparent quartz glass are indispensable in the semiconductor industry, especially in the manufacturing processes of silicon wafers and wafers; in the fields of optical fiber communication, aerospace, biology, etc., the optical fibers, glassware, windows, etc. made of quartz glass are widely used; in the field of biomedical, due to the good biocompatibility and chemical corrosion resistance of quartz glass, quartz glass can be applied to medical devices such as intraocular lenses and endoscopes. According to different raw materials, the methods for preparing high-purity transparent quartz glass are mainly divided into two categories: natural quartz glass preparation, including electrofusion method, gas melting method and plasma melting method; synthetic quartz glass preparation, including chemical vapor deposition method, hydrothermal synthesis method, sol-gel method. Compared with other methods, the electrofusion method for preparing quartz glass has a high yield and low cost, and is the most common preparation method for high-purity transparent quartz glass in China. This method is to place high-purity quartz sand raw materials in a crucible and heat the raw materials to melting in a vacuum environment to generate quartz glass.

[0003] Currently, the commonly used electrofusion method for preparing high-purity transparent quartz glass is mainly to heat high-purity quartz sand raw materials to above 1700 °C in a vacuum to make them melt, and then obtain the product through processes such as cooling and annealing. However, this method requires an extremely high vacuum degree during the firing process, which not only has high requirements for equipment, but also because the thermal conductivity of the vacuum is extremely low, very close to zero, and heat can only be transferred to the quartz raw materials from the contact with the crucible or through radiation, the heat conduction efficiency is low, and the quartz material has poor thermal conductivity. Therefore, this method takes a long time and has high energy consumption. Usually, it takes more than 24 hours to prepare a large-size quartz glass, such as the patent application CN105502896A. Solving the above problems is crucial for the production and cost control of quartz glass.

[0004] Patent CN113277715B uses a photocuring 3D printing technology to prepare the embryo body, and realizes the rapid heating of the sample by the concentrated heat release of the sintering mold in the electric furnace for the narrow internal space, and controls the entire sintering process within half an hour. However, since this method needs to use additives such as photosensitive resin, impurities will be introduced into the quartz glass; when the prefabricated embryo body is heated in a graphite mold, due to the different distances between the top and the bottom and the prefabricated embryo body, the quartz glass is unevenly heated, which will cause certain defects such as bubbles. Summary of the Invention

[0005] The present invention provides a method for preparing high-purity transparent quartz glass. The present invention can prepare large-size quartz glass with high transparency, extremely low bubble content, and low hydroxyl content, and solves the problems of long time consumption and large raw material loss in the existing production method for firing high-purity transparent quartz glass.

[0006] The specific technical solution is as follows:

[0007] A method for preparing high-purity transparent quartz glass, comprising:

[0008] Put the quartz embryo into a crucible, place induction heating elements on the upper and lower sides of the quartz embryo, and fill heat-conducting materials on the side of the quartz embryo; then put the crucible into a vacuum induction heating furnace and sinter to obtain high-purity transparent quartz glass.

[0009] The method for preparing high-purity transparent quartz glass of the present invention is an induction heating method, which has the advantages of short time consumption per unit weight, low energy consumption, and small loss of quartz raw materials.

[0010] In the method for preparing high-purity transparent quartz glass of the present invention, the crucible, the upper and lower induction heating elements, and the heat-conducting materials become multiple heat sources, and the quartz embryo is heated rapidly in all directions, avoiding defects such as gas lines caused by too large temperature difference between inside and outside. Moreover, during the heating and sintering process, the induction heating elements are always attached to the upper and lower sides of the quartz embryo, so that the quartz embryo can be heated rapidly, enabling the quartz embryo to quickly cross the cristobalite phase transition stage and completely melt into a quartz glass melt, thereby greatly shortening the time required for sintering high-purity transparent quartz glass.

[0011] Adopting the method for preparing high-purity transparent quartz glass of the present invention, the heating-up time of a small-size quartz embryo with a diameter of 5 cm and a thickness of 1 cm can be shortened to 10 min, and the heating-up time of a large-size quartz embryo with a diameter of 1 m and a thickness of 20 cm can be shortened to 1.5 h. Due to the close connection of the embryos and multiple heat transfer sources on the upper, lower, and side surfaces, the heat transfer efficiency is improved. Moreover, due to the overall uniform heating-up, the firing time is short, and the obtained quartz products have fewer defects such as bubbles and gas lines.

[0012] In addition, the method for preparing high-purity transparent quartz glass of the present invention has a low requirement for the vacuum degree of the equipment, and can greatly reduce the equipment cost required for melting.

[0013] The light transmittance of the high-purity transparent quartz glass prepared by the method for preparing high-purity transparent quartz glass of the present invention at a thickness of 2 mm and a wavelength of 1000 - 3500 nm is greater than 93%, and the total cross-sectional area of bubbles in 100 cm 3 glass is <0.03 mm 2 , and the hydroxyl content is less than 10 ppm.

[0014] The material of the crucible is preferably one that does not easily react with the quartz blank and can be inductively heated, and specifically may include one or a combination of tungsten, molybdenum, rhenium, graphite, etc.

[0015] The inductive heating element may include one or a combination of graphite paper, graphite blocks, graphite sheets, tungsten sheets, molybdenum sheets, rhenium sheets, etc.

[0016] In some preferred examples, the thickness of the inductive heating element is 0.2 - 20 mm (such as 0.5 mm, 10 mm, etc.). This is because during inductive heating, the temperature at the top and bottom of the inductive heating element is lower than that on the outer side. A thinner thickness can make the temperature distribution of the inductive heating element more uniform.

[0017] In some preferred examples, the size of the heat-conducting material is 5 - 40 mesh (such as 2 mm, 3 mm, etc.). The heat-conducting material with a preferred size can facilitate the discharge of the gas in the quartz blank during the subsequent heating process while ensuring the heat-conducting effect, and can avoid the phenomenon that the heat-conducting material sinters prior to the quartz blank.

[0018] The heat-conducting material filled on the side of the quartz blank is preferably a material with a melting point greater than 2000 °C, a heat conductivity coefficient not less than that of quartz sand, and that does not react with the quartz blank, and specifically may include one or a combination of quartz sand, diamond, etc.

[0019] In some embodiments, for the method for preparing the high-purity transparent quartz glass of the present invention, the highest sintering temperature is 1600 - 1900 °C, preferably 1640 - 1780 °C, and further preferably 1670 - 1750 °C. If the temperature is too high, the bubble size in the glass will become larger; if the temperature is too low, the quartz raw material cannot be completely melted.

[0020] In some embodiments, for the method for preparing the high-purity transparent quartz glass of the present invention, the time taken for the heating-up stage during the sintering process is within 8 min - 1.5 h. Here, the time taken for the heating-up stage includes the preheating and heat preservation time, the time taken for the heating-up process, the heat preservation time at each temperature platform, and the heat preservation time at the highest sintering temperature. If the heating-up time is too short, the thermocouple tube is easily damaged and defects such as gas lines are generated; if the heating-up time is too long, the bubble size in the glass will become larger.

[0021] The sintering process may adopt multiple heating-up stages and a multi-stage cooling process. After the heating-up is completed, cooling is carried out through a multi-stage cooling process, which can reduce the stress generated in the glass due to uneven temperature during cooling.

[0022] In some preferred examples, the multiple heating-up stages include: first preheating a vacuum induction heating furnace to 150 - 250 °C (such as 200 °C, etc.) and holding for 5 - 30 min (such as 25 min, etc.), then heating up to 1000 - 1200 °C at a heating-up rate of not less than 4 °C / s, holding for 1 - 20 min and then heating up to the highest sintering temperature at a heating-up rate of not less than 1 °C / s, and holding for 1 - 30 min. Preheating to 150 - 250 °C and holding for 5 - 30 min is to allow the quartz embryo to expel the moisture in the raw materials, avoiding the embryo absorbing moisture in the environment during the pressing end and being put into the crucible and gasifying to form bubbles in the glass; the second-stage heating up to 1000 - 1200 °C and holding is to remove the hydroxyl groups in the raw materials and make the whole quartz glass uniformly reach 1000 - 1200 °C; the third-stage rapidly heating up to the highest sintering temperature, with a heating-up rate above 1 °C / s, is to allow the quartz raw materials to quickly cross the cristobalite phase transition stage during the melting process, avoiding bubbles caused by volume expansion due to phase transition. The holding time and heating-up rate can be determined according to the height-diameter ratio and size of the prepared quartz block.

[0023] In some embodiments, for the multiple heating-up stages, when the temperature is below 1500 °C, the inside of the vacuum induction heating furnace is a protective atmosphere with a gas pressure of 0.1 - 200 Pa (such as 50 Pa, etc.), and when heating up to 1500 - 1600 °C, a protective gas is introduced until the gas pressure in the vacuum induction heating furnace is 10000 - 103000 Pa, such as 10000 Pa, 20000 Pa, 50000 Pa, 100000 Pa, 103000 Pa, etc. In the present invention, when heating up to 1500 - 1600 °C, introducing a protective gas to raise the gas pressure to 10000 - 103000 Pa can effectively inhibit the growth of bubbles in the glass melt. During the heating-up process from room temperature to 1500 °C, the gas pressure in the furnace is 0.1 - 200 Pa, reducing the requirement for the vacuum degree of the equipment and lowering the equipment cost. During the heating-up process from room temperature to 1500 °C, the quartz embryo is still in the sintering stage, and the gas pressure of 0.1 - 200 Pa is to better expel impurity gases such as water and hydroxyl groups; after heating up to 1500 - 1600 °C, the quartz sands are gradually sintered and melted into a quartz melt, and the pores are closed to form bubble defects. At this time, a protective gas is filled to 10000 - 103000 Pa to compress the bubbles.

[0024] The protective gas described in the present invention refers to a gas that does not participate in the reaction, and specifically may include one or a combination of hydrogen, helium, nitrogen, argon, krypton, etc.

[0025] In some preferred examples, the multi-stage cooling process includes: from the highest sintering temperature to 1050 - 1180 °C, the cooling rate is below 10 °C / min, then keep the temperature at 1050 - 1180 °C for more than 30 min, and then cool down to 750 - 850 °C (such as 800 °C, etc.) at a cooling rate below 10 °C / min, and finally cool naturally. Cooling the fused silica glass at the above cooling rate is because during the cooling process of the fused silica glass, the outer layer cools faster than the inner layer, and the viscosity of the fused silica glass is relatively large. If the cooling rate exceeds a certain value, due to the uneven temperature of each part of the fused silica glass, thermal stress will be generated in the glass melt, which will in turn affect the mechanical properties and thermal stability of the fused silica glass. 1050 - 1180 °C is the strain point of the fused silica glass. Keeping the temperature at this stage is to remove the stress in the fused silica glass body as much as possible; after both the inside and outside of the fused silica glass are cooled to below 800 °C, the cooling rate can be appropriately increased.

[0026] In some embodiments, when it is naturally cooled to below 200 °C, the high-purity transparent fused silica glass can be taken out.

[0027] In some embodiments, for the preparation method of the high-purity transparent fused silica glass of the present invention, during the cooling stage of the sintering process, the cooling rate of the fused silica glass melt can be controlled by adjusting the gas supply rate of the protective gas.

[0028] In some preferred examples, the current frequency of the vacuum induction heating furnace for induction heating is 50 - 10000 Hz. If the frequency is too high, when the crucible and the induction heating element are induction heated, the eddy current will concentrate on the outer surface of the crucible and the side surface of the induction heating element; when the frequency is appropriate, the eddy current can be more evenly distributed inside the crucible and the induction heating element, so as to achieve a more uniform temperature distribution and better heating effect.

[0029] The current for induction heating of the vacuum induction heating furnace of the present invention can be one or a combination of large pulse current and alternating current. The large pulse current and alternating current are adopted in the present invention to enable the induction heating elements above and below the crucible and the embryo to be heated up quickly, so as to transfer heat to the quartz raw material to make it melt quickly.

[0030] In some embodiments, the height-diameter ratio of the quartz embryo does not exceed 0.2, the diameter does not exceed 1 m, and the height does not exceed 0.2 m.

[0031] The quartz blank of the present invention can be obtained by pressing dry high-purity quartz sand using a molding press and a cold isostatic press. The present invention uses a molding press for pressing to obtain a blank with the required shape. By putting the high-purity quartz sand raw material into a flexible mold and using cold isostatic pressing, a quartz blank with any external shape can be prepared, and after firing, high-purity transparent quartz glass with the required shape can be formed in one step. When putting the raw material into the pressing mold in the present invention, a series of operations such as vibration, static elimination, and preliminary pressing can be used. This is because when high-purity quartz sand with a particle size of 0.5 to 100 μm is put into the mold, due to its small particle size, it is easy to agglomerate due to static electricity, and the quartz raw material has poor fluidity and is not easy to be evenly distributed in the mold.

[0032] In some preferred examples, the particle size of the high-purity quartz sand is 0.5 to 100 μm. The present invention uses quartz sand raw materials with a particle size ranging from 0.5 μm to 100 μm, which is convenient for pressing and reducing the gas in the preform. If the particle size is too small, there will be too many pores in the blank, and the poor fluidity is not conducive to pressing, resulting in more bubbles. If the particle size is too large, the blank cannot be pressed into shape.

[0033] The high-purity quartz sand can be one or a combination of high-purity natural quartz sand and high-purity synthetic quartz sand.

[0034] In some embodiments, the high-purity natural quartz sand with a particle size of 40 to 400 mesh can be put into a grinding machine for grinding to obtain the high-purity quartz sand. Further, the grinding time can be 3 to 15 hours, preferably 7 to 12 hours. If the selected grinding time is too long, too many impurities will be introduced into the quartz raw material. If the grinding time is too short, the quartz sand cannot be fully ground. The specific grinding time can be adjusted by the mesh number of the quartz sand, the amount of raw material put in, the grinding performance of the grinding machine, etc. The grinding machine can include one or a combination of a ball mill, a roller mill, a mortar grinder, a cutting grinder, a rotary grinder, a disk grinder, a hybrid grinder, a magnetic grinder, etc. The grinding medium is preferably one or a combination of quartz glass and corundum to reduce the entry of impurities.

[0035] In some embodiments, high-purity synthetic quartz sand with the corresponding mesh number can be obtained by a synthesis method, such as controlling the pH value and temperature in the preparation process (such as patent application CN118954521A, etc.), or crushing, grinding, and sieving the gel raw material (such as patent application CN118684232A, etc.), and spray granulating silica powder (such as patent application CN108698883A).

[0036] The total content of metal impurities Al, Ca, Fe, Na, K, Li, Mg, Cu, Ti, Mn, Cr, and Zr in the high-purity quartz sand is preferably ≤14.5 ppma. Further preferably, in the high-purity quartz sand, metal impurity Al ≤ 10 ppma, Ca ≤ 0.8 ppma, Fe ≤ 0.4 ppma, Na ≤ 0.3 ppma, K ≤ 0.3 ppma, Li ≤ 0.3 ppma, Mg ≤ 0.05 ppma, Cu ≤ 0.05 ppma, Ti ≤ 1.5 ppma, Mn ≤ 0.05 ppma, Cr ≤ 0.05 ppma, and Zr ≤ 0.6 ppma.

[0037] The molding press may include one or more of a hot pressing machine, a cold pressing machine, etc.

[0038] If the pressure during the pressing of the molding press is too small, it is difficult to form the embryo body. If the pressure is too large, phenomena such as cracking are likely to occur. Therefore, in some preferred examples, the pressure used for pressing by the molding press in the present invention is 100 - 500 MPa, and the temperature used can be from room temperature to 500 °C.

[0039] The flexible mold used for pressing by the cold isostatic press in the present invention may include one or more of rubber, latex, liquid rubber spray mold, plastic sealing bag, etc.

[0040] The present invention uses cold isostatic pressing for pressing in order to make the internal stress of the quartz embryo body uniform, reduce phenomena such as cracking, and further reduce the gas content in the embryo body. If the pressing pressure of the cold isostatic press is too small, it cannot be pressed into shape or cannot be pressed tightly, and a large amount of gas remains in the embryo body. If the pressing pressure is too large, large-scale equipment is required, increasing the production cost. Therefore, in some preferred examples, the pressure used for pressing by the cold isostatic press in the present invention is 40 - 300 MPa, and the pressing time used can be 3 - 60 min.

[0041] The shape of the transparent quartz glass prepared by the present invention can be determined by the pressing mold, and transparent quartz glass products with the required shape can be prepared according to needs.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] The present invention places the quartz embryo body in a crucible, pads induction heating elements on both the upper and lower sides of the quartz embryo body, and fills a heat-conducting material at the non-contact part between the side of the quartz embryo body and the crucible. Through induction heating, the crucible, the heat-conducting material, and the induction heating elements on the upper and lower sides of the quartz embryo body become multiple uniform heating sources closely attached to the quartz raw material, greatly reducing the overall sintering time. Further, a multi-stage heating process is adopted to reduce the formation of bubbles in the glass. After the heating is completed, the cooling rate of the quartz glass melt is controlled, and multi-stage cooling is adopted to avoid large stress and cracking caused by uneven temperature of the quartz block during cooling.

[0044] The present invention not only realizes the rapid and uniform heating of the quartz blank, but also avoids the waste of energy, solves the problems of long time consumption, high energy consumption, high requirements for equipment, and defects such as bubbles and gas lines easily generated due to uneven temperature in the current sintering process of fused quartz glass by the electric melting method, and provides a faster, simpler and energy-saving method for the sintering of fused quartz glass. By the preparation method of the present invention, large-size fused quartz glass ingots with high transparency, extremely low bubble content and low hydroxyl content can be prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic structural diagram of a sintering device in a specific embodiment of the present invention.

[0046] Figure 2 It is the transmittance spectrogram of the fused quartz glass obtained in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2.

[0047] Figure 3 It is the infrared spectrogram of the fused quartz glass sintered in Example 1. SPECIFIC EMBODIMENTS

[0048] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The operating methods without specific conditions noted in the following embodiments are usually in accordance with conventional conditions or in accordance with the conditions recommended by the manufacturer.

[0049] Refer to Figure 1 , a sintering device that can be used to prepare high-purity transparent fused quartz glass, including a vacuum induction heating furnace 1 (also called a vacuum melting furnace). The vacuum induction heating furnace 1 is internally provided with an induction heating coil 2, and the induction heating coil 2 is externally connected to a power supply 8. The current frequency used for induction heating by the power supply 8 is 50 - 10000 Hz. The vacuum induction heating furnace 1 has an inner cavity surrounded by a heat-insulating material 3, and a crucible 7 can be placed in the inner cavity. The quartz blank 5 is placed in the crucible 7, and induction heating elements 4 are arranged on both the upper and lower sides of the quartz blank 5, and a heat-conducting material 6 is filled in the gap between the side of the quartz blank 5 and the crucible 7.

[0050] Example 1:

[0051] Using the sintering device as shown in Figure 1 above, including:

[0052] Step S1: Prepare the quartz blank:

[0053] First, put the quartz sand raw material with a size of 40 - 200 mesh into a horizontal ball mill for dry grinding. The ball - to - material ratio is 20:1, and the grinding balls are quartz glass beads. Grind for 10 hours to obtain a quartz sand raw material with a particle size of 0.5 - 100 μm. Dry the ball - milled raw material. The drying temperature is 100 °C and the drying time is 24 h. Put the dried raw material into a cylindrical mold for cold pressing. The inner diameter of the mold is 100 cm, the pressing pressure is 500 MPa, and the pressing time is 30 min. Put the pressed blank into a natural rubber mold, seal both ends with a vacuum packaging machine, and then put it into a cold isostatic pressing mold. The pressing pressure is 300 MPa and the pressing time is 60 min. Then demold to obtain a cylindrical quartz blank with a diameter of 100 cm and a height of 20 cm.

[0054] In the quartz sand raw material, the metal impurities are as follows: Al ≤ 10 ppma, Ca ≤ 0.8 ppma, Fe ≤ 0.4 ppma, Na ≤ 0.3 ppma, K ≤ 0.3 ppma, Li ≤ 0.3 ppma, Mg ≤ 0.05 ppma, Cu ≤ 0.05 ppma, Ti ≤ 1.5 ppma, Mn ≤ 0.05 ppma, Cr ≤ 0.05 ppma, Zr ≤ 0.6 ppma.

[0055] Step S2: Sinter the quartz blank into quartz glass:

[0056] After demolding the blank, put it into a graphite crucible, and place graphite sheets on both the upper and lower sides of the blank. The shape of the graphite sheet is a circle with a diameter of 100 cm and a thickness of 10 mm. Fill diamond on the side of the blank, and the size of the diamond is 2 - 3 mm. Put the graphite crucible into a vacuum melting furnace, and set the maximum temperature to 1700 °C. Pre - heat the melting furnace to 200 °C and keep it warm for 25 min. The heating rate from 200 - 1200 °C is 4 °C / s, keep it warm for 20 min. The heating rate from 1200 - 1700 °C is 1 °C / s, keep it warm for 30 min. The protective atmosphere during the melting process is argon. When the temperature is lower than 1500 °C, the air pressure is 50 Pa. When the temperature rises to 1500 °C, fill gas until the air pressure is 100000 Pa. The whole sintering process takes about 88 min. Cooling stage: From the highest temperature to 1050 °C, the cooling rate is 5 °C / min. Then keep it warm at 1150 °C for 30 min. After that, cool it at a rate of 10 °C / min to 800 °C. Finally, cool it naturally to below 200 °C, and take it out to obtain high - purity transparent quartz glass. After cutting, grinding, and polishing, a sample with a thickness of 2 mm is obtained. The transmittance spectrum of the sample is as Figure 2 shown, and the infrared spectrum is as Figure 3 shown. It can be seen from the figure that the transmittance of the sample exceeds 93% in the range of 1000 - 3500 nm, and Figure 3 there is no obvious hydroxyl absorption peak in it.

[0057] Example 2:

[0058] Using the sintering device as described above Figure 1 shown, including:

[0059] Step S1: Prepare a quartz blank:

[0060] First, put quartz sand raw materials with a size of 120 - 200 mesh into a horizontal ball mill for dry grinding. The ball-to-material ratio is 20:1, and the grinding balls are corundum beads. Grind for 8 hours to obtain quartz sand raw materials with a particle size of 0.5 - 100 μm. Dry the ball-milled raw materials. The drying temperature is 100 °C, and the drying time is 24 h. Put the dried raw materials into a cylindrical mold for hot pressing. The inner diameter of the mold is 3 cm, the hot pressing temperature is 400 °C, the pressing pressure is 300 MPa, and the pressing time is 20 min. Put the pressed blank into a natural rubber mold, seal both ends with a vacuum packaging machine, and then put it into a cold isostatic pressing mold. The pressing pressure is 50 MPa, and the pressing time is 3 min. Then demold to obtain a cylindrical quartz blank with a diameter of 3 cm and a height of 0.5 cm.

[0061] In the quartz sand raw materials, the metal impurities are Al ≤ 10 ppma, Ca ≤ 0.8 ppma, Fe ≤ 0.4 ppma, Na ≤ 0.3 ppma, K ≤ 0.3 ppma, Li ≤ 0.3 ppma, Mg ≤ 0.05 ppma, Cu ≤ 0.05 ppma, Ti ≤ 1.5 ppma, Mn ≤ 0.05 ppma, Cr ≤ 0.05 ppma, Zr ≤ 0.6 ppma.

[0062] Step S2: Sinter the quartz blank into quartz glass:

[0063] After demolding the blank, put it into a graphite crucible, and place graphite paper on both the upper and lower sides of the blank. The shape of the graphite paper is a circle with a diameter of 5 cm and a thickness of 0.5 mm. Fill diamond on the side of the blank. The size of the diamond is 2 - 3 mm. Put the graphite crucible into a vacuum melting furnace, and set the maximum temperature to 1690 °C. Preheat the melting furnace to 200 °C and keep it warm for 5 min. The heating rate from 200 °C to 1000 °C is 4 °C / s, keep it warm for 1 min. The heating rate from 1000 - 1690 °C is 3 °C / s, keep it warm for 2 min. The protective atmosphere during the melting process is argon. When the temperature is lower than 1600 °C, the air pressure is 50 Pa. Inflate when the temperature rises to 1600 °C, and the air pressure after inflation is 100000 Pa. The entire sintering process takes about 15 min. Cooling stage: From the highest temperature to 1100 °C, the cooling rate is 4 °C / min. Then keep it warm at 1100 °C for 30 min. After that, cool to 800 °C at a rate of 10 °C / min. Finally, naturally cool to below 200 °C and take it out to obtain high-purity transparent quartz glass. After cutting, grinding, and polishing, a sample with a thickness of 2 mm is obtained. The transmittance spectrum of the sample is tested asFigure 2 As shown, it can be seen from the figure that the transmittance of the sample exceeds 93% in the range of 1000 - 3500 nm.

[0064] Example 3:

[0065] Adopt the sintering device as Figure 1 shown, including:

[0066] Step S1: Prepare a quartz blank:

[0067] First, put quartz sand raw materials with a size of 300 - 400 mesh into a horizontal ball mill for dry grinding. The ball-to-material ratio is 20:1, and the grinding balls are corundum beads. Grind for 8 hours to obtain quartz sand raw materials with a particle size of 0.5 - 100 μm; dry the ball-milled raw materials. The drying temperature is 100 °C and the drying time is 24 h; put the dried raw materials into a cylindrical mold for cold pressing. The inner diameter of the mold is 5 cm, the pressing pressure is 400 MPa, and the pressing time is 20 min; put the pressed blank into a natural rubber mold, seal both ends with a vacuum packaging machine, and then put it into a cold isostatic pressing mold. The pressing pressure is 50 MPa and the pressing time is 30 min; then demold to obtain a cylindrical quartz blank with a diameter of 5 cm and a height of 1 cm.

[0068] In the quartz sand raw materials, the metal impurities are Al ≤ 10 ppma, Ca ≤ 0.8 ppma, Fe ≤ 0.4 ppma, Na ≤ 0.3 ppma, K ≤ 0.3 ppma, Li ≤ 0.3 ppma, Mg ≤ 0.05 ppma, Cu ≤ 0.05 ppma, Ti ≤ 1.5 ppma, Mn ≤ 0.05 ppma, Cr ≤ 0.05 ppma, Zr ≤ 0.6 ppma.

[0069] Step S2: Sinter the quartz blank into quartz glass:

[0070] After demolding the embryo, place it in a graphite crucible, and place graphite paper on both the upper and lower sides of the embryo. The shape of the graphite paper is a circle with a diameter of 5 cm and a thickness of 0.5 mm. Fill diamond on the side of the embryo, and the diamond size is 2 - 3 mm; Place the graphite crucible in a vacuum melting furnace, and set the maximum temperature to 1690 °C. Preheat the melting furnace to 200 °C, keep it warm for 5 min, the heating rate from 200 to 1000 °C is 5 °C / s, keep it warm for 1 min, and the heating rate from 1000 to 1690 °C is 3 °C / s, keep it warm for 2 min; The protective atmosphere during the melting process is argon. When the temperature is lower than 1560 °C, the air pressure is 50 Pa. Inflate when the temperature rises to 1560 °C, and the air pressure after inflation is 100000 Pa. The entire sintering process takes about 15 min; Cooling stage: From the highest temperature to 1180 °C, the cooling rate is 2 °C / min. Then keep it warm at 1080 °C for 30 min, and then cool it at 10 °C / min to 800 °C. Finally, cool it naturally to below 200 °C, take it out, and high-purity transparent quartz glass can be obtained. After cutting, grinding, and polishing, a sample with a thickness of 2 mm is obtained. The transmittance spectrum of the sample is measured as Figure 2 shown. It can be seen from the figure that the transmittance of the sample exceeds 93% in the range of 1000 - 3500 nm.

[0071] Comparative Example 1:

[0072] Step S1: Prepare a quartz embryo:

[0073] First, put quartz sand raw materials with a size of 40 - 200 mesh into a horizontal ball mill for dry grinding. The ball-to-material ratio is 20:1, and the grinding balls are quartz glass beads. Grind for 10 hours to obtain quartz sand raw materials with a particle size of 0.5 - 100 μm; Dry the ball-milled raw materials. The drying temperature is 100 °C, and the drying time is 24 h; Put the dried raw materials into a cylindrical mold for cold pressing. The inner diameter of the mold is 3 cm, the pressing pressure is 400 MPa, and the pressing time is 20 min; Then demold to obtain a cylindrical quartz embryo with a diameter of 3 cm and a height of 0.5 cm.

[0074] In the quartz sand raw materials, the metal impurities Al ≤ 10 ppma, Ca ≤ 0.8 ppma, Fe ≤ 0.4 ppma, Na ≤ 0.3 ppma, K ≤ 0.3 ppma, Li ≤ 0.3 ppma, Mg ≤ 0.05 ppma, Cu ≤ 0.05 ppma, Ti ≤ 1.5 ppma, Mn ≤ 0.05 ppma, Cr ≤ 0.05 ppma, Zr ≤ 0.6 ppma.

[0075] Step S2: Sinter the quartz embryo into quartz glass:

[0076] After demolding the embryo, it is placed in a graphite crucible, and the graphite crucible is placed in a vacuum melting furnace. The maximum temperature is set at 1700 °C, and the heating program is as follows: starting from room temperature, it is heated to 400 °C at a heating rate of 1 °C / s, held for 5 minutes, then heated to 1000 °C at a heating rate of 1 °C / s, held for 10 minutes, then heated to 1600 °C at a heating rate of 0.3 °C / s, and then heated to 1700 °C at a heating rate of 0.125 °C / s, held for 5 minutes; during the melting process, the protective atmosphere is argon, and the gas pressure is 200 Pa. The entire sintering process takes 78 minutes. After the heating program ends, rapid water cooling is carried out; after melting, high-purity quartz glass is obtained, and layered bubbles and large bubbles can be seen in the physical object. The transmittance spectrum of the sample is measured as Figure 2 shown. It can be seen from the figure that its transmittance can reach 82% - 85% in the range of 1000 - 3500 nm.

[0077] Comparative Example 2:

[0078] In the quartz sand raw material, the metal impurities are Al ≤ 10 ppma, Ca ≤ 0.8 ppma, Fe ≤ 0.4 ppma, Na ≤ 0.3 ppma, K ≤ 0.3 ppma, Li ≤ 0.3 ppma, Mg ≤ 0.05 ppma, Cu ≤ 0.05 ppma, Ti ≤ 1.5 ppma, Mn ≤ 0.05 ppma, Cr ≤ 0.05 ppma, Zr ≤ 0.6 ppma.

[0079] The quartz sand raw material with a particle size of 100 - 120 mesh is placed in a vacuum drying oven for drying. The drying temperature is 100 °C, and the holding time is 12 hours. 20 g of the dried raw material is weighed and placed in a graphite crucible. The graphite crucible is placed on a vibrating sieve for 5 minutes; then the graphite crucible is placed in a vacuum melting furnace, the vacuum degree is maintained at 100 Pa, the protective atmosphere is argon, the maximum temperature is set at 1730 °C, and the heating program is as follows: starting from room temperature, it is heated to 400 °C at a heating rate of 1 °C / s, held for 5 minutes, then heated to 1000 °C at a heating rate of 1 °C / s, held for 10 minutes, then heated to 1600 °C at a heating rate of 0.1 °C / s, then heated to 1700 °C at a heating rate of 0.06 °C / s, and then heated to 1730 °C at a heating rate of 0.08 °C / s, held for 5 minutes; during the melting process, the protective atmosphere is argon, and the gas pressure is 100 Pa. The entire sintering process takes 165.2 minutes. After the heating program ends, rapid water cooling is carried out; after melting, high-purity quartz glass is obtained. After cutting, grinding, and polishing, a 2 mm thick sample is obtained, and obvious bubbles can be seen at the contact edge of the physical object with the graphite crucible. The transmittance spectrum of the sample is measured as Figure 2 shown. It can be seen from the figure that its transmittance can reach 85% - 87% in the range of 1000 - 3500 nm.

[0080] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A method for preparing high-purity transparent quartz glass, characterized in that: include: A quartz body (5) is placed in a crucible (7), and induction heating elements (4) are placed on the upper and lower sides of the quartz body (5), and a heat conductive material (6) is filled on the side of the quartz body (5); then the crucible is placed in a vacuum induction heating furnace (1) and sintered to obtain high-purity transparent quartz glass.

2. The preparation method according to claim 1, characterized in that: The high-purity transparent quartz glass has a 2mm thickness and a light transmittance of 1000-3500nm greater than 93%, and a 100cm 3 The total cross-sectional area of ​​bubbles in the glass is <0.03mm 2 , the hydroxyl content is less than 10ppm.

3. The preparation method according to claim 1, characterized in that: The material of the crucible (7) includes one or more combinations of tungsten, molybdenum, rhenium and graphite; The induction heating element (4) comprises one or more combinations of graphite paper, graphite block, graphite sheet, tungsten sheet, molybdenum sheet, and rhenium sheet; The thickness of the induction heating element (4) is 0.2-20 mm.

4. The preparation method according to claim 1, characterized in that: The size of the thermal conductive material (6) is 5 to 40 meshes; The heat-conducting material (6) is a material having a melting point greater than 2000° C., a thermal conductivity not less than that of quartz sand, and will not react with the quartz body (5), and specifically includes one or more of quartz sand and diamond.

5. The preparation method according to claim 1, characterized in that: The maximum sintering temperature is 1600-1900°C, preferably 1640-1780°C, and more preferably 1670-1750°C; The heating stage of the sintering process takes 8 minutes to 1.5 hours; The sintering process uses multiple heating stages and multiple cooling processes; The multiple heating stages include: first preheating the vacuum induction heating furnace (1) to 150°C to 250°C and keeping the temperature for 5 to 30 minutes, then heating the temperature to 1000 to 1200°C at a heating rate of not less than 4°C / s, keeping the temperature for 1 to 20 minutes, then heating the temperature to the highest sintering temperature at a heating rate of not less than 1°C / s, and keeping the temperature for 1 to 30 minutes; In the multiple heating stages, when the temperature is lower than 1500° C., the vacuum induction heating furnace (1) is filled with a protective atmosphere with a pressure of 0.1 to 200 Pa, and when the temperature is raised to 1500 to 1600° C., protective gas is introduced until the pressure in the vacuum induction heating furnace (1) is 10000 to 103000 Pa; The protective gas includes one or more combinations of hydrogen, helium, nitrogen, argon and krypton; The multi-stage cooling process includes: lowering the temperature from the highest sintering temperature to 1050-1180°C at a cooling rate of less than 10°C / min, then keeping the temperature at 1050-1180°C for more than 30 minutes, then cooling the temperature to 750-850°C at a cooling rate of less than 10°C / min, and finally cooling naturally; During the cooling stage of the sintering process, the cooling rate of the quartz glass melt is controlled by adjusting the ventilation rate of the protective gas.

6. The preparation method according to claim 1, characterized in that: The current frequency of induction heating in the vacuum induction heating furnace (1) is 50 to 10,000 Hz.

7. The preparation method according to claim 1, characterized in that: The aspect ratio of the quartz embryo (5) does not exceed 0.2, the diameter does not exceed 1 m, and the height does not exceed 0.2 m.

8. The preparation method according to claim 1, characterized in that: The quartz body (5) is obtained by pressing dry high-purity quartz sand using a molding machine and a cold isostatic press.

9. The preparation method according to claim 8, characterized in that: The particle size of the high-purity quartz sand is 0.5 to 100 μm; The high-purity quartz sand is one or more combinations of high-purity natural quartz sand and high-purity synthetic quartz sand; The total content of metal impurities Al, Ca, Fe, Na, K, Li, Mg, Cu, Ti, Mn, Cr and Zr in the high-purity quartz sand is ≤14.5ppma; The metal impurities in the high-purity quartz sand are Al≤10ppma, Ca≤0.8ppma, Fe≤0.4ppma, Na≤0.3ppma, K≤0.3ppma, Li≤0.3ppma, Mg≤0.05ppma, Cu≤0.05ppma, Ti≤1.5ppma, Mn≤0.05ppma, Cr≤0.05ppma, and Zr≤0.6ppma.

10. The preparation method according to claim 8, characterized in that: The molding machine includes one or more of a hot-pressing tablet press and a cold-pressing tablet press; The pressure used for pressing by the molding machine is 100-500MPa, and the temperature used is room temperature to 500°C; The flexible mold used for pressing by the cold isostatic press includes one or more of rubber, latex, liquid rubber spray mold, and plastic sealing bag; The cold isostatic press is used for pressing at a pressure of 40 to 300 MPa and a pressing time of 3 to 60 minutes.

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