Preparation method of high-purity quartz sand for quartz glass material

Abstract

The invention relates to the technical field of inorganic non-metallic material processing, in particular to a high-purity quartz sand preparation method for a quartz glass material, which comprises the following steps: placing a quartz sand raw material containing surface adsorption impurities in a tubular furnace, and synchronously introducing oxygen-containing gas into the tubular furnace for oxidation decarburization treatment to obtain decarburized quartz sand; the decarburized quartz sand is placed in an atmosphere containing water vapor to be subjected to hydroxyl removal treatment, and dehydroxylated quartz sand is obtained; performing interface activation treatment on the dehydroxylated quartz sand to obtain a temperature distribution image of the surface of the dehydroxylated quartz sand, and calculating a temperature relative standard deviation value to determine whether the interface activation treatment is qualified or not; in response to the fact that the interface activation treatment is qualified, the dehydroxylated quartz sand is placed in a reducing atmosphere to be subjected to chlorine impurity removal treatment, and dechlorinated quartz sand is obtained; and the dechlorinated quartz sand is cooled and subjected to surface passivation treatment, and the high-purity quartz sand is obtained. The purity of the quartz sand is improved, and bubble generation of the quartz sand in the quartz glass preparation process is inhibited.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of inorganic non-metallic material processing, and particularly relates to a high-purity quartz sand preparation method for quartz glass material. BACKGROUND

[0002] High-purity quartz sand is a core basic raw material for preparing quartz crucibles for semiconductors, optical fiber preform rods and high-end optical glass. The purity directly determines the optical uniformity, high-temperature stability and service life of downstream quartz glass products. At present, through the combined process of crushing, ore grinding, magnetic separation, flotation and acid leaching, the industry can effectively remove gangue minerals and most of the inclusion impurities in quartz minerals, and improve the purity of silicon dioxide to 99.9% or even 99.99% or above.

[0003] However, when such high-purity quartz sand is used to prepare high-end quartz glass with zero tolerance for defects, especially quartz crucibles for single crystal silicon drawing, a thorny problem often arises: micro-bubbles are easily produced inside the quartz glass during high-temperature melting or use. These bubbles seriously damage the optical performance and mechanical strength of the material and are one of the key factors leading to product scrap. In-depth research shows that the generation of such bubbles is not mainly due to traditional lattice metal impurities, but is closely related to specific non-metallic impurities adsorbed on the surface of quartz sand particles. During the previous purification by wet acid leaching and subsequent storage process, the huge specific surface area of quartz sand will adsorb or retain carbonaceous organic matter, hydroxyl and chloride ions. These impurities exist in the form of physical adsorption, chemical adsorption or surface bonding, and in the subsequent high-temperature melting environment of more than 1600 DEG C, will decompose carbon, condense hydroxyl or react with chlorine, produce CO2, H2O, HCl and other gases, which are encapsulated in the viscous glass liquid and form bubbles due to the inability to escape in time.

[0004] Chinese Patent Publication No. CN120117613A discloses a high-purity quartz sand strengthening chlorination purification method, which belongs to the technical field of inorganic non-metallic material processing. The method is to place quartz sand raw materials containing crystal structure impurities in a tube furnace, and simultaneously introduce gaseous chlorination agents and gaseous reducing agents into the tube furnace for roasting, to obtain purified quartz sand. The method introduces gaseous reducing agents to control the reaction atmosphere on the basis of conventional chlorination roasting purification, promotes efficient dissociation and chlorination of difficult-to-remove crystal structure impurities, and realizes deep and efficient purification of quartz sand. The method has the advantages of simple process equipment, strong raw material applicability, high impurity removal efficiency, and can be widely applied to the production of 4N5 grade and above high-purity quartz sand.

[0005] It can be seen that the high-purity quartz sand strengthening chlorination purification method has the following problems: 1. While the enhanced chlorination process can remove some chlorine-bound impurities, the high-temperature chlorination atmosphere may also form new Si-Cl bonds or residual volatile chlorine compounds on the quartz surface. If not properly treated, these chlorine impurities will be released as HCl during the melting process, forming bubbles or color centers in the quartz glass.

[0006] 2. While chlorination and reducing atmospheres can promote the removal of metallic impurities, they lack a targeted treatment mechanism for non-metallic impurities such as organic carbon, amorphous carbon, and hydroxyl groups that are physically adsorbed or chemically bonded to the quartz surface. These impurities will decompose and generate gas during subsequent high-temperature melting, forming bubble defects that affect the transparency and uniformity of the quartz glass. Summary of the Invention

[0007] Therefore, the present invention provides a method for preparing high-purity quartz sand for quartz glass materials, in order to overcome the problem in the prior art that non-metallic impurities such as carbon, hydroxyl and chlorine adsorbed on the surface of quartz sand are difficult to remove completely, resulting in bubbles being generated during high-temperature melting and seriously affecting the performance of quartz glass.

[0008] To achieve the above objectives, the present invention provides a method for preparing high-purity quartz sand for quartz glass materials, comprising: Quartz sand raw material containing surface adsorbed impurities is placed in a tube furnace, and oxygen-containing gas is simultaneously introduced into the tube furnace for oxidation and decarbonization treatment to obtain decarbonized quartz sand. The decarbonized quartz sand is placed in an atmosphere containing water vapor to remove hydroxyl groups, thereby obtaining dehydroxylated quartz sand. The dehydroxylated quartz sand is subjected to interface activation treatment. The temperature distribution image of the surface of the dehydroxylated quartz sand is obtained by using an infrared thermal imager. The relative standard deviation of temperature of several pixels in a preset area of ​​the temperature distribution image is calculated to determine whether the interface activation treatment is qualified. In response to the qualified interface activation treatment, the dehydroxylated quartz sand is placed in a reducing atmosphere for chlorine impurity removal treatment to obtain dechlorinated quartz sand; The dechlorinated quartz sand is cooled and surface passivated to obtain high-purity quartz sand.

[0009] Furthermore, the oxygen-containing gas is a mixture of oxygen and nitrogen, with an oxygen volume fraction of 5% to 20%, the oxidation and decarbonization treatment temperature is 500℃ to 800℃, and the oxidation and decarbonization treatment duration is 1 to 4 hours.

[0010] Furthermore, the temperature for the hydroxyl removal treatment is 800℃~1000℃, and the duration of the hydroxyl removal treatment is 2~6 hours.

[0011] Furthermore, the process of determining whether the interface activation treatment is qualified includes: a cooling procedure and a holding procedure of the interface activation process are started, and an infrared thermal image of the surface of the dehydroxylated quartz sand is continuously collected by an infrared thermal imager at a preset collection frequency; a temperature average value and a temperature standard deviation of a plurality of measurement points in a preset region of the infrared thermal image are calculated to calculate a temperature relative standard deviation value, and a temperature curve of the temperature relative standard deviation value changing with time is drawn; the temperature relative standard deviation value reaching a preset time after entering the holding procedure based on the temperature curve; based on the temperature relative standard deviation value being located in a preset temperature relative standard deviation value interval, it is determined that the interface activation process is qualified.

[0012] Further, the unqualified interface activation process is determined based on the temperature relative standard deviation value deviating from the preset temperature relative standard deviation value interval.

[0013] Further, in response to the unqualified interface activation process, a relative deviation value of the temperature relative standard deviation value from a middle value of the preset temperature relative standard deviation value interval is calculated, and the length of the chlorine impurity removal process is adjusted.

[0014] Further, based on the relative deviation value being greater than zero, it is determined that the chlorine impurity removal length is a product of the chlorine impurity removal length and a first compensation factor, wherein the first compensation factor is determined by subtracting a product of a time compensation coefficient and an absolute value of the relative deviation value from 1.

[0015] Further, based on the relative deviation value being less than zero, it is determined that the chlorine impurity removal length is a product of the chlorine impurity removal length and a second compensation factor, wherein the second compensation factor is determined by adding a product of a time compensation coefficient and an absolute value of the relative deviation value to 1.

[0016] Further, the reducing atmosphere is a mixture of hydrogen and argon, the volume fraction of hydrogen is 2% to 5%, the temperature of the chlorine impurity removal process is 1000 to 1200℃, and the length of the chlorine impurity removal is 1 to 3 hours.

[0017] Further, the process of the cooling and surface passivation treatment comprises: based on the end of the length of the chlorine impurity removal process, switching to an inert gas atmosphere, and cooling the dechlorinated quartz sand to a preset passivation temperature at a preset first cooling rate; when the temperature reaches the preset passivation temperature, stopping cooling and maintaining for a preset passivation time; based on a preset second cooling rate, the dechlorinated quartz sand is cooled to a preset safety temperature to obtain high-purity quartz sand.

[0018] Compared with the prior art, the present application has the beneficial effects that, for carbon impurities, the present application converts the surface and deep adsorbed organic carbon and amorphous carbon into gas for removal through controllable low-temperature oxidation treatment without causing sintering of quartz sand particles, eliminating the root causes of bubble formation and heterogeneous nucleation centers due to carbon oxidation or pyrolysis gas formation during high-temperature melting, for hydroxyl impurities, the present application promotes the migration and condensation reaction of firmly combined hydroxyls in the quartz network by using a specific partial pressure of water vapor atmosphere, realizing deep dehydroxylation, thereby ensuring that the obtained quartz glass has extremely high light transmittance in the deep ultraviolet band, for chlorine impurities, the present application uses a mild reducing atmosphere for directional removal, not only removing chlorine in various forms of combination, but also avoiding the risk of corrosion of equipment or formation of HCl bubbles and color center defects due to chlorine volatilization at high temperature.

[0019] Further, the present application provides sufficient but not excessive oxidant through 5% to 20% oxygen-rich atmosphere, ensuring that carbon can be continuously and smoothly oxidized into CO or CO2 gas, avoiding the deflagration phenomenon caused by excessive local oxygen concentration and excessive reaction, which is easy to cause instantaneous overheating and local sintering of the quartz particle surface, and instead wraps the unreacted deep carbon, and the slow and incomplete de-carbonization caused by low oxygen concentration, and the local excessive sintering of the quartz sand surface caused by high oxygen concentration, which instead wraps the internal impurities, the quartz sand particles in the temperature window of 500℃ to 800℃ have not yet undergone significant sintering densification, and the rich pore and microcrack structure is maintained, providing a smooth channel for the diffusion of oxygen into the particle interior and the escape of reaction gas products to the outside, realizing deep oxidation of the bulk carbon impurities, effectively activating the C-O reaction, and enabling various types of carbon to be fully converted and removed within 1 to 4 hours, balancing the treatment efficiency and thoroughness of carbon impurities.

[0020] Further, the present application precisely controls the water vapor partial pressure to be 30 to 60 kPa, which can reversibly break the Si-O-Si bond in the quartz network at high temperature to generate migratable Si-OH, thereby activating and accelerating the diffusion process of internal deep-seated hydroxyls to the particle surface, and these hydroxyls meet and condense to generate water molecules on the particle surface, which are quickly carried away from the reaction zone by the flowing inert gas stream, driving the dehydration reaction to continuously proceed to the right, realizing deep dehydroxylation. The treatment temperature window is 800℃ to 1000℃, ensuring the reaction rate and avoiding the problem of particle sintering caused by excessive temperature, or reaction stagnation caused by low temperature. The sufficient reaction time of 2 to 6 hours ensures the complete performance of the catalysis-migration-condensation process, avoiding the problem of "locking" hydroxyls inside due to premature densification of the surface, and realizing the dehydroxylation depth and uniformity far beyond that of conventional methods.

[0021] Further, the present application introduces controllable thermal stress on the surface of quartz sand by programmed cooling, thereby inducing the formation of micro-crack network and lattice distortion, increasing the active specific surface area of the subsurface and creating abundant diffusion short paths, so that the reducing hydrogen gas can diffuse more quickly and more deeply to the reaction interface with chlorine impurities through these micro-defect channels, and the volatile products generated by the reaction can also efficiently escape along the same path, avoiding the problem of being wrapped, optimizing the mass transfer path, and solving the incomplete removal of chlorine impurities.

[0022] Further, the present application provides a strong reducing atmosphere by using H2 / Ar mixed gas with a hydrogen volume fraction of 2% to 5%, effectively breaking the Si-Cl chemical bonds on the surface and near the surface of quartz, converting them into volatile HCl gas for complete removal, avoiding unnecessary reduction damage to the main body of the quartz silicon-oxygen network caused by excessive hydrogen, or causing uncontrollable reduction side reactions of deep metal impurities. The chlorine impurity removal treatment temperature of 1000 to 1200℃ provides sufficient reaction kinetics rate, so that the chlorine impurities can diffuse and react fully, and the time length of 1 to 3 hours balances the thoroughness of the reaction and production efficiency, which is carried out after deep dehydroxylation, ensuring the cleanliness of the reaction interface and avoiding the secondary pollution caused by the reaction of residual hydroxyl groups and hydrogen to generate water. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The step flow chart for the preparation method of high-purity quartz sand for quartz glass material of the embodiment of the present application is shown in the figure. Figure 2 The step flow chart for determining whether the interface activation treatment is qualified or not of the embodiment of the present application is shown in the figure. Figure 3 The logic judgment chart for determining the length of adjustment of chlorine impurity removal treatment of the embodiment of the present application is shown in the figure. Figure 4 The step flow chart for cooling and surface passivation treatment of the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0024] In order to make the purpose and advantages of the present application more clear and explicit, the present application will be further described below in combination with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present application, and do not limit the present application.

[0025] The preferred embodiments of the present application will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application, and are not intended to limit the protection scope of the present application.

[0026] It should be noted that in the description of the present application, the terms indicating the direction or positional relationship of "upper", "lower", "left", "right", "inner", "outer" and the like are based on the direction or positional relationship shown in the drawings, which is only for the convenience of description, and does not indicate or imply that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0027] Please refer to Figure 1 As shown in the figure, it is a step flow chart of the preparation method of high-purity quartz sand for quartz glass material according to the embodiment of the present application.

[0028] The preparation method of high-purity quartz sand for quartz glass material according to the embodiment of the present application comprises: Step S1, place the quartz sand raw material containing surface adsorbed impurities in a tube furnace, and simultaneously introduce an oxygen-containing gas into the tube furnace to perform an oxidation decarburization treatment, to obtain decarburized quartz sand; Step S2, place the decarburized quartz sand in an atmosphere containing water vapor to perform a hydroxyl removal treatment, to obtain decarboxylated quartz sand; Step S3, perform an interfacial activation treatment on the decarboxylated quartz sand, use an infrared thermal imager to obtain a temperature distribution image of the surface of the decarboxylated quartz sand, and calculate the temperature relative standard deviation value of a plurality of pixel points in a preset region of the temperature distribution image to determine whether the interfacial activation treatment is qualified; Step S4, in response to the interfacial activation treatment being qualified, place the decarboxylated quartz sand in a reducing atmosphere to perform a chlorine impurity removal treatment to obtain decchlorinated quartz sand; Step S5, cool and passivate the surface of the decchlorinated quartz sand to obtain high-purity quartz sand.

[0029] Specifically, the present application aims at carbon impurities, through controllable low-temperature oxidation treatment, without causing sintering of quartz sand particles, the surface and deep adsorbed organic carbon and amorphous carbon are completely converted into gas for removal, eliminating the root cause of bubble and heterogeneous nucleation center formed by carbon oxidation or pyrolysis gas during high-temperature melting, for hydroxyl impurities, using a specific partial pressure of water vapor atmosphere, promoting the migration and condensation reaction of firmly combined hydroxyl in the quartz network, realizing deep dehydroxy, so as to ensure that the obtained quartz glass has extremely high light transmittance in the deep ultraviolet band, for chlorine impurities, using a mild reducing atmosphere for directional removal, not only removes chlorine in various forms, but also avoids the risk of corrosion of equipment or formation of HCl bubbles and color center defects by chlorine volatilization at high temperature.

[0030] Specifically, the quartz sand raw material containing surface-adsorbed impurities is preferably quartz sand after preliminary purification by conventional processes such as mechanical crushing, physical sorting, and chemical acid leaching, and the content of silicon dioxide is usually not less than 99.9%, and the main associated impurities have been basically removed, but the surface is adsorbed or residual with impurities such as carbon, hydroxyl, chlorine and the like due to the previous treatment.

[0031] Specifically, the oxygen-containing gas is a mixture of oxygen and nitrogen, and the volume fraction of oxygen is 5% to 20%.

[0032] Specifically, the temperature of the carbon oxidation treatment is 500℃ to 800℃, and the time length of the carbon oxidation treatment is 1 to 4 hours.

[0033] In the embodiment of the present application, the tube furnace is a same high-temperature tube furnace which is modified, and a sapphire infrared window is installed on the side wall of the furnace body, with a diameter of 50 mm, and a wind cooling sleeve is arranged outside the window. A middle wave infrared thermal imager is arranged, with a response wave band of 3-5 µm and a temperature measurement range of 300℃ to 2000℃, and the light axis of the thermal imager is perpendicular to the surface of the sample through a support, and the atmosphere is switched through inert gas purging between steps, so that continuous or intermittent production is realized, which is simple to operate and can prevent pollution during material transfer, wherein the inert gas is nitrogen or argon.

[0034] Specifically, the oxygen-rich atmosphere of 5% to 20% provides sufficient but not excessive oxidant, which ensures that the carbon can be continuously and stably oxidized into CO or CO2 gas, and avoids the deflagration phenomenon caused by excessive local oxygen concentration and excessively violent reaction, which is easy to cause the surface of the quartz particles to be instantaneously overheated and locally sintered, and instead wraps the unreacted deep carbon, and the low oxygen concentration causes slow and incomplete carbon removal, and the excessively high oxygen concentration may cause excessive local sintering on the surface of the quartz sand, and instead wraps the internal impurities, and the quartz sand particles have not been significantly sintered and densified in the temperature window of 500℃ to 800℃, and the rich pore and microcrack structure is maintained, which provides a smooth channel for the diffusion of oxygen into the particle interior and the escape of reaction gas products to the outside, realizes the deep oxidation of the bulk carbon impurities, effectively activates the C-O reaction, and enables various carbon to be fully converted and removed within 1-4 hours, and the treatment efficiency and thoroughness of the carbon impurities are considered.

[0035] Specifically, the atmosphere containing water vapor is obtained by saturating the inert carrier gas with a constant-temperature hot water saturator, and the water vapor partial pressure is 30 to 60 kPa.

[0036] Specifically, the temperature of the hydroxyl removal treatment is 800℃ to 1000℃, and the time length of the hydroxyl removal treatment is 2 to 6 hours.

[0037] In the embodiment of the present application, water vapor in the water vapor partial pressure range can effectively catalyze the breaking and recombination of Si-OH bonds, promote deep dehydration, and avoid excessive water from causing hydrolysis of quartz sand.

[0038] Specifically, by accurately controlling the water vapor partial pressure in the range of 30-60 kPa, the present application can reversibly break the Si-O-Si bonds in the quartz network at high temperatures to generate migratable Si-OH, thereby activating and accelerating the diffusion process of internal deeply buried hydroxyl groups to the particle surface. These hydroxyl groups meet and condense on the particle surface to generate water molecules, which are rapidly carried away from the reaction zone by the flowing inert gas stream, driving the dehydration reaction to continuously proceed to the right, and realizing deep dehydroxylation. The treatment temperature window is 800-1000℃, which ensures the reaction rate and avoids sintering of the particles to close the diffusion channels due to excessively high temperature, or reaction stagnation due to excessively low temperature. The sufficient reaction time of 2-6 hours ensures the complete performance of the catalysis-migration-condensation process, avoids the problem of "locking" hydroxyl groups inside due to premature densification of the surface, and realizes a dehydroxylation depth and uniformity far exceeding conventional methods.

[0039] Please refer to Figure 2 The step flow chart for determining whether the interfacial activation treatment is qualified or not is shown in the figure.

[0040] Specifically, the process of determining whether the interfacial activation treatment of the dehydroxylated quartz sand is qualified or not by acquiring the temperature distribution image of the surface of the dehydroxylated quartz sand using an infrared thermal imager and calculating the temperature relative standard deviation value of a plurality of measurement points in a preset area of the temperature distribution image includes, starting the cooling program and the holding program of the interfacial activation treatment, and continuously collecting the infrared thermal image of the surface of the dehydroxylated quartz sand at a preset collection frequency through the infrared thermal imager; calculating the temperature average value and the temperature standard deviation of a plurality of measurement points in a preset area of the infrared thermal image to calculate the temperature relative standard deviation value, and drawing a temperature curve of the temperature relative standard deviation value changing with time; based on the temperature curve, the temperature relative standard deviation value reached after entering the holding program for a preset time; comparing the temperature relative standard deviation value with the interval of the preset temperature relative standard deviation value; if the temperature relative standard deviation value is located in the interval of the preset temperature relative standard deviation value, it is determined that the interfacial activation treatment is qualified; if the temperature relative standard deviation value deviates from the interval of the preset temperature relative standard deviation value, it is determined that the interfacial activation treatment is unqualified.

[0041] In the embodiment of the present application, the preset temperature relative standard deviation value interval has a value range of [1.8%, 4.0%], the preset time length has a value range of [5 minutes, 30 minutes], preferably 10 minutes, and the preset acquisition frequency has a value range of [0.5 Hz, 5 Hz], preferably 1 Hz, but the above values are not limited thereto, and the values can be adjusted according to actual needs by those skilled in the art.

[0042] In the embodiment of the present application, the cooling procedure is that the dehydroxy quartz sand is cooled from the dehydroxy treatment temperature of 800-1000 DEG C to 600-800 DEG C at a cooling rate of 50 DEG C / min under the protection of inert atmosphere.

[0043] In the embodiment of the present application, the holding procedure is that after reaching the activation treatment temperature, the holding is performed for 30-180 minutes under the inert atmosphere to complete the full relaxation of thermal stress and the stabilization of the subsurface micro defect structure.

[0044] Specifically, the present application introduces controllable thermal stress on the surface of quartz sand through programmed cooling, thereby inducing the formation of microcrack network and lattice distortion, increasing the active specific surface area of the subsurface and creating rich diffusion short paths, so that the reducing hydrogen can diffuse more quickly and deeply to the reaction interface with chlorine impurities through these micro defect channels, and the volatile products generated by the reaction can also efficiently escape along the same path, avoiding the problem of being wrapped, optimizing the mass transfer path, and solving the incomplete removal of chlorine impurities.

[0045] Please refer to Figure 3 Fig. 3 is a logic judgment diagram for determining and adjusting the time length of chlorine impurity removal treatment according to the present application.

[0046] Specifically, in response to the unqualified interface activation treatment, the relative deviation value of the temperature relative standard deviation value and the middle value of the preset temperature relative standard deviation value interval is calculated, and the process of adjusting the time length of the chlorine impurity removal treatment comprises, If the relative deviation value is greater than zero, the chlorine impurity removal time length is determined to be reduced; If the relative deviation value is less than zero, the chlorine impurity removal time length is determined to be extended.

[0047] In the embodiment of the present application, the calculation process of the relative deviation value is that the temperature relative standard deviation value and the middle value of the preset temperature relative standard deviation value interval are obtained, the difference between the temperature relative standard deviation value and the middle value is calculated, and the difference is divided by the middle value to obtain the relative deviation value.

[0048] In the embodiment of the present application, the reduced chlorine impurity removal time length is determined by the product of the chlorine impurity removal time length and the first compensation factor, and the prolonged chlorine impurity removal time length is determined by the product of the chlorine impurity removal time length and the second compensation factor, wherein the first compensation factor is 1-time compensation coefficient*absolute value of relative deviation value, and the second compensation factor is 1+time compensation coefficient*absolute value of relative deviation value.

[0049] In the embodiment of the present application, the time compensation coefficient is preferably set to 0.5, but the above value is not limited thereto, and the skilled person in the art can also adjust the value according to actual needs.

[0050] In the embodiment of the present application, if the relative deviation value is equal to zero, it is determined that the chlorine impurity removal time length is unchanged.

[0051] In the embodiment of the present application, the relative deviation value greater than zero determines that the activation is excessive, which can form too many diffusion channels, and if hydrogen is still introduced for a long time, it is easy to excessively reduce the quartz network or induce a deep metal impurity side reaction, so the chlorine impurity removal time length needs to be reduced. The relative deviation value less than zero determines that the activation is insufficient, so the diffusion and reaction interface is limited, and the chlorine impurity is difficult to remove completely under the standard time length, so the chlorine impurity removal time length needs to be prolonged.

[0052] Specifically, the reducing atmosphere is a mixed gas of hydrogen and argon, wherein the volume fraction of hydrogen is 2% to 5%.

[0053] Specifically, the temperature of the chlorine impurity removal treatment is 1000°C to 1200°C, and the time length of the chlorine impurity removal treatment is 1 to 3 hours.

[0054] Specifically, the present application provides a strong reducing atmosphere by using H2 / Ar mixed gas with a hydrogen volume fraction of 2% to 5%, effectively breaks the Si-Cl chemical bonds on the surface and near the surface of quartz, and converts them into volatile HCl gas for complete removal, avoids unnecessary reduction damage to the main body of the quartz silicon oxygen network caused by excessive hydrogen, or induces uncontrollable reduction side reactions of deep metal impurities. The chlorine impurity removal treatment temperature of 1000 to 1200°C provides sufficient reaction kinetics rate, so that the chlorine impurity can diffuse and react sufficiently, and the time length of 1 to 3 hours balances the reaction completeness and production efficiency, and is performed after deep dehydroxylation, which ensures the cleanliness of the reaction interface and avoids the generation of water by the reaction of residual hydroxyl and hydrogen to cause secondary pollution.

[0055] Please refer to Figure 4 As shown in the step flow chart of the cooling and surface passivation treatment of the embodiment of the present application.

[0056] Specifically, the process of cooling and surface passivation treatment of the dechlorinated quartz sand to obtain high-purity quartz sand comprises, Based on the end of the length of the chlorine impurity removal treatment, the inert gas atmosphere is switched to cool the temperature of the dechlorinated quartz sand to a preset passivation temperature at a preset first cooling rate; When the temperature reaches the preset passivation temperature, the cooling is stopped and a preset passivation duration is maintained; Based on a preset second cooling rate, the dechlorinated quartz sand is cooled to a preset safety temperature to obtain high-purity quartz sand.

[0057] In the embodiment of the present application, the preset first cooling rate is in the range of [10℃ / min, 50℃ / min], preferably set to 20℃ / min, the preset passivation temperature is in the range of [200℃, 400℃], preferably set to 300℃, the preset passivation duration is in the range of [30 minutes, 120 minutes], preferably set to 60 minutes, the preset second cooling rate is in the range of [5℃ / min, 30℃ / min], preferably set to 10℃ / min, and the preset safety temperature is in the range of [25℃, 150℃], preferably set to 80℃, but the above values are not limited thereto, and a person skilled in the art can adjust the values according to actual needs.

[0058] In the embodiment of the present application, through the 20-400℃ constant temperature passivation treatment under the protection of inert atmosphere, energy and time are provided for the high-activity surface of the dechlorinated quartz sand, so that the surface atoms and metastable structures of the dechlorinated quartz sand are heat relaxed and rearranged into a more stable silicon-oxygen network, self-passivation is realized, the active sites such as dangling bonds on the surface are eliminated, and the tendency of re-chemical adsorption of water molecules and hydroxyl groups during subsequent cooling and exposure to the environment is reduced. The cooling process is completed in an inert atmosphere, which isolates the main pollution source.

[0059] In the embodiment of the present application, the raw quartz sand is a surface adsorbed impurity containing quartz sand raw material with a silicon dioxide content of 99.92% after crushing, grinding to 100-200 mesh, flotation and hydrochloric acid and hydrofluoric acid leaching of local vein quartz. The carbon content is 85 ppm, the hydroxyl content is 150 ppm, and the chlorine content is 35 ppm.

[0060] Example 1: (1) Take 100g of surface adsorbed impurity containing quartz sand raw material, lay it in a corundum crucible, put it into a tube furnace, pass a mixed gas composed of 10% by volume of oxygen and 90% of argon at a flow rate of 200mL / min, heat to 650℃ at a rate of 5℃ / min, and keep the temperature for 2 hours for carbon removal by oxidation to obtain de-carbonized quartz sand.

[0061] (2) Under the protection of argon, the furnace temperature is raised to 900°C, and the wet argon saturated by a 80°C water bath is switched to be introduced, with water vapor partial pressure of 47 kPa, and the hydroxyl removal treatment is carried out for 4 hours to obtain the dehydroxyl quartz sand.

[0062] (3) The dehydroxyl quartz sand is subjected to interfacial activation treatment, under the protection of inert atmosphere, the temperature is programmed to decrease from 900°C to 700°C at a cooling rate of 50°C / min, and then the temperature is kept for 60 minutes. The surface thermal image is collected by an infrared thermal imager at a frequency of 1 Hz, the relative standard deviation of temperature is calculated, and it is confirmed that it is located in the preset interval [1.8%, 4.0%], and it is determined that the interfacial activation treatment is qualified.

[0063] (4) In response to the qualified interfacial activation treatment, the furnace temperature is raised to 1100°C, a mixed gas composed of 3% hydrogen and 97% argon by volume fraction is introduced, and the chlorine impurity removal treatment is carried out for 2 hours to obtain the dechlorinated quartz sand.

[0064] (5) The pure argon atmosphere is switched, the temperature is decreased to 300°C at a cooling rate of 20°C / min, the temperature is kept for 60 minutes, and then the temperature is cooled to 80°C at a rate of 10°C / min to obtain the first quartz sand.

[0065] Example 2: (1) 100 g of quartz sand raw material containing surface adsorbed impurities is taken, is laid in a corundum crucible, is put into a tube furnace, a mixed gas composed of 15% oxygen and 85% argon by volume fraction is introduced at a flow rate of 200 mL / min, is raised to 700°C at a rate of 5°C / min, is kept for 1.5 hours for carbon removal treatment by oxidation to obtain the de-carbonized quartz sand.

[0066] (2) Under the protection of argon, the furnace temperature is raised to 850°C, and the wet argon saturated by a 75°C water bath is switched to be introduced, with water vapor partial pressure of 38 kPa, and the hydroxyl removal treatment is carried out for 5 hours to obtain the dehydroxyl quartz sand.

[0067] (3) Under the protection of inert atmosphere, the temperature is programmed to decrease from 850°C to 650°C at a cooling rate of 50°C / min, and then the temperature is kept for 90 minutes. The surface thermal image is collected by an infrared thermal imager at a frequency of 1 Hz, the relative standard deviation of temperature is calculated, and it is confirmed that it is located in the preset interval [1.8%, 4.0%], and it is determined that the interfacial activation treatment is qualified.

[0068] (4) In response to the qualified interfacial activation treatment, the furnace temperature is raised to 1050°C, a mixed gas composed of 4% hydrogen and 96% argon by volume fraction is introduced, and the chlorine impurity removal treatment is carried out for 2.5 hours to obtain the dechlorinated quartz sand.

[0069] (5) Switch to pure argon atmosphere, reduce the temperature to 300°C at a rate of 20°C / min, keep for 60 minutes, then cool to 80°C at a rate of 10°C / min, to obtain the second quartz sand.

[0070] Example 3: (1) Take 100g of quartz sand raw material containing surface adsorbed impurities, lay it flat in a corundum crucible, put it into a tube furnace, pass a mixed gas composed of 5% by volume of oxygen and 95% of argon at a flow rate of 200 mL / min, heat to 550°C at a rate of 5°C / min, keep for 3 hours for carbon removal treatment by oxidation, to obtain decarburized quartz sand.

[0071] (2) Under argon protection, raise the furnace temperature to 950°C, switch to pass wet argon saturated by a 85°C water bath, the water vapor partial pressure is 58kPa, keep for 3 hours for hydroxyl removal treatment, to obtain dehydroxylated quartz sand.

[0072] (3) Under inert atmosphere protection, program reduce the temperature from 950°C to 750°C at a rate of 50°C / min, then keep for 120 minutes. Use an infrared thermal imager to collect surface thermal images at a frequency of 1 Hz, calculate the temperature relative standard deviation value, confirm that it is within the preset interval [1.8%, 4.0%], and determine that the interface activation treatment is qualified.

[0073] (4) In response to the qualified interface activation treatment, raise the furnace temperature to 1150°C, pass a mixed gas composed of 2.5% by volume of hydrogen and 97.5% of argon, keep for 1.5 hours for chlorine impurity removal treatment, to obtain dechlorinated quartz sand.

[0074] (5) Switch to pure argon atmosphere, reduce the temperature to 300°C at a rate of 20°C / min, keep for 60 minutes, then cool to 80°C at a rate of 10°C / min, to obtain the third quartz sand.

[0075] Comparative Example 1 (1) Take 100g of quartz sand raw material containing surface adsorbed impurities, lay it flat in a corundum crucible, put it into a tube furnace, pass a mixed gas composed of 10% by volume of oxygen and 90% of argon at a flow rate of 200 mL / min, heat to 650°C at a rate of 5°C / min, keep for 2 hours for carbon removal treatment by oxidation, to obtain decarburized quartz sand.

[0076] (2) Omit the hydroxyl removal and interface activation treatment steps, directly perform chlorine impurity removal treatment, under argon protection, raise the furnace temperature to 1100°C, pass a mixed gas composed of 3% by volume of hydrogen and 97% of argon, keep for 2 hours.

[0077] (3) Omit the cooling and surface passivation treatment steps, directly cool to room temperature under argon protection, to obtain the first comparative quartz sand.

[0078] Comparative Example 2 (1) Take 100 g of quartz sand raw material containing surface-adsorbed impurities, lay it flat in a corundum crucible, and place it in a tube furnace. Pass a mixed gas composed of 10% oxygen and 90% argon by volume at a flow rate of 200 mL / min, and raise the temperature to 650°C at a rate of 5°C / min. Perform oxidation decarburization treatment for 2 hours, and obtain decarburized quartz sand.

[0079] (2) Adjust the step sequence to perform chlorine impurity removal treatment first. Raise the furnace temperature to 1100°C under argon protection, pass a mixed gas composed of 3% hydrogen and 97% argon by volume, and maintain the temperature for 2 hours to obtain chlorine-removed quartz sand.

[0080] (3) Switch to dry argon purging, lower the furnace temperature to 900°C, pass wet argon saturated with a 80°C water bath, and maintain the temperature for 4 hours with a water vapor partial pressure of 47 kPa.

[0081] (4) Omit the interface activation treatment and cooling passivation steps, and directly cool to room temperature under inert atmosphere to obtain the second comparative quartz sand.

[0082] Comparative Example 3 (1) Take 100 g of quartz sand raw material containing surface-adsorbed impurities, lay it flat in a corundum crucible, and place it in a tube furnace.

[0083] (2) Use the traditional enhanced chlorination process, pass a mixed gas composed of 5% chlorine and 95% argon by volume into the furnace, with a total gas flow rate of 200 mL / min, and calcine at 1050°C for 2 hours.

[0084] (3) Omit the oxidation decarburization, hydroxyl removal, interface activation, and cooling passivation steps, and directly cool to room temperature under inert gas protection to obtain the third comparative quartz sand.

[0085] Perform elemental analysis on Examples 1-3 and Comparative Examples 1-3. Measure the carbon content using a high-frequency infrared carbon and sulfur analyzer; measure the hydroxyl content using a Fourier transform infrared spectrometer according to the absorption peak at 3600 cm -1 ; and measure the chlorine content using an ion chromatograph.

[0086] Take 20 g of the first quartz sand, the second quartz sand, the third quartz sand, the first comparative quartz sand, the second comparative quartz sand, and the third comparative quartz sand, respectively, and draw them into transparent quartz glass rods with a length of about 10 mm and a diameter of about 10 mm on a hydrogen-oxygen flame melting machine. Place them under an optical microscope and count the number of bubbles with a diameter greater than 50 μm.

[0087] Table 1 Performance Test Results

[0088] In the embodiments of the present application, examples 1-3 use oxidative decarburization, hydroxyl removal, interface activation, chlorine impurity removal, and cooling passivation treatment. The results show that the carbon, hydroxyl, and chlorine contents are significantly reduced, and the purity of silicon dioxide is increased to more than 99.996%. More importantly, the number of bubbles with a diameter greater than 50 μm in the quartz glass melted therefrom is less than 3 per cm3, indicating that under the combined action of the optimized mass transfer path of interface activation and the stable surface structure of cooling passivation, the surface adsorbed impurities are efficiently and completely removed, and the formation of bubbles is inhibited from the source.

[0089] In the embodiments of the present application, comparative example 1 omits the hydroxyl removal and interface activation steps after oxidative decarburization and directly performs chlorine impurity removal. The results show that the hydroxyl content is as high as 115 ppm, and the number of bubbles is more than 60 per cm3, which confirms that the incomplete reaction of chlorine impurities and the difficulty of gas product escape caused by the non-removal of hydroxyl and the non-activation of interface highlight the necessity of the hydroxyl removal and interface activation steps.

[0090] In the embodiments of the present application, comparative example 2 adjusts the step sequence, first performs chlorine impurity removal and then performs hydroxyl removal, and omits interface activation and cooling passivation. It is found that the chlorine content is relatively high (22 ppm), and the number of bubbles is 18 per cm3. This shows that if the reducing chlorine treatment is performed first, the reaction interface is not activated, the diffusion channel is insufficient, and the effect of hydroxyl removal on the partially sintered surface is limited, further verifying the synergistic advantages of the step sequence and interface activation of the present application.

[0091] In the embodiments of the present application, comparative example 3 uses the traditional strengthening chlorination process, and does not involve the steps of oxidative decarburization, hydroxyl removal, interface activation, and cooling passivation. The carbon, hydroxyl, and chlorine contents are close to the raw material level, and the number of bubbles is more than 110 per cm3, which shows that pure chlorination reduction treatment cannot effectively remove the surface adsorbed non-metallic impurities, and even the surface sintering caused by high temperature chlorination may wrap the impurities inside.

[0092] The technical solutions of the present application have been described in combination with the preferred embodiments shown in the drawings, but those skilled in the art can easily understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without deviating from the principles of the present application, and the technical solutions after these changes or replacements will fall within the protection scope of the present application.

Claims

1. A method for producing high purity silica sand for quartz glass material, characterized by, The application relates to a high-purity quartz sand production method. The quartz sand raw material containing surface-adsorbed impurities is placed in a tube furnace, and an oxygen-containing gas is synchronously introduced into the tube furnace to perform oxidation decarburization treatment, so as to obtain decarburized quartz sand; The decarburized quartz sand is placed in a water vapor-containing atmosphere to perform hydroxyl removal treatment, so as to obtain hydroxyl-removed quartz sand; Interface activation treatment is performed on the hydroxyl-removed quartz sand, an infrared thermal imager is used to obtain a temperature distribution image of the surface of the hydroxyl-removed quartz sand, and the relative standard deviation of the temperatures of a plurality of pixel points in a preset region of the temperature distribution image is calculated to determine whether the interface activation treatment is qualified; In response to the fact that the interface activation treatment is qualified, the hydroxyl-removed quartz sand is placed in a reducing atmosphere to perform chlorine impurity removal treatment, so as to obtain chlorine-removed quartz sand; The chlorine-removed quartz sand is subjected to cooling and surface passivation treatment, so as to obtain high-purity quartz sand.

2. The method of claim 1, wherein the high purity silica sand for quartz glass material is prepared by the steps of: The oxygen-containing gas is a mixture of oxygen and nitrogen, the volume fraction of oxygen is 5% to 20%, the temperature of the oxidation decarburization treatment is 500 DEG C to 800 DEG C, and the time length of the oxidation decarburization treatment is 1 to 4 hours. ​ 3. The method of claim 1, wherein the high purity silica sand for quartz glass material is prepared by the steps of: The temperature of the hydroxyl removal treatment is 800 DEG C to 1000 DEG C, and the time length of the hydroxyl removal treatment is 2 to 6 hours. ​ 4. The method of claim 1, wherein the high purity silica sand for quartz glass material is prepared by the steps of: The process of determining whether the interface activation treatment is qualified comprises the following steps: ​ A cooling program and a holding program of the interface activation treatment are started, and an infrared thermal imager is used to continuously collect infrared thermal images of the surface of the hydroxyl-removed quartz sand at a preset collection frequency; The average temperature and the standard deviation of the temperatures of a plurality of measuring points in a preset region of the infrared thermal images are calculated to calculate the relative standard deviation of the temperatures, and a temperature curve of the relative standard deviation of the temperatures changing with time is drawn; The relative standard deviation of the temperatures reaches a preset time after the holding program is entered based on the temperature curve; Based on the fact that the relative standard deviation of the temperatures is located in a preset interval of the relative standard deviation of the temperatures, it is determined that the interface activation treatment is qualified.

5. The method of claim 4, wherein the high purity silica sand for quartz glass material is prepared by the steps of: The unqualified interface activation treatment is determined based on the fact that the relative standard deviation of the temperatures deviates from the interval of the relative standard deviation of the temperatures. ​ 6. The method of claim 5, wherein the high purity silica sand for quartz glass material is prepared by the steps of: In response to the fact that the interface activation treatment is unqualified, a relative deviation value of the relative standard deviation of the temperatures and a middle value of the interval of the relative standard deviation of the temperatures is calculated, and the time length of the chlorine impurity removal treatment is adjusted. ​ 7. The method of claim 6, wherein the high purity silica sand for quartz glass material is prepared by the steps of: Based on the fact that the relative deviation value is greater than zero, it is determined that the chlorine impurity removal time length is a product of the chlorine impurity removal time length and a first compensation factor, wherein the first compensation factor is determined by subtracting a product of a time compensation coefficient and an absolute value of the relative deviation value from 1. ​ 8. The method of claim 7, wherein the high purity silica sand for quartz glass material is prepared by the steps of: Based on the fact that the relative deviation value is less than zero, it is determined that the chlorine impurity removal time length is a product of the chlorine impurity removal time length and a second compensation factor, wherein the second compensation factor is determined by adding a product of the time compensation coefficient and an absolute value of the relative deviation value to 1. ​ 9. The method of claim 1, wherein the high purity silica sand for quartz glass material is prepared by the steps of: The reducing atmosphere is a mixture of hydrogen and argon, the volume fraction of hydrogen is 2% to 5%, the temperature of the chlorine impurity removal treatment is 1000 DEG C to 1200 DEG C, and the time length of the chlorine impurity removal is 1 to 3 hours. ​ 10. The method of claim 1, wherein the high purity silica sand for quartz glass material is prepared by the steps of: The process of the cooling and surface passivation treatment comprises the following steps: ​ Switching the inert gas atmosphere based on the end of the chlorine impurity removal treatment time length, and cooling the temperature of the dechlorinated quartz sand to a preset passivation temperature at a preset first cooling rate; When the temperature reaches the preset passivation temperature, stop cooling and maintain for a preset passivation time length; Cooling the dechlorinated quartz sand to a preset safety temperature based on a preset second cooling rate to obtain high-purity quartz sand.

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