Preparation method of quartz sand and vacuum sintering device and method

Abstract

The invention belongs to the technical field of quartz sand preparation, and particularly relates to a quartz sand preparation method and a vacuum sintering device and method. The preparation method provided by the invention takes silicon dioxide as a raw material, mainly relates to a dehydroxylation reaction and calcination, is simple in steps, does not need a large amount of equipment, prepares the quartz sand in a vacuum environment, is free of pollution sources, and can effectively control the quality of the quartz sand. By adopting the preparation method, the prepared quartz sand is high in purity, the purity is 99.998% or above, the hydroxyl content is low, the granularity is large, and the quartz sand can be used as a raw material of inner-layer sand of a photovoltaic or semiconductor quartz crucible. The vacuum sintering device is low in cost, easy and convenient to operate and good in stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of quartz sand preparation, and particularly relates to a preparation method of quartz sand, a vacuum sintering device and a method. Background Art

[0002] At present, the preparation methods of quartz sand mainly include low-temperature freeze-thaw - microwave assisted method, sol-gel method, etc. However, these methods require multiple processes and various equipment to remove impurities and dehydroxylate. Any minor change in a parameter may affect the quality and performance of the product. For example, the action time of microwave, the temperature and time of freeze-thaw, etc. It requires a high level of technical skills and operating experience of the operators, and also increases the difficulty and cost of large-scale industrial production. Moreover, due to the deficiencies of the equipment used in these methods in terms of precision, reliability and stability, the temperature control or pressure control is not precise enough, which affects the removal of impurities and the dehydroxylation during the preparation process of quartz sand, and the product purity cannot reach 99%. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method of quartz sand, a vacuum sintering device and a method. The preparation method provided by the present invention has simple steps, does not require a large number of equipment, and the product purity is above 99.998%.

[0004] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a preparation method of quartz sand, comprising the following steps:

[0006] Under vacuum conditions, silica is sequentially heated to the temperature of the first dehydroxylation reaction, the first dehydroxylation reaction, the second heating to the calcination temperature, calcination, cooling to the temperature of the second dehydroxylation reaction and the second dehydroxylation reaction to obtain the quartz sand; the purity of the silica is above 99.99985%; the temperature of the first dehydroxylation reaction is 1000 - 1300 °C; the vacuum degree of the vacuum conditions is not higher than 0.01 Pa.

[0007] Preferably, the silica is amorphous silica; the particle size of the silica is 0.1 - 0.3 mm.

[0008] Preferably, the heating rate of the first heating is not higher than 100 °C / h.

[0009] Preferably, the heat preservation time of the first dehydroxylation reaction is 6 - 12 h.

[0010] Preferably, the heating rate of the second heating is not higher than 200 °C / h; the second heating is carried out under stirring conditions.

[0011] Preferably, the calcination is carried out under the condition of frying; the temperature of the calcination is 1620-1720 °C.

[0012] Preferably, the temperature reduction is natural temperature reduction.

[0013] Preferably, the temperature of the second dehydroxylation reaction is 1000-1300 °C, and the heat preservation time is 2-4 h.

[0014] The present invention also provides a vacuum sintering device for the preparation method of quartz sand described in the above scheme, including a sealing system; a heating system for heating the sealing system; a vacuum system communicated with the sealing system;

[0015] The sealing system includes a chamber; a cover covering the chamber, a hole is provided at the top of the cover; a guide rod extending into the chamber through the hole; a container connected to one end of the guide rod extending into the chamber.

[0016] The present invention also provides a method for preparing quartz sand by using the vacuum sintering device described in the above scheme, including the following steps:

[0017] Fill silicon dioxide with a purity of more than 99.99985% into the container and send it to the chamber of the sealing system. Start the vacuum system to evacuate the chamber to no higher than 0.01 Pa. Use the heating system to first heat up to the temperature of the first dehydroxylation reaction to carry out the first dehydroxylation reaction, and then second heat up to the temperature of the calcination to carry out the calcination. After the calcination, cool the chamber to the temperature of the second dehydroxylation reaction to carry out the second dehydroxylation reaction to obtain the quartz sand.

[0018] The present invention provides a method for preparing quartz sand. The preparation method provided by the present invention uses silicon dioxide as a raw material, mainly involving a dehydroxylation reaction and calcination. The steps are simple, without the need for a large number of devices. Quartz sand is prepared in a vacuum environment, without pollution sources, and the quality of the quartz sand can be effectively controlled. In a high-temperature vacuum state, a huge pressure difference will be formed inside and outside the gas-liquid inclusions, causing them to burst. At the same time, the gas-liquid inclusions in the quartz sand expand due to heat, and when the quartz sand lattice deforms, they rupture along with the change in the lattice volume, exposing the impurities inside the inclusions, and finally vaporizing and diffusing out under the influence of the internal and external concentration differences, so as to achieve the purpose of purifying the quartz sand. Compared with other methods, such as mechanical crushing method which is difficult to remove small gas-liquid inclusions, and acid-base differential corrosion method which cannot completely remove gas-liquid inclusions, etc., high-temperature treatment in a vacuum environment can more effectively remove the impurities in the gas-liquid inclusions and improve the purity of the quartz sand; in a vacuum environment, contact with oxygen, water vapor and other impurities in the air is avoided, reducing the possibility of impurities adsorbing on the surface of the quartz sand or reacting chemically with the quartz sand. At the same time, the vacuum environment helps to inhibit the volatilization and diffusion of some impurities and prevent them from re-entering the interior of the quartz sand. The high-temperature vacuum state is conducive to removing the hydroxyl groups in the quartz sand. The hydroxyl groups in quartz will affect the properties of quartz glass such as transparency, softening temperature, and viscosity. Removing hydroxyl groups is crucial for improving the quality of quartz sand.

[0019] The present invention adopts the above preparation method, and the prepared quartz sand has a high purity of more than 99.998%, a low hydroxyl content of less than 1 ppm, and a particle size of 0.1 - 0.3 mm, and can be used as a raw material for the inner layer sand of a photovoltaic or semiconductor quartz crucible.

[0020] The present invention also provides a vacuum sintering device for the preparation method of quartz sand described in the above solution. The vacuum sintering device provided by the present invention has a low cost, is easy to operate, and has good stability.

[0021] The present invention also provides a method for preparing quartz sand using the vacuum sintering device described in the above solution. The preparation method provided by the present invention can complete the preparation of quartz sand with a single device, avoiding product pollution, improving production efficiency, and being green and environmentally friendly. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the following-described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 It is a structural decomposition diagram of the vacuum sintering device provided by the present invention;

[0024] Figure 2 Schematic structural diagram after the vacuum sintering device provided by the present invention is closed;

[0025] Reference numerals: 1 is a draw bar, 2 is a cover, 3 is a container, 4 is a chamber, 5 is a heating chamber, 6 is a vacuum pipe, 7 is a vacuum pump, 8 is a hole, 10 is a sealing system, 20 is a heating system, 30 is a vacuum system, 51 is a heating component, 52 is a heat preservation component, 53 is a temperature control component. Specific embodiments

[0026] The present invention provides a method for preparing quartz sand, comprising the following steps:

[0027] Under vacuum conditions, silica is sequentially heated to the temperature of the first dehydroxylation reaction, subjected to the first dehydroxylation reaction, heated to the temperature of calcination for the second time, calcined, cooled to the temperature of the second dehydroxylation reaction, and subjected to the second dehydroxylation reaction to obtain the quartz sand.

[0028] In the present invention, under vacuum conditions, silica is heated to the temperature of the first dehydroxylation reaction and subjected to the first dehydroxylation reaction. In the present invention, the vacuum degree of the vacuum conditions is not higher than 0.01 Pa, and specifically can be 0.008 Pa, 0.006 Pa, 0.004 Pa or 0.002 Pa.

[0029] In the present invention, the silica can be amorphous silica; the amorphous silica can be prepared by chemical vapor deposition. The silica obtained by chemical vapor deposition has high original purity and good uniformity.

[0030] In the present invention, the particle size of the silica can be 0.1 - 0.3 mm, and specifically can be 0.15 mm, 0.20 mm, 0.24 mm or 0.27 mm. The present invention uses amorphous silica powder raw materials with uniform particle size and high purity. Impurities will affect the crystallization process of silica. For example, some impurities may hinder the formation of crystal nuclei, or enter the crystal lattice during crystal growth, affecting the crystal growth rate and final particle size. High-purity raw materials contribute to more regular crystal growth and more uniform particle size distribution.

[0031] In the present invention, the purity of the silica can be above 99.99985%, and specifically can be 99.99985%, 99.99988%, 99.9999% or 99.99995%.

[0032] In the present invention, before the first heating, the reaction system can also be preheated; the preheating can include heating preheating and heat preservation preheating in sequence. By preheating in the present invention, water vapor molecules in the sealing system 10 and the heating system 20 are removed.

[0033] In the present invention, the vacuum degree during heating-up preheating may not be higher than 0.01 Pa, specifically it may be 0.008 Pa, 0.006 Pa, 0.004 Pa or 0.002 Pa; the heating rate may not be higher than 200 °C / h, specifically it may be 180 °C / h, 150 °C / h, 120 °C / h, 90 °C / h, 50 °C / h or 20 °C / h; the starting temperature may be 0 °C.

[0034] In the present invention, the temperature during heat preservation preheating may not be higher than 800 °C, specifically it may be 700 °C, 600 °C, 500 °C, 400 °C, 300 °C, 200 °C or 100 °C; the vacuum degree may not be higher than 0.01 Pa, specifically it may be 0.008 Pa, 0.006 Pa, 0.004 Pa or 0.002 Pa.

[0035] In the present invention, the rate of the first heating-up may not be higher than 100 °C / h, specifically it may be 90 °C / h, 70 °C / h, 50 °C / h, 30 °C / h or 10 °C / h.

[0036] In the present invention, the temperature of the first dehydroxylation reaction may be 1000 - 1300 °C, specifically it may be 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C or 1280 °C; the vacuum degree may not be higher than 0.01 Pa, specifically it may be 0.008 Pa, 0.006 Pa, 0.004 Pa or 0.002 Pa; the heat preservation time may be 6 - 12 h, specifically it may be 7 h, 9 h or 11 h. Through the first dehydroxylation reaction in the present invention, the silica powder is fully dehydroxylated. During the dehydroxylation process, the vacuum degree of the system first rapidly rises to a certain critical value and then slowly decreases, and finally tends to be stable. According to the vacuum degree P1, it can be judged whether the dehydroxylation reaction is sufficient.

[0037] By adopting the above parameters, the slow heating rate and high-precision temperature control in the present invention are beneficial to the uniform growth of crystals; the appropriate heat preservation time allows the crystals to grow and develop moderately, and the particle size will gradually increase but will not agglomerate; the stable and relatively high vacuum degree can avoid the interference of external gases on the crystal growth process, affecting the nucleation and growth of crystals, resulting in uneven or abnormal crystal particle size.

[0038] After the first dehydroxylation reaction, the present invention continues to carry out the second heating-up to the calcination temperature and calcination under vacuum conditions. In the present invention, the rate of the second heating-up may not be higher than 200 °C / h, specifically it may be 180 °C / h, 150 °C / h, 120 °C / h, 90 °C / h, 50 °C / h or 20 °C / h; the second heating-up may be carried out under stirring conditions.

[0039] In the present invention, the calcination can be carried out under frying conditions; the temperature of the calcination can be 1620 - 1720 °C, specifically 1630 °C, 1640 °C, 1660 °C, 1680 °C or 1700 °C, the vacuum degree can be not higher than 0.01 Pa, specifically 0.008 Pa, 0.006 Pa, 0.004 Pa or 0.002 Pa, and the heat preservation time can be determined according to the dosage of silica; when the dosage of silica is 100 kg, the heat preservation time can be 1 - 3 h, specifically 1.5 h, 2 h or 2.5 h. Through calcination in the present invention, silica is converted into quartz sand, and with continuous frying of the raw materials until it is completely converted into quartz sand.

[0040] After the calcination, the present invention continues to cool down to the temperature of the second dehydroxylation reaction and carry out the second dehydroxylation reaction under vacuum conditions to obtain the quartz sand. In the present invention, the cooling can be natural cooling.

[0041] In the present invention, the temperature of the second dehydroxylation reaction can be 1000 - 1300 °C, specifically 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C or 1280 °C, the vacuum degree can be not higher than 0.01 Pa, specifically 0.008 Pa, 0.006 Pa, 0.004 Pa or 0.002 Pa, and the heat preservation time can be 2 - 4 h, specifically 2.5 h, 3 h or 3.5 h. Through the second dehydroxylation reaction in the present invention, the product of the first dehydroxylation reaction can stably exist, preventing the removed hydroxyl groups from re - combining with the quartz sand; meanwhile, some residual gas - liquid inclusions are further broken, releasing the hydroxyl groups therein and continuously promoting the dehydroxylation reaction.

[0042] In the present invention, after the second dehydroxylation reaction, it may further include cooling the obtained reaction system and then introducing a protective gas for storage.

[0043] In the present invention, the final temperature of the cooling can be room temperature; the protective gas can be nitrogen; the purity of the nitrogen can be above 99.9999999%.

[0044] The preparation method provided by the present invention has simple steps, mainly involves dehydroxylation reaction and calcination, the product quality can be effectively controlled; the sintering temperature is low, and the comprehensive production cost is relatively low; there is no pollution source in the vacuum environment, ensuring the product purity. Using the above - mentioned preparation method, the prepared quartz sand has high purity, low hydroxyl content, and the particle size is 0.1 - 0.3 mm.

[0045] The present invention also provides a vacuum sintering device for the preparation method of the quartz sand described in the above - mentioned scheme, including a sealing system 10; a heating system 20 for heating the sealing system 10; a vacuum system 30 communicated with the sealing system 10;

[0046] The sealing system 10 includes a chamber 4; a cover 2 covering the chamber 4, with a hole 8 provided at the top of the cover 2; a guide rod 1 extending into the chamber 4 through the hole 8; and a container 3 connected to the end of the guide rod 1 extending into the chamber 4.

[0047] The vacuum sintering device provided by the present invention includes a sealing system 10; the guide rod 1 can reciprocate up and down, and the moving speed can be regulated; the guide rod 1 can rotate around its own central axis, and the rotation speed can be regulated; the rotation speed of the guide rod 1 can be no greater than 5 rpm, specifically it can be 1 rpm or 3 rpm.

[0048] In the present invention, the material of the guide rod 1 is 316L, with a water-cooled structure and surface mirror polishing treatment. By adopting the above-mentioned rust-proof materials and surface treatment processes, the present invention can ensure that the silica powder is not contaminated during the dehydroxylation and calcination processes, does not affect the final purity of the quartz sand, and the product quality can be effectively guaranteed.

[0049] In the present invention, the cover 2 can reciprocate up and down, and the moving speed can be regulated; the cover 2 can rotate around its own central axis, and the rotation speed can be regulated; the central axis of the cover 2 can coincide with the central axis of the guide rod 1.

[0050] In the present invention, the diameter of the hole 8 can be the same as the diameter of the guide rod 1.

[0051] In the present invention, the material of the cover 2 is 316L, with a water-cooled structure and surface mirror polishing treatment. By adopting the above-mentioned rust-proof materials and surface treatment processes, the present invention can ensure that the silica powder is not contaminated during the dehydroxylation and calcination processes, does not affect the final purity of the quartz sand, and the product quality can be effectively guaranteed.

[0052] In the present invention, the container 3 and the guide rod 1 can move synchronously; the container 3 can reciprocate up and down with the guide rod 1, and the moving speed can be regulated; the container 3 can rotate around its own central axis with the guide rod 1, and the rotation speed can be regulated; the central axis of the container 3 can coincide with the central axis of the guide rod 1.

[0053] In the present invention, the material of the container 3 can be high-purity graphite; the ash content of the high-purity graphite can be ≤20 ppm, and the metal impurity content can be ≤0.5 ppm. By adopting the above-mentioned high-purity materials, the present invention can ensure that the silica powder is not contaminated during the dehydroxylation and calcination processes, does not affect the final purity of the quartz sand, and the product quality can be effectively guaranteed.

[0054] In the present invention, the central axis of the chamber 4 can coincide with the central axis of the guide rod 1; the chamber 4 can be hermetically connected to the cover 2 through a flange.

[0055] In the present invention, the material of the chamber 4 is 316L, with a water-cooled structure and surface mirror polishing treatment; the rust-proof material and surface treatment process can ensure that the silica powder is not contaminated during the dehydroxylation and calcination processes, without affecting the final purity of the quartz sand, and effectively guarantee the product quality.

[0056] The vacuum sintering device provided by the present invention includes a heating system 20; the heating system 20 can be a heating chamber 5; the central axis of the heating chamber 5 can coincide with the central axis of the lifting rod 1; the heating chamber 5 can be provided with a heating component 51; the heating chamber 5 can be provided with a heat preservation component 52; the heating chamber 5 can be provided with a temperature control component 53; the temperature range of the heating chamber 5 can be 0 to 1800 °C.

[0057] In the present invention, the material of the heating component 51 can be high-purity graphite; the ash content of the high-purity graphite can be ≤20 ppm, and the metal impurity content can be ≤0.5 ppm. By using the above high-purity materials in the present invention, it can be ensured that the silica powder is not contaminated during the dehydroxylation and calcination processes, without affecting the final purity of the quartz sand, and effectively guarantee the product quality.

[0058] The vacuum sintering device provided by the present invention includes a vacuum system 30; the vacuum system 30 can include a vacuum pump 7; the vacuum pump 7 can be connected to the chamber 4 through a vacuum pipeline 6. Through the vacuum system 30 of the present invention, the sealing system 10 is evacuated, so that the silica powder is in a vacuum environment.

[0059] The exploded structure of the vacuum sintering device provided by the present invention is as Figure 1 shown, including a sealing system 10, a heating chamber 5 (heating system 20) for heating the sealing system 10, a vacuum pump 7 (vacuum system 30) connected to the sealing system 10 through a vacuum pipeline 6. The sealing system 10 includes a chamber 4, a cover 2 covering the chamber 4. A hole 8 is provided at the top of the cover 2, a lifting rod 1 extending into the chamber 4 through the hole 8, and a container 3 connected to one end of the lifting rod 1 extending into the chamber 4. Among them, both the lifting rod 1 and the cover 2 can move up and down reciprocally along the central axis independently. As the lifting rod 1 descends, the container 3 first enters the interior of the chamber 4, and then the cover 2 contacts the chamber 4 and the cover 2 stops moving. At this time, the cover 2 and the chamber 4 form a sealed chamber; the lifting rod 1 and the container 3 continue to descend to a set position of the chamber 4 that externally wraps the heating chamber 5 and then stop. The lifting rod 1 starts to rotate and the raw materials can be evenly heated. The closed vacuum sintering device is as Figure 2 shown.

[0060] The present invention also provides a method for preparing quartz sand using the vacuum sintering device described in the above solution, including the following steps:

[0061] After filling the container 3 with silica having a purity of 99.99985% or more, it is sent to the chamber 4 of the sealing system 10. The vacuum system 30 is started to evacuate the chamber 4 to a pressure not higher than 0.01 Pa. The heating system 20 is used to raise the temperature to the temperature of the first dehydroxylation reaction for the first dehydroxylation reaction, and then raise the temperature to the calcination temperature for calcination. After the calcination, the temperature of the chamber 4 is lowered to the temperature of the second dehydroxylation reaction for the second dehydroxylation reaction to obtain the quartz sand.

[0062] In the present invention, the parameters and conditions of the method for preparing quartz sand using the vacuum sintering device described in the above solution can be the same as those of the method for preparing quartz sand described in the above solution, and will not be elaborated here.

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

[0064] Example 1

[0065] (1) 100 kg of silica powder with a particle size of 0.1 - 0.3 mm and a purity of 99.99985% is filled into the container 3 and sent to the heating chamber 5.

[0066] (2) Start the vacuum pump 7 to evacuate until the vacuum degree ≤ 0.01 Pa.

[0067] (3) Start heating the heating chamber 5 to raise the temperature from 0 °C to 800 °C. The heating rate at this stage is 200 °C / h, which is used to preheat the entire chamber 4 and remove water vapor molecules in the sealing system 10 and the heating system 20.

[0068] (4) Keep the temperature at 800 °C for 4 h to further preheat the entire chamber 4 and adjust the vacuum degree of the preheated chamber 4 to a stable state, with the vacuum degree ≤ 0.01 Pa.

[0069] (5) Raise the temperature to 1100 °C at a heating rate of 100 °C / h.

[0070] (6) Keep the temperature at 1100 °C for 12 h to fully dehydroxylate the silica powder.

[0071] (7) Stir the silica powder in the container 3 evenly, and at the same time raise the temperature to the calcination temperature of 1620 °C at a heating rate of 200 °C / h.

[0072] (8) Keep the temperature at 1620 °C for 3 hours.

[0073] (9) Lower the temperature to 1100 °C and keep it for 3 h.

[0074] (10) Stop heating, lower the temperature to room temperature, and introduce high-purity nitrogen to obtain low-hydroxyl high-purity quartz sand.

[0075] Example 2

[0076] (1) Charge 100 kg of silica powder with a particle size of 0.1 - 0.3 mm and a purity of 99.99985% into container 3 and send it to heating chamber 5.

[0077] (2) Start vacuum pump 7 to evacuate until the vacuum degree ≤ 0.01 Pa.

[0078] (3) Start heating chamber 5 to start heating and temperature rising, rising from 0 °C to 800 °C. The temperature rising rate at this stage is 200 °C / h, which is used to preheat the whole chamber 4 and remove water vapor molecules in sealing system 10 and heating system 20.

[0079] (4) Keep the temperature at 800 °C for 4 h to further preheat the whole chamber 4 and adjust the vacuum degree of the preheated chamber 4 to a stable state, with the vacuum degree ≤ 0.01 Pa.

[0080] (5) Raise the temperature to 1200 °C at a temperature rising rate of 100 °C / h.

[0081] (6) Keep the temperature at 1200 °C for 6 h to fully dehydroxylate the silica powder.

[0082] (7) Stir the silica powder in container 3 evenly while raising the temperature to the calcination temperature of 1620 °C at a temperature rising rate of 200 °C / h.

[0083] (8) Keep the temperature at 1620 °C for 2 hours.

[0084] (9) Lower the temperature to 1100 °C and keep it for 2 h.

[0085] (10) Stop heating, lower the temperature to room temperature, and introduce high-purity nitrogen to obtain low-hydroxyl high-purity quartz sand.

[0086] Example 3

[0087] (1) Charge 100 kg of silica powder with a particle size of 0.1 - 0.3 mm and a purity of 99.99985% into container 3 and send it to heating chamber 5.

[0088] (2) Start vacuum pump 7 to evacuate until the vacuum degree ≤ 0.01 Pa.

[0089] (3) Start heating chamber 5 to start heating and temperature rising, rising from 0 °C to 800 °C. The temperature rising rate at this stage is 200 °C / h, which is used to preheat the whole chamber 4 and remove water vapor molecules in sealing system 10 and heating system 20.

[0090] (4) Keep the temperature at 800 °C for 4 h to further preheat the whole chamber 4 and adjust the vacuum degree of the preheated chamber 4 to a stable state, with the vacuum degree ≤ 0.01 Pa.

[0091] (5) Heat up to 1200 °C at a heating rate of 50 °C / h.

[0092] (6) Keep the temperature at 1200 °C for 12 h to fully dehydrate the silica powder.

[0093] (7) Stir the silica powder in container 3 evenly while heating up to the calcination temperature of 1700 °C at a heating rate of 100 °C / h.

[0094] (8) Keep the temperature at 1700 °C for 4 hours.

[0095] (9) Cool down to 1100 °C and keep the temperature for 3 h.

[0096] (10) Stop heating, cool down to room temperature, and introduce high-purity nitrogen to obtain low-hydroxyl high-purity quartz sand.

[0097] Comparative Example 1

[0098] The preparation method of this comparative example is the same as that of Example 1, except that the temperature in step (6) is adjusted to 450 °C.

[0099] Comparative Example 2

[0100] The preparation method of this comparative example is the same as that of Example 1, except that the temperature in step (6) is adjusted to 1450 °C.

[0101] Comparative Example 3

[0102] The preparation method of this comparative example is the same as that of Example 1, except that the temperature in step (8) is adjusted to 1500 °C.

[0103] Comparative Example 4

[0104] The preparation method of this comparative example is the same as that of Example 1, except that the temperature in step (9) is adjusted to 200 °C.

[0105] Comparative Example 5

[0106] The preparation method of this comparative example is the same as that of Example 1, except that step (9) is omitted.

[0107] Comparative Example 6

[0108] The preparation method of this comparative example is the same as that of Example 1, except that the temperature in step (9) is adjusted to 450 °C.

[0109] Comparative Example 7

[0110] The preparation method of this comparative example is the same as that of Example 1, except that high-temperature resistant equipment is used and the vacuum degree is adjusted to 5 Pa.

[0111] Comparative Example 8

[0112] The preparation method of this comparative example is the same as that of Example 1, except that the heating rate in step (5) is adjusted to 400 °C / h.

[0113] Comparative Example 9

[0114] The preparation method of this comparative example is the same as that of Example 1, except that the heating rate in step (7) is adjusted to 400 °C / h.

[0115] Comparative Example 10

[0116] The preparation method of this comparative example is the same as that of Example 1, except that crystalline silica with a purity of 99.95%, a particle size of 0.1 - 0.3 mm, and a hydroxyl content of 1500 ppm is used.

[0117] Comparative Example 11

[0118] The preparation method of this comparative example is the same as that of Example 1, except that high-temperature resistant equipment is used, and steps (6), (8), and (9) are carried out under normal pressure conditions.

[0119] Test Example 1

[0120] The quartz sand of Example 1 and Comparative Examples 1 - 10 was subjected to purity detection by inductively coupled plasma mass spectrometry (ICP-MS) and hydroxyl content detection by Fourier transform infrared spectroscopy. The results are shown in Tables 1 and 2.

[0121] Table 1 Quartz sand parameters of Example 1

[0122]

[0123] Table 2 Quartz sand parameters of Comparative Examples 1 - 10

[0124]

[0125]

[0126] It can be seen from Tables 1 and 2 that the quartz sand prepared by the present invention has the advantages of high purity, low hydroxyl content, and large particle size, and is suitable for the preparation of equipment such as quartz crucibles; in Comparative Example 11, under normal pressure conditions, part of the quartz powder is still in an amorphous state and has not been completely converted into a crystalline state.

[0127] From the above examples, it can be seen that the preparation method provided by the present invention can prepare quartz sand with high purity and low hydroxyl content, with large particle size, and is suitable for the preparation of equipment such as quartz crucibles.

[0128] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all embodiments. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing quartz sand, characterized in that: The following steps are involved: Under vacuum conditions, the silicon dioxide is subjected to a first heating to a temperature for a first dehydroxylation reaction, a first dehydroxylation reaction, a second heating to a temperature for calcination, calcination, a cooling to a temperature for a second dehydroxylation reaction, and a second dehydroxylation reaction, to obtain the quartz sand; The purity of the silicon dioxide is above 99.99985%; the temperature of the first dehydroxylation reaction is 1000-1300° C., and the vacuum degree of the vacuum condition is not higher than 0.01 Pa.

2. The preparation method according to claim 1, characterized in that: The silicon dioxide is amorphous silicon dioxide; the particle size of the silicon dioxide is 0.1 to 0.3 mm.

3. The preparation method according to claim 1, characterized in that: The first heating rate is no higher than 100° C. / h.

4. The preparation method according to claim 1 or 3, characterized in that: The insulation time of the first dehydroxylation reaction is 6 to 12 hours.

5. The preparation method according to claim 1, characterized in that: The rate of the second temperature increase is no higher than 200° C. / h; and the second temperature increase is performed under stirring conditions.

6. The preparation method according to claim 1 or 5, characterized in that: The calcination is carried out under stir-frying conditions; the calcination temperature is 1620-1720°C.

7. The preparation method according to claim 1, characterized in that: The cooling is natural cooling.

8. The preparation method according to claim 1 or 7, characterized in that: The temperature of the second dehydroxylation reaction is 1000-1300° C., and the insulation time is 2-4 hours.

9. A vacuum sintering device for use in the method for preparing quartz sand according to any one of claims 1 to 8, characterized in that: It comprises a sealing system (10); a heating system (20) for heating the sealing system (10); and a vacuum system (30) connected to the sealing system (10); The sealing system (10) comprises a chamber (4); a cover (2) covering the chamber (4), wherein a hole (8) is provided on the top of the cover (2); a guide rod (1) extending into the chamber (4) through the hole (8); and a container (3) connected to one end of the guide rod (1) extending into the chamber (4).

10. A method for preparing quartz sand using the vacuum sintering device according to claim 9, characterized in that: The following steps are involved: The silicon dioxide with a purity of 99.99985% or more is loaded into a container (3) and then sent to the chamber (4) of the sealing system (10), the vacuum system (30) is started to evacuate the chamber (4) to a pressure not higher than 0.01 Pa, the heating system (20) is first heated to a temperature of a first dehydroxylation reaction to perform a first dehydroxylation reaction, and then the temperature is secondly heated to a calcination temperature to perform calcination, and after the calcination, the chamber (4) is cooled to a temperature of a second dehydroxylation reaction to perform a second dehydroxylation reaction, thereby obtaining the quartz sand.

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