Method for preparing high-purity amorphous quartz sand by thermally treating white carbon black through two-step method

Abstract

The invention discloses a method for preparing high-purity amorphous quartz sand by thermally treating white carbon black through a two-step method, which comprises the following steps: S1, soaking white carbon black powder in a mixed acid solution of hydrofluoric acid and hydrochloric acid, taking out a solid, cleaning and drying to obtain high-purity white carbon black powder; s2, pressing the high-purity white carbon black powder into white carbon black blocks; s3, preheating and heating the white carbon black block, and removing residual moisture, hydroxyl groups and carbon-based impurities in the white carbon black block to obtain a hydroxyl-removed sample; s4, performing high-temperature and low-temperature two-step heat treatment on the sample subjected to hydroxyl removal, and cooling to obtain a high-density quartz block; in the two-step heat treatment, the first high temperature means heating to 1200 DEG C, and the second low temperature means heating to 1200 DEG C, directly cooling to 1000-1100 DEG C without a heat preservation process, and preserving heat for 2-10 hours; and S5, crushing the high-density quartz block to obtain the high-purity non-crystal quartz sand.

Description

Technical Field

[0001] The invention relates to the technical field of high-purity quartz sand preparation, and in particular to a method for preparing high-purity amorphous quartz sand by heat-treating white carbon black in two steps. Background Art

[0002] With the rapid development of the photovoltaic industry, semiconductor chips, intelligent computing and other fields, the demand for silicon wafers has increased year by year, and the demand for high-purity quartz sand materials for the production of silicon wafers has also increased day by day. Especially in the production process of photovoltaic and semiconductor silicon wafers, high-purity quartz sand is an indispensable key material. Its quality and supply stability have an important impact on the quality and output of quartz crucibles, and it is a serious bottleneck problem in the semiconductor manufacturing field. At present, the high dependence on silicon-based materials has led to high-purity quartz sand becoming a national strategic material. It is necessary to vigorously develop the localization of high-purity quartz sand, and the entire process of quartz sand production does not rely on imports. At present, there are two main sources of high-purity quartz sand, one is the purification of natural quartz ore, and the other is the synthesis of high-purity quartz sand by chemical methods. Due to the small number of high-purity quartz sand ore resources in my country, the impurity content is relatively complex, and the purification difficulty is relatively high, resulting in a relatively complex process for producing high-purity quartz sand from domestic ores, resulting in higher requirements for equipment. The use of imported ores for purification will lead to higher production costs for quartz sand, resulting in an increase in the cost of the entire industrial chain, which is not conducive to the localization of silicon wafers. Synthetic quartz sand is directly synthesized from chemical raw materials to produce high-purity quartz sand, ensuring high-quality and continuous output without being restricted by region, mineral source, impurity removal process, etc.

[0003] The main component of white carbon black powder is gas-phase SiO2 nanoparticles, which appear as white fine flocculent powder, odorless, non-toxic, and pollution-free, with a particle size below 100nm. The industrial synthesis method of gas-phase white carbon black mainly involves the production of Si chloride SiCl4 or CH3SiCl3 and other industrial reagents, and the by-products are mixed with gases composed of hydrogen and oxygen to react at high temperature to obtain high-purity gas-phase SiO2 (purity> 99.8%) ultrafine powder. The synthesis process of white carbon black is simple and the raw material cost is low, so it is a relatively cheap industrial SiO2 raw material. Using white carbon black as a raw material for synthetic quartz sand effectively reduces the production cost of synthetic quartz sand, provides a long-term and stable raw material supply, and is an ideal raw material for quartz sand synthesis. White carbon black is processed through processes such as pickling and impurity removal, cold pressing, heat treatment, crushing, and screening. Among them, the heat treatment process is the key step in the densification of white carbon black, so it is necessary to explore the optimal densification heat treatment process parameters.

[0004] The traditional one-step calcination process (heating-insulating-cooling) is accompanied by rapid grain growth during the heating process, resulting in grain coarsening. Due to the uneven heating of particles at different positions, the inconsistent grain growth rate makes the particles grow unevenly during the heat treatment process, especially in the later stage of calcination, the grains grow faster, and it is difficult to obtain high-density and uniform quartz sand particles. The two-step heat treatment process controls different heat treatment temperature intervals to distinguish the two kinetic processes of grain boundary diffusion and grain boundary migration, that is, to separate the two stages of sintering densification and grain growth. At present, there are two main heating methods for the two-step heat treatment process. One is to first obtain a dense material by long-term insulation at low temperature and then sinter at high temperature for a short time to improve the bonding force and regulate the microstructure at the same time. The second method is to first provide the higher activation energy required for sintering by high temperature and short time sintering, and then sinter at low temperature for a long time to inhibit grain growth and achieve densification at the same time. This application uses these two heat treatment methods to treat white carbon black powder at the same time, and compares and analyzes the effects of the two heat treatment methods on its sintering densification behavior. Summary of the invention

[0005] In order to solve the existing process problems of preparing high-purity amorphous quartz sand by purifying, dehydroxylating and densifying industrial-grade white carbon black, the present invention proposes the following technical solutions:

[0006] [1] A two-step method for preparing high-purity amorphous quartz sand by heat treating white carbon black, comprising the steps of:

[0007] S1, soaking the white carbon black powder in a mixed acid solution of hydrofluoric acid and hydrochloric acid, taking out the solid, washing it, and drying it to obtain a high-purity white carbon black powder;

[0008] S2, pressing (specifically, cold pressing, etc.) the high-purity white carbon black powder into a white carbon black block;

[0009] S3, preheating the white carbon black block to remove residual water, hydroxyl groups and carbon-based impurities therein to obtain a sample after hydroxyl removal;

[0010] S4, subjecting the sample after the hydroxyl removal to a two-step heat treatment of first high temperature and then low temperature, and cooling to obtain a high-density quartz block; in the two-step heat treatment, the first high temperature refers to heating to 1200° C., and the second low temperature refers to heating to 1200° C. and then directly cooling to 1000-1100° C. without a heat preservation process and keeping the temperature for 2-10 hours;

[0011] S5, crushing the high-density quartz block to obtain high-purity amorphous quartz sand.

[0012] In step S1, in the mixed acid solution, the molar ratio of hydrofluoric acid to hydrochloric acid may be 1:1 to 5, for example, 1:1, 1:2, 1:3, 1:4, 1:5, etc.

[0013] In step S1, the mass ratio of the white carbon black powder to the mixed acid solution may be 1:1-3, such as 1:1, 1:2, 1:3, etc.

[0014] In step S1, the soaking time may be 6 to 48 hours, and further may be 10 to 20 hours.

[0015] In step S1, the cleaning may specifically include: repeatedly cleaning with deionized water and ethanol for several times and filtering.

[0016] In step S1, the drying may be vacuum drying. Furthermore, the vacuum drying temperature may be 115 to 120° C., and the vacuum drying time may be 24 to 72 hours.

[0017] In step S2, the pressing pressure may be 100-400 MPa.

[0018] In step S3, the white carbon black block may be preheated at a heating rate of 5 to 10°C / min, the preheating temperature may be 400 to 600°C, and the insulation time may be 2 to 10 hours.

[0019] In step S4, the heating rate and cooling rate can be independently 2 to 10°C / min, for example, 2°C / min, 3°C / min, 5°C / min, 10°C / min, etc.

[0020] In step S4, the sample after the hydroxyl removal can be subjected to a two-step heat treatment of high temperature and then low temperature in a negative pressure inert environment of -0.1 MPa or lower. The inert environment refers to an atmosphere environment that does not participate in the reaction, such as an atmosphere environment such as nitrogen and / or a rare gas (such as argon, etc.). Negative pressure can be achieved by vacuumizing after inert gas washing. The inert gas refers to a gas that does not participate in the reaction, such as a gas such as nitrogen and / or a rare gas (such as argon, etc.).

[0021] In step S5, the particle size of the high-purity amorphous quartz sand may be between 50 μm and 250 μm, and may be further classified into screening intervals of 50 μm.

[0022] In step S5, the true density of the high-purity amorphous quartz sand can be 2.23-2.27 g / cm 3 .

[0023] In step S5, the purity of SiO2 in the high-purity amorphous quartz sand is greater than 4N8.

[0024] [2] High-purity amorphous quartz sand prepared according to the method described in [1].

[0025] [3] Use of the high-purity amorphous quartz sand according to [2] in making a quartz crucible. Furthermore, the quartz crucible can be used to prepare single crystal silicon.

[0026] The method of the present invention firstly uses a mixture of hydrofluoric acid and hydrochloric acid to pickle the white carbon black to remove metal impurities inside the particles. Subsequently, the precipitate after pickling is washed and dried for multiple times to obtain high-purity white carbon black powder. The high-purity white carbon black powder is pressed to obtain a block to increase the sintering neck formation energy between the particles. A two-step staged calcination heat treatment process is adopted to densify the white carbon black by heating at high temperature first and then at low temperature, and finally a high-density quartz block in an amorphous SiO2 state is obtained. Finally, a crushing step is performed to prepare high-purity amorphous quartz sand.

[0027] The preparation technology proposed in the present invention can efficiently utilize the industrial byproduct white carbon black, significantly improve the purity of white carbon black by implementing acid purification and high-temperature roasting densification technology, and increase the density as much as possible while maintaining the amorphous SiO2 state, so as to achieve various performance indicators of photovoltaic-grade quartz sand, reduce environmental pollution and reduce the waste of silicon resources. The obtained high-purity amorphous quartz sand is suitable for making quartz crucibles.

[0028] The technology of the present invention is characterized by simple operation, high cost-effectiveness, and easy large-scale production. In addition, the technology of the present invention solves the problem of recycling white carbon black, a byproduct of silane in the prior art, improves the utilization rate of silicon resources, and can produce high-purity quartz sand with high economic value, which has important application value in the semiconductor, optoelectronics, photovoltaic and other industrial fields.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention adopts segmented heat treatment of white carbon black powder to prepare high-density high-purity amorphous quartz sand, mainly to improve the particle size and density of amorphous nano-scale SiO2 particles, and meet the application standards of industrial-grade quartz sand. Compared with the traditional one-step sintering process, the two-step sintering process shows significant advantages in particle densification. It can not only improve the formation of sintering necks between particles to promote particle growth, but also improve the efficiency of pore removal inside particles and improve the density inside sand particles. In addition, compared with the traditional high-temperature sintering method, the two-step sintering method can achieve high density at a lower temperature, thereby saving energy and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The X-ray diffraction (XRD) diagram of white carbon black after heat treatment at different temperatures;

[0032] Figure 2 Metallographic photos of silica after heat treatment at different temperatures;

[0033] Figure 3 The XRD pattern and metallographic photograph of Example 1 after heat treatment;

[0034] Figure 4 The XRD pattern and metallographic photograph of Example 2 after heat treatment;

[0035] Figure 5 The XRD pattern and metallographic photograph of Example 3 after heat treatment;

[0036] Figure 6 The XRD pattern and metallographic photograph of Example 4 after heat treatment;

[0037] Figure 7 The XRD pattern and metallographic photograph of Example 5 after heat treatment;

[0038] Figure 8 The following is a comparison chart of the true density of original silica and commercial amorphous quartz sand after two-step heat treatment in each embodiment. DETAILED DESCRIPTION

[0039] 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 are not used to limit the scope of the present invention.

[0040] Embodiment 1:

[0041] Step 1: Use an electronic balance to weigh 20g of white carbon black powder and put it into 20mL of mixed acid solution of hydrochloric acid and hydrofluoric acid with a molar ratio of 1:1, and slowly stir to mix the particles and the acid solution evenly. After acid leaching for 20 hours, remove the upper layer of acid solution, use a sand core funnel to filter the lower layer of white suspension, and repeatedly wash and filter with deionized water and ethanol to obtain white powder, vacuum dry at 120℃, and dry for 48 hours to obtain white high-purity SiO2 powder (high-purity white carbon black powder);

[0042] Step 2: Move the dried white powder into a 20 mm diameter tableting cylindrical mold and apply 400 MPa pressure to press it into a cylindrical high-purity SiO2 block;

[0043] Step 3: Move the high-purity SiO2 block into a corundum crucible and place it in a tubular furnace. Set the heating rate to 10℃ / min and raise it to 600℃, keep it for 2h, and then cool it to room temperature to remove the residual moisture and most of the hydroxyl groups and carbon-based impurities in the block.

[0044] Step 4: First, pass high-purity nitrogen into the corundum tube, and then use a mechanical pump to extract the gas in the tube to keep the pressure in the tube at -0.1MPa. Repeat the above operation three times to clean all the air in the corundum tube, and finally maintain the pressure in the tube at a negative pressure of -0.1MPa.

[0045] Step 5: The SiO2 block obtained in step 3 is subjected to densification heat treatment by a two-step calcination method. First, the temperature is heated to 1000°C at a heating rate of 10°C / min, and then heated to 1200°C at a heating rate of 5°C / min. Then, the temperature is directly cooled to 1000°C at a cooling rate of 5°C / min without a heat preservation process and kept for 10 hours. After the reaction is completed, the temperature is cooled to 300°C at a cooling rate of 5°C / min and then cooled to room temperature to obtain a high-density SiO2 block.

[0046] Step 6: The high-density SiO2 block is crushed, ground and sieved to obtain quartz sand particles with a particle size range of 50-100μm, 100-150μm, 150-200μm, and 200-250μm, and the SiO2 purity is greater than 4N8.

[0047] Embodiment 2:

[0048] The only difference from Example 1 is step 5: the SiO2 block obtained in step 3 is subjected to densification heat treatment by a two-step calcination method, firstly, the temperature is heated to 1000°C at a heating rate of 10°C / min, then heated to 1200°C at a heating rate of 5°C / min, then directly cooled to 1100°C at a cooling rate of 5°C / min without a heat preservation process and kept for 10 hours, after the reaction is completed, the temperature is cooled to 300°C at a cooling rate of 5°C / min and then cooled to room temperature to obtain a high-density SiO2 block. The rest are the same. The purity of the obtained quartz sand particles SiO2 is greater than 4N8.

[0049] Embodiment 3:

[0050] The only difference from Example 1 is step 5: the SiO2 block obtained in step 3 is subjected to densification heat treatment by a two-step calcination method, firstly, the temperature is heated to 1000°C at a heating rate of 10°C / min, then heated to 1400°C at a heating rate of 5°C / min, then directly cooled to 1200°C at a cooling rate of 5°C / min without a heat preservation process and kept for 10 hours, after the reaction is completed, the temperature is cooled to 300°C at a cooling rate of 5°C / min and then cooled to room temperature to obtain a high-density SiO2 block. The rest are the same. The purity of the obtained quartz sand particles SiO2 is greater than 4N8.

[0051] Embodiment 4:

[0052] The only difference from Example 1 is step 5: the SiO2 block obtained in step 3 is subjected to densification heat treatment by a two-step calcination method, firstly, the temperature is heated to 800°C at a heating rate of 10°C / min and kept at that temperature for 2 hours, then the temperature is heated to 1000°C at a heating rate of 5°C / min and kept at that temperature for 10 hours, after the reaction is completed, the temperature is cooled to 300°C at a cooling rate of 5°C / min and then cooled to room temperature to obtain a high-density SiO2 block. The rest is the same. The purity of the obtained quartz sand particles SiO2 is greater than 4N8.

[0053] Embodiment 5:

[0054] The only difference from Example 1 is step 5: the SiO2 block obtained in step 3 is subjected to densification heat treatment by a two-step calcination method, firstly, the temperature is heated to 800°C at a heating rate of 10°C / min and kept at that temperature for 2 hours, then the temperature is heated to 1100°C at a heating rate of 5°C / min and kept at that temperature for 10 hours, after the reaction is completed, the temperature is cooled to 300°C at a cooling rate of 5°C / min and then cooled to room temperature to obtain a high-density SiO2 block. The rest is the same. The purity of the obtained quartz sand particles SiO2 is greater than 4N8.

[0055] Comparative Example:

[0056] Step 1: Same as step 1 in Example 1.

[0057] Step 2: Move the high-purity SiO2 powder into a corundum crucible and place it in a tube furnace. Set the heating rate to 10℃ / min and raise it to 600℃. Keep it for 2h and then cool it to room temperature to remove the residual moisture and most of the hydroxyl groups and carbon-based impurities in the block.

[0058] Step 3: The SiO2 powder obtained in step 2 is subjected to densification heat treatment by a two-step calcination method. 5 g of samples are weighed as a group, and 4 groups of samples are weighed.

[0059] The first group of samples were heated to 1000°C at a heating rate of 10°C / min, and then heated to 1100°C at a heating rate of 5°C / min and kept at that temperature for 2h. After the reaction was completed, the temperature was lowered to 300°C at a cooling rate of 5°C / min and then cooled to room temperature to obtain a white powder sample.

[0060] The second group of samples were heated to 1000°C at a heating rate of 10°C / min, and then heated to 1200°C at a heating rate of 5°C / min and kept at that temperature for 2h. After the reaction was completed, the temperature was lowered to 300°C at a cooling rate of 5°C / min and then cooled to room temperature to obtain a white powder sample.

[0061] The third group of samples were heated to 1000°C at a heating rate of 10°C / min, and then heated to 1300°C at a heating rate of 5°C / min and kept at that temperature for 2h. After the reaction was completed, the temperature was lowered to 300°C at a cooling rate of 5°C / min and then cooled to room temperature to obtain a white powder sample.

[0062] The fourth group of samples were heated to 1000°C at a heating rate of 10°C / min, and then heated to 1400°C at a heating rate of 5°C / min and kept at that temperature for 2h. After the reaction was completed, the temperature was lowered to 300°C at a cooling rate of 5°C / min and then cooled to room temperature to obtain a white powder sample.

[0063] Characterization analysis:

[0064] The original white carbon black without pressure was calcined at high temperature by a one-step heat treatment process. The heat-treated sample was characterized by XRD phase, and the results were as follows: Figure 1 As shown in the figure, when the silica powder is heated to 1100℃ and 1200℃, the XRD diffraction peak is located at 22°, showing a standard amorphous peak morphology, which is consistent with the standard amorphous SiO2 (JCPDS29-0085) card, proving that the silica powder is still an amorphous structure when heated to 1200℃. When the heat treatment temperature is increased to 1300℃, the XRD results show that the crystal structure of silica undergoes a phase transition, and its diffraction peak position is consistent with the standard cristobalite (JCPDS 39-1425) card. When the heat treatment temperature is further increased to 1400℃, the XRD test results still show a cristobalite phase. Figure 2 Optical photos of four groups of samples. Figure 2 (a) and Figure 2 (b) is an optical photograph of silica powder after heat treatment at 1100℃ and 1200℃. The results show that the particle size is uneven, highly agglomerated and loose before phase transformation occurs. Figure 2 (c) and Figure 2 (d) is an optical photograph of silica powder after heat treatment at 1300℃ and 1400℃. The test results show that after the phase change temperature treatment, the silica particles agglomerated into blocks with a particle size of 200-600μm, uneven distribution, obvious grain interface and loose structure. The excessively high heat treatment temperature causes the silica powder to transform from the amorphous phase to the quartz phase. Micropores will be formed during the phase transformation, resulting in a loose particle structure after the phase transformation and reducing the density of the quartz sand. At the same time, the presence of quartz phase in the sand particles will cause the quartz sand to affect the performance of silicon ingot pulling in the application of high-purity quartz crucibles. This is mainly attributed to the presence of quartz phase in the crucible, which will cause silicon pulling to grow epitaxially according to the quartz lattice, forming polycrystalline silicon and affecting the preparation of single crystal silicon. Therefore, it is necessary to avoid its transformation to quartz during the heat treatment process, and the heat treatment temperature should be limited to below 1200℃.

[0065] Compared with the traditional one-step heat treatment process, the "low temperature first, high temperature later" and "high temperature first, low temperature later" heat treatment methods are more conducive to improving the sintering neck formation energy of nano-scale granular materials, promoting the migration of bubbles inside the sand particles to the outside of the particles, and improving the density of the sand particles to meet the application requirements of commercial amorphous quartz sand. The purified silica powder was cold pressed at 400MPa and then subjected to a two-step heat treatment. For the "low temperature first, high temperature later" heating method, the temperature insulation in the low temperature stage is conducive to the movement of the remaining hydroxyl groups to the outside of the sand particles, and the temperature insulation in the high temperature stage promotes the closure of pores to complete densification. Another "high temperature first, low temperature later" heating method, in which the temperature in the high temperature stage is conducive to activating the sintering neck performance between particles, accelerating the volume diffusion rate between particles, and rapidly increasing the relative density of the block. When the temperature drops to low temperature insulation, the size of the sintering neck formation exceeds the particle radius, and the pores between the particles will gradually close to complete the particle densification.

[0066] The cold pressed silica blocks were heat treated at 1200℃ and then at 1000℃ ( Figure 3 , Example 1), first high temperature 1200 ℃ and then low temperature 1100 ℃ heat treatment ( Figure 4 , Example 2), first high temperature 1400 ° C and then low temperature 1200 ° C heat treatment ( Figure 5 , Example 3), first low temperature 800 ℃ and then high temperature 1000 ℃ heat treatment ( Figure 6 , Example 4), first low temperature 800 ° C and then high temperature 1200 ° C heat treatment ( Figure 7 , Example 5). The samples of each example were characterized by XRD phase analysis, and the test results showed that the diffraction peaks of the samples measured in Example 1, Example 2, Example 4, and Example 5 were at around 22°, showing a standard amorphous peak morphology, which was consistent with the standard amorphous SiO2 (JCPDS29-0085) card, proving that when the reaction temperature was around 1000°C, the test sample was still in an amorphous state. When the reaction temperature was 1200°C, the sample XRD results showed a mixed phase of amorphous and cristobalite, and its diffraction peak was consistent with the standard amorphous SiO2 (JCPDS29-0085) card and the standard cristobalite (JCPDS 39-1425) card. It is proved that the heat treatment method of high temperature 1400°C followed by low temperature 1200°C will induce phase transformation and cannot meet subsequent application requirements. In addition, the metallographic structure analysis of the five example samples was carried out, and the results showed that the sample of Example 3 ( Figure 5 (b) After heat treatment at 1400°C and then at 1200°C, obvious grain boundaries appeared inside the block, proving that the treatment process caused phase transformation of the SiO2 block. Figure 3 (b) The test sample results show that the block surface is smooth and the structure is uniform, and no obvious grain precipitation occurs. Example 2 ( Figure 4(b) The test results of the sample showed that the block had obvious grain precipitation, and the grain size was 10 to 50 μm. Figure 6 (b) The test sample results show that fine grains have precipitated from the block. Example 5 ( Figure 7 (b) The test sample results show that obvious grain precipitation occurs on the surface of the block, and small grains precipitate over a large area.

[0067] In order to characterize the density of the example samples, the example samples, unheat-treated white carbon black powder and commercial amorphous quartz sand were tested for true density. The test results are shown in Figure 8 The results show that the true density of the unheat-treated silica powder is 2.1302 g / cm 3 , which is lower than the theoretical true density of amorphous SiO2 2.2g / cm 3 The true density of the sample of Example 1 obtained after two-step heat treatment is 2.2658 g / cm 3 , has reached the theoretical density of amorphous SiO2, the test result is much higher than the untreated white carbon black powder sample, and higher than the true density of commercial amorphous quartz sand, indicating that the heat treatment process can effectively remove the hydroxyl groups inside the SiO2 block and promote the closure of pores to achieve the densification requirements. As the reaction temperature increases, the density test result of Example 2 is 2.3083g / cm 3 Its density is close to the theoretical density of quartz (2.32g / cm 3 ), indicating that its crystal structure has been partially transformed into cristobalite. The true density test results of Example 4 and Example 5 are both 2.29 g / cm 3 The above proves that a small number of particles inside it have also transformed into cristobalite, which will reduce the application quality of the subsequent quartz crucible. The above results show that the heat treatment process of "high temperature first and then low temperature" can effectively improve the sintering neck performance between particles in the high temperature stage, accelerate the volume diffusion rate between particles, and quickly increase the relative density of the block; in the low temperature insulation stage, the size of the sintering neck formation exceeds the particle radius, and the pores between the particles will gradually close to complete the densification heat treatment. The heat treatment time of "high temperature first and then low temperature" is significantly shorter than that of the heat treatment process of "low temperature first and then high temperature". The "high temperature first" process has no insulation time, which can not only reduce excessive energy consumption, but also effectively inhibit the transformation of SiO2 blocks to cristobalite phase, reaching the application standard of commercial amorphous quartz sand, and is particularly suitable for making quartz crucibles for single crystal silicon preparation.

[0068] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing high-purity amorphous quartz sand by heat treating white carbon black in two steps, characterized in that: Includes steps: S1, soaking the white carbon black powder in a mixed acid solution of hydrofluoric acid and hydrochloric acid, taking out the solid, washing it, and drying it to obtain a high-purity white carbon black powder; S2, pressing the high-purity white carbon black powder into a white carbon black block; S3, preheating the white carbon black block to remove residual water, hydroxyl groups and carbon-based impurities therein to obtain a sample after hydroxyl removal; S4, subjecting the sample after the hydroxyl removal to a two-step heat treatment of first high temperature and then low temperature, and cooling to obtain a high-density quartz block; in the two-step heat treatment, the first high temperature refers to heating to 1200° C., and the second low temperature refers to heating to 1200° C. and then directly cooling to 1000-1100° C. without a heat preservation process and keeping the temperature for 2-10 hours; S5, crushing the high-density quartz block to obtain high-purity amorphous quartz sand.

2. The method according to claim 1, characterized in that In step S1: In the mixed acid solution, the molar ratio of hydrofluoric acid to hydrochloric acid is 1:1-5; The mass ratio of the white carbon black powder to the mixed acid solution is 1:1-3; The soaking time is 6 to 48 hours; The cleaning specifically includes: repeatedly cleaning with deionized water and ethanol for several times and filtering; The drying is vacuum drying, the vacuum drying temperature is 115-120° C., and the vacuum drying time is 24-72 hours.

3. The method according to claim 1, characterized in that: In step S2, the pressing pressure is 100-400 MPa.

4. The method according to claim 1, characterized in that: In step S3, the white carbon black block is preheated at a heating rate of 5 to 10°C / min, the preheating temperature is 400 to 600°C, and the insulation time is 2 to 10 hours.

5. The method according to claim 1, characterized in that In step S4, the heating rate and the cooling rate are independently 2 to 10°C / min.

6. The method according to claim 1 or 5, characterized in that: In step S4, the sample after hydroxylation is subjected to a two-step heat treatment of first high temperature and then low temperature in a negative pressure inert environment of -0.1 MPa or lower.

7. The method according to claim 1, characterized in that In step S5: The particle size of the high-purity amorphous quartz sand is 50 to 250 μm, and is further classified into screening intervals of 50 μm; The true density of the high-purity amorphous quartz sand is 2.23-2.27 g / cm 3 ; The purity of SiO2 in the high-purity amorphous quartz sand is greater than 4N8.

8. High-purity amorphous quartz sand prepared according to the method according to any one of claims 1 to 7.

9. Use of the high-purity amorphous quartz sand according to claim 8 in making a quartz crucible.

10. The use according to claim 9, characterized in that: The quartz crucible is used for preparing single crystal silicon.

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