A preparation method of synthetic quartz sand with high bulk density

Abstract

The present invention discloses a preparation method of synthetic quartz sand with high bulk density, comprising the following steps: S1. Mix organosilane and pure water, and stir to obtain a fully hydrolyzed transparent solution; S2. Add an alkane non-polar solvent to the obtained solution, control the stirring speed, and then add an emulsifier thereto, and stir to emulsify the mixed solution without stratification; S3. Add a metal-impurity-free basic reagent to the emulsion to form a silica dispersion; S4. Filter the dispersion and dry it to obtain silica particles; S5. Calcinate the silica particles in air for the first time to remove the organic substances in the particles; then perform secondary calcination to remove the hydroxyl groups to obtain synthetic quartz sand with a bulk density greater than 1.5 g / cm3 and a true density greater than 2.20 g / cm3. The present invention adopts the sol-gel method to prepare synthetic quartz sand with high bulk density and high purity, and the quartz sand is not prone to bubbles during the use of preparing quartz glass products.

Description

Technical Field

[0001] The present invention belongs to the technical field of quartz sand, and particularly relates to a preparation method of synthetic quartz sand with high bulk density. Background Art

[0002] High-purity quartz sand is the core raw material for making quartz glass equipment such as quartz crucibles, quartz ingots, and quartz rods in industries such as semiconductors and photovoltaics. The quartz glass in these industries has strict requirements on the purity, particle size distribution, shape, and inclusions of quartz sand. The applications in the photovoltaic and semiconductor industries are extremely sensitive to the contents of alkali metal elements such as Li, Na, and K and transition metal elements such as Fe in quartz glass. According to different applications, the total impurity content is required to be below 1 ppm in many places.

[0003] The raw materials of current quartz glass mainly come from purified natural quartz sand. Due to the uneven quality of natural minerals and the complex process of preparing high-purity quartz sand, the output of natural high-purity quartz sand with low impurity content and few inclusions is currently low and cannot meet the market demand at all. In addition to the purification of natural quartz sand, another technical route is the artificial synthesis of high-purity quartz sand. For example, a method for synthesizing quartz sand is mentioned in Chinese Patent CN110255570A. However, this method has a cumbersome process, high metal impurity content, long reaction time, and requires the use of concentrated acid solutions, posing potential safety and environmental protection hazards. The prepared quartz sand has large edges and corners and low bulk density, which is not conducive to the subsequent synthesis of bubble-free quartz glass. When using the high-purity quartz sand produced by this process to make quartz glass products, during the high-temperature melting process, some gases cannot be removed from the system, and a large number of small bubbles will be contained in the final product. In optical applications, the bubbles in quartz glass will affect the optical performance. In the application of single-crystalline silicon crucibles, the bubbles will cause the perforation of the crucible, resulting in the failure of single-crystalline silicon production. Therefore, the bubbles derived from quartz sand must be removed.

[0004] When preparing quartz glass by high-temperature melting of quartz sand, in addition to impurities, there are strict requirements on the particle size and bulk density of quartz sand. Generally speaking, the higher the bulk density, the more beneficial it is for subsequent high-temperature melting, and the fewer bubbles in the product. We know that under the premise of the same particle size and particle distribution, the spherical body has a higher bulk density than the angular body, and the bulk density can be characterized by the tapped density of the sand body. Therefore, under the same conditions, the spherical synthetic quartz sand body with a higher bulk density is more suitable for the high-temperature production of bubble-free or low-bubble quartz glass products than the angular natural quartz sand body or the angular synthetic quartz sand body. Summary of the Invention

[0005] In view of the deficiencies of the existing technology, the present invention provides a method for preparing synthetic quartz sand with a high bulk density. This method uses tetramethoxysilane or tetraethoxysilane as raw materials and adopts the sol-gel method to prepare spherical synthetic quartz sand with a high bulk density, so as to increase the bulk density of the quartz sand and thereby reduce the bubbles in the final fused quartz glass.

[0006] The technical solution of the present invention is as follows:

[0007] The present invention provides a method for preparing synthetic quartz sand with a high bulk density, comprising the following steps:

[0008] A method for preparing synthetic quartz sand with a high bulk density, comprising the following steps:

[0009] S1. Mix the organosilane and pure water, and stir to obtain a transparent solution that is fully hydrolyzed;

[0010] S2. Add an alkane non-polar solvent to the solution obtained in step S1, control the stirring speed, and then add an emulsifier thereto, and stir to emulsify the mixed solution to obtain an emulsion that does not separate layers;

[0011] S3. Add a metal-free basic reagent to the emulsion obtained in step S2 to form a silica dispersion;

[0012] S4. Filter the silica dispersion obtained in step S3 and dry it to obtain silica particles;

[0013] S5. First calcine the silica particles obtained in step S5 in air to remove the organic matter in the particles; then perform secondary calcination to remove the hydroxyl groups to obtain synthetic quartz sand, and the bulk density of the synthetic quartz sand is greater than 1.5 g / cm 3 , and the true density is greater than 2.20 g / cm 3 .

[0014] Preferably, in step S1, the organosilane is tetramethoxysilane or tetraethoxysilane.

[0015] Preferably, in step S1, the resistivity of the pure water > 17 megohms; the mass ratio of the organosilane to the pure water is 0.7 - 1.1:1.

[0016] Preferably, in step S2, the alkane non-polar solvent is one of cyclohexane, decane, nonane, and heptane; the mass ratio of the alkane non-polar solvent to the organosilane is 1 - 1.5:1.

[0017] Preferably, in step S2, the emulsifier is one of fatty alcohol polyoxyethylene ether with a purity of 99.99%, polyethylene glycol fatty acid ester, and sorbitol; the addition amount of the emulsifier is 0.3% - 0.5% of the mass of the organosilane.

[0018] Preferably, in step S2, the emulsion is required not to separate layers within 3 minutes.

[0019] Preferably, in step S3, the alkaline reagent is ammonia water or organic amine, the organic amine is tetramethylammonium hydroxide, and the addition amount of the alkaline reagent is 0.1%-0.3% of the mass of the organosilane.

[0020] Preferably, the concentration of ammonia water is 25%.

[0021] Preferably, in step S2, the stirring speed is 10-50 r / min.

[0022] Preferably, in step S4, the drying temperature is 150-200 °C and the time is 2-5 h.

[0023] Preferably, the primary calcination is divided into three stages. The calcination time is t at temperature T 1 , the calcination time is t at temperature T 1 , the calcination time is t at temperature T 2 , and 400 °C ≤ T 2 <T 3 <T 3 ≤ 800 °C, t 1 <t 2 <t 3 , t 2 <t 1 <t 3 , t 1 +t 2 +t 3 ≤ 6 h; the temperature of the secondary calcination is 1100-1300 °C and the time is 6-10 h.

[0024] The beneficial effects of the present invention are:

[0025] 1) The preparation process of the present invention is simple, with few process steps and easy to control; during the product preparation process, the liquid is formed into spherical silica colloidal substances by stirring, and there is no need for physical crushing, reducing the risk of introducing metal impurities;

[0026] 2) The spherical synthetic quartz sand prepared by the present invention has high purity and high bulk density, and is not prone to bubbles during use, improving the quality of the finished product. Description of the Drawings

[0027] The present invention will be further described below with reference to the drawings and embodiments:

[0028] Figure 1 It is a picture of the dried silica particles in Example 1 under a 20-fold magnifying glass;

[0029] Figure 2 It is a picture of the calcined quartz sand in Example 1 under a 50-fold microscope;

[0030] Figure 3 is the particle size distribution diagram of the calcined quartz sand in Example 1;

[0031] Figure 4 is the comparison diagram of the calcined quartz sand in Example 1 and Comparative Example 1 (where the left sample corresponds to Example 1 and the right sample corresponds to Comparative Example 1);

[0032] Figure 5 is the enlarged view of the calcined quartz sand in Example 1;

[0033] Figure 6 is the enlarged view of the calcined quartz sand in Comparative Example 1. Detailed implementation manners

[0034] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the specific implementation manners and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following descriptions, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0035] The materials and reagents used in the following examples are all commercially available. Unless otherwise specified, the reagents used in the following examples are all chemically pure.

[0036] Example 1

[0037] A preparation method of high bulk density synthetic quartz sand is as follows:

[0038] 1) Mix 580 g of tetramethyl orthosilicate and 687 g of water, and stir for 1 h to obtain a completely hydrolyzed transparent solution;

[0039] 2) Add 850 g of decane to the mixed solution in step 1, control the stirring speed to 20 revolutions per minute, then add 2 g of fatty alcohol polyoxyethylene ether with a purity of 99.99%, and stir at a speed of 20 revolutions per minute to emulsify the mixed solution to obtain a non-layered emulsion;

[0040] 3) Add 1 g of 25% ammonia water to the emulsion in step 2, and stir for 1 h to form a silica dispersion;

[0041] 4) Filter the silica dispersion obtained in step 3, and dry it at 200 °C for 3 h to obtain dry silica particles;

[0042] 5) Calcinate the obtained silica particles at 400 °C for 2 h, 500 °C for 1 h, 700 °C for 3 h, and 1100 °C for 8 h to convert them into high-purity synthetic quartz sand.

[0043] The bulk density of the synthetic quartz sand obtained in Example 1 was measured to be 1.72 g / cm 3 , and the true density was 2.21 g / cm 3 , and the total impurity content was less than 1 ppm. Figure 1 Figure for the quartz particles after drying in Example 1 under a 20-fold magnifying glass, Figure 2 Figure for the quartz sand after calcination in Example 1, Figure 3 Figure for the particle size distribution of the quartz sand after calcination. The ICP test results are shown in Table 1 below.

[0044] Table 1

[0045] Element Na K Ca Fe Li Al Mg Zn Content / ppm 0.21 0 0.11 0.12 0 0 0.15 0

[0046] Example 2

[0047] A preparation method of high-bulk-density synthetic quartz sand is as follows:

[0048] 1) Mix 580 g of tetramethyl orthosilicate and 687 g of water, and stir for 1 h to obtain a completely hydrolyzed transparent solution;

[0049] 2) Add 850 g of decane to the mixed solution in step 1, control the stirring speed to 10 revolutions per minute, then add 2 g of fatty alcohol polyoxyethylene ether with a purity of 99.99%, and stir at a speed of 10 revolutions per minute to emulsify the mixed solution to obtain a non-layered emulsion;

[0050] 3) Add 1 g of 25% ammonia water to the emulsion in step 2, and stir for 1 h to form a silica dispersion;

[0051] 4) Filter the silica dispersion obtained in step 3, and dry it at 200 °C for 3 h to obtain dry silica particles;

[0052] 5) Calcinate the obtained silica particles at 400 °C for 2 h, 500 °C for 1 h, 700 °C for 3 h, and 1100 °C for 8 h to convert them into high-purity synthetic quartz sand.

[0053] The bulk density of the synthetic quartz sand prepared in this example was 1.53 g / cm 3 , and the true density was 2.21 g / cm 3 .

[0054] Comparative Example 1

[0055] 1) Mix 580 g of tetramethyl orthosilicate and 687 g of water, and stir for 1 h to obtain a completely hydrolyzed transparent solution;

[0056] 2) Add 850 g of decane to the mixed solution in step 1, and stir at a speed of 10 revolutions per minute;

[0057] 3) Add 1 g of 25% ammonia water to the solution in Step 2, and stir for 1 h to form a silica dispersion;

[0058] 4) Dry the silica dispersion obtained in Step 3 at 200 °C for 3 h to obtain a dried silica gel block. Crush the gel block and then sieve to obtain silica particles with a size of 100 - 200 mesh;

[0059] 5) Calcinate the obtained silica particles at 400 °C for 2 h, 500 °C for 1 h, 700 °C for 3 h, and 1100 °C for 8 h to convert them into high-purity synthetic quartz sand.

[0060] The bulk density of the synthetic quartz sand obtained in this way is 1.22 g / cm 3 , and the true density is 2.21 g / cm 3 .

[0061] Calcinate the synthetic quartz sands obtained in Example 1 and Comparative Example 1 in a vacuum at 1800 °C for 3 h to obtain fused quartz glass. The results are as Figure 4 shown; the synthetic quartz sand with a high bulk density after calcination is a transparent block without bubbles, while there are many dense small bubbles in the block obtained by calcining Comparative Example 1.

[0062] It should be understood that the above specific embodiments of the present invention are only used for exemplary illustration or explanation of the principle of the present invention, and do not constitute a limitation to the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention shall be included within the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundary of the appended claims, or equivalent forms of such scope and boundary.

Claims

1. A preparation method of synthetic quartz sand with high bulk density, characterized in that, it comprises the following steps: S1. Mix organosilane and pure water, and stir to obtain a fully hydrolyzed transparent solution; wherein, the organosilane is tetramethoxysilane or tetraethoxysilane; S2. Add an alkane non-polar solvent to the solution obtained in step S1, control the stirring speed, and then add an emulsifier thereto, and stir to emulsify the mixed solution to obtain an emulsion that does not delaminate; wherein, the emulsifier is one of fatty alcohol polyoxyethylene ether with a purity of greater than or equal to 99.99%, polyethylene glycol fatty acid ester, and sorbitol; the addition amount of the emulsifier is 0.3%-0.5% of the mass of the organosilane; S3. Add a metal-free basic reagent to the emulsion obtained in step S2 to form a silica dispersion; S4. Filter the silica dispersion obtained in step S3 and dry it to obtain silica particles; S5. Calcinate the silica particles obtained in step S4 in air to remove the organic matter in the particles; then perform secondary calcination to remove the hydroxyl groups to obtain synthetic quartz sand, and the bulk density of the synthetic quartz sand is greater than 1.5 g / cm 3 , and the true density is greater than 2.20 g / cm 3 .

2. The preparation method of synthetic quartz sand with high bulk density according to claim 1, characterized in that, in step S1, the resistivity of the pure water > 17 megohms; the mass ratio of the organosilane to the pure water is 0.7-1.1:

1.

3. The preparation method of synthetic quartz sand with high bulk density according to claim 1, characterized in that, in step S2, the alkane non-polar solvent is one of cyclohexane, decane, nonane, and heptane; the mass ratio of the alkane non-polar solvent to the organosilane is 1-1.5:

1.

4. The preparation method of synthetic quartz sand with high bulk density according to claim 1, characterized in that, in step S3, the basic reagent is ammonia water or organic amine, the organic amine is tetramethylammonium hydroxide, and the addition amount of the basic reagent is 0.1%-0.3% of the mass of the organosilane.

5. The preparation method of synthetic quartz sand with high bulk density according to claim 4, characterized in that, the concentration of the ammonia water is 25%.

6. The preparation method of synthetic quartz sand with high bulk density according to claim 1, characterized in that, in step S2, the stirring speed is 10-50 r / min.

7. The preparation method of synthetic quartz sand with high bulk density according to claim 1, characterized in that, in step S4, the drying temperature is 150-200 °C and the time is 2-5 h.

8. The preparation method of synthetic quartz sand with high bulk density according to claim 1, characterized in that, The initial calcination is divided into three stages. 1 The calcination time is t 1 , at temperature T 2 The calcination time is t 2 , at temperature T 3 The calcination time is t 3 , and 400℃≤T 1 <T 2 <T 3 ≤800℃,t 2 <t 1 <t 3 , t 1 +t 2 +t 3 ≤6h; the temperature of the secondary calcination is 1100-1300℃, and the time is 6-10h.

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