Method for reducing content of metal impurities in silica sol and silica sol prepared by method

Abstract

The invention belongs to the field of silica sol materials, and relates to a method for reducing the content of metal impurities in silica sol and the silica sol prepared by the method. The method comprises the following steps: adding alkali into the prepared silica sol, adjusting the pH value to 13-14, stirring at room temperature to 60 DEG C to dissolve aluminum hydroxide or oxide to form aluminum anions (AlO2 <->), and then carrying out anion resin exchange to remove the aluminum anions, so that the effect of effectively removing the aluminum metal impurities is realized, the influence on the performance of the silica sol is small, and the method is suitable for industrial production. The pH value can be subsequently regulated and controlled to a required range by adding acid, and metal impurity ions are not introduced at the same time. According to the method, reagents which are simpler and easier to obtain are used, the removal effect on metal impurities such as aluminum is good, the influence on the performance of the silica sol is small, and the operation method is simple, efficient, low in cost and suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of silica sol materials and relates to methods for preparing and purifying silica sol. Specifically, it relates to a method for reducing the content of metallic impurities such as aluminum in silica sol and the silica sol prepared therefrom. Background Technology

[0002] Silica sol is a colloidal solution formed by dispersing amorphous nano-silica particles in water or organic solvents, with the molecular formula mSiO2·nH2O. As an important inorganic nanomaterial, it possesses a series of excellent properties such as high specific surface area, good dispersibility, good adhesion, good fire resistance and heat insulation, and good insulation. Therefore, it is widely used in casting, chemical mechanical polishing, coatings, petrochemicals, textiles, papermaking, and special ceramic composite materials. In particular, with the rise of the IC industry, the demand for silica sol in chemical mechanical polishing is constantly increasing, but the requirements for the purity of silica sol are becoming increasingly stringent.

[0003] There are three main methods for preparing silica sol: ion exchange, orthosilicate hydrolysis, and silica powder hydrolysis. Orthosilicate hydrolysis produces silica sol with the most uniform particle size and the lowest metal impurity content, but this method has extremely high raw material costs and requires the use of flammable alcohol solvents. Silica powder hydrolysis uses silicon powder waste from wafer fabs as raw material, hydrolyzing it in an alkaline solution to generate silicic acid, which then polymerizes into silica sol. Silica powder hydrolysis is a strongly exothermic reaction that generates a large amount of hydrogen gas, making the reaction difficult to control in practice. The temperature of the reactants can easily run out of control, causing the reaction rate to accelerate rapidly, and the generation of hydrogen gas creates a large amount of foam, resulting in relatively high production costs. Ion exchange, with its inexpensive raw materials, simple equipment and processes, ease of operation, and controllable product technical parameters, is widely used in the preparation of silica sol.

[0004] The preparation of silica sol by ion exchange typically uses water glass as a raw material. After ion exchange treatment, most metal ion impurities such as sodium and potassium are removed, resulting in a silicic acid solution. This solution is then subjected to polymerization at specific temperature and pH values ​​to obtain silica sol. After cation exchange with resin, metallic impurities such as aluminum, iron, zinc, magnesium, calcium, and nickel still remain in the silicic acid, with aluminum being the most abundant. These metal ions mainly exist as electrically neutral hydroxides and oxides at the pH (4-6) of silicic acid, and therefore cannot react with the ion exchange resin, thus failing to be effectively removed. This results in an aluminum content >100 ppm in the final silica sol product.

[0005] Patent CN 104591192 A discloses a method for improving the purity of orthosilicic acid solution, using water glass as raw material and subjecting it to sequential cation, cation, and anion exchange. Before the second cation exchange, acid is added to adjust the pH, converting hydroxides of elements such as aluminum into cations, thereby reducing the content of metallic impurities such as aluminum. Patent CN 101475180 A discloses a method for purifying silica sol, controlling the silica sol temperature between 0 and 60°C, sequentially passing it through a strong acid cation exchange bed and a strong base anion exchange bed, then adding a chelating agent, and finally passing it through a mixed strong acid and strong base ion exchange bed to obtain purified silica sol. Patent CN 102583406 A further improves upon CN 101475180 A by mixing silica sol with a mixed strong acid and strong base resin, stirring at a certain temperature, adding a composite chelating agent and flocculant, and controlling the pH between 1 and 5 to achieve silica sol purification.

[0006] With the continuous development of the silica sol industry, the requirements for silica sol are becoming increasingly stringent, and silica sol purification technology will continue to evolve. This invention provides a novel silica sol purification method that uses simpler and more readily available reagents, effectively removing the most abundant aluminum metal impurity, while having minimal impact on the viscosity, stability, and other properties of the silica sol. Summary of the Invention

[0007] To address the above-mentioned problems, this invention provides a method for reducing the content of metallic impurities such as aluminum in silica sol and the silica sol prepared therefrom.

[0008] The technical solution adopted in this invention is as follows:

[0009] A method for reducing the content of metal impurities in silica sol includes the following steps:

[0010] The strong acid cation exchange resin and the strong base anion exchange resin were activated and regenerated using strong acid solution and strong base solution, respectively.

[0011] Prepare a water glass solution and reflux it with stirring to form silicon dioxide seed crystals;

[0012] The activated and regenerated cation exchange resin was used to perform ion exchange on the water glass solution that had been refluxed and stirred and the water glass solution that had not been refluxed and stirred, to remove the main cations and obtain the orthosilicic acid-seed crystal solution containing seed crystals and the orthosilicic acid solution without seed crystals.

[0013] After diluting the original silica-seed crystal solution to a certain concentration, it is put into a reaction vessel with stirring and heating function as the reaction base liquid, and alkali is added as a pH adjuster. The mixture is heated to boiling and stirred. While boiling, the original silica solution without seed crystal is continuously passed into the reaction liquid to carry out the polymerization growth reaction, forming silica sol particles, and obtaining primary silica sol with a certain particle size.

[0014] An alkali is added to the primary silica sol as a pH adjuster, and the mixture is stirred at a certain temperature to dissolve aluminum hydroxide and oxides, forming free aluminum anions. Ion exchange is then performed using an activated and regenerated anion exchange resin to remove aluminum metal impurities, resulting in secondary silica sol.

[0015] Acid is added to the secondary silica sol as a pH adjuster to achieve the target pH. Then, the solid content of the silica sol is increased by ultrafiltration or evaporation concentration to obtain the target silica sol.

[0016] Preferably, the mass concentration of SiO2 in the water glass solution is 0.5-6%.

[0017] Preferably, the reflux stirring temperature is 60–100°C and the time is 4–12 hours.

[0018] Preferably, the ion exchange is carried out by static or dynamic exchange, and the pH value of the orthosilicic acid solution is 3 to 6.

[0019] Preferably, the mass concentration of SiO2 in the reaction substrate is 0.2-1.0%, and the pH value of the reaction solution is controlled at 9-12.

[0020] Preferably, the particle size of the obtained primary silica sol is 10–100 nm.

[0021] Preferably, the addition of alkali to the primary silica sol as a pH adjuster is to adjust the pH to 13-14.

[0022] Preferably, the stirring at a certain temperature to dissolve aluminum hydroxide and oxides, wherein the temperature is room temperature to 60°C and the stirring time is 2 to 4 hours.

[0023] Preferably, the target pH value is 9 to 12.

[0024] The present invention also provides a silica sol prepared by the above method.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention provides a method for reducing the content of metallic impurities such as aluminum in silica sol without requiring multiple ion exchanges and further acidification to prepare the orthosilicic acid solution, thereby reducing production costs. This invention uses simpler and more readily available reagents, achieves better removal of metallic impurities such as aluminum, and has minimal impact on the performance of the silica sol. It meets the application requirements of chemical mechanical polishing for silica sol, is simple to operate, highly efficient, uses simple and inexpensive raw materials, and is suitable for large-scale industrial production, thus having practical significance. Detailed Implementation

[0027] The present invention will be further described in detail below through specific embodiments.

[0028] This invention provides a method for reducing the content of metallic impurities such as aluminum in silica sol and the silica sol obtained therefrom. The method mainly involves adding an alkali to the prepared silica sol to adjust the pH to 13-14, and stirring at room temperature to 60°C to dissolve aluminum hydroxides or oxides, forming aluminum anions (AlO2). - Following this, anion exchange resin is used to remove aluminum anions, thus effectively removing aluminum metal impurities with minimal impact on the performance of the silica sol. The pH value can be adjusted to the desired range by adding acid without introducing metal impurity ions. The silica sol prepared according to this method achieves the following technical specifications: with a SiO2 content of 40%, aluminum content ≤10ppm, viscosity ≤5mpa·s, pH 9–13, and storage stability greater than 1 year, meeting the application requirements of silica sol in chemical mechanical polishing. The method includes the following steps:

[0029] (1) Activation and regeneration of ion exchange resins: The strong acid type cation exchange resin (brand name 732) and the strong base type anion exchange resin (brand name 717) are activated and regenerated by strong acid solution and strong base solution, respectively.

[0030] (2) Preparation of water glass solution and preparation of seed crystals: Water glass is diluted to a certain concentration with deionized water to obtain water glass solution. The solution is then refluxed and stirred at a certain temperature to pre-form a certain amount of silicon dioxide seed crystals.

[0031] (3) Preparation of orthosilicic acid solution by cation exchange: The activated and regenerated 732 cation exchange resin is used to perform ion exchange on the water glass solution that has been refluxed and stirred in step (2) and the water glass solution that has not been refluxed and stirred in step (2) through static exchange or dynamic exchange to remove the main cations such as sodium and potassium, and to prepare orthosilicic acid-seed crystal solution containing certain seed crystals and orthosilicic acid solution without seed crystals.

[0032] (4) Preparation of primary silica sol: After diluting the orthosilicic acid-seed crystal solution obtained in step (3) to a certain concentration, it is put into a reaction vessel with stirring and heating function as the reaction base liquid, and alkali is added as pH adjuster. The mixture is heated to boiling and stirred. Under boiling conditions, orthosilicic acid solution without seed crystal is continuously introduced into the reaction solution to carry out polymerization growth reaction and form silica sol particles. The size of silica particles can be controlled by controlling the amount of orthosilicic acid fed, and primary silica sol with a certain particle size is obtained.

[0033] (5) Silica sol purification treatment: At this time, the primary silica sol contains a lot of aluminum impurities. An alkali is added to the primary silica sol as a pH adjuster, and then stirred at a certain temperature to dissolve aluminum hydroxide and oxide, forming free aluminum anions. The activated and regenerated 717 type anion exchange resin is used to carry out ion exchange through static exchange or dynamic exchange. The aluminum anions are captured by the anion exchange resin, thereby removing aluminum metal impurities and obtaining secondary silica sol.

[0034] (6) Preparation of target silica sol: Add acid as a pH adjuster to the secondary silica sol to achieve the required pH without introducing metal impurity ions. Then, increase the solid content of the silica sol by ultrafiltration or evaporation concentration to obtain the target silica sol.

[0035] In step (1), the activation and regeneration of the ion exchange resin is a common method.

[0036] Preferably, in step (2), the concentration of water glass is based on the content of silicon dioxide (SiO2), and the mass concentration is 0.5-6%.

[0037] Preferably, in step (2), the reflux stirring temperature is 60-100℃ and the time is 4-12h.

[0038] In step (3), dynamic or static exchange of ion exchange resin is a common method, and the pH value of the prepared orthosilicic acid solution (orthosilicic acid-seed crystal solution and orthosilicic acid solution without seed crystal) is 3 to 6.

[0039] Preferably, in step (4), the mass concentration (SiO2%) of the reaction substrate is 0.2-1.0%.

[0040] Preferably, in step (4), the alkali is a commonly used alkali in the prior art, such as sodium hydroxide, potassium hydroxide, ammonia, tetramethylammonium hydroxide, etc.

[0041] Preferably, in step (4), the pH value of the reaction solution is controlled at 9 to 12.

[0042] Preferably, in step (4), the orthosilicic acid can be introduced by dripping at a constant rate or by adding it in batches.

[0043] Preferably, in step (4), the particle size of the obtained primary silica sol is 10-100 nm.

[0044] Preferably, in step (5), the alkali is a commonly used alkali in the prior art, such as sodium hydroxide, potassium hydroxide, ammonia, tetramethylammonium hydroxide, etc.

[0045] Preferably, in step (5), an alkali is added to adjust the pH to 13-14.

[0046] Preferably, in step (5), the temperature is room temperature to 60°C and the stirring time is 2 to 4 hours.

[0047] Preferably, in step (6), the acid is a commonly used acid in the prior art, such as hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, formic acid, acetic acid, phosphoric acid, etc.

[0048] Preferably, in step (6), the target pH value is 9 to 12, which meets the usage requirements.

[0049] In step (6), ultrafiltration or evaporation concentration is a common method, the purpose of which is to increase the solid content of silica sol to the required solid content.

[0050] To enable those skilled in the art to gain a more comprehensive understanding of this invention, specific embodiments are provided below.

[0051] In the embodiments, commercially available liquid water glass with a modulus of 3.3 (SiO2 content: 28.7%; Na2O content: 9.12%) was used to activate and regenerate the strong acid cation exchange resin (brand name 732) and the strong base anion exchange resin (brand name 717) using hydrochloric acid and sodium hydroxide solutions with a concentration of 1 mol / L, respectively.

[0052] Example 1:

[0053] Take 300g of water glass, add 1500g of water, mix well to obtain a dilute water glass solution; prepare two portions of water glass solution, take one portion and reflux and stir at 80℃ for 8h to prepare seed crystals; use 732 cation exchange resin to prepare an orthosilicic acid-seed crystal solution containing certain seed crystals and an orthosilicic acid solution without seed crystals, the pH value of the obtained orthosilicic acid solution is about 4.

[0054] Take 100g of orthosilicic acid-seed crystal solution containing a certain amount of seed crystals, add 200g of deionized water to prepare the reaction base solution, add 5g of 1mol / L sodium hydroxide solution to make the pH of the reaction solution 11, heat to boiling and stir, and add orthosilicic acid solution dropwise to the reaction solution at a rate of 2mL / min under boiling conditions to carry out the polymerization growth reaction. After adding a total of 600g of orthosilicic acid solution, stop the reaction to obtain primary silica sol.

[0055] Add 5g of 1mol / L sodium hydroxide solution to the primary silica sol, adjust the pH to 13, and then stir at 50℃ for 3h. Subsequently, use 717 type anion exchange resin to carry out ion exchange through static exchange to remove aluminum metal impurities and obtain secondary silica sol.

[0056] 3 g of 1 mol / L hydrochloric acid was added to the secondary silica sol, setting the pH to 10. The mixture was then concentrated by ultrafiltration to a solid content (SiO2 content) of 40%, yielding the target silica sol. The characterization results are shown in Table 1.

[0057] Example 2:

[0058] Take 300g of water glass, add 1800g of water, mix well to obtain a dilute water glass solution; prepare two portions of water glass solution, take one portion and reflux and stir at 90℃ for 6h to prepare seed crystals; use 732 cation exchange resin to prepare an orthosilicic acid-seed crystal solution containing certain seed crystals and an orthosilicic acid solution without seed crystals, the pH value of the obtained orthosilicic acid solution is about 4.4;

[0059] Take 50g of orthosilicic acid-seed crystal solution containing a certain amount of seed crystals, add 250g of deionized water to prepare the reaction base solution, add 6g of 1mol / L potassium hydroxide solution to make the pH of the reaction solution 11.2, heat to boiling and stir, and add orthosilicic acid solution to the reaction solution in batches at a rate of 20g / time with an interval of 0.5h to carry out the polymerization growth reaction. After adding a total of 800g of orthosilicic acid solution, stop the reaction to obtain primary silica sol.

[0060] Add 8g of 1mol / L potassium hydroxide solution to the primary silica sol, adjust the pH to 13.5, and then stir at 40℃ for 4h. Subsequently, use 717 type anion exchange resin to carry out ion exchange through static exchange to remove aluminum metal impurities and obtain secondary silica sol.

[0061] 4 g of 1 mol / L hydrochloric acid was added to the secondary silica sol, adjusting the pH to 10.5. The sol was then concentrated by ultrafiltration to a solid content (SiO2 content) of 40%, yielding the target silica sol. The characterization results are shown in Table 1.

[0062] Example 3:

[0063] Take 300g of water glass, add 2100g of water, and mix well to obtain a dilute water glass solution; prepare two portions of water glass solution, take one portion and reflux and stir at 100℃ for 4h to prepare seed crystals; use 732 cation exchange resin to prepare an orthosilicic acid-seed crystal solution containing certain seed crystals and an orthosilicic acid solution without seed crystals. The pH value of the obtained orthosilicic acid solution is about 4.6.

[0064] Take 60g of orthosilicic acid-seed crystal solution containing a certain amount of seed crystals, add 240g of deionized water to prepare the reaction base solution, add 8g of 10% tetramethylammonium hydroxide solution to make the pH of the reaction solution 12, heat to boiling and stir, and add orthosilicic acid solution to the reaction solution in batches at a rate of 25g / time with an interval of 0.5h to carry out the polymerization growth reaction. After adding a total of 1500g of orthosilicic acid solution, stop the reaction to obtain primary silica sol;

[0065] 7.5g of 10% tetramethylammonium hydroxide solution was added to the primary silica sol to adjust the pH to 13. Then, the mixture was stirred at 60℃ for 4 hours. Subsequently, ion exchange was carried out using a 717 type anion exchange resin through static exchange to remove aluminum metal impurities and obtain the secondary silica sol.

[0066] 4 g of 1 mol / L hydrochloric acid was added to the secondary silica sol, setting the pH to 10. The mixture was then concentrated by ultrafiltration to a solid content (SiO2 content) of 40%, yielding the target silica sol. The characterization results are shown in Table 1.

[0067] Comparative Example 1:

[0068] Take 300g of water glass, add 1500g of water, mix well to obtain a dilute water glass solution; prepare two portions of water glass solution, take one portion and reflux and stir at 80℃ for 8h to prepare seed crystals; use 732 cation exchange resin to prepare an orthosilicic acid-seed crystal solution containing certain seed crystals and an orthosilicic acid solution without seed crystals, the pH value of the obtained orthosilicic acid solution is about 4.

[0069] Take 100g of orthosilicic acid-seed crystal solution containing a certain amount of seed crystals, add 200g of deionized water to prepare the reaction base solution, add 5g of 1mol / L sodium hydroxide solution to adjust the pH of the reaction solution to 11, heat to boiling and stir. Under boiling conditions, add orthosilicic acid solution dropwise to the reaction solution at a rate of 2mL / min to carry out the polymerization growth reaction. After adding a total of 600g of orthosilicic acid solution, stop the reaction to obtain primary silica sol with pH 9.7. Then concentrate it to a solid content (SiO2 content) of 40% by ultrafiltration to obtain the target silica sol. The characterization results are shown in Table 1.

[0070] Table 1. Characterization results of the target silica sol in each embodiment

[0071]

[0072] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and to implement it accordingly. Those skilled in the art will understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the content disclosed in the embodiments of this specification; the scope of protection of the present invention is defined by the claims.

Claims

1. A method of reducing the content of metal impurities in a silica sol, characterized in that, The method comprises the following steps: The strong acid type cation exchange resin and the strong base type anion exchange resin are respectively activated and regenerated by using strong acid solution and strong base solution; A water glass solution is prepared and refluxed and stirred to form silica seed crystals; The cation exchange resin after activation and regeneration is used to exchange ions in the refluxed and stirred water glass solution and the water glass solution without refluxing and stirring to remove main cations, so as to obtain a primary silicic acid-seed crystal solution containing seed crystals and a primary silicic acid solution without seed crystals; The primary silicic acid-seed crystal solution is diluted to a certain concentration, and then is put into a reactor with stirring and heating function as a reaction bottom solution, and an alkali is added as a pH regulator, and the reaction solution is heated to boiling and stirred, and the primary silicic acid solution without seed crystals is continuously introduced into the reaction solution under boiling state to perform a polymerization growth reaction, so as to form silica sol particles and obtain a primary silica sol with a certain particle size; An alkali is added into the primary silica sol as a pH regulator, and the solution is stirred at a certain temperature to dissolve the aluminum hydroxide and oxide to form free aluminum anions, and then the anion exchange resin after activation and regeneration is used to exchange ions to remove aluminum metal impurities, so as to obtain a secondary silica sol; An acid is added into the secondary silica sol as a pH regulator to reach a target pH, and then the solid content of the silica sol is increased by ultrafiltration or evaporation concentration to obtain a target silica sol.

2. The method of claim 1, wherein, The mass concentration of SiO2 in the water glass solution is 0.5-6%.

3. The method of claim 1, wherein, The refluxing and stirring temperature is 60-100℃, and the time is 4-12h.

4. The method of claim 1, wherein, The ion exchange is performed by static exchange or dynamic exchange, and the pH value of the primary silicic acid solution is 3-6.

5. The method of claim 1, wherein, The mass concentration of SiO2 in the reaction bottom solution is 0.2-1.0%, and the pH value of the reaction solution is controlled to be 9-12.

6. The method of claim 1, wherein, The particle size of the obtained primary silica sol is 10-100nm.

7. The method of claim 1, wherein, The alkali is added into the primary silica sol as a pH regulator to adjust the pH value to 13-14.

8. The method of claim 1, wherein, The solution is stirred at a certain temperature to dissolve the aluminum hydroxide and oxide, wherein the temperature is room temperature-60℃, and the stirring time is 2-4h.

9. The method of claim 1, wherein, The target pH value is 9-12.

10. A silica sol prepared by the method according to any one of claims 1-9.

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