A method for preparing non-spherical ultra-high purity low-hydroxyl silica sol

Abstract

The present invention provides a method for preparing a non-spherical ultra-high purity low-hydroxyl silica sol, comprising the following steps: S1. Prepare several groups of tetramethoxysilane alcohol as solution A, mix an organic base and deionized water to obtain solution B, and mix an inorganic base and deionized water to obtain solution C; S2. Purify solution A through a dynamic method with anion and cation exchange resins; S3. Add solution B and solution C to solution A, stir well, react at a constant temperature throughout the process, and the pH of the mixed solution is 3 < pH < 12.5 during titration to prepare a seed mother liquor; the volume ratio of solution A, solution B and solution C is 1-20:1:1; S4. Mix solution A, solution B and solution C in the same proportion as described above to form a nutrient solution, and continuously add it to the mother liquor, control the concentration ratio, reaction temperature, solution pH value, reaction time, control the supersaturation rate of the reaction, and keep it lower than the consumption rate of secondary particle nucleation to obtain a non-spherical silica sol.

Description

Technical Field

[0001] This invention relates to the field of silica sol preparation technology, and in particular to a method for preparing non-spherical ultra-high purity low-hydroxyl silica sol. Background Technology

[0002] With the arrival of the 21st century, the advanced electronics manufacturing industry has developed rapidly, possessing potential economic benefits and forming a development pattern with integrated circuits, new displays, automotive electronics, and intelligent manufacturing as its hot topics. Currently, the demand for key materials in the advanced electronics manufacturing industry (such as sapphire and zirconia ceramics) has increased significantly, indicating broad development prospects. Without high-quality electronic components, there can be no excellent electronic products and equipment; the surface quality of the components directly affects the performance and lifespan of the products. Furthermore, with the miniaturization and integration of equipment, the size of components is further reduced, and the complexity of design and manufacturing continues to increase. This will pose a severe challenge to the polishing rate and overall surface smoothness of the components.

[0003] Chemical mechanical polishing (CMP) is a crucial process in the production of sapphire and zirconia ceramics. Abrasive grains are one of the three major factors affecting CMP performance, making the selection of suitable polishing abrasives paramount. Currently, traditional spherical silica abrasives suffer from low polishing rates and generate significant amounts of polishing waste. Therefore, to meet the robust demand for sapphire and zirconia ceramics and achieve the goals of increasing workpiece polishing rates and obtaining excellent surface quality, in-depth research into polishing abrasives is necessary, which has significant scientific and practical value.

[0004] Currently, research on resin exchange purification mainly involves purifying solid silicates into solutions. Patent CN200910077035 uses this method with chelating agents for impurity removal, achieving purification of single metal impurities down to the ppb level. However, once solid silicates are prepared into solutions, they form colloids, making further impurity removal extremely difficult. Patent CN109912636A purifies silicates using cation exchange resins, but it does not employ ion exchange for anionic impurities or multi-stage impurity removal. This patent adds activated carbon and distillation for further impurity removal, making the process overly complex, and the regeneration of activated carbon is also quite difficult.

[0005] In the preparation of non-spherical nano-silica particles, CN102390838A adopts a stepwise approach to control the morphology of reactants. The stepwise addition of reactants effectively controls the initial concentration from being too high. However, as the reaction proceeds, the concentration changes significantly after the reactants are consumed, resulting in large differences in morphology. Nevertheless, there is still a concentration difference between the initial concentration of reactants added in each step and the concentration added in the next step, and the reaction parameters also change accordingly, making the control of morphology and particle size less than ideal. Summary of the Invention

[0006] The present invention discloses a method for preparing a non-spherical ultra-high purity low-hydroxyl silica sol, which solves the problems of difficult impurity removal, complicated process, and unsatisfactory control of the morphology and particle size of nano-silica particles.

[0007] To solve the above technical problems, the present invention specifically adopts the following technical solutions: A method for preparing a non-spherical ultra-high purity low-hydroxyl silica sol, comprising the following steps: S1. Prepare several groups of tetramethoxysilane alcohol as solution A, mix an organic base and deionized water to obtain solution B, and mix an inorganic base and deionized water to obtain solution C; S2. Purify solution A by dynamically passing it through anion and cation exchange resins; S3. Add solution B and solution C to solution A, stir well, react at a constant temperature throughout the process, and maintain 3 < PH < 12.5 during titration to prepare a seed mother liquor; the volume ratio of solution A, solution B, and solution C is 1-20:1:1; S4. Mix the above solution A, solution B, and solution C in the same proportion as the aforementioned ratio to form a nutrient solution, and continuously add it to the mother liquor, control the concentration ratio, reaction temperature, solution PH value, and reaction time, control the supersaturation rate of the reaction, and keep it lower than the consumption rate of secondary particle nucleation to obtain a non-spherical silica sol; S5. Adsorb the prepared silica sol through a mixture of anion and cation resins, and further remove anion impurities through ion exchange.

[0008] Preferably, to remove metal impurities to the ppb level, the ion exchange method is a three-stage series dynamic ion exchange of anion + cation + anion; the exchange time is 0.1 hour - 5 hours, and the process temperature is controlled at 10 - 80 °C.

[0009] Preferably, for the silica sol obtained in step S3, the molar mass ratio of MSiO2 / M is 0.001 - 1, and components such as silane, alcohol, and deionized water are added. MSiO2 represents the silica produced during the reaction, and the organic base is selected from tetraethylammonium hydroxide, tetrabutylammonium hydroxide, ammonium hydroxide, monomethyltriethanolammonium hydroxide, tetramethylammonium hydroxide, monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine, N-methylethanolamine, monopropanolamine, and morpholine.

[0010] Preferably, the constant temperature reaction in step S3 is heated at 9 - 90 °C for 0.1 - 70 hours to obtain a silica sol.

[0011] Preferably, in step S4, the continuously added solution A, solution B, and solution C react in a temperature environment that is 3 - 90 °C lower than the temperature of the mother liquor.

[0012] Preferably, the stirring speed in step S3 is kept stable at 10-500 rpm.

[0013] Preferably, the low-hydroxyl chelating agent containing a dithiocarbamate (DTC) group is one or more of dimethyl dithiocarbamate, diethyl dithiocarbamate, trimethylchlorosilane, dibutyl dithiocarbamate, dibenzyl dithiocarbamate, dioctyl dithiocarbamate, tetramethylchlorosilane, dihydroxyethyl dithiocarbamate, triethylenetetramine didithiocarbamate, polyamine dithiocarbamate, and 1,3,5-hexahydrotriazine dithiocarbamate.

[0014] Preferably, in step S2, before solution A forms a colloid, cations are removed by hydrogen-type cation exchange using a dynamic method involving heating and continuous stirring.

[0015] Preferably, the alcohol is selected from one or more of monohydric alcohols, dihydric alcohols, and polyhydric alcohols.

[0016] The reaction mechanism and characterization of this invention are as follows: Hydrolysis-polymerization mechanism: The sol-gel method refers to the process of solidifying compounds containing highly chemically active components through solution, sol, and gel, followed by heat treatment to form oxides or other solid compounds. The sol-gel method for preparing silica microspheres often uses silicate esters (such as TMOS and TEOS) as the silicon source and alcohol as the solvent. Under acidic or alkaline conditions, the silicate ester first undergoes hydrolysis and condensation chemical reactions to form a stable silica sol system. The entire reaction process and mechanism are shown in Tables 1 and 2: The hydrolysis of silicate esters is a stepwise substitution process and also the rate-determining step. First, the oxygen atom in the water molecule undergoes nucleophilic attack on the silicon atom in tetraethyl orthosilicate, forming a five-coordinate intermediate in the presence of the catalyst ammonia (as shown in Table 1). The -OR group in Si(OR)4 is gradually replaced by -OH. Due to the instability of the hydrolysis products, they undergo dehydration condensation reactions with each other or de-alcoholization condensation reactions with silicate esters to form Si-OSi bonds (as shown in Table 2). The polysilicic acid (basic particles of silica sol) produced by the condensation reaction has a [SiO4] tetrahedral structure. According to the valence rule, each vertex of the [SiO4] tetrahedron, i.e., O2−, can share at most two such tetrahedra (corner-sharing). The four vertices of each [SiO4] tetrahedron are connected to the parent [SiO4] tetrahedron, forming a three-dimensional network structure, roughly spherical. At positions where the condensation reaction has not yet occurred, silicon atoms still carry 1 to 3 -OH groups. These basic particles, through the condensation reaction of -OH groups, will eventually connect randomly to form a three-dimensional network structure with a solid gel system.

[0017] Table 1 Hydrolysis and polymerization reaction processes Table 2 Hydrolysis and Polymerization Reaction Mechanisms Characterization of Free Hydroxyl Group Reduction: Silica gel surfaces consist of free hydroxyl groups and associated hydroxyl groups. In silica sol solutions, free hydroxyl groups are the primary adsorbents. By measuring the adsorption isotherm and infrared spectrum of silica sol, the role and content of free and associated hydroxyl groups on the surface can be explored. After surface modification, the free hydroxyl peak (~3700 cm⁻¹) on the silica gel surface is significantly reduced, while the associated hydroxyl peak (a broad peak near ~3450 cm⁻¹) shows no significant change, indicating that the modified silica gel mainly contains associated hydroxyl groups. The adsorption isotherm of the modified silica sol shows that the adsorption force drops to zero, indicating that the surface contains an amount of associated hydroxyl groups equal to that of hydrophilic silicon, but these hydroxyl groups lack adsorption capacity. Furthermore, the infrared spectrum of the modified silica sol still shows a certain amount of free hydroxyl groups, for the following reasons: 1. Geometric position: free hydroxyl groups failed to react with the modifier. 2. Steric hindrance: adjacent free hydroxyl groups are sterically hindered and cannot be modified. 3. Hydroxyl groups within micropores and closed pores remain unreacted.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. Based on the ion exchange mechanism, this invention performs a purification process before the formation of the colloidal electrical layer, achieving ppb-level removal of single metal impurities.

[0019] 2. The traditional Stber method has proven highly effective for preparing spherical silica particles of varying sizes. This invention develops an improved Stber method using a co-catalyst to prepare silica particles with fractal shapes. Stronger alkalinity promotes hydrolysis / condensation. Simultaneously, incorporating the positively charged particles generated by the dissociation of the co-catalyst into the negatively charged silica network further suppresses electrostatic repulsion between silica particles. In this improved Stber method, the growth of silica particles primarily follows an aggregation-only model; by adjusting the concentration, silica particles with different fractal dimensions (df) can be grown.

[0020] 3. Continuous liquid feeding control can ensure uniform concentration and consistent parameters during the reaction process, thereby controlling the narrow particle size distribution and relatively uniform non-spherical shape growth of nano-carbon dioxide particles.

[0021] 4. Compared to a spherical shape, this invention improves the material removal rate when polishing hard, inert materials. When polishing silicon oxide films, the polishing rate is 105% higher than with a spherical shape. When polishing sapphire and silicon wafers, the material removal rate is significantly increased, scratches are reduced, and the surface finish and smoothness meet the requirements. Attached Figure Description Figure 1This is an electron microscope image of the non-spherical silica sol from Example 1; Figure 2 This is an electron microscope image of the non-spherical silica sol from Example 2; Figure 3 This is an electron microscope image of the non-spherical silica sol in Example 3. Detailed Implementation

[0022] The specific content of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0023] Example 1 Orthosilicate purification: Through a strongly acidic cation exchange resin; Ion exchange resin: 300g of strong acid cation exchange resin; Solution dosage: 500g silicate solution; Flow rate: 188 mL / min; Through anion exchange resin Ion exchange resin: 300g of strong acid cation exchange resin; Solution dosage: 500g silicate solution; Flow rate: 188 mL / min; Then it passes through a strongly acidic cation exchange resin (as above).

[0024] The purified silicate raw material, along with diol (ultrapure), ethanol (ultrapure), distilled water, and tetraethanolamine hydroxide, were used as is without further processing. The silica nanoparticles were synthesized by hydrolyzing TEOS and ethanol. Initially, these were introduced into three different 100ml vials and continuously stirred (500 rot / min) on a stirrer. While stirring, the mixture was heated to 90°C, and the original proportions of materials were continuously added dropwise. After 30 minutes, a mixture of deionized water (10ml) and different amounts of ammonium hydroxide solution (0.5ml) was added to each vial, and stirring continued for 14 hours until the mixture became a milky white solution. Then, the three different mixtures were placed in petri dishes and dried in a low-pressure (100 mbar) tube furnace at 90°C for 3 hours. After drying, the silica nanoparticles were characterized. The structure and particle size of the silica nanoparticles were observed and measured using field emission scanning electron microscopy (FESEM).

[0025] Example 2 Orthosilicate purification: Through a strongly acidic cation exchange resin; Ion exchange resin: 300g of strong acid cation exchange resin; Solution dosage: 500g silicate solution; Flow rate: 188 mL / min; Through anion exchange resin Ion exchange resin: 300g of strong acid cation exchange resin; Solution dosage: 500g silicate solution; Flow rate: 188 mL / min; Then it passes through a strongly acidic cation exchange resin (as above).

[0026] The purified silicate raw material, along with diol (ultrapure), ethanol (ultrapure), distilled water, and tetramethylammonium hydroxide, were used as is without further processing. The silica nanoparticles were synthesized by hydrolyzing TEOS and ethanol. Initially, these were introduced into three different 120 ml vials and continuously stirred (10 rot / min) on a stirrer. While stirring, the mixture was heated to 30°C, and the original proportions of materials were continuously added dropwise. After 60 minutes, a mixture of deionized water (30 ml) and different amounts of ammonium hydroxide solution (1 ml) was added to each vial, and stirring continued for 30 hours until the mixture became a milky white solution. Then, the three different mixtures were placed in petri dishes and dried in a low-pressure (100 mbar) tube furnace at 130°C for 3 hours. After drying, the silica nanoparticles were characterized. The structure and particle size of the silica nanoparticles were observed and measured using field emission scanning electron microscopy (FESEM).

[0027] Example 3 Orthosilicate purification: Through a strongly acidic cation exchange resin; Ion exchange resin: 300g of strong acid cation exchange resin; Solution dosage: 500g silicate solution; Flow rate: 188 mL / min; Through anion exchange resin Ion exchange resin: 300g of strong acid cation exchange resin; Solution dosage: 500g silicate solution; Flow rate: 188 mL / min; Then it passes through a strongly acidic cation exchange resin (as above).

[0028] The purified silicate raw material, along with diol (ultrapure), distilled water, and diethanolamine, were used as is without further processing. The silica nanoparticles were synthesized by hydrolyzing TEOS and ethanol. Initially, these were introduced into three different 120 ml vials and continuously stirred (50 rot / min) on a stirrer. While stirring, the temperature was maintained at 9°C, and the original proportions of materials were continuously added dropwise. After 60 minutes, a mixture of deionized water (80 ml) and different amounts of ammonium hydroxide solution (2 ml) was added to each vial, and stirring continued for 60 hours until the mixture became a milky white solution. Then, the three different mixtures were placed in petri dishes and dried in a low-pressure (100 mbar) tube furnace at 150°C for 3 hours. After drying, the silica nanoparticles were characterized. The structure and particle size of the silica nanoparticles were observed and measured using field emission scanning electron microscopy (FESEM).

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing non-spherical ultra-high purity low-hydroxyl silica sol, characterized in that, It includes the following steps: S1. Prepare several groups of tetramethoxysilanol as solution A, mix an organic base and deionized water to obtain solution B, and mix an inorganic base and deionized water to obtain solution C; S2. Purify solution A by dynamically passing it through anion and cation exchange resins; S3. Add solution B and solution C to solution A, stir well, react at a constant temperature throughout the process, and keep the pH of the mixed solution at 3 < pH < 12.5 during titration to prepare a seed mother liquor; the volume ratio of solution A, solution B, and solution C is 1 - 20:1:1; S4. Mix the above solution A, solution B, and solution C in the same proportion as the previous ratio to form a nutrient solution, and continuously add the mother liquor, control the concentration ratio, reaction temperature, solution pH value, reaction time, control the supersaturation rate of the reaction, and keep it lower than the consumption rate of secondary particle nucleation to obtain non-spherical silica sol; S5. Add a hydroxyl group removal modifier to the completely reacted silica sol to reduce free hydroxyl groups, reduce the thickening effect caused by hydroxyl groups, and at the same time do not affect associated hydroxyl groups, and improve the abrasive concentration and stability; S6. Dynamically exchange the silica sol through an anion resin in a heating environment to further remove anions.

2. The method for preparing non-spherical ultra-high purity low-hydroxyl silica sol according to claim 1, characterized in that: The metal impurities are removed to the ppb level, and the ion exchange method is dynamic ion exchange in a three-stage series connection mode of anion + cation + anion; the exchange time is 0.1 hour - 5 hours, and the process temperature is controlled at 10 - 80°C.

3. The method for preparing non-spherical ultra-high purity low-hydroxyl silica sol according to claim 1, characterized in that: For the silica sol obtained in step S3, the molar mass ratio of MSiO2 / M is 0.001 - 1, and components such as silane, alcohol, and deionized water are added. MSiO2 represents the silicon dioxide generated during the reaction process, and the organic bases are selected from tetraethylammonium hydroxide, tetrabutylammonium hydroxide, ammonium hydroxide, methyltriethanolammonium hydroxide, tetramethylammonium hydroxide, monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine, N-methylethanolamine, monopropanolamine, and morpholine.

4. The method for preparing non-spherical ultra-high purity low-hydroxyl silica sol according to claim 1, characterized in that: The constant temperature reaction in step S3 is heated at 9 - 90°C for 0.1 - 70 hours to obtain silica sol.

5. The method for preparing non-spherical ultra-high purity low-hydroxyl silica sol according to claim 1, characterized in that: In step S4, the continuously added solution A, solution B, and solution C react in a temperature environment 3 - 90°C lower than the temperature of the mother liquor.

6. The method for preparing non-spherical ultra-high purity low-hydroxyl silica sol according to claim 1, characterized in that: In step S3, the stirring speed is stable at 150 - 400 rpm, and the reaction time is 11 - 30 hours.

7. The method for preparing non-spherical ultra-high purity low-hydroxyl silica sol according to claim 1, characterized in that: The chelating agent containing a dithiocarbamate (DTC) group for reducing hydroxyl groups is selected from one or more of dimethyldithiocarbamate, diethyldithiocarbamate, trimethylchlorosilane, dibutyldithiocarbamate, dibenzyldithiocarbamate, dioctyldithiocarbamate, tetramethylchlorosilane, bis(2-hydroxyethyl)dithiocarbamate, triethylenetetramine bisdithiocarbamate, polyamine dithiocarbamate, and 1,3,5-hexahydrotriazine dithiocarbamate.

8. The method for preparing non-spherical ultra-high purity low-hydroxyl silica sol according to claim 1, characterized in that: In step S2, before solution A forms a colloid, cations are removed by passing through a hydrogen-type cation resin, adopting a dynamic method of heating and continuous stirring.

9. The method for preparing non-spherical ultra-high purity low-hydroxyl silica sol according to claim 1, characterized in that: The alcohol is selected from one or more of monohydric alcohols, dihydric alcohols, and polyhydric alcohols.

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