Colloidal silica and its manufacturing method

Abstract

To provide colloidal silica containing silica particles with excellent denseness and excellent maintenability of an uneven surface shape under basic conditions, and a method for producing the colloidal silica.SOLUTION: Colloidal silica that contains silica particles having an uneven surface shape, is characterized in that (1) the silica particles have an alkoxy group content of 1000 ppm or more, and (2) the silica particles have a specific surface area reduction rate of 15.0% or less when heat-treated under basic conditions.SELECTED DRAWING: None

Description

[Technical Field] 【0001】 The present invention relates to colloidal silica and a method for producing the same, and more particularly to colloidal silica containing silica particles having a surface irregular shape and a method for producing the same. [Background technology] 【0002】 Colloidal silica is a dispersion of silica nanoparticles in a medium such as water, and is used as a property modifier in fields such as paper, textiles, and steel, as well as a polishing agent for electronic materials such as semiconductor wafers. The silica particles dispersed in colloidal silica used in these applications require high purity and density. 【0003】 As a method for producing colloidal silica that can meet the above requirements, for example, a method for producing an aqueous silica sol by adding an alkyl silicate to a reaction medium with an alkali concentration within a specific range has been disclosed (see, for example, Patent Document 1). 【0004】 However, according to the manufacturing method described in Patent Document 1, spherical particles are produced, and the shape of the silica particles is not considered. 【0005】 A method for producing colloidal silica containing silica particles having small protrusions on the particle surface has been disclosed, using a quaternary ammonium salt or the like as a hydrolysis catalyst (see, for example, Patent Document 2). Colloidal silica exhibits higher abrasive properties as an abrasive when the silica particles are deformed, such as by having protrusions on the surface. [Prior art documents] [Patent Documents] 【0006】 [Patent Document 1] Japanese Patent Application Publication No. 6-316407 [Patent Document 2] Japanese Patent Publication No. 2007-153732 [Overview of the project] 【Problems to be Solved by the Invention】 【0007】 The present inventors have found that the colloidal silica produced by the production method described in Patent Document 2 has a problem that the surface uneven shape cannot be maintained under basic conditions. 【0008】 As a result of intensive studies, the present inventors have succeeded in producing colloidal silica containing silica particles excellent in maintaining the surface uneven shape even under basic conditions. And, such colloidal silica can be suitably used as an abrasive, and the inventors have conceived that the above problems can be solved perfectly, and thus reached the present invention. 【0009】 An object of the present invention is to provide a colloidal silica containing silica particles excellent in density and in maintaining the surface uneven shape even under basic conditions, and a production method capable of producing the colloidal silica. 【Means for Solving the Problems】 【0010】 As a result of intensive studies to achieve the above object, the present inventor has found that, according to a colloidal silica containing silica particles having a surface uneven shape, the content of the alkoxy group of the silica particles being in a specific range, and the silica particles showing a reduction rate of specific surface area within a specific range when heat-treated under basic conditions, the above object can be achieved, and thus the present invention has been completed. 【0011】 That is, the present invention relates to the following colloidal silica and its production method. 1. A colloidal silica containing silica particles having a surface uneven shape, (1) the silica particles have an alkoxy group content of 1000 ppm or more, (2) the reduction rate of the specific surface area of the silica particles when heat-treated under basic conditions is 15.0% or less, The colloidal silica is characterized by the above. 2. The colloidal silica according to item 1, wherein the true specific gravity of the silica particles is 1.95 or greater. 3. The colloidal silica according to item 1 or 2, wherein the silica particles contain 5 μmol or more per gram of silica particles of at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (excluding hydroxyl groups as substituents). 4. A method for producing colloidal silica containing silica particles having an uneven surface shape, comprising: (1) a step 1 of preparing a mother liquor containing an alkaline catalyst and water, (2) Step 2, in which an alkoxysilane is added to the mother liquor to prepare a seed particle dispersion, (3) The process includes, in this order, step 3 of adding water, an alkaline catalyst, and an alkoxysilane to the seed particle dispersion. The alkali catalyst is at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (excluding hydroxyl groups as substituents). In step 3, the molar ratio (s3 / c3) of the amount of alkoxysilane added (s3 / mol) to the amount of alkali catalyst added (c3 / mol) is greater than 185 and less than or equal to 400. A method for producing colloidal silica, characterized by the following features. [Effects of the Invention] 【0012】 The colloidal silica of the present invention contains silica particles that exhibit excellent density and excellent maintenance of surface irregularities under basic conditions. Furthermore, the method for producing the colloidal silica of the present invention can produce the colloidal silica. [Brief explanation of the drawing] 【0013】 [Figure 1] This is an SEM image of the silica particles of colloidal silica produced in Example 2. [Modes for carrying out the invention] 【0014】 The colloidal silica and its manufacturing method according to the present invention will be described in detail below. 【0015】 The colloidal silica of the present invention contains silica particles having a surface uneven shape, and therefore exhibits high polishability. Furthermore, since the colloidal silica of the present invention has an alkoxy group content of 1000 ppm or more in the silica particles, the amount of alkoxy groups per unit weight of silica particles is high, and surface defects on the substrate or other object to be polished can be suppressed. Moreover, since the reduction rate of the specific surface area of ​​the silica particles of the colloidal silica of the present invention is 15.0% or less when heat-treated under basic conditions, it has excellent maintenance of the surface uneven shape under basic conditions and can maintain high polishability even under basic conditions. Furthermore, the present invention provides a method for producing colloidal silica that uses at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (excluding hydroxyl groups as substituents) as an alkaline catalyst, and performs a sol-gel reaction in step 3 with a specific molar ratio (s3 / c3) of the amount of alkoxysilane added (s3 / mol) to the amount of alkaline catalyst added (c3 / mol). This method allows for the production of colloidal silica that has few metal impurities, excellent maintenance of surface irregularities under basic conditions, and maintains high polishability even under basic conditions. 【0016】 1. Colloidal silica The colloidal silica of the present invention contains colloidal silica particles having a surface uneven shape. Silica, characterized in that (1) the silica particles have an alkoxy group content of 1000 ppm or more, and (2) the silica particles have a specific surface area reduction rate of 15.0% or less when heat-treated under basic conditions. 【0017】 In this specification, the surface irregularity shape of silica particles refers to a shape in which the surface of the silica particles has minute protrusions, and the silica particles have a shape similar to konpeito (Japanese sugar candy). Such a surface irregularity shape can be defined by the range of surface roughness (B1 / S1) calculated by dividing the BET specific surface area (B1) by the specific surface area (S1) calculated from the SEM short axis. The specific surface area (S1) can be calculated by assuming the true specific gravity of silica is 2.2 and converting the value of 2727 / SEM short axis (nm). The surface roughness (B1 / S1) is preferably 1.1 or higher, more preferably 1.4 or higher, and preferably 2.0 or lower, more preferably 1.8 or lower. 【0018】 The silica particles described above have an alkoxy group content of 1000 ppm or more. If the alkoxy group content is less than 1000 ppm, the polishability of the colloidal silica of the present invention decreases, and surface defects on the workpiece cannot be suppressed. The alkoxy group content is preferably 4000 ppm or more, and more preferably 5000 ppm or more. Furthermore, the alkoxy group content is preferably 45000 ppm or less, and more preferably 40000 ppm or less. By setting the upper limit of the alkoxy group content within the above range, the polishability of the colloidal silica of the present invention is further improved. 【0019】 The content of the above-mentioned alkoxy groups can be measured by the following method. 【0020】 (Axoxy group content (ppm)) Colloidal silica is centrifuged at 215,000 G for 90 minutes, the supernatant is discarded, and the solids are vacuum-dried at 60°C for 90 minutes. 0.50 g of the resulting dry silica is weighed and placed in 50 ml of 1 M sodium hydroxide aqueous solution. The silica is dissolved by heating at 50°C for 24 hours while stirring. The silica solution is analyzed by gas chromatography to determine the alcohol content and calculate the amount of alkoxy per gram of silica. A flame ionization detector (FID) is used as the detector for the gas chromatography. The gas chromatography analysis is performed in accordance with JIS K0114. 【0021】 (BET specific surface area (m 2 / g)) Colloidal silica was pre-dried on a hot plate and then heat-treated at 800°C for 1 hour to prepare a sample for measurement. The prepared sample was measured using the nitrogen gas adsorption method (BET method). 【0022】 (Average primary particle diameter (nm)) Assuming the true specific gravity of silica is 2.2, the BET specific surface area can be calculated as 2727 / BET specific surface area (m²) from the above BET specific surface area measurement. 2 Convert the value ( / g) to obtain the average primary particle size (nm) of the silica particles in colloidal silica. 【0023】 The above silica particles have a specific surface area reduction rate of 15.0% or less when heat-treated under basic conditions. If the specific surface area reduction rate exceeds 15.0%, the resistance of the protrusions to basic conditions decreases, the ability to maintain the surface irregularities of the silica particles under basic conditions deteriorates, and the abrasive properties under basic conditions cannot be maintained. A specific surface area reduction rate of 14.5% or less is preferable, and 14.3% or less is more preferable. Furthermore, there is no particular lower limit to the specific surface area reduction rate, and it is sufficient if it is around 0.1%. 【0024】 The reduction rate of the specific surface area mentioned above is measured by the following measurement method. (Percentage decrease in specific surface area) 800 g of colloidal silica is mixed with 3-ethoxypropylamine to adjust the pH to 9.9-10.3. The colloidal silica is placed in a flask with a reflux condenser and heated, maintaining reflux for 3 hours to perform base treatment. The pH of the base-treated colloidal silica is adjusted to 7.6-7.8, and the BET specific surface area is measured according to the BET specific surface area measurement method described above. The percentage decrease in specific surface area is calculated using the following formula based on the BET specific surface areas before and after base treatment. Percentage decrease in specific surface area (%) = (Specific surface area of ​​BET before base treatment - Specific surface area of ​​BET after base treatment) / Specific surface area of ​​BET before base treatment × 100 【0025】 The silica particles preferably have a true specific gravity of 1.95 or more. When the true specific gravity is 1.95 or more, the hardness of the silica particles is further improved, and the abrasiveness of the colloidal silica is further improved. The true specific gravity of the silica particles is more preferably 2.00 or more, and even more preferably 2.10 or more. Further, the true specific gravity is preferably 2.20 or less, and more preferably 2.16 or less. 【0026】 The true specific gravity of the silica particles can be measured by a measuring method in which colloidal silica is dried on a hot plate at 150 ° C, held in a furnace at 300 ° C for 1 hour, and then measured by a liquid phase replacement method using ethanol. 【0027】 The silica particles preferably contain at least one amine selected from the group consisting of primary amines, secondary amines and tertiary amines. The amine is not particularly limited and is represented by the following general formula (X). NR a R b R c (X) (In the formula, R a , R b , R c represents an optionally substituted alkyl group having 1 to 12 carbon atoms or hydrogen. However, when all of R a , R b , R c are hydrogen, that is, ammonia is excluded.) R a , R b , R c may be the same or different. R a , R b , R c may be linear, branched or cyclic. 【0028】 The carbon number of the linear or branched alkyl group may be 1 to 12, preferably 1 to 8, more preferably 1 to 6. Examples of the linear alkyl group include a methyl group, an e Examples of alkyl groups include ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, and octyl group. Examples of branched alkyl groups include isopropyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group, 1,1-dimethylpropyl group, 1,2-dimethylpropyl group, 2,2-dimethylpropyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 4-methylpentyl group, 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 1,3-dimethylbutyl group, 2,2-dimethylbutyl group, 2,3-dimethylbutyl group, 1-methyl-1-ethylpropyl group, 2-methyl-2-ethylpropyl group, 1-ethylbutyl group, 2-ethylbutyl group, 1-ethylhexyl group, 2-ethylhexyl group, 3-ethylhexyl group, 4-ethylhexyl group, and 5-ethylhexyl group. Preferred linear or branched alkyl groups include n-propyl, n-hexyl, 2-ethylhexyl, and n-octyl groups. 【0029】 The number of carbon atoms in the cyclic alkyl group may be, for example, 3 to 12, and preferably 3 to 6. Examples of cyclic alkyl groups include cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, and cyclooctyl group. The preferred cyclic alkyl group is the cyclohexyl group. 【0030】 In the above general formula (X), R a , R b , R c The alkyl group may be substituted. The number of substituents may be, for example, 0, 1, 2, 3, 4, and preferably 0, 1 or 2, more preferably 0 or 1. The alkyl group in this context refers to an unsubstituted alkyl group. Examples of substituents include alkoxy groups having 1 to 3 carbon atoms (e.g., methoxy, ethoxy, propoxy, isopropoxy groups), amino groups, primary amino groups substituted with linear alkyl groups having 1 to 4 carbon atoms, amino groups disubstituted with linear alkyl groups having 1 to 4 carbon atoms (e.g., dimethylamino group, di-n-butylamino group, etc.), and unsubstituted amino groups. However, hydroxyl groups are excluded as substituents. In alkyl groups having multiple substituents, the substituents may be the same or different. 【0031】 In the above general formula (X), R a , R b , R c R is a linear or branched alkyl group having 1 to 8 carbon atoms (preferably 1 to 6 carbon atoms), which may be substituted. a , R b , R c teeth The alkyl group is a linear or branched alkyl group having 1 to 8 carbon atoms (preferably 1 to 6 carbon atoms), which may be substituted with an alkoxy group having 1 to 3 carbon atoms. 【0032】 Also, R a , R b , R c It does not need to be substituted. Preferably R a , R b , R c This is an unsubstituted linear or branched alkyl group having 1 to 12 carbon atoms, or a linear or branched alkyl group having 1 to 12 carbon atoms substituted with an alkoxy group. 【0033】 The amines mentioned above include at least one amine selected from the group consisting of aliphatic etheramines such as 3-ethoxypropylamine, 2-methoxyethylamine, 2-2-ethoxyethylamine, 3-methoxypropylamine, 3-propoxypropylamine, 3-isopropoxypropylamine, 3-butoxypropylamine, 3-isobutoxypropylamine, 3-(2-ethylhexyloxy)propylamine, and 3-(2-methoxyethoxy)propylamine, and aliphatic amines such as pentylamine, hexylamine, dipropylamine, and triethylamine. Among these, aliphatic etheramines are preferred, and 3-ethoxypropylamine is more preferred, in that they can increase the content of silica particles that have even better surface unevenness under basic conditions. 【0034】 The above amines may be used individually or as a mixture of two or more. 【0035】 The content of at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (excluding hydroxyl groups as substituents) in the silica particles is preferably 5 μmol or more per gram of silica particles, and more preferably 10 μmol or more per gram of silica particles. By setting the lower limit of the amine content within the above range, the content of silica particles that maintain their surface irregularities under basic conditions in colloidal silica increases further, and the colloidal silica exhibits even greater polishability. Furthermore, the amine content is preferably 100 μmol or less per gram of silica particles, and more preferably 90 μmol or less per gram of silica particles. By setting the upper limit of the amine content within the above range, silica particles having surface irregularities become even easier to form. 【0036】 The amine content can be measured by the following method. Colloidal silica is centrifuged at 215,000 G for 90 minutes, the supernatant is discarded, and the solid is vacuum-dried at 60°C for 90 minutes. 0.50 g of the resulting dry silica is weighed and placed in 50 ml of 1 M sodium hydroxide aqueous solution. The silica is dissolved by heating at 50°C for 24 hours while stirring. The amine content is determined by analyzing the dissolved silica solution using ion chromatography. Ion chromatography analysis is performed in accordance with JIS K0127. 【0037】 The boiling point of the above amine is preferably 85°C or higher, and more preferably 90°C or higher. Having the lower limit of the boiling point within this range further suppresses vaporization during the reaction, making it suitable for use as a catalyst. Furthermore, the boiling point is preferably 500°C or lower, and more preferably 300°C or lower. 【0038】 The colloidal silica of the present invention preferably contains 20% or more silica particles having a surface irregular shape, and more preferably 30% or more, among the number of particles in any field of view at 200,000x magnification observed with a scanning electron microscope. When the lower limit of the silica particle content is within the above range, the polishability of the colloidal silica is further improved. The upper limit of the content is not particularly limited and may be 100% or 70%. 【0039】 In this specification, the content of silica particles having the above-described surface irregularity can be measured by the following measurement method. Specifically, the number of particles having the surface irregularity is counted from the number of particles in any field of view observed at 200,000x magnification with a scanning electron microscope (SEM), and the proportion of these particles is defined as the content (%). 【0040】 The SEM short diameter of the silica particles in colloidal silica is preferably 8 nm or greater, and more preferably 15 nm or greater. Having the lower limit of the SEM short diameter of the silica particles within this range further improves the polishability of the colloidal silica of the present invention. Furthermore, the SEM short diameter of the silica particles is preferably 100 nm or less, and more preferably 80 nm or less. Having the upper limit of the SEM short diameter of the silica particles within this range further reduces the occurrence of scratches on the workpiece. 【0041】 The above SEM short axis can be measured by the following method: Images of silica particles taken with a scanning electron microscope are analyzed using image analysis software (WinRoof2015, manufactured by Mitani Corporation). 1000 particles were each approximated as an ellipse, and the minor axis of the ellipse was measured. The number frequency distribution of the minor axis of the ellipse was taken, and the minor axis of the ellipse with a number frequency of 50% was defined as the SEM minor axis (nm). 【0042】 The average secondary particle diameter of the silica particles in colloidal silica is preferably 8 nm or more, and more preferably 15 nm or more. Having the lower limit of the average secondary particle diameter of the silica particles within this range further improves the polishability of the colloidal silica of the present invention. Furthermore, the average secondary particle diameter of the silica particles is preferably 400 nm or less, and more preferably 300 nm or less. Having the upper limit of the average secondary particle diameter of the silica particles within this range further reduces the occurrence of scratches on the workpiece. 【0043】 In this specification, the average secondary particle diameter of silica particles in the colloidal silica described above can be measured by the following measurement method. Specifically, a sample for dynamic light scattering is prepared by adding colloidal silica to a 0.3 wt% citric acid aqueous solution and homogenizing it. The secondary particle diameter is then measured using this measurement sample by dynamic light scattering (ELSZ-2000S, manufactured by Otsuka Electronics Co., Ltd.). 【0044】 The aspect ratio of the silica particles in colloidal silica is preferably 1.0 or higher, and more preferably 1.1 or higher. Having the lower limit of the aspect ratio within this range further improves polishability. Furthermore, the aspect ratio of the silica particles is preferably 4.0 or lower, and more preferably 3.0 or lower. Having the lower limit of the aspect ratio within this range further suppresses the occurrence of scratches on the workpiece. 【0045】 In this specification, the aspect ratio of silica particles in the above colloidal silica can be measured by the following measurement method. That is, images of silica particles taken with a scanning electron microscope are analyzed using image analysis software (Mitani Corporation's "WinRoof2015") to analyze 1000 particles. Each particle is approximated as an ellipse, and the major and minor axes of the ellipse are measured for each particle. The ratio of the major / minor axis of the ellipse for each particle is calculated, and the average value is taken as the aspect ratio. 【0046】 The colloidal silica of the present invention contains sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, cobalt, etc. It is preferable that the content of metal impurities is 1 ppm or less. A metal impurity content of 1 ppm or less makes it suitable for polishing electronic materials and the like. 【0047】 In this specification, the content of the above-mentioned metal impurities is a value measured using an atomic absorption spectrometer. 【0048】 The association ratio of silica particles in colloidal silica is preferably 1.5 or higher, and more preferably 1.7 or higher. Having the lower limit of the silica particle association ratio within this range further improves the polishability of the colloidal silica of the present invention. Furthermore, the association ratio of silica particles is preferably 5.5 or lower, and more preferably 5.0 or lower. Having the upper limit of the silica particle association ratio within this range further reduces the occurrence of scratches on the workpiece. 【0049】 In this specification, the association ratio of silica particles in the colloidal silica is a value obtained by calculating the average secondary particle diameter / average primary particle diameter of the silica particles in the colloidal silica. 【0050】 The silanol group density of silica particles in colloidal silica is 1.5 groups / nm 2 The above is preferable, with 1.6 particles / nm. 2 The above is more preferable. When the lower limit of the silanol group density is within the above range, the occurrence of scratches on the polished object is further reduced. Also, the silanol density of the silica particles is 5.0 particles / nm. 2 The following is preferable: 4.0 pieces / nm 2 The following is more preferable: When the upper limit of the silanol group density is within the above range, the polishability of the colloidal silica of the present invention is further improved. 【0051】 Furthermore, the silanol group density of silica particles in colloidal silica can be determined by the Sears method. The Sears method is described in GWSears, Jr., “Determination of Specific Surface Area of ​​Colloidal Silica”. The procedure was carried out in reference to the description in "Silica by Titration with Sodium Hydroxide," Analytical Chemistry, 28(12), 1981 (1956). A 1 wt% silica dispersion was used for the measurement, and titration was performed with a 0.1 mol / L aqueous sodium hydroxide solution. The silanol group density was calculated based on the following formula. ρ = (a × f × 60²²) ÷ (c × S) In the above formula, ρ: silanol group density (numbers / nm 2 a: Droplet volume (mL) of 0.1 mol / L sodium hydroxide aqueous solution with pH 4-9, f: 0.1 mol / L sodium hydroxide aqueous solution Solution factors, c: Mass of silica particles (g), S: BET specific surface area (m²) 2 / g) represents each respective part. 【0052】 2. Method for producing colloidal silica The present invention relates to a method for producing colloidal silica, which contains silica particles having a surface uneven shape, (1) Step 1: Prepare a mother liquor containing an alkaline catalyst and water. (2) Step 2, in which an alkoxysilane is added to the mother liquor to prepare a seed particle dispersion, (3) The process includes, in this order, step 3 of adding water, an alkaline catalyst, and an alkoxysilane to the seed particle dispersion. The alkali catalyst is at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (excluding hydroxyl groups as substituents). In the above step 3, the molar ratio (s3 / c3) of the amount of alkoxysilane added s3 (mol) to the amount of alkaline catalyst added c3 (mol) is greater than 185 and less than or equal to 400. 【0053】 (Process 1) Step 1 is the process of preparing a mother liquor containing an alkaline catalyst and water. 【0054】 The alkaline catalyst is at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (excluding hydroxyl groups as substituents). The amine used may be the same as the amine described above for colloidal silica. 【0055】 The amine content in the mother liquor is preferably 0.30 mmol / kg or more, and more preferably 0.50 mmol / kg or more. Having the lower limit of the amine content within this range makes it easier to control the particle size. Furthermore, the amine content in the mother liquor is preferably 20.0 mmol / kg or less, and more preferably 15.0 mmol / kg or less. Having the amine content within this range makes gelation less likely during the reaction. 【0056】 The method for preparing the mother liquor is not particularly limited; it can be done by adding an alkaline catalyst to water using a conventionally known method and stirring. 【0057】 The pH of the mother liquor is not particularly limited, but is preferably 9.5 or higher, and more preferably 10.0 or higher. Having the lower limit of the mother liquor's pH within the above range makes it easier to control the particle size. Furthermore, the pH of the mother liquor is preferably 12.0 or lower, and more preferably 11.5 or lower. Having the upper limit of the mother liquor's pH within the above range makes it easier to control the average secondary particle size of silica particles having a surface irregular shape, and also suppresses aggregation of seed particles in the seed particle dispersion obtained in step 2 described later, further improving the storage stability of colloidal silica. 【0058】 (Process 2) Step 2 is the step of adding alkoxysilane to the mother liquor to prepare a seed particle dispersion. 【0059】 The alkoxysilane is not particularly limited, and is as shown in the general formula (2) below. Si(OR 1 )4(2) (In the formula, R 1 (This indicates an alkyl group.) Examples of alkoxysilanes represented by [formula] include [formula]. 【0060】 In the above general formula (2), R 1 R indicates an alkyl group. 1 R is not particularly limited as long as it is an alkyl group, but is preferably a lower alkyl group having 1 to 8 carbon atoms, and more preferably a lower alkyl group having 1 to 4 carbon atoms. Specific examples of the alkyl group include methyl group, ethyl group, propyl group, isopropyl group, butyl group, pentyl group, hexyl group, etc. The alkoxysilane represented by the general formula (2) above is R 1 Tetramethoxysilane (tetramethyl orthosilicate), which has a methyl group, R 1 Tetraethoxysilane (tetraethyl orthosilicate), which has an ethyl group, R 1 Tetraisopropoxysilane, in which is an isopropyl group, is preferred. 1 Tetramethoxysilane, which has a methyl group, R 1 Tetraethoxysilane, in which the group is an ethyl group, is more preferred, and tetramethoxysilane is even more preferred. 【0061】 The alkoxysilane represented by the above general formula (2) may also be a derivative. Examples of derivatives of the alkoxysilane include low-condensate products obtained by partially hydrolyzing the alkoxysilane represented by the above general formula (2). 【0062】 The alkoxysilane represented by the above general formula (2) may be used alone or as a mixture of two or more types. 【0063】 The amount of alkoxysilane represented by the above general formula (2) added to the seed particle dispersion is not particularly limited, and the molar ratio (s2 / c1) of the amount of alkoxysilane added in step 2 s2 (mol) to the amount of alkali catalyst c1 (mol) in the mother liquor is preferably 10 or more, more preferably 100 or more, and even more preferably 150 or more. By setting the lower limit of s2 / c1 within the above range, the silica particle content in colloidal silica can be further increased. Furthermore, s2 / c1 is preferably 8500 or less, and more preferably 8000 or less. By setting the upper limit of s2 / c1 within the above range, gelation during the reaction is less likely to occur. 【0064】 In step 2, the addition time of the alkoxysilane is preferably 5 minutes or more, and more preferably 10 minutes or more. The lower limit of the addition time being within this range makes gelation less likely during the reaction. Furthermore, the addition time of the alkoxysilane is preferably 1000 minutes or less, and more preferably 600 minutes or less. If the upper limit of the addition time is within this range, productivity can be further improved and manufacturing costs can be further reduced. 【0065】 The pH of the seed particle dispersion is preferably 8.5 or lower, and more preferably 8.0 or lower. Having the upper limit of the pH of the seed particle dispersion within this range makes it easier to form silica particles with an uneven surface shape. Furthermore, the pH of the seed particle dispersion is preferably 4.5 or higher, and more preferably 4.9 or higher. Having the lower limit of the pH of the seed particle dispersion within this range further suppresses gelation. 【0066】 In step 2, the temperature of the seed particle dispersion is preferably 70°C or higher, and more preferably 75°C or higher. By setting the lower limit of the seed particle dispersion temperature within the above range, gelation during the reaction is further suppressed. Furthermore, the temperature of the seed particle dispersion is preferably 95°C or lower, and more preferably 90°C or lower. By setting the upper limit of the seed particle dispersion temperature within the above range, vaporization of alkoxysilane is further suppressed. 【0067】 (Step 3) Step 3 is the process of adding water, an alkaline catalyst, and an alkoxysilane to the seed particle dispersion. 【0068】 The alkaline catalyst is at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (excluding hydroxyl groups as substituents). The amine used may be the same as the amine described above for colloidal silica. Furthermore, the alkaline catalyst used in step 3 may be the same as the alkaline catalyst used in step 1, or it may be different. 【0069】 Step 3 forms silica particles with a surface irregular shape in the colloidal silica. The mechanism of action is not clear, but it is presumed to be as follows: In Step 3, the pH of the seed particle dispersion decreases due to the addition of alkoxysilane. In the reaction in Step 3 in which silica particles are formed, under basic and relatively high pH conditions, new seed particles are not generated, and the alkoxysilane is consumed to simply grow the silica particles, so silica particles with a surface irregular shape cannot be generated. In contrast, as the pH gradually decreases and the seed particle dispersion becomes weakly basic, the condensation rate of the hydrolysate of alkoxysilane increases, and the dissolution of the embryo, which is a precursor of seed particles, does not occur, so it is predicted that new seed particles will be generated. Furthermore, as the pH decreases to near neutral, it is thought that the seed particles generated under weakly basic conditions combine with the original seed particles generated in Step 2, and irregularities are formed on the particle surface. For this reason, it is thought that colloidal silica containing a surface irregular shape can be produced by the manufacturing method of the present invention. 【0070】 Based on the expected mechanism of action described above, in step 3, the pH of the seed particle dispersion will change from strongly basic to moderate. It is preferable that the pH decreases while being controlled to an appropriate level near the neutral point. For this reason, alkaline catalysts that maintain a high pH or alkaline catalysts that cause a rapid decrease in pH are not suitable as the alkaline catalyst used in step 3. Rather, an alkaline catalyst with buffering capacity that gradually decreases while being controlled to an appropriate pH range is preferably used. 【0071】 Based on the above mechanism of action, the pKa value, which represents the physical properties of acids and bases, is the central value of the buffering region. Therefore, in step 3, it serves as a criterion for determining whether a substance has buffering capacity that gradually decreases while being controlled to an appropriate pH range. In other words, the alkali catalyst used in step 3 is preferably an amine represented by the above general formula (X) with a pKa value of 8.5 or more and less than 11, and more preferably an amine represented by the above general formula (X) with a pKa value of 9 or more and less than 10. 【0072】 The amines represented by the above general formula (X) and their pKa values ​​are as follows: aliphatic etheramines include 3-ethoxypropylamine (9.79), 2-methoxyethylamine (9.89), 3-methoxypropylamine (9.73), 3-propoxypropylamine (9.78), 3-isopropoxypropylamine (9.82), and 3-butoxypropylamine (9.77). Aliphatic amines include pentylamine (10.63), hexylamine (10.56), dipropylamine (10.91), and triethylamine (10.75). 【0073】 The alkoxysilane used in step 3 is not particularly limited, and the same type as the alkoxysilane described in step 2 above can be used. The alkoxysilane used in step 3 may be the same as the alkoxysilane used in step 2, or it may be different, but it is preferable to use the same alkoxysilane as the one used in step 2. 【0074】 In step 3, the molar ratio (s3 / c3) of the amount of alkoxysilane added (s3 / mol) to the amount of alkali catalyst added (c3 / mol) is greater than 185. A lower limit of s3 / c3 exceeding 185 makes it easier to form surface irregularities. S3 / c3 is preferably 200 or more, and more preferably 220 or more. Also, the above s3 / c3 is 400 or less. A s3 / c3 of 400 or less further suppresses the gelation of colloidal silica. S3 / c3 is preferably 380 or less, and more preferably 350 or less. 【0075】 In step 3, in addition to the water, alkaline catalyst, and alkoxysilane mentioned above, an alcohol may be added to the seed particle dispersion. 【0076】 The alcohol used is not particularly limited as long as it is soluble in water, and it is preferable that it be the same alcohol as the by-product alcohol produced when the alkoxysilane used is hydrolyzed. For example, methanol is preferred when the alkoxysilane is tetramethyl orthosilicate, and ethanol is preferred when the alkoxysilane is tetraethyl orthosilicate. 【0077】 In step 3, the alcohol content per 100% by mass of the mixture obtained by mixing the seed particle dispersion, water, alkaline catalyst, and alcohol is preferably 25% by mass or less, and more preferably 20% by mass or less. Having the upper limit of the alcohol content within this range makes it easier to further increase the temperature of the mixture in step 3. Furthermore, the lower limit of the alcohol content is not particularly limited and may be 0% by mass or 2% by mass. 【0078】 The amount of alkoxysilane added in step 3 is not particularly limited, and the molar ratio (s3 / sp3) of the amount of alkoxysilane added in step 3 s3 (mol) to the amount of seed particles sp3 (mol) in the mixed solution of seed particle dispersion, water, alkaline catalyst, and alcohol is 0 or more and 30 or less. The lower value is preferable. By keeping the upper limit of s3 / sp3 within the above range, new nucleus particles are less likely to be generated during the reaction, and the growth of the main particles is further promoted. Note that the above molar ratio is defined assuming a seed particle molecular weight of 60.08 g / mol. 【0079】 In step 3, the temperature of the mixed solution is preferably 70°C or higher, and more preferably 75°C or higher. By setting the lower limit of the mixed solution temperature within the above range, gelation during the reaction is further suppressed. Furthermore, the temperature of the mixed solution is preferably 95°C or lower, and more preferably 90°C or lower. By setting the upper limit of the seed particle dispersion temperature within the above range, vaporization of alkoxysilane is further suppressed. 【0080】 In step 3, the addition time of the alkoxysilane is preferably 5 minutes or more, and more preferably 10 minutes or more. The lower limit of the addition time being within this range makes gelation less likely during the reaction. Furthermore, the addition time of the alkoxysilane is preferably 1000 minutes or less, and more preferably 600 minutes or less. If the upper limit of the addition time is within this range, productivity can be further improved and manufacturing costs can be further reduced. 【0081】 The colloidal silica of the present invention can be produced by the manufacturing method described above. 【0082】 The pH of colloidal silica is preferably 11.0 or lower, and more preferably 10.0 or lower. Having the upper limit of the colloidal silica's pH within this range further suppresses the dissolution of silica particles. Furthermore, the pH of colloidal silica is preferably 5.8 or higher, and more preferably 6.0 or higher. Having the lower limit of the colloidal silica's pH within this range further suppresses gelation. 【0083】 The present invention's method for producing colloidal silica may further include a step of concentrating the colloidal silica after step 3 described above. The method of concentration is not particularly limited and can be carried out by conventionally known methods. For example, such a concentration method may involve heating and concentrating at a temperature of about 65 to 100°C. 【0084】 The concentration of silica particles in the concentrated colloidal silica is not particularly limited, but is preferably about 1 to 50% by mass, with colloidal silica being 100% by mass. 【0085】 The present invention's method for producing colloidal silica may further include a step after step 3 above in which methanol, a by-product of the reaction, is removed from the system. The method for removing methanol from the system is not particularly limited, and one example is to replace the dispersion medium with pure water by adding pure water dropwise while heating the colloidal silica and maintaining a constant volume. Another example is to separate the colloidal silica from the solvent by precipitation, separation, centrifugation, etc., and then redisperse it in water. 【0086】 The colloidal silica of the present invention, and the colloidal silica produced by the manufacturing method of the present invention, can be used in a variety of applications such as abrasives and paper coatings. An abrasive containing the above colloidal silica is also one of the present inventions. The colloidal silica of the present invention can be made highly pure with a content of metal impurities such as sodium of 1 ppm or less, and is therefore particularly suitable for use as an abrasive in chemical mechanical polishing of semiconductor wafers. [Examples] 【0087】 The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. 【0088】 Example 1 (Step 1) In a flask, 6767 g of pure water was added as the solvent and 6.98 g of 3-ethoxypropylamine (3-EOPA) as the alkaline catalyst to prepare the mother liquor. The pH of the mother liquor was 11.0. (Step 2) After heating the mother liquor to an internal temperature of 80°C, add tetramethyl orthosilicate to the mother liquor. 2472g of the solution was added dropwise at a constant rate over 210 minutes while maintaining a controlled temperature to prevent internal temperature fluctuations, in order to prepare a seed particle dispersion. (Step 3) In a flask, 5704 g of pure water as the solvent, 6.50 g of 3-ethoxypropylamine (3-EOPA) as the alkaline catalyst, and 1075 g of the seed particle dispersion prepared in Step 2 were added. Next, after heating to an internal temperature of 80°C, 2397 g of tetramethyl orthosilicate was added dropwise at a constant rate over 180 minutes while maintaining a temperature that did not fluctuate. After the addition was complete, stirring was maintained for 15 minutes to prepare the colloidal silica dispersion. Next, the colloidal silica The silica dispersion was heated and concentrated under atmospheric pressure to a base volume of 800 mL until the silica concentration reached 20 wt%. Next, to remove methanol, a by-product of the reaction, the dispersion medium was replaced with 500 mL of pure water while maintaining a constant volume, and colloidal silica was prepared. 【0089】 In Example 1, the molar ratio (s3 / c3) of the amount of alkoxysilane (tetramethyl orthosilicate) added in step 3, s3 (mol), to the amount of alkaline catalyst (3-ethoxypropylamine) added, c3 (mol), was 250. 【0090】 Example 2 (Step 1) In a flask, 6767 g of pure water was added as the solvent and 10.47 g of 3-ethoxypropylamine (3-EOPA) as the alkaline catalyst to prepare the mother liquor. The pH of the mother liquor was 11.3. (Step 2) After heating the mother liquor to an internal temperature of 85°C, add tetramethyl orthosilicate to the mother liquor. 2472g of the solution was added dropwise at a constant rate over 210 minutes while maintaining a controlled temperature to prevent internal temperature fluctuations, in order to prepare a seed particle dispersion. (Step 3) In a flask, 5704 g of pure water as the solvent, 6.50 g of 3-ethoxypropylamine (3-EOPA) as the alkaline catalyst, 242 g of methanol, and 667 g of the seed particle dispersion prepared in Step 2 were placed. Next, after heating to an internal temperature of 80°C, 2397 g of tetramethyl orthosilicate was added dropwise at a constant rate over 180 minutes while maintaining a stable internal temperature. After the addition was complete, stirring was maintained for 15 minutes to prepare the colloidal silica dispersion. Next Next, the colloidal silica dispersion was heated and concentrated under atmospheric pressure to a base volume of 9000 mL until the silica concentration reached 20 wt%. Then, in order to remove the methanol produced as a by-product during the reaction, the dispersion medium was replaced with 5680 mL of pure water while maintaining a constant volume, and colloidal silica was prepared. 【0091】 In Example 2, the molar ratio (s3 / c3) of the amount of alkoxysilane (tetramethyl orthosilicate) added in step 3, s3 (mol), to the amount of alkaline catalyst (3-ethoxypropylamine) added, c3 (mol), was 250. 【0092】 Comparative Example 1 (Step 1) In a flask, 7500 g of pure water was added as the solvent and 1.35 g of 3-ethoxypropylamine (3-EOPA) as the alkaline catalyst to prepare the mother liquor. The pH of the mother liquor was 10.3. (Step 2) After heating the mother liquor to an internal temperature of 85°C, add tetramethyl orthosilicate to the mother liquor. 2740g of the seed particle dispersion was prepared by adding it dropwise at a constant rate over 60 minutes while maintaining a controlled temperature to prevent internal temperature fluctuations, and then stirring for 15 minutes. (Step 3) 50 g of 3-ethoxypropylamine (3-EOPA) was added to the seed particle dispersion as an alkaline catalyst to prepare a mixture. Separately, 5379 g of pure water was placed in a flask as a solvent, and 2382 g of the mixture of 3-ethoxypropylamine and the seed particle dispersion was added. Next, after heating to an internal temperature of 80°C, 1712.5g of tetramethyl orthosilicate was added dropwise at a constant rate over 180 minutes while maintaining a stable internal temperature. 15 minutes after the completion of the dropwise addition. A colloidal silica dispersion was prepared while maintaining constant stirring. Next, the colloidal silica dispersion was heated and concentrated under atmospheric pressure to a base volume of 800 mL until the silica concentration reached 20 wt%. Then, in order to remove methanol produced as a by-product during the reaction, the dispersion medium was replaced with 500 mL of pure water while maintaining a constant volume, and colloidal silica was prepared. The resulting particles did not have any surface irregularities. 【0093】 In Comparative Example 1, the molar ratio (s3 / c3) of the amount of alkoxysilane (tetramethyl orthosilicate) added in step 3 (s3 / mol) to the amount of alkaline catalyst (3-ethoxypropylamine) added (c3 / mol) was 100. 【0094】 Comparative Example 2 (Step 1) 9492 g of pure water as the solvent and 3.28 g of triethanolamine (TEA) as the alkaline catalyst were placed in a flask to prepare the mother liquor. The pH of the mother liquor was 9.4. (Step 2) After heating the mother liquor to an internal temperature of 80°C, 1704 g of tetramethyl orthosilicate was added to the mother liquor at a constant rate over 180 minutes while maintaining a stable internal temperature. After the supply of tetramethyl silicate to the reaction vessel was completed, the reaction mixture in the reaction vessel was heated, and methanol was distilled off from the distillation tube with a condenser. The reaction mixture prepared under the same conditions was then fed into the reaction vessel to concentrate it and prepare a seed particle dispersion with a silica concentration of 12.2 wt%. (Step 3) 5582 g of pure water as the solvent, 9.43 g of triethanolamine (TEA) as the alkaline catalyst, and 857 g of the seed particle dispersion prepared in Step 2 were placed in a flask. Next, after heating to an internal temperature of 80°C, 3878 g of tetramethyl orthosilicate was added at a constant rate over 180 minutes while maintaining a stable internal temperature. After the addition was completed, the mixture was stirred for 15 minutes. Stirring was maintained to prepare a colloidal silica dispersion. Next, the colloidal silica dispersion was heated and concentrated under atmospheric pressure to a base volume of 4500 mL until the silica concentration reached 20 wt%. Then, to remove methanol produced as a by-product during the reaction, the dispersion medium was replaced with 5680 mL of pure water while maintaining a constant volume, and colloidal silica was prepared. 【0095】 In Comparative Example 2, the molar ratio (s3 / c3) of the amount of alkoxysilane (tetramethyl orthosilicate) added in step 3 (s3 / mol) to the amount of alkaline catalyst (triethanolamine) added (c3 / mol) was 403. 【0096】 The properties of the colloidal silica of the examples and comparative examples obtained as described above were evaluated by the following method. 【0097】 (Axoxy group content (ppm)) Colloidal silica was centrifuged at 215,000 G for 90 minutes, the supernatant was discarded, and the solids were vacuum-dried at 60°C for 90 minutes. 0.50 g of the resulting dry silica was weighed and placed in 50 ml of 1 M sodium hydroxide aqueous solution. The silica was dissolved by heating at 50°C for 24 hours while stirring. The silica solution was analyzed by gas chromatography to determine the alcohol content, which was then expressed as the alkoxy content. A flame ionization detector (FID) was used for the gas chromatography. The gas chromatography analysis was performed in accordance with JIS K0114. 【0098】 (BET specific surface area (m 2 / g)) Colloidal silica was pre-dried on a hot plate and then heat-treated at 800°C for 1 hour to prepare a sample for measurement. The BET specific surface area was measured using the nitrogen gas adsorption method (BET method) described below with the prepared sample. Nitrogen gas adsorption method Pre-treatment device: BELPREP-vacII (manufactured by Microtrac-Bel Co., Ltd.) Pretreatment method: Vacuum degassing was performed at 120°C for 8 hours. Measurement device: BELSORP-miniII (Microtrac, manufactured by Bell Co., Ltd.) Measurement method: The nitrogen adsorption isotherm was measured using the constant volume method. Measurement conditions: Adsorption temperature 77K; Adsorbate: Nitrogen; Saturated vapor pressure: Measured; Adsorbate cross-sectional area: 0.162nm 2 Equilibrium waiting time (waiting time after reaching the adsorption equilibrium state (the state in which the pressure change during adsorption and desorption falls below a predetermined value)) 500 sec The specific surface area was calculated from the measurement results using the BET method. 【0099】 (Average primary particle diameter (nm)) Assuming the true specific gravity of silica is 2.2, the BET specific surface area can be calculated as 2727 / BET specific surface area (m²) from the above BET specific surface area measurement. 2 The value ( / g) was converted to determine the average primary particle size (nm) of the silica particles in colloidal silica. 【0100】 (Average secondary particle size) For dynamic light scattering (DSC) measurement, colloidal silica was prepared by adding it to a 0.3 wt% citric acid aqueous solution and homogenizing it. Using this measurement sample, the average secondary particle diameter was measured by dynamic light scattering (ELSZ-2000S, manufactured by Otsuka Electronics Co., Ltd.). 【0101】 (Percentage decrease in specific surface area) 800 g of colloidal silica was mixed with 3-ethoxypropylamine to adjust the pH to 9.9-10.3. The colloidal silica was placed in a flask with a reflux condenser and heated, and base treatment was performed under reflux for 3 hours. The pH of the base-treated colloidal silica was adjusted to 7.6-7.8, and the BET specific surface area was measured according to the BET specific surface area measurement method described above. The reduction rate of the specific surface area was calculated using the following formula based on the BET specific surface areas before and after base treatment. Percentage decrease in specific surface area (%) = (Specific surface area of ​​BET before base treatment - Specific surface area of ​​BET after base treatment) / Specific surface area of ​​BET before base treatment × 100 【0102】 (SEM short axis) Images of silica particles taken with a scanning electron microscope were approximated as ellipses for each of 1000 particles using image analysis software (WinRoof2015, manufactured by Mitani Corporation), and the minor axis of the ellipse was measured. The number frequency distribution of the minor axis of the circle was obtained, and the minor axis of the ellipse with a number frequency of 50% was defined as the SEM minor axis (nm). 【0103】 (Aspect ratio) Images of silica particles taken with a scanning electron microscope were approximated as ellipses for each of 1000 particles using image analysis software (WinRoof2015, manufactured by Mitani Corporation), and the major and minor axes of the ellipses were analyzed. The aspect ratio was measured for each particle. The ratio of the elliptic's major axis to its minor axis (elliptic major axis / elliptic minor axis) was calculated for each particle, and the average value was used as the aspect ratio. 【0104】 (Surface roughness) The surface roughness was calculated as (B1 / S1) by dividing the BET specific surface area (B1) by the specific surface area (S1) calculated from the SEM short axis. The specific surface area (S1) was calculated by assuming the true specific gravity of silica is 2.2 and converting the value of 2727 / SEM short axis (nm). 【0105】 (true specific gravity) The true specific gravity of colloidal silica was measured by a method that involved drying the silica on a hot plate at 150°C, holding it in a 300°C furnace for 1 hour, and then measuring it using a liquid-phase displacement method with ethanol. 【0106】 (Amine content) Colloidal silica was centrifuged at 215,000 G for 90 minutes. The supernatant was discarded, and the solid was vacuum-dried at 60°C for 90 minutes. 0.50 g of the resulting dry silica was weighed and placed in 50 ml of 1 M sodium hydroxide aqueous solution. The silica was dissolved by heating at 50°C for 24 hours while stirring. The silica solution was analyzed by ion chromatography to determine the amine content. Ion chromatography analysis was performed according to JIS K0127. 【0107】 (Silanol group density) The silanol group density of silica particles was determined by the Sears method. The Sears method was performed in reference to GWSears, Jr., “Determination of Specific Surface Area of ​​Colloidal Silica by Titration with Sodium Hydroxide”, Analytical Chemistry, 28(12), 1981 (1956). A 1 wt% silica dispersion was used for the measurement, and titration was performed with a 0.1 mol / L aqueous sodium hydroxide solution. The silanol group density was calculated based on the following formula. ρ = (a × f × 60²²) ÷ (c × S) In the above formula, ρ: silanol group density (numbers / nm 2 a: Droplet volume (mL) of 0.1 mol / L sodium hydroxide aqueous solution with pH 4-9, f: 0.1 mol / L sodium hydroxide aqueous solution Solution factors, c: Mass of silica particles (g), S: BET specific surface area (m²) 2 / g) represents each respective part. 【0108】 (Content of metallic impurities) The content of metal impurities was measured using an atomic absorption spectrometer. The sum of the content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt in the colloidal silica was defined as the content of metal impurities. 【0109】 [Table 1] 【0110】 *1: Comparative Example 2 did not use an amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (however, hydroxyl groups as substituents are excluded), so no amine content was detected.

Claims

[Claim 1] Colloidal silica containing silica particles, (1) The silica particles have a BET specific surface area reduction rate of 15.0% or less when heat-treated under basic conditions. (2) The silica particles have a surface roughness (B1 / S1) of 1.1 or more and 1.8 or less, which is calculated by dividing the BET specific surface area (B1) measured by the BET specific surface area measurement method described below by the specific surface area (S1) calculated from the SEM short axis. The reduction rate of the BET specific surface area, the BET specific surface area (B1), and the specific surface area (S1) calculated from the SEM short axis are measured by the following measurement method. Colloidal silica characterized by the following features. [Method for measuring the decrease rate of BET specific surface area] 800 g of colloidal silica is mixed with 3-ethoxypropylamine to adjust the pH to 9.9-10.

3. The colloidal silica is placed in a flask with a reflux condenser and heated, and base treatment is performed under reflux for 3 hours. The pH of the base-treated colloidal silica is adjusted to 7.6-7.8, and the BET specific surface area is measured according to the BET specific surface area measurement method described below. The decrease in BET specific surface area is calculated based on the BET specific surface area before and after base treatment, according to the following formula. BET specific surface area reduction rate (%) = (BET specific surface area before base treatment - BET specific surface area after base treatment) / base BET specific surface area before processing × 100 [Method for measuring BET specific surface area] Colloidal silica was pre-dried on a hot plate, then heat-treated at 800°C for 1 hour and measured. Prepare a sample for measurement. The prepared sample for measurement is subjected to nitrogen gas adsorption (BET) method. Measure the BET specific surface area. [Method for measuring specific surface area (S1) calculated from the short axis of SEM] Images of silica particles captured with a scanning electron microscope are approximated as ellipses for each of 1000 particles using image analysis software (WinRoof2015, manufactured by Mitani Corporation), and the minor axis of the ellipse is measured. The number frequency distribution of the minor axis of the ellipse is taken, and the minor axis of the ellipse with a number frequency of 50% is defined as the SEM minor axis (nm). By assuming the true specific gravity of silica is 2.2, the value of 2727 / SEM short axis (nm) is converted. Next, calculate the specific surface area (S1) from the SEM's short axis.

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