METHOD FOR PRODUCING SILICA SOL HAVING ELONGATED PARTICLE SHAPE
20200407230 ยท 2020-12-31
Assignee
Inventors
- Satoru MURAKAMI (Sodegaura-shi, JP)
- Takuya FUKUOKA (Sodegaura-shi, JP)
- Kazuya KUROIWA (Sodegaura-shi, JP)
Cpc classification
C01B33/145
CHEMISTRY; METALLURGY
B82Y40/00
PERFORMING OPERATIONS; TRANSPORTING
C01P2004/62
CHEMISTRY; METALLURGY
International classification
Abstract
A method for producing a silica sol containing a small amount of metal impurities and in which colloidal silica having an elongated particle shape dispersed in a solvent, includes: preparing a raw material liquid by adding a compound as an anion source selected from inorganic acids, organic acids, and their ammonium salts, and ammonia to a colloidal aqueous solution of activated silica having an SiO.sub.2 concentration of 1 to 6% by mass and a pH of 2 to 5 so that the mass ratio of the compound to SiO.sub.2 is 3.0 to 7.0%; and heating the raw material liquid at 80 to 200 C. for 0.5 to 20 hours. The elongated colloidal silica particles exhibit a D.sub.L/D.sub.B ratio of 2.5 or more. D.sub.L is an average particle diameter as measured by the dynamic light scattering method. D.sub.B is a primary particle diameter as measured by the nitrogen gas adsorption method.
Claims
1. A method for producing a silica sol containing elongated colloidal silica particles dispersed in a liquid medium and having an SiO.sub.2 concentration of 6 to 30% by mass, wherein the elongated colloidal silica particles have a particle length of 50 to 1,000 nm as determined by observation with an electron microscope and exhibit a D.sub.L/D.sub.B ratio of 2.5 or more and a D.sub.L of 30 to 300 nm wherein D.sub.L is an average particle diameter (nm) as measured by the dynamic light scattering method, and D.sub.B is a primary particle diameter (nm) as measured by the nitrogen gas adsorption method, the production method comprising the following steps (a) and (b): (a) a step of preparing a raw material liquid by adding at least one compound as an anion source selected from the group consisting of inorganic acids, organic acids, and ammonium salts of these acids, and ammonia to a colloidal aqueous solution of activated silica having an SiO.sub.2 concentration of 1 to 6% by mass and a pH of 2 to 5 so that the mass ratio of the compound to SiO.sub.2 is 3.0 to 7.0%; and (b) a step of heating the raw material liquid prepared in the step (a) at 80 to 200 C. for 0.5 to 20 hours, to thereby produce a silica sol.
2. The method for producing a silica sol according to claim 1, wherein the colloidal aqueous solution of activated silica used in the step (a) is prepared by bringing an aqueous alkali silicate solution exhibiting a ratio by mole of SiO.sub.2/M.sub.2O (wherein M is sodium or potassium) of 1 to 4.5 into contact with a strong acid-type cation exchange resin or with both a strong acid-type cation exchange resin and a strong base-type anion exchange resin.
3. The method for producing a silica sol according to claim 2, wherein the colloidal aqueous solution of activated silica used in the step (a) is prepared by treating the aqueous alkali silicate solution with a strong acid at a temperature of 1 to 98 C., and then bringing the treated aqueous solution into contact with a strong acid-type cation exchange resin or with both a strong acid-type cation exchange resin and a strong base-type anion exchange resin.
4. The method for producing a silica sol according to claim 2, wherein the colloidal aqueous solution of activated silica used in the step (a) is prepared by bringing the aqueous alkali solution or the treated aqueous solution into contact with a carboxylic acid-type chelating resin, a hydroxyl group-type chelating resin, and/or an amine-type chelating resin before or after contact with a strong acid-type cation exchange resin or with both a strong acid-type cation exchange resin and a strong base-type anion exchange resin.
5. The method for producing a silica sol according to claim 1, wherein the compound as an anion source used in the step (a) is at least one compound as an anion source selected from the group consisting of nitric acid, sulfuric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrochloric acid, acetic acid, formic acid, oxalic acid, citric acid, lactic acid, malic acid, gluconic acid, tartaric acid, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and an ammonium salt of any of these.
6. The method for producing a silica sol according to claim 1, wherein the colloidal aqueous solution of activated silica used in the step (a) contains colloidal particles having an average particle diameter of less than 5 nm.
7. The method for producing a silica sol according to claim 1, wherein the ammonia added in the step (a) is in the form of ammonia gas or an aqueous ammonia solution.
8. The method for producing a silica sol according to claim 1, wherein the step (a) comprises a step of adding the compound as an anion source to the colloidal aqueous solution of activated silica, followed by addition of the ammonia.
9. The method for producing a silica sol according to claim 1, wherein the step (a) comprises a step of adding the ammonia to the colloidal aqueous solution of activated silica, followed by addition of the compound as an anion source and subsequent addition of the ammonia.
10. The method for producing a silica sol according to claim 1, wherein the raw material liquid prepared in the step (a) has a pH of 8 to 12.
11. The method for producing a silica sol according to claim 1, wherein, in the step (b), the raw material liquid is heated in an autoclave apparatus at 100 C. to 180 C.
12. The method for producing a silica sol according to claim 1, wherein the method further comprises a step of bringing the silica sol produced in the step (b) into contact with a strongly acidic ion exchange resin and/or a strongly basic ion exchange resin.
13. The method for producing a silica sol according to claim 12, wherein the method further comprises a step of bringing the silica sol produced in the step (b) into contact with a carboxylic acid-type chelating resin, a hydroxyl group-type chelating resin, and/or an amine-type chelating resin before or after contact with a strongly acidic ion exchange resin and/or a strongly basic ion exchange resin.
14. The method for producing a silica sol according to claim 1, wherein the method further comprises a step of replacing the aqueous medium of the produced silica sol with an organic medium.
15. The method for producing a silica sol according to claim 1, wherein the mass ratio of each of Ca and Mg to SiO.sub.2 is 2 to 100 ppm in the silica sol.
16. The method for producing a silica sol according to claim 1, wherein the mass ratio of Na to SiO.sub.2 is 2 to 1,000 ppm, and the mass ratio of K to SiO.sub.2 is 2 to 100 ppm in the silica sol.
17. The method for producing a silica sol according to claim 1, wherein the elongated colloidal silica particles exhibit a D.sub.L/D.sub.B ratio of 3 to 30 wherein D.sub.L is an average particle diameter (nm) as measured by the dynamic light scattering method, and D.sub.B is a primary particle diameter (nm) as measured by the nitrogen gas adsorption method.
18. The method for producing a silica sol according to claim 1, wherein the silica sol is an acidic silica sol or an ammonia-containing alkaline silica sol.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] [
[0040] [
[0041] [
[0042] [
[0043] [
[0044] [
[0045] [
MODES FOR CARRYING OUT THE INVENTION
[0046] The present invention is directed to a method for producing a silica sol containing elongated colloidal silica particles dispersed in a liquid medium and having an SiO.sub.2 concentration of 6 to 30% by mass, wherein the elongated colloidal silica particles have a particle length of 50 to 1,000 nm as determined by observation with an electron microscope and exhibit a D.sub.L/D.sub.B ratio of 2.5 or more and a D.sub.L of 30 to 300 nm wherein D.sub.L is an average particle diameter (nm) as measured by the dynamic light scattering method, and D.sub.B is a primary particle diameter (nm) as measured by the nitrogen gas adsorption method, the production method comprising the following steps (a) and (b):
[0047] (a) a step of preparing a raw material liquid by adding at least one compound as an anion source selected from the group consisting of inorganic acids, organic acids, and ammonium salts of these acids, and ammonia to a colloidal aqueous solution of activated silica having an SiO.sub.2 concentration of 1 to 6% by mass and a pH of 2 to 5 so that the mass ratio of the compound to SiO.sub.2 is 3.0 to 7.0%; and
[0048] (b) a step of heating the raw material liquid prepared in the step (a) at 80 to 200 C. for 0.5 to 20 hours, to thereby produce a silica sol.
[0049] The aforementioned liquid medium is an aqueous medium (water) or an organic medium (organic solvent).
[0050] The principle of measurement of the average particle diameter D.sub.L (nm) is based on the dynamic light scattering method. For example, the average particle diameter can be measured with a dynamic light scattering particle diameter measuring apparatus (trade name: Zetasizer Nano, available from Spectris Co., Ltd.). The average particle diameter D.sub.L (nm) measured by the dynamic light scattering method falls within a range of 30 to 300 nm.
[0051] The primary particle diameter D.sub.B (nm) is calculated from the following formula: (D.sub.B nm)=2720/S wherein S is a specific surface area (m.sup.2/g) measured by the nitrogen gas adsorption method (BET method). The primary particle diameter refers to the diameter of a virtual spherical silica particle having a specific surface area equal to that of an elongated colloidal silica particle. Thus, the D.sub.L/D.sub.B ratio probably corresponds to the degree of elongation of an elongated silica particle. An elongated colloidal silica particle neither has a three-dimensional aggregation structure formed of particles, nor has a three-dimensional network structure. An elongated colloidal silica particle has a structure in which particles are connected in a rosary form and/or a chain form. Conceivably, silica particles having the same particle diameter and/or different particle diameters are connected in a rosary form and/or a chain form.
[0052] The degree of elongation of a silica particle as used herein refers to the degree of connection (length) of colloidal silica particles connected in a rosary form and/or a chain form.
[0053] In the present invention, the D.sub.L/D.sub.B ratio is 2.5 or more and may be, for example, 2.5 to 50.0, or 3.0 to 30.0, or 3.0 to 15.0.
[0054] In the present invention, the elongated colloidal silica particles may be either of crystalline particles and amorphous particles, or may be a mixture of crystalline and amorphous particles. Elongated amorphous colloidal silica particles are preferred.
[0055] The particle length of the colloidal silica particles can be determined by observation of the particle shape with an electron microscope (transmission electron microscope). The particle length is 50 to 1,000 nm or 60 to 800 nm.
[0056] The particle length of elongated colloidal silica particles as used herein is determined as follows. Specifically, as shown in
[0057] The colloidal aqueous solution of activated silica used in the step (a) can be prepared by bringing an aqueous alkali silicate solution exhibiting a ratio by mole of SiO.sub.2/M.sub.2O (wherein M is sodium or potassium) of 1 to 4.5 into contact with an ion exchange resin, for example, a strong acid-type cation exchange resin, or both a strong acid-type cation exchange resin and a strong base-type anion exchange resin. No particular limitation is imposed on the method for bringing the aqueous alkali silicate solution into contact with the ion exchange resin. For example, the aqueous alkali silicate solution is passed through a column filled with the ion exchange resin so that the aqueous alkali silicate solution comes into contact with the ion exchange resin.
[0058] The colloidal aqueous solution of activated silica can be produced by preparing the aforementioned aqueous alkali silicate solution so as to have a solid content of 1 to 10% by mass, and then bringing the aqueous alkali silicate solution into contact with the ion exchange resin. The solid content as used herein corresponds to the total amount of all components of the aqueous solution or the silica sol, except for the amount of the aqueous medium or organic medium component. The aqueous alkali silicate solution may be prepared by dilution of commercially available sodium silicate No. 1, No. 2, or No. 3 with, for example, pure water.
[0059] The strong acid-type cation exchange resin is a hydrogen-type cation exchange resin, and the hydrogen-type cation exchange resin may be prepared by passing an aqueous strong acid solution through a column filled with a cation exchange resin. Examples of the strong acid-type cation exchange resin include Amberlite (trade name) IR-120B, Amberjet 1020, and DOWEX MARATHON GH available from The Dow Chemical Company; Diaion (trade name) SK104 and Diaion PK208 available from Mitsubishi Chemical Holdings Corporation; and Duolite (trade name) C20J available from Sumika Chemtex Company, Limited.
[0060] The strong base-type anion exchange resin is a hydroxyl group-type anion exchange resin, and the hydroxyl group-type anion exchange resin may be prepared by passing an aqueous strong alkali solution through a column filled with an anion exchange resin. Examples of the strong base-type anion exchange resin include Amberlite (trade name) IRA400J, Amberlite IRA410J, and Amberjet 4400 available from The Dow Chemical Company; Diaion (trade name) SA10A and Diaion SA20A available from Mitsubishi Chemical Holdings Corporation; and Duolite (trade name) UBA120 available from Sumika Chemtex Company, Limited.
[0061] The aforementioned colloidal aqueous solution of activated silica used may have an SiO.sub.2 solid content of 1 to 10% by mass, preferably 1 to 6% by mass.
[0062] The colloidal aqueous solution of activated silica used in the step (a) may be further brought into contact with a carboxylic acid-type chelating resin, a hydroxyl group-type chelating resin, and/or an amine-type chelating resin.
[0063] Such a chelating resin contains two or more electron-donating atoms such as N, S, O, and P. Examples of such a chelating resin include NO type, SN type, NN type, and OO type chelating resins; for example, iminodiacetic acid-type (N(CH.sub.2COO).sub.2) and polyamine-type (NH(CH.sub.2CH.sub.2NH)nH) chelating resins. Specific examples include Diaion (trade name) CR11, Diaion CR20, Diaion CRB03, and Diaion CRB05 available from Mitsubishi Chemical Corporation. Adsorbed metal ions can be recycled by using an aqueous mineral acid solution (aqueous hydrochloric acid solution or aqueous sulfuric acid solution). A chelating resin containing adsorbed metal ions can be recycled by removing the metal ions with an aqueous mineral acid solution (aqueous hydrochloric acid solution or aqueous sulfuric acid solution).
[0064] The purity of the colloidal aqueous solution of activated silica used in the step (a) can be further increased by repeatedly passing the solution through a column charged (filled) with the aforementioned ion exchange resin or chelating resin.
[0065] The column can be charged (filled) with the aforementioned ion exchange resin or chelating resin, and the aforementioned aqueous solution can be passed through the column at a space velocity of 1 to 30 h.sup.1 or 1 to 15 h.sup.1.
[0066] The purity of the colloidal aqueous solution of activated silica used in the step (a) can be further increased by treating the solution with a strong acid at a temperature of 1 to 98 C., and then bringing the treated solution into contact with a strong acid-type cation exchange resin or with both a strong acid-type cation exchange resin and a strong base-type anion exchange resin. The colloidal aqueous solution of activated silica is probably in the form of an aqueous solution of colloidal silica fine particles (e.g., a particle diameter of 5 nm or less, or less than 5 nm, or 3 nm or less, or 1 nm or less). In some cases, such colloidal particles may contain metal impurities. When the metal impurities contained in the colloidal particles cannot be removed with the ion exchange resin or the chelating resin, the colloidal aqueous solution of activated silica can be treated with an aqueous acid solution at 1 to 98 C., preferably at room temperature, to thereby elute the metal impurities from the interior of the colloidal particles into the aqueous solution. The metal impurities are separated (through adsorption) from the aqueous solution by bringing the solution into contact with the aforementioned ion exchange resin or chelating resin. Thus, the purity of the colloidal aqueous solution of activated silica can be increased, to thereby increase the purity of the finally produced silica sol.
[0067] The compound as an anion source used in the step (a) may be at least one compound as an anion source selected from the group consisting of nitric acid, sulfuric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrochloric acid, acetic acid, formic acid, oxalic acid, citric acid, lactic acid, malic acid, gluconic acid, tartaric acid, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and an ammonium salt of any of these. For example, an aqueous solution of, for example, nitric acid, sulfuric acid, or oxalic acid may be used. Such an anion source may be added in the form of an ammonium salt, or may be used as an ammonium salt converted by ammonia used for pH adjustment. The concentration of the aqueous solution used may be, for example, 0.1 to 50% by mass, or 0.1 to 10% by mass, or 0.1 to 5% by mass, or 0.1 to 1% by mass, or 0.1 to 0.2% by mass.
[0068] The ammonia used in the step (a) for pH adjustment may be in the form of ammonia gas or an aqueous ammonia solution. For example, ammonia gas is introduced directly into the colloidal aqueous solution of activated silica for pH adjustment, or an aqueous ammonia solution is added to the colloidal aqueous solution of activated silica for pH adjustment. The aqueous ammonia solution may be used at a concentration of 28% by mass, or may be used after being diluted with pure water to a concentration of 1 to less than 28% by mass.
[0069] The step (a) includes, for example, a step of adding the aforementioned compound as an anion source to the aforementioned colloidal aqueous solution of activated silica, followed by addition of the aforementioned ammonia.
[0070] The step (a) includes, for example, a step of adding the aforementioned ammonia to the aforementioned colloidal aqueous solution of activated silica, followed by addition of the aforementioned compound as an anion source and subsequent addition of the aforementioned ammonia.
[0071] The pH of the raw material liquid (colloidal aqueous solution of activated silica) prepared in the step (a) may be adjusted to 8 to 12, or 9 to 11, or 9 to 10.
[0072] The step (b) involves heating of the raw material liquid (colloidal aqueous solution of activated silica) prepared in the step (a) at 80 to 200 C., or 100 to 180 C., or 120 to 150 C. with stirring for 0.5 to 20 hours, to thereby produce a silica sol. The heating of the raw material liquid with an autoclave apparatus at a temperature of 100 to 200 C. or 100 to 180 C. can produce a silica sol containing dispersed elongated colloidal silica particles having a high degree of deformation. An ammonia-containing alkaline silica sol having a pH of 8 to 11 or 9 to 11 is produced through the step (b).
[0073] The silica sol produced in the step (b) may be optionally subjected to concentration with an ultrafiltration membrane, or evaporative concentration under reduced pressure or at ambient pressure, so as to adjust the concentration of SiO.sub.2 to 6 to 30% by mass.
[0074] The silica sol produced in the step (b) can be brought into contact with a strongly acidic ion exchange resin and/or a strongly basic ion exchange resin, to thereby prepare a silica sol of high purity. For example, the silica sol produced in the step (b) can be brought into contact with a strongly acidic ion exchange resin, or with both a strongly acidic ion exchange resin and a strongly basic ion exchange resin, to thereby prepare a silica sol of high purity.
[0075] The silica sol produced in the step (b) can be brought into contact with a carboxylic acid-type chelating resin, a hydroxyl group-type chelating resin, and/or an amine-type chelating resin before or after contact with a strongly acidic ion exchange resin and/or a strongly basic ion exchange resin, to thereby prepare a silica sol of high purity. For example, the silica sol produced in the step (b) can be brought into contact with a carboxylic acid-type chelating resin, a hydroxyl group-type chelating resin, and/or an amine-type chelating resin after contact with a strongly acidic ion exchange resin or with both a strongly acidic ion exchange resin and a strongly basic ion exchange resin, to thereby prepare a silica sol of high purity.
[0076] The silica sol produced in the step (b) can be brought into contact with a strongly acidic ion exchange resin, to thereby produce an acidic silica sol.
[0077] The aqueous medium of the aforementioned acidic silica sol can be replaced with an organic medium (organic solvent), to thereby produce an organosilica sol. This solvent replacement can be performed by evaporation with an apparatus such as a rotary evaporator. The solvent replacement does not cause a change in the D.sub.L/D.sub.B ratio of elongated colloidal silica particles.
[0078] Examples of usable organic solvents include alcohols, glycols, esters, ketones, nitrogen-containing solvents, and aromatic solvents. Specific examples of such solvents include organic solvents, such as methanol, ethanol, propanol, ethylene glycol, propylene glycol, glycerin, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether, propylene glycol monoethyl ether acetate, acetone, methyl ethyl ketone, dimethylformamide, N-methyl-2-pyrrolidone, toluene, xylene, and dimethylethane. Other examples of usable solvents include polyethylene glycol, silicone oil, and reactive diluents containing radical-polymerizable vinyl and epoxy groups.
[0079] The surfaces of elongated colloidal silica particles may be treated with a silane coupling agent such as tetraethoxysilane, trimethylmonoethoxysilane, or hexamethyldisilane.
[0080] The resultant silica sol may contain Ca and Mg as metal impurities, wherein the mass ratio of Ca to SiO.sub.2 is 2 to 100 ppm or 2 to 50 ppm, and the mass ratio of Mg to SiO.sub.2 is 2 to 100 ppm or 2 to 50 ppm.
[0081] The silica sol may also contain Na and K, wherein the mass ratio of Na to SiO.sub.2 is 2 to 1,000 ppm or 2 to 500 ppm, and the mass ratio of K to SiO.sub.2 is 2 to 100 ppm or 2 to 50 ppm.
[0082] The silica sol produced in the step (b) can be brought into contact with a strongly acidic ion exchange resin, to thereby prepare an acidic silica sol, and then high-purity ammonia gas or aqueous ammonia solution can be added to the acidic silica sol, to thereby prepare an ammonia-containing alkaline silica sol.
EXAMPLES
[0083] [Evaluation of Physical Properties of Silica Sol]
[0084] 1) pH
[0085] The pH was measured with a pH meter (available from DKK-TOA CORPORATION).
[0086] 2) Electrical conductivity
[0087] The electrical conductivity was measured with an electrical conductivity meter (available from DKK-TOA CORPORATION).
[0088] 3) SiO.sub.2 concentration
[0089] The mass of SiO.sub.2 was determined from the difference between the mass of a residue obtained by baking of the silica sol at 1,000 C. and the mass of metal elements (in terms of oxide) contained in the silica sol in an amount of 1 ppm or more among all metal elements measured by the metal element analysis as described in 7) below. The SiO.sub.2 concentration was calculated on the basis of the determined mass of SiO.sub.2.
[0090] 4) D.sub.L particle diameter (average particle diameter as measured by the dynamic light scattering method)
[0091] The D.sub.L particle diameter was measured with a dynamic light scattering particle diameter measuring apparatus (Zetasizer Nano, available from Spectris Co., Ltd.).
[0092] 5) D.sub.B particle diameter (primary particle diameter as measured by the nitrogen gas adsorption method) p An aqueous silica sol was brought into contact with a hydrogen-type strongly acidic cation exchange resin, to thereby remove sodium adsorbed on the surface of the silica sol. Thereafter, the silica sol was dried at 300 C. and then ground to prepare a powder sample. The specific surface area S (m.sup.2/g) of the resultant powder sample was measured by the BET method with a nitrogen adsorption specific surface area measuring apparatus (Monosorb MS-16, available from Yuasa Ionics Co., Ltd.), to thereby determine the D.sub.B particle diameter (nm).
[0093] The D.sub.B particle diameter was calculated by the following formula (II) (through conversion of colloidal silica particles into spherical particles).
D.sub.B (nm)=2720/S (m.sup.2/g)(II)
[0094] 6) Electron microscopic observation
[0095] The particles were photographed with a transmission electron microscope (JEM-1010, available from JEOL Ltd.) at an acceleration voltage of 100 kV.
[0096] The resultant TEM (transmission electron microscope) photograph was used to determine the particle length of elongated colloidal silica particles (average of 50 randomly selected particles). Specifically, as shown in
[0097] 7) Metal element analysis
[0098] The metal element analysis was performed with an atomic absorption spectrophotometer (Spectra AA, available from Agilent Technologies, Inc.) and an ICP emission spectrophotometer (CIROS120 EOP, available from Rigaku Corporation).
[0099] The amounts of measured metals (Si, Na, K, Mg, and Ca) were used to calculate the mass ratio of the metals to SiO.sub.2 whose amount was determined as described above in 3) SiO.sub.2 concentration.
[0100] [Determination of Deformation]
[0101] : D.sub.L particle diameter/D.sub.B particle diameter=2.5 or more
[0102] Determination of growth of elongated silica particles by observation with a transmission electron microscope.
[0103] X: D.sub.L particle diameter/D.sub.B particle diameter=less than 2.5
[0104] Insufficient growth of elongated silica particles.
[0105] Gelation: Gelation refers to formation of a gel.
Example 1
[0106] Water was added to commercially available sodium water glass (JIS No. 3 sodium water glass: SiO.sub.2 concentration: 28.8% by mass, Na.sub.2O concentration: 9.47% by mass, ratio by mole of SiO.sub.2/Na.sub.2O: 3.1 to 3.3), to thereby prepare an aqueous sodium silicate solution having an SiO.sub.2 concentration of 3.8% by mass. The aqueous sodium silicate solution was passed through a column filled with a hydrogen-type strongly acidic cation exchange resin (Amberlite IR-120B, available from The Dow Chemical Company), to thereby prepare a colloidal aqueous solution of activated silica having an SiO.sub.2 concentration of 3.4% by mass and a pH of 2.9.
[0107] A stirring bar was added to a 500-ml styrol bottle, and 351.3 g of the above-prepared activated silica was added thereto. While the activated silica was stirred with a magnetic stirrer, 5.2 g of 10% by mass aqueous nitric acid solution (serving as an anion source) was added, and then 4.8 g of 28% aqueous ammonia solution was added. Thereafter, 8.7 g of pure water was added, and the resultant mixture was stirred for one hour, to thereby prepare a raw material liquid having an SiO.sub.2 concentration of 3.2%.
[0108] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 2
[0109] A raw material liquid of Example 2 was produced in the same manner as in Example 1, except that the amount of 10% by mass aqueous nitric acid solution was changed to 8.1 g, the amount of 28% by mass aqueous ammonia solution was changed to 5.9 g, and the amount of pure water was changed to 4.7 g.
[0110] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 3
[0111] A raw material liquid of Example 3 was produced in the same manner as in Example 1, except that 10% by mass nitric acid serving as an anion source was changed to 0.5 g of oxalic acid dihydrate, the amount of 28% by mass aqueous ammonia solution was changed to 4.1 g, and the amount of pure water was changed to 14.0 g.
[0112] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 4
[0113] A raw material liquid of Example 4 was produced in the same manner as in Example 1, except that 10% by mass nitric acid serving as an anion source was changed to 0.6 g of oxalic acid dihydrate, the amount of 28% aqueous ammonia solution was changed to 3.6 g, and the amount of pure water was changed to 14.4 g.
[0114] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 5
[0115] A raw material liquid of Example 5 was produced in the same manner as in Example 1, except that 10% by mass nitric acid serving as an anion source was changed to 7.4 g of 8% by mass sulfuric acid, the amount of 28% by mass aqueous ammonia solution was changed to 5.4 g, and the amount of pure water was changed to 14.4 g.
[0116] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Comparative Example 1
[0117] A raw material liquid of Comparative Example 1 was produced in the same manner as in Example 1, except that the amount of 10% by mass aqueous nitric acid solution was changed to 3.0 g, the amount of 28% by mass aqueous ammonia solution was changed to 3.9 g, and the amount of pure water was changed to 11.8 g.
[0118] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Comparative Example 2
[0119] A raw material liquid of Comparative Example 2 was produced in the same manner as in Example 1, except that the amount of 10% by mass aqueous nitric acid solution was changed to 9.3 g, the amount of 28% by mass aqueous ammonia solution was changed to 4.9 g, and the amount of pure water was changed to 4.5 g.
[0120] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. The product removed from the autoclave was found to undergo gelation.
[0121] Tables 1 and 2 show the silica source, SiO.sub.2 concentration, and pH of the colloidal aqueous solution of activated silica used for the production of each of the raw material liquids of Examples 1 to 5 and Comparative Examples 1 and 2, and the type and amount of an anion source added to the colloidal aqueous solution of activated silica.
[0122] Tables 3 and 4 show the physical properties and heating conditions of the raw material liquids prepared in Examples 1 to 5 and Comparative Examples 1 and 2.
[0123] Tables 5 to 7 show the results of evaluation of the physical properties and determination of deformation of the silica sols produced in Examples 1 to 5 and Comparative Example 1 and those of the gel produced in Comparative Example 2.
[0124] Tables 4 and 5 show the results of evaluation of the physical properties and determination of deformation of the silica sols produced in Examples 1 to 5 and Comparative Example 1.
[0125]
TABLE-US-00001 TABLE 1 (a) Raw material liquid Example 1 Example 2 Example 3 Example 4 Silica source Activated Activated Activated Activated silica silica silica silica SiO.sub.2 3.4 3.4 3.4 3.4 concentration (wt %) pH of activated 2.9 2.9 2.9 2.9 silica Anion source Nitric acid Nitric acid Oxalic acid Oxalic acid Anion/silica (wt %) 4.4 6.8 3.0 3.6
TABLE-US-00002 TABLE 2 (a) Raw material Comparative Comparative liquid Example 5 Example 1 Example 2 Silica source Activated Activated Activated silica silica silica SiO.sub.2 3.4 3.4 3.4 concentration (wt %) pH of activated silica 2.9 2.9 2.9 Anion source Sulfuric acid Nitric acid Nitric acid Anion/silica (wt %) 5.0 2.5 7.8
TABLE-US-00003 TABLE 3 Example 1 Example 2 Example 3 Example 4 (a) Physical properties of raw material liquid pH 9.61 9.61 9.64 9.60 Electrical conductivity 4160 5740 4050 4380 S/cm (b) Heating conditions Temperature ( C.) 140 140 140 140 Time (hr) 8 8 8 8
TABLE-US-00004 TABLE 4 Comparative Example 5 Example 1 Example 2 (a) Physical properties of raw material liquid pH 9.60 9.61 9.61 Electrical conductivity S/cm 5150 3080 6820 (b) Heating conditions Temperature ( C.) 140 140 140 Time (hr) 8 8 8
TABLE-US-00005 TABLE 5 Example 1 Physical properties of silica sol pH 10.1 Electrical conductivity S/cm 3490 D.sub.L particle diameter (nm) 37.4 D.sub.B particle diameter (nm) 12.3 D.sub.L/D.sub.B ratio 3.0 Deformation Particle length (nm) by observation with electron microscope 153 SiO.sub.2 % by mass 3.2 Na/SiO.sub.2 (ppm) 962 K/SiO.sub.2 (ppm) 4 Mg/SiO.sub.2 (ppm) 35 Ca/SiO.sub.2 (ppm) 34
TABLE-US-00006 TABLE 6 Example 2 Example 3 Example 4 Physical properties of silica sol pH 10.1 10.1 10.0 Electrical conductivity S/cm 5220 3420 3830 D.sub.L particle diameter (nm) 171.9 38.5 71.4 D.sub.B particle diameter (nm) 13.2 12.4 12.5 D.sub.L/D.sub.B ratio 13.0 3.1 5.7 Deformation Particle length (nm) by observation with electron microscope 743 543 494 SiO.sub.2 % by mass 3.2 3.2 3.2
TABLE-US-00007 TABLE 7 Comparative Comparative Example 5 Example 1 Example 2 Physical properties of silica sol pH 10.1 10.2 Gelation Electrical conductivity S/cm 4570 2360 Gelation D.sub.L particle diameter (nm) 85.2 23.6 Gelation D.sub.B particle diameter (nm) 13.9 11.6 Gelation D.sub.L/D.sub.B ratio 6.1 2.0 Gelation Deformation X Gelation Particle length (nm) by observation with electron microscope 514 46 SiO.sub.2 % by mass 3.2 3.2 3.2
INDUSTRIAL APPLICABILITY
[0126] A silica sol which contains a small amount of metal impurities and in which colloidal silica having an elongated particle shape is dispersed in a solvent can be readily produced by addition of a compound as an anion source and ammonia as an alkali source to an aqueous activated silica solution and heating of the resultant mixture at a predetermined temperature.
[0127] A silica sol containing non-spherical colloidal silica particles is expected to exhibit various effects (e.g., bonding force, adsorption force, and optical transparency) depending on the shape of the particles. Thus, the silica sol can be used in a variety of applications including microfillers for various coating agents, binders, modifiers, catalyst carriers, and abrasives for electronic materials (e.g., an abrasive for a silicon wafer, and a CMP abrasive for a device wafer for polishing a silicon oxide film or a metal such as copper or aluminum).