Standard for high purity quartz sand

Quartz, scientifically known as a group of minerals composed of silicon dioxide (SiO2), features silicon and oxygen atoms arranged in a repetitive three-dimensional pattern. Silicon dioxide can appear in many different forms and crystal structures, with the most common being quartz, cristobalite, and tridymite. High-purity quartz is a highly refined product obtained from natural quartz minerals through processing and purification, with stringent impurity content requirements, typically less than 50μg/g, and nearly no tolerance for metal ions like potassium, sodium, iron, titanium, or hydroxyl (-OH) groups.

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Currently, there is no clear standard for the concept and classification of high-purity quartz. Based on researchers' viewpoints and current international technology levels, quartz with a purity of ω(SiO2)'3N-5N and ω(Fe2O3)<10×10-6 can be considered high-purity quartz, while those with 6N-7N can be classified as ultra-high-purity quartz. Quartz sand with a purity of 99.9% can be used to make transparent glass; at 99.99% purity, quartz sand can be used in manufacturing semiconductor filters, liquid crystal displays, and optical glass. Quartz with 99.95% purity is considered low-grade high-purity quartz, 99.99% purity as medium-grade high-purity quartz, and 99.997% purity as high-grade high-purity quartz.

The processing and purification technology of quartz has developed alongside modern industrial needs, making high-purity quartz indispensable in modern industry. It can be used to produce silicon metal, optical fibers, quartz glass, and other high-performance materials, widely applied in electronics, integrated circuits, communication, laser technology, and aerospace industries. The wide range of applications and high added value of processed and purified quartz make it highly valuable.

To obtain high-quality, high-grade high-purity quartz materials, natural crystals are often used as raw materials, which are then purified and processed. However, high-quality quartz raw material resources are limited globally, and the reserves of natural crystals are depleting yearly. The gradual depletion of natural crystal resources at the end of the 20th century and the beginning of the 21st century has promoted the rapid development of high-purity quartz preparation technology using quartzite, silica, and vein quartz as raw materials.

High-purity quartz is initially made from first- and second-grade natural crystals, which are then selected, purified, and processed. The particularity of the formation of natural crystals determines that it has two inherent deficiencies: first, small reserves, poor mining conditions, scarce resources, and high prices, which make it difficult to meet the needs of large-scale industrial production; second, affected by changes in the formation environment, the chemical composition of mineral crystals is unstable, which leads to large fluctuations in the chemical composition of raw materials in large-scale industrial applications, making it difficult to standardize raw materials, and making it difficult to meet the needs of large-scale, stable, high-purity quartz high-end product production.

Deep Processing Technology of Quartz Sand

Physical Methods

1. Magnetic Separation Process

Magnetic separation is a purification method that removes magnetic impurities from quartz minerals through the action of a magnetic field. This process can remove both magnetic impurities and inclusions containing magnetic impurities. Since quartz is non-magnetic, it cannot be magnetized by a magnetic field, while most Fe and Ti impurities are paramagnetic and can be magnetized. Thus, magnetic separation can effectively remove Fe and Ti impurities, achieving high quartz sand content. Magnetic separation is simple and effective for removing magnetic impurities, and it can be divided into strong magnetic separation and weak magnetic separation. Weak magnetic fields remove stronger magnetic impurities like magnetite, while strong magnetic fields remove weaker magnetic impurities like hematite, ilmenite, and garnet.

2. Flotation Process

The flotation purification method utilizes the different crystal structures and surface properties of quartz minerals and impurities (mainly feldspar silicate minerals). It employs various collectors or surface activators to adjust the surface characteristics of quartz and impurities, facilitating their separation. Depending on the chosen collectors, flotation can be classified into cationic collector flotation, anionic-cationic mixed collector flotation, and anionic collector flotation. Common cationic collectors include fatty amine collectors, significantly influenced by pH. The most common anionic collectors are oleic acid and sodium oleate, with pure quartz not floating in sodium oleate without the activation of high-valence metal cations. Amphoteric collectors, containing multiple functional groups, exhibit excellent foam performance and combine some advantages of single collectors.

The flotation process can be affected by many factors, such as temperature, choice of flotation reagents, pH control, etc. Before flotation, quartz sand is ground into small particles to allow physical separation of various minerals, and calcination followed by water quenching can improve the flotation effect.

3. Calcination Process

Calcination involves heating quartz to high temperatures, then quenching it in water, which aids in purifying the quartz. This process has two main effects in quartz purification. First, thermal-assisted crushing reduces energy consumption and prevents over-crushing. Second, it facilitates subsequent impurity removal processes by causing abrupt changes in internal stress, creating cracks and exposing inclusions, making impurities easier to remove in later purification steps.

4. Acid Leaching Process

The most challenging impurities to remove from quartz crystals are those directly substituting into the quartz lattice. Physical separation methods like grinding, sieving, density separation, and magnetic separation are ineffective because these impurities are uniformly distributed in the lattice. Since quartz is insoluble in acids other than HF, chemical means can be used to dissolve various metal impurities from the quartz surface, fissures, or structural layers through acid leaching, achieving a higher purification level. Commonly used acids include sulfuric acid, hydrochloric acid, oxalic acid, and hydrofluoric acid. Mixed acid leaching can produce a synergistic effect for better impurity removal, often employing mixed acids for leaching. Factors influencing acid leaching include acid choice, concentration and dosage, solution temperature, leaching time, and stirring, which enhances contact between the acid and quartz surface, improving the purification effect.

5. Chlorination Roasting Purification Process

Chlorination roasting is a highly effective method for removing lattice impurities from quartz. Under specific temperature and atmospheric conditions, introducing chlorinating agents transforms metal oxide impurities into metal chlorides. Given their generally low boiling points, these chlorides can be volatilized and separated from quartz. During chlorination roasting, the chemical potential gradient between the quartz surface and its interior allows the diffusion and expulsion of inclusions, achieving deeper purification. Common chlorinating agents include Cl2, HCl, NaCl, and NH4Cl. These agents, stronger oxidants than O2 at high temperatures, can chlorinate and remove Al2O3, Fe2O3, and TiO2 impurities. Chlorination roasting offers simple equipment, excellent impurity removal, and high efficiency, making it a highly effective quartz purification method. Additionally, pollutant gases can be treated, such as Cl2 being treated with NaOH, minimizing environmental impact.

6. Hydrometallurgical Techniques

Typically used for leaching and extracting metals from mineral ores, hydrometallurgical techniques can also remove and separate metal minerals from non-metallic ores, especially for iron-containing minerals. In quartz purification, traditional chemical processes include microbial leaching, high-temperature leaching, high-pressure leaching, and catalytic high-temperature leaching. These techniques have introduced new methods for producing high-grade quartz sand and reducing acid consumption. Hydrometallurgical techniques primarily utilize acids to separate quartz and valuable metal elements from impurity minerals. Microbial leaching reduces acid consumption and costs compared to simple acid leaching. High-temperature leaching accelerates leaching through heating, increasing impurity metal element leaching rates. Increasing pressure during high-temperature leaching effectively reduces acid consumption. Introducing stable liquid catalysts in catalytic leaching improves efficiency without using HF, enhancing quartz ore purification.

Microbial leaching offers low cost and pollution, requiring only room temperature for the process. The treated leaching solution can be discharged after simple processing. However, its application is limited by humidity, temperature, pH, water consumption, microbial strains, and leaching methods (dump leaching and tank leaching).

High-temperature leaching is one of the most commonly used techniques, with easy operation and low-cost equipment advantages in industrial production. Leaching temperatures range from 20-100', significantly improving leaching speed and rate at low costs. However, acid consumption and pollution from impurity dissolution are major drawbacks.

High-temperature, high-pressure leaching outperforms simple high-temperature leaching, significantly improving purification speed. However, it exposes equipment to a fluorine-rich environment, causing severe corrosion and reducing equipment lifespan. Catalytic high-temperature, high-pressure leaching avoids fluorides, offers simple components, low consumption, reusable leaching agents, and environmental friendliness, yielding excellent purification results.

Chemical Methods

Chemical Synthesis

Chemical synthesis of high-purity quartz generally involves direct and indirect methods. Direct methods include chemical vapor deposition (CVD) and plasma-enhanced chemical vapor deposition (PCVD) using silicon halides like silicon tetrachloride. These methods produce synthetic quartz glass with uniformity, high transmittance, and low production costs. However, the process generates toxic, corrosive gases like HCl or Cl2, increasing equipment corrosion and environmental impact. Indirect methods, compared to direct methods, offer doping control (e.g., F, Ti, Al, B, and rare earths) and hydroxyl content control for superior quartz glass properties.

1. Direct Methods

(1) Chemical Vapor Deposition (CVD)

CVD involves the hydrolysis or oxidation of silicon-containing gaseous compounds (e.g., SiCl4, SiH4, and Si4O4(CH3)8) in a hydrogen-oxygen flame, producing SiO2 particles that deposit layer by layer on a rotating substrate to form transparent quartz glass. CVD-produced high-purity quartz features low impurity content and excellent optical uniformity, although high hydroxyl content affects optical properties. CVD quartz glass is widely used in integrated circuits, precision instruments, and military aerospace.

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(2) Sol-Gel Method

The sol-gel method converts a solution of silicon alkoxide (e.g., tetraethyl orthosilicate, TEOS) into a gel through hydrolysis and polycondensation reactions. The gel is then dried and sintered to produce high-purity SiO2 powder. The sol-gel method offers fine particle size control and uniformity, enabling the synthesis of high-purity SiO2 powder with specific properties (e.g., low density, high specific surface area, and low impurity content). The sol-gel method is widely used in producing high-performance optical materials and advanced ceramic materials.

2. Indirect Method

Aerosol Method

The aerosol method converts silicon-containing gaseous compounds (e.g., SiCl4 and SiH4) into fine SiO2 particles through high-temperature pyrolysis or oxidation reactions. The aerosol method offers excellent particle size control and uniformity, enabling the synthesis of high-purity SiO2 powder with specific properties (e.g., fine particle size, high specific surface area, and low impurity content). The aerosol method is widely used in producing high-performance optical materials and advanced ceramic materials.

Applications of High-Purity Quartz Sand

Quartz is a fundamental material in industrial production. Its simplest uses include filtration and absorbents, casting sand, fillers, or abrasives. In some high-tech industries, the applications of quartz are also very extensive and important. High-purity quartz, which is of high added value, can be used in the production of optical fibers and monocrystalline silicon for the electronics industry and photovoltaic cells. Another special category includes laboratory glassware for synthesis and analytical chemistry, which also holds considerable value. According to statistics, in the production chain using quartz as a raw material, silicon metal is priced at 255 euros per ton, silicon tetrachloride is priced at 630 euros per ton; high-purity quartz with an impurity content of less than 20 ppm can reach a value of euros per ton, and ultra-pure quartz used in the electronics industry can sell for up to 80,000 euros per ton.

Quartz glass is an industrial technical glass made by melting a single component of silicon dioxide. It is high-temperature resistant, has a low coefficient of expansion, thermal shock resistance, excellent chemical stability, and superior electrical insulation. With the advancement of science and technology, high-purity quartz is widely used in high-tech industries such as fiber optic communications, solar photovoltaics, aerospace, electronics, and semiconductors. The excellent performance of quartz glass mainly depends on its purity. High-purity quartz sand, with high purity and low impurity content, is the best raw material for manufacturing high-performance quartz glass.

High-purity quartz sand plays a crucial role as the primary raw material in glass batch mixtures, accounting for 60%-80% of the mixture. The quality of the glass batch not only affects the quality of optical glass products but also impacts the service life of glass melting furnaces. The use environment of optical glass products requires very high standards for impurity content, refractive index, light transmittance, and microscopic defects. All these factors strictly demand high-quality quartz sand as the main raw material. For high-precision, high-resolution optical glass, high-purity quartz sand is an excellent raw material.

Semiconductor Industry

The semiconductor industry is the foundation of the global information industry. The widespread application of semiconductor products has driven the advent of the information and intelligent era. The most commercially valuable in semiconductors are silicon and some of its binary compounds, such as silicon carbide. These high-performance materials are widely used in the electronic information field, being manufactured into various high-tech products like chips with excellent performance. Every year, chip manufacturers and designers significantly improve the performance of their products, and the reduced prices make high-tech products increasingly accessible to consumers. The global semiconductor industry showed a yearly increasing trend from to . In this field, high-purity quartz is used to produce higher-performance elemental silicon and other compound materials, which are widely applied in the semiconductor field.

Optical Fiber

Quartz glass can be used to manufacture optical fibers, which are very fine strands with a diameter of less than 8 millimeters. Digital data is transmitted through optical fibers in the form of light. Optical cables made of optical fibers play an irreplaceable important role in modern communication transmission. Moreover, high-purity quartz also has certain optical properties; it can form polarized laser beams and, using high-purity quartz as a window, can manufacture fiber lasers with prisms, filters, and timing devices. High-quality quartz crystals are also used for prisms and lenses in optical instruments. Thus, optical fibers made from high-purity quartz raw materials have very high added value.

Solar Cells

The solar energy industry is a very hot high-tech industry, with the annual output of solar cells increasing year by year. China has also invested heavily in the photovoltaic industry. Producing solar cells requires a large amount of high-purity quartz. In a modern society advocating green energy, the demand for solar cells is very high, so the demand for high-purity quartz in the photovoltaic industry is also enormous. The solar-grade silicon produced from high-purity quartz is of considerable added value; for example, the solar-grade silicon produced by Siemens and its subsidiaries can sell for up to 40 euros per kilogram.

In summary, high-purity quartz sand is a critical material in various high-tech industries, ranging from semiconductors to solar cells, owing to its exceptional purity and minimal impurity content. Its applications significantly contribute to advancements in technology and the production of high-performance products.

USA1 - High Purity Silica Sol and its Production Method - Google Patents

High Purity Silica Sol and its Production Method Download PDF

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Publication number

USA1

USA1 US13/727,791 USA USA1 US A1 US A1 US A1 US A US A US A US A1 US A1 US A1

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Prior art keywords

solution

concentration

high purity

silicate

silica sol

Prior art date

-12-28

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Kazuhiro Nakayama

Akira Nakashima

Michio Komatsu

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JGC Catalysts and Chemicals Ltd

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JGC Catalysts and Chemicals Ltd

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-12-28

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-12-27

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-01-16

-12-27 Application filed by JGC Catalysts and Chemicals Ltd filed Critical JGC Catalysts and Chemicals Ltd

-03-14 Assigned to JGC CATALYSTS AND CHEMICALS LTD. reassignment JGC CATALYSTS AND CHEMICALS LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KOMATSU, MICHIO, NAKASHIMA, AKIRA, NAKAYAMA, KAZUHIRO

-01-16 Publication of USA1 publication Critical patent/USA1/en

-03-21 Application granted granted Critical

-03-21 Publication of USB2 publication Critical patent/USB2/en

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-06-20 Adjusted expiration legal-status Critical

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• RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 title claims abstract description 98
• manufacturing process Methods 0.000 title claims abstract description 44
• VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 244
• solution Substances 0.000 claims abstract description 156
• silicon dioxide Substances 0.000 claims abstract description 118
• aqueous solution Substances 0.000 claims abstract description 99
• BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 claims abstract description 76
• alkali metal silicate Inorganic materials 0.000 claims abstract description 58
• NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 claims abstract description 32
• ion exchange resin Substances 0.000 claims abstract description 26
• ion-exchange polymer Polymers 0.000 claims abstract description 26
• feed solution Substances 0.000 claims abstract description 21
• ion exchange Methods 0.000 claims abstract description 20
• ultra-filtration Methods 0.000 claims abstract description 20
• cationic group Chemical group 0.000 claims abstract description 7
• mixing Methods 0.000 claims abstract description 5
• MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 29
• particle Substances 0.000 claims description 20
• oxidant agent Substances 0.000 claims description 19
• mixture Substances 0.000 claims description 7
• buffering agent Substances 0.000 claims description 3
• heterocyclic compounds Chemical class 0.000 claims description 3
• pH adjusting agent Substances 0.000 claims description 3
• surface-active agent Substances 0.000 claims description 3
• NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 abstract description 40
• method Methods 0.000 abstract description 36
• potassium silicate Nutrition 0.000 abstract description 20
• impurity Substances 0.000 abstract description 11
• metal Inorganic materials 0.000 abstract description 10
• metal Substances 0.000 abstract description 10
• copper Inorganic materials 0.000 abstract description 7
• nickel Inorganic materials 0.000 abstract description 7
• starting material Substances 0.000 abstract description 3
• conventional method Methods 0.000 abstract 1
• coesite Inorganic materials 0.000 description 44
• cristobalite Inorganic materials 0.000 description 44
• stishovite Inorganic materials 0.000 description 44
• tridymite Inorganic materials 0.000 description 44
• HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 36
• VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 21
• Sodium Silicate Substances 0.000 description 21
• sodium silicate Inorganic materials 0.000 description 21
• XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 18
• comparative effect Effects 0.000 description 17
• KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 12
• measurement Methods 0.000 description 10
• membrane Substances 0.000 description 10
• substance Substances 0.000 description 10
• solid Substances 0.000 description 7
• KKCBUQHMOMHUOY-UHFFFAOYSA-N Na2O Inorganic materials [O-2].[Na+].[Na+] KKCBUQHMOMHUOY-UHFFFAOYSA-N 0.000 description 6
• cation exchange resin Substances 0.000 description 6
• colloidal silica Substances 0.000 description 6
• OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 5
• fine particle Substances 0.000 description 5
• KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 4
• QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
• acid Substances 0.000 description 4
• acidificating effect Effects 0.000 description 4
• carbon Inorganic materials 0.000 description 4
• filtrate Substances 0.000 description 4
• GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 3
• XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
• alkali Substances 0.000 description 3
• cation exchange Methods 0.000 description 3
• evaporation Methods 0.000 description 3
• heat treatment Methods 0.000 description 3
• nitric acid Inorganic materials 0.000 description 3
• preparation method Methods 0.000 description 3
• semiconductor Substances 0.000 description 3
• silicates Chemical class 0.000 description 3
• silicon Inorganic materials 0.000 description 3
• silicon Substances 0.000 description 3
• titration Methods 0.000 description 3
• QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
• KFSLWBXXFJQRDL-UHFFFAOYSA-N Peracetic acid Chemical compound CC(=O)OO KFSLWBXXFJQRDL-UHFFFAOYSA-N 0.000 description 2
• FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
• absorption reaction Methods 0.000 description 2
• alkali metal Inorganic materials 0.000 description 2
• alkali metal oxide Inorganic materials 0.000 description 2
• alkali metals Chemical class 0.000 description 2
• cullet Substances 0.000 description 2
• dispersion medium Substances 0.000 description 2
• electronic material Substances 0.000 description 2
• glass Substances 0.000 description 2
• metal oxide Inorganic materials 0.000 description 2
• metal oxides Chemical class 0.000 description 2
• neutralization reaction Methods 0.000 description 2
• NROKBHXJSPEDAR-UHFFFAOYSA-M potassium fluoride Chemical compound [F-].[K+] NROKBHXJSPEDAR-UHFFFAOYSA-M 0.000 description 2
• product Substances 0.000 description 2
• weighing Methods 0.000 description 2
• RPAJSBKBKSSMLJ-DFWYDOINSA-N (2s)-2-aminopentanedioic acid;hydrochloride Chemical class Cl.OC(=O)[C@@H](N)CCC(O)=O RPAJSBKBKSSMLJ-DFWYDOINSA-N 0.000 description 1
• H2SiO3 Inorganic materials 0.000 description 1
• K2SiF6 Inorganic materials 0.000 description 1
• CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 1
• OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
• Potassium silicate Substances 0.000 description 1
• NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
• abrasive agent Substances 0.000 description 1
• ammonia Inorganic materials 0.000 description 1
• ammoniac Drugs 0.000 description 1
• aqueous medium Substances 0.000 description 1
• binding agent Substances 0.000 description 1
• caesium Inorganic materials 0.000 description 1
• calcination Methods 0.000 description 1
• calibration curve Methods 0.000 description 1
• cations Chemical class 0.000 description 1
• ceramic Substances 0.000 description 1
• chelating agent Substances 0.000 description 1
• chemical reaction Methods 0.000 description 1
• chemical substances by application Substances 0.000 description 1
• chromium Inorganic materials 0.000 description 1
• colloidal system Substances 0.000 description 1
• combustion reaction Methods 0.000 description 1
• diluting Methods 0.000 description 1
• dispersion Substances 0.000 description 1
• effects Effects 0.000 description 1
• electrolyte Substances 0.000 description 1
• fiber Substances 0.000 description 1
• filtration Methods 0.000 description 1
• gelation Methods 0.000 description 1
• QFWPJPIVLCBXFJ-UHFFFAOYSA-N glymidine Chemical compound N1=CC(OCCOC)=CN=C1NS(=O)(=O)C1=CC=CC=C1 QFWPJPIVLCBXFJ-UHFFFAOYSA-N 0.000 description 1
• graphite Inorganic materials 0.000 description 1
• graphite Substances 0.000 description 1
• ICIWUVCWSCSTAQ-UHFFFAOYSA-N iodic acid Chemical compound OI(=O)=O ICIWUVCWSCSTAQ-UHFFFAOYSA-N 0.000 description 1
• ions Chemical class 0.000 description 1
• iron Inorganic materials 0.000 description 1
• lithium Inorganic materials 0.000 description 1
• PAZHGORSDKKUPI-UHFFFAOYSA-N lithium metasilicate Chemical compound [Li+].[Li+].[O-][Si]([O-])=O PAZHGORSDKKUPI-UHFFFAOYSA-N 0.000 description 1
• lithium silicate Inorganic materials 0.000 description 1
• pH adjustment Methods 0.000 description 1
• polishing Methods 0.000 description 1
• potassium Inorganic materials 0.000 description 1
• potassium fluoride Substances 0.000 description 1
• potassium fluoride Nutrition 0.000 description 1
• potassium silicate Inorganic materials 0.000 description 1
• NNHHDJVEYQHLHG-UHFFFAOYSA-N potassium silicate Chemical compound [K+].[K+].[O-][Si]([O-])=O NNHHDJVEYQHLHG-UHFFFAOYSA-N 0.000 description 1
• powder Substances 0.000 description 1
• purification Methods 0.000 description 1
• quartz Substances 0.000 description 1
• resin Substances 0.000 description 1
• resin Polymers 0.000 description 1
• rubidium Inorganic materials 0.000 description 1
• salts Chemical class 0.000 description 1
• silicon dioxide Nutrition 0.000 description 1
• sodium Inorganic materials 0.000 description 1
• sodium Substances 0.000 description 1
• sodium chloride Substances 0.000 description 1
• stabilizer Substances 0.000 description 1
• stirring Methods 0.000 description 1
• sulfur Inorganic materials 0.000 description 1
• sulfur Substances 0.000 description 1
• AQLJVWUFPCUVLO-UHFFFAOYSA-N urea hydrogen peroxide Chemical compound OO.NC(N)=O AQLJVWUFPCUVLO-UHFFFAOYSA-N 0.000 description 1
• weight loss Effects 0.000 description 1

Classifications

• • C'CHEMISTRY; METALLURGY
  • C01'INORGANIC CHEMISTRY
  • C01B'NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00'Silicon; Compounds thereof
  • C01B33/113'Silicon oxides; Hydrates thereof
  • C01B33/12'Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/14'Colloidal silica, e.g. dispersions, gels, sols
  • C01B33/157'After-treatment of gels
  • C01B33/158'Purification; Drying; Dehydrating
• • C'CHEMISTRY; METALLURGY
  • C09'DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09G'POLISHING COMPOSITIONS; SKI WAXES
  • C09G1/00'Polishing compositions
  • C09G1/02'Polishing compositions containing abrasives or grinding agents
• • C'CHEMISTRY; METALLURGY
  • C01'INORGANIC CHEMISTRY
  • C01B'NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00'Silicon; Compounds thereof
  • C01B33/113'Silicon oxides; Hydrates thereof
  • C01B33/12'Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/14'Colloidal silica, e.g. dispersions, gels, sols
• • C'CHEMISTRY; METALLURGY
  • C01'INORGANIC CHEMISTRY
  • C01B'NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00'Silicon; Compounds thereof
  • C01B33/113'Silicon oxides; Hydrates thereof
  • C01B33/12'Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/14'Colloidal silica, e.g. dispersions, gels, sols
  • C01B33/141'Preparation of hydrosols or aqueous dispersions
  • C01B33/142'Preparation of hydrosols or aqueous dispersions by acidic treatment of silicates
  • C01B33/143'Preparation of hydrosols or aqueous dispersions by acidic treatment of silicates of aqueous solutions of silicates
  • C01B33/'Preparation of hydrosols or aqueous dispersions by acidic treatment of silicates of aqueous solutions of silicates using ion exchangers
• • C'CHEMISTRY; METALLURGY
  • C09'DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K'MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00'Materials not provided for elsewhere
  • C09K3/14'Anti-slip materials; Abrasives
  • C09K3/'Abrasive particles per se

Definitions

• This invention relates to a high purity silica sol and its production method.
• Silica sols which are substantially free from metal impurities (Fe, Cr, Ni, Cu, etc.) have been proposed.
• Such high purity silica sol is suitable for use as an abrasive for electronic materials such as semiconductor silicon wafer because presence of such metal impurities in the silica sol results in the dispersion of the metal impurities into the interior of the wafer during polishing of the wafer and loss of wafer quality, and hence, in the poor performance of the semiconductor device formed by using such wafer.
• Examples of the high purity silica sol that has been proposed include those disclosed in the Patent Literatures 1 to 3.
• Patent Literature 1 discloses a method for producing a colloidal silica comprising the steps of contacting an aqueous solution of an alkali silicate with a cation-exchange resin to prepare an aqueous solution of activated silicic acid, contacting the aqueous solution of activated silicic acid with a chelating agent, allowing development of the colloid particles, and concentrating the silica by ultrafiltration simultaneously with the removal of the chelated metal impurities. Also disclosed is that the colloidal silica produced has a Cu content in relation to silica of up to 100 ppb or a Ni content in relation to silica of up to ppb.
• Patent Literature 2 discloses a production method comprising the steps of preparing a solution of aqueous solution of an alkali metal silicate salt having a strong acid or a salt of a strong acid added thereto, treating the solution with an ion-exchange resin, adding another solution obtained by similar steps to the solution obtained by the ion exchange to prepare a silica sol, treating the resulting silica sol with an ion-exchange resin, and adding ammonia to the resulting silica sol.
• Such production method is capable of producing a stable aqueous colloidal silica having an average particle diameter in the range of 10 to 30 m ' , a SiO 2 concentration of 30 to 50% by weight, and content of polyvalent metal oxides other than the silica in relation to the silica of up to 300 ppm from an alkali metal silicate salt containing a polyvalent metal oxides as impurities.
• Patent Literature 3 discloses a method for producing a high purity colloidal silica comprising the first step of subjecting water glass to cation exchange treatment to prepare an aqueous silica solution, the second step of adding an acid and hydrogen peroxide to the aqueous silica solution to conduct another cation exchange treatment, and the third step of mixing the aqueous silica solution with ammoniac alkali for preparation of the colloidal silica.
• Such production method is capable of producing a high purity colloidal silica and a high purity synthetic quartz powder adapted for various applications such as an abrasive agent for a silicon wafer, binding of a ceramic fiber, an adhesion binder for a phosphor in the CRT production, and a gelation agent of an electrolyte in a battery.
• An object of the present invention is to provide a method for producing a high purity silica sol which has enabled use of water glass for the starting material, and which has enabled decrease in the content of Cu and Ni as the metal impurities.
• Another method of the present invention is to provide a high purity silica sol which has a reduced content of Cu and Ni as the metal impurities.
• the present invention provides the following (1) to (8).
• a method for producing a high purity silica sol comprising the steps of
• the present invention provides a method for producing a high purity silica sol which has enabled use of water glass for the starting material, and which is capable of producing a high purity silica sol having a reduced content of Cu and Ni as the metal impurities.
• the present invention also provides a high purity silica sol having a reduced content of Cu and Ni as the metal impurities.
• the present invention provides a method for producing a high purity silica sol comprising the following steps (1) to (4).
• Such method for producing a high purity silica sol is hereinafter also referred to as 'the production method of the present invention'.
• the production method of the present invention preferably further comprises the step of adding an oxidizing agent to at least one member selected from the group consisting of the aqueous solution of an alkali silicate (a), the purified aqueous solution of the alkali silicate (b), and the purified silicate solution.
• the oxidizing agent is preferably aqueous solution of hydrogen peroxide.
• the step (3) is preferably a step comprising adjusting pH of the purified silicate solution to the range of up to 2, and subjecting the purified silicate solution to an ion exchange process using a chelating ion exchange resin to produce the high purity silicate solution.
• the present invention also provides a high purity silica sol having an average particle size of 2 to 300 nm, and a Cu concentration and a Ni concentration (in relation to the dry silica) of up to 50 ppb.
• silica sol of the present invention Such high purity silica sol is hereinafter also referred to as 'the silica sol of the present invention'.
• the silica sol of the present invention can be obtained by using the production method of the present invention.
• an aqueous solution of an alkali silicate (a) containing an alkali silicate is first prepared.
• the aqueous solution of an alkali silicate (a) is water having an alkali silicate such as sodium silicate, potassium silicate, or lithium silicate dissolved therein, and an alkali means an alkali metal such as Li, Na, K, Rb, Cs, or Fr.
• An exemplary aqueous solution of an alkali silicate (a) is 'water glass' which is sodium silicate dissolved in water.
• Concentration of the SiO 2 in the aqueous solution of an alkali silicate (a) is not particularly limited.
• the SiO 2 concentration is preferably 15 to 30% by weight, more preferably 20 to 28% by weight, and most preferably 22 to 26% by weight.
• the concentration of the SiO 2 in the aqueous solution of an alkali silicate (a) is determined by adding hydrochloric acid and aqueous solution of sodium hydroxide to the aqueous solution of an alkali silicate (a) for neutralization, and adding solution of potassium fluoride and conducting titration of the generated alkaline content with hydrochloric acid. More specifically, SiO 2 concentration is measured by the following reaction:
• the concentration of the alkaline content in the aqueous solution of an alkali silicate (a) is determined, for example, in the case of aqueous solution of sodium silicate, by adding hydrochloric acid to the aqueous solution of sodium silicate for neutralization, and further adding excessive hydrochloric acid, and conducting back titration with sodium hydroxide solution to thereby determine the amount of the Na 2 O.
• the measurement is conducted in similar manner in the case of other alkalis.
• an aqueous solution of an alkali silicate (a) is not particularly limited, and a method known in the art may be used for the production.
• an aqueous solution of an alkali silicate (a) may be obtained by dissolving solid sodium silicate (sodium silicate cullet or the like) in aqueous solution of sodium hydroxide, and more specifically, by dissolving sodium silicate cullet in aqueous solution of sodium hydroxide at a high temperature (for example, a temperature of at least 150° C.) for a sufficient time (for example, at least 30 minutes) to produce an aqueous solution of sodium silicate.
• the aqueous solution of an alkali silicate (a) may preferably have a molar concentration ratio of the SiO 2 to the alkali oxide (SiO 2 /alkali oxide) of 1 to 7, more preferably 2 to 6, still more preferably 2.5 to 5, and most preferably 3.0 to 3.5.
• a molar concentration ratio of the SiO 2 to the alkali oxide (SiO 2 /alkali oxide) of 1 to 7, more preferably 2 to 6, still more preferably 2.5 to 5, and most preferably 3.0 to 3.5.
• Use of an excessively low molar concentration ratio is not preferable because increase in the amount of the alkali metal removed in the cation exchange step is uneconomical.
• an excessively high molar concentration is not preferable, since the aqueous solution of an alkali silicate (a) will be unstable, and use of such unstable solution is not practical.
• an oxidizing agent is preferably added before the ultrafiltration of the aqueous solution of an alkali silicate (a).
• the inventors of the present invention have found that, in such a case, the Cu concentration and the Ni concentration are even more reduced in the high purity silica sol produced by the production method of the present invention.
• Exemplary oxidizing agents include aqueous solution of hydrogen peroxide, peracetic acid, urea peroxide, nitric acid, iodic acid (HIO 3 ), and ozone, and use of aqueous solution of hydrogen peroxide is preferable.
• the same oxidizing agents may be used in the addition of an oxidizing agent to the purified aqueous solution of the alkali silicate (b) or the purified silicate solution as described below, and use of an aqueous solution of hydrogen peroxide is also preferable.
• Amount of the oxidizing agent added to the aqueous solution of an alkali silicate (a) is preferably 0.001 to 20% by weight, and more preferably 0.01 to 10% by weight in relation to the dry silica
• the 'content in relation to the dry silica' means weight ratio of the weight of the component of interest (in this case, the oxidizing agent) to the weight of the SiO 2 in the silica-containing component (in this case, the aqueous solution of an alkali silicate (a)).
• the 'content in relation to the dry silica' is hereinafter used in such meaning.
• step (1) ultrafiltration of such aqueous solution of an alkali silicate (a) is conducted.
• the ultrafiltration may be accomplished by using an ultrafiltration membrane which has been known in the art.
• the molecular weight cut-off of the ultrafiltration membrane is preferably 100 to , more preferably to , and most preferably to .
• a purified aqueous solution of an alkali silicate (b) can be obtained by conducting such ultrafiltration.
• the resulting purified aqueous solution of the alkali silicate (b) has a SiO 2 concentration of 15 to 30% by weight, more preferably 20 to 28% by weight, and still more preferably 20 to 26% by weight.
• the SiO 2 concentration in the purified aqueous solution of the alkali silicate (b) may be determined as in the case of the SiO 2 concentration in the aqueous solution of an alkali silicate (a) as described above.
• An oxidizing agent is preferably added to the purified aqueous solution of the alkali silicate (b).
• the inventors of the present invention have found that such addition of the oxidizing agent results in the further reduction of the Cu concentration and Ni concentration in the high purity silica sol produced by the production method of the present invention.
• Amount of the oxidizing agent added to the purified aqueous solution of the alkali silicate (b) is preferably 0.001 to 20% by weight, and more preferably 0.01 to 10% by weight in relation to the dry silica content.
• step (2) of the production method of the present invention is described.
• the purified aqueous solution of the alkali silicate (b) is subjected to an ion exchange process to remove at least a part of the cationic component in the purified aqueous solution of the alkali silicate (b).
• the ion exchange process employed is not particularly limited, and the ion exchange process may be the one known in the art such as the one using a cation exchange resin.
• the product of the step (2) as described above is a purified silicate solution having at least a part of the cationic components (and typically, substantially all of the cationic components) removed therefrom.
• the SiO 2 concentration in the purified silicate solution is preferably 1 to 15% by weight, more preferably 1 to 10% by weight, and still more preferably 2 to 8% by weight.
• the SiO 2 concentration of the purified silicate solution is the value determined by calcining the purified silicate solution at ° C. for 1 hour and weighing the remaining content (solid content) assuming that the entire solid content is the SiO 2 .
• the purified silicate solution is subjected to an ion exchange process using a chelating ion exchange resin.
• the inventors of the present invention made an intensive study, and found that a silica sol having an extremely low Cu concentration and Ni concentration can be obtained by conducting the ultrafiltration of step (1) and the ion exchange process using a chelating ion exchange resin of step (3).
• the purified silicate solution is preferably passed through the chelating ion exchange resin at a space velocity of about 0.5 to 10 h ' 1 , more preferably at about 1.5 to 5.0 h ' 1 , and more preferably at about 2 to 4 h ' 1 .
• the ion exchange process using the chelating ion exchange resin is preferably conducted after adding the oxidizing agent to the purified silicate solution.
• the inventors of the present invention have found that, in such a case, the Cu concentration and the Ni concentration are further reduced in the high purity silica sol produced by the production method of the present invention.
• Amount of the oxidizing agent added to the purified silicate solution is preferably 0.001 to 20% by weight, and more preferably 0.01 to 10% by weight in relation to the dry silica.
• the ion exchange using the chelating ion exchange resin is preferably conducted after adjusting the pH of the purified silicate solution to the range of up to 2 (and preferably 1 to 2).
• the inventors of the present invention have found that, in such as case, the Cu concentration and the Ni concentration are further reduced in the high purity silica sol produced by the production method of the present invention.
• the ion exchange using the chelating ion exchange resin is still more preferably conducted after adding the oxidizing agent to the purified silicate solution and then adjusting the pH of the purified silicate solution to the range of up to 2.
• the inventors of the present invention have found that, in such as case, the Cu concentration and the Ni concentration are further reduced in the high purity silica sol produced by the production method of the present invention.
• Amount of the oxidizing agent added is preferably in the range of 0.01 to 20% by weight, and more preferably 0.01 to 10% by weight in relation to the dry silica weight.
• the means employed for adjusting the pH of the purified silicate solution to the range of up to 2 (and preferably 1 to 2) is not particularly limited, and the pH may be adjusted by adding an acid known in the art such as hydrochloric acid.
• a high purity silicate solution is produced by the step (3) as described above.
• step (4) of the production method of the present invention is described.
• a part of the high purity silicate solution (seed solution) is adjusted to alkaline pH, and then, this solution is mixed with another part of the high purity silicate solution (feed solution).
• an alkali may be added to this seed solution to adjust the solution to an alkaline pH. More specifically, the seed solution is adjusted to a pH in the range of 10 to 13 (and preferably 11 to 12), and then mixed with the feed solution by adding the feed solution to the seed solution maintained to the temperature in the range of 20 to 98° C. (more preferably 50 to 95° C., and still more preferably 80 to 90° C.).
• the feed solution maintained to a temperature in the range of 1 to 30° C., and more preferably 1 to 20° C. is added to the seed solution.
• the feed solution is gradually added to the seed solution which had been preferably adjusted to the pH and temperature as described above so that the silica fine particles develop in the seed solution to thereby produce the silica sol.
• the solution After adding the feed solution to the seed solution, the solution is preferably maintained at a high temperature (about 80 to 90° C.) for several hours to thereby promote smooth development of the silica fine particles.
• the step (4) as described above is capable of producing a high purity silica sol having both the Cu concentration (weight concentration) and the Ni concentration (weight concentration) which are up to 50 ppb in relation to the dry silica.
• the Cu concentration and the Ni concentration in relation to the dry silica are preferably low as in the case of the silica sol of the present invention as described below. Also, the average particle diameter is preferably the same as that of the silica sol of the present invention as described below.
• the SiO 2 concentration (% by weight) of the high purity silica sol is measured by adding sulfuric acid to the high purity silica sol, evaporating the solution to dryness, and weighing the remaining solid after strong heating. Sulfuric acid and hydrofluoric acid are then added, and after evaporating the solution to dryness, remaining solid is weighed. The calculation is conducted by assuming that the weight loss corresponds the weight of the silica (SiO 2 ).
• the Cu concentration and the Ni concentration in the high purity silica sol may be measured by adding nitric acid and hydrofluoric acid to the silica sol, heating the solution, evaporating the solution to dryness, dissolving the solid content by the addition of nitric acid and water and heating, and diluting the solution by adding water, and evaluating the concentration with a graphite atomic absorption spectrometer.
• the Cu concentration and the Ni concentration in relation to the dry silica are determined as a ratio of Ni concentration and the Cu concentration in relation to the dry silica.
• the silica fine particles contained in the silica sol of the present invention has an average particle diameter of 2 to 300 nm, preferably 5 to 100 nm, and more preferably 10 to 80 nm.
• the average particle diameter of the silica fine particles is the one obtained by conducting the measurement according to Sears method.
• Sears method is a method conducted by the following procedures 1) to 6).
• pH electrode is set, and 0.1 mol/L aqueous solution of sodium hydroxide is added dropwise with stirring to adjust the pH to 4.0.
• Volume V (ml) of the 0.1 mol/L aqueous solution of sodium hydroxide consumed from pH 4.0 to 9.0 per 1.5 g of SiO 2 is calculated by the following equation (3).
• Specific surface area is calculated from the following equation (4).
• Average particle diameter D 1 (nm) is calculated by the following equation (5).
• V ( A ' f ' 100 ' 1.5)/( W ' C ) (3)
• the silica sol of the present invention typically has a Cu concentration (weight concentration) (in relation to the dry silica) of up to 50 ppb, preferably up to 40 ppb, more preferably up to 30 ppb, still more preferably up to 20 ppb, and most preferably up to 10 ppb.
• the silica sol of the present invention typically has a Ni concentration (weight concentration) (in relation to the dry silica) of up to 50 ppb, preferably up to 40 ppb, more preferably up to 30 ppb, still more preferably up to 20 ppb, and most preferably up to 10 ppb.
• the silica sol of the present invention does not substantially contain carbon. More specifically, carbon content of the silica sol of the present invention is preferably up to 0.5% by weight, more preferably up to 0.3% by weight, and still more preferably up to 0.1% by weight.
• the carbon content of the silica sol of the present invention is determined by burning the silica sol in a high-frequency furnace of carbon and sulfur analyzer, and analyzing CO and CO 2 in the combustion product by infrared absorption.
• the SiO 2 concentration, Cu concentration, and Ni concentration of the silica sol of the present invention are the values measured by the same procedures as those used in measuring the SiO 2 concentration, Cu concentration, and Ni concentration of the high purity silica sol obtained by the production method of the present invention
• the silica sol of the present invention is a high purity silica sol containing silica fine particles having an average particle diameter as described above, and having a Cu concentration and a Ni concentration as described above.
• the dispersion medium used for the silica sol of the present invention is not particularly limited.
• the dispersion medium is preferably an aqueous medium, and more preferably water.
• the silica sol of the present invention is not particularly limited for its concentration of the solid content.
• the concentration is preferably 5 to 60% by weight, more preferably 10 to 50% by weight, and still more preferably 20 to 40% by weight.
• the pH of the silica sol of the present invention is not particularly limited.
• the pH is preferably 8 to 12, and more preferably 9 to 11.
• the silica sol of the present invention may contain a stabilizer known in the art such as HCl and NaOH.
• the method used for producing the silica sol of the present invention is not particularly limited while it may be produced by the production method of the present invention.
• the silica sol of the present invention is well adapted for use as an abrasive.
• An abrasive composition containing the silica sol of the present invention is suitable for use as an abrasive of electronic materials such as semiconductor silicon wafer since the Ni and the Cu concentrations are lower than those of conventional abrasive.
• such abrasive composition may further comprise at least one member selected from the group consisting of an abrasive aid, surfactant, heterocyclic compound, pH adjusting agent, and buffering agent.
• aqueous solution of sodium silicate having a SiO 2 concentration of 24.06% by weight, a Na 2 O concentration of 7.97% by weight, a Cu concentration (in relation to the dry silica) of 460 ppb, and Ni concentration (in relation to the dry silica) of 640 ppb (also referred to as 'water glass A') was prepared.
• the SiO 2 concentration, Na 2 O concentration, Cu concentration, and Ni concentration were measured by the procedure as described above.
• This aqueous solution of sodium silicate was filtered by using an ultrafiltration membrane (SEP- manufactured by Asahi Kasei Chemicals Corp. having a molecular weight cut-off of ), and purified aqueous solution of an alkali silicate (b) was obtained as the filtrate.
• SEP- manufactured by Asahi Kasei Chemicals Corp. having a molecular weight cut-off of
• purified aqueous solution of an alkali silicate (b) was obtained as the filtrate.
• the SiO 2 concentration of the purified aqueous solution of the alkali silicate (b) was measured by the procedure as described above.
• the SiO 2 concentration was 23.2% by weight.
• the SiO 2 concentration of the resulting purified silicate solution was measured by the procedure as described above.
• the SiO 2 concentration was 4.7% by weight.
• aqueous solution of hydrogen peroxide 0.56% by weight in relation to the dry silica
• hydrochloric acid 1% by weight hydrochloric acid was added to adjust the pH to 2.
• the solution was passed through a chelating ion exchange resin (CR-11 manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h ' 1 to prepare a high purity silicate solution at a pH of 2.0.
• the SiO 2 concentration of the resulting high purity silicate solution was 4.5% by weight.
• a part of the resulting high purity silicate solution (414.4 g) was separated for use as the seed solution, and another part of the high purity silicate solution (10.18 kg) was separated for use as the feed solution.
• This silica sol was concentrated to 12% by weight by using an ultrafiltration membrane (SIP-) manufactured by Asahi Kasei Chemicals Corp., and further concentrated to 30% by weight by using a rotary evaporator to thereby produce a high purity silica sol.
• SIP- ultrafiltration membrane manufactured by Asahi Kasei Chemicals Corp.
• the average particle diameter of the resulting high purity silica sol measured by the Sears method was 17.8 nm.
• the Cu concentration (in relation to the dry silica) and the Ni concentration (in relation to the dry silica) of the resulting silica sol were measured by the procedure as described above, and the silica sol had a Cu concentration (in relation to the dry silica) of less than 1 ppb and an Ni concentration (in relation to the dry silica) of 7 ppb.
• Example 1 the aqueous solution of sodium silicate was filtered through an ultrafiltration membrane (SEP- having a molecular weight cut-off of ) to obtain the purified aqueous solution of an alkali silicate (b) as the filtrate.
• Example 2 the same aqueous solution of sodium silicate was filtered through an ultrafiltration membrane (SIP- manufactured by Asahi Kasei Chemicals Corp. having a molecular weight cut-off of ) to obtain the purified aqueous solution of an alkali silicate (b) as the filtrate.
• SIP- manufactured by Asahi Kasei Chemicals Corp. having a molecular weight cut-off of
• Example 2 aqueous solution of hydrogen peroxide was added to the purified silicate solution, and hydrochloric acid was added to the solution to adjust the pH to 2 before the passing of the solution through the chelating ion exchange resin.
• Example 2 the addition of the aqueous solution of hydrogen peroxide, and also, the pH adjustment with the hydrochloric acid were not carried out, and the purified silicate solution was passed through the same chelating ion exchange resin at the same space velocity to obtain a high purity silicate solution at a pH of 2.7.
• the SiO 2 concentration of the resulting high purity silicate solution measured by repeating the procedure as described above was 4.5% by weight.
• Example 1 The procedure of Example 1 was repeated except for those as described above, and the measurement was conducted by as in the case of Example 1.
• the resulting silica sol had an average particle diameter of 17.8 nm, a Cu concentration (in relation to the dry silica) of 30 ppb, and a Ni concentration (in relation to the dry silica) of 20 ppb.
• Example 1 The procedure of Example 1 was repeated except that an aqueous solution of sodium silicate (hereinafter also referred to as 'water glass B') having a SiO 2 concentration of 24.64% by weight, a Na 2 O concentration of 8.08% by weight, a Cu concentration (in relation to the dry silica) of 690 ppb, and a Ni concentration (in relation to the dry silica) of 240 ppb was used instead of the water glass A used in Example 1.
• water glass B aqueous solution of sodium silicate having a SiO 2 concentration of 24.64% by weight, a Na 2 O concentration of 8.08% by weight, a Cu concentration (in relation to the dry silica) of 690 ppb, and a Ni concentration (in relation to the dry silica) of 240 ppb was used instead of the water glass A used in Example 1.
• Example 1 The procedure of Example 1 was repeated except for those as described above, and the measurement was conducted by as in the case of Example 1.
• the resulting silica sol had an average particle diameter of 17.6 nm, a Cu concentration (in relation to the dry silica) of 24 ppb, and a Ni concentration (in relation to the dry silica) of 9 ppb.
• Example 1 The procedure of Example 1 was repeated except that an aqueous solution of sodium silicate (hereinafter also referred to as 'water glass C') having a SiO 2 concentration of 24.43% by weight, a Na 2 O concentration of 7.40% by weight, a Cu concentration (in relation to the dry silica) of 450 ppb, and a Ni concentration (in relation to the dry silica) of 160 ppb was used instead of the water glass A used in Example 1.
• water glass C an aqueous solution of sodium silicate having a SiO 2 concentration of 24.43% by weight, a Na 2 O concentration of 7.40% by weight, a Cu concentration (in relation to the dry silica) of 450 ppb, and a Ni concentration (in relation to the dry silica) of 160 ppb was used instead of the water glass A used in Example 1.
• Example 1 The procedure of Example 1 was repeated except for those as described above, and the measurement was conducted by as in the case of Example 1.
• the resulting silica sol had an average particle diameter of 17.6 nm, a Cu concentration (in relation to the dry silica) of 23 ppb, and a Ni concentration (in relation to the dry silica) of less than 1 ppb.
• the resulting aqueous solution of sodium silicate having the aqueous solution of hydrogen peroxide added was filtered through an ultrafiltration membrane (SIP- having a molecular weight cut-off of ) to obtain purified aqueous solution of the alkali silicate (b) as the filtrate.
• SIP- having a molecular weight cut-off of
• the purified silicate solution was passed through a chelating ion exchange resin (CR-11 manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h ' 1 to obtain a high purity silicate solution at a pH of 2.7.
• the SiO 2 concentration of the resulting high purity silicate solution measured by the procedure as described above was 4.5% by weight.
• Example 2 The following process was conducted by repeating the procedure of Example 1. More specifically, 191.1 g of 5% by weight potassium hydroxide aqueous solution was added to the pure water, and then, the seed solution was added to the solution, and the solution was heated. When the solution reached 83° C., the solution was maintained at this temperature for 30 minutes, and then, the feed solution was added at a constant rate for 11 hours with the temperature maintained. When all of the feed solution was added to the seed solution, the solution was heated for 1 hour to maintain the solution at 83° C. to thereby produce a high purity silica sol.
• the resulting silica sol had an average particle diameter of 17.6 nm, a Cu concentration (in relation to the dry silica) of 5 ppb, and a Ni concentration (in relation to the dry silica) of less than 1 ppb.
• the SiO 2 concentration of the resulting silicate solution was measured by the procedure as described above. The SiO 2 concentration was 4.7% by weight. This silicate solution was diluted with pure water to 4.5% by weight.
• silicate solution 414.4 g was separated for use as the seed solution, and another part of the silicate solution (10.63 kg) was separated for use as the feed solution.
• Example 2 The following process was conducted by repeating the procedure of Example 1. More specifically, 191.1 g of 5% by weight potassium hydroxide aqueous solution was added to pure water, and then, the seed solution was added to the solution, and the solution was heated. The solution was maintained at this temperature for 30 minutes, and then, the feed solution was added at a constant rate for 11 hours with the temperature maintained. When all of the feed solution was added to the seed solution, the solution was heated for 1 hour to maintain the solution at 83° C. to thereby produce a silica sol.
• the resulting silica sol had an average particle diameter of 17.6 nm, a Cu concentration (in relation to the dry silica) of 235 ppb, and a Ni concentration (in relation to the dry silica) of 610 ppb.
• silicate solution was passed through a chelating ion exchange resin (CR-11 manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h ' 1 to obtain an ion-exchanged silicate solution which had passed through the chelating ion exchange resin at a pH of 2.7.
• the SiO 2 concentration was 4.5% by weight.
• Example 2 The following process was conducted by repeating the procedure of Example 1. More specifically, 191.1 g of 5% by weight potassium hydroxide aqueous solution was added to pure water, and then, the seed solution was added to the solution, and the solution was heated. The solution was maintained at this temperature for 30 minutes, and then, the feed solution was added at a constant rate for 11 hours with the temperature maintained. When all of the feed solution was added to the seed solution, the solution was heated for 1 hour to maintain the solution at 83° C. to thereby produce a silica sol.
• the resulting silica sol had an average particle diameter of 17.7 nm, a Cu concentration (in relation to the dry silica) of 80 ppb, and a Ni concentration (in relation to the dry silica) of 150 ppb.
• Comparative Example 2 The procedure of Comparative Example 2 was repeated except that water glass B was used instead of water glass A. The measurement was also conducted by repeating the procedure of Comparative Example 2.
• the resulting silica sol had an average particle diameter of 17.8 nm, a Cu concentration (in relation to the dry silica) of 105 ppb, and a Ni concentration (in relation to the dry silica) of 187 ppb.
• Comparative Example 2 The procedure of Comparative Example 2 was repeated except that water glass C was used instead of water glass A. The measurement was also conducted by repeating the procedure of Comparative Example 2.
• the resulting silica sol had an average particle diameter of 17.6 nm, a Cu concentration (in relation to the dry silica) of 113 ppb, and a Ni concentration (in relation to the dry silica) of 97 ppb.
• Example 1 A Molecular Yes Yes Yes weight,
• Example 2 A Molecular No No Yes weight,
• Example 3 B Molecular No No Yes weight,
• Example 4 C Molecular No No Yes weight,
• Example 5 B B Molecular Yes No Yes weight, Comparative A No No No No Example 1 Comparative A No No No Yes Example 2 Comparative B No No No Yes Example 3 Comparative C NO NO No Yes Example 4
• Example 1 to 5 the aqueous solution of sodium silicate was filtered through an ultrafiltration membrane, and the purified silicate solution was further passed through the chelating ion exchange resin.
• both the Cu concentration and the Ni concentration in relation to the dry silica were up to 50 ppb. More specifically, the Cu concentration in relation to the dry silica was up to 30 ppb, and simultaneously, the Ni concentration in relation to the dry silica was up to 20 ppb.
• Example 1 the aqueous solution of sodium silicate was filtered through an ultrafiltration membrane, and after adding aqueous solution of hydrogen peroxide to the purified silicate solution and further adding hydrochloric acid for adjustment of the pH to 2, the solution was passed through the chelating ion exchange resin.
• the Cu concentration and the Ni concentration in relation to the dry silica were even lower in the high purity silica sol obtained in such Example 1, and both the Cu concentration and the Ni concentration were up to 10 ppb.
• Example 5 aqueous solution of hydrogen peroxide was added to the aqueous solution of sodium silicate, and the solution was filtered through an ultrafiltration membrane, and then, passed through the chelating ion exchange resin.
• the Cu concentration and the Ni concentration in relation to the dry silica were even lower in the high purity silica sol obtained in such Example 5, and both the Cu concentration and the Ni concentration were up to 5 ppb.
• the silica sol obtained in Comparative Examples 1 to 4 exhibited high Cu and Ni concentration, that is, the Cu concentration in relation to the dry silica of 80 to 235 ppb, and the Ni concentration in relation to the dry silica of 97 to 610 ppb.

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Abstract

A method for producing a high purity silica sol is provided. This method has enabled use of water glass for the starting material, and the resulting silica sol has a reduced metal impurity Cu and Ni content compared to conventional methods. The method comprises (1) ultrafiltration of an aqueous solution of an alkali silicate; (2) ion exchange process for removal of at least a part of cationic components in the purified aqueous solution of an alkali silicate; (3) another ion exchange process using a chelating ion exchange resin to obtain high purity silicate solution; and (4) adjustment of a part of the high purity silicate solution (seed solution) to alkaline pH and mixing of this solution with another part of the solution (feed solution) to produce a high purity silica sol having a Cu concentration and a Ni concentration (in relation to the dry silica) of up to 50 ppb.

Description

TECHNICAL FIELD
• This invention relates to a high purity silica sol and its production method.
BACKGROUND ART
• Silica sols which are substantially free from metal impurities (Fe, Cr, Ni, Cu, etc.) have been proposed. Such high purity silica sol is suitable for use as an abrasive for electronic materials such as semiconductor silicon wafer because presence of such metal impurities in the silica sol results in the dispersion of the metal impurities into the interior of the wafer during polishing of the wafer and loss of wafer quality, and hence, in the poor performance of the semiconductor device formed by using such wafer.
• Examples of the high purity silica sol that has been proposed include those disclosed in the Patent Literatures 1 to 3.
• Patent Literature 1 discloses a method for producing a colloidal silica comprising the steps of contacting an aqueous solution of an alkali silicate with a cation-exchange resin to prepare an aqueous solution of activated silicic acid, contacting the aqueous solution of activated silicic acid with a chelating agent, allowing development of the colloid particles, and concentrating the silica by ultrafiltration simultaneously with the removal of the chelated metal impurities. Also disclosed is that the colloidal silica produced has a Cu content in relation to silica of up to 100 ppb or a Ni content in relation to silica of up to ppb.
• Patent Literature 2 discloses a production method comprising the steps of preparing a solution of aqueous solution of an alkali metal silicate salt having a strong acid or a salt of a strong acid added thereto, treating the solution with an ion-exchange resin, adding another solution obtained by similar steps to the solution obtained by the ion exchange to prepare a silica sol, treating the resulting silica sol with an ion-exchange resin, and adding ammonia to the resulting silica sol. Also disclosed is that such production method is capable of producing a stable aqueous colloidal silica having an average particle diameter in the range of 10 to 30 mμ, a SiO2 concentration of 30 to 50% by weight, and content of polyvalent metal oxides other than the silica in relation to the silica of up to 300 ppm from an alkali metal silicate salt containing a polyvalent metal oxides as impurities.
• Patent Literature 3 discloses a method for producing a high purity colloidal silica comprising the first step of subjecting water glass to cation exchange treatment to prepare an aqueous silica solution, the second step of adding an acid and hydrogen peroxide to the aqueous silica solution to conduct another cation exchange treatment, and the third step of mixing the aqueous silica solution with ammoniac alkali for preparation of the colloidal silica. Also disclosed is that such production method is capable of producing a high purity colloidal silica and a high purity synthetic quartz powder adapted for various applications such as an abrasive agent for a silicon wafer, binding of a ceramic fiber, an adhesion binder for a phosphor in the CRT production, and a gelation agent of an electrolyte in a battery.
CITATION LIST Patent Literature
• [Patent Literature 1] Japanese Patent Application Laid-Open No. -
• [Patent Literature 2] Japanese Patent Application Laid-Open No. 6-
• [Patent Literature 3] Japanese Patent Application Laid-Open No. -
SUMMARY OF INVENTION Technical Problem
• However, there is a strong demand for the development of a high purity silica sol having a reduced content of the metal impurities.
• There is also a demand for use of water glass for the production of a high purity silica sol. Production of a high purity silica sol using water glass has been difficult.
• An object of the present invention is to provide a method for producing a high purity silica sol which has enabled use of water glass for the starting material, and which has enabled decrease in the content of Cu and Ni as the metal impurities. Another method of the present invention is to provide a high purity silica sol which has a reduced content of Cu and Ni as the metal impurities.
Solution to Problem
• In order to solve the problems as described above, the inventors of the present invention conducted an intensive study and completed the present invention.
• The present invention provides the following (1) to (8). (1) A method for producing a high purity silica sol comprising the steps of
• • (1) conducting ultrafiltration of an aqueous solution of an alkali silicate (a) to obtain purified aqueous solution of the alkali silicate (b);
  • (2) subjecting the purified aqueous solution of the alkali silicate (b) to an ion exchange process to remove at least a part of cationic components in the purified aqueous solution of the alkali silicate (b) to obtain purified silicate solution;
  • (3) subjecting the purified silicate solution to an ion exchange process using a chelating ion exchange resin to obtain high purity silicate solution; and
  • (4) adjusting a part of the high purity silicate solution (seed solution) to alkaline pH and mixing this solution with another part of the high purity silicate solution (feed solution) to produce the high purity silica sol having a Cu concentration and a Ni concentration (in relation to the dry silica) of up to 50 ppb.
    (2) A method for producing a high purity silica sol according to the above (1) further comprising the step of adding an oxidizing agent to at least one member selected from the group consisting of the aqueous solution of an alkali silicate (a), the purified aqueous solution of the alkali silicate (b), and the purified silicate solution.
    (3) A method for producing a high purity silica sol according to the above (2) wherein the oxidizing agent is aqueous solution of hydrogen peroxide.
    (4) A method for producing a high purity silica sol according to any one of the above (1) to (3) wherein the step (3) is preferably a step comprising adjusting pH of the purified silicate solution to the range of up to 2, and subjecting the purified silicate solution to an ion exchange process using a chelating ion exchange resin to produce the high purity silicate solution.
    (5) A high purity silica sol having an average particle size of 2 to 300 nm, and a Cu concentration and a Ni concentration (in relation to the dry silica) of up to 50 ppb.
    (6) A high purity silica sol of the above (5) produced by the production method of any one of the above (1) to (4).
    (7) An abrasive composition containing the high purity silica sol of the above (5) or (6).
    (8) An abrasive composition according to the above (7) further comprising at least one member selected from the group consisting of abrasive aid, surfactant, heterocyclic compound, pH adjusting agent, and buffering agent.
Advantageous Effects of Invention
• The present invention provides a method for producing a high purity silica sol which has enabled use of water glass for the starting material, and which is capable of producing a high purity silica sol having a reduced content of Cu and Ni as the metal impurities. The present invention also provides a high purity silica sol having a reduced content of Cu and Ni as the metal impurities.
DESCRIPTION OF EMBODIMENTS
• Next, the present invention is described in detail.
• The present invention provides a method for producing a high purity silica sol comprising the following steps (1) to (4).
• • (1) the step of conducting ultrafiltration of an aqueous solution of an alkali silicate (a) to obtain purified aqueous solution of the alkali silicate (b),
  • (2) the step of subjecting the purified aqueous solution of the alkali silicate (b) to an ion exchange process to remove at least a part of cationic components in the purified aqueous solution of the alkali silicate (b) to obtain purified silicate solution,
  • (3) the step of subjecting the purified silicate solution to an ion exchange process using a chelating ion exchange resin to obtain high purity silicate solution, and
  • (4) the step of adjusting a part of the high purity silicate solution (seed solution) to alkaline pH and mixing this solution with another part of the high purity silicate solution (feed solution) to produce the high purity silica sol having a Cu concentration and a Ni concentration (in relation to the dry silica) of up to 50 ppb.
• Such method for producing a high purity silica sol is hereinafter also referred to as 'the production method of the present invention'.
• The production method of the present invention preferably further comprises the step of adding an oxidizing agent to at least one member selected from the group consisting of the aqueous solution of an alkali silicate (a), the purified aqueous solution of the alkali silicate (b), and the purified silicate solution.
• In the production method of the present invention, the oxidizing agent is preferably aqueous solution of hydrogen peroxide.
• In the production method of the present invention, the step (3) is preferably a step comprising adjusting pH of the purified silicate solution to the range of up to 2, and subjecting the purified silicate solution to an ion exchange process using a chelating ion exchange resin to produce the high purity silicate solution.
• The present invention also provides a high purity silica sol having an average particle size of 2 to 300 nm, and a Cu concentration and a Ni concentration (in relation to the dry silica) of up to 50 ppb.
• Such high purity silica sol is hereinafter also referred to as 'the silica sol of the present invention'.
• The silica sol of the present invention can be obtained by using the production method of the present invention.
• First, the production method of the present invention is described.
<Step (1)>
• The step (1) of the production method of the present invention is described.
• In the step (1), an aqueous solution of an alkali silicate (a) containing an alkali silicate is first prepared.
• The aqueous solution of an alkali silicate (a) is water having an alkali silicate such as sodium silicate, potassium silicate, or lithium silicate dissolved therein, and an alkali means an alkali metal such as Li, Na, K, Rb, Cs, or Fr.
• An exemplary aqueous solution of an alkali silicate (a) is 'water glass' which is sodium silicate dissolved in water.
• Concentration of the SiO2 in the aqueous solution of an alkali silicate (a) is not particularly limited. The SiO2 concentration, however, is preferably 15 to 30% by weight, more preferably 20 to 28% by weight, and most preferably 22 to 26% by weight.
• The concentration of the SiO2 in the aqueous solution of an alkali silicate (a) is determined by adding hydrochloric acid and aqueous solution of sodium hydroxide to the aqueous solution of an alkali silicate (a) for neutralization, and adding solution of potassium fluoride and conducting titration of the generated alkaline content with hydrochloric acid. More specifically, SiO2 concentration is measured by the following reaction:
• 
  H2SiO3+6KF+H2O'K2SiF6+4KOH
• The concentration of the alkaline content in the aqueous solution of an alkali silicate (a) is determined, for example, in the case of aqueous solution of sodium silicate, by adding hydrochloric acid to the aqueous solution of sodium silicate for neutralization, and further adding excessive hydrochloric acid, and conducting back titration with sodium hydroxide solution to thereby determine the amount of the Na2O. The measurement is conducted in similar manner in the case of other alkalis.
• The method used for producing the aqueous solution of an alkali silicate (a) is not particularly limited, and a method known in the art may be used for the production. For example, an aqueous solution of an alkali silicate (a) may be obtained by dissolving solid sodium silicate (sodium silicate cullet or the like) in aqueous solution of sodium hydroxide, and more specifically, by dissolving sodium silicate cullet in aqueous solution of sodium hydroxide at a high temperature (for example, a temperature of at least 150° C.) for a sufficient time (for example, at least 30 minutes) to produce an aqueous solution of sodium silicate.
• The aqueous solution of an alkali silicate (a) may preferably have a molar concentration ratio of the SiO2 to the alkali oxide (SiO2/alkali oxide) of 1 to 7, more preferably 2 to 6, still more preferably 2.5 to 5, and most preferably 3.0 to 3.5. Use of an excessively low molar concentration ratio is not preferable because increase in the amount of the alkali metal removed in the cation exchange step is uneconomical. Also, an excessively high molar concentration is not preferable, since the aqueous solution of an alkali silicate (a) will be unstable, and use of such unstable solution is not practical.
• As described below, an oxidizing agent is preferably added before the ultrafiltration of the aqueous solution of an alkali silicate (a). The inventors of the present invention have found that, in such a case, the Cu concentration and the Ni concentration are even more reduced in the high purity silica sol produced by the production method of the present invention.
• Exemplary oxidizing agents include aqueous solution of hydrogen peroxide, peracetic acid, urea peroxide, nitric acid, iodic acid (HIO3), and ozone, and use of aqueous solution of hydrogen peroxide is preferable.
• The same oxidizing agents may be used in the addition of an oxidizing agent to the purified aqueous solution of the alkali silicate (b) or the purified silicate solution as described below, and use of an aqueous solution of hydrogen peroxide is also preferable.
• Amount of the oxidizing agent added to the aqueous solution of an alkali silicate (a) is preferably 0.001 to 20% by weight, and more preferably 0.01 to 10% by weight in relation to the dry silica
• The 'content in relation to the dry silica' means weight ratio of the weight of the component of interest (in this case, the oxidizing agent) to the weight of the SiO2 in the silica-containing component (in this case, the aqueous solution of an alkali silicate (a)). In the present invention, the 'content in relation to the dry silica' is hereinafter used in such meaning.
• In the step (1), ultrafiltration of such aqueous solution of an alkali silicate (a) is conducted.
• The ultrafiltration may be accomplished by using an ultrafiltration membrane which has been known in the art. The molecular weight cut-off of the ultrafiltration membrane is preferably 100 to , more preferably to , and most preferably to .
• A purified aqueous solution of an alkali silicate (b) can be obtained by conducting such ultrafiltration.
• Preferably, the resulting purified aqueous solution of the alkali silicate (b) has a SiO2 concentration of 15 to 30% by weight, more preferably 20 to 28% by weight, and still more preferably 20 to 26% by weight.
• The SiO2 concentration in the purified aqueous solution of the alkali silicate (b) may be determined as in the case of the SiO2 concentration in the aqueous solution of an alkali silicate (a) as described above.
• An oxidizing agent is preferably added to the purified aqueous solution of the alkali silicate (b). The inventors of the present invention have found that such addition of the oxidizing agent results in the further reduction of the Cu concentration and Ni concentration in the high purity silica sol produced by the production method of the present invention.
• Amount of the oxidizing agent added to the purified aqueous solution of the alkali silicate (b) is preferably 0.001 to 20% by weight, and more preferably 0.01 to 10% by weight in relation to the dry silica content.
<Step (2)>
• Next, the step (2) of the production method of the present invention is described.
• In the step (2), the purified aqueous solution of the alkali silicate (b) is subjected to an ion exchange process to remove at least a part of the cationic component in the purified aqueous solution of the alkali silicate (b).
• The ion exchange process employed is not particularly limited, and the ion exchange process may be the one known in the art such as the one using a cation exchange resin.
• The product of the step (2) as described above is a purified silicate solution having at least a part of the cationic components (and typically, substantially all of the cationic components) removed therefrom.
• The SiO2 concentration in the purified silicate solution is preferably 1 to 15% by weight, more preferably 1 to 10% by weight, and still more preferably 2 to 8% by weight.
• The SiO2 concentration of the purified silicate solution is the value determined by calcining the purified silicate solution at ° C. for 1 hour and weighing the remaining content (solid content) assuming that the entire solid content is the SiO2.
<Step (3)>
• Next, the step (3) of the production method of the present invention is described.
• In the step (3), the purified silicate solution is subjected to an ion exchange process using a chelating ion exchange resin.
• The inventors of the present invention made an intensive study, and found that a silica sol having an extremely low Cu concentration and Ni concentration can be obtained by conducting the ultrafiltration of step (1) and the ion exchange process using a chelating ion exchange resin of step (3).
• The purified silicate solution is preferably passed through the chelating ion exchange resin at a space velocity of about 0.5 to 10 h'1, more preferably at about 1.5 to 5.0 h'1, and more preferably at about 2 to 4 h'1.
• In the step (3), the ion exchange process using the chelating ion exchange resin is preferably conducted after adding the oxidizing agent to the purified silicate solution. The inventors of the present invention have found that, in such a case, the Cu concentration and the Ni concentration are further reduced in the high purity silica sol produced by the production method of the present invention.
• Amount of the oxidizing agent added to the purified silicate solution is preferably 0.001 to 20% by weight, and more preferably 0.01 to 10% by weight in relation to the dry silica.
• In the step (3), the ion exchange using the chelating ion exchange resin is preferably conducted after adjusting the pH of the purified silicate solution to the range of up to 2 (and preferably 1 to 2). The inventors of the present invention have found that, in such as case, the Cu concentration and the Ni concentration are further reduced in the high purity silica sol produced by the production method of the present invention.
• In the step (3), the ion exchange using the chelating ion exchange resin is still more preferably conducted after adding the oxidizing agent to the purified silicate solution and then adjusting the pH of the purified silicate solution to the range of up to 2. The inventors of the present invention have found that, in such as case, the Cu concentration and the Ni concentration are further reduced in the high purity silica sol produced by the production method of the present invention.
• Amount of the oxidizing agent added is preferably in the range of 0.01 to 20% by weight, and more preferably 0.01 to 10% by weight in relation to the dry silica weight.
• The means employed for adjusting the pH of the purified silicate solution to the range of up to 2 (and preferably 1 to 2) is not particularly limited, and the pH may be adjusted by adding an acid known in the art such as hydrochloric acid.
• A high purity silicate solution is produced by the step (3) as described above.
<Step (4)>
• Next, the step (4) of the production method of the present invention is described.
• In the step (4), a part of the high purity silicate solution (seed solution) is adjusted to alkaline pH, and then, this solution is mixed with another part of the high purity silicate solution (feed solution).
• After separating a part of the high purity silicate solution for use as the seed solution, an alkali may be added to this seed solution to adjust the solution to an alkaline pH. More specifically, the seed solution is adjusted to a pH in the range of 10 to 13 (and preferably 11 to 12), and then mixed with the feed solution by adding the feed solution to the seed solution maintained to the temperature in the range of 20 to 98° C. (more preferably 50 to 95° C., and still more preferably 80 to 90° C.).
• Preferably, the feed solution maintained to a temperature in the range of 1 to 30° C., and more preferably 1 to 20° C. is added to the seed solution.
• The feed solution is gradually added to the seed solution which had been preferably adjusted to the pH and temperature as described above so that the silica fine particles develop in the seed solution to thereby produce the silica sol.
• After adding the feed solution to the seed solution, the solution is preferably maintained at a high temperature (about 80 to 90° C.) for several hours to thereby promote smooth development of the silica fine particles.
• The step (4) as described above is capable of producing a high purity silica sol having both the Cu concentration (weight concentration) and the Ni concentration (weight concentration) which are up to 50 ppb in relation to the dry silica.
• The Cu concentration and the Ni concentration in relation to the dry silica are preferably low as in the case of the silica sol of the present invention as described below. Also, the average particle diameter is preferably the same as that of the silica sol of the present invention as described below.
• The SiO2 concentration (% by weight) of the high purity silica sol is measured by adding sulfuric acid to the high purity silica sol, evaporating the solution to dryness, and weighing the remaining solid after strong heating. Sulfuric acid and hydrofluoric acid are then added, and after evaporating the solution to dryness, remaining solid is weighed. The calculation is conducted by assuming that the weight loss corresponds the weight of the silica (SiO2).
• The Cu concentration and the Ni concentration in the high purity silica sol may be measured by adding nitric acid and hydrofluoric acid to the silica sol, heating the solution, evaporating the solution to dryness, dissolving the solid content by the addition of nitric acid and water and heating, and diluting the solution by adding water, and evaluating the concentration with a graphite atomic absorption spectrometer.
• After determining the SiO2 concentration, the Cu concentration, and the Ni concentration as described above, the Cu concentration and the Ni concentration in relation to the dry silica are determined as a ratio of Ni concentration and the Cu concentration in relation to the dry silica.
• Next, the silica sol of the present invention is described.
• The silica fine particles contained in the silica sol of the present invention has an average particle diameter of 2 to 300 nm, preferably 5 to 100 nm, and more preferably 10 to 80 nm.
• In the present invention, the average particle diameter of the silica fine particles is the one obtained by conducting the measurement according to Sears method.
• Sears method is a method conducted by the following procedures 1) to 6).
• 1) The sample at an amount corresponding to 1.5 g of SiO2 is collected in a beaker, and transferred to a thermostatic reactor at 25° C. Pure water is added to a volume of 90 ml. The following procedure is conducted in a thermostatic reactor maintained at 25° C.
• 2) 0.1 mol/L aqueous solution of hydrochloric acid is added until the pH is 3.6.
• 3) 30 g of sodium chloride is added, and the solution is diluted with pure water to 150 ml, and the solution is stirred for 10 minutes.
• 4) pH electrode is set, and 0.1 mol/L aqueous solution of sodium hydroxide is added dropwise with stirring to adjust the pH to 4.0.
• 5) The sample with the pH adjusted to 4.0 is titrated with 0.1 mol/L aqueous solution of sodium hydroxide, and amount of the aqueous solution of sodium hydroxide added and the pH value of at least 4 points are recorded in the pH range of 8.7 to 9.3 to depict a calibration curve by plotting the amount of the 0.1 mol/L aqueous sodium hydroxide in the X axis and the corresponding pH value in the Y axis.
• 6) Volume V (ml) of the 0.1 mol/L aqueous solution of sodium hydroxide consumed from pH 4.0 to 9.0 per 1.5 g of SiO2 is calculated by the following equation (3). Specific surface area is calculated from the following equation (4). Average particle diameter D1 (nm) is calculated by the following equation (5).
• 
  V=(A×f×100×1.5)/(W×C)''(3)
• 
  SA1=29.0V'28''(4)
• 
  D1=/(ρ×SA1)''(5)
• • (ρ: density of the sample)
    In the equation (3),
  • A: amount (ml)) of the 0.1 mol/L aqueous solution of sodium hydroxide required for titration from pH 4.0 to 9.0 per 1.5 g of SiO2,
  • f: titer of the 0.1 mol/L sodium hydroxide solution,
  • C: SiO2 concentration (%) of the sample, and
  • W: amount of the sample collected (g).
• The silica sol of the present invention typically has a Cu concentration (weight concentration) (in relation to the dry silica) of up to 50 ppb, preferably up to 40 ppb, more preferably up to 30 ppb, still more preferably up to 20 ppb, and most preferably up to 10 ppb.
• The silica sol of the present invention typically has a Ni concentration (weight concentration) (in relation to the dry silica) of up to 50 ppb, preferably up to 40 ppb, more preferably up to 30 ppb, still more preferably up to 20 ppb, and most preferably up to 10 ppb.
• Preferably, the silica sol of the present invention does not substantially contain carbon. More specifically, carbon content of the silica sol of the present invention is preferably up to 0.5% by weight, more preferably up to 0.3% by weight, and still more preferably up to 0.1% by weight.
• The carbon content of the silica sol of the present invention is determined by burning the silica sol in a high-frequency furnace of carbon and sulfur analyzer, and analyzing CO and CO2 in the combustion product by infrared absorption.
• The SiO2 concentration, Cu concentration, and Ni concentration of the silica sol of the present invention are the values measured by the same procedures as those used in measuring the SiO2 concentration, Cu concentration, and Ni concentration of the high purity silica sol obtained by the production method of the present invention
• The silica sol of the present invention is a high purity silica sol containing silica fine particles having an average particle diameter as described above, and having a Cu concentration and a Ni concentration as described above.
• The dispersion medium used for the silica sol of the present invention is not particularly limited. The dispersion medium, however, is preferably an aqueous medium, and more preferably water.
• Also, the silica sol of the present invention is not particularly limited for its concentration of the solid content. The concentration, however, is preferably 5 to 60% by weight, more preferably 10 to 50% by weight, and still more preferably 20 to 40% by weight.
• Also, the pH of the silica sol of the present invention is not particularly limited. The pH is preferably 8 to 12, and more preferably 9 to 11.
• The silica sol of the present invention may contain a stabilizer known in the art such as HCl and NaOH.
• The method used for producing the silica sol of the present invention is not particularly limited while it may be produced by the production method of the present invention.
• The silica sol of the present invention is well adapted for use as an abrasive.
• An abrasive composition containing the silica sol of the present invention is suitable for use as an abrasive of electronic materials such as semiconductor silicon wafer since the Ni and the Cu concentrations are lower than those of conventional abrasive.
• Preferably, such abrasive composition may further comprise at least one member selected from the group consisting of an abrasive aid, surfactant, heterocyclic compound, pH adjusting agent, and buffering agent.
EXAMPLES Example 1 Purification of Aqueous Solution of Sodium Silicate
• An aqueous solution of sodium silicate having a SiO2 concentration of 24.06% by weight, a Na2O concentration of 7.97% by weight, a Cu concentration (in relation to the dry silica) of 460 ppb, and Ni concentration (in relation to the dry silica) of 640 ppb (also referred to as 'water glass A') was prepared. The SiO2 concentration, Na2O concentration, Cu concentration, and Ni concentration were measured by the procedure as described above.
• This aqueous solution of sodium silicate was filtered by using an ultrafiltration membrane (SEP- manufactured by Asahi Kasei Chemicals Corp. having a molecular weight cut-off of ), and purified aqueous solution of an alkali silicate (b) was obtained as the filtrate.
• The SiO2 concentration of the purified aqueous solution of the alkali silicate (b) was measured by the procedure as described above. The SiO2 concentration was 23.2% by weight.
[Preparation of Purified Silicate Solution]
• Pure water was added to g of the thus obtained purified aqueous solution of an alkali silicate (b) so that the SiO2 concentration was 5.0% by weight.
• 18 kg of the resulting purified aqueous solution of the alkali silicate (b) having SiO2 concentration of 5.0% by weight was passed through 6 L of a strongly acidic cation exchange resin (SK1BH manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h'1 to obtain 18 kg of purified silicate solution having a pH of 2.7.
• The SiO2 concentration of the resulting purified silicate solution was measured by the procedure as described above. The SiO2 concentration was 4.7% by weight.
[Preparation of High Purity Silicate Solution]
• Next, 160 g of aqueous solution of hydrogen peroxide (0.56% by weight in relation to the dry silica) was added to 18 kg of the purified silicate solution, and 1% by weight hydrochloric acid was added to adjust the pH to 2. The solution was passed through a chelating ion exchange resin (CR-11 manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h'1 to prepare a high purity silicate solution at a pH of 2.0.
• The SiO2 concentration of the resulting high purity silicate solution was 4.5% by weight.
[Production of High Purity Silica Sol]
• A part of the resulting high purity silicate solution (414.4 g) was separated for use as the seed solution, and another part of the high purity silicate solution (10.18 kg) was separated for use as the feed solution.
• Next, 191.1 g of 5% by weight potassium hydroxide aqueous solution was added to 725.8 g of pure water, and then, the seed solution was added to this solution, and the solution was heated. When the solution reached 83° C., the solution was maintained at this temperature for 30 minutes, and then, the feed solution was added at a constant rate for 11 hours with the temperature maintained. When all of the feed solution was added to the seed solution, the solution was heated for 1 hour to maintain the solution at 83° C., and the solution was then cooled to room temperature to prepare the silica sol. This silica sol was concentrated to 12% by weight by using an ultrafiltration membrane (SIP-) manufactured by Asahi Kasei Chemicals Corp., and further concentrated to 30% by weight by using a rotary evaporator to thereby produce a high purity silica sol.
• The average particle diameter of the resulting high purity silica sol measured by the Sears method was 17.8 nm.
• The Cu concentration (in relation to the dry silica) and the Ni concentration (in relation to the dry silica) of the resulting silica sol were measured by the procedure as described above, and the silica sol had a Cu concentration (in relation to the dry silica) of less than 1 ppb and an Ni concentration (in relation to the dry silica) of 7 ppb.
Example 2
• In Example 1, the aqueous solution of sodium silicate was filtered through an ultrafiltration membrane (SEP- having a molecular weight cut-off of ) to obtain the purified aqueous solution of an alkali silicate (b) as the filtrate. In Example 2, the same aqueous solution of sodium silicate was filtered through an ultrafiltration membrane (SIP- manufactured by Asahi Kasei Chemicals Corp. having a molecular weight cut-off of ) to obtain the purified aqueous solution of an alkali silicate (b) as the filtrate.
• Also, in Example 1, aqueous solution of hydrogen peroxide was added to the purified silicate solution, and hydrochloric acid was added to the solution to adjust the pH to 2 before the passing of the solution through the chelating ion exchange resin. In Example 2, the addition of the aqueous solution of hydrogen peroxide, and also, the pH adjustment with the hydrochloric acid were not carried out, and the purified silicate solution was passed through the same chelating ion exchange resin at the same space velocity to obtain a high purity silicate solution at a pH of 2.7. The SiO2 concentration of the resulting high purity silicate solution measured by repeating the procedure as described above was 4.5% by weight.
• The procedure of Example 1 was repeated except for those as described above, and the measurement was conducted by as in the case of Example 1.
• The resulting silica sol had an average particle diameter of 17.8 nm, a Cu concentration (in relation to the dry silica) of 30 ppb, and a Ni concentration (in relation to the dry silica) of 20 ppb.
Example 3
• The procedure of Example 1 was repeated except that an aqueous solution of sodium silicate (hereinafter also referred to as 'water glass B') having a SiO2 concentration of 24.64% by weight, a Na2O concentration of 8.08% by weight, a Cu concentration (in relation to the dry silica) of 690 ppb, and a Ni concentration (in relation to the dry silica) of 240 ppb was used instead of the water glass A used in Example 1.
• The procedure of Example 1 was repeated except for those as described above, and the measurement was conducted by as in the case of Example 1.
• The resulting silica sol had an average particle diameter of 17.6 nm, a Cu concentration (in relation to the dry silica) of 24 ppb, and a Ni concentration (in relation to the dry silica) of 9 ppb.
Example 4
• The procedure of Example 1 was repeated except that an aqueous solution of sodium silicate (hereinafter also referred to as 'water glass C') having a SiO2 concentration of 24.43% by weight, a Na2O concentration of 7.40% by weight, a Cu concentration (in relation to the dry silica) of 450 ppb, and a Ni concentration (in relation to the dry silica) of 160 ppb was used instead of the water glass A used in Example 1.
• The procedure of Example 1 was repeated except for those as described above, and the measurement was conducted by as in the case of Example 1.
• The resulting silica sol had an average particle diameter of 17.6 nm, a Cu concentration (in relation to the dry silica) of 23 ppb, and a Ni concentration (in relation to the dry silica) of less than 1 ppb.
Example 5
• 232.8 g of 3.0% by weight aqueous solution of hydrogen peroxide (0.567% by weight in relation to the dry silica) was added to 5 kg of water glass B, and the mixture was thoroughly stirred.
• The resulting aqueous solution of sodium silicate having the aqueous solution of hydrogen peroxide added was filtered through an ultrafiltration membrane (SIP- having a molecular weight cut-off of ) to obtain purified aqueous solution of the alkali silicate (b) as the filtrate.
• Next, pure water was added to the resulting purified aqueous solution of the alkali silicate (b) so that the SiO2 concentration was 5.0% by weight. The resulting 5.0% by weight purified aqueous solution of the alkali silicate (b) was passed through 6 L of a strongly acidic cation exchange resin (SK1BH manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h'1 to obtain a purified silicate solution at a pH of 2.7.
• Next, the purified silicate solution was passed through a chelating ion exchange resin (CR-11 manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h'1 to obtain a high purity silicate solution at a pH of 2.7. The SiO2 concentration of the resulting high purity silicate solution measured by the procedure as described above was 4.5% by weight.
• The following process was conducted by repeating the procedure of Example 1. More specifically, 191.1 g of 5% by weight potassium hydroxide aqueous solution was added to the pure water, and then, the seed solution was added to the solution, and the solution was heated. When the solution reached 83° C., the solution was maintained at this temperature for 30 minutes, and then, the feed solution was added at a constant rate for 11 hours with the temperature maintained. When all of the feed solution was added to the seed solution, the solution was heated for 1 hour to maintain the solution at 83° C. to thereby produce a high purity silica sol.
• The measurement was conducted as in the case of Example 1.
• The resulting silica sol had an average particle diameter of 17.6 nm, a Cu concentration (in relation to the dry silica) of 5 ppb, and a Ni concentration (in relation to the dry silica) of less than 1 ppb.
Comparative Example 1
• Pure water was added to the water glass A used in Example 1 so that the SiO2 concentration was 5.0% by weight.
• 18 kg of the resulting 5.0% by weight aqueous solution of sodium silicate was passed through 6 L of a strongly acidic cation exchange resin (SK1BH manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h'1 to obtain 18 kg of silicate solution.
• The SiO2 concentration of the resulting silicate solution was measured by the procedure as described above. The SiO2 concentration was 4.7% by weight. This silicate solution was diluted with pure water to 4.5% by weight.
• Next, a part of the thus obtained silicate solution (414.4 g) was separated for use as the seed solution, and another part of the silicate solution (10.63 kg) was separated for use as the feed solution.
• The following process was conducted by repeating the procedure of Example 1. More specifically, 191.1 g of 5% by weight potassium hydroxide aqueous solution was added to pure water, and then, the seed solution was added to the solution, and the solution was heated. The solution was maintained at this temperature for 30 minutes, and then, the feed solution was added at a constant rate for 11 hours with the temperature maintained. When all of the feed solution was added to the seed solution, the solution was heated for 1 hour to maintain the solution at 83° C. to thereby produce a silica sol.
• The measurement was conducted by as in the case of Example 1.
• The resulting silica sol had an average particle diameter of 17.6 nm, a Cu concentration (in relation to the dry silica) of 235 ppb, and a Ni concentration (in relation to the dry silica) of 610 ppb.
Comparative Example 2
• Pure water was added to the water glass A used in Example 1 so that the SiO2 concentration was 5.0% by weight.
• 18 kg of the resulting 5.0% by weight aqueous solution of sodium silicate was passed through 6 L of a strongly acidic cation exchange resin (SK1BH manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h'1 to obtain 18 kg of silicate solution. The SiO2 concentration of the resulting silicate solution was measured by the procedure as described above. The SiO2 concentration was 4.7% by weight.
• Next, 18 kg of the silicate solution was passed through a chelating ion exchange resin (CR-11 manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h'1 to obtain an ion-exchanged silicate solution which had passed through the chelating ion exchange resin at a pH of 2.7. The SiO2 concentration was 4.5% by weight.
• Next, a part of the thus obtained ion-exchanged silicate solution which had passed through the chelating ion exchange resin (414.4 g) was separated for use a the seed solution, and another part of the ion-exchanged silicate solution which had passed through the chelating ion exchange resin (10.63 kg) was separated for use as the feed solution.
• The following process was conducted by repeating the procedure of Example 1. More specifically, 191.1 g of 5% by weight potassium hydroxide aqueous solution was added to pure water, and then, the seed solution was added to the solution, and the solution was heated. The solution was maintained at this temperature for 30 minutes, and then, the feed solution was added at a constant rate for 11 hours with the temperature maintained. When all of the feed solution was added to the seed solution, the solution was heated for 1 hour to maintain the solution at 83° C. to thereby produce a silica sol.
• The measurement was conducted by as in the case of Example 1.
• The resulting silica sol had an average particle diameter of 17.7 nm, a Cu concentration (in relation to the dry silica) of 80 ppb, and a Ni concentration (in relation to the dry silica) of 150 ppb.
Comparative Example 3
• The procedure of Comparative Example 2 was repeated except that water glass B was used instead of water glass A. The measurement was also conducted by repeating the procedure of Comparative Example 2.
• The resulting silica sol had an average particle diameter of 17.8 nm, a Cu concentration (in relation to the dry silica) of 105 ppb, and a Ni concentration (in relation to the dry silica) of 187 ppb.
Comparative Example 4
• The procedure of Comparative Example 2 was repeated except that water glass C was used instead of water glass A. The measurement was also conducted by repeating the procedure of Comparative Example 2.
• The resulting silica sol had an average particle diameter of 17.6 nm, a Cu concentration (in relation to the dry silica) of 113 ppb, and a Ni concentration (in relation to the dry silica) of 97 ppb.
• TABLE 1 Cu (in relation to Ni (in relation to Water SiO2 Na2O Molar the dry silica, the dry silica, glass (%) (%) ratio ppb) ppb) A 24.06 7.97 3.12 460 640 B 24.64 8.08 3.15 690 240 C 24.43 7.40 3.41 450 160
• TABLE 2 Purifi- pH Ion cation by H2O2 adjustment exchange Water ultra- treat- of silicate by chelating glass filtration ment solution resin Example 1 A Molecular Yes Yes Yes weight, Example 2 A Molecular No No Yes weight, Example 3 B Molecular No No Yes weight, Example 4 C Molecular No No Yes weight, Example 5 B Molecular Yes No Yes weight, Comparative A No No No No Example 1 Comparative A No No No Yes Example 2 Comparative B No No No Yes Example 3 Comparative C NO NO No Yes Example 4
• TABLE 3 Particle Cu (in relation to Ni (in relation to size (nm) the dry silica, ppb) the dry silica, ppb) Example 1 17.8 <1 7 Example 2 17.8 30 20 Example 3 17.6 24 9 Example 4 17.6 23 <1 Example 5 17.6 5 <1 Comparative 17.6 235 610 Example 1 Comparative 17.7 80 150 Example 2 Comparative 17.8 105 187 Example 3 Comparative 17.6 113 97 Example 4
• In Examples 1 to 5, the aqueous solution of sodium silicate was filtered through an ultrafiltration membrane, and the purified silicate solution was further passed through the chelating ion exchange resin. For the high purity silica sols obtained in such Examples 1 to 5, both the Cu concentration and the Ni concentration in relation to the dry silica were up to 50 ppb. More specifically, the Cu concentration in relation to the dry silica was up to 30 ppb, and simultaneously, the Ni concentration in relation to the dry silica was up to 20 ppb.
• In Example 1, the aqueous solution of sodium silicate was filtered through an ultrafiltration membrane, and after adding aqueous solution of hydrogen peroxide to the purified silicate solution and further adding hydrochloric acid for adjustment of the pH to 2, the solution was passed through the chelating ion exchange resin. The Cu concentration and the Ni concentration in relation to the dry silica were even lower in the high purity silica sol obtained in such Example 1, and both the Cu concentration and the Ni concentration were up to 10 ppb.
• In Example 5, aqueous solution of hydrogen peroxide was added to the aqueous solution of sodium silicate, and the solution was filtered through an ultrafiltration membrane, and then, passed through the chelating ion exchange resin. The Cu concentration and the Ni concentration in relation to the dry silica were even lower in the high purity silica sol obtained in such Example 5, and both the Cu concentration and the Ni concentration were up to 5 ppb.
• In contrast, the silica sol obtained in Comparative Examples 1 to 4 exhibited high Cu and Ni concentration, that is, the Cu concentration in relation to the dry silica of 80 to 235 ppb, and the Ni concentration in relation to the dry silica of 97 to 610 ppb.

Claims (8)

1. A method for producing a high purity silica sol comprising the steps of (1) conducting ultrafiltration of an aqueous solution of an alkali silicate (a) to obtain purified aqueous solution of the alkali silicate (b); (2) subjecting the purified aqueous solution of the alkali silicate (b) to an ion exchange process to remove at least a part of cationic components in the purified aqueous solution of the alkali silicate (b) to obtain purified silicate solution; (3) subjecting the purified silicate solution to an ion exchange process using a chelating ion exchange resin to obtain high purity silicate solution; and (4) adjusting a part of the high purity silicate solution (seed solution) to alkaline pH and mixing this solution with another part of the high purity silicate solution (feed solution) to produce the high purity silica sol having a Cu concentration and a Ni concentration (in relation to the dry silica) of up to 50 ppb. 2. A method for producing a high purity silica sol according to claim 1 further comprising the step of adding an oxidizing agent to at least one member selected from the group consisting of the aqueous solution of an alkali silicate (a), the purified aqueous solution of the alkali silicate (b), and the purified silicate solution. 3. A method for producing a high purity silica sol according to claim 2 wherein the oxidizing agent is aqueous solution of hydrogen peroxide. 4. A method for producing a high purity silica sol according to claim 1 wherein the step (3) is preferably a step comprising adjusting pH of the purified silicate solution to the range of up to 2, and subjecting the purified silicate solution to an ion exchange process using a chelating ion exchange resin to produce the high purity silicate solution. 5. A high purity silica sol having an average particle size of 2 to 300 nm, and a Cu concentration and a Ni concentration (in relation to the dry silica) of up to 50 ppb. 6. A high purity silica sol of claim 5 produced by the production method of claim 1. 7. An abrasive composition containing the high purity silica sol of claim 5. 8. An abrasive composition according to claim 7 further comprising at least one member selected from the group consisting of abrasive aid, surfactant, heterocyclic compound, pH adjusting agent, and buffering agent. US13/727,791 -12-28 -12-27 High purity silica sol and its production method Active -06-20 USB2 (en)

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* Cited by examiner, ' Cited by third party Publication number Priority date Publication date Assignee Title USA1 (en) * -09-05 -03-07 Nissan Chemical Industries, Ltd. Method for producing purified alkali silicate aqueous solution and silica sol CNA (en) * -05-25 -09-02 ''''''' Preparation method and application of glass coating liquid JPA (en) * -09-25 -04-28 ''''''''' Light-emitting device CNA (en) * -08-31 -02-15 ''''''''''' Preparation method for preparing silica sol for catalyst high in purity and uniform in particle size CNA (en) * -12-07 -05-29 ''''''''''''' Aluminium is modified acidic silicasol and preparation method thereof CNA (en) * -03-02 -09-10 '''''''''''' Silica solution and preparation method thereof CNA (en) * -07-10 -10-02 ''''''''''''''' Method for preparing high-concentration silica sol with ultra-large particle size by using water glass USB2 (en) -10-20 -12-15 Nissan Chemical Industries, Ltd. Method for producing purified aqueous solution of silicic acid CNA (en) * -09-29 -02-02 '''''''''''''' Method for preparing low-metal-content high-purity silicic acid USB2 (en) -02-26 -11-14 Nissan Chemical Corporation Method for producing silica sol having elongated particle shape

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* Cited by examiner, ' Cited by third party Publication number Priority date Publication date Assignee Title USA1 (en) * -09-05 -03-07 Nissan Chemical Industries, Ltd. Method for producing purified alkali silicate aqueous solution and silica sol USB2 (en) * -09-05 -08-18 Nissan Chemical Industries, Ltd. Method for producing purified alkali silicate aqueous solution and silica sol USB2 (en) -09-05 -04-10 Nissan Chemical Industries, Ltd. Method for producing purified alkali silicate aqueous solution and silica sol JPA (en) * -09-25 -04-28 ''''''''' Light-emitting device CNA (en) * -05-25 -09-02 ''''''' Preparation method and application of glass coating liquid USB2 (en) -10-20 -12-15 Nissan Chemical Industries, Ltd. Method for producing purified aqueous solution of silicic acid CNA (en) * -08-31 -02-15 ''''''''''' Preparation method for preparing silica sol for catalyst high in purity and uniform in particle size CNA (en) * -12-07 -05-29 ''''''''''''' Aluminium is modified acidic silicasol and preparation method thereof USB2 (en) -02-26 -11-14 Nissan Chemical Corporation Method for producing silica sol having elongated particle shape CNA (en) * -03-02 -09-10 '''''''''''' Silica solution and preparation method thereof CNA (en) * -07-10 -10-02 ''''''''''''''' Method for preparing high-concentration silica sol with ultra-large particle size by using water glass CNA (en) * -09-29 -02-02 '''''''''''''' Method for preparing low-metal-content high-purity silicic acid

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