JP2002137913A - Silica gel and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silica gel, which is optimized in a micropore distribution property to obtain an efficient gas replacement and is superior in dimensional stability less prone to cause cracks and split. SOLUTION: In manufacturing a silica gel, aggregate of silica gel particles is formed by removing a dispersion medium from a dispersion liquid of silica particles. The silica gel is composed of aggregate of fused silica gel particles with micropore of 0.004-10 μm in diameter, measured with a mercury porosi- meter. Micropores of 0.05-0.5 μm in diameter occupy 50% or more of total micropores.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a silica gel and a method for producing the same. Specifically, the present invention provides silica gel useful as a quartz glass precursor and a method for producing quartz glass using the silica gel.

[0002]

2. Description of the Related Art High-purity quartz glass is used for a lining material of a crucible for pulling a silicon single crystal, a furnace tube and a jig used in a semiconductor manufacturing process, an outer cladding of an optical fiber, and the like. These quartz glasses are required to have high purity, low internal silanol groups, high viscosity when melted by heating (hereinafter referred to as high-temperature viscosity), and low bubble content, as well as high purity. ing.

[0003] US Patent No. 4,042,361 discloses a method of preparing a silica sol using fumed silica as a raw material, drying the silica sol to produce crushed pieces, and then firing the silicon sol to pull up a silicon single crystal. An attempt to obtain high-purity quartz glass for use in crucibles and the like is described.

[0004] Japanese Patent Publication No. 5-505167 discloses about 3
B. ~ 1000 μm diameter, about 1 m ² / g or less nitrogen.
E. FIG. T. Surface area, total impurity content below about 50 ppm,
A method is disclosed for producing non-porous dense silica particles having a metal impurity content of about 15 ppm from an aqueous dispersion of fumed silica.

Japanese Patent Application Laid-Open No. 11-171558 discloses a method of manufacturing a preform of an optical fiber in which a slurry of fumed silica is gelled in a mold, then the gel body is extruded, dried and sintered. A method for forming a preform is disclosed.

[0006]

As described above, a silica slurry in which fumed silica is dispersed in a dispersion medium composed of a polar solvent such as water is dried and quartz glass is passed through porous silica gel. Manufacturing methods are known.

[0007] The above method has the following problems.

That is, when the silica slurry is gelled to produce silica gel, there is a problem that the gel shrinks greatly and the shrinkage tends to cause chipping or cracking. In order to solve the above problem and improve the yield of silica gel, it is considered important to increase the concentration of the silica slurry. In order to increase the concentration of the silica slurry, it is also important to effectively disintegrate the silica particles and to disperse them almost completely into primary particles. Is considered to be easy to produce.

By the way, among the fumed silicas currently available, silica having the largest primary particle diameter is about 50 m ^2.
/ G of silica (the average primary particle size of the silica particles is about 0.05 μm). When 50 m ² / g of fumed silica is used, the solid content concentration of the silica dispersion is at most about 55% by weight, and the mode of the pore diameter of the silica gel obtained by drying the silica dispersion is about 5% by weight. It exists near 0.05 μm.

[0010] Accordingly, there has been a demand for a silica gel which does not cause chipping or cracking after drying and has no bubbles in the quartz glass obtained by sintering the same.

[0011]

Means for Solving the Problems The present inventors have intensively studied to solve the above problems. As a result, by using substantially spherical fused silica particles different from fumed silica, it is possible to obtain a dispersion having a high slurry concentration that could not be achieved with fumed silica, and silica gel obtained by drying this It has been found that chipping and cracking can be suppressed very effectively, and that the obtained silica gel is sintered to obtain quartz glass having extremely few residual bubbles, thereby completing the present invention.

That is, according to the present invention, among pores having a pore diameter of 0.004 to 10 μm, which are composed of aggregates of fused silica particles and measured by a mercury porosimeter, a pore diameter of 0.05
The silica gel is characterized in that the proportion of pores of 0.5 μm to 50 μm is 50% or more.

Further, the present invention relates to a fused silica in which particles having a particle diameter of less than 0.1 μm are 5% by weight or less of all particles, and particles having a particle diameter of 0.1 to 5 μm are 20% by weight or more of all particles. The present invention also provides a method for producing silica gel, wherein a dispersion medium is removed from a particle dispersion to form an aggregate of the fused silica particles.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

It is important to use fused silica particles for the silica gel of the present invention. The fused silica particles are dense and generally spherical silica particles because silica is melted and generated at a temperature equal to or higher than the melting point in the gas phase. Fused silica particles synthesized by a gas phase method usually have a certain degree of particle size distribution. When a dispersion is prepared using such fused silica particles, a high-concentration slurry is easily obtained, and when the dispersion is gelled, a high-density gel is easily obtained.

On the other hand, as the spherical silica particles, highly monodisperse spherical silica particles produced by hydrolyzing silicon alkoxide such as methyl silicate in methanol containing ammonia water are also known. Although the silica particles are of extremely high purity, they are relatively expensive, and because they are synthesized in the liquid phase, the silica particles contain water, and alcohol and unreacted alkoxy groups in the reaction solution. There is a problem of containing organic matter. Using such silica particles as raw material for quartz glass, 10
When heating and sintering at a temperature of 00 ° C. or more, there is a concern that bubbles or black carbide may be generated due to water or organic matter decomposition gas (carbon dioxide) generated from inside the silica particles. In addition, when trying to produce a silica gel molded body using silica particles having high monodispersity as described above, cracking is likely to occur due to a large shrinkage rate,
There are problems that the strength of the gel is low and that bubbles and carbides are generated.

In the silica gel of the present invention, the proportion of the pores having a pore diameter of 0.05 to 0.5 μm among the pores having a pore diameter of 0.004 to 10 μm measured by a mercury porosimeter is 50% or more. It is important that

The silica gel of the present invention can be converted into quartz glass by means such as sintering. However, before sintering, water and organic substances contained in the silica gel are removed by vaporization (hereinafter referred to as degassing). It is preferable that the above-mentioned pore characteristics are important. Further, as described later, the silica gel of the present invention is 500 to 1%.
The impurity element can be removed by exposing to a chlorine-containing gas atmosphere such as chlorine or thionyl chloride at 200 ° C. (hereinafter, referred to as high-purification treatment). It is desirable that the pores having the pore diameters described above are open so that they can be performed.

As described above, the silica gel of the present invention has a content of 0.1%.
If the ratio of the pores having a pore diameter of less than 05 μm increases, the gas permeation efficiency decreases, so that the efficiency of the degassing treatment and the purification treatment may decrease.

On the other hand, if the number of pores having a pore diameter larger than 0.5 μm increases, the strength of the silica gel becomes insufficient, and cracks or chips may be easily generated in the silica gel. Also,
When large pores are present, bubbles are left inside the glass when sintering at a high temperature to produce quartz glass.

The silica gel of the present invention has a total pore volume of 0.1.
It is preferably 1 to 0.5 cc / g. When the total pore volume is less than 0.1 cc / g, there is a concern that the efficiency of the degassing treatment or the purification treatment is reduced or the treatment takes a long time. If it exceeds 0.5 cc / g, there is a concern that the strength of the silica gel may be reduced, or bubbles may remain when the silica gel is sintered at a high temperature to produce a quartz glass powder or a quartz glass molded body.

When the silica gel of the present invention is applied to a relatively large molded product of 10 cm ³ or more, the ratio of pores having a pore diameter of 0.05 to 0.5 μm is 50% or more, Further, when the total pore volume is in the range of 0.1 to 0.5 cc / g, the mechanical strength of the silica gel is high, and the gas permeability is high, so that the efficiency of the degassing treatment and the purification treatment is high. High and preferred.

The silica gel of the present invention has an impurity element content of 50 ppm or less, preferably 10 ppm or less.

For the analysis of the impurity element, a known chemical analysis means can be suitably adopted. For example, after dissolving silica gel with hydrofluoric acid, a microanalyzer such as atomic absorption, ICP emission, and ICP-MS can be used. Note that the content of the impurity element in the present invention means Na, K, Ti, Fe, C
It refers to the total content of the eight elements r, Ni, Cu, and Zr.

As will be described later, the silica gel of the present invention can be used to produce compact quartz glass powder or transparent quartz glass by sintering. When applied to various kinds of quartz glass products used in lining materials and semiconductor manufacturing processes, it is particularly important to have high purity. In order to keep the content of the impurity element in the above range, it is a matter of course to use high-purity fused silica particles used as a raw material, but not to be contaminated by the impurity element in the silica gel production process. It is important to. In addition,
As described later, the purity of the silica gel can be increased by performing a purification treatment with a chlorine-containing gas.

The silica gel of the present invention can be used as a precursor of quartz glass. That is, as described later, the silica gel of the present invention can be converted into quartz glass by sintering at a temperature of 1000 to 1650 ° C.

The silica gel of the present invention can be used as a powder or a molded product. As described above, the powder and the compact can be converted into a quartz glass powder and a quartz glass compact by sintering.

The practical average particle diameter of the quartz glass powder is in the range of 10 to 1000 μm, preferably 30 to 70 μm.
Since it is in the range of 0 μm, and more preferably in the range of 50 to 500 μm, the silica gel may be pulverized so as to fall within this range.

Since the silica gel of the present invention is formed of aggregates of fused silica particles and is very easy to be pulverized, it is preferable to pulverize the powder and then sinter it to obtain quartz glass powder. . Of course, after sintering silica gel to convert it to quartz glass, it may be pulverized.

The method of pulverizing silica gel or quartz glass obtained by sintering the silica gel is not particularly limited. Various dry pulverization means may be used, or wet pulverization may be followed by drying again. The dry method is industrially advantageous because it does not need to be dried again.

As a typical pulverizer, known pulverizers such as an automatic mortar, a ball mill, a roll mill, a vibration mill, a pin mill, a disk mill, a crusher, and an air-flow crusher can be used. Since the silica gel of the present invention is relatively soft and easily pulverized, a pulverizer made of a polymer such as Teflon (registered trademark) or a pulverizer coated with a polymer can also be used. Among the above, a pulverizer that can obtain a desired average particle diameter with less contamination of impurities may be used. Further, in order to make the average particle diameter uniform, the particles can be screened with a sieve or the like.

The method for producing the silica gel of the present invention is not particularly limited, but the following method may be mentioned as a typical example.

That is, particles having a particle diameter of less than 0.1 μm account for 5% by weight or less of all particles, particles having a particle diameter of 0.1 to 5 μm account for 20% by weight or more of all particles, and fused silica particles A method for producing silica gel, characterized in that a dispersion medium is removed from a dispersion having a concentration of 60% by weight or more to form an aggregate of the fused silica particles.

The above-mentioned particle size means the primary particle size of the fused silica particles, and the particle size can be measured by an electron microscope or the like.

In the dispersion of fused silica particles used in the present invention, particles having a particle diameter of less than 0.1 μm are 5% of all particles.
It is preferable that the content be not more than weight%. 0.1 μl of the dispersion
If particles having a particle diameter of less than 5% by weight are present in an amount of more than 5% by weight, the ratio of pores having a pore diameter of less than 0.05 μm tends to increase when silica gel is produced. May require a long time.

Accordingly, in the present invention, it is preferable to use fused silica particles having a content of particles having a particle diameter of less than 0.1 μm of 5% by weight or less. In the case where fused silica particles containing more than 5% by weight of particles having a particle size of less than 0.1 μm are used, they can be removed at the stage of forming a dispersion. As a method of removing such fine particles, a method of removing a supernatant containing many fine particles by centrifugation or natural sedimentation, a method of separating fine particles to a filtrate side by filtration, and the like can be employed.

In the dispersion of fused silica particles used in the present invention, particles having a particle size of 0.1 to 5 μm account for 20% by weight or more, preferably 30% by weight or more of all particles.

In the present invention, silica gel can be produced by removing the dispersion medium from the dispersion of the fused silica particles to form an aggregate of the fused silica particles. Is less than 20% by weight, the strength of the silica gel is insufficient and the silica gel may be easily broken. In addition, the ratio of pores having a pore diameter of 0.05 to 0.5 μm, which is the preferred pore distribution described above, is 50%.
In order to prepare silica gel having the above pore distribution, it is necessary that the silica gel contains 20% by weight or more of fused silica particles having the above-mentioned particle diameter.

The dispersion of fused silica particles used in the present invention has a dispersion of more than 5 μm and not more than 1000 μm, preferably 5 μm or less.
Silica particles having a particle diameter of more than μm and not more than 100 μm can be contained in a proportion of not more than 80% by weight of all the particles. The silica particles have substantially no air bubbles inside the particles and may be any as long as they do not impair the purity or the like.
For example, not only fused silica particles but also spherical or crushed quartz glass can be used as fused silica having the above particle diameter.

As described above, when silica particles having a particle diameter larger than 5 μm are added, the pore distribution of the obtained silica gel is not affected, the total pore volume can be reduced, and the dispersion of the dispersion liquid can be reduced. Since it is possible to further increase the silica concentration, it is effective when producing a large molded product.

In the method of the present invention, the above 0.1 to 5
It is preferable that the fused silica particles having a particle diameter of μm have a certain width of particle size distribution. When silica particles having high monodispersity are used, it may be difficult to prepare a dispersion having a high silica concentration, or the strength of silica gel produced using the dispersion may be low.

The dispersion medium used in the method of the present invention includes:
There is no particular limitation as long as the silica particles are dispersed, and various polar solvents can be used. Water is most preferred as the polar solvent. In addition to water, alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, and a mixed solvent of the above-mentioned water and alcohol can also be used.

It is desirable that the fused silica particles in the dispersion used in the method of the present invention be well dispersed near the primary particles. In the present invention, rather than fine particles such as fumed silica, relatively large fused silica particles of at least 0.1 μm or more are used, so that a dispersion liquid having a high degree of dispersion of high concentration silica particles can be relatively easily prepared. it can.

The dispersion may be produced by mixing the fused silica particles and the dispersion medium and then subjecting the mixture to a known wet pulverization such as a propeller mixer, a ball mill, a bead mill, a colloid mill, a homogenizer, an ultrasonic homogenizer, a high-pressure homogenizer, and a mill. And a device capable of crushing and dispersing can be used.

In the method of the present invention, it is desirable that the dispersion liquid is not contaminated by the impurity element in the above step. If the dispersion is contaminated, the purity of the silica gel may decrease. From such a point of view, an apparatus using a resin or ceramics or a member coated with them for the liquid contact part is preferable.

The higher the silica concentration in the dispersion, the higher the productivity is. Also, since the dispersion medium needs to be dried in the next step, the higher the silica concentration, the lighter the load in the drying step. preferable. When a silica gel molded body is produced, the higher the concentration of the dispersion liquid, the smaller the shrinkage ratio, and the occurrence of cracks and chips can be suppressed.

As described above, as a device capable of easily producing a high-concentration dispersion liquid having high productivity, excellent pulverization (dispersion) performance, particularly low contamination, a grinding machine (for example, trade name: Super Mascoloider, Masuko Sangyo Co., Ltd.
Manufactured) can be suitably adopted. In particular, the supermass colloider has low contamination and can efficiently produce a dispersion of fused silica particles having a high concentration of 60% by weight or more. Furthermore, when a whetstone made of a silicon-based compound such as silicon carbide or silicon nitride is used for the liquid contact part, even if contamination from the whetstone occurs, the probability that impurity elements other than silicon are mixed is low,
It is suitable. Moreover, the dispersion liquid can remove coarse particles other than the fused silica particles by filtration or centrifugation.

In preparing the above dispersion, various additives can be added in addition to the fused silica particles and the dispersion medium. For example, in order to improve the stability and dispersibility of silica, a pH adjuster such as an acid or an alkali, various salts, a dispersant, a surfactant, a water-soluble polymer, and the like can be added. When the silica gel of the present invention is converted to quartz glass by sintering at a high temperature, any volatile and / or combustible compound can be added without any particular limitation. For example,
In order to improve the dispersibility of the fused silica particles and to improve the strength of the silica gel after drying, it is a preferable embodiment to add ammonia or an amine. Also, PV
A water-soluble polymer such as A or polyamine or a surfactant may be added to improve the strength of the silica gel.

Next, when the dispersion medium is removed to form an aggregate of the fused silica particles, the dispersion medium is mainly removed by a drying method. The drying method is not particularly limited, and may be, for example, natural drying, but it is preferable to use various dryers industrially. For such drying, for example, a steam dryer, a blast dryer, a hot blast dryer, a vacuum dryer, a conveyor dryer, a conical dryer, a rotary kiln, a spray dryer, and the like can be used.

The drying time and the drying temperature are not particularly limited. The drying time may be selected from the range of several hours to several days, and the drying temperature may be selected from the range of room temperature to several hundred degrees Celsius. When water is used as the dispersion medium, industrially, after drying at a temperature of about 100 ° C. for several to several tens of hours to remove most of the water once, in order to avoid bumping of the dispersion, 100 to 300 It is preferable to remove the remaining water for several to several tens of hours at a temperature in the range of ° C. and to dry. When the drying is performed rapidly, relatively large bubbles are generated inside the silica gel, and there is a concern that the bubbles may remain in the finally produced quartz glass. Therefore, in the above-mentioned drying step, it is preferable to dry slowly so that bubbles are not generated inside the aggregate of the fused silica particles.

In the method of the present invention, as described above, the silica concentration in the dispersion can be increased by using fused silica particles having a large particle size. Therefore, the concentration of the fused silica particles in the dispersion used is 60% by weight or more,
Preferably 65% by weight or more, more preferably 70% by weight
More preferably, it is the above. The higher the concentration of the fused silica particles in the dispersion, the less the load on the subsequent drying step can be reduced. In particular, when the silica gel is a molded product, cracks and chips are less likely to occur during the production of the molded product as the silica concentration increases. Further, the molded article has excellent dimensional stability. In the case of a dispersion using fumed silica conventionally used in this field, the upper limit of the silica concentration in the dispersion was about 50% by weight.

In the method of the present invention, the aggregate of fused silica particles obtained by removing the dispersion medium can be treated at 500 to 1200 ° C. in a chlorine-containing gas atmosphere. As the chlorine-containing gas, chlorine, thionyl chloride, and the like are preferable. The concentration is preferably in the range of 1 to 30% by volume, and can be used after being diluted with an inert gas such as helium. The processing time may be between tens of minutes and several hours. By the above treatment, metal oxides other than silicon in the aggregate can be converted to chloride and removed as chloride gas. In order to carry out the above treatment efficiently, the silica gel having the pore distribution characteristics of the present invention is particularly useful, as described above.

Further, in the present invention, the silica gel is heated at a temperature of 1000 to 1650 ° C. and sintered to produce quartz glass. The heating time may be between several hours and several tens of hours.

Silica gel powder is 1000 to 1400 ° C.
By firing at a temperature in the range described above, it can be converted into a dense quartz glass powder. By firing at the above temperature, the fused silica as a raw material sinters to a dense quartz glass powder. If the temperature is lower than 1000 ° C., dense quartz glass may not be obtained. If the temperature exceeds 1400 ° C., the quartz glass powder may be fused together.

Further, the molded product of silica gel is 1200-200.
By sintering at 1650 ° C., a quartz glass compact without bubbles is obtained. If the temperature is lower than 1200 ° C., the sintering may be insufficient. An electric furnace or the like can be used for the firing. In addition, as the atmosphere at the time of firing, oxygen, air, nitrogen, helium, argon, chlorine, in a vacuum, or the like can be used.

[0056]

The silica gel of the present invention uses fused silica particles as a raw material and has a specific pore distribution characteristic, so that gas in the pores can be efficiently replaced. By sintering the silica gel, quartz glass having high purity, few bubbles inside, and low silanol group concentration can be manufactured at low cost.

[0057]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples. (Test method) Measurement of Particle Size The particle size of the silica particles was measured by analyzing a scanning electron microscope image or a transmission electron microscope image with an image analyzer. In addition, about the average particle diameter of a quartz glass powder, the particle size distribution analyzer (LS-230 made by Beckman Coulter) was used as a simple measuring method. 2. Measurement of total pore volume and pore distribution For measurement of the total pore volume and pore distribution of the quartz glass precursor, a mercury porosimeter (manufactured by Quantachrome Co., Ltd.)
Polemaster-60) was used. Note that a cell having an inner diameter of the capillary of 2 mm was used. 3. Analysis of impurity element content The impurity content in the silica gel was determined by chemical analysis. That is, after dissolving silica gel in hydrofluoric acid, ICP-MS
Quantitative analysis was performed using the instrument. Here, Na, K, Ti, Fe, Cr, Ni, Cu,
The eight elements of Zr were analyzed, and the total content was determined. The lower detection limit of each element at this time is at least 0.1 p.
pm or less. 4. Measurement of refractive index of quartz glass powder Pure water (refractive index: n _D ²⁵ = 1.33) and glycerin (n _D
²⁵ = 1.47), slurries each having a quartz glass powder concentration of 5% by weight were prepared, and then several kinds of each slurry were mixed at an appropriate ratio. Subsequently, the absorbance of the mixture at a wavelength of 593 nm was measured using a spectrophotometer, and the refractive index of the mixture at a wavelength of 593 nm was measured using an Abbe refractometer. The absorbance and the refractive index were measured at 25 ° C.

The absorbance measured above was plotted with respect to the refractive index, the value of the refractive index at which the absorbance was minimized was determined, and the refractive index at which the above-mentioned minimum was taken was defined as the refractive index of the quartz glass powder. 5. Number of bubbles in quartz glass powder A mixed solution having a refractive index of 1.42 was adjusted using pure water and glycerin, and the quartz glass powder was immersed therein. The mixed solution containing the quartz glass powder was spread on a slide, and the number of bubbles in each powder was observed using an optical microscope. (Production of Fused Silica Particles) Fused silica particles (Silica A and Silica B) were produced according to the following steps by the following method.

First, siloxane (octamethylcyclotetrasiloxane, boiling point: 175 ° C.) purified to 99.99% purity was vaporized by a vaporizer from a tank, and gaseous siloxane was converted to oxygen and 1 mole of siloxane. The mixture was mixed so as to be 5 mol of oxygen and supplied from the central port of the triple tube burner.

On the other hand, hydrogen was supplied as a combustible gas from the annular port adjacent to the central port of the triple tube burner, and oxygen was supplied from the annular port adjacent to the outside to form an outer peripheral flame.

The ratio of each gas supplied from the triple tube burner, that is, the ratio of hydrogen to 1 mol of siloxane, the theoretical calorific value of siloxane and hydrogen to 1 mol of generated silica, and the amount of siloxane and hydrogen required for complete combustion of siloxane and hydrogen. The amount of oxygen (including the oxygen contained in the siloxane) indicated by the ratio to the amount of oxygen was changed as shown in Table 1. Table 1 also shows the average gas supply speed in the multi-tube burner.

In the reactor, the molten particles separated from the peripheral flame were cooled in a dispersed state and led to a bag filter of a solid-gas separator together with a gas flow to obtain fused silica particles.

Silica A was a fused silica particle having a spherical particle shape and an average particle diameter of 0.4 μm and a wide distribution from 0.1 to 0.6 μm.

Silica B was a fused silica particle having a spherical particle shape and an average particle diameter of 0.2 μm and a wide distribution from 0.07 to 0.5 μm.

As silica C and D, commercially available fused spherical silica was used.

The silica C was a fused silica particle having a spherical particle shape and an average particle diameter of 2 μm and a wide distribution from 0.05 to 8 μm.

Silica D was a fused silica particle having a spherical particle shape and an average particle diameter of 8 μm and a wide distribution from 1 to 40 μm.

[0068]

[Table 1]

Example 1 (Production of silica gel) The following experiment was carried out using silica A shown in the above-mentioned production example of fused silica particles.

The silica A was mixed with pure water so as to have a solid content of 70% by weight. The mixture became a slurry. Next, Super Mass Colloider (Masuyuki Sangyo)
The powder was subjected to a dispersion treatment using The dispersion conditions are as follows: the diameter of the disk is 250 mm, and the gap between the disks is 2 mm.
00 μm and the number of revolutions of the disk was 1800 rpm. Note that a whetstone made of an inorganic-organic composite material obtained by solidifying 46-mesh SiC powder with a resin binder was used for the disk. The above treatment produced a fluid dispersion. In addition, it turned out that the said dispersion liquid can be prepared up to 80 weight%.

Subsequently, the above dispersion liquid was placed in a quartz glass vat, charged in a blow dryer, dried at 100 ° C. for 24 hours, and further dried at 180 ° C. for 24 hours to obtain a silica gel molded body. . In addition, the above silica gel molded body,
It was a lump having a diameter of about 10 mm, and its strength was hard, and as a result of observing chipping and cracking, no chipping or cracking was present.

FIG. 1 shows the results of measuring the pore distribution of the silica gel using a mercury porosimeter.

From the pore distribution data, the total pore volume was 0.21 cc / g, and the proportion of pores having a pore diameter of 0.05 to 0.5 μm was 87%.

As a result of analyzing the impurity element in the silica gel, the content of the impurity element was 2.5 ppm.

Further, a part of the above silica gel was set in a tube furnace, and heated to 900 ° C. for 30 minutes while flowing a helium gas containing 10% by volume of thionyl chloride to perform a high-purity treatment. When the silica gel was analyzed for impurities, the content of the impurity element was 0.8 ppm or less (8 ppm or less).
It was found that all the elements sharply decreased to below the lower limit of detection). (Production of quartz glass powder) Next, the above silica gel was pulverized using a roll mill made of ceramics, and then coarse and fine powders were removed using a polyethylene sieve. Using a sieve with an opening of 420 μm for coarse powder and 149 μm for fine powder, powder in the range of 150 to 420 μm was fractionated to adjust the particle size distribution.

Subsequently, the silica gel powder having the adjusted particle size distribution was put into a quartz crucible, and was put into a crucible using an electric furnace.
Firing at 0 ° C. for 10 hours produced a quartz glass powder. The heating rate at that time is 7 ° C./mi up to 800 ° C.
n and 0.75 ° C./min thereafter. After cooling,
The powder was taken out and its physical properties were examined. The fired powder was pure white.

The average particle size of the powder was measured by a particle size distribution analyzer and found to be about 250 μm. When the powder was observed with an optical microscope, the shape of the particles was irregular. As a result of observing the surface of the powder with a scanning electron microscope, primary particles of the original fused silica particles were not observed, and the surface was smooth. The powder has a refractive index of 1.46 and a true density of 2.
20 g / cm ³ and the BET specific surface area were 0.4 m ² / g. When the powder was analyzed by an X-ray diffractometer, it was found that there was no crystalline peak and the powder was amorphous. Therefore, it was confirmed that the powder was nonporous and dense quartz glass powder.

Further, when the powder was observed with an optical microscope, particles containing air bubbles were hardly found inside the powder.

From the above, it was found that the quartz glass powder produced in this example was a dense quartz glass powder containing almost no air bubbles inside the particles. (Production of quartz glass molded body) The above-mentioned dispersion liquid was poured into a Teflon cylindrical container, and a cover having a pinhole was opened.
In a constant temperature bath. One week later, when taken out, a cylindrical white quartz glass precursor (silica gel molded body) having a diameter of about 50 mm and a thickness of about 20 mm was obtained.

Further, the silica gel compact was dried in the air for several days, and then dried at 150 ° C. for a whole day and night. As a result of observing the obtained silica gel molded body, there was no chipping or cracking.

Subsequently, the temperature was raised to 1450 ° C. at a rate of 0.5 ° C./min in an electric furnace, and baked for 12 hours. After the cooling, the sample was taken out, and a transparent quartz glass molded body without bubbles was obtained.

Examples 2 to 3 In Example 2, silica gel powder and silica gel compact were manufactured in the same manner as in Example 1 by using silica B and silica C in Example 3, respectively. Quartz glass compacts were manufactured and their physical properties were evaluated.

Table 2 shows the results.

Example 4 Silica gel and silica gel were prepared in the same manner as in Example 1 except that silica A and silica D were used as fused silica particles, and a powder obtained by mixing silica A and silica D at a weight ratio of 4: 6 was used. A molded body was produced, and a quartz glass powder and a quartz glass molded body were produced, and their physical properties were evaluated.

Table 2 shows the results.

Comparative Example 1 (Production of Silica Gel) Fumed silica having a specific surface area of 50 m ² / g was mixed with pure water so as to have a solid concentration of 55% by weight. The fumed silica has an average particle size of 50
It contained silica with a particle size of 10 nm up to 100 nm in nm. Because the above mixture has a high solid content concentration,
It was not liquid but powdery. Stirring and kneading were repeated using a Teflon rod until the water and the powder were uniformly mixed. The mixture has a bulk of about 1 / compared to the original fumed silica.
However, the properties remained powder.

Next, the powder was dispersed in the same manner as in Example 1. By the above-mentioned dispersion treatment, the raw material powder became a fluid slurry. The slurry gelled within one hour and lost fluidity, but the volume of the slurry was reduced to about 1/10 compared to the original volume of fumed silica.

The following treatments were carried out in the same manner as in Example 1 to prepare and evaluate silica gel powder and silica gel compacts and silica glass powder and quartz glass compacts. Table 2 shows the results.

When fumed silica is used,
It was not possible to prepare a dispersion of at least 60% by weight or more.

Comparative Example 2 Silica gel powder was prepared in the same manner as in Example 1 except that instead of the fused silica particles, highly monodisperse silica particles produced by hydrolyzing methyl silicate in methanol containing ammonia water were used. Then, a silica gel molded body was produced, and further a quartz glass powder and a quartz glass molded body were produced, and their physical properties were evaluated.

The shape of the silica particles is truly spherical.
The average particle size was 0.4 μm. The particle diameter of the particles is in the range of 0.35 to 0.45 μm,
The particles were extremely monodisperse.

Table 2 shows the results.

Comparative Example 3 A silica gel powder and a silica gel molded body were produced in the same manner as in Example 1 except that silica D was used, and a quartz glass powder and a silica glass molded body were produced, and the physical properties of each were evaluated. .

Table 2 shows the results.

[0095]

[Table 2]

[0096]

[Brief description of the drawings]

FIG. 1 is a diagram showing the pore distribution of silica gel in Example 1 and Comparative Example 1.

Continued on front page F term (reference) 4G014 AH02 AH06 AH08 AH12 AH14 AH21 AH23 4G072 AA25 BB01 BB05 CC18 DD04 DD05 DD06 GG01 HH16 HH29 JJ01 QQ01 RR07 TT01 TT09 UU21

Claims (11)

[Claims] 1. A method for producing an aggregate of fused silica particles having a pore diameter of 0.004 to 10 as measured by a mercury porosimeter.
A silica gel characterized in that the proportion of pores having a pore diameter of 0.05 to 0.5 μm in the pores of μm is 50% or more. 2. The silica gel according to claim 1, wherein the total pore volume is 0.1 to 0.5 cc / g. 3. The silica gel according to claim 1, wherein the content of the impurity element is 50 ppm or less. 4. The method according to claim 1, which is a quartz glass precursor.
The silica gel according to any one of the above. 5. The silica gel according to claim 1, wherein the silica gel is a powder. 6. The method according to claim 1, wherein the silica gel is a molded product.
The silica gel according to any one of the above. 7. Particles having a particle diameter of less than 0.1 μm are 5% by weight or less of all particles, particles having a particle diameter of 0.1 to 5 μm are 20% by weight or more of all particles, A method for producing silica gel, wherein a dispersion medium is removed from a dispersion having a concentration of 60% by weight or more to form an aggregate of the fused silica particles. 8. The method for producing silica gel according to claim 7, wherein the dispersion medium is water. 9. The fused silica particles having a particle size exceeding 5 μm and
Silica particles having a particle diameter of not more than
The method for producing silica gel according to any one of claims 7 to 8, wherein the content is 0% by weight or less. 10. An agglomerate of fused silica particles obtained by removing a dispersion medium is mixed with a chlorine-containing gas in an atmosphere of 500 to 12%.
The method for producing silica gel according to any one of claims 7 to 9, wherein the treatment is performed at 00C. 11. The silica gel obtained by the method of claim 7 is heated at a temperature of 1000 to 1650 ° C.
A method for producing quartz glass, comprising sintering.