JPH10182140A - Production of synthetic quartz glass powder and formed quartz glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a molded synthetic glass produced by the melt-molding of synthetic quartz glass powder and having suppressed thermal deformation in the use of the molded glass at a high temperature by producing synthetic quartz glass powder by baking silica gel powder and mixing the obtained synthetic quartz glass powder until the scattering of the measured silanol concentration values falls within a specific range. SOLUTION: Synthetic glass powder produced by baking silica gel powder is mixed until the scattering of the measured silanol concentration values falls within ±5%. Preferably, silica gel powder is baked to obtain synthetic quartz glass powder, the powder is charged into a mixer, the mixed powder is extracted 1/5 pt.wt. at a time based on 1 pt. of the total weight of the charged mixture, 10g each of the mixture is sampled when 1/5, 2/5, 3/5, 4/5 and 5/5 of the mixture are extracted, the silanol concentration is measured and the mixing is continued until the scattering of the values becomes ±5%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz of high purity and a small amount of bubbles which is preferably used mainly in the field of semiconductor manufacturing such as a crucible for pulling a silicon single crystal, a furnace tube for heat treatment of a silicon wafer, and the optical field such as an optical fiber. The present invention relates to a method for producing a synthetic quartz glass powder from which a glass molded body can be obtained.

[0002]

2. Description of the Related Art In recent years, glass products used in the optical communication field, the semiconductor industry, and the like have undergone very strict control over their quality. The method for producing such high-purity glass mainly includes (1) a method of purifying and using natural quartz, (2) hydrolysis of a gaseous silicon compound such as silicon tetrachloride in an oxyhydrogen flame, and heat. (3) a method using synthetic quartz powder obtained by firing silica gel powder obtained by hydrolysis / gelation in a liquid phase such as silicon alkoxide, etc. , Etc. are known.

[0003]

However, the method (1) has a limit in reducing the content of trace impurities, and the method (2) has a problem that the production cost is extremely high. In the method (3) using silica gel, in particular, the method using silica gel powder using silicon alkoxide as a raw material, a synthetic quartz glass having a low trace impurity content can be obtained at lower cost than the method (2).

[0004] On the other hand, as a requirement other than the content of impurities, in applications where a quartz glass product is used in a high temperature region of 1000 ° C or higher, it is required that deformation due to a decrease in viscosity of the glass is small. In particular, it is known that this high-temperature viscosity has a correlation with the residual silanol concentration in the glass, but the synthetic quartz glass powder obtained by the hydrolysis method of silicon alkoxide has a large amount of residual silanol groups, and There was a problem that the molded body manufactured using the method had a relatively low high-temperature viscosity as compared with that obtained from natural quartz powder. Therefore, in order to improve the high-temperature viscosity as much as possible, a method for producing low-silanol silica by baking in an atmosphere having a low steam partial pressure (Japanese Patent Laid-Open No. 2-289)
No. 416) is known. However, when the gel obtained by hydrolysis of silicon alkoxide is fired by batch firing using a large crucible or the like, the diffusion rate of water vapor desorbed from the gel and the rate of heat conduction inside the powder are short, and so on. It is difficult to reduce the silanol concentration over time, and the resulting synthetic quartz glass powder may have a large difference in silanol concentration between the position near the surface of the fired crucible and the center of the powder layer. Was.
In order to solve these problems, a method of supplying a gas having a low water vapor partial pressure to the inside of the powder layer during firing (Japanese Patent Laid-Open No. 8-2)
No. 6741), a method in which a heat-resistant structure having good heat conductivity is inserted into a silica gel powder layer and calcined (Japanese Patent Application Laid-Open No. 8-175821); A method of controlling the gas supply amount such that a gas having a low pressure does not cause bubbling, that is, a gas flows uniformly in the powder layer without generating a short path of the gas (Japanese Patent Application No. 7-280726). Although devised by the inventors and greatly improved, even with these techniques, the fused silica glass powder obtained by melting and molding the obtained fused silica glass powder, when used at high temperatures, is not uniform. Deformation may occur.

Although this is considered to be a deformation due to a difference in thermal deformation rate depending on the part of the quartz glass product, the correlation with the amount of silanol measured in the synthetic quartz glass powder is unclear, No measures were found.

[0006]

Means for Solving the Problems In order to overcome the above-mentioned problems, the present inventors have conducted further intensive studies. As a result, the above-mentioned problems were solved by sufficiently mixing the synthetic quartz glass powder after batch firing. Having found the surprising fact that it can be solved, the present invention has been reached. That is, the present invention relates to a method for producing a synthetic quartz glass powder by calcining a silica gel powder and, after calcining the gel powder, subjecting the obtained synthetic quartz glass powder to a variation in silanol concentration within a measured value ± 5%. The present invention resides in a method for producing a synthetic quartz glass powder characterized by mixing.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
First, the silica gel powder used in the present invention is not particularly limited. For example, a silica sol is prepared by dispersing fumed silica or the like in water, and this is used as a colloid dispersion method using silica gel, hydrolysis of alkoxysilane, silicate, or the like. A hydrolysis method for obtaining silica gel by hydrolysis of a possible silicon compound may be mentioned, but the hydrolysis method is particularly preferred because the physical properties of silica gel are particularly excellent and the raw material can be easily purified to a high degree by purification. Since it is only an alcohol, it can be easily removed without causing corrosion of a container or the like, and silica gel powder obtained by hydrolyzing alkoxysilane is preferable.

The production of silica gel powder by hydrolysis of alkoxysilane is carried out by reacting alkoxysilane with water according to a method known as the so-called sol-gel method. As the tetraalkoxysilane used as a raw material, a C1-4 lower alkoxysilane such as tetramethoxysilane or tetraethoxysilane or an oligomer which is a low condensate thereof is easily hydrolyzed, and carbon remains in the silica gel. It is preferable because of its small number.

The amount of water used is usually selected from the range of 1 to 10 equivalents of the alkoxy group in the alkoxysilane. At this time, if necessary, an organic solvent such as an alcohol or an ether which is compatible with water may be mixed and used. Representative examples of the alcohol used include lower aliphatic alcohols such as methanol and ethanol. Here, in the present invention, with respect to organic solvents such as alkoxysilane, water, and alcohol introduced into the reaction system, it is preferable to remove foreign substances through a filter before being introduced into the reaction system in advance. In this way, the synthetic quartz glass powder finally obtained by passing through a filter is prevented from being devitrified at the time of melt molding, and a molded article having particularly excellent transparency can be obtained.

In this hydrolysis reaction, hydrochloric acid as a catalyst,
It may be in the presence of an acid such as acetic acid or an alkali such as ammonia. Of course, the water used here,
All substances to be introduced into the reaction system, such as a catalyst, have high purity. Gelation of the hydrolysis product is performed under heating or at room temperature. When heating is performed, the rate of gelation can be increased, so that the gelation time can be adjusted by adjusting the degree of heating. In order to obtain silica gel, any of these known methods can be adopted without particular limitation, but generally, the whole is formed into one gel rather than forming silica gel as a precipitate, and this is crushed and crushed. The silica gel powder is preferably subjected to the following steps because the resulting quartz powder has particularly excellent physical properties, does not require extra steps such as separation from supernatant, and has a good yield.

The silica gel thus obtained is subdivided, if necessary, by pulverization or the like to obtain a silica gel powder. In general, the silica gel is dried prior to the calcination described below. In this case, the gel may be finely divided and then dried, or dried and finely divided. In any case, the particles are subdivided so that the particle size after drying is 10 to 1000 μm, preferably 100 to 600 μm, and the average particle size is 150 to 300 μm. The drying temperature varies depending on the conditions, but is usually 50 to 200 ° C. The operation can be performed either batchwise or continuously. The degree of drying is usually from 5 to 30% by weight in terms of liquid content. The dried silica gel powder thus obtained is fired. At this time, the dried silica gel powder can be directly heated in a temperature range of 1000 to 1300 ° C. to make it nonporous to obtain a synthetic quartz powder.
It is desirable to perform the heat treatment at 1000 to 1300 ° C. after performing the heat treatment at a temperature of 00 to 500 ° C. to sufficiently reduce the carbon concentration. This is for the following reason.

In the dry silica gel powder obtained by the above method, an unreacted alkoxy group and a part of the by-produced alcohol usually remain even when the by-produced alcohol is removed by drying. Actually, when the carbon concentration in the dried silica gel powder is measured, it is usually 1 to 3% by weight, though it varies depending on the drying conditions. When this silica gel powder is heated in an oxygen-containing gas in a temperature range of 1000 to 1300 ° C. to make the pores non-porous, most of the carbon is burnt and removed in the process of raising the temperature, but part of the synthetic quartz powder is converted to unburned carbon When synthetic quartz powder containing unburned carbon is used, CO2
It has been clarified by the inventors of the present invention that it becomes a gas or CO gas to cause bubbles (see Japanese Patent Application No. 7-28).
0726). Therefore, it is necessary to remove substantially all of the unburned carbon before sealing the silica gel.

[0013] Here, by further research of the present inventors,
When the residual carbon in the dried silica gel powder is brought into contact with an oxygen-containing gas in a temperature range of 300 ° C. or higher, it decreases while generating CO and CO2, and the rate of decrease increases as the treatment temperature is increased. Non-porous is 600
It was clarified that the reaction progressed rapidly in the temperature range of ℃ or more. Therefore, it is desirable to reduce the carbon concentration to 1000 ppm or less by a heat treatment at a temperature of 300 to 500 ° C., and then to perform a heat treatment at 1000 to 1300 ° C. as described below. The container used for the heating operation in the temperature range of 1000 to 1300 ° C. is made of a material that is heat-resistant and does not cause contamination of synthetic quartz powder with impurities, for example, a crucible made of quartz. The above-described firing step is desirably performed while flowing a dry gas. Examples of the drying gas include an inert gas such as nitrogen and argon, oxygen, air, and a mixed gas thereof, but air is preferred from the viewpoint of economy.

The gas to be used is sufficiently removed from the water contained by a method such as adsorption, and the dew point is kept at -20 ° C or lower, preferably -40 ° C or lower. If the dew point is higher than this range, the residual silanol concentration of the obtained synthetic quartz glass powder is undesirably high. It is convenient to distribute the drying gas by circulating it on the surface of the powder layer filled in the container, or by supplying it from an insertion tube inserted into the powder layer. Among these methods, the method of supplying with an insertion tube inserted into the powder layer is advantageous because a synthetic quartz glass powder having uniform characteristics can be obtained even when firing is performed using a large-capacity container. However, when the gas is supplied from the insertion tube in the powder layer, the gas flow rate is desirably selected from a region where the powder does not exhibit the bubbling phenomenon. When the bubbling phenomenon occurs, although the reason is not clear, the reduction rate of the silanol decreases, and further, the powder spills out of the container.

When the bubbling phenomenon starts, the powder near the dry gas inlet starts to dance on the surface of the powder layer, and when the flow rate is further increased, large bubbles burst as if the bubbles of the so-called "blood pond hell" burst. Since it flutters, it can be easily confirmed that the bubbling phenomenon has occurred. The material of the insertion tube is preferably a material that does not generate impurities such as quartz, as in the case of the container. Thus, the silanol concentration in the synthetic quartz glass powder is 100 ppm or less,
The calcination is preferably continued until it reaches 60 ppm. The firing step described above may be performed by either a batch method or a continuous method. In particular, the effect of the present invention is remarkably exhibited in a case where the batch method is used.

In the present invention, the synthetic quartz glass powder thus obtained is mixed as described below. That is, mixing is performed until the variation in the measured value of the silanol concentration is within ± 5%. By mixing to this extent, the thermal deformation of the quartz glass product, which is a molded product obtained by melt molding as described above, when used at a high temperature can be suppressed. If it is preferably within ± 3%, the effect of preventing thermal deformation when used at a high temperature is further excellent. In order to determine whether or not the variation in the measured value of the silanol concentration is within ± 5%, specifically, a silica gel powder is fired to obtain a synthetic quartz glass powder, and then the obtained synthetic quartz glass powder is mixed. Charged to the machine, withdrawn 1/5 weight to the total amount charged, each weight was 1/5, 2/5, 3/5, 4/5,
At the time when 5/5 is extracted, when the silanol concentration is measured by sampling 10 g at a time, the variation in the measured silanol concentration is determined to be within ± 5%. That is, the object of the present invention is achieved by mixing to such an extent that the variation of the silanol concentration obtained by such a sampling method is within ± 5%.

As a mixing means, any method such as a method of mixing in a conical type blender and tumbling and mixing using a kiln may be used. However, in order to maintain the high purity of the synthetic quartz glass powder, Attention must be paid to the material with which the powder contacts. Preferably, the portion of the mixer that comes into contact with the synthetic quartz glass powder is made of a high-purity resin compound containing few metallic impurities, specifically, a resin compound having an ash content of 5% or less. It is more preferable to use a resin compound having an ash content of 3% or less. The type of the resin compound is not particularly limited, but specific examples include polytetrafluoroethylene, polyethylene, and polypropylene. Alternatively, it is preferable to use quartz glass as the material of the contact portion with the synthetic quartz glass powder.

The synthetic quartz glass powder obtained according to the present invention suppresses the thermal deformation at the time of high temperature use when it is melt-molded into a quartz glass product. The reason for this is not clear,
According to the present invention, it is supposed that there is still considerable variation in the silanol concentration in the synthetic quartz glass powder depending on the surface of the container used for firing, the portion near the wall, near the center, etc. They came to mind. Then, when the present inventors measured the silanol concentration in the synthetic quartz glass powder, it was found that there was still a concentration difference of about 10 to 15% depending on the measurement location. Therefore, when the powder is melt-molded in this state to produce a quartz glass product, the silanol concentration in the molded product also becomes uneven, particularly in applications where it is used in a high-temperature region of 1000 ° C. or higher, and partial thermal deformation occurs. It is presumed that a problem such as the occurrence of a location that is likely to occur may occur.
For this reason, by performing the mixing according to the present invention, it is thought that the unevenness of the silanol concentration in the quartz glass powder is reduced, which is one of the causes of suppressing the thermal deformation of the quartz glass product at the time of high temperature use. It is also conceivable that the mixing causes a desirable effect on the synthetic quartz glass powder.

The synthetic quartz glass powder subjected to the mixing treatment in this manner is melt-molded by a known method to obtain a quartz glass molded body. The molding method may be appropriately selected depending on the use of the molded article. For example, if the use is a crucible, an arc melt method is used, and if the jig is used for an IC, a method is once formed into an ingot by a Bernoulli method using an oxyhydrogen flame. And a method of heating and melting under vacuum using a carbon mold. Crucibles for pulling silicon single crystals manufactured using the synthetic quartz glass powder obtained according to the present invention, quartz glass members for semiconductor manufacturing such as diffusion furnace tubes and jigs, optical communication such as optical fibers, and glass products in the optical field. The product suppresses thermal deformation when used at high temperatures, and such synthetic quartz glass powder can be suitably used as a raw material for obtaining a high-quality glass molded body.

[0020]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. Example 1 15 kg of ultrapure water was charged into a jacketed horizontal cylindrical reactor having a ribbon-type stirring blade, and then stirring was started at 20 rpm. Then, add 25 kg of tetramethoxysilane to 3
Charged over minutes. This reactor uses a jacket-type reactor, and the temperature of hot water flowing through the jacket is 4
5 ° C. Thereafter, when a uniform sol was obtained, stirring was stopped, and the contents were allowed to stand for 30 minutes. When the change in the contents was observed through the glass window of the reaction vessel, the gelation occurred 40 minutes after the completion of the charging. Thereafter, again, the rotation of the stirring blade was started, and after coarsely pulverizing the gel to a size smaller than the fist size, the valve installed at the bottom of the reactor was opened,
The bulk gel was removed from the reactor.

This lump gel is pulverized with a SUS304 co-mill pulverizer, and the obtained pulverulent gel is vacuum-dried, and the particle size is adjusted using a vibrating classifier.
Was obtained as a dry gel powder. 75 kg of this dry gel powder
Was placed in a 550 mmφ × 600 mmH quartz glass crucible, covered, and set in an electric furnace. A 30 mmφ hole was formed in the center of the lid, and a quartz glass tube having an inner diameter of 10 mm was inserted into the powder through this hole, and was inserted from the lower part of the crucible to a position of about 1 cm. Then, baking was performed while supplying dehumidified air having a dew point of −50 ° C. through the quartz tube. The firing temperature pattern is 600 ° C. at the indicated value of the thermocouple position for controlling the electric furnace.
The temperature was raised to 600 ° C. for 10 hours, and further raised to 1200 ° C. for 5 hours, and then held at 1200 ° C. for 25 hours. After firing, near the center of the surface in the crucible, near the center of the side wall, near the center of the bottom, and sample the fired powder in the center of the powder,
When measured by the infrared absorption method, 103
109, 112, and 122 ppm. The whole amount of the fired powder was charged into a conical-type blender whose inside was coated with polytetrafluoroethylene, and 3 rpm.
For 30 minutes. From the synthetic quartz glass powder after the completion of the mixing operation, 1/5 weight of the whole charged amount was withdrawn, and each weight was 1/5, 2/5, 3/5, and 4/5.
When 5, 5/5 were extracted, 10 g of each sample was sampled and the silanol concentration was measured.
At 8, 111, 109, and 112 ppm, the variation was within ± 2% with respect to the average value of 110 ppm.
A tube outside diameter of 100 m
When formed into a quartz glass tube having a diameter of mφ (thickness of 3 mm) and a length of 200 mm and heat-treated at 1200 ° C. for 50 hours, deformation in the direction of gravity was observed, but no uneven deformation was observed.

Comparative Example 1 Synthetic quartz glass powder produced under the same conditions as in Example 1 (silanol concentration unevenness was 1% at each position in the fired crucible).
(0.3, 109, 112, 122 ppm) was charged in a quartz crucible, and a high-purity polyethylene scoop (width 100 mm, length 150 mm, depth 80 mm) was inserted into the powder and stirred about five times. Thereafter, this powder was arbitrarily sampled at five points, and the silanol concentration was measured. The results were 104, 112, 115, 110, and 1, respectively.
22 ppm, and the variation was ± 8% with respect to these average values of 113 ppm. Using this synthetic quartz glass powder, a quartz glass tube similar to that of Example 1 was manufactured and heat-treated at 1200 ° C. for 50 hours. As a result, uneven deformation was observed as compared with Example 1.

[0023]

According to the present invention, there can be obtained a synthetic quartz glass powder in which the thermal deformation of a molded article at a high temperature is suppressed.

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Claims (7)

[Claims] 1. In producing silica glass powder by firing silica gel powder, the silica gel powder is fired, and the obtained synthetic silica glass powder is subjected to a process until the variation in the measured value of silanol concentration is within ± 5%. A method for producing a synthetic quartz glass powder, which comprises mixing. 2. The silica gel powder is calcined to obtain a synthetic quartz glass powder, and then the obtained synthetic quartz glass powder is charged into a mixer. , 2/5, 3/5, 4/5, and 5/5 were sampled 10 g at a time and the silanol concentration was measured until the variation of the measured silanol concentration was within ± 5%. The method for producing a synthetic quartz glass powder according to claim 1, wherein the mixing is performed by a mixer. 3. The method for producing a synthetic quartz glass powder according to claim 1, wherein the silica gel powder is obtained by hydrolyzing a silicon alkoxide. 4. The method for producing a synthetic quartz glass powder according to claim 1, wherein the firing is performed by a batch method. 5. A resin compound having an ash content of 5% or less in a portion of the mixer used for mixing the synthetic quartz glass powder, which is in contact with the synthetic quartz glass powder. A method for producing the synthetic quartz glass powder according to the above. 6. The synthetic quartz glass powder according to claim 1, wherein a portion of the mixer used for mixing the synthetic quartz glass powder which is in contact with the synthetic quartz glass powder is made of quartz glass. Manufacturing method. 7. A quartz glass compact obtained by melt-molding the synthetic quartz glass powder obtained by the production method according to claim 1.