JPH08165131A - Apparatus for producing synthetic quartz glass - Google Patents

Abstract

PURPOSE: To provide a method for producing a high-purity synthetic quartz glass uniformly containing aluminum and hardly containing OH group and Cl group and having high temperature viscosity. CONSTITUTION: This synthetic quartz glass is obtained by hydrolyzing a solution obtained by mixing and stirring a methylsilicate and aluminum alkoxide, hydrolyzing the resultant solution in the presence of ammonia to afford silica particles containing aluminum, dehydrating the silica particles by solid-liquid separation, further heating the silica particles to decarbonize the silica particles, sintering the decarbonized material to afford a synthetic quartz glass ingot, grinding, sieving, magnetically grading and purifying the synthetic quartz glass ingot containing aluminum to provide the synthetic quartz glass powder and melting the powder under ordinary pressure, pressure or vacuum. When the glass is produced, in the sintering step, the glass powder is once transferred to crystals of α-cristobalite and the crystals are melted and vitrified under vacuum or reduced pressure at 1800 to 1950 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing synthetic quartz glass, and more particularly to a method for producing synthetic quartz glass having a high temperature viscosity higher than that of an electromelted natural glass.

[0002]

2. Description of the Related Art As a conventional method for producing synthetic quartz glass, silica fine particles obtained by hydrolyzing a silicon compound such as silicon tetrachloride in a hydrogen flame are deposited on a carrier, which is directly melted and synthesized. A quartz glass is produced by a direct method (Japanese Patent Publication No. 3-31010), an ester silane such as methyltrimethoxysilane is used as the silicon compound, a porous glass base material is prepared, and this is fused to obtain synthetic quartz glass. , The so-called soot method (Japanese Patent Publication 4-20
No. 853), and a so-called plasma method in which a mixed gas of a silicon compound, oxygen and hydrogen chloride is reacted in a high frequency plasma flame to generate silicon dioxide, and the silicon dioxide is deposited on a carrier (Japanese Patent Publication No. Sho 63). -38343
Or an alkoxysilane is hydrolyzed in the presence of an acid or an ammonia catalyst to obtain silica fine particles,
There is a so-called sol-gel method in which the obtained silica fine particles are sintered to obtain synthetic quartz glass.

On the other hand, aluminum is an intermediate oxide for repairing a network structure split by an alkali metal (Na etc.) in synthetic quartz glass, that is, aluminum cannot form a continuous network structure by itself, but SiO It is thought that it exists as an oxide that fills the voids between the tetrahedra of ₄ and forms a continuous network structure under certain conditions.The presence of this aluminum strengthens the network structure and increases the high temperature viscosity. It is expected to improve. Aluminum-doped synthetic quartz glass utilizing the action of aluminum has been conventionally produced for the purpose of obtaining high temperature viscosity.

As a conventional method for producing aluminum-doped synthetic quartz glass, for example, an aluminum compound is added to a sol solution produced by hydrolyzing an alkyl silicate with a basic reagent, dried, and sintered to synthesize. After diffusing an aluminum alkoxide into a tubular silica porous body obtained by a method of obtaining quartz glass (Japanese Patent Laid-Open No. 63-123825) or by spin gelation of a sol solution containing silica fine particles as a main component, A method of drying and sintering to obtain a base material for an optical fiber (JP-A-62-100)
442) and other sol-gel synthesis methods are known.

[0005]

However, there are problems in the conventional method for producing synthetic quartz glass and the conventional method for producing aluminum-doped synthetic quartz glass.

[0006] For example, in the conventional method for producing synthetic quartz glass, the synthetic quartz glass obtained by the direct method is
The H group content is 200 to 1,000 ppm, the Cl group content is about 150 ppm at maximum, and the high temperature viscosity is low. The synthetic quartz glass obtained by the soot method also has a maximum OH group content of about 300 ppm and a maximum Cl group content of about 100 ppm, and since chlorine remains even after chlorine dehydration, sufficient high temperature viscosity is obtained. I can't get it.

In the synthetic quartz glass obtained by the plasma method, the content of OH groups is almost 0, but the content of Cl groups is about 1,000 ppm at the maximum, and the production cost is high, and mass production is difficult. Further, in the synthetic quartz glass obtained by the sol-gel method, the Cl group content is almost 0, but the OH group content is about 800 ppm at maximum,
When the acid catalyst is used, the OH group remains, and when the acid catalyst is hydrochloric acid, the Cl group remains, so that sufficient high temperature viscosity cannot be obtained.

On the other hand, in the method for producing aluminum-doped synthetic quartz glass, the synthetic quartz glass obtained by the sol-gel method has an OH group and therefore has a low viscosity at high temperature, and therefore is suitable for use in a heat-resistant synthetic quartz glass member. Is not suitable.

The present inventors obtained by hydrolyzing methyl silicate in the presence of ammonia to obtain aluminum-containing spherical silica particles, dehydrating, decarburizing and sintering them, and at this time doping alumina. A method has been proposed in which a glass body is crushed, sieved, purified, and then sintered with an oxyhydrogen flame to make it transparent to obtain high-viscosity quartz glass (Japanese Patent Publication No. 5-4156).
No. 5), this method is not sufficient in terms of aluminum content and viscosity uniformity.

Therefore, the present inventors further hydrolyzed a solution prepared by mixing and stirring methyl silicate and aluminum alkoxide in the presence of ammonia to obtain aluminum-containing spherical silica particles, which were dehydrated, decarburized, Also proposed is a method of sintering, crushing the obtained glass body, refining after sieving, and then melting to obtain a synthetic quartz glass member, wherein the content of aluminum is 0.1 to 1,000 ppm, and the obtained synthetic quartz is The result shows that the lower limit of high temperature viscosity of glass is equal to or higher than that of natural glass (Japanese Patent Application No. 6-182353). The present invention is a further development of this.

That is, the present invention solves the conventional problems, and an object thereof is to produce a synthetic quartz glass having high purity and high temperature viscosity which contains aluminum uniformly and hardly contains OH groups and Cl groups. To provide a method.

[0012]

In order to achieve the above object, a method for producing synthetic quartz glass according to claim 1 of the present invention is to prepare a solution obtained by mixing and stirring methyl silicate and aluminum alkoxide. , Hydrolyzing in the presence of ammonia to obtain aluminum-containing silica particles,
The solid-liquid separated and dehydrated silica particles are further heated to decarburize and then sintered to obtain a synthetic quartz glass ingot, and the aluminum-containing synthetic quartz glass ingot is crushed, sieved and magnetically separated. In the method for producing synthetic quartz glass by refining it to obtain synthetic quartz glass powder and melting it under normal pressure, pressure or vacuum, in the sintering step, after the crystal transition to α-cristobalite, It is characterized in that it is melted and vitrified at 1,800 to 1,950 ° C. under vacuum or reduced pressure.

The method for producing synthetic quartz glass according to claim 2 of the present invention is the method according to claim 1, which is amorphous and has a metal element content other than aluminum of 10 ppb or less. And the content of OH groups and Cl groups is 1 ppm or less, and the annealing point is 1,250.
It is characterized in that a synthetic quartz glass having a strain point of 1,140 ° C. or higher is obtained.

The present invention will be described in more detail below.

The aluminum alkoxide used in the present invention preferably exists as a liquid at ordinary temperature and pressure, has a relatively low hydrolysis temperature, and is close to the hydrolysis rate of methyl silicate.
c- butyrate _{(Al (sec-C 4 H} 9 O 3)) is most suitable. Then, this aluminum alkoxide is dropped into methyl silicate and uniformly mixed and stirred by a stirrer.

At this time, the fixing rate of aluminum in the added aluminum alkoxide was about 100% after vitrification, and the addition amount of aluminum alkoxide to methyl silicate and the content of aluminum in the synthetic quartz glass were determined. Are proportional to each other. Therefore, it is necessary to add an aluminum alkoxide according to the calculated Al content of SiO ₂ . (The obtained aluminum content has an error of less than 5% with respect to the calculated value.) The aluminum alkoxide needs to be measured in a dry atmosphere in a sealed container.

Here, the weight ratio of methyl silicate to aluminum alkoxide in the starting material and the aluminum content in the obtained synthetic quartz glass are shown as an example in the case where aluminum sec-butyrate is used as the aluminum alkoxide. Shown in.

[0018]

[Table 1]

Next, each step of the method of the present invention will be described in detail.

(Hydrolysis reaction) The hydrolysis reaction of methyl silicate and aluminum alkoxide, which are starting materials, is continuously carried out using, for example, a 5 liter reactor. 20 wt% ammonia water was continuously (150 cc / min) introduced into the reactor with respect to the starting material of 210 cc / min,
Hydrolysis is performed with stirring with a stirrer to obtain silica particles having an aluminum content of 500 to 5,000 ppm. The hydrolysis reaction formulas of methyl silicate and aluminum alkoxide are shown below. Si (OCH ₃ ) ₄ + 2H ₂ O → SiO ₂ + 4CH ₃ OH 2Al (C ₄ H ₉ O) ₃ + 3H ₂ O → Al ₂ O ₃ + 6C ₄ H ₉ O
H

(Dehydration) Next, the obtained aluminum particles containing aluminum are subjected to solid-liquid separation by a centrifugal separator or a press. The lower the water content of the obtained dehydrated powder, the lower the load on heating during decarburization in the next step, and therefore the lower the water content, the better. The current water content is about 30-40%.

(Decarburization) Decarburization is carried out by heating to 800 to 1200 ° C. in an atmosphere containing oxygen. More preferably, the temperature is 1,000 to 1,100 ° C. If the temperature is 800 ° C. or lower, oxidation is unlikely to occur, while if the temperature is 1,200 ° C. or higher, fusion between silica particles begins to occur, such being undesirable. Further, the atmosphere needs to be an atmosphere containing oxygen in order to oxidize the silica particles. In order to further accelerate the drying and the oxidation, it is preferable to ventilate a gas containing oxygen. The furnace used is not particularly limited, but a rotary kiln is preferable from the viewpoint of promoting drying and oxidation.

(Sintering) After decarburization, α-cristobalite is crystallized at 1,750 ° C. or lower to once crystallize. Then, it is melted and vitrified at a melting and vitrifying temperature of 1,800 ° C. or higher under vacuum or reduced pressure and then sintered. By once crystallizing and then sintering as described above, an amorphous substance close to a crystalline form is obtained.

In the crystal transition to α-cristobalite, aluminum becomes a crystal nucleus, and as the temperature gradually rises, the formation of the nucleus and the crystal growth proceed in sequence. At this time, a rapid temperature rise is not preferable for crystallization, and in the temperature range in which nuclei are formed (1,300 to 1,600 ° C) and the temperature range in which crystals are grown (1,600 to 1,800 ° C), respectively. It is desirable to keep the temperature once.

The atmosphere and temperature conditions for the molten vitrification differ depending on the required level of the synthetic quartz glass member, but the temperature conditions must be 1800 ° C. or higher. The molten vitrification temperature tends to increase as the aluminum content increases, and in the case of the aluminum content in the range of the present invention, it is 1,800.
It does not vitrify completely below ℃. In particular, in order to obtain a product containing no bubbles, under high vacuum of 10 ⁻² torr or more,
It is necessary to heat to 1,800 to 1,950 ° C. 1,
When it exceeds 950 ° C, sublimation becomes severe.

Next, a method of processing the obtained synthetic quartz glass ingot into synthetic quartz glass will be described.

(Crushing) The synthetic quartz glass ingot is crushed by using a jaw crusher, a hammer mill, a disc mill, a ball mill or the like.

(Sieving) The crushed particles are sieved to a particle size suitable for the intended use. For example, 200 to 35 for crucibles
About 0 μm is preferable.

(Purification) Purification is carried out for the purpose of removing contamination during pulverization and is selected from washing with water, HF treatment, hydrochloric acid treatment, magnetic separation, flotation and the like. If the degree of contamination is low, purification can be omitted.

(Melting) The obtained synthetic quartz glass powder is subjected to 1,500 to 1,950 in an atmosphere of an inert gas (Ar, N ₂ etc.) under normal pressure, reduced pressure, pressurization or air flow. Melts at a temperature of ° C. The melting atmosphere can be under vacuum, but it may be restricted by work, so it is selected according to the required application. If the melting temperature is less than 1,500 ° C., quartz will not melt. Further, at 1,950 ° C. or higher, quartz sublimes, resulting in poor yield. 1, depending on particle size
Since some of them do not melt at 750 ° C, more preferably 1750 to 1,900 ° C.

The synthetic quartz glass thus obtained is an amorphous substance close to the crystalline type. Also, it contains aluminum uniformly, and the content rate of aluminum is 5
The range is from 00 to 5,000 ppm. Furthermore, the content of OH groups and Cl groups is less than 1 ppm, the slow cooling point, which is an index of high temperature viscosity, exceeds 1,250 ° C, and the strain point also exceeds 1,140 ° C. It has the same or better characteristics as electromelted products.

[0032]

According to the method for producing synthetic quartz glass of the present invention,
In the melting and vitrifying step, the crystals are once transformed into Tα-cristobalite and then melted and vitrified to be amorphous, so that the obtained synthetic quartz glass has an amorphous structure close to the crystalline form. Further, the content rate of aluminum can be easily controlled, aluminum having a content rate of 500 to 5,000 ppm is uniformly distributed, and substantially no OH group and Cl group are contained. As a result, a high-purity high-temperature viscous synthetic quartz glass having a high-temperature viscosity higher than that of a conventional electric fused product of natural quartz glass can be obtained.

[0033]

EXAMPLES Hereinafter, the production of a synthetic quartz glass crucible will be described as an example, and the synthetic quartz glass production method of the present invention will be described in more detail based on preferred examples and comparative examples. It is not limited to.

(Example 1) 100 kg of methyl silicate
On the other hand, 180 g of aluminum sec-butyrate was dropped, and the mixture was stirred and mixed for 5 minutes. This was used as the starting material for the reaction. Then, in a 5 liter reactor containing 3 liters of 20 wt% ammonia,
The solution was continuously added dropwise at a dropping rate of cc / min and hydrolyzed at 40 to 50 ° C to continuously obtain a reaction solution.

When this reaction solution was filter-pressed, spherical silica particles 40k having a particle size of 200 to 700 nm were obtained.
g (water content 35%) was obtained.

Next, the obtained spherical silica particles were placed in a quartz container and kept in the presence of clean air at a temperature of 1,000 ° C. to 1 ° C.
When the temperature was raised over 0 hour and the temperature was maintained for 1 hour for dehydration and decarburization, the weight was 34 kg.

An internal volume of 0.1 m ³ (50 cm × 50
(cm x 40 cm) packed in a carbon case 10 ^-2 torr
Under vacuum at 1,200 ° C for 1 hour at 1,500
Sintering was performed by holding at 1 ° C. for 1 hour and at 1,800 ° C. for 1 hour. As a result, it is transparent in appearance and has a height of 6c at about 50 cm square.
32 kg of synthetic quartz glass ingot of m was obtained.

Next, this synthetic quartz glass ingot was crushed by a conical ball mill (made of iron) and further 45-60.
It was sieved to # and then magnetically separated. Furthermore, 2
After soaking in 0 wt% hydrochloric acid for 5 hours, 1 wt% in 10 wt% HF
It was immersed for 0 minutes, washed with water and purified to obtain synthetic quartz glass powder.

Using the obtained synthetic quartz glass powder, the synthetic quartz glass powder is heated and melted by an arc rotation method,
An 18 ″ synthetic quartz glass crucible was obtained. The obtained crucible pieces were measured for purity, viscosity, OH group and Cl group content, and high temperature viscosity (strain point, annealing point). The results shown were obtained.

(Example 2) Aluminum se in the starting material
Example 1 except that the amount of c-butyrate was 359.7 g.
An 18 ″ synthetic quartz glass crucible was obtained by performing the same treatment as described above. The obtained crucible pieces were evaluated for purity, viscosity, OH group and Cl group content, and high temperature viscosity (strain point, annealing point). Upon measurement, the results shown in Table 2 were obtained.

(Example 3) Aluminum se in the starting material
The same treatment as in Example 1 was performed except that the amount of c-butyrate was changed to 1798.5 g to obtain an 18 ″ synthetic quartz glass crucible. The obtained crucible pieces had purity, viscosity, and OH.
When the contents of groups and Cl groups and the high temperature viscosity (strain point, annealing point) were measured, the results shown in Table 2 were obtained.

(Comparative Example 1) Aluminum se in the starting material
The same treatment as in Example 1 was carried out except that c-butyrate was changed to 18.0 g to obtain an 18 ″ synthetic quartz glass crucible. The obtained crucible pieces were evaluated for purity, viscosity, OH group and Cl group. When the content and the high temperature viscosity (strain point, annealing point) were measured, the results shown in Table 2 were obtained.

(Comparative Example 2) 100 kg of methyl silicate
The same mixture as in Example 1 was used as the starting material except that aluminum sec-butyrate was not added to the starting material, and the same treatment as in Example 1 was performed except for the above, to obtain an 18 ″ synthetic quartz glass crucible. , Purity, viscosity, OH
When the contents of groups and Cl groups and the high temperature viscosity (strain point, annealing point) were measured, the results shown in Table 2 were obtained.

Comparative Example 3 Using conventional electric fused natural quartz glass powder, synthetic quartz glass powder was heated and melted by the arc melting method to obtain an 18 ″ synthetic quartz glass crucible. The pieces were measured for purity, viscosity, OH group and Cl group content, and high temperature viscosity (strain point, slow cooling point), and the results shown in Table 2 were obtained.

[0045]

[Table 2]

The synthetic quartz glass crucible pieces shown in Table 2 were measured for purity, content of OH groups and Cl groups, and high temperature viscosity (strain point, annealing point) by the following methods.

[Purity] Trace elements were quantified using a MIP-MS elemental analyzer (P-7000 model manufactured by Hitachi, Ltd.).

[OH group content] Using an IR (infrared) measuring instrument (IR-Spectrophotometer, Type A-3, manufactured by JASCO Corporation), it was roughly estimated by the peak height of 2.7 μm, which is the OH group absorption wavelength.

[Cl group content] Reactor IRIGA-II
Type (installed by Rikkyo University), neutrons were made to collide with the sample to cause a nuclear reaction, and γ-rays were detected by a high-purity Ge detector and a multichannel wave height analyzer to determine the Cl group content.

[High temperature viscosity (strain point, slow cooling point)] Strain point,
The annealing point is a typical thermal property and a physical property that is an index of high temperature viscosity (Asakura Shoten "Glass Handbook").
(See page 637). The strain point is shown as the temperature when the viscosity is 4 × 10 ¹⁴ poise (log η = 14.5), and the annealing point is
The temperature is shown when the viscosity is 4 × 10 ¹³ poise (log η = 13.0). In the narrow temperature range, the plot of log η with respect to the reciprocal of the absolute temperature has a linear relationship.
℃, 1,150 ℃, 1,200 ℃, 1,250 ℃, 1,
The elongation amount ΔL was measured at 300 ° C. (Fi
(by the ber-elongation method), each η was obtained, and in the figure, the vertical axis: log η, the horizontal axis: the reciprocal of absolute temperature were plotted to obtain a straight line. From the obtained straight line, the temperature corresponding to log η = 14.5 was determined as the strain point, and the temperature corresponding to log η = 13.0 was determined as the annealing point.

[Fiber-elongation method] 4 mm × 2 mm
A sample of × 40 mm is heated and Δt = 120 to 3,000.
ΔL (cm) of the sample in seconds was obtained, and the viscosity was obtained using the following formula. Here, W = 500, A = 0.4, B = 0.2, L =
4.0 ΔL = extension amount, Δt = measurement time

[0052]

EFFECT OF THE INVENTION According to the method for producing synthetic quartz glass of the present invention, in the melting and vitrifying step, the crystal is once transformed into α-cristobalite, and then it is melted to be vitrified into an amorphous material. Quartz glass has an amorphous substance close to the crystalline form. Further, the content rate of aluminum can be easily controlled, aluminum having a content rate of 500 to 5,000 ppm is uniformly distributed, and substantially no OH group and Cl group are contained. As a result, a high-purity synthetic quartz glass having a viscosity at a temperature higher than that of a conventional electric fused product of natural quartz glass can be obtained. Further, according to the present invention, such a high-purity synthetic quartz glass having high-temperature viscosity can be easily obtained by existing equipment, and a heat-resistant jig material, a high-purity semiconductor jig material, or a semiconductor crucible can be obtained. Can be suitably used as.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayuki Suzuki Masayuki Suzuki, 28, Nishi-Fukushima, Kubiki-mura, Nakakubiki-gun, Niigata Prefecture 1 Shin-Etsu Chemical Co., Ltd.

Claims (2)

[Claims] 1. A solution obtained by mixing and stirring methyl silicate and an aluminum alkoxide is hydrolyzed in the presence of ammonia to obtain silica particles containing aluminum, which are solid-liquid separated and dehydrated. After the silica particles were further heated to decarburize and then sintered to obtain a synthetic quartz glass ingot, the aluminum-containing synthetic quartz glass ingot was crushed, sieved, magnetically separated, and purified to obtain synthetic quartz glass powder. In the method for producing synthetic quartz glass by melting it under normal pressure, pressure or vacuum, in the above-mentioned sintering step, the crystal transition is once made into α-cristobalite, and then 1,800 under vacuum or reduced pressure. A method for producing synthetic quartz glass, which comprises melting and vitrifying at 1,950C. 2. A non-crystalline material close to a crystalline form, having a metal element content other than aluminum of 10 ppb or less, an OH group and Cl group content of 1 ppm or less, and an annealing point of 1,250. The method for producing synthetic quartz glass according to claim 1, wherein a synthetic quartz glass having a strain point of 1,400 ° C. or higher is obtained.