JPS61186232A - Production of tubular quartz glass - Google Patents

Abstract

PURPOSE:To obtain the titled inexpensive and high-quality glass having high dimensional accuracy and purity, by gelatinizing a raw material consisting of a hydrolyzed solution of an alkyl silicate with an acidic catalyst and a hydrolyzed solution of it with a basic catalyst, drying and sintering it. CONSTITUTION:(a) An alkyl silicate such as ethyl silicate, etc. is hydrolyzed with (b) an acidic catalyst to give the solution A, the component a is hydrolyzed with (c) a basic catalyst to give the solution B containing silica fine particles having 0.01-1.0mu average particle diameter, which is concentrated to give 15-1.0g/cc silica concentration to prepare the concentrated solution B, pH of one or both of the solutions is adjusted to 3-6, and the solution A is blended with the solution B in a blending ratio of silica in the A solution/silica in the solution B=0.2-3 (molar ratio), to give raw material sol. It is put in a cylindrical container, gelatinized at 5-60 deg.C while rotating at the maximum centrifugal gravity of 1,000G to give wet gel, which is heated to 40-160 deg.C at <=120 deg.C/hr rate of heating, contracted and dried to give dry gel, which is sintered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing tubular quartz glass by a sol-gel method using an alkyl silicate as a raw material.

[Prior art]

Since quartz glass can now be manufactured with high purity, it has recently been used for crucibles and boats used in the manufacture of semiconductors, as well as furnace core tubes for diffusion furnaces, and its usefulness has been recognized. Also. It is also used for glass instruments such as beakers for physics and chemistry, cells for optical measurement, etc.
Applications to substrates for PT (thin film transistors) are also attracting attention, and demand is expected to further increase in the future.

In this way, 5 quartz glass can be used in a wide variety of fields.
The manufacturing method, quality, and shape vary depending on the purpose of use. Recently, optical fibers made mainly of quartz glass have been used as optical transmission media in optical communications aimed at high-capacity transmission. When manufacturing a base material for this optical fiber, tubular quartz glass is required as a starting material or for adjusting the outer diameter. The tubular quartz glass used at this time is required not only to have high dimensional accuracy but also to be of high quality. That's no good.

The extremely high price of optical fiber is a major bottleneck in reducing the cost of optical fiber.

Currently, commercially available tubular quartz glass is mainly manufactured using the following three methods.

l) A method of cleaning natural quartz and melting it.

2) S? using high purity s 6 CA4 or sea as raw material? : How to make O.

8) Method of melting natural silica sand.

Products made by method 8 cannot be used for optical communication due to their purity, but in any case, processing at high temperatures is required, and the characteristics of these production methods are that they are difficult to produce tubular quartz glass with high circularity. is extremely difficult.

Recently, attempts have been made to manufacture tubular quartz glass for optical fibers using the sol-gel method. The advantages of the sol-gel method include that it is easy to purify the metal alkoxide raw material, resulting in highly pure quartz glass, and that transparent quartz glass can be obtained below the transition point, resulting in low manufacturing costs. It will be done.

However, in the general sol-gel method.

The drawback was that it was difficult to obtain large-sized ones.

Raunovich et al. gelled a hydrosil solution in which ultrafine powdered silica was suspended in water in a cylindrical container with a central rod, then pulled out the central rod to form a tubular gel, which was then dried and sintered to reduce the inner diameter. 1.7 crn, outer diameter 2.
A relatively large tubular quartz glass with 8 sides and a length of 25 cm was obtained. This method is thought to be less likely to cause cracks or cracks because large pores are created in the dry gel.

In addition, in our patent (Organization A 20672, method for manufacturing tubular quartz glass), a sol solution in which ultrafine powder silica is suspended in a hydrolyzed solution of alkyl silicate using an acidic axial medium is used as a raw material, and the sol solution is rotated in a 5-cylindrical container. A tubular gel is formed by gelling while drying, and by drying and sintering it, the maximum outer diameter is 2.6tY, inner diameter is 1.6on, and length is 52mm.
The tubular quartz glass of (1) is obtained.

With this method, larger pores can be obtained because the dry gel has large pores and the bonding force between fine silica particles is stronger than in the previous method. In addition, since gelation is performed while rotating, a larger gel can be produced than in the previous method, and the roundness is also high.

[Problem that the invention seeks to solve]

By the way, both of the above inventions include a step of dispersing finely powdered silica in a liquid phase. Methods for dispersing powder in liquid include stirring and application of ultrasonic waves, but in any case, it takes a tremendous amount of energy and a long time to obtain a homogeneous dispersion, but it is completely homogeneous. It is difficult to form a dispersion liquid that is suitable for use, and for example, residual lumps become defects in the final glass and deteriorate the quality.Furthermore, general commercially available fine powder silica contains impurities such as
It contains several ppm to several hundred ppm of Ai, Fg, etc., and is not preferable as a raw material for optical glass as in the present invention.

The present invention solves the above problems, and its purpose is to achieve high quality by preparing a high-purity sol with good dispersibility in the sol-gel method using alkyl silica as a raw material. An object of the present invention is to provide a method for manufacturing tubular quartz glass.

[Means for solving problems]

In the method for producing tubular quartz glass in the present invention, firstly, a hydrolysis solution of an alkyl silicate using an acidic catalyst (Liquid A) and a hydrolysis solution of an alkyl silicate using a basic catalyst (Liquid B) are prepared.
Prepare liquid). In the hydrolysis of alkyl silicate, the powder particle size is completely different depending on the catalyst used.

In particular, when a basic catalyst is used, silica particles larger than those using an acidic catalyst can be synthesized to any size depending on conditions such as the amount of catalyst, the amount of alkyl silicate relative to the solvent, the amount of water, and the temperature. By the way, in order to obtain large-sized dry gel and ultimately quartz glass, it is essential that the dry gel contains large pores, but (B) relatively large particles in the liquid play this role, and (A ) The small particles in the liquid are thought to have the effect of strengthening the bonding force between the silica particles in the liquid.

The silica particle size of the liquid (under these conditions) is 0.01μ
If it is less than m, there is no meaning, whereas if it is too large, sedimentation will occur, which is disadvantageous when preparing a uniform sol solution. In particular, in the present invention, since the raw material sol is gelled while being rotated, considering the action of centrifugal gravity, the maximum diameter of the silica particles is 1°0 μm.

As described above, in the present invention, liquids (A) and (B) are synthesized in a liquid phase and are mixed together to form a raw material sol, so a special dispersion process is not necessary. Furthermore, since the raw material reagents used can be easily purified, products with high purity can be obtained.

Now, although it depends on the synthesis conditions in solution (B), the silica concentration is generally very low.This means that unless the amount of solvent relative to the alkyl silicate during synthesis is increased to a certain extent, the silica will not have a uniform particle size distribution. This is due to the inability to synthesize particles. In order to produce a dry gel with good yield, it is better to have a high silica concentration in the sol, but if it is too high, dispersibility deteriorates and quality deteriorates.

Therefore, it is necessary to concentrate the liquid (B), but due to the above constraints, the range is 0, 1517/CC-1, Oy
/cc is desirable.

Furthermore, the properties of the produced dry gel vary greatly depending on the mixing ratio of liquid (A) and liquid (B). As previously mentioned,(
A) As the proportion of liquid increases, the pores contained become smaller, making cracking and foaming more likely to occur. (B) When the proportion of liquid increases, the pores themselves become larger, but disadvantageous phenomena such as a decrease in the strength of the dry gel itself and an increase in the sintering temperature occur. Based on this, the mixing ratio of liquids (A) and (B) is s(o, the molar amount contained in each liquid is M (A)
, M), then M (A) )' M(B)=
A range of 0.2 to 8 is a necessary condition for obtaining large and high quality quartz glass.

The silica sol of the present invention has a high P content in its gelation time.
H-dependent. Normally, the gelation time is shortest around pH 13, and it gels instantly, but if the pH is below 9, it will remain stable for a long time. - Neutralization of the base occurs and the pH value of the mixed sol becomes just about 6, which immediately turns into a gel, which is disadvantageous in subsequent operations. Therefore, it is necessary to adjust the pH of the two liquids in advance before mixing them so that the pH value of the sol liquid after mixing becomes a desired value. The methods are: ■ (A) Lower the PR of the liquid ■ (B) Lower the PH of the liquid ■ (A) and CB) Lower the PH of both liquids by more than 8
Law is considered. No matter which method is used, there is no difference in the subsequent sol state or final quality.

It is also possible to perform final pH adjustment by adding aqueous ammonia, hydrochloric acid, etc. to the sol solution after mixing.

FIG. 1 shows a diagram of an apparatus for producing a cylindrical gel.

As a method, the sol solution after the PHpl adjustment is poured into a cylindrical container, placed in a two-rotation device, and gelled while being rotated. By such rotational gelation, a cylindrical gel with high roundness can be obtained.

Explaining the rotation conditions for gelling while rotating.As explained earlier, the raw material in the one-piece production method contains fine silica particles with a size of 0.01 to 1.01 tm, so it is centrifuged with 5 rotations. The force causes the particulate silica to settle, causing non-uniformity in the composition of the sol and eventually the gel. Such non-uniformity in the composition of the gel not only causes cracks during drying or sintering, but also has a negative impact on the optical properties. The rotation time must be controlled within a range that does not cause sedimentation of the fine silica particles in the raw material sol. The controlling factors for the precipitation of particulate silica are the number of rotations during rotational gelation, the rotation time, and the composition of the raw sol, assuming that the size of the target tubular quartz glass is constant. The time for five rotations of the gel is uniquely determined by the balance between the above-mentioned gel heating time and the yield of dry gel, and the raw material sol composition is optimized in relation to the subsequent sintering conditions. For this reason, the sedimentation of particulate silica must be controlled mainly by the rotational speed. cannot be determined because it depends on the particle size of the particulate silica and the distance from the central axis in the cylindrical rotating container, but for example, using a particulate silica sound of about 500x, 5
In the case of a rotating container with a size of crnφ, if the particulate silica in the outermost part of the container is subjected to centrifugal gravity of 500 G for 80 minutes or more, a severe sedimentation phenomenon will occur.In addition, if the raw material is a sol solution that does not contain particulate silica. However, if centrifugal gravity of 100OG or more is applied, cracks will occur during gelation.

From this, the number of rotations during 5-turn gelation must be selected within a range in which the centrifugal gravity exerted on the raw sol solution does not exceed 1000 ().

When producing a large dry gel, the yield will be poor if the container and drying conditions are not appropriate.

Therefore, a container and drying conditions that can improve the yield will be explained.

The drying process to turn wet gel into dry gel is the most important process that affects the yield, but in order for wet gel to shrink without cracking, it is necessary that drying proceed uniformly inside the wet gel. To achieve this, it is best to dry as slowly as possible, but after considering productivity and other factors, we decided to increase the temperature at a rate of 120°C/h with an open area ratio of 10% or less.
If the temperature is raised to a temperature of 40 to 160° C. below r and dried at a temperature within that temperature range, the dry gel can be completely formed in a relatively short period of time with a good yield. At that time, it is a good method to obtain a dry gel with a good yield and discharge rate with relatively little effort, by drying the gelled cylindrical rotating container with a lid having the above opening ratio. If a method is used in which the gel is transferred to a container with a container and dried therein, a dry gel can be obtained with a higher yield. In this case, a method of transferring a plurality of wet gels to the container and drying them therein is desirable as a method that increases productivity without affecting the yield.

In the method for manufacturing tubular quartz glass of the present invention, the step of sintering the dry gel consists of the following seven steps.

It is certainly possible to omit 4') (5).

When using tubular quartz glass for optical fibers as a cladding material, the amount of OH groups should be at least 1 pp.
It must be less than or equal to m. In such a case, of course, (
4) De-OH treatment by salt accumulation etc., accompanied by (5)
It becomes necessary to carry out cumulative desalination treatment, etc. However, for jacket tubes used for adjusting the outer diameter of optical fibers, even if the amount of OH groups is several hundred ppm, it has almost no effect. As described above, since the quality required varies depending on the application, the processes in (4) and (5) are not necessarily necessary.

1) Process of desorption water treatment 2) Process of decarbonization 8) Process of promoting dehydration condensation reaction 4) Process of removing OH group 5) Process of dechlorination or defluorination 6 ) Step of pore-closing treatment 7) Step of transparent vitrification treatment The step of treating desorbed water in (1) has the greatest effect on the yield in the sintering process, but the physical adsorption of a large amount into the dry gel Targetally adsorbed water can be removed by heat treatment at approximately 400°C. However, if the temperature is raised rapidly at this time, cracks tend to occur and the yield decreases. However, if the temperature increase rate is too low, the processing takes too much time and increases manufacturing costs. As a result of detailed investigation, the upper limit of desorption water treatment without decreasing the yield is approximately 400℃/h.
r, and it is desirable to hold the temperature at a predetermined temperature up to 400°C for at least one hour at least once.This is because holding the temperature at a predetermined temperature for at least one hour allows for more uniform desorption within the gel. This is because it creates a condition in which the adsorbed water reaction occurs, which helps improve yield.

In the step (2) of decarbonizing, the decarbonizing treatment is performed by heat treatment in the range of 400 to 900°C.

At this time, the ammonia and acid salts (ammonium salts) present inside the gel can also be removed. Furthermore, as in the case of desorption water treatment, the temperature increase rate affects the yield, but a temperature increase rate of 80 to 20 b/hr is practical. When carrying out the one-shot process, the presence of 02 gas is required in the atmosphere.

(8) In the step of promoting the dehydration condensation reaction,
The dehydration condensation reaction is accelerated at a heating rate of 80 to 400°C/
The purpose of this single process, which involves raising the temperature to a predetermined temperature within the range of 900 to 1200°C for hr and holding it at that temperature for 30 minutes or more at least once, is to promote the dehydration condensation reaction inside the gel. Let me.

If you proceed to the next step without going through the nine steps to reduce unreacted OH groups, a large amount of OH removal base will be consumed during the OH removal treatment, which will cause the transparent glass to deteriorate. Although the rate of temperature rise affects the yield in the three-step process in which foaming is often performed during the chemical treatment, the above range is practical.

The purpose of the OH group removal process (4) is to remove OH groups that have a particularly serious effect on the transmission loss of the optical fiber. In this step, a carrier gas such as He that does not contain moisture or other impurities and an OH removing base with a flow rate ratio of 1 to 40q6 to the carrier gas are fed into a sintering furnace while heating at a temperature of 700 to 1100°C. By heating at a certain temperature. In order to completely remove the OH groups, it is necessary to make the ratio of the OH removing base to the carrier gas at least 1%, but it is preferably in the range of 1 to 40%. The deOH base is (35(-
oH) to react with (yo57-cl) or (3Ei-
Reagents such as F) are selected, but for reasons such as economic efficiency and ease of handling, C121SOCl, SF6, CF
4 IC2II'6. C3F Hatake is practical.

The purpose of the dechlorination or defluorination treatment in (5) is to remove chlorine or fluorine present in the gel after the previous OH group removal treatment. If the sintering process is carried out, foaming tends to occur due to chlorine or fluorine remaining in the glass when processing the transparent glass or drawing it to make an optical fiber. The dechlorination treatment or the defluorination treatment is carried out at a temperature range of 800 to 1200° C. while feeding 02 in a range of 1 to 100q6 into a sintering furnace with respect to a carrier gas such as He.

The pore closing f ratio treatment (6) is performed by making the furnace a vacuum or raising the temperature while feeding He gas into the furnace. Atmospheric gases are trapped in the glass, and bubbling phenomenon tends to occur during transparent glass ratio processing, and the temperature increase rate affects the yield, but it is suitable for 80~b. What is the temperature at which closed pores form in glass?

When preparing the sol, (A) the mixing ratio of the liquid (with the liquid), the silica concentration in the sol, (B) the average particle size of the silica in the liquid, (B)
) It is necessary to investigate in advance the sample to be subjected to the pore-closing f-ratio treatment because it varies depending on the particle size distribution of silica in liquid, pore size distribution in gel, water content in gel, temperature increase speed, etc. In the examples of the present invention, the temperature was in the range of 900 to 1350°C.

After performing the pore-closing treatment, the temperature is raised to a predetermined temperature in the range of 1,200 to 1,600° C., and held at that temperature for a predetermined period of time to perform the transparent vitrification treatment described above, thereby obtaining tubular quartz glass.

In the method for manufacturing tubular quartz glass of the present invention.

The optimal temperature program for each sintering condition is the mixing ratio of (A) liquid and (B) liquid when adjusting the sol, the silica concentration in the sol, (B) the average particle size of silica in I, (B) It varies depending on the particle size distribution of the silica in liquid, the pore size distribution in the gel, the water content in the gel, etc., and is selected from the above-mentioned temperature range and heating speed.

By the above operations, a high-quality tubular quartz glass having a sufficient size can be manufactured with a high yield.The present invention will be explained in detail based on the following examples.

[Example 1] ■ (A) Preparation of liquid 'f'74 'M Commercially available ethyl silicate 579
200 f of 0.02N hydrochloric acid was added to °Ov, and the mixture was vigorously stirred to hydrolyze it to obtain liquid (A).

■ Preparation of liquid (B) Purified commercially available ethyl silica) 864.9 f, absolute ethanol 2187 f, ammonia water (29%) 7
The mixture was mixed with 800 f of water, stirred for 2 hours, and then left in the apparatus overnight to obtain liquid (B). When the particle size was measured using a particle size distribution meter, the average particle size was 0.15 μm.

(2) Concentration step of liquid (B) The liquid (B) prepared in (2) was concentrated under reduced pressure. The concentration of silica contained in the stock solution was 0.069, but this was concentrated under reduced pressure to 0.401A.

(2) PH adjustment before mixing After concentration, the pH value of solution (B) was 8.80, and that of solution (A) was 2.10. (using 2N hydrochloric acid) solution P
The H value was lowered to 5.0. At this time, 5 for particle size distribution measurement -
When the particle size was measured using ζ filtration, there was no change compared to step ⑶.

(2) 650 mA of liquid (A) obtained in mixing step (2) and 620 mA of liquid (B) obtained in step (2) were mixed. At this time, the silica amount ratio M (A) / M (B) from each is 0
．． It is 67.

The pH value of the liquid mixture was 4.80.

■ Rotational gelling Figure 1 shows a diagram of the apparatus for rotating gelling. 1256 m of raw sol liquid obtained in step ①, #total inner diameter 5 minor φ, length 1.0
It was poured into an Oo7+ vinyl chloride lined steel pipe.

After sealing with silicone rubber.

It was attached to a rotating device. The sample was rotated at a rotational speed of 70 rpm until the monitor sample resembled a gel.

The time required for gel ratio was 65 minutes. The dimensions of the wet gel were an outer diameter of 5 cm, an inner diameter of 8 cm, and a length of 98 cm.

■ After leaving the 10 wet gels obtained in the drying process ■ in a rotating container for 2 days, they were placed in a stainless steel box-shaped container (vertical: 15 cm, horizontal: 120 cm, sub-height: 20 cm) with a lid of 1% opening ratio.
on), and heated to room temperature (25℃) at a heating rate of 2℃/h.
) to 70℃ and held at this temperature for 12 days, a stable dry gel (
Outer diameter 8.8 Secondary inner diameter 2. Ocpn length 640) was obtained.

Next, this dry gel was placed in a quartz tubular sintering furnace and heated from 80°C to 200°C at a heating rate of 80°C/hr, held at this temperature for 5 hours, and then heated at a heating rate of 80°C/hr.
from 200℃ to aOO″C, and at this temperature 5
I held it for a while and did all the water inhalations. Next, heating rate 8
Heating from 800°C to 1100°C at 0°C/hr,
This temperature was maintained for 80 minutes to perform decarbonization, dechlorination ammonium treatment, and acceleration treatment of dehydration condensation reaction. Subsequently, the temperature was lowered to 700℃ and He 2 A / min r C
Hold for 80 minutes while flowing a mixed gas of 12O, 21 r/min, then increase the temperature to 60°C without flowing only He.
Heated at 800'C-E/hr. H at 800℃
e 21Vmin, Cl2O,2,4/? 7tin
The mixture was maintained for 1 hour while flowing a mixed gas of 1 to 1, and then heated to 900°C at a temperature increase rate of 60°C/hr without flowing only He. He 21e/min, Cl2O at 900℃
. 2. Hold for 1 hour while flowing a mixed gas of θ,
OH group removal treatment was performed. Next, to He2/mi
oao for n, 4. The mixture was heated to 1050''C at a heating rate of 60°C/hr without flowing a mixed gas of θ'rrbtn, and was held at this temperature for 1 hour to perform dechlorination treatment.

Next, without flowing only He, the temperature increase rate was 30℃/h.
r te1250 ”C't t'7)O heat, ?C(7
) A pore-closing treatment was carried out by holding the sample at a temperature of 30 minutes. Next, all the samples were transferred to a box-type furnace, and the heating rate was 60°C from 1200°C.
"When heated to 1350°C with C7hγ and held at this temperature for 1 hour, it becomes non-porous and becomes transparent tubular quartz glass (outer diameter 2.
There were no cracks in the sintering process, and the yield was 100%.

When the amount of OH groups contained in this tubular quartz glass was measured by infrared absorption spectrum, no absorption peak at h2-70 Am was observed, and it was confirmed that the amount was 1 ppm or less.

In addition, the dimensional accuracy is within ±1% of the inner and outer diameter tolerance, and there are no inclusions or foreign substances.
It was found that the product did not foam when heated to ℃ and was brought into a molten state, so it could be used as a tubular quartz glass for manufacturing optical fibers.

Furthermore, the following sintering was performed using the same dry gel. Placed in a quartz tubular sintering furnace and heated at a heating rate of 30°C/h.
r from 30°C to 200°C, held at this temperature for 5 hours, and then heated at a heating rate of 3 (200°C at 1'C/hr).
The mixture was heated from .degree. C. to 800.degree. C. and kept at this temperature for 5 hours to completely remove the adsorbed water. Next, the temperature increase rate is 30℃/h
r Heat from 800'C to 1000'C and hold at this temperature for a period of time to decarbonize.

Desalination f-hyammonium treatment and dehydration condensation reaction acceleration treatment were performed. Further, the temperature was increased to 1100°C at 60°C/hr and held immediately, and the temperature was increased to 1150°C at 60°C/hr and held for 20 hours to promote the dehydration condensation reaction in an open pore state as much as possible. The quantity was reduced. Subsequently, the tube was heated to 1250° C. at a heating rate of 30° C./hr while flowing at He f 2 Z/min, and held at this Im degree for 1 hour to perform hole-closing f-ratio treatment.

Subsequently, the sample was transferred to a box furnace and heated from 1250°C to 1350°C at a heating rate of 60°C/hr, and when held at this temperature for 1 hour, it became a transparent tubular quartz glass with no pores. When the amount of OH groups was measured, it was found to be 4° Oppm, but no foaming occurred even when heated to 2000° C. in a molten state using a ring heater.

In this way, sufficient tubular quartz glass can be produced to be used as a jacket tube for adjusting the outer diameter during optical fiber manufacturing, even without OH group removal treatment using chlorine, etc., and accompanying dechlorination treatment. Obtained.

[Example 2] Step (2) in Example 1 was changed as follows.

Anhydrous ethanol 2 to purified ethyl silicate 468f
δOOmA, ammonia water (29%) 250m! , water 1
After mixing 65f and stirring for 2 hours, the particle size was measured using a particle size distribution analyzer that was installed overnight, and the average particle size was 0.84.
It was μm. In addition, when the particle size of the silica particles that had settled at the bottom of the container once left still was measured, all of them were larger than IAm. From this, it was found that the inclusion of silica particles with a temperature of 11° C.m or more in the sol is disadvantageous in obtaining a uniform dispersion.

The drying process was performed in exactly the same manner as in Example νu1.

The bulk density of the dry gel is 0, 86 t/1wr"
This was considerably smaller than 1.0817 cm'' in Example 1.

○ When sintering was performed with only He treatment without chlorine treatment in Sintering Example 1, and the OH base needle was measured, 2
50 ppmT! there were. From this, Honjitsu 2II!
As in example 8, (B)′g! It has been found that dehydration during the sintering process is promoted by increasing the silica particle size of i.

Furthermore, by performing chlorine treatment in the same manner as in Example 1, the water content could be reduced to less than 1 pprn, and a high quality tubular quartz glass was obtained.

[Example 8] (6) When preparing the liquid, hydrolysis was performed in the same manner as in Example 1 using 1N nitric acid.

The adjustment and concentration of liquid (B) was carried out in the same manner as in Example 1.

After concentration, the pH of solution (B) was adjusted to 4.0 with 2N ammonia water.
After adjusting the pH to 0, the mixed sol was mixed with liquid (A), and the pH of the mixed sol was 8.2. An -added sol with such a low pH value will not gel even after several days if left at room temperature.

Then, by dropping 0.2N ammonia water,
The PFI' was adjusted to 4.90 and used as a raw material sol.

A rotating gel was heated in the same manner as in Example 1, but in this embodiment, the rotation speed was set to kl 000 rpm.

The wet gel was dried in the same manner as in Example 1 to obtain a dry gel.

Next, this dry gel was placed in a quartz tubular sintering furnace and heated from 80'C to 200'ct at a heating rate of 80°C/hr, held at this temperature for 5 hours, and then heated at a heating rate of 80°C/hr.
h? - and heated from 2oooC to aoo'c and held at this temperature for 5 hours to completely remove the adsorbed water. Subsequently, the material was heated from aoo'c to 1000° C. at a temperature increase rate of 80° C./hr, and held at this temperature for 60 minutes to perform decarbonization, dechlorination ammonium treatment, and acceleration treatment of dehydration condensation reaction. Subsequently, the temperature was lowered to 800℃ and He 2A/min, C1
Hold for 80 minutes while flowing a mixed gas of 20.2 A/min, then increase the temperature to 60°C without flowing only He.
/hr and heated at 900°C-h. He2 at 900℃
7/min, C120, 2It/'qnz n mixed gas? Hold for 1 hour while flowing, then Ozo for He 21/min, 4! The reactor was heated to 1050° C. at a temperature increase rate of 60° C./hr without flowing a mixed gas of 300° C., and was held at this temperature for 1 hour to perform a desalination treatment. Next, without flowing only He, the heating rate was 80℃/
Heat to 1250°C at hr.

This temperature was maintained for 80 minutes to perform pore-closing ratio treatment.

Next, the sample was transferred to a box furnace and heated at a rate of 6 from 1200℃.
Heated in a trench at 1350°C at 0°C/hr, and at a temperature of 1
After holding for a period of time, a transparent tubular quartz glass with no pores was obtained. The amount of OH groups contained in this is 10 at the center of the glass body.
Although about ppm was detected, no foaming occurred even in the molten state.

[Example 4] After preparing solutions (A) and (B) in the same manner as in Example 1, experiments were conducted by variously changing the conditions for concentrating solution (B) in step (2). (Number of samples: 884 = 12 bottles) At this time, since the mixing volume ratio of ←) M with the liquid is different, the PH values after mixing are different, but 0. IN ammonia water or 0.
The final pH value in all cases was adjusted to 6.0 using IN hydrochloric acid.

■Cracks■Cracks○From the results of the complete product, the silica concentration of solution (B) is 0.15r.
It has been found that it is necessary to concentrate until the concentration reaches , a or higher. Incidentally, the gel with cracks and cracks was sintered in the same manner as in Example 1, but there were no quality problems and high quality quartz glass was obtained.

By the way, during concentration, when the silica concentration exceeded 1.09, the viscosity suddenly increased, making it impossible to form a uniform dispersion. Therefore, it was also found that further concentration has no merit.

[Example 6] Experiments were conducted by changing the mixing ratio of liquid (A) and liquid (B).

-O- Other sol preparation, drying, and sintering steps were performed in the same manner as in Example 1. (Number of samples axa = 1s) Also in this case (
Since the mixing volume ratio of liquid A) and liquid (B) is different, the pH value after mixing is different, but 0.1N ammonia water, 0.1N ammonia water,
Alternatively, 0°l normal sulfuric acid was used to adjust the final pH value to 5.0 in both cases.

From the above results, it was found that M)/M(B) in the range of 0.2 to 8 is a condition for manufacturing large-sized, high-quality tubular quartz glass.

[Example 6] Five tubular wet gels were produced in the same manner as in Example 1, and the rotating container was used as a drying container. When dried in a constant temperature bath at 60°C with lids with an open area ratio of 1% on both ends, eight of the gels cracked on the way, and the remaining two had no cracks or cracks, but the dry gel was more severely bent than in Example 1. Ta.

[Example 7] In the same manner as in Example 1, all five tubular wet gels were manufactured and transferred to dry containers with different opening ratios.

These were placed in a constant temperature bath at 60°C and observed.

From this, the aperture ratio is 1. (Even if it is 1% to 5%, there is a possibility that the gel will not crack if it is dried at a lower temperature, but the drying speed will be significantly slower.

It was not efficient, and although the gel yield was good in the one with an aperture ratio of 0.5%, it took 5 days to dry. In the end, it was found that the aperture ratio should be about 1 to 2 circles due to the trade-off between drying speed and gel yield.

[Example 8] A raw material sol was prepared in the same manner as in Example 1. Experiments were conducted by varying the rotational speed during rotational gelation.

The final pH value of the raw sol was adjusted to 5゜lO using a pan, and the effective rotation time (the time the sol was rotated until it became a gel)
All of them have been arranged accordingly.

* G = 980 crn/sec 2 The wet gel state of the gel at 8,000 revolutions was good, but when it was dried, a peeling phenomenon was observed on the inner surface. This is due to sedimentation of particles due to centrifugal gravity.
It is thought that a layer with a low particle concentration was formed on the inner surface layer, and it was found that too vigorous rotation was disadvantageous.

[Example 9] ■ Preparation of liquid (A) Add 0.1N hydrochloric acid 8009 to purified commercially available methyl silicate 685F and stir vigorously to hydrolyze it.A)
It was made into a liquid.

■ Preparation of solution (B) Add purified commercially available methyl silicate 685F to 6200 mA of anhydrous methanol and 575 mI of aqueous ammonia (29%).
After mixing 800v of water and stirring for 2 hours, the particle size was measured overnight using a particle size analyzer (B) iffl, and the average particle size was 0.019 μm.

■ (Bl) liquid concentration/PH adjustment step After concentrating the (B) liquid adjusted in step ■ under reduced pressure until the silica concentration becomes 0.45@taka, P
H(@ lowered to 4.50.

■ Mixing/PH adjustment = 37- (+3) IgL obtained in (A) solution 918 mA and step ■
When 570mk was mixed, the pH became 4.35.

With all this 0.2N ammonia water, pH = 4.80
Adjusted to.

■ 1256 mA of the sol obtained in the rotary gelation process ■ was poured into a salt f vinyl lined steel pipe with an inner diameter of 5 mm and a length of 100 cm.
After covering with silicone rubber, it was attached to a rotating device 1
It was rotated at a rotation speed of 1500 γpm until the monitor sample gelled.

The time required for gelation was 70 minutes. Through this process, a tubular wet gel with an outer diameter of 5.0 cIn, an inner diameter of 80 m, and a length of 98 ins was obtained.

■ Drying process ■ After leaving the wet gel obtained in step ■ in a rotating container for 8 days, it was placed in a stainless steel box-shaped container (vertical: 15 cm, horizontal: 120 cm, height: 20 m) with a lid with an opening ratio of 1.596.
) and placed in a dryer. This total temperature increase rate is 5℃/
When heated from room temperature (25°C) to ω°C at h and held at this temperature for 15 days - = 38 - A stable dry gel (outer diameter 8.
5 cm, inner diameter 2.1 mm, length 69 cm) was obtained.

■ Sintering Next, this dry gel was placed in a quartz tubular sintering furnace and heated from 80°C to 200°C at a heating rate of 80°C/hr, held at this temperature for 5 hours, and then heated from 200°C to 800°C.
The sample was heated at a temperature increase rate of 80° C./hr to 80° C./hr, and held at this temperature for 5 hours to perform desorption of water. Next, the temperature increase rate is 80℃
/ hr from 800° C. to 1050° C. and held at this temperature for 80 minutes to perform decarbonization, desalting, ammonium treatment, and acceleration treatment of dehydration condensation reaction.

Subsequently, the temperature decreased to 700℃ and He 21!7m1n,
The mixture was held for 80 minutes while flowing a mixed gas of C120, 2,1z/min, and then heated to 800°C at a temperature increase rate of 60°C/hr without flowing only He gas. 80
He 21r/min at 0℃, C120,21! r/
The mixture was maintained for 1 hour while flowing a full mixed gas of min., and then heated at a heating rate of 60°C/hr and 900'ct without flowing only He gas. He 2 A/m at 900°C
In.

The mixture was maintained for 1 hour while flowing a mixed gas of Cl 20 and ur/min to perform OH group removal treatment. Followed by H
The mixture was heated to 1000° C. at a temperature increase of 60° C./hr while flowing a mixed gas of 4 A/min at 020° C./min to e 21° C., and was held at this temperature for 1 hour to perform dechlorination treatment. Next, since only He gas is completely flowed, the temperature increase rate is 80
Heat to 1250 °C at °C/hr.

This temperature was maintained for 80 minutes to perform a pore-closing treatment.

Next, transfer to a 5-box furnace and increase temperature from 1250℃ to ℃/h.
The glass was heated to 1500° C. to obtain a transparent tubular quartz glass (outer diameter 2.70, inner diameter 1.6 cm, length 52 c1n).

The quality, OH group amount, etc., were completely equivalent to those obtained in Example 1.

From this, it can be expected that the process of the present invention will produce quartz glass of the same quality regardless of the alkyl group of the alkyl silicate used as the raw material.

[Example 10] A tubular dry gel was produced in the same manner as in Example 9, and sintered under the following conditions.

Next, this dry gel was placed in an all-quartz tubular sintering furnace and heated from 80°C to 200°C at a heating rate of 80°C/hr, held at this temperature for 5 hours, and then heated from 200°C to 800°C.
The sample was heated to 'C at a rate of temperature increase of 80°C/hr and held at this temperature for 5 hours to perform desorption of water. Subsequently, it was heated from 800°C to 1050°C at a temperature increase rate of 80°C/hr, and held at this temperature for 80 minutes to perform decarbonization, dechlorination ammonium treatment, and acceleration treatment of dehydration condensation reaction. Subsequently, the temperature was lowered to 700℃ and He 21A/min, C
F 40.2 A/min of the mixed gas was kept flowing for 80 minutes, and then the heating rate was increased to 6 without flowing He gas only.
It was heated to 800°C at 0°C/hr. He at 800℃
2k/rnin.

CF40.2. The temperature was maintained for 1 hour while flowing a mixed gas of
Heated to 900 °C at °C/hr. He at 900℃
2 i/min, OF 40.2A/min
The mixture was maintained for 1 hour while flowing with a mixed gas of 1 to remove OH groups.

Next, Ot 0.41 for He 24/rnin
! Temperature increased to 60℃/h while flowing mixed gas at /min.
It was heated to 1000° C. at r and held at this temperature for 1 hour to perform a fluoride removal treatment. Subsequently, without flowing only He gas, it was heated to 1250° C. at a temperature increase rate of 80° C./hr, and held at this temperature for 80 minutes to perform a pore-closing treatment.

Next, it was transferred to a 5-box furnace, heated from 1250°C to 1400°C at a temperature increase rate of 60°C/hr, and held at 1400°C for 2 hours to obtain a transparent tubular quartz glass.

The OH group contained was measured and found to be less than 1 ppm. ? ! The mixture was heated to about 2000° C. using a ring heater to bring it to a melted state, but no foaming phenomenon was observed.

It is known that the refractive index of glass can be lowered by cumulatively containing fluorine in quartz glass. If optical fiber is used as the material, the optical fiber base material can be produced at a much lower cost than the base fibers that use germanium-containing cores, which are currently commonly used.

〔Effect of the invention〕

By the sol-gel method as described above, it is possible to obtain a tubular quartz glass of low cost, high quality, and high dimensional accuracy, and it can be used as a support tube or a jacket tube when manufacturing an optical fiber base material. In addition, by using tubular quartz glass containing fluorine and a low refractive index as a cladding material for a pure silica glass core, it is possible to manufacture optical fibers at a lower cost, making it possible to manufacture optical fibers at a lower cost. All can be supplied at low price.

[Brief explanation of drawings]

FIG. 1 is a diagram of a device for producing cylindrical gel. In FIG. 1, 1 is the rotating container 2, the motor 8 is the bearing 4, and the fixing jig 5 for fixing the rotating container 1 to the motor 2 and the bearing 8 is the motor 2. The guide rail 6 on which the bearing is completely fixed serves as a support base. that's all

Claims (20)

[Claims] (1) In a method for manufacturing tubular quartz glass by the sol-gel method using alkyl silicate as the main raw material, a hydrolyzed solution of alkyl silicate using an acidic catalyst (liquid A) and a hydrolyzing solution of alkyl silicate using a basic catalyst (liquid B) A method for manufacturing tubular quartz glass, which is characterized by using a mixed solution of (liquid) as a raw material sol, gelling it into a tubular shape, drying and sintering it to form transparent glass. (2) The above liquid (B) has an average particle size of 0.01 μm to 1.0 μm.
2. The method for producing tubular quartz glass according to claim 1, wherein the sol solution contains silica particles with a diameter of between 0 μm. (3) The liquid (B) is concentrated to a silica concentration of 0.15 g/cc to 1.0 g/cc before being mixed with the liquid (A). The method for producing tubular quartz glass according to item 2. (4) The mixing ratio of liquid (A) and liquid (B) is M(A)/M(B)= 4. A method for manufacturing tubular quartz glass according to claims 1 to 3, characterized in that the mixing is performed so that the ratio of the two components is 0.2 to 3. (5) For the mixed sol of liquids (A) and (B), either adjust the pH of liquid (A) or (B) or both before mixing the two liquids, or adjust the pH after mixing the two liquids. 5. A method for manufacturing tubular quartz glass according to claims 1 to 4, wherein the pH value is adjusted to a range of 3 to 6 and post-gelation is performed. (6) The method for producing tubular quartz glass according to any one of claims 1 to 5, characterized in that the method for producing the tubular gel includes gelling the raw sol while rotating it in a cylindrical container. (7) The rotational speed during rotational gelation is such that the maximum centrifugal gravity exerted on the raw material sol is 1000G (G = 980cm/sec^2
) The method for manufacturing tubular quartz glass according to claim 6, characterized in that the method is controlled to be as follows. (8) In the wet gel drying step, the wet gel is dried by covering both ends of the cylindrical rotating container with a lid having an opening ratio of 10% or less. A method for manufacturing tubular quartz glass. (9) In the drying process, the wet gel is taken out from the cylindrical rotating container, the wet gel is transferred to a container having an opening ratio of 10% or less, and the wet gel is dried in the container. A method for producing tubular quartz glass according to items 1 to 8. (10) After gelling at a temperature in the range of 5 to 60°C, the temperature is raised to a temperature of 40 to 160°C at a temperature increase rate of 120°C/hr or less, and dried by shrinkage to create a dry gel. A method for manufacturing tubular quartz glass according to claims 1 to 9. (11) The step of sintering the dry gel consists of the following five steps.
13. A method for manufacturing an optical fiber preform according to item 12. 1) Process of desorption water treatment 2) Process of decarbonization treatment 3) Process of promoting dehydration condensation reaction 4) Process of pore closing treatment 5) Process of transparent vitrification treatment (12) The step of sintering the dry gel consists of the following seven steps.
11. The method for producing tubular quartz glass according to item 10. 1) Process of desorption water treatment 2) Process of decarbonization 3) Process of promoting dehydration condensation reaction 4) Process of removing OH group 5) Process of dechlorination or defluorination 6 ) Step of performing pore closing treatment 7) Step of performing transparent vitrification treatment (13) 20 to 400°C at a heating rate of 400°C/hr or less
Claim 11 or 12, characterized in that the desorption water treatment is performed by raising the temperature to a predetermined temperature in the range of and holding it at that temperature for at least one hour at least once. Method for manufacturing tubular quartz glass. (14) 400-90 at a heating rate of 80-400℃/hr
15. The method for manufacturing tubular quartz glass according to claims 11 to 14, wherein the decarbonization treatment is performed by raising the temperature to a predetermined temperature within the range of 0°C. (15) 900-12 at a heating rate of 30-400℃/hr
Raise the temperature to a predetermined temperature within the range of 00℃, and at that temperature
15. The method for producing tubular quartz glass according to claims 11 to 14, characterized in that the dehydration condensation reaction is accelerated by carrying out a holding process for at least one minute. (16) At a temperature in the range of 700 to 1100°C, the flow rate ratio for He gas, O_2 gas, N_2 gas, Ar gas, or a mixture thereof is 1 to 1.
De-O while feeding 40% range of de-OH base into the furnace.
Claim 1 characterized in that H group treatment is performed.
The method for producing tubular quartz glass according to items 2 to 15. (17) As the OH removing base, Cl_2, SOCl, S
17. The method for producing tubular quartz glass according to claim 16, wherein the OH group removal treatment is performed using any one of F_6, CF_4, C_2F_6, and C_3F_8. (18) After the OH group removal treatment, He gas or Ar gas or N_
Flow rate ratio of 1 to 2 gases or a mixture thereof
18. The method for producing tubular quartz glass according to claims 12 to 17, wherein the dechlorination treatment or defluorination treatment is performed by feeding 100% O_7 into the furnace. (19) Make the inside of the furnace a vacuum or feed He gas into the furnace at a heating rate of 30 to 400°C/hr to 900°C.
Claim 11, characterized in that the pore-closing treatment is performed by raising the temperature to a predetermined temperature within the range of ~1350°C and holding it at that temperature for 1 hour or more at least once. 19. The method for producing tubular quartz glass according to item 18. (20) After pore closing treatment, 1200 to 1600
The tubular quartz glass according to claims 11 to 19, characterized in that the transparent vitrification treatment is performed by raising the temperature to a predetermined temperature in the range of °C and holding at that temperature for a predetermined time. Production method.