JPS6217027A - Preparation of quartz glass - Google Patents

Abstract

PURPOSE:To obtain quartz glass having high quality stably by mixing soln. prepd. by hydrolyzing alkyl silicate with a basic reagent and soln. prepd. by hydrolyzing alkyl silicate with an acidic reagent, and transforming obtd. sol to gel, and drying and sintering the gel. CONSTITUTION:Soln. contg. fine silica particles obtd. by hydrolyzing alkyl silicate such as ethyl silicate with a basic reagent such as aq. ammonia) is mixed with soln. obtd. by hydrolyzing alkyl silicate with an acidic reagent (e.g. dil. HCl) in a specified proportion to prepare sol. Then, obtd. sol is transferred to a specified vessel where it is transformed to gel. Obtd wet gel if dried to prepare dry gel, which is sintered to form a transparent glass body. By this method, quartz glass having high and uniform quality contg. quite small amt. of impurities such as metal ion, crystals, bubbles, or amorphous foreign matters is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing quartz glass by a sol-gel method.

[Conventional technology]

Several methods for producing silica glass using the sol-gel method have been reported. ((1) Nogami, Nakatani et al., Tonr
nalof Won-Crystalline Sol
:ds.

57.191 (1980) (2) Rabinopich et al.
Ionrnalof Non-Crystalline
8o11ds, 47, 435 (1982) (8)
Toki et al., Japanese Patent Application No. 58-257577) Among them, the method of Toki et al. is obtained by using a sol in which the pH value of a metal alkoxide hydrolysis solution □ is adjusted to 5 to 6, in which ultrafine powdered silica is well and uniformly dispersed. Because it has a structure in which porous dry gel is sintered, quartz glass of a size that is difficult to produce in the other two examples (for example, 15 cm
15 zXl 5 cm ) with a high yield, and is the most excellent method for producing quartz glass.

[Problem that the invention seeks to solve]

However, in the conventional manufacturing method of Toki et al., impurities such as metal ions, crystals, bubbles, etc.
It tends to contain irregularly shaped foreign matter, which poses a quality problem when used in applications that require particularly high quality, such as base materials for optical fibers and quartz substrates for photomasks.

Therefore, the present invention solves these conventional quality problems, and its purpose is to manufacture homogeneous, high-quality quartz glass that is free from impurities such as metal ions, crystals, bubbles, and irregularly shaped foreign substances. We are here to provide you with a way to do so.

[Means for solving problems]

The method for producing quartz glass of the present invention includes a first solution containing silica fine particles obtained by hydrolyzing an alkyl silicate with a basic reagent, and a first solution containing silica particles obtained by hydrolyzing an alkyl silicate with an acidic reagent. a second solution at a predetermined ratio, a step of transferring the obtained sol solution to a predetermined container and gelling it to make a wet gel, a step of drying the wet gel to make a dry gel, a step of drying the dry gel. It is characterized by a step of sintering it into a transparent glass body.

The method for producing quartz glass of the present invention allows the selection of high-purity liquid raw materials as raw materials, thereby producing essentially high-quality quartz glass without impurities such as metal ions, dull objects, dust, dirt, and other foreign substances. However, in order to economically produce large sizes with good yield, it is desirable to select the following conditions.

1) The average particle size of the silica fine particles contained in the first solution is in the range of 0.01 to 1.0 μm. 2) The concentration of the silica fine particles contained in the first solution is 10 μm.
5 P/d or more 5) The first solution and the second solution are mixed at a predetermined molar ratio of silicon contained in the range of 20:80 to 80:20 4) In the sol solution The effective silica concentration is Q, 10ff/
5) Adjust the pH value of the sol solution to a predetermined value of 3 or higher and then gel it. 6) Dry the wet gel in a container with an opening ratio of 10% or less. 7) Drying wet gel at temperature increase rate from 40℃ to 120℃
/ hr or less to a predetermined temperature in the range of 50 to 160°C 8) The process of sintering the dry gel to form a transparent glass body consists of the following five steps (1) Process of deadsorbed water treatment (2) Process of decarbonization process (8) Process of dehydration condensation reaction (4) Process of pore closing process (5) Process of transparent vitrification process 9) Deadsorbed water process The treatment is carried out by raising the temperature to a predetermined temperature in the range of 20 to 400 °C at a temperature increase rate of 400 °C / hr or less, and maintaining it at that temperature for 1 hour or more if necessary. 10) The decarbonization treatment is carried out at a temperature increase rate of TO~400℃/h
11) The dehydration condensation reaction is accelerated at a heating rate of 1 to 400°C.
℃/hr to a predetermined temperature within the range of 900 to 1500℃, and if necessary, hold at that temperature for 30 minutes or more 12) Perform the pore-closing treatment at a heating rate of 30 to 400℃/hr. h
Raise the temperature to a predetermined temperature within the range of 900 to 1,400 °C with r, and if necessary, hold at that temperature for more than 1 hour. 15) Transparent vitrification treatment to a predetermined temperature in the range of 1,200 to 2,000 °C. Conditions 1), 3) and 5), which are performed by raising the temperature and holding it at that temperature for a predetermined period of time, are mainly conditions for producing a porous dry gel that is difficult to break during the sintering process, and condition 2). Condition 4) is mainly a condition for producing a wet gel with a composition that is difficult to break during the drying process, Condition 6) is a drying condition for producing a dry gel with a good yield, and Condition 7
)8)9)10)11)12)15) are sintering conditions for producing a transparent glass body with good yield.

By using the above method, it is possible to produce high-quality quartz lath with significantly less impurities such as metal ions, crystals, bubbles, and irregularly shaped foreign substances than conventional methods. Foreign matter in shape can be reduced.

14) The pore-closing treatment is performed using one of the following three methods. (1) Pore-closing in a He atmosphere (2) Pore-closing under reduced pressure (8) In a He atmosphere This condition, in which the inside of the closed pore is filled with He or the pressure is reduced and the pores are closed by reducing the pressure, is mainly due to
This is a condition for eliminating the spaces contained in micro bubbles and foreign matter of micrometers or less, and by using this method,
For example, it is possible to easily produce extremely high-quality quartz glass used in applications that require particularly high quality, such as optical fiber base materials and quartz substrates for photomasks.

Moreover, the extremely high quality quartz glass produced in this manner can be produced more stably and with a high yield by using the following method in combination.

1) Use high-purity raw materials for the first solution and the second solution, and remove minute dust and foreign matter by distillation, filtration, etc. 2) Before transferring the sol solution to the designated container, The operation must be performed in a clean environment of class 3000 or less, preferably class 100 or less. 3) The first solution contains 50 to 100
After applying a centrifugal force of 00 (), the vasa is used to mix with the second solution 4) After the first solution is passed through a filter with a 50 μm diameter or more at least once. , mixing with the second solution; 5) filtering the second solution one or more times using a filter finer than a 50μ vortex and then mixing with the first solution; 6) filtering the sol solution through a filter finer than a 50μ groove. 7) Apply vacuum treatment to the sol solution at least once during the process up to gelation 8) Transfer the sol solution to a designated container and apply 50 to 500G
gelatinization while applying centrifugal force of Preparation of solution (ethyl silicate) 167 aor, absolute ethanol 558
5@j, 29% ammonia water 109m, water 58 (L6f
After stirring vigorously for 2 hours, the mixture was allowed to stand overnight in a cool, dark place to grow fine silica particles. After concentrating this solution under reduced pressure, the alcohol content of the concentrated solution was replaced with water in order to increase the yield of the drying process. After that, the pH value was adjusted to 4.0 using 2N hydrochloric acid to prevent rapid gelation when mixed with the hydrolysis solution, and the pH was further filtered using an α6μ membrane filter. Particle size Q, 18μ
A dispersion solution of silica fine particles of m was prepared and used as a first solution.

(2) Preparation of second solution 1 lLo2 normal hydrochloric acid 95 (Lot) was added to ethyl silicate 157L9f and hydrolyzed with vigorous stirring to prepare a second solution.

■ Preparation of sol solution and gelation Mix the first solution and the second solution, then adjust the pH value to 4.69″ using 2N aqueous ammonia and water, and adjust the volume to 4000″ A sol □ solution was prepared. (Effective silica concentration α22 o t/-j"
) This sol solution was transferred to a cylindrical container (inner diameter 50 mm, height 2100 tea) to a depth of 2000 cm, degassed at 50 torr for 2 minutes, and sealed with 7 taps. Gelation occurred 40 minutes after adjusting the pH of the stain, and a wet gel was obtained.
All steps were performed in a class 100 clean room. Ethyl silicate, ethanol, and water were purified by distillation, and hydrochloric acid and aqueous ammonia were obtained by filtering blade reagents with extremely low metal ion impurities through a 0.2μ membrane filter.

■Drying 10 wet gels prepared in the same manner were aged for 5 days in a closed state, and then transferred to a rotating drying container with an opening ratio of 0.2%.
When dried at 60℃ while rotating at a speed of 1
In 7 days, nine pieces of dry gel that did not crack even when left at room temperature were obtained at a yield of 90%. The bulk density of the dry gel was (L72?/ctA).

Next, the nine pieces of dry gel were placed in a sintering furnace, and the heating rate was 30.
Heat to 200"C at °C/hr, hold at this temperature for 5 hours, then increase temperature to 30"C at a heating rate of SO"C/hr.
It was heated to 0°C and kept at this temperature for 5 hours to perform desorption water treatment. Subsequently, it was heated from 300° C. to 9020° C. at a temperature increase rate of 60° C./hr, and held at this temperature for 2 hours to perform decarbonization, dechlorination ammonium treatment, and acceleration treatment of dehydration condensation reaction. Next, the temperature was lowered to 800°C, held for 30 minutes while flowing a He2t/i mixed gas, then heated to 900°C at a heating rate of 60°C, held at that temperature for 1 hour, and then heated at a heating rate of 60°C/ Heat to 1000℃ at hr, hold at that temperature for 5 hours, and remove O2.
H group treatment was performed. Subsequently, while flowing 117 m of 02 gas, it was heated to 1100° C. at a temperature increase rate of 60° C./hr, and was maintained at this temperature for 50 hours to perform dechlorination treatment. Subsequently, while flowing He gas only, the material was heated to 1250° C. at a temperature increase rate of 30° C., and held at this temperature for 30 minutes to perform a pore-closing treatment. Subsequently, the sample was heated from 1250° C. to 1450° C. at a heating rate of 60° C./hr, and when held at this temperature for 1 hour, it became non-porous, and nine cylindrical transparent glasses were obtained with a yield of 100%.

The size of the transparent glass is 212 m in outer diameter and 928 m in length.
fur *Weight 862? Therefore, the yield of raw material is approximately 1
It was 00%.

Furthermore, it was confirmed by visual inspection that the transparent glass had excellent homogeneity and was full of transparency.

By drawing the transparent glass and using fluoropolymer as the cladding, one optical fiber with a core diameter of 200 μm and a cladding diameter of 300 μm can be produced from one transparent glass.
Obtained more than 0km. The transmission loss of the optical fiber is α85
It was confirmed that the μ groove was 4 (L B / K m or more) and that it could be used as an optical fiber for LAN.

In addition, since the transparent glass itself has extremely good light transmittance, it can be used as is or as a Q fiber with a groove of several hundred microns in diameter.
It can be used as a quartz rod for several light transmissions. This light transmitting quartz rod can be used for lighting of farms built inside the space stage or for lighting of underwater farms.

[Example 2] A sol solution prepared in the same manner as in Example 1 was gelled using a rotation gelling method, and the outer diameter was 50 m and the inner diameter was 25 m.
A tubular wet gel with a length of 2000 m was prepared. When 10 pieces of the wet gel were dried and sintered using the same method as in Example 1, 10 pieces of transparent glass were obtained with a yield of 100%.

The size of the transparent glass is outer diameter 252 ras, inner diameter 1
1.6 gourds, length 928+1! It was II.

By drawing the transparent glass and using a fluorine-based polymer as a cladding, from one transparent glass tube,
With a core diameter of 200 .mu.m and a cladding diameter of 300 .mu.m, an optical power of 7 IPA of 8 ICm or more was obtained. The transmission loss of the optical fiber was 4 dBΔ or less at a and 85 μm, and it was confirmed that it could be sufficiently used as an optical fiber for LAN.

Furthermore, since the transparent glass is tubular, it can be used for support tubes in the MOVI method, jacket tubes as base materials used in the WAD method and MCJVD method, and Talarad tubes used in the rod-in-tube method.

In particular, since the transparent glass contains almost no water (100 ppb or less), it is used especially when manufacturing high-quality optical fibers.

[Example 3] The sol solution prepared in the same manner as in Example 1 was
The mixture was transferred to a Teflon container with an inner dimension of 100 rms to a depth of 80 rms, gelled, dried and sintered more slowly than in Example 1, and a quartz glass with a thickness of 92 tR0 x 37 mm was produced. The quartz glass transmits ultraviolet and visible light well, and also sufficiently transmits light at the wavelength of the 200% groove.
It can be used as a photomask for use in manufacturing VLSIs of 1M bits or more. Furthermore, since the quartz glass obtained in this example was thick, it could be processed into lenses, prisms, etc. Lenses made in this way are 256 in 1)
[Effects of the Invention] As described above, according to the present invention, fine silica particles obtained by hydrolyzing an alkyl silicate with a basic reagent are added to a solution. A high-purity sol solution obtained by mixing a first solution containing the alkyl silicate and a second solution obtained by hydrolyzing an alkyl silicate with an acidic reagent at a predetermined ratio is transferred to a predetermined container to form a gel. In order to make a wet gel by drying the wet gel to make a porous dry gel and then sintering it to make a transparent glass, impurities such as metal ions, crystals, etc.
High-quality quartz glass with very few air bubbles and irregularly shaped foreign matter can be produced. In addition, in the sintering process, H
By performing the process in an E atmosphere, under reduced pressure, or under reduced pressure after creating a He atmosphere, even minute bubbles of 1 μm or less and irregularly shaped foreign matter can be almost completely removed, and extremely high quality quartz glass can be produced. . Furthermore, by using means for preventing the incorporation of dust, foreign matter, etc., and means for removing them, the above-mentioned extremely high quality quartz glass can be produced stably and with a high yield.

that's all ′ζ7′

Claims (2)

[Claims] (1) a first solution containing fine silica particles obtained by hydrolyzing an alkyl silicate with a basic reagent;
A step of preparing a wet gel by transferring a sol solution obtained by mixing a second solution obtained by hydrolyzing an alkyl silicate with an acidic reagent at a predetermined ratio into a predetermined container and gelling it; A method for producing quartz glass, comprising the steps of drying a gel to form a dry gel, and sintering the dry gel to form a transparent glass body. (2) A patent claim characterized in that in the step of sintering to form a transparent glass body according to claim 1, the pore-forming treatment is performed using one of the following three methods. A method for producing quartz glass according to item 1. 1) Close the pores in a He atmosphere 2) Close the pores under reduced pressure 3) Close the pores under reduced pressure after creating a He atmosphere