JPH06271321A - Production of glass body - Google Patents

Abstract

PURPOSE:To obtain a glass body excellent in light transmittance in a short time without generating bubbles in the glass body. CONSTITUTION:A glass body is produced by heat-treating a porous body. At the time of treat-treating the porous body in a furnace, the gas in the furnace is discharged to attain reduced pressure, gas of the same kind is blown into the furnace and the porous body is heat-treated. This process is preferably repeated plural times. The degree of reduced pressure is preferably increased in accordance with the repetition of heat treatment..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a glass body having a high light transmittance such as an optical element.

[0002]

2. Description of the Related Art A porous body used as a precursor for producing a glass body is a sol-gel method or a chemical vapor deposition method (CV).
D method, VAD method). High-purity silica glass produced by the process of heat-treating a porous body to obtain a glass body is considered to be applied to crucibles, boats, diffusion furnaces, etc. used in the production of semiconductors, and many Research is being done. However, in order to manufacture a bulk body from a porous body, it is difficult to perform firing without generating bubbles.

Bubbles are generated when the pores in the porous body become non-porous. When the porous gel is heated and sintered, Si-
The dehydration polycondensation reaction of OH progresses to form closed pores first, but these closed pores are free from pores when heat-treated at a high temperature in a gas atmosphere having high diffusivity such as helium. It is known to collapse to form a transparent glass body (S. Satoh et al, Jou.
rnal of Non-Crystalline S
olds 55 (1983), p455-p45
7). Conventionally, the porous S has been used to utilize this characteristic.
A method of heat treating io ₂ in the range of 600 ° C. to 800 ° C. in an inert gas atmosphere or a protective atmosphere (in particular, a helium gas atmosphere) (JP-A-61-295243), 900 ° C. to 1400 ° C. There are a method of sintering in a helium gas atmosphere (Japanese Patent Laid-Open No. 61-236617), a method of sintering under a reduced pressure in which helium gas is introduced (Japanese Patent Publication No. 64-330).

[0004]

However, in each of the above-mentioned conventional methods, since the water generated from the porous body is adsorbed again to the pores and the surface of the porous body, the water in the porous body is sufficiently removed. However, it is difficult to effectively prevent the generation of bubbles. JP-A-61-29
In the method described in Japanese Patent No. 5243 or Japanese Patent Application Laid-Open No. 61-236617, the water generated when the porous body is sintered is not easily collected outside the system because of being accumulated inside the furnace. Becomes a helium gas atmosphere containing water vapor, and is fired in a state where water is adsorbed again on the surface of the sintered body or in the pores. This water was a cause of forming minute bubbles in the glass. In addition,
In the method described in Japanese Patent No. 330, heat treatment is performed in a closed system in a helium gas atmosphere whose pressure is reduced during sintering. In other words, since the heat treatment is performed by reducing the pressure inside the furnace, the concentration of the carrier gas that transfers heat is low, the conductivity of the heat emitted from the heating element is poor, and it takes a long time to sinter. Further, since the sintering is performed in a closed system, the water generated from the porous body is not discharged out of the system, which causes the generation of minute bubbles as described above.

That is, in the conventional method, even if a glass body that is mechanically strong is obtained by these causes, very fine bubbles remain in the glass body. These bubbles have the drawbacks of causing light scattering and deteriorating the optical characteristics, and of requiring a long heat treatment to obtain a desired glass body.

The present invention has been made in view of the above-mentioned conventional problems, and a glass body capable of obtaining a glass body excellent in light transmittance in a short time without generating bubbles in the glass body. It is intended to provide a manufacturing method.

[0007]

In order to solve the above-mentioned problems, the present invention provides a method for producing a glass body, in which a glass body is produced by heat-treating the porous body. In addition, after the gas inside the furnace was exhausted to reduce the pressure, the same kind of gas was injected into the inside of the furnace to perform heat treatment.

In the method for producing a glass body of the present invention, the step of exhausting the gas inside the furnace to reduce the pressure and then injecting the gas into the furnace again for heat treatment may be repeated a plurality of times. In FIG. 1, in the process of repeating such exhaust,
It is a graph which shows the relationship between heat processing temperature and the pressure in a furnace.
In FIG. 1, the solid line shows the temperature change and the broken line shows the pressure change.

Further, when it is repeated a plurality of times, the pressure reduction in the second and subsequent heat treatment steps may be further reduced than the previous pressure reduction. FIG. 2 is a graph showing the relationship between the heat treatment temperature and the pressure in the furnace when the degree of pressure reduction is increased each time the gas is exhausted in the process of repeating the exhaustion. In FIG. 2, the solid line shows the temperature change and the broken line shows the pressure change.

The depressurization process and the normal pressure process may be performed while the temperature of the gel is maintained, or during the temperature rise. Here, in the depressurizing process, as shown in FIG. 3, a step of performing a heat treatment after rapidly exhausting the inside of the furnace and a step of performing a heat treatment while gradually exhausting the inside of the furnace as shown in FIG. Including both.

[0011]

The porous body produced by the sol-gel method or the VAD method contains a large amount of water. Therefore, when performing vitrification by heat-treating this porous body, evaporation of water adsorbed in the pores and the surface of the gel and water generated by dehydration reaction of silanol groups accompanying non-pore formation With evaporation of.

For the firing of the porous body, it is important to reduce the amount of water present in the porous body and effectively remove the water produced by the dehydration reaction of the silanol groups. Because when the heat treatment temperature rises to some extent,
Since the dehydration condensation reaction of Si-OH proceeds and the open pores in the porous body disappear, the water remaining in the porous body until after the closing and the water generated when the closed pores contract are gasified. , Because the pressure of the gas causes foaming. If water in the porous body is not sufficiently removed during firing, or if the water generated from the porous body is adsorbed again on the pores or the surface of the porous body, the water remains inside the closed pores and the glass foams. Cause

The use of the method of the present invention has the following effects. When non-porous, it is fired, for example, in a helium gas atmosphere, but by performing this at normal pressure, the helium gas diffuses in the gel and functions sufficiently as a carrier to transfer heat to the center of the glass. Conducts heat to promote dehydration condensation of silanol groups in the porous body. In addition, the helium gas has a role of discharging moisture generated by dehydration condensation out of the system. The opening is crushed to become a closed hole, and helium gas is confined in the closed hole. However, since helium gas has a higher permeability to the SiO ₂ skeleton than oxygen gas or air, it is confined in the closed hole. Since helium gas can diffuse in the SiO ₂ skeleton, the closed holes can be finally closed.

Conventionally, it takes an enormous amount of time to exhaust the helium gas containing water in the furnace by continuously flowing the helium gas at normal pressure, and it is impossible to quickly remove the water in the furnace. there were. However, the method of the invention,
In other words, after heat-treating with helium gas, the step of repeatedly depressurizing and exhausting the inside of the furnace (sintering once in a helium gas atmosphere, then depressurizing the inside of the furnace and helium containing water generated from the porous body) It is possible to efficiently keep the state in which the helium gas does not always contain water at the time of firing by performing the step of firing the gas by exhausting the gas and newly adding helium gas. Therefore, it is possible to prevent moisture from being re-adsorbed to the pores and the surface of the porous body, and the re-generation of the silanol group due to breaking of the Si-0-Si network bond. Furthermore, since the porous body is heated in a reduced pressure atmosphere in the furnace, it is possible to reduce the vapor pressure of water and more effectively remove the water adsorbed in the pores of the porous body. . From the above, by repeating the process of injecting helium gas and heat-treating after depressurization exhaust, more effective water removal can be performed, and eventually the generation of bubbles when vitrifying a porous body is prevented. can do.

As a means to bring about a further great effect, as shown in FIG. 2, it is considered that the temperature holding process and the exhaust process are repeated a plurality of times, and the degree of pressure reduction in the furnace is increased each time the exhaust is performed. Since the evaporation of water can be controlled stepwise by this means, it is possible to remove water more effectively without applying a large stress to the porous body and shorten the sintering time. It will be possible.

As shown in FIG. 3, when the heat treatment is performed after the furnace is rapidly evacuated, the water contained in the porous material can be removed in a short time. Further, as shown in FIG. 4, when the heat treatment is performed while gradually exhausting the inside of the furnace, the water contained in the porous body can be evaporated little by little and continuously. Since a large stress is not applied to, the sintering can be performed without breaking the gel. These vacuum exhaust steps may be appropriately selected in consideration of the amount of water contained in the porous body and the strength of the porous body.

The present invention is also effective for the following problem of black coloring of the glass body. The residual organic substances contained in the dry gel are mainly due to unreacted alkoxy groups, and if heated in an atmosphere with a high oxygen partial pressure, these organic substances become a gas and go out of the system. If it is low, it will be steamed and will remain inside the gel in the form of carbon and will be colored black (Glass-ceramics manufacturing technology by the sol-gel method and its application, written by Masayuki Yamane, p154-). p156, Applied Technology Publishing (19
89)). Effective effects can be obtained by applying the means of the present invention to the combustion process of this organic substance. That is, in the step of burning an organic substance using oxygen or a mixed gas containing oxygen such as air, by repeatedly depressurizing the gas and reinjecting the gas, the removal of water in the porous body described above is performed. Similarly to the above, it is possible to quickly and surely remove the water and carbon compounds generated by the decomposition of the organic matter.

[0018]

Example 1 Si (OC ₂ H ₅ ) 4 was used as a silica raw material. 10.6 g of Si (OC ₂ H ₅ ) ₄ and 1 part of ethanol
After adding 8.4 g and stirring for 1 hour, a solution obtained by mixing 10 ml of water and 3 ml of 1N hydrochloric acid was added dropwise to obtain a sol.
This sol was cast in a polypropylene tube container having a diameter of 18 mm, left in a constant temperature bath at 50 ° C. for gelation, further aged, and dried to obtain a porous dry gel.

This porous gel was heated to 250 ° C. in air and held for 5 hours, and then heated to 600 ° C. and held for 5 hours. After this, the air is replaced with helium gas,
After raising the temperature to 0 ° C and holding it for 4 hours, exhausting the inside of the furnace to reduce the pressure to 10 mmHg, holding it for 3 hours, then injecting helium gas to normal pressure again and holding it for 3 hours, and then slowly holding it in the furnace. Chilled The glass body obtained by this heat treatment was colorless and transparent, and was a glass having excellent light transmittance without scattering even when irradiated with a laser beam.

Comparative Example 1 A porous dry gel prepared in the same manner as in Example 1 was heated in air to 250 ° C. and held for 5 hours, and then heated to 600 ° C. and held for 5 hours. . Then, the air was replaced with helium gas, the temperature was raised to 900 ° C., the temperature was maintained for 10 hours, and the furnace was gradually cooled. The glass body obtained by this heat treatment was colorless and transparent as far as the naked eye could see, but when exposed to laser light, scattering was observed, and it was found that minute bubbles were present in the glass body.

[0021]

[Embodiment 2] Si and zirconia are used as raw materials for Si
(OCH ₃ ) ₄ and Zr (O ⁿ C ₄ H ₉ ) ₄ were used.
To 10.6 g of Si (OCH ₃ ) ₄ were added 9.2 g of ethanol and 1.26 g of 1N hydrochloric acid, and the mixture was stirred at 30 ° C. for 1 hour, and the solution was added with Zr (O ⁿ C ₄ H ₉ ) ₄ 5.75 g. After adding a solution mixed with 15.0 g of isopropanol and stirring for 1 hour, a solution obtained by mixing 15 ml of water, 3 ml of 1N nitric acid and 23.0 g of ethanol was added dropwise to obtain a sol. This sol was cast in a polypropylene tube container having a diameter of 18 mm, left in a constant temperature bath at 50 ° C. for gelation, further aged, and dried to obtain a porous dry gel.

The porous body was kept at 250 ° C. for 3 hours while continuously flowing oxygen gas at room temperature, then evacuated for 1 hour and decompressed to 10 mmHg, and then oxygen gas was injected to normal pressure for 1 hour. It was held, exhausted for 1 hour, and depressurized to 1 mmHg. Next, inject helium gas up to atmospheric pressure to obtain 7
Hold at 00 ° C for 3 hours and evacuate at 700 ° C for 1 hour.
After the pressure was reduced to mmHg, helium gas was injected to normal pressure, held for 1 hour, evacuated for 1 hour, and reduced to 1 mmHg. After this, helium gas was further injected to bring the pressure to 9
The temperature was raised to 00 ° C., maintained for 3 hours, and then gradually cooled in the furnace. The glass body obtained by this heat treatment was colorless and transparent, and was a glass having excellent light transmittance without scattering even when irradiated with a laser beam.

[0023]

Example 3 Si (O) is used as a raw material for silica and titania, respectively.
C ₂ H ₅ ) ₄ and titanium dioxide (anatase type) manufactured by Kojundo Chemical Laboratory Co., Ltd. were used. Si (OC ₂ H ₅ ) ₄ 10.
To 6 g, 9.2 g of ethanol and 1.26 g of 1N hydrochloric acid were added, and the mixture was stirred at 30 ° C. for 1 hour. TiO ₂ was added to the solution.
A solution prepared by ultrasonically dispersing 6.2 g of particles in 15.0 g of ethanol was added and stirred for 1 hour, and then a solution of 15 ml of water, 3 ml of 1N nitric acid and 15.0 g of ethanol was added to form a sol. Obtained. This sol was cast into a polypropylene tube container with a diameter of 18 mm and
The gel was left to stand in a constant temperature bath at 0 ° C., gelled, further aged, and dried to obtain a porous dry gel.

The dried gel of this porous body was heat-treated to 250 ° C. while continuously flowing oxygen gas at room temperature, and then the furnace was evacuated and the pressure was reduced to 10 mmHg and kept for 1 hour. Oxygen gas was injected again, the pressure was maintained at normal pressure for 1 hour, the gas was evacuated to 1 mmHg, and the pressure was maintained for 1 hour. After this,
Inject oxygen gas to atmospheric pressure and hold at 600 ℃ for 3 hours,
It was evacuated, depressurized to 10 mmHg, and held for 1 hour. In addition, oxygen gas was injected up to atmospheric pressure and kept for 1 hour.
The pressure was reduced to mHg and kept for 1 hour. After that, the oxygen gas was replaced with helium gas to return to normal pressure, the temperature was raised to 900 ° C., the temperature was maintained for 3 hours, and then exhausted at 850 ° C. to 10 mm.
Depressurize to Hg and inject helium gas to atmospheric pressure to reach 90
Hold at 0 ° C. for 3 hours. After that, the gas is evacuated and the pressure is reduced to 1 mmHg, and then helium gas is again injected to the normal pressure to 100
The temperature was raised to 0 ° C., held for 3 hours, and then gradually cooled in the furnace. After that, the glass body obtained by this heat treatment was colorless and transparent, and was a glass having excellent light transmittance without scattering even when irradiated with a laser beam.

[0025]

As described above, according to the method for producing a glass body of the present invention, it is possible to produce a glass body which has no bubbles in the glass body and is excellent in light transmittance in a short time. .

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a heat treatment temperature and a pressure in a furnace in a process of repeating exhaust.

FIG. 2 is a graph showing the relationship between the heat treatment temperature and the pressure in the furnace when the degree of pressure reduction is increased each time the gas is exhausted in the process of repeating the exhaust.

FIG. 3 is a graph showing the relationship between the heat treatment time and the pressure in the furnace when the heat treatment is performed after the furnace is rapidly evacuated in the depressurization process.

FIG. 4 is a graph showing the relationship between the heat treatment time and the pressure in the furnace when the heat treatment is performed while gradually exhausting the furnace in the depressurization process.

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[Procedure amendment]

[Submission date] May 14, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

Conventionally, it takes an enormous amount of time to exhaust the helium gas containing moisture in the furnace by continuously flowing the helium gas at normal pressure, and it is impossible to quickly remove the moisture in the furnace. there were. However, the method of the invention,
In other words, after heat-treating with helium gas, the step of repeatedly depressurizing and exhausting the inside of the furnace (sintering once in a helium gas atmosphere, then depressurizing the inside of the furnace and helium containing water generated from the porous body) It is possible to efficiently keep the state in which the helium gas does not always contain water at the time of firing by performing the step of firing the gas by exhausting the gas and newly adding helium gas. Therefore, it is possible to prevent moisture from being re-adsorbed to the pores and the surface of the porous body, and the re-generation of silanol groups due to the breaking of the Si—O—Si network bond. Furthermore, since the porous body is heated in a reduced pressure atmosphere in the furnace, it is possible to reduce the vapor pressure of water and more effectively remove the water adsorbed in the pores of the porous body. . From the above, by repeating the process of injecting helium gas and heat-treating after depressurization exhaust, more effective water removal can be performed, and eventually the generation of bubbles when vitrifying a porous body is prevented. can do.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

[0018]

Example 1 Si (OC ₂ H ₅ ) ₄ was used as a silica raw material. 10.6 g of Si (OC ₂ H ₅ ) ₄ and 1 part of ethanol
After adding 8.4 g and stirring for 1 hour, a solution obtained by mixing 10 ml of water and 3 ml of 1N hydrochloric acid was added dropwise to obtain a sol.
This sol was cast in a polypropylene tube container having a diameter of 18 mm, left in a constant temperature bath at 50 ° C. for gelation, further aged, and dried to obtain a porous dry gel.

Claims (3)

[Claims] 1. In a method for producing a glass body, in which a glass body is produced by heat-treating a porous body, when the heat treatment is performed on the porous body, the gas inside the furnace is exhausted to reduce the pressure, and then the inside of the furnace is depressurized. A method for manufacturing a glass body, comprising the step of injecting the same kind of gas into the glass and heat-treating the same. 2. The method for manufacturing a glass body according to claim 1, wherein the step of exhausting the gas in the furnace to reduce the pressure and then again injecting the gas into the furnace and performing the heat treatment is repeated a plurality of times. 3. The method for producing a glass body according to claim 2, wherein the pressure reduction in the second and subsequent heat treatment steps is further reduced compared to the previous time.