JP3188517B2 - Manufacturing method of quartz glass - Google Patents

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 high-purity silica glass used for optical materials and heat-resistant materials, and more particularly, to a porous silica preform synthesized by a vapor phase axial method. Is subjected to a predetermined de-OH group treatment and a transparent vitrification treatment to produce high-purity quartz glass.

[0002]

2. Description of the Related Art In recent years, as a method for producing high-purity quartz glass used as an optical material or a heat-resistant material, a method of vitrifying a silica porous base material synthesized by a vapor phase shafting method has attracted attention. Have been.

In the gas phase axial alignment method, first, an oxyhydrogen flame is formed by a burner, and a silicon compound such as silicon halide, which is a glass raw material, is circulated through the oxyhydrogen flame to generate silica fine particles by a hydrolysis reaction. In this method, the silica fine particles are adhered and deposited on a starting member, and the silica fine particles are grown in the axial direction to grow and synthesize a porous silica base material. Subsequently, the porous silica base material is heated in a He atmosphere. The treatment densifies the pores of the porous silica matrix to obtain a transparent glass. At this time,
A gas having an H group action, for example, a halogen such as Cl ₂ ,
By flowing a gas such as a halogen compound such as SOCl ₂ , the OH group concentration in the quartz glass can be easily controlled, for example, the OH group concentration can be reduced to 1 ppm or less.
The removal of the OH group, that is, the removal of the OH group, is caused by the removal of the OH group by adsorption of the OH group working gas into the porous silica base material. Glass properties such as refractive index, absorption spectrum, heat resistance, etc. greatly affect the concentration of OH groups remaining in the glass, and especially when used for optical materials and heat-resistant materials, control of the OH group concentration in the glass. Is an important factor.

Conventionally, quartz glass has been used as a furnace core tube for flowing a gas for deOH-removing treatment. In the case of a quartz glass furnace core tube, another furnace such as alumina is used. Compared to the case where a core tube is used, it has a feature that high-purity quartz glass can be obtained.

However, when a quartz glass furnace core tube is used at a temperature at which the porous silica matrix becomes transparent vitrified, the quartz glass furnace core tube is softened due to the high temperature of 1500 ° C. or more. Deformation occurred, and it was impossible to reuse a quartz glass core tube. Another problem is that devitrification (crystallization) occurs on the surface of the quartz glass, and the crystallized portion and the glass portion caused by the devitrification have different thermal expansion coefficients, so that they are damaged when the temperature of the electric furnace is raised again. occured.

For this reason, a method has been proposed in which the de-OH group treatment and the transparent vitrification treatment are performed in separate furnace core tubes (Japanese Patent Laid-Open No. 60-1985).
186427). This method is performed at 1100-1300 ° C
The de-OH treatment is performed in an electric furnace for de-OH treatment equipped with a quartz glass furnace core at a temperature within the range described above, and the transparent vitrification electricity equipped with a carbon furnace core at a temperature of 1350 ° C or higher. This is a method of performing vitrification treatment in a furnace. According to this method, the life of the quartz glass furnace core tube is remarkably improved and the obtained quartz glass is prevented from being devitrified because the deoxidation treatment using the quartz glass furnace core tube is performed at a relatively low temperature. Can prevent damage.

[0007]

SUMMARY OF THE INVENTION
In the case of a method in which the base treatment and the transparent vitrification treatment are performed using an electric furnace equipped with a different furnace core tube, glass having a distribution in the OH group concentration, particularly a distribution in the radial direction, is often obtained. That is, while the OH group concentration at the radial center in the glass ingot is 1 ppm or less, several to several tens ppm of OH groups remain on the outer surface. Non-homogeneous glass having such an OH group concentration distribution cannot be used as an optical material, and furthermore, the yield at the time of processing is significantly reduced, which is a serious problem.

An object of the present invention has been made in view of the above problems, and an object of the present invention is to produce a highly pure and homogeneous quartz glass having a residual OH group concentration of 1 ppm or less with good reproducibility. It is to provide a way to do it.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have conducted a dehydration-based treatment and a transparent vitrification treatment using an electric furnace equipped with a furnace core tube of different materials. It is possible to solve the problem by maintaining the atmosphere containing the gas having an OH-removing function until the temperature in the furnace becomes 500 ° C. or less when the temperature is lowered after the OH-removing treatment is completed. The present inventors have found that the present invention has been made. That is, the present invention relates to a method for producing quartz glass in which the deOH-based treatment and the transparent vitrification treatment are performed using different furnace core tubes. This is a method for producing quartz glass in which the silica porous base material is maintained in an atmosphere containing the gas having an OH-removing function until the temperature becomes below, and then a vitrification treatment is performed.

Hereinafter, the present invention will be described in more detail.

In the case where the deOH-based treatment and the transparent vitrification treatment are performed using different furnace core tubes, the silica porous base material is taken out of the electric furnace for the deOH-based treatment after the deOH-treated, and the transparent glass is removed. It is necessary to lower the temperature to a temperature at which it can be handled each time the deOH-based treatment is completed, because the furnace must be transferred to an electric furnace for chemical treatment.

In the present invention, when the temperature is lowered after the completion of the de-OH-based treatment, the temperature in the electric furnace for de-OH-based treatment is reduced to 50%.
It is characterized in that it is maintained in an atmosphere containing a gas having a deOH group action until the temperature becomes 0 ° C. or lower.

[0013] The temperature in the electric furnace for deOH group treatment is 500 ° C.
The following method is not particularly limited.

The lower the temperature at which the atmosphere containing a gas having an OH-removing function is maintained, the more effective it is. However, when the temperature in the electric furnace exceeds 500 ° C., quartz glass having an OH-group concentration distribution is obtained. Therefore, it is necessary to maintain an atmosphere containing a gas having a deOH group action until the temperature becomes 500 ° C. or less.

In order to maintain this atmosphere, a gas having an OH-removing action is circulated, and the flow rate of the gas having an OH-removing action is controlled so that the pressure in the furnace core tube is increased. Is preferred.

The gas having an action of removing an OH group used in the present invention is not particularly limited as long as it is a gas having an action of removing an OH group. For example, Cl ₂ , F
_And halogens such as SOCl ₂ , SiCl ₄ and CF ₄ , and gases such as ammonia and CO. These gases may be used alone, but many of these gases are harmful, special and expensive, and are preferably used in a mixture with an inert gas. As the inert gas used at this time, for example, N ₂ , H
e, Ar and the like. In addition, the higher the concentration of the gas having an action of removing OH groups in the case of a mixed gas, the higher the effect is. For ease of exhaust gas treatment,
0.5 to 5% by volume is preferred. The purity of these gases is preferably as high as possible to obtain high-purity glass, and a purity of 99% or more is preferable.

Since many gases having an OH-removing function are harmful and corrosive, a furnace core tube made of quartz glass is suitable for the furnace core tube used at the time of the OH-removing treatment. Further, by using a high purity quartz glass furnace core tube, impurities from the quartz glass furnace core tube can be further prevented, and high purity quartz glass can be obtained.

The temperature of the deOH group treatment is not particularly limited as long as it is a commonly used temperature. However, in order to prevent the quartz core tube from being deformed or damaged and to perform the deOH group efficiently. Is preferably 850 to 1350 ° C, more preferably 1100 to 1300 ° C.

The electric furnace to be used is not particularly limited. However, in order to perform the treatment efficiently, a soaking length longer than the entire length of the porous silica base material (for example, a temperature range within a set temperature ± 10 ° C.) is used. Is preferred. Furthermore, by processing in such an electric furnace, a more homogeneous glass,
In particular, a homogeneous glass can be obtained in the axial direction.

After the OH removal treatment, the porous silica base material is cooled to be taken out. The present invention is characterized in that during this cooling, the atmosphere in the furnace core tube is maintained at an atmosphere containing a gas having a deOH-removing action.

The porous silica pre-processed in this manner is cooled to a temperature at which it can be handled, taken out of the electric furnace for de-OH-based treatment, and transferred to an electric furnace for transparent vitrification. And a vitrification treatment is performed at a higher temperature. This transparent vitrification treatment may be performed by a commonly used method, for example, in an atmosphere containing He gas at least 70% or more, preferably 90% or more.
Heating is performed in a temperature range of 00 to 1600 ° C. At the time of the transparent vitrification treatment, in the electric furnace having a soaking length shorter than the entire length of the silica porous preform after the deOH-based treatment, the transparent glass is sequentially placed from the lower end of the silica porous preform after the deOH-based treatment in an electric furnace. Treatment. By performing the treatment in this manner, the gas in the glass escapes from the gap in the upper porous state portion during the heat shrinkage, and a transparent glass can be easily obtained. The material of the furnace core tube used in the transparent vitrification process is, for example, carbon, SiC
Various ceramics such as can be used,
Carbon is preferred because it is easy to process, can have a large diameter, can be highly purified, and is stable at high temperatures.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 An electric furnace 11 for deOH-based treatment having a soaking length Z1 (temperature range within a set temperature ± 10 ° C.) of 1200 mm shown in FIG.
A quartz glass furnace core tube 12 having a diameter of 280 mm is inserted into the furnace core material, and a silica porous base material 13 (outer diameter 250 mmφ, length 1
000 mm) was suspended from a lifting device 15 by a support rod 14 and rotated. Next, N ₂ gas flows through the furnace core lower end 16 at a flow rate of 20 L / min and Cl ₂ gas flows at a flow rate of 0.2 L / min (Cl ₂ concentration: 1.0% by volume). After heating to 8 ° C and treating for 8 hours,
The electric furnace heater output was turned off, and the electric furnace was cooled. During that time, the temperature in the electric furnace was monitored, and N ₂ gas was supplied at 20 l / min until the temperature reached 300 ° C.
The flow of Cl ₂ gas was continued at 0.2 liter / min, the temperature in the electric furnace became 300 ° C. or less, and the flow of only Cl ₂ gas was stopped. Thereafter, after sufficiently cooling, the silica porous preform after this treatment was taken out of the furnace core tube and cut off from the joint portion 17.

Next, the soaking length Z2 shown in FIG.
A 280 mmφ carbon furnace core tube 22 is inserted into a transparent vitrification electric furnace 21 having a temperature range of 10 ° C. and 250 mm, and a silica porous base material 23 subjected to a deOH-base treatment is supported thereon by a support rod. The suspension was suspended from an elevating device 25 by 24 and rotated. Next, from the furnace core tube lower end 26, He
Gas was introduced at a rate of 20 l / min, and the temperature of the electric furnace was raised to 1550 ° C. After the temperature was raised, the temperature was lowered at 2.0 mm / min, and the glass was moved from the lower end to the soaking section to obtain a transparent glass. The dimensions of the obtained glass were 125 mm in outer diameter,
The length was 550 mm.

To measure the OH group concentration of the obtained glass, 50 mm, 280 mm,
A plate having a thickness of 10 mm was cut out from the position of 500 mm, and further, 10 mm was cut out in the radial direction. Of these, samples 1 to 7 were taken in order from the center to the outer periphery. These cut samples were polished to a wavelength of 2.7.
The infrared absorption spectrum at 3 μm was measured, and the OH group concentration was measured from the transmittance. Table 1 shows the results. It was 1 ppm or less in all the measured samples.

Further, the glass was treated under the same conditions to
Although the same evaluation was carried out by producing 0 pieces, the OH group concentration was 1 ppm or less in all cases.

[0027]

[Table 1]

Example 2 After completion of the deOH group treatment, at the time of cooling, N ₂ ;
Min, Cl ₂ ; 0.1 liter / min (Cl ₂ concentration 0.5 vol%), and the same conditions as in Example 1 were carried out except that the temperature at which Cl ₂ was stopped was changed to 500 ° C. When the obtained glass was evaluated in the same manner as in Example 1, it was possible to obtain a glass of 1 ppm or less for all the samples.

Comparative Example 1 The same operation as in Example 1 was performed except that Cl ₂ was stopped immediately after the deOH group treatment. The same evaluation as in Example 1 was performed on the obtained glass. Table 1 shows the obtained results.
Shown along with.

COMPARATIVE EXAMPLE 2 After completion of the deOH group treatment, N ₂ ;
Min, Cl ₂ ; 0.2 liter / min (Cl ₂ concentration 1.0 vol%) was passed, and the temperature at which Cl ₂ was stopped was set to 800 ° C., and the same conditions as in Example 1 were used. . The same evaluation as in Example 1 was performed on the obtained glass. The results obtained are shown in Table 1.

[0031]

As is clear from the above description, the use of the method of the present invention has the effect of producing a highly pure and homogeneous quartz glass having a residual OH group concentration of 1 ppm or less with good reproducibility. Have

[Brief description of the drawings]

FIG. 1 is a view showing an electric furnace for deOH group treatment in the present invention.

FIG. 2 is a view showing an electric furnace for transparent vitrification treatment in the present invention.

[Explanation of symbols]

 11: Electric furnace for OH removal treatment 12: Furnace core tube made of quartz glass 13: Porous silica base material 14: Support rod 15: Elevating device 16: Lower end of furnace core tube 17: Joint part 21: Electricity for transparent vitrification treatment Furnace 22: Furnace core tube made of carbon 23: Porous silica base material 24: Support rod 25: Elevating device 26: Lower end of furnace core tube Zl: Soaking length Z2: Soaking length

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tomiyoshi Kubo 33-80 Suetakenaka, Kudamatsu City, Yamaguchi Prefecture (56) References JP-A-60-186427 (JP, A) JP-A-4-325433 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C03B 8/04 C03B 20/00 C03B 37/00-37/16

Claims (1)

(57) [Claims] In the de-OH-based treatment step of heating the synthesized silica porous base material by passing a gas having a de-OH-based action, the silica porous base material is treated using an electric furnace equipped with a quartz glass core tube. Then, in a transparent vitrification step in which the treated silica porous preform is further heat-treated at a high temperature, a method for producing quartz glass is performed using an electric furnace equipped with a furnace core tube made of a material different from quartz glass. When the temperature is lowered after completion of the deOH group treatment, the silica porous base material is continuously maintained in an atmosphere containing a gas having the deOH group action until the temperature becomes 500 ° C. or lower, and then the transparent glass A method for producing quartz glass, characterized by performing a chemical conversion treatment.