JP2559395B2 - High-purity transparent glass manufacturing method and manufacturing apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and a manufacturing apparatus for obtaining a dense and high-purity transparent glass by heating a porous body composed of glass fine particles. Since the glass obtained by the method of the present invention has a high purity, it is suitable for use as a glass for optical fibers.

[Conventional technology]

As a literature relating to a method for heating a porous body (hereinafter abbreviated as a porous body) composed of glass fine particles to obtain dense high-purity transparent glass, for example, Research Practical Report Vol.
No. 10 (1980) pp.1719-1729,
It is described that when He is used as the atmosphere gas, residual bubbles tend to shrink and disappear, which is advantageous for transparent vitrification. Further, in the above-mentioned document, the limit value (critical radius) of whether or not the residual bubbles shrink or disappear is calculated. The critical radius is about 10 ^-1 cm when using He, whereas it is about 10 ^-4 cm for other inert gases (N ₂ , Ar), which is about 1000 times different. Even from such knowledge, in the conventional technology,
In order to obtain transparent glass, it was essential to heat the porous body in He atmosphere.

[Problems to be solved by the invention]

In the prior art, in order to obtain a transparent glass containing no bubbles from a porous body, it was essential to sinter the porous body in a He atmosphere. There was a problem like this.

Since He is an expensive gas, it is difficult to perform heat treatment at low cost.

It is also difficult to obtain a large amount of He gas in a stable manner.

As the porous body becomes larger, even if He, which has a larger critical radius than other gases, is used, bubbles still remain.

The present invention has been made in view of the above problems,
The present invention proposes a novel and economical method and manufacturing apparatus for obtaining a transparent glass that is dense, has no residual air bubbles, is high-quality, and is suitable as an optical fiber glass without using He gas.

[Means for solving problems]

The present invention relates to a method for obtaining transparent glass by heating a porous body composed of fine glass particles, in which a furnace core tube and heating means surrounding the outer periphery of the furnace core tube are provided inside the pressure vessel, and inside the furnace tube. And a high-purity transparent material characterized in that the inside of the heating means is placed in communication with the inside of the pressure vessel, the porous body is held in the core tube, and heating is performed while maintaining the entire inside of the pressure vessel in vacuum. A method for manufacturing glass is provided.
As a particularly preferred embodiment of the present invention, using a high-purity quartz or high-purity carbon core tube as the core tube, while introducing a gas containing Cl ₂ into the pressure vessel prior to the heat treatment of the porous body. A method may be mentioned in which the atmosphere inside the furnace core tube is replaced with a high-purity inert gas during the subsequent heating treatment of the porous body.

Further, the present invention is an apparatus for obtaining transparent glass by heating a porous body composed of glass fine particles in a furnace core tube, which is 1) a pressure vessel having a vacuum evacuation means and a gas supply means, 2). A heating means installed inside the pressure vessel and communicating with the inside of the pressure vessel; and 3) a core tube installed inside the heating means and communicating with the inside of the heating means and the inside of the pressure vessel. An apparatus for producing high-purity transparent glass is provided. In a particularly preferred embodiment of the present invention, the gas supply means is connected to the lower part of the core tube by penetrating the pressure vessel and the heating means.

The present invention will be specifically described below with reference to the drawings. First
The figure shows an example of an apparatus for carrying out the present invention, which comprises a pressure vessel 1, a core tube 2, a heater 3, a heat insulating material 4, a gas inlet 5, a gas outlet 6, and a vacuum pump 7. It is configured.

The porous body 8 is held in the core tube 2, and the entire pressure vessel 1 is evacuated by the vacuum pump 7 to maintain a vacuum of 1600.
Heat to below ℃. In addition, various gases are introduced into the pressure vessel 1 and exhausted by the gas introduction port 5, the discharge port 6, and the vacuum pump 7 as needed. The present invention is characterized in that it is heated and made transparent in a vacuum. However, when heated and made into a vitrified material in a vacuum as described above, the critical radius becomes very large, and therefore bubbles remain in the porous body. There is no.

By the way, in a vacuum, when heating a porous body formed by aggregating glass fine particles to obtain a dense high-purity transparent glass, a high-purity heating atmosphere becomes a problem. Has been resolved.

First, since the core tube was provided in the pressure vessel, the heat insulating material, which is considered to be the main cause of atmospheric pollution, was separated from the heating atmosphere. As a material for the core tube, high-purity quartz or high-density high-purity carbon is suitable in terms of heat resistance and low emission of impurities. Since the entire pressure vessel is kept vacuum here, the core tube is not deformed or broken.

Here, the high-purity quartz in the present specification refers to one having a Cu content of 0.05 ppm or less and an Fe content of 1 ppm or less. Further, its OH group content is also preferably 1 ppm or less in order to improve heat resistance. The high-purity carbon has a Cu content of 0.05 ppm or less, an Fe content of 0.1 ppm or less, and a total ash content of 20 ppm or less.

Secondly, prior to the heat treatment of the porous body, the gas existing in the pressure vessel is heated by heating the interior of the pressure vessel while introducing a gas containing Cl ₂ (air baking). It is thought that most of them are adsorbed on a heat insulating material having a large surface area.), Which becomes chloride with a high vapor pressure and is discharged to the outside of the pressure vessel. Accordingly, the subsequent heat treatment of the porous body can be performed in a higher purity atmosphere.

Thirdly, by replacing the atmosphere inside the core tube with the high-purity inert gas such as Ar or N ₂ (excluding He) during each step of heat treatment of the porous body, heat insulating material, heater, core tube, etc. The impurities released from the inside of the pressure vessel are discharged outside without remaining in the pressure vessel. At this time, the amount of gas introduced is v (/
Min), the volume of the pressure vessel is V (), and the pressure is P (torr), the gas replacement frequency is Since it can be expressed by, when P is small, the inside of the pressure vessel can be efficiently replaced with a small amount of gas. The high-purity inert gas has a purity of 99.999% or more.

Examples of the porous body used in the present invention include publicly known
Examples include those obtained by depositing glass fine particles by a flame hydrolysis method such as the VAD method or OVD method, those obtained by pressure molding high-purity SiO ₂ powder, and those obtained by the sol-gel method. In addition to these methods, any high-purity porous glass body which does not crystallize quartz glass during sintering may be used.

In the present invention, the entire pressure vessel is evacuated and heated, but the degree of vacuum at this time needs to be less than 1 torr when the pressure is reduced while blowing N ₂ or Ar. This is the critical radius in He of 1 atm and N of 10 ^-4 atm (~ 1 torr).
_This is because the critical radii in ₂ or Ar are almost equal.

In the case of sintering and making transparent without blowing N ₂ or Ar, it is necessary to make it 10 ⁻² torr or less. When it is 10 ^-2 torr or less, the concentration of impurities is sufficiently reduced without blowing N ₂ or Ar.

As the Cl ₂ gas introduced into the container prior to the heat treatment, for example, Cl ₂ 1 to 5%, N ₂ or Ar 99 to 95%, and a total pressure of 1 atm are used.

 The heating in the present invention is performed at 1600 ° C or lower.

〔Example〕

Example 1 A glass rod having a diameter of 1.5 cm including a portion to be a core of an optical fiber afterward was fixed by press-molding glass fine particles by CIP (Cold Static Pressure Breathing) to a diameter of 10 cm.
A composite of cm porous glass and glass rod was prepared.
This composite was held in the pressure vessel shown in FIG. Dense high-purity carbon was used as the core tube 2. temperature,
A heat treatment was performed while adjusting the pressure as shown in Table 1 below, and the porous glass portion was made into a dense transparent glass.

The obtained transparent glass had one surface devitrified (crystallized), but could be easily removed by flame-polishing the surface. No bubbles were present at the interface with the glass rod or inside the newly obtained transparent glass. When spinning this transparent glass, the loss at 1.3μ is 0.40 dB / km
I was able to obtain In addition, there was no weak strength distribution over the entire length of this fiber, at which a tensile force of 700 g broke it.

Example 2 A dense high-purity carbon furnace tube was set in a pressure vessel, the pressure vessel was heated to 1500 ° C., and 2% Cl was added.
Dry N ₂ gas containing ₂ windsock, the purity of inner pressure container rows Natsuta. Separately, on the same glass rod as in Example 1, VA
Glass fine particles were laminated by method D to form a composite of porous glass and glass rod having a diameter of 13 cm. The composite was heat-treated in the highly-purified pressure vessel in the same manner as in Example 1 to make the porous glass portion a dense transparent glass.

The surface of the obtained transparent glass was smooth, and no bubbles were present at the interface with the glass rod and inside the newly obtained transparent glass. When this transparent glass was spun, a fiber with a loss at 1.3μ of 0.37 dB / km was obtained.

Example 3 A porous glass containing GeO ₂ in the center portion prepared by the VAD method was held in a pressure vessel subjected to the same purification treatment as in Example 2, and heat treatment was performed under the conditions shown in Table 2.

The surface of the obtained dense transparent glass was smooth, and no bubbles were present inside. On the periphery of this glass rod,
After adding the cladding portion of the optical waveguide and spinning, a fiber of 0.35 dB / km was obtained.

〔The invention's effect〕

The present invention is expensive, it is possible to obtain a high-purity and dense glass without using He, which is difficult to obtain in large quantities, and since it is less likely to cause bubbles than sintering in He, it is of high quality. Transparent glass can be obtained at low cost. Further, by introducing a Cl ₂ gas prior to the heat treatment or replacing the heat treatment atmosphere, substances such as transition metals having absorption at the wavelength used in optical communication can be reduced to the ppb order, so the present invention is for optical fibers. It is very effective as a glass manufacturing method and manufacturing apparatus.

[Brief description of drawings]

FIG. 1 is a schematic sectional view illustrating an embodiment of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ichiro Tsuchiya 1 Tayacho, Sakae-ku, Yokohama-shi Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Shunichi Mizuno 1 Taya-cho, Sakae-ku, Yokohama Sumitomo Electric Industries, Ltd. Yokohama Works (56) References JP-A-56-63833 (JP, A) JP-A-59-137334 (JP, A)

Claims (6)

(57) [Claims] 1. A method for obtaining a transparent glass by heating a porous body composed of fine glass particles, wherein a furnace core tube and heating means surrounding the outer circumference of the furnace core tube are provided inside the pressure vessel.
Further, the inside of the furnace core tube and the inside of the heating means are placed in communication with the inside of the pressure vessel, the porous body is held in the furnace core tube, and heating is performed while maintaining the entire inside of the pressure vessel under vacuum. And a method for producing high-purity transparent glass. 2. The method for producing high-purity transparent glass according to claim 1, wherein the core tube is made of high-purity quartz or high-purity carbon. 3. Prior to the heat treatment of the porous body, while introducing a gas containing Cl ₂ into the pressure vessel, the entire pressure vessel is heated to be highly purified. Item 1. A method for producing a high-purity transparent glass according to item 1. 4. A method of heat-treating the porous body while introducing a high-purity inert gas (excluding He) directly into the core tube to replace the atmosphere in the core tube. A method for producing a high-purity transparent glass according to item 1. 5. An apparatus for obtaining transparent glass by heating a porous body, which is an aggregate of glass fine particles, in a furnace core tube, which is 1) a pressure vessel having a vacuum evacuation means and a gas supply means, 2). A heating means installed inside the pressure vessel and communicating with the inside of the pressure vessel; and 3) a core tube installed inside the heating means and communicating with the inside of the heating means and the inside of the pressure vessel. High-purity transparent glass manufacturing equipment. 6. The apparatus for producing high-purity transparent glass according to claim 5, wherein the gas supply means penetrates the pressure vessel and the heating means and is connected to the lower part of the core tube. .