JPH05294658A - Production of quartz-based glass - Google Patents

Abstract

PURPOSE:To provide a method for producing quartz-based glass in which the high-purity quartz-based glass can be produced from a porous glass compact formed by using a forming assistant. CONSTITUTION:The objective quartz-based glass is produced. In the process, a porous glass compact containing a forming assistant is initially heat-treated at a temperature within the range of 400-800 deg.C in an atmosphere containing chlorine and oxygen and further heat-treated at >=800 deg.C temperature in an atmosphere containing the chlorine.

Description

Detailed Description of the Invention

[Object of the Invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing silica-based glass used for optical or optical communication, and more particularly to a method for producing silica-based glass from a porous glass compact molded using a molding aid. ..

[0003]

2. Description of the Related Art As a method for producing quartz glass, a method is known in which silica powder is molded and the obtained porous glass molded body is made into transparent glass. At this time, in order to improve the moldability, it is generally performed to add a molding aid to silica powder to mold a porous glass molded body.

In this case, the molding aid contained in the porous glass molded body must be removed, and such molding aid removal (hereinafter referred to as degreasing) has conventionally been carried out using oxygen or an inert gas. It is performed in an atmosphere such as. Then, particularly in the production of high-purity products, purification is performed in a chlorine atmosphere or the like after degreasing.

[0005]

Even if the step of degreasing a porous glass molding containing a molding aid is carried out in an oxygen or inert gas atmosphere, the alkali and alkali contained in the molding aid and silica powder It is almost impossible to remove the earth metal, transition metal, etc., and if these impurities remain, the following adverse effects are brought about.

That is, alkali and alkaline earth metals cause crystallization in the vitrification process of the molded body,
Since the transition metal itself has a light absorption peak, the light transmittance is deteriorated. Therefore, in the production of silica glass used for optical waveguides and optical components that require high purity, purification is performed after the degreasing step.

By the way, it is widely known that in refining the porous glass body, heat treatment is performed at a temperature of at least 800 ° C. or higher in the presence of chlorine gas. However, in the porous glass molded body containing the molding aid, a large amount of impurities mainly contained in the molding aid adheres to the surface of the silica particles constituting the porous glass body.
When the refining is performed at a temperature higher than 00 ° C., impurities on the surface penetrate into the inside of the particles, which makes it very difficult to purify the porous molded body.

On the other hand, the porous glass molded body was refined at 400 ° C. in an atmosphere of thionyl chloride + oxygen, and further 1000
A method of refining again at ℃ is known (Grastech Ber
Volume 60, No. 4, 125-132, 1987). However, even if this method is adopted, it is very difficult to obtain transparent glass from a porous glass molded body containing a molding aid.

The present invention has been made in view of the above circumstances, and provides a method for producing a silica-based glass capable of obtaining a high-purity silica-based glass from a porous glass molding formed by using a molding aid. The purpose is to provide.

[0010]

In order to solve the above-mentioned problems, the present invention provides a porous glass molded body containing a molding aid in a range of 400 to 8 in an atmosphere containing chlorine and oxygen.
Provided is a method for producing a silica-based glass, which comprises performing a heat treatment at a temperature in the range of 00 ° C. and further performing a heat treatment at a temperature of 800 ° C. or higher in an atmosphere containing chlorine.

In the present invention, as the first step, the porous glass molded body is heat-treated at a temperature in the range of 400 to 800 ° C. in an atmosphere containing chlorine and oxygen.
The reason is as follows.

That is, as described above, when the porous glass molded body containing the molding aid is directly subjected to the heat treatment at a temperature higher than 800 ° C., impurities adhering to the particle surface are irrespective of whether chlorine is mixed or not. This is because it penetrates into the inside of the particles, and some of the pores of the molded body are closed, the subsequent purification is not effectively performed, and degreasing becomes insufficient at less than 400 ° C. Here, the chlorine source contained in the atmosphere is not limited to chlorine gas, and it is also possible to use, for example, thionyl chloride, which generates chlorine gas by reacting in the apparatus.

Next, in the second step, 400 to 800 ° C.
For the porous glass body heat-treated at a temperature in the range of,
Heat treatment is performed at a temperature of 800 ° C. or higher in an atmosphere containing chlorine. This process corresponds to the conventional purification process.

The porous glass molded article referred to in the present invention is cast and extruded using so-called silica glass powder such as pure silica powder, or powder obtained by adding dopants such as phosphorus, aluminum and boron to pure silica powder. It is molded using a molding method generally used in the field of ceramics such as pressure molding.

Further, the molding aid is an additive having a function of imparting moldability to the quartz-based powder, which is difficult to mold, or a function of improving the strength of the molded body, and the powder agglomerates are converted into primary particles. Also included are those having a function of decomposing, a function of improving releasability from a molding die, a function of modifying the surface of powder, and a function of lowering interfacial tension.

Specific examples of the molding aid include polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, glycerin, etc., and organic substances such as acrylic acid oligomer, stearic acid, ethylene glycol, tetramethylene glycol, etc. Further, there are metal alkoxides such as tetraethoxysilane. But,
The material is not limited to these, and other substances can be used. Further, the addition amount and the compounding ratio of these are not limited to a specific range, and may be appropriately set depending on the molding method.

[0017]

In the present invention, first, heat treatment is carried out in an atmosphere containing oxygen and chlorine gas at a temperature in the range of 400 to 800 ° C. to remove the molding aid of the porous glass molded body and at the same time, It becomes possible to remove impurities, particularly alkali and alkaline earth metals, transition metals and the like contained in the molding aid and the quartz glass powder that form the porous glass molded body. In this case, it becomes possible to remove these impurities adhering to the silica glass powder particles of the molded body. Further, by using chlorine, these impurities can be removed without adhering to the surface of the silica-based glass powder particles, and the impurities generated from the device etc. adhere to the surface of the porous glass molded body. It is also possible to prevent Then, heat treatment in a chlorine-containing atmosphere at 800 ° C. or higher, which is generally performed, is performed to further improve the refining effect.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. Here, as an example, a method of manufacturing a high-purity optical fiber made of silica glass will be described.

FIG. 1 is a schematic view showing a pressure molding apparatus for manufacturing a porous molded body from quartz glass powder.
This apparatus includes a molding rubber mold 13 in which a high pressure applying device 11 is filled with a molding target and a support cylinder 17 attached to the outside thereof.
Are set, and the high pressure applying device 11 applies pressure to the object to be molded in the molding rubber mold 13 through the pressure medium 15 such as lubricating oil filled around the molding rubber mold to press-mold it. It is a thing. Reference numeral 19 is a molded rubber mold 1.
3 is a lower lid, 12 is an upper lid, and 14 is a pressure medium inlet / outlet port.

Using this apparatus, a porous glass molded body was molded as follows. First, a glass rod 18 having a core in the center thereof and a part of a clad around the core was placed in the molded rubber mold 13.

The molding rubber mold 13 used here was made of nitrile rubber and had an inner diameter of 50 mmφ and a length of about 270 mm. The molding rubber mold 13 may be made of silicon rubber. Also, the glass rod 18
Is manufactured by the VAD method, which is one of the vapor phase methods, and has a clad / core of about 3, an outer diameter of 7.5 mmφ, a length of about 260 mm, and a relative refractive index of about 0.35%. Was used.

As the powder for forming the porous glass molded body, a commercially available silica powder having an average particle size of about 8 μm was used. Polyvinyl alcohol (hereinafter referred to as PVA) as a molding aid and pure water were added to this powder to give a concentration of about 60.
% Slurry. This slurry was dried and granulated using a spray dryer. The average particle size of the granulated particles at this time was about 150 μm. The concentration of the molding aid PVA in the particles was 2% by weight.

The silica powder 16 thus obtained was filled in a molding rubber mold. At this time, in order to uniformly fill the powder 16, the lower lid 19 was filled while vibrating with a vibrator (not shown). The packing density was about 0.9 g / cm ³ .
After filling, the upper lid 12 is closed, and the support cylinder 17 is placed outside the molding rubber mold.
Attached. This is because the support cylinder 17 is adapted to apply the pressure only in the radial direction when the pressure is applied.

After that, the molded rubber mold 13 to which the support cylinder 17 was attached was set in the high-voltage applying device 11. In this case, the pressure medium 15 enters from the pressure medium inlet / outlet 14 and pressure is applied to the molding rubber mold 13. Molding condition is 1.5 to
A pressure of n / cm ² was applied for 1 minute, and then the pressure was slowly reduced over about 20 minutes. After decompression, the high voltage application device 11
From the above, the molded rubber mold 13 to which the support cylinder 17 was attached was taken out, the upper lid 12 was opened, and the porous glass molded body was taken out. As shown in FIG. 2, the porous glass molded body 21 was formed around the glass rod 18. Of course, neither cracks nor cracks were generated in the porous glass molded body, and naturally, the glass rod 18 at the center was not cracked. The outer diameter of the obtained porous glass molded body was about 40 mmφ.

Next, a molding aid for the obtained porous glass molded body and impurities contained in the porous glass body particles, particularly alkali metal, alkaline earth metal and transition metal adhering to the surface of the powder are added. In order to remove it, heat treatment (degreasing step) was performed. In this heat treatment, as shown in FIG. 3, the glass rod 18 and the porous glass molded body 21 formed around the glass rod 18 are inserted into the furnace core tube 32 of the heating furnace 31, and the furnace core tube 32 is mixed with oxygen and nitrogen. It was performed in an atmosphere in which chlorine gas was supplied into the gas at a flow rate of about 10% of the flow rate of oxygen. The flow rate ratio of oxygen and nitrogen was set to 1: 4. The heating condition is that the temperature is raised from room temperature to 600 ° C. at a rate of 2 ° C./min.
It was kept at 00 ° C for 5 hours.

The porous glass body after this heat treatment was purified and vitrified using another furnace. This purification process was performed at a temperature of 1200 ° C. in a He, Cl ₂ atmosphere. Next, the temperature was raised to 1600 ° C. and transparent vitrification was performed in a He atmosphere.

No bubbles and cracks were observed in the optical fiber preform obtained by these series of steps.

This optical fiber preform was drawn by a usual method to manufacture an optical fiber. The transmission loss of the obtained optical fiber was 0.36 dB / km, which was equivalent to that produced by the vapor phase method.

In the above examples, the case where the porous glass molded body was formed by the pressure molding method was shown, but the present invention is not limited to this, and the same heat treatment is applied even when it is molded by the casting molding method and the extrusion molding method. An optical fiber having equivalent characteristics was obtained. Further, not only the optical fiber but also the optical waveguide substrate, the quartz glass rod, the pipe and the like can be manufactured with high purity.

For comparison, an optical fiber was produced under the same conditions as in the above-mentioned example except that chlorine gas was not used during the heat treatment (degreasing). As a result, the transmission loss of the optical fiber obtained was 0.42 dB / km, which was larger than that of the example. The results of comparing the impurities contained in the preform in the optical fiber at this time with those of the example are shown below.

Example Comparative Example Na <0.001 0.02 Ca <0.001 0.01 Fe <0.005 0.01 (unit: ppm by weight) From these results, porous glass moldings were prepared using chlorine. By heat-treating (degreasing) the impurities adhered to the particles and the impurities generated by contamination from the device etc. are prevented from adhering to the surface of the porous glass molded body, and as a result, the purification effect performed in the next step It became clear that it improved.

Next, for comparison, an optical fiber preform was produced under the same conditions as in the example except that the temperature in the heat treatment (degreasing) was 400 ° C. As a result, many bubbles were recognized in the preform, and it could not be used as an optical fiber.

[0033]

Industrial Applicability According to the present invention, there is provided a method for producing a silica-based glass capable of obtaining a high-purity silica-based glass from a porous glass molded body that is molded using a molding aid.

[Brief description of drawings]

FIG. 1 is a schematic view showing a pressure molding device for manufacturing a porous molded body used in the present invention from a silica glass powder.

FIG. 2 is a view showing a state in which a porous glass molded body is formed around a glass rod.

FIG. 3 is a schematic diagram showing a furnace for heat-treating a porous glass molded body used for carrying out the present invention.

[Explanation of symbols]

11 ... High-voltage applying device, 12 ... Upper lid, 13 ... Molded rubber mold,
14 ... Pressure medium inlet / outlet, 15 ... Pressure medium, 16 ... Silica powder, 17 ... Support cylinder, 18 ... Core rod, 19 ... Lower lid,
21 ... Porous glass molding, 31 ... Heating furnace, 32 ... Furnace core tube.

Front page continuation (72) Inventor Kazuaki Yoshida 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (1)

[Claims] 1. A porous glass molded body containing a molding aid is added in an atmosphere containing chlorine and oxygen in an amount of 400 to 80.
A method for producing a silica-based glass, which comprises performing a heat treatment at a temperature in the range of 0 ° C. and further performing a heat treatment at a temperature of 800 ° C. or higher in an atmosphere containing chlorine.