JPS6144727A - Production of glass for optical fiber - Google Patents

Abstract

PURPOSE:In processing sol formed from an alkoxide into transparent glass, to obtain optically transparent and uniform glass for optical fiber without producing bubbles, by gelatinizing and drying the sol under given conditions. CONSTITUTION:An alkoxide is diluted with a solvent, and hydrolyzed with water to give sol. The sol is heated at a temperature lower than the boiling point of the solvent and gelatinized. Then, the gel material is heated and dried at a temperature lower than the boiling point of the solvent until the gel material is released from the wall of a container. The gel material dried at the low temperature is dried at a temperature >= the boiling points of the solvent and water to give a porous gel material. The porous gel material is treated at a high temperature.

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention relates to a method for manufacturing optical fiber glass, more specifically a method for manufacturing low temperature glass using an alkoxide as a raw material, which prevents cracking during the manufacturing process and improves optical performance. The present invention relates to a method for producing uniform and high-purity glass.

[Background of the invention]

Conventionally, glass has been manufactured by melting mixed raw materials in an electric furnace. In particular, silica glass, which contains more than 90% SiO2, requires a temperature of nearly 2000°C to melt, so it was devised to produce glass ingots by dropping powder onto a seed rod.
A method was applied in which an oxyhydrogen flame burner was used as the heating source.

In recent years, a method has been proposed for producing transparent quartz-based glass at a relatively low temperature of 1200 to 1300'C by using alkoxide as a raw material and slowly hydrolyzing it. FIG. 1 schematically shows each step of this manufacturing method (generally called the sol-gel method). Parable number fSi (OCe l(
s) Dilute a with alcohol and add water to produce liquid sol 1.

Next, heat at a temperature of 100°C or less to gel (
Step (2), a solid gel 2 is obtained.

Furthermore, by slowly heating Gel 2 at a temperature of 100°C to 150°C for about a week to volatilize the alcohol and excess water caused by the reaction, the volume will be reduced to 1/2 to 1/3.
Obtain a gel 3 that has shrunk (Step ①).

Next, the temperature is gradually raised to 1,200 to 1,300°C to obtain glass (step ①).

Generally, the electric furnace 7 is provided with a gas inlet 5 and a gas outlet 6, the sample 4 is placed in a container 8 such as a quartz crucible, and heat treatment is performed without opening the atmosphere.

By undergoing the above treatment, quartz glass, which normally requires melting at 200°C, can now be obtained at a relatively low temperature of about 1300°C.

The glass sample 9 finally obtained is 1/3 of the starting volume.
It has shrunk to ~115.

The sol-gel method has the advantage of being able to synthesize glass at low temperatures and also being able to synthesize glasses with compositions that cannot be obtained using normal melting methods. However, even though the temperature is rising slowly, the volume shrinks significantly, so uneven stress is applied to the sample, which may lead to destruction. The problem becomes more noticeable as the size increases, and the current situation is that glass plates with very small dimensions have not been replaced.

[Summary of the invention]

The present invention has been made in view of the above points, and it is possible to obtain a porous gel body without cracking, and to make it optically stable even during the subsequent high-temperature treatment without entrapment of air bubbles or foaming. An object of the present invention is to provide a method for manufacturing transparent and uniform glass for optical fibers.

Therefore, according to the method for producing optical fiber glass according to the present invention, alkoxide is diluted with a solvent, water is added to hydrolyze it to produce a sol, and then water and solvent are evaporated to form a porous gel body. The present invention is a method for producing glass for optical fibers, in which a porous gel body is formed, and the porous gel body is treated at a high temperature to be made into transparent glass, which is characterized by including the following steps.

I. A step of heating the sol at a temperature lower than the boiling point of the solvent to gel it.

II. A step of heating at a temperature lower than the boiling point of the solvent and drying until the gel body leaves the container wall.

III. A step of drying the gel body by raising the temperature to a temperature higher than the boiling point of the solvent and water.

According to the method for manufacturing optical fiber glass according to the present invention,
Porous glass can be obtained without cracking, and optically transparent and uniform glass for optical fibers can be manufactured.

(Detailed description of the invention) The present invention will be explained in more detail.

According to the method for manufacturing optical fiber glass according to the present invention,
After adding a solvent to an aqueous alkoxide solution and hydrolyzing it to generate a sol, the water and solvent are evaporated to form a porous gel body, and this porous gel body is treated at high temperature to produce transparent vitrification. This method of manufacturing fiber glass is characterized by including the following steps.

I. A step of heating the sol at a temperature lower than the boiling point of the solvent to gel it.

In the above-mentioned vitrification process, in order to obtain transparent glass without foaming, it is necessary to prevent the pores from closing completely even at temperatures exceeding 1100"C, and to reduce the amount of moisture contained and the organic components generated by the reaction. It is necessary to sufficiently volatilize the glass and then transform it from porous to transparent glass with closed pores.For this purpose, the conditions in this gelation process are very important, and these conditions can cause the above-mentioned It has become clear that the temperature at which the pores close (hereinafter referred to as Tc) is determined.

As is clear from Example 1 described later, the higher the gelation temperature, the higher the Tc. However, if gelation occurs at a temperature exceeding the boiling point of the solvent or water, the solvent and water will boil violently, causing the solution to deteriorate. The disadvantage is that more than half of it transpires. That is, the formed gel body becomes very porous and easily cracks. Therefore, this gelation step needs to be performed at a temperature lower than the boiling point of the solvent. More preferably, gelation is carried out at a temperature as high as possible below the boiling point of the solvent.

II. A step of heating at a temperature lower than the boiling point of the solvent and drying until the gel body leaves the container wall.

The gel body heated and gelled as described above is heated at a temperature lower than the boiling point of the solvent before being dried at high temperature to form a porous gel body.

This is because if the gel body is rapidly dried at high temperatures, there is a risk that the gel body will crack when the container and the gel body are separated. In the present invention, it has been found that cracking of the porous gel body can be prevented by pre-drying at a temperature slightly lower than the temperature in the gelling process (see Example 3). Even if the gelling temperature in the gelling step is high, cracking of the gel body can be prevented.

III. A step of drying the gel body by raising the temperature to a temperature higher than the boiling point of the solvent and water.

If the gel body is dried at a temperature lower than the boiling point of the above-mentioned solvent after leaving the container, cracks may occur in the same way as when the temperature exceeds 100° C. in the transparent vitrification process. Therefore, in this drying step, the temperature is gradually raised to a temperature higher than the boiling point of the solvent and water.

The temperature is preferably raised gradually to 100°C or higher, more preferably to about 150 to 200°C.

Example 1 Whether the pores of the dried gel were closed or not was determined by measuring the specific surface area using the BET method using samples treated at various temperatures. The temperature treatment was carried out by using a dry gel, increasing the temperature from room temperature to a predetermined temperature at a rate of about 140° C./hour, and maintaining the temperature for 1 hour. High temperature treatment is He
This was done under a gas atmosphere.

The composition of the sol is St (OC2Hs) 4 20vol
%, Ge (OC4Hs) b 2vo1%, C2
H50H48v.

1%, ) 1g030%.

FIG. 2 shows the specific surface area versus treatment temperature in the transparent vitrification process of samples gelled at 50°C, 75°C, and 100°C. The respective Tcs were 920″c (50°C gelling), 1010°C (75°C gelling), 1100°C (10°C
0°C gelation).

From the results shown in FIG. 1, it has become clear that the higher the temperature of gelling, the more Tc moves to the higher temperature side, which has an advantageous effect on transparent vitrification.

However, the boiling points of the raw materials and solvent used here are Si (OC2Hs) a (165,5
~168℃), Ge (OCA H9) a (2
99℃), 02Hs OH (78,3℃), 1(20(
100°C), therefore, when gelling was performed at 100°C, the water and alcohol boiled before gelation, resulting in the inconvenience that more than half of the solution was lost.

On the other hand, when each dried gel was treated at a high temperature of 1250''C, it was confirmed that it became transparent only when gelatinized at 100°C.

Example 2 An experiment was conducted to determine Tc using ammonia solutions of various concentrations instead of 120 in the sol composition solution shown in Example 1.

The results for the sample gelled at 70°C are shown in Figure 3.

Addition of ammonium solution moves 'Tc to the higher temperature side, but this depends on the concentration of the ammonia solution. For example, FIGS. 3A, B, and C show a solution having the composition of Example 1, 0.00324.0.00162.0.
This is the measured value when using an ammonia aqueous solution of 000648 mol/I). When an ammonium aqueous solution is used in this way, a gel body suitable for transparent vitrification can be obtained, but on the other hand, when the concentration is further increased, it becomes more likely to crack when drying.

Therefore, the next problem is how to obtain a homogeneous porous gel body that dries without cracking in step (1).

Generally, moving Tc to the high temperature side corresponds to obtaining a porous body with large pores during gelling, and the gel body is in a state where it is more easily broken when drying.

Example 3 At a temperature of 1300° C., a sol solution having a composition confirmed to be transparent and vitrified was subjected to drying treatment while measuring weight loss (see FIG. 4).

Drying at 50-110'C, approximately 10°C every 24 hours.
The temperature was raised between Weight loss is given in g/hour.

Gelation was carried out at 70°C, and once the temperature was lowered to 50°C, it was left to stand for 2 to 3 days and the experiment was started after confirming that the gel body had separated from the side of the container.

This situation is shown in FIG. This treatment was carried out because if drying is continued at 70°C after gelation, cracks often appear due to sudden separation from the sides.

By this treatment, it was possible to almost completely prevent cracks that would occur when the container was separated from the container.

Figure 4 shows the boiling points (b, p,), which correspond to the boiling points of ethyl alcohol and water, respectively. It quickly cracked and turned into small blocks.

Furthermore, if drying is stopped at a temperature below the boiling point of alcohol and water, which are solvents, the same cracking will occur when the temperature exceeds 100°C in the next high-temperature treatment. As mentioned above, the drying process is desirably continued at a temperature of at least 100°C or higher, and preferably continues to about 150 to 200°C).

Example 4 FIG. 6 is a schematic diagram of an apparatus for implementing the method according to the present invention, in which 2 is a solid gel, 8 is a container, 10 is a hanging device for hanging the container, and 11 is a device for weighing. 2 is a valve for adjusting the degree of sealing, 13 is a discharge hole for discharging evaporated solvent and water, and 14 is a constant temperature device that can control the temperature.

A solution of Si (OC2Hs ) a diluted with C2H50H was prepared, and an ammonia aqueous solution was added to the solution while stirring it with ultrasonic vibration. This sol solution is hung together with the container 8 on the hook of the electronic balance 11 using the hanging device 10, and
It was installed in 4. In order to carry out the hydration continuously, it was necessary to avoid shaking due to wind and accumulation, and for this purpose we also installed a hood inside to prevent the wind.

If there is a lot of space in the constant temperature device 14, the effect of opening and closing the valve will be reduced, so it is necessary to cover the opening block of the container 8 with aluminum foil or the like in advance and make a small hole.

Further, although only one container is shown in the figure, it is also possible to simultaneously dry a larger number of gel bodies while using the weight loss of one container as a monitor.

After gelatinizing at 70°C, the gel was allowed to separate from the container at 50 to 70°C, and then the temperature and opening/closing of the valve were controlled while monitoring weight loss.

It was necessary to slow the heating rate near the boiling point and to reduce the degree of valve opening to avoid cracking the gel body. The weight loss is on average less than 1 g/hour from 50 to 110°C, and at most 3 g/hour.
It never exceeded an hour.

Immediately after gelation, the volume was 100 mm in diameter and 20 mm in length (approximately IA), but after drying (up to 110°C) the volume was 6 mm in diameter.
Qmm, the length was 95fl. Drying took about 10 days, and no cracks occurred in the dried gel.

■ Perform high temperature treatment at a heating rate of approximately 100℃/hour in an e atmosphere, diameter 35 cranes, length 50 fl, weight approximately 100.
G's transparent and unbreakable quartz glass has been replaced.

Incidentally, in the apparatus shown in FIG. 6 described above, it is of course possible to automatically control the drying process. for example,
There is also a method in which the degree of opening and closing (degree of sealing) of the valve is set in advance for a certain temperature, and weight loss is taken as a signal and fed back to the temperature increase rate.

[Effects of the Invention] As explained above, the transparent vitrifiable gel body has the disadvantage of being very easy to break when drying, but it can be used to control the amount of evaporation in a device that can adjust the temperature and degree of sealing. By gelling at a lower temperature, drying until the gel body shrinks and leaves the container wall, and then increasing the temperature to a temperature above the boiling point of the solvent and water, a uniform dry gel body can be obtained without cracking. It has the advantage that large-sized glass with excellent homogeneity for use in optical fibers can be manufactured in large quantities.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the conventional glass synthesis method using the sol-gel method, Figure 2 is a graph showing the relationship between high temperature treatment temperature and specific surface area of samples with varying gelation temperatures, and Figure 3
The figure is a graph showing the relationship between high temperature treatment temperature and specific surface area when an ammonia aqueous solution is used, Figure 4 is a weight loss during the drying process, Figure 5 is a schematic diagram showing the gel drying process according to the present invention, and Figure 6 1 is a schematic diagram of an apparatus for carrying out the method of the invention for controlling temperature and degree of sealing while measuring weight loss; FIG. 1... Sol, 2... Gel, 3... Shrinked gel, 4... Sample, 5... Gas introduction hole, 6.
...Gas exhaust port, 7...Electric furnace, 9...Glass sample, 10...Hanging tool, 11...Electronic balance, 12.
... Control valve, 13... Exhaust port, 14... Constant temperature device. Applicant's agent Masaki Amemiya Figure 4 1N (0C) Figure 5 7o・C50"C11 (Jl;

Claims (1)

[Claims] (1) Dilute the alkoxide with a solvent, add water and hydrolyze it to generate a sol, then evaporate the water and solvent to form a porous gel body, and treat this porous gel body at high temperature. A method for producing glass for optical fiber which is made into transparent glass, the method comprising the following steps. I. A step of heating the sol at a temperature lower than the boiling point of the solvent to gel it. II, heating at a temperature lower than the boiling point of the solvent and drying until the gel body leaves the container wall; III, a step of drying the gel body by raising the temperature to a temperature higher than the boiling point of the solvent and water.