JPH09309735A - Production of silica glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a synthetic silica glass having viscosity characteristics at high temperature similar to a natural one by reacting a porous glass material of silica including a prescribed hydroxyl group with a halogenated silane under a specific condition and treating the resultant product to form a silica glass material. SOLUTION: A porous glass material of silica obtained by a flame hydrolysis of a silane compound (e.g. tetrachlorosilane) is preheated preferably in a reduced pressure atmosphere and below the reaction temperature, further reacted with a halogenated silane, preferably methyltrichlorosilane or tetrachlorosilane, in an inactive gas atmosphere at 300-800 deg.C. Thereafter, the resultant product is treated under a reduced pressure by an evacuation at a temperature of 850 deg.C or more and the beginning temperature of a sintering (1000 deg.C) or less and further compacted at high temperature of 1600 deg.C or more under a reduced pressure to form the objective transparent glass material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing quartz glass obtained by treating a porous body produced by flame hydrolysis.

[0002]

2. Description of the Related Art The production of synthetic quartz glass is well known by densifying a porous body mainly obtained by flame hydrolysis of silicon halide at high temperature. The synthetic quartz glass thus obtained has undergone a flame hydrolysis step and therefore contains a large amount of OH groups in the porous body. The presence of a large amount of OH groups in the quartz glass unfavorably lowers the viscosity of the glass, lowers the heat resistance, and causes absorption in the near-infrared region even when it is used as a base glass for a communication optical fiber.

As a countermeasure against this, in Japanese Patent Laid-Open No. 54-127914, a glass forming raw material is thermally oxidized or hydrolyzed to adhere a glass forming substance containing silicon dioxide (SiO ₂ ) as a main component to the end face of a supporting rod. Then, a porous glass sintered body is produced, and the porous glass sintered body is exposed to a glass forming raw material gas containing a halogen element at 800 to 1000 ° C., and then made into a transparent glass to produce an anhydrous glass base material. Is disclosed.
Glass forming raw materials include SiCl ₄ , SiBr ₄ , GeCl ₄ , BB
Examples are r ₃ , POCl ₃ , PCl _{3 and the} like.

Further, Japanese Patent Laid-Open No. 54-134128 discloses that a de-OH group reaction of a porous preform produced by flame hydrolysis can be carried out without causing transparent vitrification. Contains halogen compounds at a temperature of 500 ° C
It is carried out in an atmosphere of He and then vitrified into a glass at a temperature of 1000 to 1600 ° C.

Further, in Japanese Patent Laid-Open No. 55-10412, a glass forming substance containing silicon dioxide (SiO ₂ ) as a main component is adhered to a supporting rod by an oxyhydrogen burner flame to obtain a porous glass body. . Then, helium gas (He) 2 l / min,
Liquid chlorine-containing compounds (S ₂ Cl ₂ , SCl ₂ , SiCl ₄ , PC
( ₃ , CCl _4, etc.) are sent to a heating furnace, and the porous glass body is heated to 1500 ° C. in a chlorine gas atmosphere obtained by thermally decomposing the generated vapor to perform transparent vitrification. At this time, prior to the transparent vitrification, the porous glass body is preferably preliminarily dehydrated with chlorine gas at 800 ° C.,
Is disclosed.

[0006]

The synthetic quartz glass obtained by these methods has been used as an optical fiber for optical communication because of its small amount of impurities. However, the quartz whose raw material has a viscosity at high temperature is natural quartz. Lower than glass and deformation in the hot working process was recognized as a major drawback. Therefore, even in the semiconductor industry field where a large amount of quartz glass is used, its use is limited. An object of the present invention is to provide a method for producing synthetic quartz glass having high temperature viscosity characteristics comparable to those of natural quartz glass.

[0007]

The synthetic quartz glass obtained by the conventional production method is accompanied by a hydrolysis reaction, so that the obtained porous body contains a large amount of OH groups. This OH group reduces the viscosity of the glass and has absorption at a specific wavelength,
Since it is not preferable as the base material glass for optical fibers, a chlorine-based gas is usually used to carry out a dehydration treatment in which it is reacted with the OH groups in the porous body to be removed, as described above. However, a considerable amount of chlorine remains in the porous body by the dehydration treatment using a chlorine-based gas.

As a result of earnest studies, the present inventors have found that chlorine remaining in the porous body is one of the causes of lowering the viscosity at high temperature of quartz glass densified by heat treatment. In order to increase the viscosity at a high temperature, it is sufficient to completely perform dehydration between the dehydration treatment of the porous body and the densification step, and reduce the residual chlorine concentration to a level that does not affect the viscosity. Therefore, the above problems have been solved. The method for producing quartz glass of the present invention is a method in which a silica porous glass body containing a hydroxyl group obtained by flame hydrolysis of a silane compound and a halogenated silane are reacted at a temperature of 300 to 800 ° C. in an inert gas atmosphere. It is characterized in that it is evacuated at a temperature not lower than 850 ° C. and not higher than the sintering start temperature, and then densified under a high temperature reduced pressure of not lower than 1600 ° C. to obtain a transparent quartz glass body.

At this time, it is preferable to use methyltrichlorosilane or tetrachlorosilane as the halogenated silane. Prior to supplying the reaction gas to the silica porous glass body, it is preferable to preheat the porous silica glass body in a reduced pressure atmosphere at a reaction temperature or lower. further,
As the silica porous glass body, a silicon halide alone or a porous body obtained by flame hydrolysis of a mixture of silicon halide and aluminum halide can be used. As disclosed in Japanese Examined Patent Publication No. 7-115881, synthetic quartz glass containing a trace amount of aluminum has improved viscosity at high temperature, but it is possible to further improve the viscosity by applying the method of the present invention. The heat resistance can be increased.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION According to the method for producing quartz glass of the present invention, the halogenated silane used as a reaction gas is
An embodiment using methyltrichlorosilane (SiCH ₃ Cl ₃ ) will be described in detail as an example. First, tetrachlorosilane is hydrolyzed by a known method to deposit silica fine particles to form a porous body. The porous body is set in a quartz glass furnace core tube provided in an electric furnace and heated to a predetermined temperature. At this time, it is preferable to remove the water adsorbed on the porous body by keeping the porous body at a temperature lower than the reaction temperature for a certain period of time.

Next, methyltrichlorosilane vapor is flown while being diluted with nitrogen gas to react the OH groups bonded to the porous material with methyltrichlorosilane. At this time, the following reaction is considered to occur. In the formula, Me represents a methyl group. Si-OH + SiMeCl ₃ → Si-O-SiMeCl ₂ + HCl The porous body after the reaction is transferred into a reduced pressure atmosphere of 1 × 10 ⁻³ mmHg or less and heated. When the heating temperature exceeds about 600 ℃, exchange of Si-O bond and Si-C bond occurs in the porous body, and chlorine of methyltrichlorosilane is converted into Cl ₂ MeSiOSiMeCl ₂
Since it is discharged as a part of molecules such as, it is desirable that heating is performed for a sufficient time from 600 ° C. to the sintering start temperature while exhausting.

Thereafter, the temperature is further raised to a temperature of about 1600 to 1800 ° C. to make the porous body into a dense transparent glass. At this time, large molecules such as Cl ₂ MeSiOSiMeCl ₂ cannot be dissolved in the glass and are discharged, resulting in extremely small residual chlorine. On the other hand, when the dehydration reaction is performed by the conventional method, the substitution reaction between the OH group and the chlorine atom in the porous body is the main, so chlorine molecules are generated by heating in the heating step for densifying the porous body. However, since this chlorine molecule is small enough to dissolve in the glass,
It will remain in the glass.

The reaction temperature between the porous material and methyltrichlorosilane is preferably 300 to 800 ° C. If the temperature is lower than 300 ° C, the reaction does not proceed, and if the temperature exceeds 800 ° C, a large amount of methyltrichlorosilane is adsorbed on the porous body, and it is thermally decomposed by the subsequent heating to generate carbon fine particles, and the obtained quartz glass is colored. Sometimes. When ethyl trichlorosilane or the like having a larger number of carbon atoms is used, or when two or more substitution products such as dimethyldichlorosilane are used, similarly, pyrolytic carbon is generated or the silane molecule becomes large. Since the dehydration reaction may be delayed, it is necessary to appropriately adjust the reaction time and the heating rate depending on the silane compound used.

Furthermore, it is also possible to use tetrachlorosilane as the reaction gas. In this case, the residual chlorine becomes a little larger than that in the case of using methyltrichlorosilane, and there is a tendency that the degree of improvement in viscosity becomes slightly smaller accordingly, but tetrachlorosilane is also used as a raw material for producing a porous body. Therefore, there is no need to use any other material, which is convenient in manufacturing. Further, tetrachlorosilane does not thermally decompose to generate carbon, and the reaction temperature can be raised to complete the dehydration treatment in a short time.

After the reaction between the porous body and the halogenated silane at a temperature of 300 to 800 ° C., the porous body was evacuated at a temperature of 850 to 1000 ° C. and then densified under a high temperature and reduced pressure of 1600 ° C. or more. By doing so, a transparent quartz glass body is obtained.
It should be noted that 1000 ° C. is a temperature at which sintering of the porous body substantially starts. Hereinafter, the present invention will be described based on Examples.

[0016]

【Example】

Examples 1 to 7; about 1 kg of a columnar quartz glass porous body having a diameter of 100 mm, obtained by flame hydrolysis of tetrachlorosilane, was installed in an electric furnace and made of a quartz glass furnace core tube (diameter 200). mm). Next, after exhausting the inside of the furnace core tube, the furnace core tube was heated to 300 ° C. (the gas may be exhausted while heating) and preheated at this temperature for 60 minutes. Then, the temperature was raised to the reaction temperature, and methyltrichlorosilane vapor or tetrachlorosilane vapor was supplied as a reaction gas with the OH group in the porous body while being diluted with N ₂ gas to cause a reaction. The porous materials used in Examples 1 and 5 were obtained by flame hydrolysis of a mixed gas of tetrachlorosilane and aluminum halide, and the usage ratio was 5% by weight of aluminum in the porous body. It was adjusted to contain about ppm. In other examples and comparative examples described later, a porous body obtained by flame hydrolysis of only tetrachlorosilane was used.
The reaction conditions are as shown in Table 1.

[0017]

[Table 1]

The heating was carried out at the reaction temperature shown in the table, while maintaining that temperature for the indicated reaction time. In addition,
The flow rate of N ₂ gas is 1 mol / hr. After the reaction was completed, the treated porous body was transferred into a vacuum furnace and heated to 900 ° C,
After reducing the pressure to 1 × 10 ^-3 mmHg or less, hold it for 1 hour, then
The temperature was raised to ° C to obtain a densified transparent quartz glass.

Comparative Examples 1 and 2; Further, as Comparative Example 1, dehydration reaction was carried out using a conventional chlorine gas as a reaction gas. In Comparative Example 2, the porous body was densified without using a reaction gas. Other processing conditions are the same as those in the example and are as shown in Table 1. The natural product is a quartz glass obtained by melting natural quartz with an oxyhydrogen flame.

OH and chlorine remaining in the obtained quartz glass were measured by infrared absorption spectroscopy and nephelometric chlorine analysis, respectively, and further heated at 1280 ° C. to measure the viscosity at that temperature by the beam bending method. did. The results are shown in Table 2.
Shown in

[0021]

[Table 2]

The quartz glass obtained in Examples 1 to 7 has a viscosity at a high temperature which is about the same as or higher than that of a natural product using natural quartz as a raw material. Even if there was, it was difficult to deform. Further, the quartz glass of Examples 1 and 5 using a mixture of tetrachlorosilane and aluminum halide as the raw material of the porous body,
Further, the viscosity at high temperature was increased, and the heat resistance was extremely improved. On the other hand, the quartz glass of Comparative Example 1 was sufficiently dehydrated, but the residual concentration of chlorine was high, and Comparative Example 2
In the quartz glass of No. 3, OH remained although it was slightly reduced due to the densification in vacuum. Therefore, the silica glass obtained in Comparative Examples 1 and 2 had a considerably low viscosity at high temperature. In addition, the high viscosity at high temperature of natural products made from natural quartz despite the high OH concentration is due to the difference in glass structure due to the difference in starting materials.

[0023]

As described above in detail, a silica porous glass body containing a hydroxyl group is treated with methyltrichlorosilane or tetrachlorosilane in an inert gas atmosphere at a temperature of 300 to 300.degree.
After reacting at 800 ℃, it is evacuated at a temperature of 850 ℃ or higher and below the sintering start temperature, and then densified under high temperature and reduced pressure of 1600 ℃ or higher. Quartz glass having a high viscosity comparable to that at high temperature was obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuhiro Sato 2-13-60 Kitafu, Takefu City, Fukui Prefecture Shin-Etsuishi Ei Takefu Factory Co., Ltd.

Claims (4)

[Claims] 1. A silica porous glass body containing hydroxyl groups obtained by flame hydrolysis of a silane compound and a halogenated silane are reacted at a temperature of 300 to 800 ° C. in an inert gas atmosphere, and then at 850 ° C. or higher. A method for producing a quartz glass, which comprises evacuating at a temperature not higher than a sintering start temperature and then densifying at a high temperature and a reduced pressure of 1600 ° C. or more to obtain a transparent quartz glass body. 2. The method for producing quartz glass according to claim 1, wherein the halogenated silane is methyltrichlorosilane or tetrachlorosilane. 3. The quartz glass according to claim 1, wherein the silica porous glass body is preheated in a reduced pressure atmosphere and at a reaction temperature or lower prior to supplying the reaction gas to the silica porous glass body. Manufacturing method. 4. A porous body obtained by flame hydrolysis of silicon halide alone or a mixture of silicon halide and aluminum halide, as the silica porous glass body. 1. The method for producing quartz glass according to 1 or 3.