JP3295444B2 - Method for producing porous silica preform - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas phase alignment method (VAD).
The present invention relates to a method for producing a porous silica preform according to the present invention, and more particularly, to a method for producing a porous silica preform without delamination on the side surface of the porous silica preform. By sintering the porous silica base material manufactured by the VAD method, quartz glass is obtained.

[0002]

2. Description of the Related Art In general, as a method for producing a porous silica preform by the VAD method, a gaseous glass raw material, hydrogen gas, oxygen gas and an inert gas are supplied to a burner and flame-hydrolyzed to produce silica fine particles. Is produced, and the silica fine particles are adhered and deposited on a starting member made of quartz or the like to produce a silica porous base material.

In this method, a silicon compound such as silicon tetrachloride or silane trichloride is used as a gaseous glass material.
Flame hydrolysis of gaseous glass raw materials generates high-temperature gas containing water, hydrogen chloride, unreacted glass raw materials, and other non-adhered silica fine particles composed of nitrogen, etc. The base material is manufactured. The container is provided with an exhaust port for exhausting these high-temperature gases, and a gas to be supplied to the burner for reasons such as performing smooth exhaust in the container and controlling the temperature distribution on the surface of the porous silica base material. Is supplied with another secondary gas.

[0004] By supplying a secondary gas into a container, the silica porous matrix is improved in the reproducibility, stability and synthesis yield of the reaction by smooth exhaust and control of the temperature distribution on the surface of the porous silica matrix. Various methods for producing a material have been proposed.

[0005] For example, 1) When producing an optical fiber preform by the VAD method, the flame treatment is performed while controlling the inflow rate and temperature of the gas for discharging excess reactants and waste gas and controlling the temperature of the reaction vessel. To improve the reproducibility and stability of the reaction by forming a porous preform (Japanese Patent Publication No. 57-5134). 2) Using a low-temperature nitrogen gas or argon gas By laminating glass particles while cooling by spraying,
Method for improving the adhesion efficiency of glass particles
3) In a method of depositing and growing a porous silica base material in a container having an air supply port and an exhaust port, a gas is introduced from the air supply port through a control valve or an air filter. A method of improving the uniformity in the longitudinal direction by discharging the gas from the exhaust port, measuring the gas state in the container, and keeping the gas flow rate constant (Japanese Patent Laid-Open No. 60-908)
No. 44), 4) Apparatus for producing a porous optical fiber preform in a direction crossing the gas flow in a reaction vessel in which gas flows uniformly in a rectified state (Japanese Patent Application Laid-Open No. Sho 62-171939).
No.).

[0006]

However, the method 1) has a problem that it is necessary to control the temperature of the vessel, which complicates the management of the structure of the apparatus and the temperature control and increases the operating cost. ing. In the method 2), since a low-temperature secondary gas is directly blown onto the porous silica base material, an increase in the synthesis yield can be expected, but there is a problem that the stability of the flame is deteriorated and peeling is likely to occur. . In method 3),
Since the pressure and air volume near the secondary gas supply port are measured, there is a problem that sufficient flame stability cannot be obtained without responding sharply to the pressure fluctuation near the flame that is actually reacting. is there. In the case of producing a silica porous base material using the apparatus of 4), in order to efficiently discharge the non-adhered silica fine particles in the reaction vessel, a considerable exhaust flow rate and a considerable secondary gas flow rate accompanying the exhaust flow rate are required. Because of the necessity, when producing a large-sized porous base material, cracks and peeling on the side surface of the porous silica base material have not yet been reliably prevented.

As described above, the method of producing a porous silica matrix by supplying a secondary gas into a container requires a considerable amount of gas to efficiently exhaust high-temperature gas containing non-adhered silica fine particles. A large amount of exhaust flow is required, and most of the exhaust flow is secondary gas supplied into the container. Therefore, in practice, the flow rate of the secondary gas is several times to several tens times larger than the flow rate of the combustion gas from the burner, and the supply of the secondary gas to the container induces turbulence of the flame formed by the burner. As a result, the reproducibility and stability of the synthesis are adversely affected, resulting in a decrease in the synthesis yield, particularly in the initial stage of depositing the silica fine particles on the starting member.
At the interface between the weakly bonded starting member and the silica fine particles or in the vicinity thereof, there is a problem that cracks and peeling occur on the side of the porous silica base material, and this is practical especially in the production of large porous silica base materials. She lacked gender. Once cracking or peeling occurs in the porous silica base material, they grow in a chain as long as synthesis is continued, and it is very difficult to continue synthesis by, for example, dropping pieces falling into the burner opening. In addition, quartz glass obtained by sintering a porous silica base material having cracks and peeling has cracks and structural defects on its surface and inside. (4) The yield is extremely poor if it is not suitable for applications such as high temperature heat resistant materials, optical materials and electronic component materials, or even if only suitable portions are cut out and processed.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the reproducibility and stability of synthesis and the yield of synthesis without delamination on the side surface of the porous silica base material. To provide a method for producing a porous silica preform.

[0009]

In the initial stage of depositing silica fine particles on the starting member, peeling of the porous silica base material may be caused by peeling or cracking at the interface between the starting member and the silica fine particles having weak binding properties and in the vicinity thereof. Meaning of cracks, 1) caused by flame turbulence, 2) caused by cooling of porous silica base material of secondary gas, 3) caused by wind pressure of secondary gas, 4) inside container Some are caused by impact when the separated pieces of the silica fine particles adhered to the wall surface or the like fall into contact with the porous silica base material. 5) Projections in the container, such as those caused by contact with an exhaust pipe or a temperature sensor.

There is no method other than 4) for improving the exhaust efficiency, but for that purpose, a certain amount is required for the exhaust gas flow rate and the secondary gas flow rate. Therefore, the causes of 1) to 3) are serious in the actual production of the porous silica base material. The separation of the porous silica matrix occurs at most 4 to 5 hours after the start of the synthesis, and after that, no separation occurs for reasons other than 4) and 5).

The inventors of the present invention have pursued these causes and have studied diligently to take countermeasures. As a result, the importance of protecting the stability of the flame at the stage of depositing and depositing the silica fine particles on the starting member in the early stage of the synthesis is emphasized. Is essential, and a baffle plate is installed in the container so that the secondary gas flow supplied to the container does not directly contact the starting member, and silica is used so as not to disturb the flame, which is the combustion gas flow from the burner. By manufacturing a porous preform, the risk of exfoliation of the silica porous preform, which tends to occur at the initial stage when depositing silica fine particles on the starting member, is drastically reduced, and the reproducibility of the synthesis of the silica porous preform and The inventors have found that the stability and the synthesis yield can be improved, and have completed the present invention.

That is, according to the present invention, a gaseous glass material is jetted from an oxyhydrogen flame burner and flame-hydrolyzed in a vessel, and silica fine particles generated by the hydrolysis are deposited on a starting member. In a method for producing a porous silica preform for feeding gas and exhausting gas generated during flame hydrolysis, the secondary gas flow fed into the container is prevented from directly contacting the starting member. A method for producing a porous silica preform, characterized by producing a porous silica preform by installing a baffle plate in a container.

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

In the present invention, a porous silica base material is manufactured by providing a baffle plate so that the secondary gas sent into the container does not directly contact the starting member.

The position where the baffle plate is provided is not particularly limited as long as the secondary gas fed into the container does not directly contact the starting member, and the position where the secondary gas is fed is different. In the container, the position where the baffle plate is provided also changes.

The shape, material and the like of the baffle plate are not particularly limited, but the same material as the reaction vessel, for example, quartz glass or highly corrosion-resistant metal is preferable from the viewpoints of heat resistance, corrosion resistance, prevention of contamination of impurities, and the like. .

The present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing an example of the apparatus according to the present invention, and FIG. 2 is a view of the apparatus shown in FIG. 1 as viewed from above. FIG. 1 shows an example in which the baffle plate 6 is attached to the support rod 5 for pulling up the porous silica base material 3 because the secondary gas 8 is supplied from above the container 4. FIG. 3 is an explanatory view showing another example of the apparatus according to the present invention, and FIG. 4 is a view of the apparatus of FIG. 3 viewed from above. In FIG. 3, the secondary gas 8 is fed into the container 4 from a position facing the exhaust gas 7 with the porous silica base material 3 interposed therebetween. This is an example in which it is attached to the wall of the container 4 so as not to directly contact the base material 3.

By installing the baffle plate as described above, the secondary gas does not directly contact the porous silica base material, but the secondary gas goes around the baffle plate and comes into contact with the porous silica base material. Since it mixes moderately with the atmosphere gas in the container and exchanges heat and reduces the wind pressure at the same time, the above-mentioned causes of peeling 1) to 3) can be improved, and peeling of the porous silica matrix is drastically reduced. Things.

[0019]

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

EXAMPLE 1 Using the apparatus shown in FIG. 1, a support rod 5 having a burner 1 and a baffle plate 6 attached to a container 4 is set at a predetermined position, and silicon tetrachloride is supplied to the burner 1 as a gas 2 to be supplied to the burner. 10Nl /
min, hydrogen 254 Nl / min, oxygen 120 Nl / m
In, nitrogen was supplied at 62 Nl / min to synthesize a porous silica preform 3. Exhaust gas 7 at 6000 Nl / min
, And the synthesis was carried out for 14 hours by adjusting the flow rate of the secondary gas 8 so that the pressure in the container indicated by the pressure gauge 9 in the container was -20 to 0 mmAq. As a result, a silica porous base material having a synthesis yield of 62.0% and no peeling was obtained.

COMPARATIVE EXAMPLE 1 Using the apparatus shown in FIG. 1, a silica porous matrix was synthesized in the same manner as in Example 1 except that the baffle plate 6 was removed. The synthesis was stopped because peeling occurred on the side surface of the material.

Example 2 Using the apparatus shown in FIG. 3, a burner 1 and a support rod 5 were set at predetermined positions in a container 4 on which a baffle plate 6 was attached, and silicon tetrachloride was supplied to the burner 1 as a gas 2 to be supplied to the burner. 8Nl / m
in, hydrogen 254 Nl / min, oxygen 109 Nl / mi
n, nitrogen 62Nl / min to supply silica porous matrix 3
Was synthesized. Exhaust gas 7 was exhausted at a constant rate of 6000 Nl / min, and synthesis was performed for 7 hours by adjusting the flow rate of the secondary gas 8 so that the pressure in the container indicated by the pressure gauge 9 in the container became -20 to 0 mmAq. As a result, the synthesis yield was 7
At 2.3%, a silica porous base material without peeling was obtained.

Comparative Example 2 A porous silica preform was synthesized in the same manner as in Example 2 except that the baffle plate 6 was removed using the apparatus shown in FIG. Synthesis was stopped because peeling occurred on the side surface.

[0024]

As is apparent from the above description, according to the method of the present invention, the secondary gas is fed into the container, and the silica porous material which is likely to be generated at the initial stage when the silica fine particles are deposited on the starting member. This has the effect of producing a porous silica base material having no separation of the base material and improved reproducibility, stability and synthesis yield of synthesis.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one example of an apparatus according to the present invention.

FIG. 2 is a view of the device of FIG. 1 as viewed from above.

FIG. 3 is an explanatory view showing another example of the device according to the present invention.

FIG. 4 is a view of the apparatus of FIG. 3 as viewed from above.

[Explanation of symbols]

 1: Burner 2: Gas supplied to burner 3: Silica porous base material 4: Container 5: Support rod 6: Baffle plate 7: Exhaust gas 8: Secondary gas 9: Pressure gauge in the container

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideaki Okada 885-4 Obata, Tokuyama City, Yamaguchi Prefecture (56) References JP-A-60-90844 (JP, A) JP-A-61-247634 (JP, A) JP-A-61-197439 (JP, A) JP-A-56-88838 (JP, A) JP-A-54-173057 (JP, U) JP-A-1-122044 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) C03B 8/04 C03B 37/018

Claims (1)

(57) [Claims] 1. A gaseous glass material is ejected from an oxyhydrogen flame burner and flame-hydrolyzed in a container, and silica fine particles generated thereby are deposited on a starting member, and a secondary gas is fed into the container. In the method for producing a porous silica preform for exhausting a gas generated during flame hydrolysis, a secondary gas stream fed into the container is obstructed in the container so as not to directly contact the starting member. A method for producing a porous silica preform, comprising: installing a plate to produce a porous silica preform.