JPH05155630A - Production of silica porous base material - Google Patents

Abstract

PURPOSE:To provide a producing method of a silica porous base material causing neither crack nor peeling at the side face part thereof, improved in reproducibility, stability, and yield of the synthsis. CONSTITUTION:In producing a silica porous base material by VAD method, the silica porous base exhausting a definite quantity of an exhaust gas flow whose rate is 7.5-15 times the total gas flow rate in terms of standard state to be fed to a burner is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a vapor phase axial method (VAD).
Method) for producing a porous silica preform, and more specifically, a method for producing a porous silica preform having no cracks or peeling on the side surface of the porous silica preform. Quartz glass is obtained by sintering a porous silica preform manufactured by the VAD method.

[0002]

2. Description of the Related Art Generally, 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 obtain 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 porous silica preform.

In this method, silicon compounds such as silicon tetrachloride and silane trichloride are used as a gaseous glass raw material.
In flame hydrolysis of gaseous glass raw materials, high temperature gas containing water, hydrogen chloride, unreacted glass raw materials, and other non-adhered silica fine particles made of nitrogen, etc. is generated, so that the silica porous base material is isolated from the outside. Manufactured in a container. The container is provided with an exhaust port for exhausting these high-temperature gases, and the gas to be supplied to the burner is used for the purpose of performing smooth exhaust in the container and controlling the temperature distribution on the surface of the porous silica preform. Separately, secondary gas is supplied.

In the production of porous silica preform, a method of exhausting high temperature exhaust gas generated by flame hydrolysis of a gaseous glass raw material has a great influence on the reproducibility and stability of the synthesis and the improvement of the synthesis yield. Furthermore, the physical properties and productivity of the obtained silica porous base material are greatly influenced.

Therefore, various methods have been proposed for producing a porous silica preform characterized by a method of exhausting high-temperature exhaust gas generated by flame hydrolysis of a gaseous glass raw material.

For example, 1) when manufacturing an optical fiber preform by the VAD method, controlling the inflow amount and temperature of the gas for discharging the excess reactant and waste gas, controlling the temperature of the reaction vessel, and flame treatment. To improve the reproducibility and stability of the reaction by forming a porous base material (Japanese Patent Publication No. 57-35134), 2) controlling the pressure or air volume of the exhaust gas discharged from the container. To stably obtain a desired diameter of the porous silica preform (Japanese Patent Laid-Open No. 58-20745), 3) deposit the porous silica preform in a container having an air supply port and an exhaust port. In the growing method, a gas is introduced into the container from the air supply port through the control valve and the air filter and discharged from the exhaust port, the gas state in the container is measured, and the gas flow rate is kept constant. By , To improve the poor accuracy of the pressure measurement derived from the corrosive hot gases, a method to improve the longitudinal uniformity of the silica porous preform (JP 60-9084
No. 4).

[0007]

However, in the method 1), it is necessary to control the temperature of the container, and there is a problem that the structure of the apparatus and the management of the temperature control are complicated and the operating cost becomes high. There is. In the method 2), since the pressure of the exhaust gas itself or the air volume is controlled, it is difficult to control the subtle pressure fluctuation and air volume fluctuation, and the temperature fluctuation is large, so that the flame stability is poor, and as a result, the synthesis yield and It has a drawback that productivity is poor and cracks and peeling easily occur on the side surface of the silica porous matrix. Once cracks and exfoliation occur in the silica porous matrix, they grow in a chain as long as the synthesis is continued, and it is very difficult to continue the synthesis because the exfoliated pieces fall into the burner mouth. Also,
Quartz glass obtained by sintering a porous silica base material with cracks and peeling has cracks and structural defects on its surface and inside. , Is it not suitable for applications such as optical materials and electronic component materials?
Alternatively, even if only an appropriate portion is cut out and processed, there is a problem that the yield is significantly deteriorated. In the method of 3), since the pressure and the air volume near the secondary gas supply port are measured, it does not respond sharply to the pressure fluctuations near the actually reacting flame, and sufficient flame stability is obtained. Since it cannot be obtained, it has the same problems as the above method 2).

The present invention has been made in view of the above problems, and an object thereof is to prevent reproducibility of synthesis, stability, and synthesis yield without causing cracks or peeling on the side surface of the porous silica matrix material. Provided is an improved method for producing a porous silica preform.

[0009]

In order to solve the above problems, the present inventors have made various studies on the relationship between the exhaust gas flow rate and the total gas flow rate supplied to the burner, and as a result,
When the exhaust gas flow rate is less than 7.5 times the standard state conversion with respect to the total gas flow rate supplied to the burner and when it exceeds 15 times, cracks and peeling often occur on the side surface of the silica porous matrix, Further, they have found that the exhaust flow rate has a great influence on the reproducibility and stability of the synthesis of the silica porous matrix and the synthesis yield, and thus completed the present invention.

That is, according to the present invention, a gaseous glass raw material is jetted from an oxyhydrogen flame burner and flame-hydrolyzed in a container, silica fine particles produced thereby are deposited on a starting member, and the secondary particles are stored in the container. In a method for producing a silica porous matrix in which a gas is fed and exhaust gas generated during flame hydrolysis is exhausted, the total gas flow rate supplied to the burner is 7.5 to 15 times the standard state. A method for producing a porous silica preform characterized by exhausting a fixed amount of exhaust gas.

The present invention will be described in more detail below.

In the method of the present invention, the exhaust gas flow rate is 7.5 to 15 times as much as the standard state of the total gas flow rate supplied to the burner. When the total gas flow rate supplied to the burner is converted to less than 7.5 times and exceeds 15 times the standard state, cracks and peeling often occur on the side surface of the porous silica preform. The reason for this is not clear, but the following can be considered.

That is, when the exhaust gas flow rate is relatively small with respect to the total gas flow rate supplied to the burner, the exhaust gas flow disturbs the flame to a small extent, and the flame stability tends to be improved, resulting in efficient silica fine particles. Is promoted and the synthetic yield is improved. However, on the other hand, among the silica fine particles generated in the container, the unadhered silica fine particles that could not be deposited in the flame were not sufficiently discharged to the outside of the container. However, this may cause cracking or peeling of the side surface of the porous silica base material. On the other hand, when the exhaust gas flow rate is relatively large with respect to the total gas flow rate supplied to the burner, the exhaust gas flow disturbs the flame to a large extent, and the flame stability tends to decrease, resulting in efficient deposition of silica fine particles. Being marginalized reduces the synthetic yield. In this case, since the unadhered silica fine particles that could not be deposited in the flame were relatively well discharged to the outside of the container, the layer of the silica fine particles loosely attached to the surface of the porous silica preform became thin. The cracks and peeling occur due to the instantaneous temperature change of the porous silica preform due to the disturbance of the flame.

In the present invention, in order to obtain flame stability, exhaust gas must be exhausted at a constant exhaust gas flow rate. Fluctuations in the exhaust gas flow rate cause flame turbulence, which lowers the synthesis rate of the silica porous base material due to the deterioration of the deposition efficiency of the silica fine particles, and cracks and peeling of the side surfaces of the silica porous base material due to the strength of adhesion of the silica fine particles. Cause of.

In the present invention, since the exhaust gas flow rate is 7.5 to 15 times as much as the standard state of the total gas flow rate supplied to the burner, most of the exhaust gas flow rate is supplied into the container. It is a secondary gas.

The flow rate of the secondary gas supplied into the container is preferably controlled so that the pressure inside the container is -20 to 0 mmAq. When the pressure in the container is lower than -20 mmAq, the exhaust pressure is high, and even a small change in the exhaust pressure causes turbulence of the flame, which is not preferable. Further, when the pressure inside the container is higher than 0 mmAq, the secondary gas flow rate is excessive, so that it is difficult to efficiently discharge the unattached silica fine particles to the outside of the container, which is not preferable.

The secondary gas in the present invention is not particularly limited, but it is preferable to use clean air and / or an inert gas because impurities are prevented from being mixed in the porous silica base material.

[0018]

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

Example 1 Using the apparatus shown in FIG. 1, a burner 1 was set in a container 4 at a predetermined position, and silicon tetrachloride 8 was used as a gas 2 to be supplied to the burner.
Nl / min, hydrogen 284Nl / min, oxygen 109N
l / min and 62 Nl / min of nitrogen were supplied (total gas flow rate of 463 Nl / min) to synthesize the porous silica matrix 3. The exhaust gas generated in the container was discharged to the outside of the container through the exhaust port 5, and the flow rate was controlled by the exhaust gas flow rate regulator 7. Since the exhaust gas is a high-temperature gas containing water, hydrogen chloride, unreacted glass raw material, and other non-adhered silica fine particles composed of nitrogen, etc., the exhaust treatment device 6 removes dust, harm, and heat-treats, and then uses the blower 8. Released into the atmosphere. At this time,
The exhaust gas 9 is exhausted at a constant rate of 4500 Nl / min, which is 9.7 times the total flow rate of the gas 2 supplied to the burner, and the in-vessel pressure indicated by the in-vessel pressure gauge 11 is -20 to 0 m.
Adjust the flow rate of the secondary gas 10 to be 17 mAq.
Time synthesis was performed. As a result, a silica porous base material having a synthetic yield of 77.2% and free from cracks or peeling on the side surface was obtained.

Example 2 Using the apparatus shown in FIG. 1, silicon tetrachloride 8Nl / mi was used as a burner.
n, hydrogen 275 Nl / min, oxygen 116 Nl / mi
n, nitrogen 62 Nl / min is supplied (total gas flow rate 461
Nl / min), and a silica porous base material was synthesized. Exhaust gas flow rate of 13.0 of total gas flow rate supplied to burner
A certain amount of gas was exhausted at 6000 Nl / min, which was doubled, and the secondary gas flow rate was adjusted so that the pressure in the container was −20 to 0 mmAq, and synthesis was performed for 10.5 hours. As a result, a silica porous base material having a synthetic yield of 68.1% and free from cracks or peeling on the side surface was obtained.

Example 3 Using the apparatus of FIG. 1, silicon tetrachloride of 10 Nl / m was used as a burner.
in, hydrogen 304 Nl / min, oxygen 120 Nl / mi
n, nitrogen 62 Nl / min is supplied (total gas flow rate 496
Nl / min), and a silica porous base material was synthesized. The exhaust gas flow rate was exhausted at a constant rate of 4500 Nl / min, which is 9.1 times the total gas flow rate supplied to the burner, and the secondary gas flow rate was adjusted so that the internal pressure of the container was -20 to 0 mmAq, and synthesis was performed for 12 hours. I went. As a result, the synthetic yield was 6
At 5.3%, a silica porous base material having no cracks or separation on the side surface was obtained.

Comparative Example 1 Using the apparatus shown in FIG. 1, silicon tetrachloride of 8 Nl / mi was used as a burner.
n, hydrogen 284 Nl / min, oxygen 109 Nl / mi
n, nitrogen 62 Nl / min is supplied (total gas flow rate 463
Nl / min), and a silica porous base material was synthesized. The exhaust gas flow rate was exhausted at a fixed amount of 3333 Nl / min, which was 7.2 times the total gas flow rate supplied to the burner, and the secondary gas flow rate was adjusted so that the internal pressure of the container was -20 to 0 mmAq, and synthesis was performed. As a result, peeling occurred on the side surface of the silica porous base material 2 hours after the start of the synthesis, so the synthesis was stopped.

Comparative Example 2 Using the apparatus of FIG. 1, the burner was made of silicon tetrachloride 8 Nl / mi.
n, hydrogen 275 Nl / min, oxygen 116 Nl / mi
n, nitrogen 62 Nl / min is supplied (total gas flow rate 461
Nl / min), and a silica porous base material was synthesized. Exhaust gas flow rate of 16.3 of total gas flow rate supplied to burner
When a certain amount of gas was exhausted at 7500 Nl / min, which was doubled, and the secondary gas flow rate was adjusted so that the pressure in the container became −20 to 0 mmAq, the synthesis was performed.
After 5 hours, the side surface of the silica porous matrix was peeled off, so the synthesis was stopped.

Comparative Example 3 Using the apparatus of FIG. 1, a burner was made of silicon tetrachloride of 10 Nl / m.
in, hydrogen 304 Nl / min, oxygen 120 Nl / mi
n, nitrogen 62 Nl / min is supplied (total gas flow rate 496
Nl / min), and a silica porous base material was synthesized. The exhaust gas flow rate was 6.7 times the total gas flow rate supplied to the burner, and a certain amount of gas was exhausted at 33 Nl / min, and the secondary gas flow rate was adjusted so that the internal pressure of the container was -20 to 0 mmAq, and synthesis was performed. However, after 3 hours from the start of the synthesis, peeling occurred on the side surface of the porous silica base material, so the synthesis was stopped.

Comparative Example 4 Using the apparatus shown in FIG. 1, silicon tetrachloride 8Nl / mi was used as a burner.
n, hydrogen 275 Nl / min, oxygen 116 Nl / mi
n, nitrogen 62 Nl / min is supplied (total gas flow rate 461
Nl / min), and a silica porous base material was synthesized. Exhaust gas flow rate of 15.2 of total gas flow rate supplied to burner
When a certain amount of gas was exhausted at 7,000 Nl / min, which was double, and the secondary gas flow rate was adjusted so that the internal pressure of the container was −20 to 0 mmAq, the synthesis was performed.
After 5 hours, the side surface of the silica porous matrix was peeled off, so the synthesis was stopped.

Comparative Example 5 Using the apparatus shown in FIG. 1, silicon tetrachloride of 10 Nl / m was used as a burner.
in, hydrogen 304 Nl / min, oxygen 120 Nl / mi
n, nitrogen 62 Nl / min is supplied (total gas flow rate 496
Nl / min), and a silica porous base material was synthesized. The exhaust gas flow rate was exhausted at a constant amount of 4500 Nl / min, which is 9.1 times the total gas flow rate supplied to the burner, and the secondary gas flow rate was adjusted so that the internal pressure of the container was -50 to -20 mmAq. When I went, 3 after starting the synthesis
The synthesis was stopped because peeling occurred on the side surface of the porous silica preform after a lapse of time.

[0027]

As is apparent from the above description, according to the present invention, cracks are generated in the side surface of the porous silica preform due to the instability of the flame due to the variation of the exhaust gas flow rate and the exhaust pressure in the conventional method. There is no peeling or peeling, and the effect is that the reproducibility and stability of the synthesis in the production of the silica porous base material and the synthesis yield can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an apparatus used in the present invention.

[Explanation of symbols]

 1: Burner 2: Gas supplied to burner 3: Silica porous base material 4: Container 5: Exhaust port 6: Exhaust gas treatment device 7: Exhaust gas flow controller 8: Blower 9: Exhaust gas 10: Secondary gas 11: Pressure gauge in container

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eiji Shioda 276-376 Osaki, Hofu City, Yamaguchi Prefecture (72) Inventor Hideaki Okada 885-4 Obata, Tokuyama City, Yamaguchi Prefecture

Claims (2)

[Claims] 1. A gaseous glass raw material is jetted from an oxyhydrogen flame burner to undergo flame hydrolysis in a container, silica fine particles produced thereby are deposited on a starting member, and a secondary gas is fed into the container. However, in the method for manufacturing a silica porous base material for exhausting exhaust gas generated during flame hydrolysis, the total gas flow rate supplied to the burner is 7.5 in terms of standard state.
A method for producing a porous silica preform, comprising exhausting a fixed amount of the exhaust gas flow rate of 15 times. 2. The method for producing a silica porous base material according to claim 1, wherein the flow rate of the secondary gas is controlled so that the pressure in the container is −20 to 0 mmAq.