JP7404144B2 - Method for manufacturing porous glass particles and method for manufacturing optical fiber base material - Google Patents

Description

The present invention relates to a method for manufacturing porous glass particles and a method for manufacturing an optical fiber preform.

Patent Document 1 discloses a method for manufacturing porous glass particles by ejecting raw material gas from a burner and reacting in a flame, and depositing the generated glass particles on a starting member. An optical fiber preform can be obtained by subjecting the porous glass particles to a sintering treatment or the like. Generally, silicon tetrachloride (SiCl ₄ ) is used as the raw material gas.

JP2013-249232A

Since hydrochloric acid is produced when silicon tetrachloride is reacted, there are issues in terms of environmental impact and processing costs. Therefore, in recent years, organic silicon compounds have been increasingly used as the raw material gas.
Here, when using a flammable raw material gas such as an organic silicon compound, it is necessary to prevent the flame from progressing into the burner (backfire) when extinguishing the fire. On the other hand, when the fire is extinguished by gradually decreasing the flow rate of oxygen gas as in Patent Document 1, soot is generated due to incomplete combustion of the raw material gas, which may lead to deterioration of the quality of the optical fiber preform.

The present invention has been made in consideration of these circumstances, and provides a method for producing porous glass particles and a light source capable of suppressing soot generation while preventing backfire when using a flammable raw material gas. An object of the present invention is to provide a method for manufacturing a fiber base material.

In order to solve the above problems, a method for manufacturing porous glass particles according to one aspect of the present invention supplies a premixed gas containing a flammable raw material gas and oxygen to a burner, and supplies the premixed gas to the A deposition step in which glass particles generated by combustion at the outlet of a burner are deposited on a starting member to form soot, and a flow rate of the raw material gas contained in the premixed gas is reduced. a production stop step of reducing the mixing ratio of the raw material gas to the oxygen to be within a non-combustible region and stopping the production of glass particles at the outlet; At the time when reaching the impossible region, the speed difference ΔV (=V1-V2) between the ejection velocity V1 of the premixed gas at the outlet and the combustion velocity V2 of the premixed gas is greater than or equal to zero, and the production stop step In this case, the time required for reducing the mixing ratio from the value in the deposition step to zero is within 10 seconds .

According to the above aspect of the present invention, when using a flammable raw material gas, it is possible to prevent backfire and suppress the generation of soot.

FIG. 1 is a schematic diagram showing a manufacturing apparatus according to the present embodiment. FIG. 2 is a schematic diagram showing the configuration of the supply device of FIG. 1. FIG. It is a figure showing the control content of the premixed gas concerning this embodiment. It is a figure which shows the control content of the premixed gas based on the modification of this embodiment. It is a figure which shows the control content of the premixed gas based on a comparative example.

Hereinafter, a method for manufacturing a porous glass particle according to the present embodiment will be explained based on the drawings. The porous glass microparticles obtained according to this embodiment can be produced by applying, for example, an outside vapor deposition method (OVD method) or a vapor phase axial deposition method (VAD method). , an optical fiber preform can be obtained.

The OVD method is a method in which a glass soot layer is formed by depositing glass particles on the outer surface of a starting member such as a glass rod, and then the glass soot layer is sintered by heating to obtain transparent glass.
The VAD method is a method of obtaining transparent glass by starting the deposition of glass particles from the tip of a starting member such as a glass rod to form a cylindrical glass soot, and then sintering the glass soot by heating. be.

(Porous glass particle manufacturing device)
As shown in FIG. 1, the apparatus for manufacturing porous glass particles of this embodiment (hereinafter referred to as manufacturing apparatus 1) includes a reaction vessel 2, a pair of rotating chucks 3, a burner 4, a rail 5, and a supply A device 10 is provided. Although the number of burners 4 is one in FIG. 1, a plurality of burners 4 may be arranged at predetermined intervals in the longitudinal direction of the starting member M.
A pair of rotary chucks 3 support both ends of the starting member M. The starting member M is rotated within the reaction vessel 2 by the rotating chuck 3 .

The rail 5 extends in the same direction as the longitudinal direction of the starting member M. The burner 4 is movable along the rail 5. That is, the burner 4 is movable along the longitudinal direction of the starting member M. All or part of the feeding device 10 may also move along the rail 5 together with the burner 4 .
Note that the burner 4 may be moved in a reciprocating manner along the rail 5 in the longitudinal direction. Alternatively, for example, the rail 5 may be formed into an annular shape, and the plurality of burners 4 may be moved so as to circulate in one direction on the rail 5.
Although not shown, the manufacturing apparatus 1 may be configured to reciprocate the starting member M instead of the burner 4 along the longitudinal direction.

At the outlet 4a of the burner 4, a flame is generated by combustion of a premixed gas Gm, which will be described later, or by combustion of a combustible gas Gf supplied to the burner 4. In this specification, the flame generated by combustion of combustible gas Gf is referred to as "combustible gas combustion flame F1", and the flame generated by combustion of premixed gas Gm is referred to as "raw material combustion flame F2". Glass particles are generated by reacting the raw material gas contained in the premixed gas Gm within the raw material combustion flame F2. By depositing the glass particles on the surface of the starting member M, a deposited layer (soot L) of glass particles is formed. As a result, a porous glass particle body is obtained. In FIG. 1, the soot L has an effective portion E and an end portion P. The effective part E is a part where the thickness of the soot L is stable and the optical fiber can be used as a product when the optical fiber preform is drawn.

In this embodiment, an organic silicon compound is used as the source gas. Examples of the organic silicon compound include alkylcyclosiloxanes, with octamethylcyclotetrasiloxane (OMCTS) being particularly suitable. OMCTS is also called "D4", where "D" is a unit of (CH ₃ ) ₂ -Si-O-, and D4 means a structure in which four D units are connected in a ring. D4 (C ₈ H ₂₄ O ₄ Si ₄ ) is widely used industrially and is easily available, but D3 (C ₆ H ₁₈ O ₃ Si ₃ ), D5 (C ₁₀ H ₃₀ O ₅ Si ₅ ), etc. May be used. Further, D3, D4, and D5 may be used alone or in combination. Organic silicon compounds do not generate hydrochloric acid even when subjected to an oxidation reaction, so they contribute to reducing environmental impact and manufacturing costs by eliminating the need for hydrochloric acid processing equipment.

However, since organosilicon compounds are flammable, flashback is likely to occur. Flashback is a phenomenon in which a raw material combustion flame F2 is generated inside the burner 4 or the piping by igniting the raw material remaining inside the burner 4 or inside the piping connected to the burner 4 (burner line 12, etc. described below). It is. In this embodiment, in order to prevent the occurrence of backfire and to suppress the generation of soot due to incomplete combustion of the raw material gas, the flow rate control when stopping the supply of the raw material gas to the burner 4 is devised. Details of the supply device 10 and flow rate control will be described below.

(supply device)
As shown in FIG. 2, the supply device 10 includes a raw material supply line 11, a burner line 12, a vent line 13, a purge gas supply line 14, and a control section 15. The raw material supply line 11 is provided with a first valve 11a, a flow rate adjustment section 11b, and a vaporization unit 11d. Further, the raw material supply line 11 is connected to a carrier gas supply line 11c and an oxygen supply line 11e.

The upstream side of the raw material supply line 11 is connected to a liquid raw material supply source (not shown). The liquid raw material supply source supplies the liquid raw material to the raw material supply line 11 . The supply source may include, for example, a container containing a liquid raw material and connected to the raw material supply line 11, and a pressurized gas pipe supplying a pressurized gas having low solubility in the liquid raw material to the container. In this case, by supplying pressurized gas from the pressurized gas pipe to the container, the pressure inside the container can be increased, and the liquid raw material can be supplied from the container to the raw material supply line 11. A degassing device for degassing dissolved gas from the liquid raw material may be provided between the closed container and the flow rate adjustment section 11b.

A downstream end of the raw material supply line 11 branches toward a burner line 12 and a vent line 13 . The first valve 11a is located upstream of the flow rate adjustment section 11b and the vaporization unit 11d, and switches whether or not to flow the liquid raw material into the raw material supply line 11. The flow rate adjustment section 11b is located between the first valve 11a and the vaporization unit 11d, and adjusts the flow rate of the liquid raw material flowing toward the vaporization unit 11d. The flow rate adjustment unit 11b is an MFC (Mass Flow Controller) or the like.

The carrier gas supply line 11c supplies carrier gas to the raw material supply line 11. As the carrier gas, an inert gas such as argon (Ar), helium (He), nitrogen (N ₂ ), or oxygen (O ₂ ) can be used. The carrier gas may contain multiple types of gas.
The oxygen supply line 11e is connected to the downstream side of the vaporization unit 11d, and supplies oxygen (O ₂ ) to the raw material supply line 11. As a result, a premixed gas Gm is obtained. Oxygen is required to make the raw material gas combustible.

The burner line 12 is connected to the downstream end of the raw material supply line 11. The downstream end of the burner line 12 is connected to the burner 4 . Burner line 12 supplies premixed gas Gm to burner 4 . The burner line 12 is provided with a second valve 12a. The second valve 12a is configured to open and close the burner line 12. When the second valve 12a is open, the premixed gas Gm can flow toward the burner 4. A purge gas supply line 14 is connected to a portion of the burner line 12 between the second valve 12a and the burner 4.

The vent line 13 is provided with a third valve 13a. The third valve 13a is configured to open and close the vent line 13. A processing device (not shown) is provided downstream of the vent line 13. When the third valve 13a is open and the second valve 12a is closed, the premixed gas Gm flowing from the raw material supply line 11 passes through the vent line 13 and heads toward the processing device.

Purge gas supply line 14 supplies purge gas to burner 4 . As the purge gas, an inert gas such as nitrogen can be used. The purge gas supply line 14 is provided with a fourth valve 14a. The fourth valve 14a is configured to open and close the purge gas supply line 14. When the fourth valve 14a is open, purge gas can flow towards the burner 4.

The control section 15 is electrically connected to the first valve 11a, the second valve 12a, the third valve 13a, the fourth valve 14a, and the flow rate adjustment section 11b. The control unit 15 outputs a signal for switching the opening and closing of each valve 11a to 14a, and a signal for instructing the flow rate setting value by the flow rate adjustment unit 11b. Note that the control section 15 may be a part of the flow rate adjustment section 11b. Alternatively, the control unit 15 may be configured to control not only the supply device 10 but also the entire manufacturing device 1. As the control unit 15, an integrated circuit such as a microcontroller, an IC (Integrated Circuit), an LSI (Large-scale Integrated Circuit), or an ASIC (Application Specific Integrated Circuit) can be used.

The liquid raw material is introduced into the vaporization unit 11d together with the carrier gas with its flow rate controlled by the control unit 15 and the flow rate adjustment unit 11b, where it is vaporized, and then mixed with oxygen to become the premixed gas Gm. Premixed gas Gm is supplied to burner 4 from burner line 12 . When using D3, D4, or D5 as a raw material, when the number of D units contained in the premixed gas Gm is n1 and the amount of oxygen is n2, the number of D units in the premixed gas Gm and oxygen are The mixing ratio R (molar ratio) is represented by R=n1/n2.

The mixing ratio R is preferably 0.68≦R≦1.00. When the mixture ratio R exceeds 1.00, there is a lack of oxygen necessary for combustion of the raw materials, resulting in incomplete combustion and soot may be generated. When the mixture ratio R is less than 0.68, the combustion reaction becomes unstable, the raw material combustion flame F2 is disturbed, the glass particle deposition efficiency decreases, and the glass particles adhere to the burner 4. Note that when the carrier gas contains oxygen, the amount n2 of oxygen at the mixture ratio R is the sum of the amounts of oxygen supplied from the carrier gas supply line 11c and the oxygen supply line 11e.

Note that, for example, when the raw material is D4, 1 mole of the raw material contains 4 D units, so if the amount of the raw material is m, it should be noted that n1=m×4. When the mixture ratio R' of the premixed gas Gm is expressed by the amount m of substance D4, R'=m/n2. Therefore, in order to satisfy 0.68≦R≦1.00, 0.17≦R'≦0.25. Similarly, it should be noted that when the raw material is D3, n1=m×3, and when the raw material is D5, n1=m×5. Further, when raw materials having different numbers of D units such as D3, D4, and D5 are mixed and used, the value of n1 is calculated by considering the number of D units with respect to the amount of substance of each raw material.

In addition to the burner line 12, a combustible gas pipe and an oxygen pipe are connected to the burner 4. The flammable gas pipe supplies combustible gas Gf such as hydrogen (H ₂ ) and methane (CH ₃ ) to the burner 4 . The oxygen pipe supplies oxygen to the burner 4.

The burner 4 has a premixed gas port from which the premixed gas Gm is ejected, and a port from which the combustible gas Gf and oxygen are mixed and ejected. At the outlet 4a of the burner 4, the combustible gas Gf and oxygen are mixed and burned to generate a combustible gas combustion flame F1. The premixed gas Gm ignites the combustible gas combustion flame F1, and the raw materials react in the raw material combustion flame F2, thereby generating glass particles. The combustible gas combustion flame F1 may surround the raw material combustion flame F2. In this case, it is possible to suppress the generated glass particles from diffusing outward and to stabilize the temperature of the raw material combustion flame F2. In order to configure the combustible gas combustion flame F1 to surround the raw material combustion flame F2, for example, a premixed gas port is arranged in the center of the burner 4, and the combustible gas Gf and oxygen are arranged around the premixed gas port. A spouting port may also be provided.

(Method for producing porous glass microparticles)
Next, a method for manufacturing a porous glass particulate body according to this embodiment will be described.

First, the starting member M is attached to the rotating chuck 3.
Next, with the starting member M being rotated by the rotary chuck 3, glass fine particles are deposited on the starting member M while relatively reciprocating the burner 4 and the starting member M in the longitudinal direction (deposition step). More specifically, the control unit 15 opens the first valve 11a and the second valve 12a, and closes the third valve 13a and the fourth valve 14a. Further, the flow rate adjustment unit 11b adjusts the flow rate of the liquid raw material flowing toward the vaporization unit 11d so that the mixture ratio R of the premixed gas Gm supplied to the burner 4 falls within an appropriate range. As a result, the premixed gas Gm is combusted at the outlet 4a of the burner 4, thereby generating glass particles. The soot L is formed by depositing the glass particles on the starting member M rotated by the rotary chuck 3.

The burner 4 may reciprocate with respect to the starting member M between the two ends P while continuing to generate glass particles. Alternatively, when moving from within the range of the effective area E to outside of the range, the generation of glass particles may be once stopped, and when entering the range of the effective area E again, the generation of glass particles may be restarted. In order to stop the production of glass particles, the mixture ratio R of the premixed gas Gm supplied to the burner 4 is lowered to be outside the combustible range (production stop step). The generation stop step is performed when the formation of the soot L is completed or when the burner 4 moves out of the range of the effective portion E as described above. In the generation stop step, the combustion of the combustible gas Gf supplied to the burner 4 is also stopped, and both the combustible gas combustion flame F1 and the raw material combustion flame F2 may be extinguished, or the combustible gas combustion flame F1 is generated. Alternatively, only the generation of glass particles may be stopped. More specifically, when the formation of the soot L is completed, both the combustible gas combustion flame F1 and the raw material combustion flame F2 are extinguished in the generation stop step. When the formation of soot L is not completed and the burner 4 is temporarily moved outside the range of the effective part E, in the generation stop step, only glass particles are generated while the combustible gas combustion flame F1 is generated. stop.
After the production stop step, the second valve 12a may be closed and the fourth valve 14a may be opened to supply purge gas to the burner 4. Thereby, the premixed gas Gm remaining in the burner 4 and the burner line 12 can be discharged to the outside of the burner 4.

By completing the formation of soot L through the deposition process, porous glass particles are obtained. Moreover, an optical fiber preform can be obtained by subjecting the porous glass particles to a sintering process. In addition to the sintering process, the optical fiber preform may be subjected to a dehydration process or a doping process, if necessary.
Moreover, an optical fiber can be obtained by drawing an optical fiber preform.

Here, in the generation stop step, if the supply of the premixed gas Gm to the burner 4 is stopped, for example by closing the second valve 12a and opening the third valve 13a, without changing the mixture ratio R, the The ejection speed of the premixed gas Gm decreases and eventually reaches zero. Even if the flow rate of the premixed gas Gm decreases in this way, the combustion of the premixed gas Gm continues as long as the mixture ratio R is within the combustible range. When the combustion speed V2 of the premixed gas Gm exceeds the ejection speed V1 of the premixed gas Gm from the burner 4, a phenomenon (backfire) in which the raw material combustion flame F2 advances into the burner 4 occurs. When flashback occurs, dirt or damage may occur inside the burner 4 or the burner line 12.

Therefore, in this embodiment, during the production stop step, the flow rate of the raw material is changed to zero in a short time without changing the flow rate of at least one of the oxygen and carrier gas contained in the premixed gas Gm. That is, the mixture ratio R of the premixed gas Gm is lowered in a short time to be outside the combustible range. As a method of lowering the mixture ratio R, the set flow rate of the flow rate adjustment section 11b may be set to zero, or the first valve 11a may be closed. By not changing the flow rate of at least one of the oxygen and the carrier gas, it is possible to suppress a decrease in the ejection velocity V1 of the premixed gas Gm from the outlet 4a of the burner 4, and prevent flashback from occurring. After the mixture ratio R falls outside the combustible range, the second valve 12a is closed and the third valve 13a is opened to switch the flow path of the premixed gas Gm from the burner line 12 to the vent line 13.

The above control contents will be explained in more detail using FIGS. 3(a) and 3(b). Below, the ejection speed of the premixed gas Gm from the burner 4 is expressed as V1, and the combustion speed of the premixed gas Gm is expressed as V2. In FIGS. 3(a) and 3(b), the horizontal axis is time. The vertical axis of FIG. 3(a) is the mixture ratio R of the premixed gas Gm, and the vertical axis of FIG. 3(b) is the difference ΔV (=V1−V2 ).

As shown in FIG. 3(a), the mixture ratio R includes a stable region A1, an incomplete combustion region A2, an unstable combustion region A3, and a non-combustible region A4. Stability region A1 is a region where oxygen and raw materials are mixed in an appropriate ratio and combustion is stable. When the raw material is D3, D4, D5, etc., the range of 0.68≦R≦1.00 is the stable region A1. In the stable region A1, glass particles are generated evenly, and the amount of soot generated due to incomplete combustion is negligible. In the incomplete combustion region A2, the value of the mixture ratio R exceeds the stable region A1, and since there is too little oxygen in the raw material, a non-negligible amount of soot is generated due to incomplete combustion. If soot adheres to the soot L, the quality of the optical fiber preform will deteriorate.

The unstable combustion region A3 is a region where the value of the mixture ratio R is lower than the stable region A1, the amount of raw material gas released from the burner 4 is too small, and the generation of glass particles becomes unstable. If the generation of glass particles becomes unstable, for example, the generated glass particles may adhere to the burner 4. The non-combustible region A4 is a region where the premixed gas Gm does not burn due to too little oxygen or too little source gas.

In FIGS. 3A and 3B, the deposition process is performed during the time t≦T1. During the deposition process, the flow rate of the raw material is appropriately adjusted by the flow rate adjustment section 11b, and the mixture ratio R is within the stable region A1. The magnitude of ΔV during the deposition process is denoted Va. Va is the difference obtained by subtracting the combustion speed V2 from the ejection speed V1 determined by the flow rates of the raw material gas, carrier gas, and oxygen contained in the premixed gas Gm. The ejection speed V1 in the deposition process is set so that Va has a positive value.

At time t=T1, when the deposition process ends, the flow rate adjustment unit 11b reduces the flow rate of the raw material, but the flow rates of oxygen and carrier gas contained in the premixed gas Gm are maintained, so that the mixture ratio R gradually increases. descend. Therefore, the mixture ratio R passes from the stable region A1, passes through the unstable combustion region A3, and reaches the non-combustible region A4. The time point when the mixture ratio R reaches the non-combustible region A4 from the unstable combustion region A3 is expressed as T2, and the time point when the mixture ratio R becomes 0 is expressed as T3. Further, the magnitude of the speed difference ΔV at time T3 is expressed as Vb. Vb is the difference obtained by subtracting the combustion speed V2 from the ejection speed V1 determined by the flow rates of the carrier gas and oxygen contained in the premixed gas Gm. Vb has a smaller value than Va because the flow rate of the source gas has decreased. In this embodiment, the flow rates of oxygen and carrier gas contained in the premixed gas Gm are set so that the value of Vb is greater than or equal to zero.

Here, if the speed difference ΔV is a positive value, even if the mixture ratio R is within the stable region A1 or the unstable combustion region A3 (that is, within the range where the premixed gas Gm can be combustible), Combustion of the mixed gas Gm does not proceed into the burner 4. Then, when the mixture ratio R reaches the non-combustible region A4, combustion of the premixed gas Gm naturally stops. Therefore, as shown in FIGS. 3(a) and 3(b), by making the speed difference ΔV a value of zero or more at the time (T2) when the mixture ratio R reaches the non-combustible region A4, the generation It is possible to prevent backfire from occurring during the stopping process.

As shown in FIG. 3(a), during a part of the time between T1<t≦T2, the mixture ratio R falls within the unstable combustion region A3. As described above, in the unstable combustion region A3, the reaction of the raw material gas becomes unstable, and phenomena such as glass particles adhering to the burner 4 occur. Although this phenomenon has a small effect on the quality of the optical fiber preform, it becomes a factor that makes it necessary to clean the burner 4 more frequently. Therefore, the time interval (from T1 to T2) from when the mixture ratio R starts decreasing until the mixture ratio R reaches the non-combustible region A4 is preferably as short as possible.

After the mixture ratio R is set to zero at t=T3, the second valve 12a is closed and the third valve 13a is opened to flow the premixed gas Gm toward the vent line 13. In FIG. 3(b), T4 is the point in time when the second valve 12a is closed and the third valve 13a is opened. At t=T4, since V1=0, ΔV=-V1.

Note that although Vb is greater than or equal to zero in FIGS. 3A and 3B, Vb may be a negative value. Also in this case, as shown in FIGS. 4(a) and 4(b), if the value of the speed difference ΔV at time T2 is zero or more, it is possible to prevent the occurrence of flashback.

As explained above, in the method for manufacturing a porous glass particulate body of the present embodiment, a premixed gas Gm containing a flammable raw material gas and oxygen is supplied to the burner 4, and the premixed gas Gm is supplied to the outlet of the burner 4. In the premixed gas Gm, by the deposition step of depositing the glass particles generated by combustion in step 4a on the starting member M to form the soot L, and by reducing the flow rate of the raw material gas contained in the premixed gas Gm. It includes a production stop step of lowering the mixture ratio R of the raw material gas to oxygen so that it falls within the non-combustible region A4, and stopping the production of glass particles at the outlet 4a of the burner 4. In the generation stop step, at time T2 when the mixture ratio R reaches the non-combustible region A4, the difference ΔV (= V1 - V2 ) is greater than or equal to zero.

In this manner, by lowering the mixture ratio R in the generation stop step, it is possible to prevent the generation of soot due to the mixture ratio R passing through the incomplete combustion region A2, and to stabilize the quality of the optical fiber preform. Further, since the speed difference ΔV is equal to or greater than zero at time T2 when the mixture ratio R reaches the non-combustible region A4, it is possible to prevent flashback from occurring.

Further, in the production stop step, the time (from T1 to T3) for reducing the mixing ratio R from the value in the deposition step to zero may be within 10 seconds. In this case, the time during which the mixture ratio R is within the unstable combustion region A3 becomes shorter. Therefore, it is possible to prevent a large amount of glass particles from adhering to the burner 4.

Further, the premixed gas Gm may include an inert carrier gas. In this case, the proportion of oxygen in the premixed gas Gm becomes small, and the unstable combustion region A3 can be narrowed. Therefore, in the generation stop step, combustion of the premixed gas Gm can be stopped more quickly.

Further, in the production stop step, the mixture ratio R may be set to zero by closing the first valve 11a provided in the raw material supply line 11. In this case, the time from T1 to T3 can be made shorter, and the time during which the mixture ratio R is within the unstable combustion region A3 can be shortened.

Furthermore, by manufacturing an optical fiber preform by subjecting the porous glass particles obtained as described above to a sintering treatment, etc., it is possible to provide a high-quality optical fiber preform that suppresses the adhesion of soot and the like. .

The above embodiment will be described below using specific examples. Note that the present invention is not limited to the following examples.

(Example 1)
D4 was used as a raw material and Ar was used as a carrier gas. In the deposition process, the flow rate of the liquid D4 is adjusted by the flow rate adjustment unit 11b so that the mixing ratio of the premixed gas Gm supplied to the burner 4 is R = 0.76 (R' = 0.19). did. An MFC was used as the flow rate adjustment section 11b. At the end of the deposition process, the burner 4 was moved to the position of the end P, and then the set value of the flow rate of the flow rate adjustment part 11b was set to zero, thereby reducing the mixing ratio R. The time it took for the mixing ratio R to go from 0.76 to zero was 10 seconds. At this time, the flow rates of the carrier gas and oxygen in the premixed gas Gm were not changed. The state of the raw material combustion flame F2 at the outlet 4a of the burner 4 temporarily became unstable, but soon changed to a stable state. Therefore, the second valve 12a was closed and the third valve 13a was opened to extinguish the flammable gas combustion flame F1, but no backfire occurred and no soot was attached to the soot L. Furthermore, the amount of glass particles adhering to the burner 4 was very small, and was in a non-problematic range.

(Example 2)
In order to lower the mixture ratio R, the first valve 11a was closed without changing the set value of the flow rate adjustment section 11b. The time it took for the mixing ratio R to go from 0.76 to zero was 1 second or less. The other points are the same as in the first embodiment. In Example 2, no flashback occurred and no soot was attached to the soot L. Further, there was almost no adhesion of glass particles to the burner 4.

(Example 3)
The setting value of the flow rate adjustment part 11b was changed over 15 seconds until the mixture ratio R became zero from 0.76. The other points are the same as in the first embodiment. In Example 3, no flashback occurred and no soot was attached to the soot L. However, glass particles were attached to the outlet 4a of the burner 4, and cleaning was required.

(Comparative example 1)
At the end of the deposition process, the second valve 12a was closed and the third valve 13a was opened while the first valve 11a remained open without changing the set value of the flow rate adjustment section 11b. The other points are the same as in the first embodiment. After the fire was extinguished, observation revealed that glass particles were attached to the inside of the burner line 12, indicating that flashback had occurred.

(Comparative example 2)
At the end of the deposition process, the flow rate of the premixed gas Gm supplied to the burner 4 was set to zero so as not to change the value of the mixture ratio R. Other points are the same as in Example 1. After the fire was extinguished, observation revealed that glass particles were attached to the inside of the burner line 12, indicating that flashback had occurred.

Let us consider the above results. In Comparative Examples 1 and 2, as shown in FIGS. 5A and 5B, the speed difference ΔV decreases to a negative value (-V2) while the mixture ratio R remains constant. This means that the premixed gas Gm remains in the burner 4 and the burner line 12 without being ejected from the outlet 4a of the burner 4 in a combustible state. As a result, in the deposition process, the raw material combustion flame F2 that was outside the outlet 4a of the burner 4 propagates into the burner 4 and into the burner line 12 (that is, backfire occurs), and the glass particles are scattered inside the burner 4 and into the burner line 12. Generated within 12.

On the other hand, in Examples 1 to 3, the fire is extinguished by lowering the mixture ratio R while maintaining the speed difference ΔV at a value of zero or more and reaching the non-combustible region A4. This prevented backfire from occurring. Furthermore, since the transition of the mixture ratio R does not pass through the incomplete combustion region A2, it was possible to suppress soot from adhering to the soot L.

Note that the technical scope of the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention.

For example, in the embodiment described above, an organic silicon compound is used as a raw material for glass particles. However, the above embodiment can also be suitably applied to cases where other combustible raw materials are used.

Further, the configuration of the supply device 10 may be changed as appropriate. For example, the oxygen supply line 11e may be connected upstream of the vaporization unit 11d. Alternatively, oxygen may be supplied to the raw material supply line 11 along with the carrier gas from the carrier gas supply line 11c.

In addition, the components in the above-described embodiments may be replaced with well-known components as appropriate without departing from the spirit of the present invention, and the above-described embodiments and modifications may be combined as appropriate.

4... Burner 4a... Outlet 11... Raw material supply line 11a... First valve (valve) A4... Non-combustible area Gm... Premixed gas L... Soot M... Starting member

Claims (4)

A deposition process in which a premixed gas containing a flammable raw material gas and oxygen is supplied to a burner, and the premixed gas is combusted at the outlet of the burner, thereby depositing glass fine particles on a starting member to form soot. process and
By reducing the flow rate of the raw material gas contained in the premixed gas, the mixing ratio of the raw material gas to the oxygen in the premixed gas is lowered to be within a non-combustible region, and the generation of glass particles at the outlet is stopped. and a generation stop step,
In the generation stop step, when the mixture ratio reaches the non-combustible region, a speed difference ΔV (=V1-V2) between the ejection velocity V1 of the premixed gas at the outlet and the combustion velocity V2 of the premixed gas ) is greater than or equal to zero, and
A method for producing a porous glass particulate material , wherein in the production stop step, it takes less than 10 seconds for the mixing ratio to decrease from the value in the deposition step to zero . The method for producing porous glass microparticles according to claim 1 , wherein the premixed gas includes an inert carrier gas. 3. The method for producing porous glass microparticles according to claim 1 , wherein in the production stop step, the mixing ratio is set to zero by closing a valve provided in a raw material supply line. A method for manufacturing an optical fiber preform, comprising the step of sintering a porous glass particle body obtained by the manufacturing method according to any one of claims 1 to 3 .

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