JP2005255502A - Method for manufacturing transparent glass body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a transparent glass body in which the concentration of a doped halogen element is increased to enlarge the difference of specific refraction index from that of pure quartz glass, and free from refoaming in a process for drawing the resultant transparent glass body to manufacture an optical fiber. <P>SOLUTION: After a porous preform is manufactured using SiO<SB>2</SB>powder having ≥130 m<SP>2</SP>/g specific surface area and having Si-OH group formed on the surface in the concentration of ≥1 piece /nm<SP>2</SP>as a starting raw material, a halogen is incorporated into the porous preform and the porous preform is sintered, or the porous preform is manufactured after the halogen is previously incorporated into the SiO<SB>2</SB>powder, and is sintered. The porous preform is manufactured by supplying the SiO<SB>2</SB>powder into a burner and jetting it together with the flame on a target to deposit SiO<SB>2</SB>fine particle or by compaction-forming the SiO<SB>2</SB>powder in a forming die or by pouring slurry of SiO<SB>2</SB>powder into the forming die and performing dehydration-forming. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

TECHNICAL FIELD The present invention relates to a method for producing a transparent glass body, and more specifically, an optical fiber using SiO ₂ powder as a starting material and increasing a relative refractive index difference with respect to pure quartz glass by increasing a halogen doping amount. It is related with the manufacturing method of the transparent glass body which is a base material for glass body manufacture.

As a typical method for producing a transparent glass body which has been generally used, a gas phase glass material such as SiCl ₄ as a main material and GeCl ₄ , POCl ₃ and BBr _{3 as} a dopant material is used as Ar. Glass fine particles (hereinafter referred to as a porous preform) produced by being supplied to an oxyhydrogen burner together with a carrier gas such as the like and ejected into a flame of the burner to cause a hydrolysis or oxidation reaction, A porous preform obtained by precipitation and deposition on a relatively moving target (hereinafter referred to as a starting material) is sintered at a high temperature to form a transparent glass body.

  In such a method using a gas phase raw material as a starting material (gas phase synthesis method), as described in, for example, Patent Document 1 (page 3, upper left column), glass fine particles are extracted from the gas phase with an auxiliary rod ( A method of directly depositing in the direction perpendicular to the axis of the starting material (OVD method), a method of depositing glass fine particles directly from the gas phase on the front surface of the rod (starting material) (VAD method), a glass particle from the gas phase using a burner There are a method of directly depositing on the inner wall of the pure quartz glass tube (MCVD method) and a method of depositing glass particles directly from the gas phase on the inner wall of the pure quartz glass tube using plasma (PCVD method). The porous preform obtained by these methods is sintered by heating at a high temperature to form a transparent glass body. For example, this is drawn into a desired diameter and length to obtain an optical fiber. A desired glass body is obtained by subjecting the glass body to predetermined processing.

In addition, as another method for producing a porous preform, for example, as described in Non-Patent Document 1, after hydrolyzing a metal alkoxide such as tetraethoxysilane, this is baked to obtain a porous preform. A so-called sol-gel method is known. In addition to attempts to put it into practical use for mass production of porous preforms by the sol-gel method, as disclosed in Patent Document 1, for example, SiO ₂ particles obtained from gas phase glass materials are collected. In addition, a method has been proposed in which this is heated to grow a porous preform on the starting material.

JP-A-61-76631 S. Shibata, `` Sol-gel-derived silica preforms for optical fibers '', Journal of Non-Crystalline Solid, 178 (1994), 272-283

  By the way, in a transparent glass body, various elements are usually doped into its starting material or porous preform to change or improve the optical properties of the transparent glass body. For example, a halogen element is added to the transparent glass body. When doped, when the halogen is fluorine (F), the refractive index of the transparent glass body obtained from pure quartz glass can be lowered, and when it is chlorine (Cl), the refractive index can be increased. Are known.

  In order to increase the refractive index difference between the transparent glass body and pure quartz glass by doping with a halogen element, it is conceivable to increase the amount of the halogen element to be doped. When a porous preform is produced by vapor phase synthesis from a gas phase glass raw material such as the OVD method, there is a limit to the concentration of halogen that can be doped. Therefore, the absolute value of the relative refractive index difference with respect to pure quartz glass is limited. Since it is about 0.8% or less when doped with fluorine, it is desired to develop a method for producing a transparent glass body having a refractive index difference larger than that of conventional quartz glass compared with that of pure quartz glass.

When manufacturing a transparent glass body, compared to the case where a porous preform is manufactured from a glass raw material in a gas phase state and this is used as a transparent glass body, the case where the porous preform is manufactured by the sol-gel method However, there is a possibility that a higher concentration of halogen element can be doped in the porous preform, and the relative refractive index difference with respect to pure quartz glass may be made larger. However, when a transparent glass body obtained from a porous preform produced by the sol-gel method is to be drawn, for example, to form an optical fiber, moisture or chlorine gas adsorbed on the surface of the porous preform is used. When dewatering, there were problems such as re-foaming by chlorine gas adsorbed on the surface and a long time for drying to remove moisture.
FIG. 7 shows the SiO ₂ surface OH group and Cl when a porous preform made of SiO ₂ having Si—OH groups (OH groups bonded to Si) is brought into contact with Cl ₂ gas for dehydration. The chemical changes on the surface due to the reaction with the _two gases are schematically shown. When the porous preform is dehydrated with, for example, Cl ₂ gas, the OH groups on the SiO ₂ surface are replaced with Cl, and this is baked. Even if they are consolidated, there is an adverse effect that Cl is separated as Cl ₂ gas and re-foamed in a later step.

  The present invention solves the above problems, increases the concentration of the halogen element to be doped, can increase the refractive index difference (the absolute value of the relative refractive index difference) with respect to pure quartz glass, and draws a transparent glass body. An object of the present invention is to provide a method for producing a transparent glass body in which re-foaming is hardly observed in the process of producing an optical fiber (glass body).

In order to increase the concentration of the halogen element doped in the porous preform, the present inventors relate to a method for producing a porous preform, which is a precursor of a transparent glass body, and the surface characteristics of the starting material used at that time. As a result of detailed studies, instead of using a gas phase raw material as a starting material, SiO ₂ powder having a specific surface area and having a specific concentration of Si-OH groups on the surface is used as a starting material. The porous preform is obtained by ejecting this from the flame of the burner to the starting material and depositing and depositing on the starting material, or by molding the SiO ₂ powder. so as to add a halogen element or, alternatively the porous preform using the SiO ₂ powder after allowed to contain a pre halogen to the SiO ₂ powder If manufactured, the concentration of the halogen to be doped can be further increased as compared with the case where a porous preform is produced from a glass material in a vapor phase by a conventional VAD method, OVD method, or the like. In addition, the present inventors have found that a porous preform with little re-foaming can be obtained in the drawing process of the transparent glass body, which is a subsequent process in the production of the transparent glass body, and that the above-mentioned problems can be solved.

That is, this invention solves the said subject with the method of following (1)-(9).
(1) In a method for producing a transparent glass body using SiO ₂ powder as a raw material, a specific surface area is 130 m ² / g or more, and Si—OH having a concentration of 1 (pieces / nm ² ) or more per unit square nanometer on the surface A method for producing a transparent glass body, comprising producing a porous preform using SiO ₂ powder on which a group is formed, adding a halogen to the porous preform, and further sintering the halogen preform .
(2) The porous preform is manufactured by transporting the SiO ₂ powder to a burner and ejecting the SiO ₂ powder onto the target to deposit SiO ₂ fine particles on the target. The manufacturing method of the transparent glass body as described in.
(3) The method for producing a transparent glass body according to (1), wherein the porous preform is produced by compacting the SiO ₂ powder with a mold.
(4) The method for producing a transparent glass body according to (1), wherein the porous preform is produced by pouring a liquid in which the SiO ₂ powder is dispersed into a mold and drying the liquid.

(5) In the method for producing a transparent glass body using SiO ₂ powder as a raw material, the specific surface area is 130 m ² / g or more, and Si—OH having a concentration of 1 (pieces / nm ² ) or more per unit square nanometer on the surface Halogen is previously contained in the SiO ₂ powder on which the group is formed, and after the porous preform is produced using the SiO ₂ powder containing the halogen, the porous preform is sintered. A method for producing a transparent glass body.
(6) The method for producing a transparent glass body according to any one of (1) to (5), wherein the halogen supply source is silicon halide.
(7) The method for producing a transparent glass body according to any one of (1) to (6), wherein the halogen is fluorine (F).

(8) The method for producing a transparent glass body according to any one of (1) to (7), wherein the specific surface area of the SiO ₂ powder is 400 m ² / g or less.
(9) The method for producing a transparent glass body according to any one of (1) to (8), wherein the sintering temperature is 900 to 1300 ° C.

  In the present specification, a porous glass fine particle deposit comprising a core or a core and a clad layer adhered to and deposited on a starting material is referred to as a porous preform, and the porous preform is subjected to a high temperature sintering furnace. What was sintered and made transparent by heating is called a transparent glass body.

According to the method for producing a transparent glass body of the present invention, since a powder composed of SiO ₂ particles having Si—OH groups on the surface thereof is used as a starting material, added halogen elements and Si—OH groups on the surface of SiO ₂ particles are used. There is no liberation of added halogen element.
In addition, since a powder composed of SiO ₂ particles having a large specific surface area is used, the number of halogen elements bonded to Si—OH groups on the particle surface increases. Therefore, the concentration of halogen doped in the transparent glass body is increased as compared with the case of producing by vapor phase synthesis by a method such as VAD method or OVD method, and a glass body having a larger relative refractive index difference than that of pure quartz glass is obtained. be able to.

Furthermore, when a halogen-containing transparent glass body having GeO ₂ added to the core is produced by the production method of the present invention, the amount of GeO ₂ added can be reduced. When an optical fiber is manufactured, transmission loss is further reduced.
Furthermore, when the porous preform obtained by the present invention is sintered to form a transparent glass body, the sintering temperature can be lowered as compared with the prior art, so that the added halogen is prevented from evaporation and the manufacturing cost is reduced. Is possible.

Next, the present invention will be described in more detail.
In the method for producing a transparent glass body of the present invention, a porous preform is first produced using a powder of SiO ₂ particles having a specific surface area as a starting material and having Si—OH groups on the surface thereof. A process (porous preform manufacturing process), a process of adding and doping a halogen element to the obtained porous preform (halogen element adding process), and heating and sintering the halogen-doped porous preform SiO ₂ particles having a specific specific surface area and having OH groups (Si—OH groups) bonded to Si on the surface thereof, which are produced through a transparent glass body (sintering process). previously after adding a halogen element, step (a porous preform manufacturing process for producing a porous preform of the powder of the SiO ₂ particles as the starting material, i.e. manufacturing of the porous preform to And simultaneously) and doped halogen element, heating the resulting porous preform, is to manufactured through a step of the transparent glass body is sintered (sintering step).

FIG. 6 schematically shows a change in surface composition due to a chemical reaction when SiO ₂ particles having Si—OH groups on the surface thereof and SiF ₄ gas are in contact with the particle surface. When SiO ₂ particles having bonded OH groups and SiF ₄ gas are brought into contact with each other, a chemical reaction of the following formula 1 or 2 is caused on the particle surface, and when the reaction of formula 1 is caused, as shown in FIG. Then, HF gas is generated, and OH and SiF ₃ of the Si—OH group are substituted and bonded to Si on the surface of the particles, whereby F is taken into the SiO ₂ particles.
SiF ₄ + SiOH → Si—O—SiF ₃ + HF (Formula 1)
SiF ₄ + 2SiOH → Si—O—SiF ₂ —O—Si + 2HF [Formula 2]

In the method for producing a transparent glass body of the present invention, the specific surface area is 130 mm ² / g or more from the point that the concentration of the halogen element to be doped can be further increased, and the surface has a number per unit square nm. Is a powder of SiO ₂ particles having a Si—OH group of 1 (pieces / nm ² ) or more. However, when a glass body is produced using SiO ₂ powder having a specific surface area larger than 400 mm ² / g, the glass body is produced by drawing with moisture adsorbed on the surface when the porous preform is produced. This is not preferable because refoaming is likely to occur. Therefore, as a starting material for producing the transparent glass body of the present invention, SiO ₂ particles having a specific surface area of about 130 to 400 m ² / g, more preferably about 130 to 380 m ² / g are used as a starting material. It is preferable.
In addition, as the SiO ₂ powder having a specific surface area in the above range and having a Si—OH group on the surface thereof, for example, SiO ₂ fine particles commercially available under the trade name of AEROSIL, among commercially available SiO ₂ powders A material having a desired specific surface area and a concentration of Si—OH groups bonded to the particle surface is appropriately selected and used.

In the method for producing a transparent glass body of the present invention, several methods can be adopted as a method for producing a porous preform (porous preform producing step). Among them, as a first porous preform manufacturing method, in the apparatus used for the gas phase synthesis method by the conventional VAD method, OVD method, etc., the above-mentioned SiO ₂ is applied to the portion to which the gas phase raw material is supplied. A powder supply device for supplying powder is provided, from which the raw material powder of SiO ₂ is supplied to the burner, and the supplied SiO ₂ powder is jetted toward the starting material together with the flame from the burner and melted in the flame Alternatively, a softened SiO ₂ powder is deposited and deposited on the starting material.

  FIG. 1 schematically shows an example of an apparatus for carrying out the first porous preform production method in the method for producing a transparent glass body of the present invention. In order to explain the present invention, FIG. Only necessary portions are shown, and a device not shown in the figure can be used as appropriate. Moreover, in each drawing of this specification, a common component is represented by the same number, and description is also abbreviate | omitted below.

The apparatus illustrated in FIG. 1 has substantially the same configuration as an external method known as the OVD method.
In FIG. 1, a starting material 1 made of, for example, a glass rod or the like is coupled to a rotating means 2, and a reaction vessel 4 is disposed surrounding the starting material 1. The burner 6 is arranged in combination with the moving means 30 so that it can reciprocate substantially in parallel with the longitudinal rotation axis of the starting material 1. Separately from this, the raw material SiO ₂ powder 20 is supplied to the raw material powder supply tank 11 through the raw material powder supply pipe 14 and opened and closed by opening and closing a valve 15 provided in the middle thereof, and stored.

When the porous preform is manufactured, the raw material SiO ₂ powder 20 in the raw material powder supply tank 11 that has been fluidized from the raw material suction pipe 22 is sucked by operating the ejector 21, and this is vented from the carrier gas supply pipe 13. Mixed with a carrier gas (carrier gas A) such as argon (Ar) gas, conveyed through the raw material powder supply line 16 together with the carrier gas A, and mixed gas supplied from the mixing gas supply line 17 along the way ( The raw material powder 20 of SiO ₂ is supplied together with the carrier gases A and B from the pipe 18 mixed with the carrier gas B) and communicating with the raw material powder supply line 16 to the center port 7 of the burner 6. When operating the ejector 21, for example, a fluidizing gas such as air is vented through the mesh 12 from the vent 36 provided in the bottom side wall of the raw material powder supply tank 11, and the raw material powder supply tank 11. The raw material powder 20 is sucked out by sucking out the raw material powder 20 (SiO ₂ powder) from the raw material suction pipe 22 while operating the vibration device 37 provided on the wall surface or the like to fluidize the raw material powder 20 in the tank 11. It can be done more smoothly.

A burner 6 such as an oxyhydrogen burner is provided with a central port 7 at the center, and an outer port 8 is arranged concentrically on the outer periphery. Hydrogen (H ₂ ), methane (CH ₄ ), A combustible gas such as ethylene (C ₂ H ₄ ), an auxiliary combustible gas such as oxygen (O ₂ ) and dry air, and a seal gas other than that are supplied. The burner 6 is reciprocated substantially parallel to the rotation axis of the starting material 1 by the moving means 30, and the flame 9 from the burner 6 is sprayed on the starting material 1 rotating around the axis by the rotating means 2. The raw material SiO ₂ powder 20 melted or softened by the above is sequentially deposited on the starting material 1 or glass fine particles (porous preform 10) mainly composed of SiO ₂ already deposited on the starting material 1. And the porous preform 10 is formed around the starting material 1 (in the radial direction).

  In this example, the burner 6 is reciprocated by the moving means 30 substantially in parallel with the rotating shaft of the rotating starting material 1. On the contrary, the burner 6 is fixed and illustrated. Further, there is provided a moving means for the starting material 1 which is not provided, so that the starting material 1 is reciprocated substantially parallel to the rotation axis while rotating the starting material 1, or both the rotating starting material 1 and the burner 6 are substantially parallel and relative to each other. It is also possible to use a burner row in which a plurality of burners are juxtaposed in the rotation axis direction of the starting material 1 as the burner 6.

  3A and 3B are cross-sectional views illustrating a specific example of the burner 6 that can be used in the method for manufacturing a transparent glass body of the present invention. The burner 6 illustrated in FIG. 1 is a multi-tube burner and only one outer port 8 is shown for simplification of the drawing. However, the actually used multi-tube burner is shown in FIG. A five-pipe burner having four outer ports consisting of a second port 31, a third port 32, a fourth port 33, and a fifth port 34 with a partition wall 35 facing toward the outer periphery of the center port 7 A seven-port burner having seven ports, a center port 7 for supplying raw material powder, and a plurality of outer ports 8 for venting various gases around the center port 7 as shown in FIG. A burner having a known structure, such as a provided burner, can be used.

As the various gases such as carrier gas used for the production of the transparent glass body of the present invention, a gas conventionally used for the production of the glass body is appropriately used. For example, the raw material SiO ₂ powder 20 flows. As the carrier gas A to be transported to the burner 6, helium (He) gas, Ar gas, nitrogen (N ₂ ) gas, dry air, and other gases are used, and the raw material powder transported with the carrier gas A if desired. In addition to the carrier gas A, a combustible gas such as H ₂ gas, CH ₄ gas, C ₂ H ₄ gas, or an auxiliary combustion gas (carrier gas B) such as O ₂ gas or dry air is mixed into the burner 6. Supplied.
As an example of a combination of these gases, for example, the burner illustrated in FIG. 3A is used, and a mixed gas of He and H ₂ is introduced into the center port 7 as the carrier gas A, and the second port 31 of the burner 6 is introduced. For example, Ar gas, O ₂ gas for the third port 32, Ar gas for the fourth port 33, and H ₂ gas for the fifth port 34. And B are supplied to the burner 6 in any combination.

  FIG. 2 illustrates an example of another apparatus for carrying out the first porous preform production method in the method for producing a transparent glass body according to the present invention. An embodiment in the case of carrying by gas is schematically shown, and the apparatus illustrated in FIG. 2 has substantially the same configuration as the VAD method (shafting method). As a means for supplying the powder raw materials 20 and 20a to the burner 6, a predetermined amount of both raw material powders 20 and 20a are respectively placed on the meshes 12 and 12a provided in the vicinity of the bottoms of the raw material powder supply tanks 11 and 11a. By supplying and storing the raw material powder supply pipes 14 and 14a by opening and closing 15a, the ejectors 21 and 21a are operated while the carrier gas A supplied from the respective carrier gas supply pipes 13 and 13a is vented, The raw material powder is fluidized, and the powder raw materials 20 and 20a sucked from the raw material powder suction pipes 22 and 22a are conveyed through the respective raw material powder supply lines 16 and 16a, and mixed at the confluence of the raw material powder supply lines 16 and 16a. Both raw material powders 20 and 20a are continuously conveyed through the raw material powder supply line 16 and further mixed with the mixing powder supplied from the middle. Except for the point that both raw material powders 20 and 20a are mixed with (carrier gas B) and supplied to the central port 7 of the burner 6 via the pipe 18 communicating with the raw material powder supply lines 16 and 16a. And the structure of the apparatus for supplying each carrier gas is substantially the same as the structure illustrated in FIG.

  In this example, while the ejectors 21 and 21a are operated, fluidized gas such as air passes from the vents 36 and 36a provided on the bottom side walls of the raw material powder supply tanks 11 and 11a through the meshes 12 and 12a. At the same time, the vibration devices 37 and 37a provided on the wall surfaces of the raw material powder supply tanks 11 and 11a are operated, and the center in the raw material powder supply tanks 11 and 11a is further rotated by the rotating means 38 and 38a. The raw material powder 20 from the raw material suction pipes 22 and 22a is made to rotate by rotating the drive shafts 39 and 39a provided on the front and rotating the stirring blades 40 and 40a attached to the tips thereof to fluidize the raw material powders 20 and 20a. , 20a is easily sucked out.

  The mixing amount of the two kinds of raw material powders is appropriately adjusted according to the amount of raw material powders stored in the raw material supply tanks 11 and 11a, the flow rate of the carrier gas to be vented, and the like. When three or more kinds of raw material powders are used, the third and fourth raw material supply tanks may be arranged in addition to the raw material tanks 11 and 11a in the apparatus shown in FIG.

Also in the production method of the present invention, a transparent glass obtained by using a metal oxide powder other than this as the raw material powder together with the above-mentioned SiO ₂ having a predetermined specific surface area and Si—OH group concentration on the surface, which is the main raw material It is possible to adjust the optical characteristics of the body and the characteristics such as viscosity at the time of melting. For example, the refractive index of the transparent glass body obtained with the addition of GeO ₂ to about 15% SiO ₂ can rise 1%, by adding TiO ₂ to SiO _2, the thermal expansion coefficient of the transparent glass body obtained Can be reduced.

In the case of this example using the apparatus illustrated in FIG. 2, the starting material 1 is rotated about the vertical direction by the rotating means 2. The flame 9 is sprayed on the starting material 1, and the raw material SiO ₂ powder 20 (glass fine particles) contained in the flame 9 is melted or softened in the flame 9, and the rotating starting material 1 or the same is added to the rotating material. The porous preform 10 is formed by adhering to the lower part of the glass fine particles that have started to adhere and deposit, and the starting material 1 is pulled up by the lifting means 3 to start the porous preform 10. It is deposited below the material 1 and grows.

In addition, in order to manufacture the porous preform by the first manufacturing method, it is not limited to the above-described method using the apparatus illustrated in FIGS. 1 and 2, and the MCVD method, the PCVD method, etc. Supplying powder raw material particles mainly composed of SiO ₂ particles instead of the gas phase raw material to the apparatus used in each of the production methods conventionally known as a method for producing a porous preform by vapor phase synthesis of A porous preform can also be produced according to each gas phase synthesis method.

In the present invention, the porous preform manufacturing method (porous preform manufacturing step) includes, in addition to the above-mentioned first porous preform manufacturing method, raw material SiO ₂ powder or, if necessary, SiO ₂ powder Other than this, a method (second porous preform production method) in which a mixture of metal compound powders, which are the second and third components, is filled in a mold for molding and pressed to form a molded body, Disperse the raw material SiO ₂ powder in a solvent such as water or alcohol, or if necessary, a mixture of the SiO ₂ powder and other metal compound powders as the second and third components to form a slurry. A method such as a method (third porous preform production method) is also possible, such as a method (third porous preform production method) that is allowed to stand in a measuring cylinder, volatilizes the solvent, dehydrates and then dehydrates and then forms into a molded body. Simple porous preform It is recommended as a method for producing a beam.

  The porous preform obtained as described above is then heated to a predetermined temperature, heated to a predetermined temperature, and another halogen-doping heating furnace (not shown) provided with a ventilation means that can ventilate the furnace. The element is doped with a halogen element by heat treatment at a predetermined temperature of 1000 to 1400 ° C. while a gas of halide is passed through the furnace by the ventilation means.

FIG. 4 shows a temperature rise curve (temperature rise time vs. temperature) when the porous preform obtained in the previous step (porous preform manufacturing step) is heat-treated while passing a halogen gas in the halogen element addition step. Relationship). As shown in FIG. 4, for example, a predetermined temperature around 1000 ° C. (for example, around 1000 ° C.) is used while an inert gas such as He and Ar is ventilated to replace the inside of the container containing the porous preform with the inert gas. The temperature is increased to t ₁ ), and then, in addition to the inert gas or in place of the inert gas, a halide gas is passed through the furnace and maintained at that temperature (t ₁ ) for a certain period of time. It is added and contained in the porous preform. Next, for example, the porous preform in the vicinity of 1400 ° C. is heated to a predetermined temperature (t ₂ ) at which the porous preform can be transparent, sintered, and held for a certain period of time, and then the halide gas aeration and heating are stopped. To obtain a transparent glass body of the present invention in which a porous preform is doped with halogen (halogenation and sintering step).

Examples of the halogen compound gas for doping the halogen element include gases composed of fluorine compounds such as SiF ₄ , CF ₄ , C ₂ F ₆ , CCl ₂ F ₆ , and SF ₆ , and chlorine compounds such as SiCl ₄ and CCl ₄ . Among these halogen compounds, fluorine is particularly useful because it has the effect of lowering the refractive index and has a large change in refractive index per unit dope and is preferable as a refractive index adjusting agent. More preferably, a compound gas is used. In particular, a material doped with fluorine is optimal as a base material for an optical fiber that does not cause transmission loss in a wavelength region used for optical communication.
This halogen element addition step is omitted when a porous preform is manufactured using SiO ₂ powder to which a halogen element has been added in advance as a starting material in the porous preform manufacturing step. This halogen element addition step may be provided for adjusting the concentration of the halogen element doped in the porous preform to be obtained.

Next, an example explains the present invention.
[Example 1]
As the raw material powder 20, the concentration of Si—OH groups bonded to the surface is ² to 3.3 / nm ² , the specific surface area when measured by the BET method is 380 m ² / g, and average primary particles A SiO ₂ fine particle powder having a diameter of 7 nm {trade name: AEROSIL (trademark) 380 (manufactured by Nippon Aerosil Co., Ltd.) is used, and the apparatus shown in FIG. Using a pure silica rod as the starting material 1 and a multi-tube burner shown in FIG. 3A as the burner 6, a transparent glass body is manufactured through the following steps in sequence.

(Porous preform manufacturing process)
The raw material powder 20 is placed in the raw material supply tank 11, Ar gas as carrier gas A is vented from the carrier gas supply pipe 13 at a supply rate of about 5 L / min, and fluidized gas is supplied from the vent 36 at the lower part of the raw material supply tank 11. Air is fed into the inside through the mesh 12, the vibration device 37 is operated, and the stirring blade 40 is rotated by the driving means 38, and the raw material powder 20 is fluidized to suck out the raw material powder 20 by the ejector 21. The powder 20 is sent to the raw material powder supply line 16 together with Ar gas at a supply rate of about 8 g / min. In this example, since only the SiO ₂ fine particle powder is used as the raw material powder 20, the other raw material supply tank 11a is not used, and the raw material powder supply line 16a communicating with the unused raw material supply tank 11a is The valve 15a is closed and closed.

The raw material powder 20 that has been transferred to the Ar gas and has flowed through the raw material powder supply line 16 is mixed with O ₂ gas (carrier gas B) supplied from the gas line 17 for mixing, and burner via the pipe 18. 6 is ejected from the central port 7 into the flame 9, and the starting material 1 is gradually pulled upward while adhering and depositing the porous preform to the lower end of the starting material 1, and is porous in the axial direction of the starting material 1. The preform 10 is grown.
At this time, Ar gas, H ₂ gas, Ar gas, and O ₂ gas for sealing are supplied to the second port 31, the third port 32, the fourth port 33, and the fifth port 34 of the burner 6 through the pipe 19, respectively. . Feed rate to the central port 7 of the burner 6, a SiO ₂ powder 10～11G / min, the feed rate of Ar gas as a carrier gas for transporting the SiO ₂ powder 5L / min and as described above, the carrier gas B (O ₂ gas) is adjusted to ₂ L / min. The supply speed of each gas supplied to the second port 31 to the fifth port 34 of the burner 6 is such that the sealing Ar gas flowing to the second port 32 is approximately 3 L / min and H is allowed to flow to the third port 32. ₂ gas is approximately 20 L / min, Ar gas flowing through the fourth port 33 is approximately 3 L / min, and O ₂ gas flowing through the fifth port 34 is approximately 15 L / min.

(Halogen element addition process and sintering process)
Next, supply of the raw material powder 20 and each carrier gas to the burner 6 is stopped, and the porous preform 10 obtained in the porous preform manufacturing process is separated from the reaction vessel 4 and is not shown in the figure. It is transferred into a vessel (quartz furnace core tube), He gas is supplied from the pipe 19 at 15 SLM, and the temperature rise curve shown in FIG. The temperature in the furnace tube is heated and raised in an electric furnace according to
When the temperature of the reactor core tube in the reaction vessel reaches 1050 ° C. (t ₁ = 1050 ° C.), the supply of He gas is stopped, and then the SiV ₄ gas is supplied from the pipe 19 at a flow rate of 1000 cc / min. F is added to the porous preform 10 by maintaining the temperature of the inner core tube at 1050 ° C. (1 to 3 hours).

Next, the temperature was further raised while continuing the flow of SiF ₄ gas, the temperature in the reaction vessel (core tube) was maintained at 1200 ° C. (t = 1200 ° C.) for about 10 minutes, and F was doped. The transparent glass body of Example 1 is obtained.

  FIG. 5 shows the refractive index distribution of the transparent glass body of Example 1 manufactured in this way as a relative refractive index difference (Δn) with respect to pure quartz glass. In FIG. 5, the horizontal axis indicates the distance in the radial direction of the transparent glass body, and the vertical axis indicates the relative refractive index difference with respect to pure quartz glass (the transparent glass body and pure quartz glass of Example 1 with respect to the refractive index of pure quartz glass). The ratio of the refractive index difference) is expressed as a percentage, and when manufactured by the conventional manufacturing method, the relative refractive index difference with respect to pure quartz glass is about -0.75%, whereas the example The transparent glass body 1 has a relative refractive index difference of about -1.26% with respect to pure quartz glass.

[Example 2]
As a raw material powder, the concentration of Si—OH groups bonded to the surface is 2.8 to 4 / nm ² , the specific surface area when measured by the BET method is 200 m ² / g, and the average primary particle diameter SiO ₂ fine particle powder {trade name: AEROSIL ™ 200 (manufactured by Nippon Aerosil Co., Ltd.) is used. As a manufacturing apparatus, the apparatus shown in FIG. 1 in which powder supply means is retrofitted to a VAD apparatus is used, and the starting material 1 and the burner 6 are the same as those in Example 1, and the transparent glass body is sequentially processed through the following steps. To manufacture.

(Porous preform manufacturing process)
The raw material powder 20 is put into the raw material supply tank 11, Ar gas (carrier gas A) is vented from the carrier gas supply pipe 13 at a flow rate of about 5 L / min, and fluidized from the pipe 37 below the raw material supply tank 11. The air is passed through the mesh 12 and flows into the raw material supply tank 11 as well as the vibration device 37 is operated to fluidize the raw material powder 20. The ejector 21 sucks the raw material powder from the raw material powder suction pipe 22. The raw material powder 20 is transported in the raw material powder supply line 16 by the carrier gas A, mixed with the O ₂ gas (carrier gas B) supplied from the mixing gas supply line 17, and is supplied to the burner 6 via the pipe 18. The gas is supplied to the center port 7 and ejected from the center port 7 into the flame 9. The burner 6 is reciprocated by the moving means 30 substantially in parallel with the axial direction of the starting material 1 rotating about the axis by the rotating means 2, and the raw material powder 20 ejected into the flame 9 is started. The porous preform 10 is manufactured by adhering and depositing around the substrate and gradually depositing it in the axial direction of the starting material 1. At this time, the same gas as in the first embodiment is supplied to the second port 31 to the fifth port 34 of the multi-tube burner.

(Halogen element addition process and sintering process)
Next, supply of the raw material powder and each carrier gas to the burner 6 is stopped, and the porous preform 10 obtained in the porous preform manufacturing process is separated from the reaction vessel 4 (quartz furnace core tube). Then, the transparent glass body of Example 2 doped with F element is obtained in the same manner as in the halogenation step and sintering step of Example 1 below.

Example 3
(Porous preform manufacturing process)
As the raw material powder, the same SiO ₂ fine particle powder as in Example 1 (trade name: AEROSIL (trademark) 380 (manufactured by Nippon Aerosil Co., Ltd.) was used, and the raw material powder (SiO ₂ fine particle powder) and water had a weight of 1: 2. The mixture is mixed in a ratio, packed in a mold and pressed with a vise to produce a porous preform molded body made of SiO ₂ fine particle powder.

(Halogen element addition process and sintering process)
Instead of the porous preform 10 obtained in the manufacturing process of the porous preform of Example 1, the porous preform obtained by press-molding the SiO ₂ fine particle powder as described above was halogenated in Example 1. Transferred to the reaction vessel (quartz furnace core tube) used in the process and sintering process, and obtained by press-molding the above-mentioned SiO ₂ fine particle powder in the same manner as the halogenation process and sintering process of Example 1 The resulting porous preform is doped with F and sintered to produce the transparent glass body of Example 3.

Example 4
(Porous preform manufacturing process)
As the raw material powder, the same SiO ₂ fine particle powder as that used in Example 1 (trade name: AEROSIL ™ 380 (manufactured by Nippon Aerosil Co., Ltd.) is used. This raw material powder (SiO ₂ fine particle powder) and water are mixed at a weight ratio of 1: 5 to prepare a water slurry of SiO ₂ fine particle powder, which is put into a graduated cylinder, and the water in the slurry evaporates. The SiO ₂ fine particle powder solidified so as not to lose its shape is taken out from the graduated cylinder and left to stand for one week to dry naturally. The molded body is heated at 90 ° C. for 5 hours, and further heated at 200 ° C. for 5 hours. Thus, a molded body of a porous preform made of SiO ₂ fine particle powder is produced.

(Halogen element addition process and sintering process)
In place of the porous preform obtained in the porous preform production process of Example 3, a porous preform molded body obtained by molding the SiO ₂ fine particle powder as described above was used as in Example 3. In the same manner as in the halogen addition step, F is doped into this porous preform, and this is sintered to produce the transparent glass body of Example 4.

Example 5
The same fine powder as the starting material used in Example 2 as the starting material {Product name: AEROSIL (trademark) 200 (manufactured by Nippon Aerosil Co., Ltd.); A transparent glass body of Example 5 is manufactured in the same manner as in Example 1 except that SiCl ₄ gas is used instead of SiF ₄ gas.

Example 6
As a raw material powder, the concentration of Si—OH groups bonded to the surface is 2.8 to 4 / nm ² , the specific surface area when measured by the BET method is 130 m ² / g, and the average primary particle diameter SiO ₂ fine particle powder having a particle size of 16 nm {trade name: AEROSIL ™ 130 (manufactured by Nippon Aerosil Co., Ltd.), and SiCl ₄ instead of SiF ₄ gas as the gas supplied into the reaction vessel from the pipe 19 in the halogen element addition step A transparent glass body of Example 6 is produced in the same manner as Example 2 except that gas is used.

[Comparative Example 1]
(Porous preform manufacturing process)
As raw material powder, SiCl ₄ vaporized by heating is supplied to a burner together with Ar gas, and the concentration of Si—OH groups bonded to the surface produced by flame hydrolysis is 2 to 4 / nm ² . Yes, SiO ₂ fine particle powder having a specific surface area of 25 m ² / g as measured by the BET method and an average primary particle diameter of 200 nm is used as a raw material powder.
As a production apparatus, a conventional VAD production apparatus by vapor phase synthesis not provided with a raw material powder supply apparatus is used, and the above-mentioned SiO ₂ fine particle powder is supplied as a raw material instead of a raw material gas into an oxyhydrogen burner, and used as a starting material. A porous pre-foam made of SiO ₂ is produced on the starting material by blowing out the flame of the burner.

(Halogen element addition process and sintering process)
After obtaining the porous preform as described above, the supply of the raw material powder and the carrier gas to the burner is stopped, and the porous preform obtained in the porous preform manufacturing process is replaced with the porous preform. The porous preform obtained in the same manner as in Example 1 was transferred to a reaction vessel (quartz furnace core tube) different from the reaction vessel used in the production of the above, and SiF ₄ gas was passed through the reactor core tube. A transparent glass body of Comparative Example 1 doped with the F element is obtained.

[Comparative Example 2]
The transparent glass of Comparative Example 2 is the same as Comparative Example 1 except that SiCl ₄ gas is used in place of SiF ₄ gas as the halogen-containing gas that flows into the reaction vessel in the halogen element addition step of the obtained porous preform. Manufacture the body.

[Comparative Example 3]
As the raw material powder, the concentration of Si—OH groups bonded to the surface is 2 to 4 / nm ² , the specific surface area when measured by the BET method is 50 m ² / g, and the average primary particle diameter is 40 nm. A transparent glass body of Comparative Example 3 is produced in the same manner as in Example 1 except that SiO ₂ fine particle powder {trade name: OX ™ 50 (manufactured by Nippon Aerosil Co., Ltd.) is used.

Table 1 shows the refractive index change {relative refractive index difference (Δn)} with respect to quartz glass} of each of the transparent glass bodies of Examples 1 to 6 and Comparative Examples 1 to 3. Table 1 shows the change in refractive index, the production method of the porous preform, which is a precursor of each transparent glass body, the raw material used (raw material compound or product name), the average primary particle diameter (nm) of the raw material powder, the ratio The surface area (m ² / g), the OH group concentration on the particle surface {number of OH per unit square nm (number / nm ² )} and the atmosphere for halogen addition in the halogen element addition step (the composition of the atmospheric gas) are also shown. .
In the manufacturing methods of the examples and comparative examples shown in Table 1, the powder supply device is provided in the device for the VAD method (the device illustrated in FIG. 2), and the powder raw material is supplied to the gas phase raw material supply unit. A material that employs a manufacturing method for manufacturing a porous preform is abbreviated as “VAD + powder”, and a powder supply device is provided in the device for the OVD method (the device illustrated in FIG. 1) in the gas phase raw material supply unit. "OVD + powder" that uses a manufacturing method that supplies powder raw material to manufacture a porous preform, and a manufacturing method that uses a raw material powder in a mold to manufacture a porous preform Is abbreviated as “slurry”, and a production method for producing a porous preform by molding from a slurry in which raw material powder is dispersed in a solvent such as water is abbreviated as “slurry”. A porous preform manufactured by the conventional manufacturing method It was commonly abbreviated as VAD. "

As can be seen from the comparison between Examples 1 to 4 shown in Table 1 and Comparative Example 1, as a raw material, a powder of SiO ₂ particles having a certain concentration or more of OH groups on the surface is used, and this is doped with F as a halogen element. In this case, the transparent glass body manufactured by the manufacturing method of the present invention has a relative refractive index difference of about −0.73% with respect to the pure quartz glass of the transparent glass body manufactured by the conventional VAD method. The relative refractive index difference with respect to pure quartz glass is -1.01 to -1.26, and the refractive index is remarkably lowered as compared with pure quartz glass. As can be seen from the comparison between Examples 5 and 6 and Comparative Example 2, when Cl is doped as a halogen element, the relative refractive index with respect to the pure quartz glass is higher than that of the transparent glass body manufactured by the conventional VAD method. The difference is getting bigger.

Further, as can be seen from the comparison between Example 1 and Comparative Example 2, the specific surface area of the SiO ₂ particles used is not limited even when SiO ₂ particles having a certain concentration or more of OH groups on the surface are used as starting materials. If it is small, the relative refractive index difference of the transparent glass body obtained with respect to pure quartz glass is small, and as can be seen from the comparison between Example 6 and Comparative Example 2, the specific surface area of the SiO ₂ particles used is 130 m ² / g. If it is more than about, the relative refractive index difference with respect to pure quartz glass can be made larger than the transparent glass body manufactured by the conventional VAD method.

It is the figure which showed typically an example of the apparatus for manufacturing the porous preform at the time of implementing the manufacturing method of this invention. It is the figure which showed typically another example of the apparatus for manufacturing the porous preform at the time of implementing the manufacturing method of this invention. It is the figure which showed typically the multiple tube burner used in the manufacturing method of this invention. It is a figure which illustrates the temperature rising curve of the reaction container in the halogen addition process in the manufacturing method of this invention. It is a figure which illustrates the relative refractive index distribution with respect to the pure quartz glass of the transparent glass body obtained by the manufacturing method of this invention. The chemical reaction at the particle surface at the time of the SiO ₂ powder used as the raw material powder is contacted with the fluorine compound gas in the present invention is a diagram schematically showing. The chemical reaction at the particle surface at the time of the SiO ₂ powder used as the raw material powder is contacted with chlorine gas in the present invention is a diagram schematically showing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Starting material, 2 Rotating means 3 Elevating means, 4 Reaction container 5 Exhaust hole, 6 Burner 7 Center port, 8 Outer port 9 Flame, 10 Porous preform 11, 11a Raw material powder supply tank, 12, 12a Mesh 13, 13a Carrier gas, 14, 14a Raw material powder supply pipe 15, 15a Valve, 16 Raw material powder supply line 17 Mixing gas supply, 18, 19 Pipe 20, 20a Raw material powder, 21 Ejector 22 Raw material powder suction pipe, 30 Moving means 31 1st 2 port, 32 3rd port 33 4th port, 34 5th port 35 Bulkhead 36, 36a Vent 37, 37a Vibration device 38, 38a Rotating means 39, 39a Rotating shaft 40, 40a Stirring blade

Claims (9)

In the method for producing a transparent glass body using SiO ₂ powder as a raw material, a specific surface area is 130 m ² / g or more, and Si—OH groups having a concentration of 1 (units / nm ² ) or more per unit square nanometer are formed on the surface. A method for producing a transparent glass body, comprising: producing a porous preform using the SiO ₂ powder that has been prepared, adding a halogen to the porous preform, and further sintering the halogen. _{2. The} porous preform is manufactured by transporting the SiO ₂ powder to a burner and ejecting the SiO ₂ powder onto the target to deposit SiO ₂ fine particles on the target. A method for producing a transparent glass body. The method for producing a transparent glass body according to claim 1, wherein the porous preform is produced by compacting the SiO ₂ powder with a mold. The method for producing a transparent glass body according to claim 1, wherein the porous preform is produced by pouring a liquid in which the SiO ₂ powder is dispersed into a mold and drying the liquid. In the method for producing a transparent glass body using SiO ₂ powder as a raw material, a specific surface area is 130 m ² / g or more, and Si—OH groups having a concentration of 1 (units / nm ² ) or more per unit square nanometer are formed on the surface. allowed to advance contain a halogen in the SiO ₂ powder that is, after manufacturing a porous preform by using SiO ₂ powder which contains the halogen, and characterized in that sintering said porous preform A method for producing a transparent glass body.   The method for producing a transparent glass body according to any one of claims 1 to 5, wherein the halogen supply source is silicon halide.   The method for producing a transparent glass body according to any one of claims 1 to 6, wherein the halogen is fluorine (F). The method for producing a transparent glass body according In any one of claims 1 to 7, characterized in that the specific surface area of the SiO ₂ powder is less than 400m ² / g. The method for producing a transparent glass body according to any one of claims 1 to 8, wherein the sintering temperature is 900 to 1300 ° C.

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