Apparatus for manufacturing optical fiber porous preform

Abstract

To provide an apparatus for manufacturing an optical fiber porous preform without corroding the inside of the apparatus even when using a halogen based compound raw material as the raw material of glass fine particles.SOLUTION: In an apparatus for manufacturing an optical fiber porous preform, capable of depositing the optical fiber porous preform by hydrolyzing a halogen compound raw material, an internal structural material including a chamber housing or a part of a drive mechanism is constituted using valve single metal except aluminum and zinc or alloy using the valve metal except aluminum and zinc as a main body. The halogen compound raw material may be one or more selected from a group of silicon tetrachloride, trichlorosilane and germanium tetrachloride.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus for manufacturing a porous preform for an optical fiber. [Background technology]

[0002] In the production of transparent optical fiber glass preforms, glass particles are deposited on a target such as a glass rod to form a porous optical fiber preform. The porous optical fiber preform is then dehydrated and vitrified in a firing furnace to obtain the optical fiber glass preform.

[0003] In the process of forming a porous preform for optical fiber, to obtain a high-quality appearance without defects such as bubbles or foreign matter after transparent vitrification, the chamber is isolated from the external environment by a housing, and glass particles are deposited in a clean chamber with few particles. Typical methods for forming porous preforms for optical fiber include the VAD method and OVD method. In these methods, outside air is introduced into the chamber through a filter, maintaining a clean environment inside the chamber, and glass particles are generated in a burner flame.

[0004] In the VAD method, a porous preform for optical fiber is produced by depositing glass particles onto a rotating target rod while pulling up a shaft connected to a drive mechanism installed at the top of the chamber.

[0005] In the OVD method, porous preforms for optical fibers are produced by depositing glass particles onto a rotating target rod while a traveling shaft to which a burner is fixed is driven left and right. Alternatively, similar porous preforms for optical fibers can be produced using a structure in which the rotating target itself is driven up and down.

[0006] The raw material for glass particles is a halogen compound primarily composed of silicon (Si) or germanium (Ge). Si-based halides such as silicon tetrachloride (SiCl4) or trichlorosilane (SiHCl3) are hydrolyzed in a burner flame to form silica (SiO2) in a fine particle state. In addition, germanium tetrachloride (GeCl4) or other compounds may be premixed with Si-based halides and hydrolyzed in a burner flame to form an optical waveguide with a higher refractive index relative to SiO2.

[0007] In addition to the halogen compounds used as raw materials, a combustion flame is formed by supplying a flammable gas, typically hydrocarbon gas or hydrogen gas, and oxygen, which acts as a combustion support gas, to the burner. The combustion reaction produces gaseous carbon dioxide (CO2) or water (H2O).

[0008] When gaseous H2O generated by the combustion reaction in the burner flame comes into contact with a halide, a hydrolysis reaction occurs, producing SiO2 and GeO2, while at the same time generating corrosive and toxic gaseous hydrogen chloride.For this reason, the VAD and OVD methods have a mechanism to create negative pressure inside the chamber housing and actively exhaust the reaction gas to abatement equipment.

[0009] However, it is difficult to completely discharge the generated hydrogen chloride gas to the detoxification equipment. The hydrogen chloride gas that cannot be discharged to the detoxification equipment drifts within the enclosure due to the air currents inside the chamber. In addition, the gaseous H2O that did not contribute to the hydrolysis reaction also drifts within the enclosure, just like hydrogen chloride.

[0010] In this way, the humidity inside the chamber housing during deposition of the porous optical fiber preform may be higher than that of the external environment, and the atmosphere may contain hydrogen chloride gas. The temperature inside the chamber housing varies from low to high depending on the location, and in low-temperature areas below the hydrochloric acid dew point, condensation as dilute hydrochloric acid may often occur.

[0011] The structural materials that make up the chamber housing and the internal starting mechanism are primarily made of carbon steel with an acid-resistant coating, uncoated stainless steel, or uncoated nickel-based materials. When dilute hydrochloric acid condenses on the surface of these materials, they corrode, forming rust (corrosion products) on the surface. These corrosion products cause dust generation and can lead to a deterioration in the quality of the clarified optical fiber glass base material. Therefore, if necessary, equipment repairs are required, such as removing the rust that has formed on the surface with a polishing machine and then repainting the surface. Equipment with widespread material corrosion can require repairs that last for several days, which can reduce productivity.

[0012] One way to prevent corrosion inside the equipment is to use raw materials that do not generate hydrogen chloride gas, which is the main cause of corrosion. For example, a method for manufacturing a porous preform for optical fiber using octamethylcyclotetrasiloxane (OMCTS), a typical example of an organosiloxane, a halogen-free Si-based raw material, as disclosed in Patent Document 1, is considered. Because this manufacturing method does not generate hydrogen chloride gas, the chamber housing, internal structural materials, and drive mechanism are not easily corroded. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Patent Publication No. 2022-094218 Summary of the Invention [Problem to be solved by the invention]

[0014] However, OMCTS has a boiling point 100°C higher than that of SiCl4, a typical example of a halogen-based compound raw material. Stably supplying OMCTS as a gas to a burner requires ingenuity in the vaporizer, piping heating after vaporization, piping insulation structure, and selection of the premixed gas flow rate, making it difficult to handle. For this reason, OMCTS cannot be used in existing equipment designed for synthesizing glass particles from halogen-based compounds without extensive equipment modifications.

[0015] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an apparatus for manufacturing a porous preform for optical fiber that does not corrode the inside of the apparatus even when a halogen-based compound raw material is used as the raw material for glass particles. [Means for solving the problem]

[0016] In order to solve the above problems, the fiber porous preform manufacturing apparatus according to an embodiment of the present invention is an apparatus for depositing a porous preform for optical fiber by hydrolyzing a halogen compound raw material, and is characterized in that the internal structural materials, including the chamber housing, or part of the driving mechanism are made of a valve metal other than aluminum and zinc, or an alloy mainly composed of a valve metal other than aluminum and zinc.

[0017] In the present invention, the halogen compound raw material is preferably one or more selected from the group consisting of silicon tetrachloride, trichlorosilane, and germanium tetrachloride. These halogen compound raw materials generate hydrogen chloride through hydrolysis reaction in the burner flame.

[0018] In the present invention, a part of the structural material or starting mechanism constituting the apparatus including the chamber housing may be exposed to a corrosion-accelerating environment at a temperature below the hydrochloric acid dew point. The valve metal element, excluding aluminum and zinc, constituting the member exposed to the corrosion-accelerating environment at a temperature below the hydrochloric acid dew point may be titanium, tantalum, zirconium, hafnium, niobium, or molybdenum. Alternatively, the valve metal element may be an alloy containing titanium, tantalum, zirconium, hafnium, niobium, or molybdenum as a main component. [Effects of the Invention]

[0019] In the present invention, structural materials or parts of the drive mechanism constituting the apparatus, including the chamber housing, that are exposed to temperatures below the hydrochloric acid dew point are not corroded by condensed dilute hydrochloric acid, thereby preventing a decrease in productivity due to apparatus repairs. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram of an apparatus for manufacturing a porous optical fiber preform using a VAD method. [Figure 2] 1 is a schematic diagram of an apparatus for manufacturing a porous preform for an optical fiber by an OVD method. DETAILED DESCRIPTION OF THE INVENTION

[0021] After extensive research, we discovered that certain valve metal materials are effective for metal components that do not corrode even at temperatures below the dew point of hydrogen chloride gas, even for the components of optical fiber porous preform manufacturing equipment. Valve metals are metals whose surfaces are uniformly coated with an oxide film of the metal through anodic oxidation, exhibiting excellent corrosion resistance. This oxide film allows current to flow in only one direction and is extremely difficult to pass in the opposite direction. Representative valve metals include aluminum, zinc, tantalum, niobium, titanium, hafnium, zirconium, tungsten, bismuth, and antimony. These valve metals form denser and thicker oxide films than SUS304 and Ni-based superalloys, and are therefore expected to be resistant to environments where hydrogen chloride gas condenses below the dew point.

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings, in which: FIG.

[0023] (Example of application to a VAD method manufacturing device for porous preforms for optical fibers) Figure 1 is a schematic diagram of an apparatus for manufacturing a porous optical fiber preform using the VAD method. In the VAD method, a glass particle deposition burner 2 is used inside a chamber housing 1 to deposit glass particles onto the tip of a target rod 7, causing a porous optical fiber preform 10A to grow radially. The porous optical fiber preform 10A is gradually pulled upward by a rotary lifting mechanism 3 via a metal shaft 8, causing the porous optical fiber preform 10A to grow vertically. A seal member 9 is attached to the shaft 8 and the chamber housing 1. The chamber housing 1 is also equipped with an air inlet 4 with a filter that takes in outside air 6.

[0024] The halogen-based compound raw material SiCl4, SiHCl3, or GeCl4 is supplied as a gas to the burner 2. The burner 2 is also supplied with flammable gases such as hydrogen and oxygen, a combustion-supporting gas. The combustion reaction generates gaseous water, and the halogen-based compound raw material undergoes hydrolysis in the combustion flame. The SiO2 or GeO2 glass particles produced by the hydrolysis reaction adhere to the tip of the base material. A mixture 5A of the remaining glass particles and hydrogen chloride gas produced by the hydrolysis reaction is discharged through the metal exhaust port 11 to the abatement system 12A. While most of the hydrogen chloride gas is discharged to the abatement system 12A, some floats within the chamber housing 1 and corrodes the metal shaft 8 and the exhaust port 11. When the surface temperature drops below the hydrochloric acid dew point, corrosion progresses significantly, even for components made of SUS304 stainless steel.

[0025] Hereinafter, the effectiveness of applying the present invention to an apparatus for manufacturing a porous optical fiber preform by the VAD method will be explained with reference to Examples 1 and 2 and Comparative Examples 1 to 3.

[0026] [Example 1] The porous optical fiber preform was manufactured by constructing the metal shaft 8 and the metal exhaust port 11 using the elemental metals titanium, tantalum, zirconium, hafnium, niobium, and molybdenum. After manufacturing the porous optical fiber preform, there was no change in the shaft surface.

[0027] [Example 2] The porous optical fiber preform was manufactured by constructing the metal shaft 8 and the metal exhaust port 11 from titanium alloy, tantalum alloy, zirconium alloy, hafnium alloy, niobium alloy, or molybdenum alloy. After manufacturing the porous optical fiber preform, there was no change in the shaft surface.

[0028] [Comparative Example 1] The porous preform for optical fiber was manufactured by constructing the metal shaft 8 and the metal exhaust port 11 from SUS304 and SUS316L. After manufacturing the porous preform for optical fiber, brown corrosion products were visually confirmed on the shaft surface.

[0029] Comparative Example 2 The porous preform for optical fiber was manufactured by constructing the metal shaft 8 and the metal exhaust port 11 from pure nickel and Hastelloy C276, a nickel-based superalloy. After manufacturing the porous preform for optical fiber, green corrosion products were visually confirmed on the shaft surface.

[0030] Comparative Example 3 A porous preform for optical fiber was manufactured by constructing a metal shaft 8 and a metal exhaust port 11 from aluminum and zinc. After manufacturing the porous preform for optical fiber, white corrosion products were visually confirmed on the surface of the shaft.

[0031] (Example of application to an optical fiber porous preform manufacturing device using the OVD method) Figure 2 is a schematic diagram of an apparatus for manufacturing a porous optical fiber preform using the OVD method. In the OVD method, glass particles are deposited on a target rod 107 held by a holding and rotating mechanism 103 inside a chamber housing 101. A glass particle deposition burner 102 is installed on a rail 104 and moved horizontally via a horizontal movement mechanism 105 to produce a porous optical fiber preform 10B with a uniform outer diameter in the longitudinal direction. A densifying burner 109 is preferably installed to prevent cracks from occurring at the deposition end as the porous optical fiber preform 10B grows in the outer diameter direction. The chamber housing 101 is equipped with a filtered air inlet 106 that takes in outside air.

[0032] The glass particle deposition burner 102 is supplied with a gaseous halogen-based compound precursor, such as SiCl4, SiHCl3, or GeCl4. The burner 102 is also supplied with a flammable gas, such as hydrogen, and oxygen, a combustion-supporting gas. The combustion reaction generates gaseous water, and the halogen-based compound precursor undergoes a hydrolysis reaction in the combustion flame. The SiO2 or GeO2 glass particles produced by the hydrolysis reaction adhere to the tip of the base material. A mixture 5 of the remaining glass particles and hydrogen chloride gas produced by the hydrolysis reaction is exhausted to the abatement system 12B through a metal exhaust hood 108. While most of the hydrogen chloride gas is exhausted to the abatement system, some of it floats within the chamber housing 101, corroding the chamber housing 101 and the gripping / rotating mechanism 103. Corrosion progresses particularly rapidly on the chamber housing side surface 101B, where the surface temperature is constantly below 100°C and below the hydrochloric acid dew point.

[0033] Hereinafter, the effectiveness of applying the present invention to an apparatus for manufacturing a porous optical fiber preform by the OVD method will be explained with reference to Examples 3 and 4 and Comparative Examples 4 to 6.

[0034] [Example 3] The chamber housing side surface 101B was made of a single metal selected from titanium, tantalum, zirconium, hafnium, niobium, and molybdenum to manufacture the porous optical fiber preform 10B. After manufacturing the porous optical fiber preform, there was no change in the chamber housing side surface 101B.

[0035] [Example 4] The chamber housing side surface 101B was made of titanium alloy, tantalum alloy, zirconium alloy, hafnium alloy, niobium alloy, or molybdenum alloy to manufacture the porous optical fiber preform 10B. After manufacturing the porous optical fiber preform, there was no change in the chamber housing side surface 101B.

[0036] Comparative Example 4 The chamber housing side surface 101B was made of SUS304 and SUS316L, and the porous preform for optical fiber 10B was manufactured. After manufacturing the porous preform for optical fiber 10B, brown corrosion products were visually confirmed on the chamber housing side surface 101B.

[0037] Comparative Example 5 The chamber housing side surface 101B was made of pure nickel and Hastelloy C276, a nickel-based superalloy, and a porous preform for optical fiber was manufactured. After manufacturing the porous preform for optical fiber, green corrosion products were visually confirmed on the chamber housing side surface 101B.

[0038] Comparative Example 6 The chamber housing side surface 101B was made of aluminum and zinc, and a porous preform for optical fiber was manufactured. After manufacturing the porous preform for optical fiber, white corrosion products were visually confirmed on the chamber housing side surface 101B.

[0039] From the above examples and comparative examples, it has been confirmed that valve metals such as titanium, tantalum, zirconium, hafnium, niobium, and molybdenum, and their alloys, except for aluminum and zinc, are not corroded in environments where hydrogen chloride gas is below the dew point temperature and corrodes, and when these materials are used in an optical fiber porous preform manufacturing apparatus, the frequency of equipment repairs can be reduced.

[0040] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention. In other words, appropriate modifications are possible within the scope of the technical idea expressed in the present invention, and forms incorporating such modifications and improvements are also included within the technical scope of the present invention. [Explanation of symbols]

[0041] 1. Chamber housing 2. Burner for depositing glass particles 3-rotation lifting mechanism 4 Air supply port 7 Target Stick 8 shafts 9 Sealing material 10A Porous Preform for Optical Fiber 11 Exhaust port 12A Harm removal equipment 101 chamber housing 102 Burner for depositing glass particles 103 Grip rotation mechanism 104 Rail 105 Horizontal movement mechanism 106 Air supply port 107 Target Stick 108 Exhaust Hood 109 Burner 10B Porous preform for optical fiber 12B Harm removal equipment

Claims

1. An apparatus for depositing a porous preform for optical fiber by hydrolyzing a halogen compound raw material, characterized in that a part of the structural material or driving mechanism constituting the apparatus is formed from a valve metal other than aluminum and zinc, or an alloy mainly containing a valve metal other than aluminum and zinc.

2. 2. The apparatus for manufacturing a porous preform for optical fiber according to claim 1, wherein the halogen compound raw material is one or more selected from the group consisting of silicon tetrachloride, trichlorosilane, and germanium tetrachloride.

3. 3. The apparatus for manufacturing a porous preform for an optical fiber according to claim 1, wherein a part of a structural material or a starting mechanism constituting the apparatus is exposed to a temperature equal to or lower than the dew point of hydrochloric acid.

4. 3. The apparatus for manufacturing a porous preform for optical fiber according to claim 1, wherein the valve metal other than aluminum and zinc is any one of titanium, tantalum, zirconium, hafnium, niobium, and molybdenum.

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