KR100312230B1 - Manufacture method of metal doped silica glass - Google Patents

Abstract

The present invention provides a method for producing silica glass using a sol-gel method, comprising: a first step of hydrolyzing a metal alkoxide; A second step of mixing a greater amount of fumed silica with deionized water than the metal alkoxide so that the gel to be formed follows the drying characteristics of the fumed silica and the molar ratio with the metal alkoxide is 1: 0.1 or less so that the strength of the wet gel increases; A third step of forming a sol by mixing the hydrolyzate of the first step with the mixture of the second step; A fourth step of injecting the sol into a mold to gelate the sol; A fifth step of demolding and drying the gel; And a sixth process of sintering and drying the dried gel to vitrify the silica gel.

Description

Manufacturing method of silica glass doped with metal {MANUFACTURE METHOD OF METAL DOPED SILICA GLASS}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing silica glass, and more particularly, to a method of manufacturing silica glass doped with metal such as germanium by a sol-gel method. It is about.

Silica glass, which is a preform of optical fibers, is used for Vapor-phase Axial Deposition (VAD), Outer Chemical Vapor-phase Deposition (OCVD), Plasma Chemical Vapor-phase Deposition (PCVD), and Modified Chemical Vapor-phase Deposition (MCVD). It is prepared by the vapor deposition method such as)) or the liquid phase method such as the sol-gel method.

In particular, the sol-gel method is different from the chemical vapor deposition method in which a raw material gas in a gaseous state is deposited to prepare a silica glass in a solid state. Manufacture. Therefore, the sol-gel method is relatively low temperature production cost compared to chemical vapor deposition method is low production cost, easy to control the composition and high productivity, it is a very useful manufacturing method for producing silica glass.

The sol-gel method includes a method using silicon alkoxide as a starting material and a method using fumed silica. The method of using the silicon alkoxide is disclosed in British Patent No. 2,041,913 and the like, and the method of using the fumed silica is disclosed in detail in US Patent No. 4,419,115 and the like, respectively.

In order to manufacture the optical fiber base material by the sol-gel method, an overcladding tube that forms the core rod and the cladding portion that forms the core portion of the optical fiber is manufactured, and then the overcladding tube is the core. Over-jacket the outer circumference of the rod.

In the optical fiber, the core portion is a portion where signal light is transmitted. Therefore, since the refractive index of the core portion must be higher than the refractive index of the clad portion, the core rod is doped with an additive such as germanium to increase the refractive index.

On the other hand, in the conventional silica glass manufacturing method using silicon alkoxide, when doping the above-described additives such as germanium to the core rod, the doping is relatively doped throughout the core rod because it is bonded in the mesh structure formed by the silicon alkoxide polymerization (Polymerization) While uniformly made, there is a problem that cracking occurs after drying due to small pores as well as a large shrinkage of the gel during drying. In addition, conventional silica glass manufacturing method using silicon alkoxide has to be applied to considerably relaxed drying conditions due to the cracking problem occurs during drying, or to dry only by exposing a limited part of the mold, in which case the drying speed is too slow to reduce productivity There was a problem.

In addition, in the conventional silica glass manufacturing method using fumed silica, when doping an additive such as germanium to the core rod, the shrinkage of the gel during drying and low cracking after drying due to the large pores, while the additive is not applied to the entire core rod There was a problem that can not be uniformly doped.

SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide a method for producing silica glass in which a metal such as germanium is uniformly doped in a core while preventing cracks that may occur during drying.

In order to achieve the above object, the present invention provides a method for producing silica glass using a sol-gel method, the first step of hydrolyzing a metal alkoxide; A second step of mixing a greater amount of fumed silica with deionized water than the metal alkoxide so that the gel to be formed follows the drying characteristics of the fumed silica and the molar ratio with the metal alkoxide is 1: 0.1 or less so that the strength of the wet gel increases; A third step of forming a sol by mixing the hydrolyzate of the first step with the mixture of the second step; A fourth step of injecting the sol into a mold to gelate the sol; A fifth step of demolding and drying the gel; And a sixth process of sintering and drying the dried gel to vitrify the silica gel.

1 is a flow chart showing a sol-gel process for producing a metal-doped silica glass according to a preferred embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, if it is determined that detailed descriptions of related known functions or configurations may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

1 is a flowchart illustrating a sol-gel process for preparing germanium-doped silica glass according to a preferred embodiment of the present invention. That is, in the embodiment according to FIG. 1, germanium alkoxides among metal alkoxides will be described as an example.

As shown in FIG. 1, the process of preparing germanium-doped silica glass according to an embodiment of the present invention is largely performed by germanium alkoxide hydrolysis process (10), mixing process of fumed silica with deionized water (20), and sol formation process. 30, a molding process 30, a gel forming process 40, a demolding process 50, a drying process 60, and a sintering process 70. At this time, the germanium alkoxide hydrolysis process (10) and the execution order of the mixing process of the fumed silica and deionized water (20) is not affected in the practice of the present invention.

The germanium alkoxide hydrolysis process (hereinafter, referred to as hydrolysis process) is a process of adding water to the germanium alkoxide and then hydrolyzing it under an acid catalyst (Hydrosis). Through the hydrolysis process, the alkoxide group (-OR) of the germanium alkoxide is reacted with water to be replaced with a hydroxyl group (-OH). As the acid catalyst, an acid such as hydrochloric acid, nitric acid or sulfuric acid may be selectively used. The acid catalyst lowers the electron density around the germanium atom to increase the affinity with the electrons, thereby facilitating the reaction with water, shortening the hydrolysis time and improving the hydrolysis rate.

The mixing process of fumed silica and deionized water (20, or less mixing process) is a process of mixing and dispersing fumed silica and deionized water. At this time, the weight ratio of the fumed silica and deionized water is not particularly limited, but may be adjusted to about 50:50 depending on the embodiment. The mixing process 20 is performed in a mixer such as a high shear mixer, and may add ultrasonic grinding and centrifugation to improve the uniformity of the mixed result and to remove impurities. Although it may vary depending on the composition of the mixture, if the viscosity of the sol in the mixing process (20) is not easy to ultrasonic grinding and centrifugation operation, the ultrasonic grinding and centrifugation operation after the sol forming process 30 to be described later You can also do it.

The sol forming process 30 is a mixture of the fumed silica and deionized water obtained in the mixing process 20 and deionized water to form a sol by mixing and dispersing the germanium alkoxide hydrolyzate obtained in the hydrolysis process 10 It is a process. At this time, the germanium alkoxide should be added to the mixture in the state having fluidity after hydrolysis. In the sol formation process 30, an organic base such as tetramethylammonium hydroxide or an acidic solution, a binder such as polyvinyl alcohol, may be used for controlling acidity (pH) as necessary. And plasticizers can be added. At this time, the acidity (pH) of the sol is adjusted to be 4 or less, which is possible by controlling the addition amount of the organic base, an organic organic compound such as an acidic solution, and an initially charged catalyst. After forming the sol in this manner, bubbles in the sol are removed by using a vacuum pump or the like.

The molding process 40 is a process of forming a core rod-shaped mold by injecting a sol formed in the sol forming process 30 into a mold. The mold is formed using polystyrene or Teflon, and is composed of a tube-shaped cylindrical part and an upper and lower disc part for blocking open ends of the cylindrical part. After the molding process 40, in order to shorten the gelation time according to the embodiment, the ambient temperature is raised to within 80 ° C, or a separate gelling agent may be added.

In the gel formation process 50, formamide (amide) is added to increase the pH of the sol injected into the mold to promote gelation and accelerate drying, or ammonium fluoride is a material containing fluorine ions. It is a process of adding a gelling agent such as (Ammonium fluoride) and aging it at room temperature to form a gel. The germanium alkoxide mixed by hydrolysis produces particles of several nm, which are very small in size compared to fumed silica when gelled, thereby being bonded to the negative curvature of the fumed silica having relatively large particles to improve gel strength. Let's do it.

The demolding process 60 is a process of separating the core rod-shaped gel formed in the mold through the gel forming process 50 from the mold. The demolding process 60 may be performed in a water tank to prevent damage to the gel that may occur during demolding. That is, the mold formed by removing the upper and lower disc portions is placed in a water tank and then pushed out by hydraulic pressure from one side, and the gel formed in the mold is separated from the mold.

The drying process 70 is a process of drying the gel separated from the mold in a constant temperature and humidity chamber and decomposing residual moisture and organic matter in the gel through low temperature heat treatment. After the low temperature heat treatment, it is heated to 900 to 1000 ° C. in a chlorine (Cl) gas atmosphere to remove metal impurities and hydroxide (OH) groups in the gel. As described above, the hydrolyzate of germanium alkoxide having a small particle size and the fumed silica having a relatively large particle size are mixed to form a gel having a high filling rate, thereby increasing the strength of the gel and uniformly doping the germanium particles in the gel. Of course, it prevents the cracking phenomenon occurring during the drying process. That is, the method for producing silica glass of the present invention uses less than a few% germanium alkoxide, which is a relatively small amount compared to fumed silica, and thus gel properties are determined by the fumed silica having good drying properties in the gel composition germanium alkoxide and fumed silica. This shortens the drying time of the gel and improves the drying state.

The sintering process 80 is a process of sintering and vitrifying the gel after the drying process 70. The sintering process 80 is performed by heating the gel to 1350 ° C to 1400 ° C in a sintering furnace under a helium (He) gas atmosphere. When the sintering process 80 is completed, a core rod, which is a high purity silica glass doped with a metal such as germanium, is uniformly doped.

As described above, the method of manufacturing the metal-doped silica glass according to the embodiment of the present invention improves the optical properties of the optical fiber produced from the silica glass by uniformly doping metal particles such as germanium in the silica glass, and gel drying. It is effective to improve the quality of the silica glass by preventing the crack phenomenon occurs during.

In addition, the method of manufacturing the metal-doped silica glass according to the embodiment of the present invention has the effect of shortening the drying time to improve the productivity of the silica glass.

Claims (9)

In the method for producing silica glass using the sol-gel method, A first step of hydrolyzing the metal alkoxide; A second step of mixing a greater amount of fumed silica with deionized water than the metal alkoxide so that the gel to be formed follows the drying characteristics of the fumed silica and the molar ratio with the metal alkoxide is 1: 0.1 or less so that the strength of the wet gel increases; A third step of forming a sol by mixing the hydrolyzate of the first step with the mixture of the second step; A fourth step of injecting the sol into a mold to gelate the sol; A fifth step of demolding and drying the gel; And a sixth process of sintering and drying the dried gel to vitrify the gel. The method of claim 1, wherein the metal alkoxide is germanium alkoxide. The method of claim 1, wherein the acidity (pH) of the sol is controlled to 4 or less. 2. The method of claim 1, wherein the fourth step is to add a gelling agent. 5. The method of claim 4, wherein the gelling agent is an amide-based material. 5. The method of claim 4, wherein the gelling agent uses a material containing fluorine ions. 6. The method of claim 1, wherein the vitrification of the gel of the sixth step is performed by sintering in a helium (He) gas atmosphere. The method of claim 1, wherein the hydrolyzate of the metal alkoxide in the first step is a result of hydrolysis of the metal alkoxide under an acid catalyst. 10. The method of claim 8, wherein the acid catalyst is hydrochloric acid, nitric acid or sulfuric acid.