KR100346198B1 - Fabrication method of doped silica glass by sol-gel process - Google Patents

Abstract

The present invention provides a method for producing doped silica glass using a sol-gel method, comprising: a sol forming step of forming a sol by mixing fumed silica and deionized water; A hydrolyzate forming step of adding an acidic catalyst to a metal alkoxide having two alkoxide groups and then hydrolyzing it; A mixing step of mixing the hydrolyzate with the sol produced in the sol forming step; It provides a method for producing doped silica glass using a sol-gel method, characterized in that it comprises a molding step of putting the mixture produced by the mixing step into a mold and gelling.

Description

Method for producing doped silica glass using sol-gel method {FABRICATION METHOD OF DOPED SILICA GLASS BY SOL-GEL PROCESS}

The present invention relates to silica glass production, and more particularly, to a method for producing doped silica glass using the sol-gel process.

Silica glass, which is a raw material for making high-purity glass products such as photomasks and optical fibers for semiconductor manufacturing, is manufactured by a natural quartz method, a synthetic quartz method, or a sol-gel method.

In particular, the sol-gel method has a purity and uniformity of the molecular unit because the purity is corrected by removing impurities from the starting material (Start material) through centrifugation, etc., unlike other manufacturing methods, the productivity is high because it is a liquid phase method, The composition and structure of the product can be controlled relatively freely. In addition, the sol-gel method is a manufacturing method with high economical efficiency because most of the processes except for the sintering process is made at a low temperature. The silica glass manufacturing process by the sol-gel method is described in detail in US Patent No. 5,240,488, 'Manufacture of vitreous silica product via a sol-gel process using a polymer additive'.

The sol-gel process is a method of forming a polymeric sol using silicon alkoxide as a starting material, and a colloidal sol using fumed silica. There is a way. 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.

Meanwhile, in order to manufacture a core rod for manufacturing an optical fiber using the silica glass, an additive such as germanium is doped to increase the refractive index. In this case, the doping method using an alkoxide has the advantage that the additive is uniformly doped in the silica glass, but the problem of the large shrinkage during drying, which is an inherent disadvantage of the silica glass made using the alkoxide, and the crack due to the pores do.

In order to solve the above problems, an object of the present invention is a method of manufacturing doped silica glass using a sol-gel method that can reduce the shrinkage rate and prevent cracking during drying of the silica glass even while the additive is doped to the silica glass uniformly. To provide.

In order to achieve the above object, the present invention provides a method for producing a doped silica glass using a sol-gel method, comprising: forming a sol by mixing fumed silica and deionized water; A hydrolyzate forming step of adding an acidic catalyst to a metal alkoxide having two alkoxide groups and then hydrolyzing it; A mixing step of mixing the hydrolyzate with the sol produced in the sol forming step; It provides a method for producing doped silica glass using a sol-gel method, characterized in that it comprises a molding step of putting the mixture produced by the mixing step into a mold and gelling.

1 is a flow chart showing a doped silica glass manufacturing method using a sol-gel method according to a preferred embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

102 silica fume 104 deionized water

202 metal alkoxide 204 acid catalyst

302: Gelling Agent

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 flow chart showing a doped silica glass manufacturing method using a sol-gel method according to a preferred embodiment of the present invention. As illustrated in FIG. 1, the doped silica glass manufacturing method using the sol-gel process according to the preferred embodiment of the present invention may include a sol forming step 100, a hydrolyzate forming step 200, a mixing step 300, and a molding. It consists of a step 400, a demolding step 500, a drying step 600, a low temperature heat treatment step 700 and a sintering step 800. In particular, the present invention hydrolyzes the metal alkoxide 202 having two alkoxide groups under acidic catalyst 204, and the hydrolyzate produced therefrom is added to the mixture of fumed silica 102 and deionized water 104 to Note that there is a characteristic in forming the

1. Brush forming step

The sol forming step 100 is a step of forming a sol by mixing the silica fume 102 and deionized water (104). The mixing weight ratio of the fumed silica and deionized water is preferably 6: 4 to 4: 6 or 5: 5, but the mixing weight ratio may vary according to embodiments.

2. Hydrolyzate Formation Step

The hydrolyzate forming step 200 is a step of hydrolyzing by adding an acid catalyst 204 to the metal alkoxide 202 having two alkoxide groups.

The metal alkoxide 202 is a doping material having two alkoxide groups in a symmetrical position, and the amount of water required for hydrolysis is small, thereby reducing the amount of alcohol generated during hydrolysis, thereby improving strength of the gel. It also prevents cracking caused by the rapid volatilization of alcohol during drying. Diethyldieethoxygermane is used as the metal alkoxide 202.

The hydrolyzate content may be 1 wt% or more and 10 wt% or less based on the sol generated in the sol forming step 100. When the content of the hydrolyzate exceeds 10wt%, not only the strength of the gel is rather weak but also a high risk of cracking during drying, and when the content of the hydrolyzate is less than 1wt%, the strength improvement effect of the gel is weak. It also slows down gelation.

The acidic catalyst 204 shortens the hydrolysis and condensation time of the particles inside the sole. The acidic catalyst 204 has a greater time reduction effect than the basic catalyst. As the acid catalyst 204, dilute hydrochloric acid or sulfuric acid is used.

3. Mixing step

The mixing step 300 is a step of mixing the hydrolyzate formed in the hydrolyzate forming step 200 with the brush generated in the brush forming step.

The sol is a mixture of the metal alkoxide hydrolyzate having two alkoxide groups, thereby preventing the formation or randomly branched polymer of the network structure and oligomer or polymer is the neck between the particles Because of the bridging, the strength of the gel is increased and the doping of the additive is uniform.

The gelling agent 302 may be added to the mixture of the mixing step 300. The gelling agent 302 shortens the time it takes for the brush to gel. As the gelling agent 302), one of ammonium fluoride, tetramethylammonium hydroxide, and formamide may be used. After the mixing step 300, it is possible to remove bubbles contained in the brush using a vacuum pump or the like.

4. Steps After Mixing

The molding step 400 is a step of gelling the mixture produced by the mixing step 300 in a mold having a predetermined shape. After the molding step 400, an aging process is performed to stabilize the silica particles in the sole.

The demolding step 500 is a process of separating the primary dry gel produced by the molding step 400 from the mold. The demolding step 500 may be performed using water pressure in a water tank to prevent damage to the primary dry gel.

The drying step 600 is a process of forming the secondary dry gel by drying the primary dry gel separated from the mold by the demolding step 500 using a constant temperature and humidity chamber or the like.

The low temperature heat treatment step 700 is heat-treating the formed secondary dry gel while supplying gas such as chlorine, hydrogen, oxygen, decomposes organic matters such as residual moisture and binder in the secondary dry gel, and metallic impurities and hydroxide ( OH) group and the like. Since the low temperature heat treatment step 700 is a process of removing impurities in the secondary dry gel as described above, it is also called a purification process.

The sintering step 800 is a process of producing high-purity silica glass to be finally obtained by sintering and drying the secondary dry gel passed through the low temperature heat treatment step 700 at a high temperature. The sintering step 800 is performed by heating the organic-treated secondary dry gel by using a furnace (furnace) to move up and down in the sintering furnace in a helium (He) gas atmosphere at least 1300 ℃. When the sintering step 800 is completed, a substrate tube or overjacketing tube, which is high purity silica glass, is obtained.

<Example>

Deionized water and fumed silica (Degussa, Aerosil-OX50) are mixed in a mixing weight ratio of 5: 5 to form a sol. Apart from the formation of the sol, an acidic catalyst is mixed with diethyl diethoxy germany and hydrolyzed to form a hydrolyzate.

The hydrolyzate is then added to the brush before gelation. At this time, the amount of the hydrolyzate is adjusted to be less than 10% by weight based on the sole. This is because, when the hydrolyzate content is less than 1% by weight, not only the gelation rate is slow but also the strength improvement effect of the gel is insignificant, and when it exceeds 10% by weight, the strength of the gel is rather weak.

Furthermore, after adding a hydrolyzate to the sol, formamide which is a gelling agent is added thereto. Thereafter, the doped silica glass is produced through molding, demolding, drying, low temperature heat treatment, and sintering.

As described above, the doped silica glass manufacturing method using the sol-gel method according to the embodiment of the present invention can ensure sufficient dispersion of the acidic sol as well as uniform doping of additives, and improve the strength of the wet gel. After drying, the shrinkage of the gel is less effective to produce doped silica glass.

Claims (6)

In the method for producing doped silica glass using the sol-gel method, A sol forming step of forming a sol by mixing fumed silica and deionized water; A hydrolyzate forming step of adding an acidic catalyst to a metal alkoxide having two alkoxide groups and then hydrolyzing it; A mixing step of mixing the hydrolyzate with the sol produced in the sol forming step; And a molding step of putting the mixture produced by the mixing step into a mold and gelling the gel. The method of claim 1, The metal alkoxide is a diethyl diethoxy germane characterized in that the doped silica glass manufacturing method using a sol-gel method. The method of claim 1, The acid catalyst as a dilute hydrochloric acid or sulfuric acid, characterized in that the doped silica glass manufacturing method using the sol-gel method. The method of claim 1, The mixing step is a doped silica glass manufacturing method using a sol-gel method characterized in that the addition of a gelling agent. The method of claim 4, wherein The gelling agent is a method for producing doped silica glass using the sol-gel method, characterized in that using ammonium fluoride, tetramethylammonium hydroxide or formamide. The method of claim 1, The content of the hydrolyzate is a method of producing doped silica glass using a sol-gel method, characterized in that 1wt% or more based on the sol formed in the sol forming step.