KR100824986B1 - A composition for transparent silica glass and a method of preparing silica glass using the same - Google Patents

Abstract

The present invention provides a composition for preparing silica glass comprising silica powder, dispersant, deionized water, gelling agent, and formamide. The invention also comprises the steps of preparing a silica sol by mixing silica powder, dispersant and deionized water; Adding a gelling agent and formamide to the silica sol; Injecting the sol into a mold to gel it in the mold; Removing the gelled formed body from the mold to obtain a wet gel; Drying the wet gel; Primary heat treating the dried gel at 300 to 600 ° C .; Second heat treatment of the heat-treated resultant at 500 to 1000 ° C; And it provides a method for producing a silica glass comprising the step of sintering the secondary heat-treated product in a vacuum atmosphere.

Silica Glass, Vacuum Sintered, Sol-Gel

Description

A composition for manufacturing transparent silica glass and a method for producing silica glass using the same {A COMPOSITION FOR TRANSPARENT SILICA GLASS AND A METHOD OF PREPARING SILICA GLASS USING THE SAME}

Field of invention

The present invention relates to a composition for preparing transparent silica glass and a method for preparing silica glass using the same, and more particularly, to a method for manufacturing transparent silica glass by vacuum sintering a composition for preparing transparent silica glass and a dried molded article prepared therefrom. .

Prior art

As a method of manufacturing silica glass, the sol-gel process is a liquid phase process, which has high productivity and can freely control the composition of the product, and has an advantage of high economical efficiency since the manufacturing process is generally performed at a low temperature as compared to the existing method. Numerous methods have been attempted to produce bulk glass, in particular high silica glass, via a sol-gel process. As one of these methods, a sol-gel process using an alkoxide has been proposed. However, this method is limited in size and has a disadvantage of low economic efficiency.

In order to solve this problem, a sol-gel process using ultrafine particles small enough to have colloidal properties has been proposed. According to this method, it is possible to manufacture a large size silica glass of a certain size or more, and to economically manufacture an over-cladding tube for an optical fiber, or a high purity silica glass for semiconductor manufacturing and various other applications. Brief description of the technique for preparing silica glass through the sol-gel process using such ultrafine particles is as follows.

In the sol-gel process, a process of (1) preparation of silica sol, (2) gelation of sol, (3) drying of gel, and (4) vitrification through heat treatment of dry gel are performed. Various processes are provided for the processes of (1) to (3), and the vitrification process through heat treatment of the dry gel (4), which is the final densification process, generally removes organic matter from the gel by first heat treatment of the dried gel. Subsequently, the gel from which the organic substance has been removed is sintered in a hydroxyl group and an impurity removing step and in an inert gas atmosphere such as air or helium to complete silica glass of high purity.

According to this method, large silica substrates can be prepared relatively easily through an adopted sol-gel process. However, in the case of sintering in air, it is very difficult to manufacture transparent silica glass that is close to the theoretical density due to excessive tendency of crystallization and excessive presence of residual pores in the sintered body as it rises to a high temperature during sintering.

On the other hand, when sintering in a gas atmosphere such as helium, which is most widely known as an improved sintering method, the sintering performance is superior to that in air, and the side effects of crystallization of glass can be eliminated as much as possible. . However, when sintering in a helium atmosphere, there is a disadvantage in that excessive fine bubbles remain in the sintered body due to incomplete sintering, thereby degrading the final glass quality. In order to remove such fine bubbles, a method of raising the sintering temperature to a higher temperature than that used in the sintering under helium atmosphere is used. However, the disadvantage that the deformation of the silica substance becomes severe with increasing sintering temperature is highlighted. Removal of microbubbles is not satisfactory.

In order to solve the above problems, the present invention is to provide a composition for producing transparent silica glass close to the theoretical density.

Another object of the present invention is to provide a method for producing transparent silica glass close to the theoretical density.

In order to achieve the above object, the present invention provides a composition for preparing silica glass comprising silica powder, dispersant, deionized water, gelling agent, and formamide.

The invention also comprises the steps of preparing a silica sol by mixing silica powder, dispersant and deionized water; Adding a gelling agent and formamide to the silica sol; Injecting the sol into a mold to gel it in the mold; Removing the gelled formed body from the mold to obtain a wet gel; Drying the wet gel; Primary heat treating the dried gel at 300 to 600 ° C .; Second heat treatment of the heat-treated resultant at 500 to 1000 ° C; And it provides a method for producing a silica glass comprising the step of sintering the secondary heat-treated product in a vacuum atmosphere.

Hereinafter, the present invention will be described in more detail.

The composition for producing silica glass of the present invention includes silica powder, dispersant, deionized water, gelling agent, and formamide.

The silica powder preferably has a specific surface area of 20 to 50 m ² / g and a powder of ultrafine particles having an average particle size of 40 to 100 nm. Commercially available fumed silica can be preferably used in the present invention.

The dispersing agent and the gelling agent in the above components may be used all compounds used in the production of conventional silica glass, it is not limited to the compounds described below.

Dispersants that may be used in the present invention include ammonium salt-based compounds, specific examples of which are quaternary ammonium hydroxide tetramethylammonium hydroxide (TMAH), or tetraethylammonium hydroxide (TEAH). Dispersants not only help the silica to be uniformly dispersed in the composition, but also serve to electrostatically stabilize the sol in which the silica is dispersed.

As the gelling agent, water-soluble aliphatic esters of acids may be used, and preferred examples thereof include ethyl lactate, methyl lactate, ethyl formate, methyl formate, ethyl glycolate and methyl glycolate.                     

The formamide is a drying aid that is slowly reacted with water, converted to weak acidity, and serves to improve the drying ability of the gel.

The content of each component of the composition for preparing silica glass of the present invention can be easily determined according to the desired density of the silica glass. According to a preferred embodiment of the present invention, silica comprising 40 to 60 parts by weight of silica powder, 1 to 5 parts by weight of dispersant, 40 to 60 parts by weight of deionized water, 0.5 to 5 parts by weight of gelling agent and 0.1 to 20 parts by weight of formamide. A composition for preparing glass is provided. Formamide as a drying aid is preferably used 2 to 30 parts by weight based on 100 parts by weight of the dispersant.

The composition for producing silica glass of the present invention may further include a plasticizer. As the plasticizer, polyhydric alcohol may be preferably used. Specific examples thereof include glycerin, ethylene glycol, 2-methylpropane-1,2,3-triol, and the like. The plasticizer is preferably used in an amount of 0.1 to 3 parts by weight.

Silica glass manufacturing method of the present invention comprises the steps of preparing a silica sol by mixing the silica powder, dispersant and deionized water; Adding a gelling agent and formamide to the silica sol; Injecting the sol into a mold to gel it in the mold; Removing the gelled formed body from the mold to obtain a wet gel; Drying the wet gel; Primary heat treating the dried gel at 300 to 600 ° C .; Second heat treatment of the heat-treated resultant at 500 to 1000 ° C; And sintering the secondary heat-treated result in a vacuum atmosphere.                     

In the first step of the silica glass manufacturing process of the present invention, a stable colloidal silica sol is prepared by mixing the silica powder, the dispersant, and the deionized water using a blender, followed by aging. Into the silica sol a gelling agent and a composition for preparing silica glass in the form of a sol containing formamide as a drying aid is injected into a mold and gelated. In addition, before the gelling agent and formamide are added, a bubble may be removed from the silica sol by using a vacuum pump, followed by addition of the gelling agent and the formamide drying aid, followed by injection into a mold to gelate.

The gelled molded body is removed from the mold to obtain a wet gel. The wet gel is preferably dried at 30 to 50 ° C. for at least 48 hours. The primary heat treatment process of the dried gel is carried out at a temperature increase rate of 5 to 50 ℃ / hr at a temperature of 300 to 600 ℃. This heat treatment removes organic matter present in the gel. The first heat treated gel is second heat treated at a temperature rising rate of 100 ° C./hr at a temperature of 500 to 1000 ° C. During this secondary heat treatment process, a high purity process is performed using a chlorine gas atmosphere, in which residual hydroxyl groups and other metallic impurities are removed. At the same time, oxygen or a fluorine compound gas is flowed to remove the chlorine component remaining in the silica molded body. At this time, the heat treatment is preferably performed at 900 to 1100 ℃.

In the present invention, unlike the conventional method of sintering the secondary heat-treated molded body in the air or helium atmosphere as described above, it is sintered in a vacuum atmosphere to provide silica glass which is excellent in transparency and close to the theoretical density (2.202 g / cm ³ ). do. Formamide used as a drying aid in the present invention has a disadvantage of improving the drying ability of the gel but making the pores of the dried gel relatively large to make sintering difficult. However, if the sintering in a vacuum atmosphere as in the present invention can solve this problem. The vacuum sintering process is carried out by heating to a temperature of 1200 to 1700 ℃ in a vacuum atmosphere of 10 ^-1 to 10 ^-6 Torr (Torr) for 0.1 to 100 hours at that temperature.

The following presents a preferred embodiment to aid the understanding of the present invention. However, the following examples are provided only to more easily understand the present invention, and the present invention is not limited to the following examples.

Examples and Comparative Examples

Example 1

Blending apparatus of 1000 g of silica powder (Aerosil OX-50 (Degussa, Germany)), 1000 g of deionized water and 200 g of tetramethylammonium hydroxide (TMAH) having a specific surface area of 50 m ² / g or less and an average particle size of 40 nm or less The mixture was sufficiently mixed with to obtain a sol in which silica particles were uniformly dispersed. Then, the sol was defoamed sufficiently for at least 10 minutes by using a vacuum pump, and the sol was stabilized by standing in air at least 24 hours. 100 g of ethyl lactate and 50 g of formamide were added to the sol, and then the mixture obtained by uniformly mixing was injected into a tube for molding. When gelation was completed, the wet gel was separated from the molding mold and dried for 48 hours at 50 ° C. in air. Then, the dried gel was heated up to 500 ° C. at a temperature increase rate of 10 ° C./hr, and the organic material in the dried gel was removed by first heat treatment at this temperature for 5 hours. The organic material-free gel was heated to 900 ° C. at 100 ° C./hr and subjected to a second heat treatment, and maintained at this temperature for 5 hours. At this time, the secondary heat treatment process was carried out in a chlorine gas atmosphere to remove hydroxyl groups and metal impurities. Then, the chlorine component remaining in the silica molded body was removed by maintaining the oxygen atmosphere while raising the temperature at a rate of 100 ° C./hr to 1100 ° C. Finally, a silica glass tube was prepared by heating up to 1350 ° C. at a heating rate of 100 ° C./hr under a vacuum atmosphere of 10 ⁻³ Torr and sintering at this temperature for 1 hour.

Example 2

A silica glass tube was prepared in the same manner as in Example 1 except that the amount of formamide was used at 100 g and sintered at 1320 ° C. under vacuum of 10 ⁻² torr during vacuum sintering.

Example 3

A silica glass tube was prepared in the same manner as in Example 1 except that the amount of ethyl lactate was 50 g and sintered at 1320 ° C. under vacuum of 10 ⁻⁴ torr during vacuum sintering.

Comparative Example 1

Silica glass tubes were prepared in the same manner as in Example 1 except that the mixture was sintered in air instead of in a vacuum atmosphere.

Comparative Example 2

A silica glass tube was prepared in the same manner as in Example 1 except that the sintered in helium atmosphere instead of the vacuum atmosphere.

The amount of residual microbubbles in the silica glass tubes prepared according to the above Examples and Comparative Examples was analyzed using a laser scattering method. The silica glass obtained in Comparative Examples 1 and 2 contained more than 50 vol% of residual microbubbles than the silica glass obtained in Examples 1 to 3.

In the case of vacuum sintering a dry molding agent prepared using the silica glass composition of the present invention, it is possible to reduce microbubbles, improve transparency, and close to theoretical density, compared to sintering in a conventional air atmosphere or helium atmosphere. Transparent silica glass can be produced.

Claims (8)

delete delete delete delete a) to prepare a silica sol by mixing 40 to 60 parts by weight of silica powder, 1 to 5 parts by weight of dispersant and 40 to 60 parts by weight of deionized water having a specific surface area of 20 to 50 m ² / g and an average particle size of 40 to 100 nm. Doing; b) adding 0.5 to 5 parts by weight of a gelling agent and 0.1 to 20 parts by weight of formamide to the silica sol; c) gelling in the mold by injecting the sol prepared in step b) into the mold; d) removing the gelled formed body from the mold to obtain a wet gel; e) drying the wet gel; f) first heat treating the dried gel at 300 to 600 ° C; g) second heat treatment of the heat-treated resultant at 500 to 1000 ° C; And h) sintering the secondary heat-treated product under vacuum atmosphere To include, wherein the sintering in the vacuum atmosphere is carried out for 0.1 to 100 hours at a temperature of 1320 to 1700 ℃ at a vacuum pressure of 10 ^-1 to 10 ^-6 Torr. The method of claim 5, further comprising the step of removing bubbles present in the silica sol using a vacuum pump after step a). The method of claim 5, wherein 2 to 30 parts by weight of formamide is added based on 100 parts by weight of the dispersant. delete