KR20000074724A - Manufacturing method of silica glass for sol-gel process - Google Patents

Abstract

PURPOSE: A fabrication method of silica glass by sol-gel process is provided to minimize remained Cl2 gas used in OH- ion removing, resulting in improving the purity of silica glass demanding for optical fiber or semiconductor. CONSTITUTION: The fabrication method of silica glass by sol-gel process comprises the steps of: forming a sol by mixing silica, dispersing agent, binder, gelling agent and deionized water; molding sol after removing bubbles, then gelling; drying, then demolding gel at 30-80°C and 65-80% of relative humidity; heat-treating at 50-500°C at a rate of 5-50°C/hr for removing organics, then heating to 500-1000°C at a rate of 50-100°C/hr for removing remained OH- ions under a Cl2 gas atmosphere; holding at 800-1000 for 1-10hrs. under O2 gas or O2 +He gas atmosphere for removing remained Cl- ions; heating to 1100-1400°C at a rate of 100°C/hr and then holding for 8hrs. under a He gas atmosphere. This method is very useful for fabricating long and wide-typed silica glass tubes of the following size: inner diameter; 22-27mm, outer diameter; 67-81mm, length; about 1000mm.

Description

Manufacturing method of silica glass for sol-gel process

The present invention relates to a method for producing silica glass for sol-gel process, and more particularly, to a method for preparing silica glass for sol-gel process that can minimize the amount of residual chlorine gas used in the hydroxyl group removal reaction.

The sol-gel process is a liquid phase process, which has high productivity and can freely control the composition of the product, and because the process is generally performed at a low temperature, it is very economical and is very useful when manufacturing high purity silica glass for optical fibers or semiconductors.

Hereinafter, a brief description of a method of manufacturing a silica glass overcladding tube using a sol-gel process is as follows.

First, silica particles are dispersed in water to form a sol. The sol formed is left to mature for a predetermined time. The aged sol is then poured into a mold and gelated. Once gelling is complete, the gel is separated from the mold and then dried.

Thereafter, the dried gel is first heat treated to remove organic matter in the gel. Subsequently, the hydroxyl group removal reaction and the sintering reaction are performed on the gel from which the organic material has been removed to complete the silica glass overcladding tube.

Since the reactivity of the sol-gel process as described above depends on factors such as gelation reaction temperature, composition, pressure, pH, solvent, etc., these factors should be appropriately controlled to control the reactivity to the desired range.

On the other hand, the hydroxyl group removal reaction is carried out in a chlorine gas atmosphere, the sintering reaction is usually carried out in a helium gas atmosphere. As described above, since the sintering reaction is performed immediately after the hydroxyl group removing reaction, some of the chlorine gas used in the hydroxyl group removing reaction remains so that they are trapped in the sintering process and remain in the pores after vitrification. These pores are a major cause of breakage when the fiber is pulled out.

In order to solve this problem, the residual chlorine gas was removed by maintaining the helium gas for a predetermined period after the hydroxyl group removal reaction. However, according to this method, the efficiency of removing residual chlorine gas was not satisfactory.

The technical problem to be achieved by the present invention is to solve the above problems to provide a method for producing a silica glass for sol-gel process that can efficiently remove the remaining chlorine used in the hydroxyl group removal reaction.

In the present invention to achieve the above technical problem. (a) mixing silica, dispersant, binder, gelling agent and deionized water to form a sol;

(b) removing the bubbles from the formed sol and then molding and gelling;

(c) demolding the obtained gel to dry it;

(d) removing organics from the dried gel and then removing hydroxyl groups; And

(e) maintaining the resultant at 800 to 1000 ℃ in an oxygen gas atmosphere, and then sintering provides a method for producing a silica glass for sol-gel process characterized in that it comprises.

In step (e), it is preferable to use helium gas together with oxygen gas. The reason is that helium gas serves as a carrier of oxygen gas.

Preferably, the organic material removal process of step (d) is made by heat treatment at 50 to 500 ℃, hydroxyl group removal process is carried out by heat treatment at 500 to 1000 ℃ under a chlorine gas atmosphere. In the step (e), the sintering process after maintaining for a predetermined period in an oxygen atmosphere is preferably performed by heat treatment at 1100 to 1450 ° C. in a helium gas atmosphere.

The production method according to the present invention is characterized in that the chlorine gas used during the hydroxyl group removal reaction is maintained for a predetermined period of time in the oxygen gas atmosphere after the hydroxyl group removal reaction in order to suppress the influence on the sintering process which is a subsequent process. At this time, it is preferable that the temperature maintained in the oxygen gas atmosphere is 800 to 1000 ° C, and the time maintained at this temperature can be changed depending on the remaining chlorine gas content.

The presence of chlorine gas in the reaction system can be confirmed using water. This is because, in more detail, water reacts with chlorine gas to emit light pale green.

The method for producing silica glass according to the present invention having the above-described characteristics will be described in more detail.

First, silica, additives and deionized water are mixed and then a sol is formed. Subsequently, bubbles are removed from the sol using a vacuum pump.

Although the said additive is not specifically limited, A dispersing agent, a binder, a plasticizer, a gelling agent, etc. are used. Herein, the dispersant, binder, plasticizer, and gelling agent are not particularly limited as long as they are materials commonly used in the production of silica glass. And the content of each substance is also normal.

The gelling agent is a water-soluble aliphatic ester of an acid selected from the group consisting of formic acid, lactic acid and glycolic acid, and specific examples thereof include methyl formate, methyl lactate, ethyl lactate, and the like. As the dispersant, tetramethylammonium hydroxide and tetraethylammonium hydroxide which are quaternary ammonium hydroxides are used. These materials 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.

In addition, a polyhydric alcohol (polyhydric alcohol) is used as a plasticizer. Specific examples include glycerin, ethylene glycol, 2-methylpropane-1,2,3-triol, and the like. As the binder, polyethyloxazoline, polyvinylacetate, or the like is used.

The sol formed according to the above procedure is molded and then gelled. Subsequently, when the gelation is completed after a predetermined period of time, the gelled resultant is de-molded.

The demolded gel is then dried at a temperature of 30-80 ° C. and a relative humidity of 65-80%.

Subsequently, the dried gel is heat-treated at 50 to 500 ° C. (raising rate: 5 to 50 ° C./hr) to remove organic matter remaining in the gel. Thereafter, the temperature is increased to 500 to 1000 ° C (heating rate: 50 to 100 ° C / hr) and heat-treated for a predetermined time. This heat treatment is carried out in a chlorine gas atmosphere in which residual hydroxyl groups are removed.

Thereafter, the remaining chlorine gas is removed by maintaining at 800 to 1000 ° C. for 1 to 10 hours in an oxygen gas atmosphere. In this process, oxygen gas and helium gas may be used in addition to oxygen gas. The flow rate of the oxygen gas is not particularly limited, but is 500 to 2000 sccm, preferably 1000 to 1500 sccm.

Subsequently, the resultant is heated to 1100 to 1400 ° C. (heating rate: 100 ° C./hr) under a helium gas atmosphere and heat treated for about 8 hours to complete the silica glass tube.

The silica glass manufacturing method described above is a method that can be usefully applied regardless of the specifications of the silica glass overcladding tube. In particular, it is a very useful method for producing a large silica glass tube having an inner diameter of 22 to 27 mm, an outer diameter of 67 to 81 mm, and a length of about 1000 mm.

Example 1

500 g of fume silica (Aerosil OX-50, Degussa), 52 ml of 25 wt% tetraammonium hydroxide (TMAH) aqueous solution, 500 g deionized water, 60 g ethyl lactate and 2.1 g polyethyloxazoline are mixed To form a sol.

The sol was then aged for 15 hours and then bubbled from the sol using a vacuum pump. This bubble-free sol was poured into a mold and gelated.

Once gelling was complete, the wet gel was removed from the mold and dried for 4 days at 30 ° C. and 80 RH% in a thermo-hygrostat.

Subsequently, the dried gel was heated to about 500 ° C. (raising rate: 50 ° C./hr) and heat-treated at this temperature for 5 hours to remove organic matter contained in the gel.

Thereafter, the resultant was heat treated at about 1000 ° C. (raising rate: 100 ° C./hr) for 5 hours in a chlorine (Cl ₂ ) gas atmosphere to remove residual hydroxyl groups in the gel. Subsequently, residual chlorine gas was removed at about 900 ° C. using oxygen (O ₂ ) gas and helium gas.

The resultant product was sintered at about 1400 ° C. (heating rate: 100 ° C./hr) for 8 hours under a helium atmosphere to complete a silica glass tube. At this time, the inner diameter of the silica glass tube was 22 mm, the outer diameter was 67 mm, and the length was 1000 mm.

Example 2

In the remaining chlorine gas removal process using oxygen and helium gas, a silica glass tube was prepared in the same manner as in Example 1 except that only oxygen gas was used instead of oxygen and helium gas.

Comparative example

A silica glass tube was prepared in the same manner as in Example, except that the remaining chlorine gas removal process using oxygen and helium gas was omitted.

When extracting the optical fiber using the silica glass tube prepared according to Example 1-2 and Comparative Example, the number of breaks were investigated.

As a result, in Example 1-2, the number of breaks was significantly reduced compared with the case of Comparative Example. This is because in the case of Example 1-2, the number of pores that can be captured by the remaining chlorine in the sintering process can be reduced.

According to the present invention, it is possible to minimize the amount of residual chlorine gas used in the hydroxyl group removal reaction. As such, when the residual amount of chlorine gas is minimized, the purity of the finally obtained silica glass is improved.

Claims (5)

(a) mixing silica, dispersant, binder, gelling agent and deionized water to form a sol; (b) removing the bubbles from the formed sol and then molding and gelling; (c) demolding the obtained gel to dry it; (d) removing organics from the dried gel and then removing hydroxyl groups; (e) maintaining the resultant in an oxygen gas atmosphere at 800 to 1000 ° C. for a predetermined time, and then sintering the method for producing silica glass for sol-gel process. The method of claim 1, wherein in the step (e) in addition to oxygen gas helium gas is used together, the method for producing a silica glass for sol-gel process. The method of claim 1, wherein the step of removing the organic material of the step (d) is a method for producing a silica glass for sol-gel process, characterized in that the heat treatment at 50 to 500 ℃. The method of claim 1, wherein the hydroxyl group removing step (d) is performed by heat treatment at 500 to 1000 ° C. under a chlorine gas atmosphere. The sol-gel process according to claim 1, wherein in the step (e), the sintering process after maintaining for a predetermined time in an oxygen atmosphere is performed by heat treatment at 1100 to 1450 ° C. under a helium gas atmosphere. Method for producing silica glass.