KR20010001881A - heat-treatment apparatus for silica glass forming gel - Google Patents

Abstract

PURPOSE: An apparatus for thermal-treating gel to eliminate organics and OH- for silica glass formation is provided, which prevents the remaining water vapor in a process tube from condensing into water in an end cap. Therefore, the crystallization of gel arising from the water in thermal-treating process is effectively prevented, resulting in active glassification of gel for high purity silica glass. CONSTITUTION: The apparatus comprises; a quartz process tube(20) through a furnace body(21); several heaters(24) near the process tube for heating a sample in the process tube; a doughnut-typed refractory plug(23) installed in the both ends of the process tube for insulating the tube; a quartz end cap(22) linked to the both ends of the tube for blocking gas leakage, having a hole to pass the process gas such as air, O2, Cl2 or He ; a heating element(26) surrounding the end cap.

Description

Heat treatment apparatus for silica glass forming gel {heat-treatment apparatus for silica glass forming gel}

The present invention relates to a heat treatment apparatus for a gel for forming silica glass, and more particularly, a heat treatment for a gel for forming silica glass, which can minimize the influence of moisture that may cause crystallization of the gel in a high temperature heat treatment process for vitrification of the gel. Relates to a device.

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 subjected to low temperature heat treatment to remove organic matter in the gel, and then a hydroxyl group removal reaction is performed. Subsequently, the resultant from which the organics and the hydroxyl groups have been removed is subjected to high temperature heat treatment to complete the silica glass overcladding tube.

The organic matter removal reaction and the hydroxyl group removal reaction in the gel described above are usually performed in a heat treatment apparatus as shown in FIG. 1.

Referring to FIG. 1, in a conventional heat treatment apparatus, a process tube 10 penetrates inside a furnace body 11, and a heater 14 is provided at upper and lower regions of the process tube 10. It is provided, respectively, and the structure which heats the sample placed in the upper part of the sample support 15 in the process tube 11 is carried out. And a donut-shaped refractory plug 13 for insulating the process tube 10 from the outside is inserted at both end inlets of the process tube 10. In this way, end caps 12 for preventing process gas leakage are coupled to both ends of the process tube 10 into which the refractory plug 13 is inserted, and a hole is formed in the quartz end cap 12. Through which the process gas enters or exits the process tube 10.

When the organic material and the hydroxyl group are removed from the gel by using the heat treatment apparatus of FIG. 1, water vapor in the process tube 10 generated during the heat treatment of the gel is caused by the temperature difference between the process tube 10 and the end cap 12. Condenses on the end caps to form water. The water thus formed has a problem of causing crystallization of the gel in the high temperature heat treatment process for vitrification of the gel which is a subsequent step of the hydroxyl group removal process.

The technical problem to be solved by the present invention is to maintain the temperature of the end cap within a predetermined range so that water vapor is not condensed in the end cap in order to solve the above problems, silica glass which can suppress the crystallization of the gel due to moisture in the high temperature heat treatment process It is to provide a heat treatment apparatus for forming gel.

1 is a view schematically showing the configuration of a heat treatment apparatus of a conventional silica glass forming gel,

2 is a view schematically showing the configuration of a heat treatment apparatus of a silica glass forming gel according to the present invention.

<Description of Major Symbols in Drawing>

10, 20 .. Process tube 11, 21. Furnace body

12, 22 .. End cap 13, 23 .. Refractory plug

14, 24. Heating means 15, 25. Sample holder

26. Heating element

In the present invention to achieve the above technical problem, the furnace body,

A process tube passing through the furnace body,

A plurality of heating means for heating a sample which is installed in an adjacent region of the process tube,

A donut refractory plug inserted at both end portions of the process tube to insulate the process tube;

End caps coupled to both ends of the process tube into which the refractory plug is inserted to prevent process gas leakage;

Provided is a heat treatment apparatus for a silica glass forming gel having a heating member surrounding an outer circumferential surface of the end cap.

Preferably, the temperature range of the end cap is maintained at 140 to 160 ° C using the hitty member. Here, if the temperature range of the end cap exceeds 160 ℃, it causes deformation of the polymer sealing member in contact with the end cap, and if the temperature of the end cap is less than 140 ℃ it is not preferable because the moisture removal is not made sufficiently. .

Hereinafter, with reference to Figure 2, it will be described with respect to the manufacturing apparatus of the silica glass forming gel according to an embodiment of the present invention.

Referring to the configuration of the heat treatment apparatus according to the present invention, the quartz process tube 20 penetrates inside the furnace body 21, and the adjacent region of the quartz process tube 20 can be seen in the figure. Likewise, six heaters 24 are provided to heat the sample placed on the sample holder 25 to a predetermined temperature.

Moreover, the refractory plug 23 is inserted in the both terminal inlet of the quartz process tube 20, and the heat processing efficiency of a gel is improved by insulating the inside of the process tube 20. FIG. Here, the refractory plug 23 is doughnut-shaped so that process gas can pass through a hole formed therein.

As described above, quartz end caps 22 are coupled to both end regions of the process tube 20 insulated with the refractory plugs 23 so that process gases such as air, oxygen, helium, chlorine, etc. To prevent leakage. At this time, a hole is formed in the quartz end cap 12 so that a process gas can pass therethrough, and a heating member 26 is wrapped on the outer circumferential surface thereof to insulate the quartz end cap 12 so that the temperature of the end cap is 140 to 160 ° C. Keep it. Here, the heating member is not particularly limited to any form.

Hereinafter, a method of manufacturing a silica glass tube by a sol-gel process using the heat treatment apparatus of the present invention shown in FIG. 2 will be described.

First, silica, additives and deionized water are mixed and dispersed to form a sol.

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 300 to 500 ° C. (raising rate: 5 to 50 ° C./hr) to remove organic matter remaining in the gel, and then to 800 to 1000 ° C. to remove hydroxyl and alkali metal impurities in the gel. Preferably, it heats up to 850-900 degreeC (heating rate: 100 degreeC / hr), and heat-processes for predetermined time.

The heat treatment process as described above is performed in the heat treatment apparatus of FIG. In Fig. 2, a heating tape, which is a heating member, is attached to the outer circumferential surface of the end cap 22, so that the temperature in the end cap can be maintained at 140 to 160 ° C, so that little moisture remains in the end cap.

Subsequently, the silica glass tube is completed by heating up at 1300-1500 degreeC (heating rate: 100 degreeC / hr) in a helium gas atmosphere, and heat-processing at this temperature for about 5-8 hours.

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. It is a particularly useful method for producing large silica glass tubes.

Hereinafter, the present invention will be described in detail with reference to the following examples, but the present invention is not limited only to the following examples.

Example

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 It was.

Subsequently, bubbles in the sol were removed using a vacuum pump, and then aged for 15 hours. This bubble-free sol was poured into a mold and gelated. At this time, an acrylic tube having an inner diameter of 100 mm and a stainless rod having an outer diameter of 33 mm were used as the mold.

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 using oxygen (O ₂ ) and helium (He) gas.

The heat treatment apparatus used in the above heat treatment process is as shown in FIG. 2, wherein a heating tape is attached to the outer circumferential surface of the quartz end cap 22 coupled to both end portions of the quartz process tube 20 to about 150 ° C. Maintained.

The resultant was sintered at about 1400 ° C. (heating rate: 100 ° C./hr) for 4 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.

Comparative example

A silica glass tube was completed in the same manner as in Example, except that the heat treatment apparatus of FIG. 1 without a heating tape attached to the outer circumferential surface of the quartz end cap was used.

According to the Examples and Comparative Examples, the presence of water in the quartz end cap was examined before removing the organic material and the hydroxyl group from the gel during the silica glass tube preparation and before the sintering process.

As a result, in the case of the comparative example, water was formed in the quartz end cap, whereas in the case of the example, such a phenomenon was hardly observed.

In addition, the purity of the silica glass tube prepared according to the above Examples and Comparative Examples was investigated.

As a result of the measurement, the silica glass tube manufactured according to the comparative example was not so high in purity as the vitrification of the gel was prevented in the subsequent sintering process due to the moisture formed in the end cap after the hydroxyl group removal process, whereas the purity was not high. It was found that the vitrification of the gel smoothly resulted in the improvement of purity compared to the comparative example.

By using the heat treatment apparatus of the present invention, it is possible to prevent the water vapor remaining in the dried process tube from condensing in the end shock in the heat treatment process for removing organic matter and hydroxyl groups from the gel. As a result, the crystallization of the gel can be effectively prevented in the high temperature heat treatment process for vitrification of the gel. As a result, the vitrification of the gel is smoothly obtained, and thus the silica glass having improved purity characteristics can be obtained.

Claims (3)

Furnace Body, A process tube passing through the furnace body, A plurality of heating means for heating a sample which is installed in an adjacent region of the process tube, A donut refractory plug inserted at both end portions of the process tube to insulate the process tube; End caps coupled to both ends of the process tube into which the refractory plug is inserted to prevent process gas leakage; A heat treatment apparatus for a silica glass forming gel, comprising a heating member surrounding an outer circumferential surface of the end cap. The apparatus of claim 1, wherein the temperature of the end cap is maintained at 140 to 160 ° C. by using the heating member. The heat treatment apparatus of the silica glass forming gel according to claim 1, which is used for removing organic substances and hydroxyl groups from the gel.