JPH0558682A - Production of silica-based glass having refractive index distribution - Google Patents

Abstract

PURPOSE:To provide a process for easily and economically producing a large- sized r-GRIN glass free from fault in an easily dryable and bakable state. CONSTITUTION:A mixture containing a silicon alkoxide, a Ti compound and water is gelatinized to obtain an SiO2-TiO2 wet gel, which is immersed in an aqueous solution containing 3-30wt.% of HCl, 0.5-20wt.% of H2O2 and 1-30wt.% of one or more organic solvents to form a Ti concentration distribution in the gel by dissolving the Ti component from the outer part of the gel. The gel is dried and baked to obtain the objective glass. The effect is further improved by using acetone as the organic solvent and an alkoxide as the Ti compound and selecting super-critical drying as the drying method.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention uses Ti-sol method
The present invention relates to a method for easily and inexpensively producing a large silica glass having a concentration distribution of components, that is, a refractive index distribution.

[0002]

2. Description of the Related Art A rod-shaped glass having a refractive index distribution, especially a radial distribution is r-GRIN (Radial Grad).
The present invention is rapidly expanding as an optical material such as a lens array of a copying machine and a connector for optical fiber. These r-GRI
Examples of the method for manufacturing the N lens include an ion exchange method, a molecular stuffing method for porous glass, and a CVD method. However, it is difficult to obtain a large-sized product by these methods, and the size of Δn (change in refractive index) is limited. On the other hand, a multi-component wet gel prepared by the sol-gel method is dipped in a solution to elute the components (for example, Ti, Pb, etc.) that increase the refractive index from the outside to give a distribution, and dried and fired to form glass. In this method, a large rod lens can be synthesized by increasing the size of the gel, and the flexibility of the component concentration is increased, so that a large Δn is expected to be imparted. The following two methods are known as typical methods for synthesizing a r-GRIN lens by the sol-gel method.

(1) A method of immersing a PbO-B ₂ O ₃ -SiO ₂ system wet gel in potassium nitrate to form a distribution of Pb by mutual diffusion of Pb ions and K ions, followed by drying and firing. (2) Dip a TiO ₂ —SiO ₂ system wet gel in an HCl solution to preferentially elute Ti to form a Ti distribution, and then dry it.
How to bake.

[0004]

The conventional sol-gel method for synthesizing r-GRIN glass has the following problems. That is, the larger the gel, the longer it takes to form an appropriate refractive index distribution, and the lower its accuracy becomes. Moreover, damage such as cracks is likely to occur during drying, and a careful drying process for a long period of time is required. Furthermore, the silica-Ti shown in (2) above
In the system, since the acidity of the gel increases when leaching Ti with HCl solution to elute Ti, damage such as shrinkage cracks easily occurs during the dipping process and the subsequent drying process. The more serious Moreover, when trying to obtain a large glass by these methods, it is difficult to completely remove bubbles,
It becomes a factor that inhibits the optical characteristics.

An object of the present invention is to solve the above-mentioned problems, and to provide a method for producing a large-sized r-GRIN glass easily and inexpensively, which can be easily dried and fired without damage. is there.

[0006]

That is, according to the present invention, a mixture containing a silicon alkoxide, a Ti compound, and water is gelled to prepare a SiO ₂ —TiO ₂ wet gel.
The wet gel was treated with HCl at 3 to 30% by weight and H ₂ O ₂ at 0.
5 to 20% by weight, 1 to 30% by weight of one or more organic solvents
A silica-based silica having a refractive index distribution characterized by being dried and calcined after a step of forming a concentration distribution of Ti in the gel by immersing it in an aqueous solution containing Is a method of manufacturing glass,
As a result, the above object can be achieved.

The present invention reacts a mixture containing a silicon alkoxide, a Ti compound, and water to produce a Si produced.
O ₂ —TiO ₂ system wet gel is added with HCl 3 to 30 wt%,
The greatest feature is that the Ti component is eluted by immersing in an aqueous solution containing 0.5 to 20% by weight of H ₂ O ₂ and 1 to 30% by weight of one or more organic solvents. In the present invention, the elution of the Ti component means that Ti atoms or Ti ions in the SiO ₂ —TiO ₂ wet gel and compounds or derivatives containing the same are dissolved from the wet gel.

HC for elution of Ti component used in the present invention
The gel dipping treatment in 1 / H ₂ O ₂ / organic solvent aqueous solution is
Compared with the conventionally known dipping treatment in a solution containing only HCl, it has the following advantages.

There are few problems such as gel shrinkage and cracking during immersion. The elution speed of the Ti component is high, and the target Ti concentration distribution can be easily formed by immersion for a short time.

Baking and vitrification of the dried gel can be performed smoothly, and there are few problems such as crystallization and devitrification. Of these, the effect of hydrogen peroxide water is particularly noted. The component that directly affects the elution of the Ti component is HCl, but the presence of H ₂ O ₂ remarkably promotes the elution effect of HCl. Also, by using an organic solvent, during immersion treatment,
Shrinkage and cracking of the gel during drying are suppressed.

The Ti compound used in the present invention is not particularly limited, but Ti alkoxides such as Ti propoxide and Ti butoxide are preferable. It should be noted that when a Ti salt such as titanium tetrachloride is used, it is difficult to form a gel that is homogeneous and has good retention.

The organic solvent in the HCl / H ₂ O ₂ / organic solvent aqueous solution used in the present invention is not particularly limited, but examples thereof include alcohol, hexane, THF (tetrahydrofuran), benzene, toluene and acetone. And the like, or a combination of two or more of them, and among them, acetone is most effective. Preferred weight% of this aqueous solution
To give an example of the composition, HCl / H ₂ O ₂ / acetone / water =
5-20 / 1-10 / 3-15 / 55-90 are mentioned.

In the present invention, the method of drying the wet gel after elution treatment of the Ti component to form a concentration distribution of Ti in the gel and then drying the wet gel is not particularly limited, but it can be broadly classified into atmospheric drying and super-drying. Examples include critical drying. The gel often breaks or cracks because capillary stress acts on the pores during drying. On the other hand, since no stress is generated during drying, even a large gel can be dried without cracks or cracks. Supercritical drying is roughly divided into a method of removing the solvent under the supercritical conditions of the solvent in the gel (for example, alcohol) itself and a method of extracting and removing the solvent under the supercritical conditions of a CO ₂ -organic solvent mixed system. To be done. In the former case, the critical temperature of an ordinary organic solvent (for example, alcohol) is as high as about 250 ° C., and a high temperature is required for the treatment. The latter can be processed from 31 ° C, which is the critical temperature of CO ₂ in principle, and can be processed at a low temperature. In the case of SiO ₂ —TiO ₂ type gel, TiO ₂ crystallizes when the former supercritical drying at high temperature is performed,
It does not become a homogeneous and transparent glass even after firing. Therefore, it is preferable to adopt the latter supercritical drying method at a low temperature. Generally, it is desirable to carry out the treatment at about 50 to 100 ° C. In this case, it is particularly preferable to replace most of the liquid content in the gel with a desired organic solvent and then use a mixed system of the organic solvent and CO ₂ . Here, the majority of the liquid content in the gel usually means 80% by weight or more of the liquid content. This solvent exchange treatment is advantageous because supercritical conditions can be set easily and surely for the drying treatment.

In this case, the mixed system under supercritical conditions is not particularly limited, but an ethanol-CO ₂ system is preferable. For example, a temperature of 35 to 80 ° C. and a pressure of 130 to 160
The condition is kg / m ² .

There are no particular restrictions on the firing of the dried gel, and any temperature and atmospheric conditions can be selected. For example, the temperature is 800 ° C. to 800 ° C. in an oxygen atmosphere for 10 hours and 800 in a helium atmosphere.
8 hours at ˜1250 ° C.

TiO _{2 of the} SiO ₂ —TiO ₂ system wet gel
_{The two} components are preferably in the range of 3 to 20 mol%. The silicon alkoxide used in the present invention has the formula Si (O
R) ₄ (R represents methyl, ethyl, propyl, butyl and the like), and oligomers formed by partial hydrolysis of these compounds. The oligomer preferably has an average of 3 to 6 mers.

In the present invention, in addition to the metal component of the silicon alkoxide and the Ti compound, other metal atom can be appropriately used.
For example, a metal alkoxide, for example, an alkoxide such as triethoxyborane [B (OC ₂ H ₅ ) ₃ ], a metal salt, a metal simple substance, for example, an alkali such as Na, Mg, Ba or Sr,
Examples thereof include alkaline earth metals and the like, and B-containing compounds such as boric acid (H ₃ BO ₃ ). These metal atoms are silicon alkoxide, T, which is a precursor of the wet gel.
It can be added to a mixture containing the i compound and water at appropriate times. In addition, as described above, H used when eluting the Ti component
It may be added by being present in a Cl-containing solution.

In the present invention, the method for forming the SiO ₂ —TiO ₂ wet gel is not particularly limited, and any known means can be used. Therefore, the hydrolysis reaction of the gel-forming material to be hydrolyzed containing at least silicon alkoxide and the polymerization reaction conditions (including aging etc.) between the hydrolysis products can be appropriately selected as desired conditions Can be set. The conditions of such a reaction system include temperature, pressure, amount of water for hydrolysis, pH and the like.

In the present invention, the amount of water used for hydrolysis for gel formation varies depending on the type of hydrolyzable compound such as silicon alkoxide, but it is usually 0 with respect to the hydrolyzable group of those compounds. .2 to 5 times mol, preferably 0.5 to 1.5 times mol.

Further, in the present invention, SiO ₂ --TiO ₂
In forming the system wet gel, in addition to the above essential metal components,
Any regulator having a function of regulating gel formation can be added, and examples thereof include β-diketone compounds such as acetylacetone and bases such as piperidine.

The technique of eluting Ti component from SiO ₂ --TiO ₂ type gel using the HCl / H ₂ O ₂ / organic solvent aqueous solution of the present invention is not limited to SiO ₂ --TiO ₂ type Ti. Metallic element (Ge
, Ta, Pb, may be applied to SiO ₂ based gel with Al, etc.) to the component.

[0022]

The aqueous solution for elution of the Ti component used in the present invention is H
In addition to Cl, H ₂ O ₂ and an organic solvent such as acetone are mixed and adjusted to have a predetermined composition.

H ₂ O ₂ contained in this aqueous solution has a function of enhancing the elution effect of Ti, which is SiO ₂ -T.
decomposes unreacted alkoxide groups and the like in the iO ₂ gel,
It is considered that this is because chlorine easily attacks the Ti site. Also, by using an organic solvent, especially acetone,
The gel cracking and drying are improved because the liquid content inside the gel pores after Ti concentration gradient generation can be easily exchanged with a desired organic solvent while maintaining the balance of the gel, and the optimum supercritical conditions are set. It is thought to be possible.

[0024]

EXAMPLES Hereinafter, specific examples of the present invention will be described.
The present invention is not limited to this.

Example 1 To 44.5 g of an average pentamer oligomer of Si ethoxide, 13.2 g of Ti butoxide, 2.5 g of acetylacetone and 19.4 g of ethanol were added to obtain a homogeneous solution. To this, a mixed solution of 0.55 g of piperidine and 16.3 g of water was added, and gelled in a polypropylene container of 35 mmφ to make TiO ₂ 11.6.
A homogeneous and transparent SiO ₂ —TiO ₂ -based cylindrical gel containing 10% was obtained. This wet gel was aged at 60 ° C for 3 days, then taken out from the container and concentrated HCl aqueous solution (36 wt% HCl) 30 ml /
Hydrogen peroxide solution (30 wt% H ₂ O ₂ ) 10 ml / acetone 10 ml / water 77 ml mixed solution (HCl 9.
7% by weight, H ₂ O ₂ 2.5% by weight, acetone 6% by weight, water 81.8% by weight) for 8 hours. After that, the gel was thoroughly washed with ethanol, and most of the liquid content in the gel pores was exchanged with ethanol.
CO ₂ was flown under g / m ² to extract and remove ethanol to obtain a cylindrical dry gel of 33 mmφ × 100 mmh.
This was heated to 800 ° C. in an oxygen atmosphere, and after 800 ° C. in a helium atmosphere, and finally kept at 1250 ° C. for 5 hours to obtain a transparent non-porous glass having a size of 13 mmφ × 40 mmh. Cut both ends of this glass to make a radial T
As a result of investigating the i distribution, Ti in a parabolic shape with the center at the top
It was confirmed that it has a density distribution and has the performance as an r-GRIN lens.

Example 2 Tetraethoxy orthosilicate [Si (OC ₂ H ₅ )]
₄ ... Abbreviated as TEOS] 2.8 g of an aqueous solution of HCl adjusted to pH 2 for a mixed solution of 41.2 g and ethanol 50 g
(0.8 times the mole of TEOS) and after partially hydrolyzing, mix with 12 g of Ti butoxide to 20 Torr.
After removing a part of the solvent at 80 ° C. under reduced pressure, ethanol was newly added to obtain a homogeneous solution with a total volume of 60 ml. To this solution, add an aqueous solution of piperidine whose pH is adjusted to 11.5.
After adding g and stirring, gelation was performed in a 35 mmφ polypropylene container to obtain a homogeneous and transparent SiO ₂ —TiO ₂ columnar gel containing 15 mol% of TiO ₂ . After aging this wet gel for 3 days at 60 ° C, remove it from the container and
1 aqueous solution (36 wt% HCl) 30 ml / hydrogen peroxide water (30 wt% H ₂ O ₂ ) 10 ml / acetone 20 ml /
A mixed solution of 90 ml of water (HCl 8.4% by weight, H
2.2% by weight of ₂ O ₂ , 10.4% by weight of acetone, water
79% by weight) for 8 hours. After that, the gel was thoroughly washed with ethanol, and most of the liquid content in the gel pores was replaced with ethanol, and then placed in a high-pressure extraction cell while immersed in ethanol at 50 ° C. under 140 kg / m ² .
Flush CO ₂ and extract and remove ethanol to 33mmφ
A columnar dry gel of 73 mmh was obtained. 800 ° C
Oxygen atmosphere up to 800 ° C, helium atmosphere after 800 ° C, and finally keep at 1250 ° C for 5 hours, 13mmφ
A transparent, non-porous glass having a size of × 30 mmh was obtained. As a result of cutting the both ends of this glass and investigating the Ti distribution in the radial direction, it was confirmed that a parabolic Ti concentration distribution with the center at the apex was formed, and that it had the performance as an r-GRIN lens.

Comparative Example 1 The wet gel prepared in Example 1 was treated with concentrated HCl aqueous solution (36 wt% HCl) 30 ml / hydrogen peroxide water (30 wt% H ₂
O ₂₎ was immersed for 8 hours in a solution prepared by mixing 10 ml / water 87 ml, cracks gel occurs, it was difficult to ensure the integrity. Also, concentrated HCl aqueous solution (36 wt% HC
1) The gel obtained by immersing the gel in a mixed solution of 30 ml / acetone 10 ml / 87 ml of water for 8 hours in the same manner as in Example 1 was dried and calcined to examine the Ti concentration distribution of the glass. The elution was insufficient, the difference between the outside and the center was small, and the refractive index profile required for the r-GRIN lens was not obtained.

[0028]

INDUSTRIAL APPLICABILITY The present invention not only prevents damage such as shrinkage and cracking of the SiO ₂ —TiO ₂ system wet gel and eases the management thereof, but also easily forms a Ti concentration distribution in a short time,
Since it can be dried, a large size silica glass having a good refractive index distribution free from residual bubbles and devitrification can be easily manufactured by baking this.

Claims (4)

[Claims] 1. A mixture containing a silicon alkoxide, a Ti compound, and water is gelled, and SiO ₂ --TiO _{2 is used.}
System wet gel is prepared, and the wet gel is immersed in an aqueous solution containing 3 to 30% by weight of HCl, 0.5 to 20% by weight of H ₂ O ₂ and 1 to 30% by weight of one or more organic solvents. A method for producing a silica-based glass having a refractive index distribution, which comprises drying and firing the gel after a step of forming a Ti concentration distribution in the gel by eluting the Ti component from the outside. 2. The method for producing a silica-based glass having a refractive index distribution according to claim 1, wherein the Ti compound is a Ti alkoxide. 3. The method for producing a silica-based glass having a refractive index distribution according to claim 1, wherein one of the organic solvents in the aqueous solution is acetone. 4. The gel is dried under a supercritical condition of a mixed system of the organic solvent and CO ₂ after exchanging most of the liquid content in the gel after the step with an organic solvent. The method for producing a silica-based glass having the refractive index distribution according to claim 1.