JPS6126524A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To produce quartz glass of high quality without cracking, foaming nor crystallizing in a sintering step, by adding a very small amount of a metal compond to the process before gelation in production of the quartz glass by the sol- gel method. CONSTITUTION:At least an alkyl silicate and ultrafine powdery silica are used as raw materials to produce quartz glass by the sol-gel method. In the process, a metal element in an amount of <=50ppm based on the weight of the quartz glass after the sintering is added thereto before gelation. The element to be added is preferably an inexpensive alkali metal or alkaline earth metal having great effect is preferred, and, e.g. NaCl, is used. Thus, the aimed quartz glass of high quality is produced without cracking, foaming nor crystallizing in the sintering step. The amount of the metal element to be added is very small, and the metal element tends to be unevenly ditributed in the surface. The element can be removed by grinding, etc. and the quality can be improved. Therefore, the resultant quartz glass can be applied to quartz substrates for photomasking, quartz glass fibers for optical communication, various optical cells, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to the production of quartz glass by a sol-gel process.

[Prior art]

Quartz glass began to be used in crucibles, boards, diffusion furnaces, etc. during the IC manufacturing process, and its usefulness was demonstrated, and with the development of products with fewer hydroxyl groups and better optical uniformity, BACKGROUND OF THE INVENTION Recently, quartz glass fibers have been attracting attention as they are used for various optical applications, especially for optical communications.

In this way, quartz glass is used in various fields.

Its scope of use is also expanding. However, the manufacturing cost of quartz glass is high, and the high price has become a problem. A sol-gel method has been attempted as a method for manufacturing inexpensive, high-quality quartz glass.

As a method for obtaining large-sized quartz glass using the sol-gel method, ultrafine powdered silica was added to the sol obtained by hydrolyzing alkyl silicate, and after adjusting the pH to 3 to 6, There is a method of drying at 50 to 90°C and sintering.The problems of cracking during dry gel production and cracking during sintering [- were solved at the same time, and quite large quartz glass (41 nchφ or more)] can now be manufactured at low cost.

However, before sintering is complete and the glass becomes completely transparent, foaming and crystallization have already begun, making it impossible to produce high-quality quartz glass. Furthermore, it has been observed that when the sintering atmosphere is changed or when sintering is performed in an overcrowded state, cracks are more likely to form.

These problems that occur during the sintering process cannot be completely eliminated by using a sintering program.Effective methods may vary depending on the dispersion conditions of the ultrafine powder silica and the drying conditions of the gel. Not yet.

〔the purpose〕

The present invention solves these problems and eliminates cracks, foaming, and crystallization during the sintering process.
Our goal is to provide a method for producing high quality quartz glass.

〔overview〕

The method for producing quartz glass of the present invention is a method for producing quartz glass by a sol-gel method using at least alkyl silicate and ultrafine powder silica as raw materials, in which metal elements are added to the weight of the quartz glass after sintering before gelation. It is characterized by adding 50 ppm or less to the water and uniformly dispersing it.

The additive elements are effective and inexpensive Ns, , K,
Alkali metals such as Ca and alkaline earth metals are suitable. The amount added is determined by considering the purity and crystallization of quartz glass.
A suitable amount is 0.5 to 5 ppm based on the weight of quartz glass after sintering. The addition method is effective because a metal salt such as a chloride is dissolved in pure water to form an ion state, and then dropped into the sol and stirred, so that the calculated amount of the element can be uniformly added, and there is almost no effect on the pH.

〔Example〕

Hereinafter, the present invention will be described in detail based on examples.

Example 1゜Ethyl silicate 440mj! and 560 ml of a 0.05 N hydrochloric acid aqueous solution were vigorously stirred to obtain a colorless and transparent homogeneous solution, and fine silica powder (AerOL3j, 1°0
X-5'0) 150 S' was gradually added and thoroughly stirred (hereinafter referred to as Sol A). Apart from that, N a,
Prepare a CI 0.01 aqueous solution and add 34 m to Zolha.
1 (NFI/5i02 = 5 pprn) and stirred for 10 minutes. Furthermore, after adjusting the pH to 4.5 by dropping ammonia water, we weighed 5007 and determined the diameter.
Transferred to a 20Cr Teflon container.

A lid with a pinhole was placed on it and dried at 60°C to obtain a dry gel. When transferred to a sintering furnace and heated in a trench at 1200°C at a heating rate of 180°C/hr, it becomes completely transparent and has a diameter of 101 mm.
:nn quartz glass could be manufactured.

Even when heated in a trench at 1300°C, no foaming or crystallization was observed.

When the quartz glass was melted and atomic absorption analysis was performed, the content of N8 was approximately 4 ppm, which was lower than the amount added. IMA (Ion Micro Analyzer (J')
-), it was found that N8 was unevenly distributed near the surface.

From the surface polished in Step 1, N8 could hardly be detected.

Example 2 Sol A to C! RC12n, o 1% aqueous solution 57me
(Ca/s+n2=5ppm) was added dropwise and stirred for 10 minutes, and the pH was adjusted to 4.5 with aqueous ammonia.

Thereafter, the same treatment as in Example 1 was carried out, and when the dry gel was heated, it became completely transparent at 1200°C. Again, foaming and crystallization were not observed at temperatures below 1600°C.

V example.

Sol A, Ic Na, CI 0.01% aqueous solution 7 ml (N a /R102=1 ppm) (r
Add dropwise and stir for 10 minutes, then add PH4 with ammonia water.
, 5. Thereafter, the same treatment as in Example 1 was carried out, and the dry gel was heated at 1200°C for 30 minutes.
1, and at some points it became completely transparent. No foaming or crystallization was observed even when heated at 1300°C in an enclosure.

Example 4 Sol A Ic N Fl, Ol O, 01% aqueous solution 6
9 tn/ (N a/5ioz=10T1r+m)f
jC@ Lower it and rub it for 10 minutes, then wash it with ammonia water.
)l was adjusted to 4.5. Thereafter, the same treatment as in Example 1 was carried out, and when the dry gel was heated, it became completely transparent at 1150°C.

No foaming or crystallization was observed even when heated to 1300°C.

Example 5 Dry gel (diameter 14
m, thickness 0.7α+) were stacked in a sintering furnace, and 18
When heated to 1200° C. at a temperature increase rate of 0° C./hr, all five sheets became completely transparent and no cracks were generated at all.

In terms of quality, there was no difference in quality compared to when only one sheet was sintered, and no foaming or crystallization was observed.

Example 6゜Sol p, f. While keeping the temperature at -20°C, 28KH2 ultrasonic waves were irradiated for 2 hours to improve dispersion, and 1500G centrifugal force was applied for 10 minutes to sediment insufficiently dispersed giant particles. . The sol was further passed through a 10 μm filter to prepare a highly homogeneous sol. 20 ml of a 1% aqueous solution (N a / 5 ins - 3 ppm) of NPClo was added dropwise thereto and stirred for 10 minutes, and then aqueous ammonia was added dropwise to the solution.
Adjusted to 4.2.

It was dried at 60°C to form a dry gel, which became completely transparent when heated at 1200°C. The quality of the resulting quartz glass was extremely high (it contained no bubbles or crystals at all. Even when exposed to a condensing lamp, nothing could be detected with the naked eye, and its optical properties were also extremely good.

Comparative Example 1 A dry gel prepared in the same manner as in Example 1 without adding any metal element to Sol A was heated to 1300°C at a temperature increase rate of 180°C/hr. It had not progressed and was white like dry gel. 1300
After being kept at ℃ for 1 hour, the transparentization was completed, but bubbles were already formed, fuss, and α-cristobalite crystals were also observed.

When exposed to a condensing lamp, cloudiness was observed, indicating that sintering was not completely completed.

Comparative Example 2゜No metal element was added to Sol A, and 5 sheets of dry gel prepared in the same manner as in Example 1 were stacked in a KV8 furnace.
When heated to 1300° C. at a temperature increase rate of 180° C./hr, all five sheets developed cracks, and especially the three sheets in the middle were finely cracked. As in Comparative Example 1, clearing did not progress at all.

〔effect〕

As described above, according to the present invention, in the method for producing quartz glass by the sol-gel method using at least alkyl silicate and ultrafine powder silica as raw materials, sintered quartz By adding 50 ppm or less based on the weight of the glass, it is possible to produce high-quality quartz glass without cracking, foaming, or crystallization during the sintering process.

Although metal elements are added, the amount added is extremely small, and is at the same level as the impurity concentration in quartz glass manufactured by a method of melting natural quartz. Additionally, since additive elements tend to be unevenly distributed on the surface, it can also be used as high-purity quartz glass by polishing techniques.

The greatest advantage of the present invention is that quartz glass with extremely excellent optical properties can be produced, which can be applied to quartz substrates for photomasks, quartz glass fibers for optical communication, various optical cells, etc. Furthermore, since there is no cracking during the sintering process, it is an extremely effective means for mass production.

that's all

Claims (1)

[Scope of Claims] 1) In a method for producing quartz glass by a sol-gel method using at least an alkyl silicate and ultrafine powdered silica as raw materials, a metal element is added before gelation in an amount of 50 ppm based on the weight of the quartz glass after sintering. A method for producing quartz glass characterized by adding the following: 2) The method for producing quartz glass according to claim 1, wherein preferable additive elements are all alkali metals such as Na, K, and Ca, and alkaline earth metals. 3) The preferred addition amount is based on the weight of quartz glass after sintering,
The method for producing quartz glass according to claim 1 or 2, wherein the content is 0.5 to 5 ppm. 4) A preferred addition method is a method of dissolving a metal salt such as a chloride in pure water to make it into an ionized state, dropping it into a sol, and then uniformly dispersing it by stirring. - The method for producing quartz glass according to any one of Item 3.