JPH09295826A - Production of high-purity transparent silica glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a high-purity transparent silica glass, not containing bubbles, suitable for applications such as various kinds of optical materials utilizing light transmittance, a high-temperature type liquid crystal substrate, a high-temperature type liquid crystal substrate, a jig for producing semiconductors used at a high temperature for a long period of time. SOLUTION: High-purity amorphous silica powder having impurities of <=1ppm each of Na, K, Mg, Ca, Fe and Al obtained by reacting an aqueous solution of an alkali metal silicate with an acid and purifying the reaction product is used as a starting raw material. The powder is kept in an atmosphere under reduced pressure of <=10Torr at >=1,713 deg.C of the melting temperature of cristobalite to eliminate bubbles having >=1mm in diameter to obtain a transparent silica glass, which is then treated by a hot hydrostatic press apparatus at 1,200-1,350 deg.C under 100-200MPa Ar or N2 gas pressure to eliminate bubbles having <1mm in diameter in the glass.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing high-purity transparent silica glass in which bubbles are eliminated. It can be used as various optical materials that utilize optical transparency, materials for high-temperature liquid crystal substrates, and the like.

[0002]

2. Description of the Related Art Various synthetic silica powders are mixed under reduced pressure atmosphere.
A method for producing a transparent silica glass by heating to 800 to 1900 ° C. has been conventionally known. For example, JP
-37120, JP-A-3-5329, JP-A-2-229
In 735, silica powder obtained by calcining a gel obtained by hydrolyzing alkoxysilane is mixed under reduced pressure atmosphere for 150 minutes.
A method for producing a transparent silica glass by heating to 0 to 2200 ° C. is disclosed.

According to the above-mentioned manufacturing method, a highly pure transparent silica glass can be obtained relatively easily, but the obtained glass contains bubbles. The form of the bubbles varies depending on the manufacturing method, such as the case where fine bubbles of 10 to 100 μm are scattered or the case where large bubbles of 0.5 to 2 mm are scattered. Further, when such glass is kept at 1200 to 1500 ° C. for a long time, there is a phenomenon that the periphery of bubbles is crystallized.

Therefore, there is a problem that it is not suitable for various optical materials utilizing light transmittance, high temperature type liquid crystal substrates and the like, and semiconductor manufacturing jigs which are used at high temperature for a long time.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is suitable for various optical materials utilizing optical transparency, high temperature type liquid crystal substrates and the like, and semiconductor manufacturing jigs which are used at high temperature for a long time. It is an object of the present invention to provide a method for producing a high-purity transparent silica glass having no bubbles.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that an amorphous silica powder obtained from an aqueous solution of alkali silicic acid has a pressure of 1713 ° C. in a reduced pressure atmosphere. The present invention was found to be effective in eliminating bubbles of less than 1 mm in the glass by heating to the above temperature and subjecting the obtained transparent silica glass to hot isostatic pressing. That is, according to the present invention, by refining silica obtained by reacting an aqueous solution of an alkali metal silicic acid with an acid, high-purity amorphous containing each impurity of Na, K, Mg, Ca, Fe, and Al at 1 ppm or less. A silica powder is used as a starting material, and the temperature is set to a cristobalite melting temperature of 1713 ° C. or higher in a reduced pressure atmosphere of 10 torr or less to obtain transparent silica glass. This glass is subjected to a hot isostatic pressing apparatus at 1200 to 1350 ° C. In the temperature range of 100 to 200 MPa of Ar or N ₂ gas pressure to eliminate bubbles having a diameter of less than 1 mm in the glass.

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

Amorphous silica powder as a starting material is silica obtained by acid treatment of an aqueous alkali silicate solution.
This method is described, for example, in JP-A-62-3011 and JP-A-6-301.
2-3012, JP-A-62-283809 and JP-A-62-283810, the viscosity value is 2
To 500 poises, an alkaline silicate aqueous solution is extruded through a nozzle having a pore size of 1 mm or less into a coagulation bath consisting of a water-miscible organic medium or a 4N acid solution having a concentration to coagulate the resulting fibrous gel. After treatment with a liquid containing
Impurities such as Na, K, Mg, and C were washed by washing with water to remove impurities, and then heat-treated at 1000 ° C. or higher.
Amorphous silica in which a, Fe, and Al are all 1 ppm or less can be obtained. This powder is filled in a heat resistant container, for example, a high-purity carbon crucible and subjected to heat treatment, but it is necessary to adjust the powder particle size before use. The particle size can be adjusted by dry grinding such as a well-known ball mill. The particle size range is preferably adjusted to 30 to 500 μm. A more preferable range is 30 to 200.
μm.

In the step of forming transparent silica glass, silica powder filled in a heat-resistant container is put under a reduced pressure atmosphere of 10 torr or less,
It is performed by heating to a temperature of 1713 ° C. or higher for the cristobalite melting temperature. The heat treatment is usually carried out in a vacuum electric furnace of carbon resistance heating type or high frequency heating type. It is preferable that the decompression degree is low, and 10 ⁻¹ to 10 during heating
It is ideal to maintain ^-3 torr, but it is difficult because the sublimation of silica occurs due to the temperature rise, and it is sufficient to suppress it to 10 torr or less. The heating temperature requires a cristobalite melting temperature of 1713 ° C. or higher. Preferred condition is 1
It is to hold at 800 to 1850 ° C. for 10 minutes or more.

The characteristic required for the transparent silica glass obtained here is that it does not contain bubbles having a diameter of 1 mm or more. This is because the bubble diameter that can be eliminated in the next step, hot isostatic pressing, has a critical value, and it is difficult to eliminate bubbles of 1 mm or more. The firing and heating conditions for achieving these required characteristics are 180 ° C. under a reduced pressure atmosphere.
An operation of holding the temperature in the temperature range of 0 to 1850 ° C. for 5 minutes or more to finish the vitrification, and then introducing an inert gas such as N ₂ or Ar into a pressurized state while keeping the temperature to shrink the bubbles. Is to do. The gas pressure is preferably 0.2 MPa or more, more preferably 0.4 to 1.
It is in the range of 0 MPa.

The hot isostatic pressing process of the obtained glass is carried out at a temperature range of 1200 to 1350 ° C. for 100 to 200.
It is performed by applying Ar or N ₂ gas pressure of MPa. The reason for defining the temperature range from 1200 to 1350 ° C. is 120
0.1 mm even if a pressure of 200 MPa is applied at 0 ° C or lower
The above bubbles cannot be extinguished, and 1350 ° C
In the above, the bubbles can be effectively extinguished even at a pressure of 100 MPa, but the crystallization of the glass becomes remarkable.

A pressure of 100 MPa or more is required to extinguish bubbles, and Ar gas is the most common pressure medium, but N ₂ gas can also be used.
The bubble disappearance rate by hot isostatic pressing depends on the bubble diameter, pressure, and glass viscosity. The larger the bubble diameter and the higher the viscosity of the glass, the slower the extinction rate. In the case of the high-purity transparent silica glass of the present invention having a glass viscosity of 10 ¹³ to 10 ^13.3 poise at 1200 ° C., preferable treatment conditions are 13
00 ° C., 150 MPa, 1 to 4 hours.

The glass subjected to the hot isostatic pressing has a density of about 0.6% higher than that of the untreated glass, which is 2.212 to
A value of 2.228 g / cm ³ is shown. 1150-1250
The original density of 2.20 to 2.
It can be returned to 21 g / cm ³ .

The present invention will be further described below with reference to examples, but the present invention is not limited to the examples.

[0015]

Example 1 An alkaline silicate aqueous solution was treated with an acid, washed with water to remove impurities, and the silica calcined at 1200 ° C. was pulverized using a nylon pot and nylon ball to obtain an average particle size of 100 μm.
It was prepared so that m. The results of chemical analysis of the obtained powder are shown in Table 1.

[0016]

[Table 1]

This powder was filled in a carbon container subjected to high-purity treatment, placed in a carbon resistance heating furnace, and the degree of vacuum was 10 ^-3.
The pressure was reduced to torr, the temperature was raised to 1850 ° C. at 300 ° C./hr, and the temperature was maintained for 5 minutes.
It was introduced until it reached gf / cm ^2, and held for another 5 minutes. The degree of vacuum during holding was 1 torr. Cooling was allowed to cool with the gas pressure applied. The density of the transparent silica glass obtained ^was 2.210g / cm ^3.

Next, this glass was placed in a hot isostatic press, and Ar gas was used as a pressure medium, at 600 ° C./hr for 1 hour.
Raise to 300 ° C and apply pressure of 150MPa 1
It was held for hr.

When the density of the obtained glass was measured,
It was 2.222 g / cm ³ .

The amount of bubbles in the glass before and after the hot isostatic pressing treatment is as shown in Table 2, and it was found that the treatment resulted in no bubbles.

[0021]

[Table 2]

Example 2 The powder obtained by the same production method as in Example 1 was further pulverized,
The average particle size was adjusted to 50 μm. This powder was made into transparent silica glass by the same method as in Example 1, and hot isostatic pressing was performed at 1250 ° C. and 150 ° C. using Ar as a pressure medium.
It was performed at 4 MPa for 4 hours.

The amount of bubbles, the density and the amount of OH of the glass before and after the hot isostatic pressing were measured and the results shown in Table 3 were obtained.

[0024]

[Table 3]

As is clear from Table 3, it was found that the treatment resulted in no bubbles.

Example 3 Part of the bubble-free glass obtained in Example 1 was placed in an atmospheric furnace and kept at 1200 ° C. for 10 hours. There was no apparent change in the glass taken out. When I measured the density,
It was 2.210 g / cm ³ and was found to return to the value before the hot isostatic pressing treatment. In addition, no re-generation of bubbles was observed inside the glass.

[0027]

According to the manufacturing method of the present invention, the silica glass obtained by melting the high-purity powder can be made bubble-free by hot isostatic pressing. Therefore, it can be used for applications requiring light transmittance which has not been conventionally available due to bubbles, for example, various optical materials such as high-temperature liquid crystal substrates, prisms, and lenses. It can also be used as a material that could not be used due to crystallization around bubbles, for example, as a material for various jigs and tools for semiconductor manufacturing.

Claims (1)

[Claims] 1. A silica obtained by reacting an aqueous solution of an alkali metal silicic acid with an acid is refined to obtain Na, K, M.
A high-purity amorphous silica powder in which each impurity of g, Ca, Fe, and Al is 1 ppm or less is used as a starting material.
Cristobalite melting temperature 17 in a reduced pressure atmosphere of rr or less
The temperature is set to 13 ° C. or higher, and a step of forming a transparent silica glass in which bubbles having a diameter of 1 mm or more are extinguished, and a hot isostatic pressing device is used for this glass, and Ar of 100 to 200 MPa in a temperature range of 1200 to 1350 ° C. or A process for producing high-purity transparent silica glass, which comprises applying N ₂ gas pressure to eliminate bubbles having a diameter of less than 1 mm in the glass.