JPH0624771A - High-purity opaque quartz glass and its production - Google Patents

Abstract

PURPOSE:To obtain quartz glass of high purity and high opacity by flame- melting amorphous silica particles of a specific quality. CONSTITUTION:Silica particles containing less than 1ppm of alkaline earth metals, Fe and Al, respectively and having main particle sizes more than 200mum at the shortest diameter are crushed and classified to prepare amorphous silica particles having the absorptivity rho in infrared absorption by diffuse reflection satisfying equations: 0.2>=rho3400>=0.01 and 0.3>=rho3740>=0.01. The particles are ground with a rolling ball mill (the diameter of the grinding medium is 0.5 to 50mm) so that more than 90wt.% of the particles have more than 200mum at the shortest diameter. The particles are subjected to fire flame treatment in a customary manner to give the title quartz glass containing less than 1ppm of alkaline earth metals, Fe and Al, respectively and having less than 1% light transmission at 200 to 5,000nm wavelength, when the product is cut 10nm thick and polished.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a high-purity opaque quartz glass and a method for producing the same.

[0002]

2. Description of the Related Art Opaque quartz glass is used as a heat ray shielding material utilizing its opacity, for example, as a flange material for a diffusion tube or the like. In general, opaque quartz glass is manufactured by heating and melting silicic acid raw material powder to form glass. The heating and melting method includes a Bernoulli method for melting in a flame such as an argon-oxygen plasma flame, an oxyhydrogen flame, or a vacuum melting method for heating and melting silica filled in a container under high vacuum. As a raw material for opaque quartz glass, natural silica stone or low-grade quartz has been used. Many fine bubbles are contained in these raw materials, and when the raw materials are melted, the bubbles remain as they are, and opaque quartz glass is obtained. Further, as a method for producing opaque quartz glass, a method has been proposed in which fine powder such as carbon and silicon nitride is added as a foaming agent to a siliceous raw material powder such as silica stone, silica sand, α-quartz, and cristobalite and heated and melted. (For example, JP-A-4-65
No. 328, etc.).

[0003]

In recent years, with the progress of high integration of LSI in the field of semiconductor, the demand for high purity of raw materials used becomes strict, and even in the field where low purity products have been used in the past. , High-purity products have begun to be sought. A typical field is the above-mentioned flange material, and it is desired to supply an opaque and high-purity quartz material, that is, a high-purity opaque quartz glass. However, conventionally used natural raw materials for producing opaque quartz glass contain a large amount of impurities in addition to fine bubbles. It is extremely difficult to remove these impurities, and it is said that high purification by purification is impossible. On the other hand, relatively high-purity quartz has a small amount of air bubbles present in the crystal-particularly, fine air bubbles, so the opacity does not increase even when melted, and the obtained quartz glass becomes translucent. Nothing more than. For this reason, high-purity opaque quartz glass manufactured using natural raw materials has not been known so far.

In addition, in the method of adding fine powder such as carbon and silicon nitride as a foaming agent to the siliceous raw material powder and heating and melting the mixture, solid particles are mixed and solid-phase reaction / decomposition reaction is involved. It is difficult to control so that the fine bubbles are evenly dispersed. Further, in the flame melting method, it is difficult to complete the reaction because the residence time of the fine particles in the flame is extremely short, and the added foaming agent may remain as foreign matter in the melt. Further, there is a problem in that the siliceous raw material and the foaming agent react with each other to cause a phenomenon that the melt is colored.

An object of the present invention is to provide a high purity opaque quartz glass having a very low impurity content, a high purity and a high opacity, and a method for producing the same.
"Opaque quartz glass" referred to in this specification has a thickness of 10 m.
Regarding a sample obtained by cutting and polishing to m, it is a quartz glass having a light transmittance of 1% or less in a wavelength range of 200 to 5000 nm when measured with a spectrophotometer.

[0006]

Means for Solving the Problems As a result of earnest studies on a method for producing high-purity opaque quartz glass, the present inventors have found that the content of each element of alkali (earth) metal, Fe and Al is low, By including high-purity amorphous silica, which contains fine bubbles of, and which contains a silanol group as a vaporizable component at a concentration in a specific range uniformly, as a raw material for flame melting, without using a special additive, The present invention has been completed by finding that it is possible to obtain quartz glass having high purity and high opacity by heating and melting in a flame.

The first aspect of the present invention is that "the content of each element of alkali metal, alkaline earth metal, Fe and Al is 1 ppm or less, and the wavelength is 200 to 200 when cut and polished to a thickness of 10 mm. High-purity opaque quartz glass having a light transmittance of 1% or less in the region of 5000 nm. ”
Is the gist.

A second aspect of the present invention is, "In the method for producing opaque quartz glass by flame-melting silica particles, the content of each element of alkali metal, alkaline earth metal, Fe and Al is 1 ppm as the silica particles. Absorbance value ρ at each of the following positions of infrared absorption by the diffuse reflection method obtained by pulverizing and sizing silica particles mainly having particles having a shortest diameter of 200 μm or more is in the following range: A method for producing a high-purity opaque quartz glass, characterized by using amorphous silica particles, which are in the range: infrared absorption position, (cm ^-1 ) absorbance value ρ 3400 0.2 ≧ ρ ₃₄₀₀ ≧ 0.01 3740 0.3 ≧ ρ ₃₇₄₀ ≧ 0.01 ”is the main point.

In a preferred embodiment, the silica particles are prepared by a wet method and calcined, and the minimum particle size in the stage before crushing and sizing is 200 μm.
It is preferable that the particles are 90% by weight or more of particles having a size of m or more.

The present invention will be described in detail below. The high-purity opaque quartz glass of the present invention has an extremely low content of impurities, and has a low content of alkali metals, alkaline earth metals, Fe and Al.
The content of each element is 1 ppm or less. The high-purity opaque quartz glass of the present invention has a high opacity, and when cut and polished to a thickness of 10 mm and measured by a spectrophotometer, the light transmittance is 1% or less in the wavelength range of 200 to 5000 nm. .

In the method of the present invention, when silica particles are subjected to flame melting treatment to produce opaque quartz glass, the raw material silica for flame melting treatment is amorphous, and alkali metal, alkaline earth metal, Fe and Al are used. The content of each element is less than 1ppm and the shortest diameter is 200μ
By preparing silica particles having an absorbance value of infrared absorption by a diffuse reflection method within a specific range defined by the present invention, which is obtained by pulverizing and sizing silica particles whose main component is m or more. To use. Silica particles satisfying the above requirements are subjected to flame melting treatment to be vitrified to obtain high-purity opaque quartz glass.

The silica particles used as the raw material silica for flame melting treatment in the method of the present invention should contain as few impurities as possible, and alkali metal elements such as Na and K and alkaline earth metals such as Mg and Ca should be included. The content of each element, Fe and Al, must be 1 ppm or less. It is also preferably porous.

Such amorphous silica particles have been proposed by the present inventors in Japanese Patent Laid-Open Nos. 62-3011, 62-3012, 62-283809 and 62-283809. According to the method described in each publication, a fine fibrous coagulated product obtained by extruding an aqueous solution of an alkali metal silicate into a water-miscible organic medium or an acid solution is treated with an acid-containing liquid to extract impurities. It can be obtained by removing. As the alkali metal silicate, sodium salt, potassium salt, lithium salt or the like of silicic acid can be used. Further, amorphous silica particles obtained by using silicon tetrachloride or silicic acid alkoxide as a raw material can also be used.

In an embodiment, an aqueous solution of an alkali metal silicate having a viscosity in the range of 2 to 500 poise, preferably 2 to 200 poise, is used, and the pore size is 0.3 to 1 mm, preferably 0.5 to 10.
From the nozzle in the range of 0.8 mm, extrude into a coagulation bath consisting of a water-miscible organic medium or an acid solution with a concentration of 4 N or less to coagulate into fibrous or columnar or granular particles, and treat the resulting gel with an acid-containing liquid. To do. After the treatment with the acid-containing liquid, it may be washed with water if necessary. Further, the silica thus obtained may be heat-treated.

The nozzle used is made of a noble metal alloy such as a gold-platinum alloy or a tetrafluoroethylene-based resin in order to prevent the occurrence of troubles in which the alkali metal silicate gelated in the coagulation bath adheres to the nozzle surface. Alternatively, the nozzle surface is preferably coated with a noble metal alloy or a tetrafluoroethylene-based resin.

Examples of the water-miscible organic medium used in the coagulation bath include alcohols such as methanol, ethanol and n-propanol, esters such as methyl acetate and ethyl acetate, ketones such as acetone and methyl ethyl ketone, and dimethylacetamide. Examples thereof include amides such as dimethylformamide, dimethylsulfoxide and the like.

The acid used in the coagulation bath is an inorganic acid such as sulfuric acid, nitric acid or hydrochloric acid, and it is preferable to use sulfuric acid or nitric acid. As the acid solution, an aqueous solution of these acids is practically used. preferable. The acid concentration is in the range of 0.1 to 4 N, preferably 0.5 to 3 N, and more preferably 1 to 2 N. The coagulation bath temperature is preferably kept in the range of 10 to 60 ° C.

For purification of silica obtained by reacting an aqueous solution of an alkali metal silicate with a water-miscible organic medium or acid, mineral acids such as sulfuric acid, nitric acid and hydrochloric acid, peroxides such as hydrogen peroxide and chelates are used. Known methods such as washing with an aqueous solution containing a substance selected from agents and the like can be used.

In this way, porous high-purity amorphous silica having a low impurity content can be obtained. That is, Al, P, B as impurities, alkali metal elements such as Na and K, alkaline earth metal elements such as Mg and Ca,
To obtain amorphous silica in which the content of each transition metal element such as Ti, Cr, Fe, Cu, Mo is 1 ppm or less and the specific surface area measured by the BET method is 100 m ² / g or more. You can

The opacity of quartz glass is due to the inclusion of many fine bubbles in the glass and the incident light being scattered at the interface between the vitreous and the bubbles. In the method of the present invention, in order to include a large number of fine bubbles in the glass,
Using high-purity amorphous silica particles uniformly containing silanol groups as a vaporizable component in a specific range of concentration as a flame melting raw material, without using a special additive, with high purity, and, Obtain quartz glass with high opacity.

The silanol groups contained in silica exist in various forms, and their infrared absorption spectra are assigned as follows. Infrared absorption position, (cm ^-1 ) morphology of silanol group 3400 Surface adsorbed water-derived silanol group 3680 Internal silanol group 3740 Isolated silanol group Among these, the cause of air bubbles is the silanol group derived from surface-adsorbed water. It is an isolated silanol group, and both are related to the adsorption of water. In the method of the present invention,
Since silica containing a uniform silanol group is flame-melted, it is possible to obtain a silica glass having a high opacity in which many fine bubbles are uniformly distributed.

In the method of the present invention, when the absorbance value of infrared absorption by the diffuse reflection method is used as an index of the silanol group concentration of the raw material silica for flame melting treatment, the absorbance values ρ at the respective infrared absorption positions are as follows: It has been found that the content within the following range is necessary for obtaining opaque quartz glass. The absorbance value ρ is obtained from the difference between the absorbance value at each peak position and the absorbance value on the baseline. Infrared absorption position, (cm ^-1 ) Absorbance value ρ 3400 0.2 ≧ ρ ₃₄₀₀ ≧ 0.01 3740 0.3 ≧ ρ ₃₇₄₀ ≧ 0.01

In order to prepare the raw material silica particles for flame-melting treatment suitable for the method of the present invention, which has an infrared absorption value within the above-specified range defined by the present invention, the silica particles are prepared by a wet method. When it is prepared, it is preferable to perform a firing treatment prior to the flame melting treatment.

The firing temperature is 10 as the firing condition.
00 to 1500 ° C, preferably 1050 to 1300 ° C, more preferably
The range of 1100 to 1250 ° C is preferable. When the calcination temperature is lower than 1000 ° C., the vaporized components such as water and silanol remaining in the obtained calcined silica particles are too much, and the absorbance value of infrared absorption is out of the range defined by the present invention. The ingot obtained by flame-melting such silica particles becomes hollow and is not suitable for the purpose of the present invention. On the other hand, when the baking temperature exceeds 1500 ° C., water and silanol volatilize to generate bubbles, and the component for generating bubbles becomes insufficient, and the absorbance value of infrared absorption also deviates from the range defined by the present invention. The quartz glass obtained by flame-melting such silica particles becomes transparent or translucent, and it is difficult to obtain the opaque quartz glass intended by the present invention.

The firing time is in the range of 1 minute to 10 hours, preferably 30 minutes to 6 hours, more preferably 1 to 5 hours.

The atmosphere in which the baking treatment is performed is not particularly limited,
An inert gas atmosphere such as argon or helium, an oxidizing atmosphere such as air or oxygen, or a chlorine-containing atmosphere capable of effectively removing impurities in silica can be used.

The apparatus used for the firing treatment is
Any material can be used as long as it can maintain the raw material silica at a predetermined temperature, and a tubular furnace, a box furnace, a tunnel furnace or the like can be used. Further, the heating source is optional, and electric heat or combustion gas is an economical heat source. In addition, plasma heating and an image furnace can also be used.

The silica particles that have been subjected to the firing treatment are subjected to a particle size adjusting treatment such as pulverization / classification and sizing if necessary so as to be suitable for the flame melting treatment. The order of the calcination treatment and the particle size adjustment treatment on the silica particles is arbitrary, but it is preferable to perform the particle size adjustment treatment after the calcination treatment.

When the particle size of silica particles used as a raw material for flame melting processing is adjusted, a usual crushing device-for example, a rolling ball mill such as a pot mill, a tube mill, a conical ball mill or a compartment mill, a vibrating ball mill, or a tower type is used. A medium agitating mill such as a crusher or a stirring tank type mill or a roll mill can be used, and a rolling ball mill or a vibrating ball mill is preferably used.

The material of the crushing medium that comes into contact with the crushed material, such as the main part of the crushing device or the balls and rods used as necessary, is
It may be appropriately selected from silica glass, fused quartz, quartz, agate or siliceous material such as silica stone.

The size of the crushing medium made of a rigid body such as a ball used as necessary has a diameter in the range of 0.5 to 50 mm, preferably 10 to 40 mm.

The raw material silica for flame melting treatment used in the method of the present invention is obtained by subjecting amorphous silica particles having a shortest diameter of 200 μm or more to firing treatment or particle size adjusting treatment, if necessary, prior to the flame melting treatment. It is preferably prepared by In other words, the amorphous silica particles for preparing the raw material silica for the flame melting treatment used in the method of the present invention is a stage before the firing treatment and the particle size adjusting treatment, which are performed as necessary before the flame melting treatment. It is preferable that the shortest diameter is 200 μm or more.

When the silica particles are prepared by a wet method, the silica glass obtained is transparent or translucent when the silica particles having a shortest diameter of less than 200 μm are fired and then flame-melted to be vitrified. In many cases, it is extremely difficult to obtain the opaque quartz glass targeted by the present invention. On the other hand, when the silica particles having the shortest diameter of 200 μm or more are subjected to a firing treatment and flame-melted as they are or as the particle size is adjusted, surprisingly, the opaque quartz glass intended by the present invention can be obtained. I was able to.

Although this mechanism is not clear, it may be related to the formation process of silica particles. Generally, particles having a large particle size are generated by agglomeration of primary particles. When large silica particles are generated, it takes a gradual aggregation structure,
A large number of pores are formed in the particles. It is presumed that these pores remain even if the particles are subjected to the firing treatment, and remain as a large number of bubbles in the melt when the particles are further subjected to the flame melting treatment. It is thought to increase the opacity of.

From the above, the amorphous silica particles for preparing the raw material silica for flame melting treatment used in the method of the present invention are mainly composed of particles having a shortest diameter of 200 μm or more. is necessary. The shortest diameter is
It is not necessary that only particles having a diameter of 200 μm or more be present, and even particles having a shortest diameter of less than 200 μm can be present in an amount of about 10% by weight.

A high-purity amorphous material having a low content of impurities, containing silanol groups uniformly as a vaporizable component in a concentration within a specific range, and containing a large number of fine bubbles, satisfying the requirements specified in the present invention. The high-purity opaque quartz glass of the present invention having a high purity and a high opacity is obtained by heating and melting the high-quality silica in a flame under the conditions usually performed without using a special additive. Furthermore, by selecting the type of raw material silica to be used, particle size, crushing treatment conditions, and firing treatment conditions, it is possible to control the size and amount of bubbles included in the raw material and the content of the volatile component,
It is possible to obtain a high-purity opaque quartz glass having an arbitrary opacity.

[0037]

EXAMPLES The method of the present invention will be specifically described below with reference to Examples and Comparative Examples. The present invention is not limited to the examples below. Example 1 1-1) Preparation of amorphous dry silica JIS No. 3 water glass was heated and concentrated to give a viscosity at 20 ° C.
It was set to 300 cps. About 8 liters of this water glass was pressurized with a pump, passed through a filter (opening 70 μm), and then a nozzle (pore diameter: 0.
5mm, 50 holes) 8% by weight kept at 50 ℃
0.4m / s into a coagulation bath containing 300 liters of sulfuric acid
Extruded at the speed of. The silica obtained in fibrous form is immersed in 10 times the amount of newly prepared 8 wt% sulfuric acid aqueous solution and stirred at a temperature of about 95 ° C for about 1 hour to extract impurities, and then 10 times the amount of silica. It was washed twice with pure water. After the above extraction and washing operations were repeated 5 times, the wet silica obtained by dehydration with a centrifuge was dried with a hot air dryer at a temperature of 150 ° C for 8 hours to obtain a water content (weight reduction rate based on calcined silica).
3.7 kg of amorphous dry silica having a content of 7% by weight was obtained. The shortest diameter of the particles of this amorphous dry silica was 250 μm.

1-2) Preparation of Raw Material Silica Particles for Flame Melting Treatment The amorphous dry silica was put into a quartz crucible and heated in an electric furnace at a temperature of 1250 ° C. for 2 hours to carry out a firing treatment.
It was crushed by using a quartz ball mill, and classified and sized to obtain raw material silica particles for flame melting treatment having an average particle diameter of 200 μm. The flame-melting raw material silica particles thus obtained had a true specific gravity of 2.20 and an impurity content of Na: 0.3.
ppm, K: 0.1 ppm or less, Mg: 0.1 ppm or less, Ca: 0.1
ppm, Al: 0.4 ppm, Fe: 0.2 ppm.

Regarding the raw material silica for flame melting treatment, Fourier transform infrared spectroscopic analyzer FTIR (Perkin Elmer 1710
Type) was used to measure infrared absorption by the diffuse reflection method. And each absorbance value at the position of the infrared absorption position 3400 cm ^-1 and 3740cm ^-1, each absorbance value ρ obtained from the difference between the absorbance values on the baseline was used as an index of the silanol group concentration. Each absorbance value ρ is ρ ₃₄₀₀ = 0.120, ρ ₃₇₄₀ = 0.05
It was 5.

1-3) Quartz vitrification The above-mentioned raw material silica particles for flame melting treatment were subjected to flame melting treatment by a conventional method to obtain a quartz glass ingot. The obtained ingot has an impurity content of Na: 0.3 ppm, K
: 0.1 ppm or less, Mg: 0.1 ppm or less, Ca: 0.1 ppm, Al
: 0.4 ppm, Fe: 0.2 ppm, high-purity quartz glass. Further, the above ingot contained many fine bubbles and was visually opaque. Regarding the quartz glass plate sample obtained by cutting and polishing the ingot to a thickness of 10 mm, the light transmittance was measured using a spectrophotometer. The light transmittance in the wavelength range of 200 to 5000 nm was 1
% Or less.

Example 2 and Comparative Examples 1 to 4 Amorphous dry silica having a shortest diameter of 250 μm obtained according to the method of Example 1 was crushed using a quartz ball mill and classified and sized. Amorphous sized silica particles having an average particle size of 270 μm were obtained. The amorphous sized silica particles were calcined under the various conditions shown in Table 1 to obtain silica particles having different infrared absorbance values. (Example 2 and Comparative Examples 1-2).
For comparison, amorphous dry silica having a shortest diameter of 140 μm obtained according to the method of Example 1 except that a nozzle having a hole diameter of 0.2 mm was used, in the order and conditions shown in Table 1. The particles were subjected to a sizing treatment and a calcination treatment to obtain silica particles having an infrared absorbance value within the range specified by the present invention. (Comparative Examples 3 to 4). These various silica particles were used as raw material silica particles for flame melting treatment, and were subjected to flame melting treatment by a conventional method to be vitrified to obtain a quartz glass ingot. The shortest diameter of each amorphous dry silica before sizing and firing treatment, the characteristic value of each prepared raw material silica particle for flame fusion treatment, and the condition of the obtained quartz glass ingot are combined with Example 1, It is shown in Table-1. The raw material silica particles for each flame melting treatment and the content of impurities in the obtained quartz glass ingot are both
Na: 0.3 ppm, K: 0.1 ppm or less, Mg: 0.1 ppm or less, C
a: 0.1 ppm, Al: 0.4 ppm, Fe: 0.2 ppm.

[0042]

[Table 1]

As shown in Table 1, when silica particles satisfying the requirements specified in the present invention are subjected to flame melting treatment, the objective of the present invention is high purity, highly pure quartz glass with high opacity. Can be obtained. (Example 1
2). On the other hand, when the shortest diameter or infrared absorption value of the silica particles before sizing / calcination does not satisfy the requirements specified in the present invention, when the flame melting treatment is performed, the present invention However, it is not possible to obtain the desired quartz glass with high opacity. (Comparative Examples 1 to 4).

[0044]

As the raw material silica particles for flame melting treatment,
By using silica particles satisfying the requirements specified in the present invention, the content of each element of alkali metal, alkaline earth metal, Fe and Al is 1 ppm or less without using any special additive, and, Efficient production of highly pure and highly opaque quartz glass with extremely low impurities and having a light transmittance of 1% or less in the wavelength range of 200 to 5000 nm when cut and polished to a thickness of 10 mm. You can The opaque quartz glass obtained by the method of the present invention has an extremely low impurity content compared to that obtained by the conventional method and can control the opacity, so that it is a semiconductor jig, particularly a flange material for a diffusion tube. Can be suitably used as. Furthermore, the method of the present invention has the advantages that it is more economical than the conventional method and the manufacturing cost can be reduced.

Claims (4)

[Claims] 1. Light in the wavelength range of 200 to 5000 nm when the content of each element of alkali metal, alkaline earth metal, Fe and Al is 1 ppm or less, and when cut and polished to a thickness of 10 mm. High-purity opaque quartz glass with a transmittance of 1% or less. 2. A method for producing opaque quartz glass by flame-melting silica particles, wherein the content of each element of alkali metal, alkaline earth metal, Fe and Al is 1 ppm or less as the silica particles. , The shortest diameter is 2
Amorphous silica obtained by pulverizing and sizing silica particles mainly composed of particles having a size of 00 μm or more and having an absorbance value ρ at each of the following positions of infrared absorption by a diffuse reflection method within the following range: A method for producing a high-purity opaque quartz glass, which comprises using particles. Infrared absorption position, (cm ^-1 ) Absorbance value ρ 3400 0.2 ≧ ρ ₃₄₀₀ ≧ 0.01 3740 0.3 ≧ ρ ₃₇₄₀ ≧ 0.01 3. The method for producing a high-purity opaque quartz glass according to claim 2, wherein the silica particles are prepared by a wet method and calcined. 4. The high-purity opaque quartz glass according to claim 2 or 3, wherein the silica particles are 90% by weight or more of particles having a shortest diameter of 200 μm or more as a particle size before crushing and sizing. Manufacturing method.