JPH04144928A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To improve yield of quartz glass by blending amorphous SiO2 powder with water and water-soluble gelling agent to give SiO2 slip and forming, drying and burning the slip. CONSTITUTION:The first amorphous SiO2 powder prepared by hydrolyzing Si alkoxide and having 0.5-10mum particle size is blended with the second amorphous SiO2 powder having <=0.1mum particle diameter and contained at a mixed ratio of <=80wt.% to afford mixed amorphous SiO2 powder. 30-100 pts.wt. water and 0.3-5.0wt.% dispersing agent such as polycarboxylic acid ammonium salt are added to 100 pts.wt. of the resultant mixed powder and further 0.5-10 pts.wt. water-soluble gelling agent such as ammonium alginate or NH4NO3 is added to the mixture to form SiO2 slip. Then the SiO2 slip is poured into a mold and gelatinized and cured and then taken out and dried at 4i40% relative humidity. Then the gel is heated at 900 deg.C and defatted and then sintered at 1200-1700 deg.C to provide the transparent quartz glass in high yield.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for manufacturing transparent or translucent high-purity quartz glass useful for semiconductor cleaning baths, high-purity powder sintering containers, physical and chemical experiments, and the like.

[Conventional technology]

Silica glass has been used in many industrial fields because it has excellent heat resistance, acid resistance, and translucency. The following methods are generally known for producing quartz glass. The first method is a melting method. This method involves refining raw quartz, melting it at a high temperature, injecting it into a mold, shaping it, and then cooling it. The second method is the sol-gel method. This method is currently the most commonly used method, for example,
It is described in Japanese Patent No. 2-176931. The method described in this publication is for manufacturing silica glass by firing a fine gel powder obtained by hydrolyzing a silicate ester or a mixture of a silicate ester and a metal alkoxide or metal salt. be. Furthermore, a third method for producing quartz glass is a method using ultrafine powdered silica. This method was published in Japanese Unexamined Patent Publication No. 60-4
Publication No. 31833, U.S. Patent No. 4042361,
and 4419115 specification, furthermore, JP-A-60-2
As disclosed in Japanese Patent No. 1821, a method in which finely powdered silica is mixed during hydrolysis of ethyl silicate, a method in which only finely powdered silica is used for sintering, or a method similar thereto.

[Problem to be solved by the invention]

The first method has the advantage that large (30 cm or more) and transparent quartz glass can be obtained. However, this method has the disadvantage that natural raw materials are limited, and in order to obtain quartz glass with a purity of 4N (99°99%) or higher, it must be purified many times, resulting in high production costs. . Furthermore, since it is a melting method, there is a limit to the shape of the product, and products with complex shapes cannot be obtained with satisfactory precision. On top of that,
Since the melting temperature is 2000° C. or higher, there is a drawback that energy costs are required for heating. The second sol-gel method is an excellent manufacturing method that can produce highly pure and transparent quartz glass because it is easy to purify the metal alkoxide and can be sintered at a low temperature of 1000 to 1200°C. However, on the other hand, in the step of drying the gel, which is one step in the manufacturing process, the dry gel tends to crack or break due to shrinkage of the gel, making it difficult to produce large products and having a low yield. The third method yields transparent and highly pure quartz glass, but each method has its advantages and disadvantages, and in reality, the manufacturing method is also used differently depending on the intended use of the quartz glass. However, all of these manufacturing methods have limitations on the molding method, so
In terms of mass production, there is a drawback that large-sized quartz glass cannot be obtained industrially with a high yield. The present invention has been made in view of the above circumstances, and an important object of the present invention is to provide a method for producing quartz glass that can produce transparent or translucent quartz glass at low cost and with a high yield. There is something to do.

[Means to solve the problem]

The present inventors have developed the invention with the aim of achieving the above-mentioned object, and the present invention has been developed by adding a water-soluble gelling agent to a silica slip consisting of amorphous silica powder and water. , is characterized in that it is formed into a molded body, which is dried and then fired. As used herein, the term "water-soluble gelling agent" refers to a substance that gels and solidifies when dissolved in water. As a water-soluble gelling agent having this physical property, for example,
Agar, gelatin curdland (trademark of Shikinichi Yakuhin Industries, Ltd.), etc., which dissolve in water and gel when heated, can be used, and organic polymers such as ammonium alginate and methyl cellulose, which dissolve in water and gel at room temperature, can be used. Inorganic chemicals such as molecules, ammonium nitrate, hydrochloric acid, and sulfuric acid can be used. The water-soluble gelling agent preferably does not contain alkali metals or alkaline earth metals. This is because water-soluble gelling agents containing these metals tend to cause devitrification or cristobalite to occur in the resulting quartz glass. The amount of the water-soluble gelling agent added is preferably adjusted to a range of 0.5 to 10 parts by weight per 100 parts by weight of the amorphous silica powder. If the amount of the water-soluble gelling agent added is less than 0.5 part by weight, the slip will be difficult to solidify, resulting in deformation when the mold is removed, making it impossible to form a molded product with high precision. On the other hand, if the amount of the water-soluble gelling agent added is more than 10 parts by weight, the water-soluble gelling agent becomes an impurity in the step of sintering the molded body, and the resulting silica glass tends to have devitrification or cristobalite. By the way, in the method for producing quartz glass of the present invention, preferably, in addition to the amorphous silica powder and water, a dispersant is added to uniformly disperse the amorphous silica powder. Furthermore, the following first silica powder and second silica powder are preferably used as the amorphous silica powder. The first silica powder has a volume average particle size of 0. A monodisperse, spherical amorphous silica powder with a size of 5μ or more and 10μ or less is used. As the second silica powder, a super fine silica powder having a volume average particle diameter of 0.1 μm or less is used. When mixing the first silica powder and the second silica powder, the mixing ratio of the second silica powder is adjusted to 80% by weight or less. In the manufacturing method of the present invention, in order to obtain highly pure quartz glass, it is preferable that the purity of the amorphous silica powder is 99.9% or more. The first amorphous silica powder can be obtained using purified silicon alkoxide as a highly pure raw material. That is, when silicon alkoxide is dropped into a mixed solution of alcohol and aqueous ammonia, and at the same time another aqueous ammonia is added dropwise to adjust the pH to 10 or more, silica precipitates are generated by hydrolysis of the silicon alkoxide. After settling the precipitate, the alcohol and aqueous ammonia are evaporated and dried, resulting in a purity of 99.9% or more and a particle size of 0. 5
Approximately spherical amorphous silica powder with a size of μ to 10 μ is obtained. In the step of hydrolyzing silicon alkoxide to obtain the first silica powder, the particle size of the silica precipitate precipitated by hydrolysis changes depending on the amount of silicon alkoxide dropped per unit time. Therefore, the particle size can be controlled by adjusting the amount of silicon alkoxide dropped. The smaller the amount of silicon alkoxide dropped, the smaller the particle size, and the larger the amount, the larger the particle size. For example, when using ethyl silicate containing 30% by volume of silica, it is usually 0. 0.5 to 5 drops per minute
Amorphous silica powder with a particle size of 10μ is obtained. As the silicon alkoxide used, methyl silicate, ethyl silicate, propyl silicate, etc. are preferably used. When using an amorphous silica powder obtained by mixing the first amorphous silica powder and the second amorphous silica powder in this way,
By lowering the firing temperature, large molded bodies of 30ca+ or more can be easily manufactured. Second amorphous silica powder g> Particle size is smaller than that of the first silica powder. Therefore, the second silica powder has a lower melting temperature than the first silica powder. Therefore, by mixing the second silica powder with the first silica powder, when sintering the compact, compared to the case of using only the first amorphous silica powder with a large particle size, The temperature can be lowered to lower the sintering temperature. As the firing temperature increases, silica glass tends to generate cristobalite. Silica glass, which can be fired at low temperatures, has the advantage of preventing cristobalite. However, if 80 parts by weight or more of the second amorphous silica powder is added in order to lower the firing temperature, the firing temperature will be lower, but the dried molded product will tend to crack, making it impossible to manufacture large products. . As the second amorphous silica powder L, for example, those commercially available under trade names such as Cabosil, Aerosil (manufactured by Degussa), D, C, Silica (manufactured by Dow Corning) can be used. A dispersant is added to the amorphous silica powder and water to improve dispersibility. As the dispersant, organic dispersants commonly used in the ceramic industry, such as ammonium polycarboxylate and SMA-1440H (manufactured by Alcoa), can be used. Amount of dispersant added? 4. Preferably, the amount is adjusted to 0.3 to 5.0% by weight based on the amorphous silica powder. In the method for producing quartz glass of the present invention, a slip is formed by adding a water-soluble gelling agent dissolved in water to a mixture of amorphous silica powder, water, and preferably a dispersant. The slip is poured into a mold and shaped. The optimal formwork is one that does not dissolve impurities from the surface of the formwork into the slip, such as ζf1 synthetic resin or wood. The silica slip poured into the mold is cured by a heated gelling agent. After that, the mold is removed and the cured molded product is taken out and dried. The external environment for drying has a relative humidity of 40% or more. In this dry environment, a dried molded article can be obtained in several days or more. The drying conditions for the molded article are preferably such that the relative humidity is 40% or more, more preferably in the range of 60 to 95%. This is because if the humidity is 40% or less, cracks and cracks will easily occur in the molded product. Another method is to pour a slip consisting of amorphous silica powder, water, and a dispersant into a mold, and then add a water-soluble gelling agent dissolved in water to the slip in the mold. After the slip has hardened, it can also be degreased and dried. Furthermore, when forming a slip by adding a water-soluble gelling agent that gels by heating, it is preferable that the temperature of the entire slip before addition or after addition be 60°C.
It is best to heat it above ℃. The amount of water added to the amorphous silica powder is preferably adjusted to 30 to 100 parts by weight based on 100 parts by weight of the mixture. If it is less than 30 parts by weight, it will be difficult to disperse the slip, and the viscosity will be high, making it easy for air bubbles to enter the inside. If the amount is more than 100 parts by weight, the molded product will be difficult to solidify and will take a long time to dry. The dried molded product is preferably degreased by firing at around 900°C for 1 to 2 hours while increasing the temperature with a temperature gradient of 1 to b minutes to completely remove organic matter contained inside the dried molded product. It is decomposed and then sintered in a temperature range of 1200 to 1700°C to obtain the desired quartz glass. If the temperature gradient is set to 5° C./min or less and the temperature is raised slowly, splitting and cracking of the dried molded product can be prevented. As for the firing conditions, translucent quartz glass can be obtained by sintering at less than 1500° C. under a reduced pressure of about 1X10-3 to 1X10-5 torr. Transparent quartz glass can be obtained by sintering in a He atmosphere at a temperature of 1500° C. or higher.

[Effect]

The manufacturing method of the present invention does not dry a gel to obtain a dry molded body, as in the conventional sol-gel method. In the manufacturing method of the present invention, a silica slip is solidified with a water-soluble gelling agent, molded, and dried. The molded body solidified in this state can minimize cracks and cracks during the drying process. Furthermore, in the method for producing quartz glass of the present invention, silica slip can be added to the silica glass and molded using a water-soluble gelling agent. Therefore, various shapes can be easily molded without using conventional plaster molds.

【Example】

Examples of the present invention will be described in detail below. However, the examples shown below are illustrative of the manufacturing method for embodying the technical idea of this invention, and the method of this invention uses the materials used and various conditions in each process as shown below. It is not specific. The quartz glass manufacturing method of the present invention can be modified in various ways within the scope of the claims. [Example 1] A first amorphous silica powder is manufactured through the following steps. ■ Prepare a mixture of 60σ ethanol and 10 volumes of 18% ammonia water and heat it to 50°C. (2) Next, prepare 80 volumes of purified commercially available ethyl silicate (silica equivalent content: 30 W/V%) and 10 M of the same <18% ammonia water. ■ A mixed solution of ethanol and ammonia water was maintained at 50°C and stirred, and the ammonia water mixed ethyl silicate obtained in step (■) was added dropwise to this at a dropping rate of 3α/min.
At the same time, aqueous ammonia is added dropwise to adjust the pH to always be 10.0 or higher. ■ After finishing dropping ethyl silicate, silica precipitates due to hydrolysis. ■ After that, the liquid temperature was raised to 60°C and left for 2 days to evaporate ethanol and ammonia, and then the target particle size of 3 μm, almost spherical, monodisperse first amorphous silica powder 24
Using the first silica powder obtained in nine or more steps, quartz glass is manufactured in the following steps. ■ To 7 kg of the first silica powder obtained, add 3 kg of second silica powder having a volume average particle size of 0.05μ, and 5 kg of pure water.
kg and 150 g of dispersant were added, stirring was done half way to make a silica slip. Aerosil 0X-50 (trademark of Degussa) is used as the second silica powder. Ammonium polycarboxylate is used as a dispersant. ■ After dispersing the obtained silica slip in a ball mill for 17 hours, the balls are separated. ■ On the other hand, as a water-soluble gelling agent, curdlan was added at 70°C.
Dissolve in hot water to create a 5% aqueous solution. (2) Maintain a 5% curdlan aqueous solution at 60°C, mix it with the silica slip obtained in (2), and stir for 10 minutes. (2) After stirring, pour the mixture into a synthetic resin molded container as shown in Figure 1. The molded container shown in this figure has a square planar shape, and is marked by A, B, C, and D in the figure. H was set to the following value. A = 300 mm B = 280 mm C = 10 mm D = 10 mm H = 300 mm ■ Heat a molded container, pour the silica slip into it, keep it at room temperature for 3 hours to gel, and then gradually cool it to solidify the slip. ■ After confirming that the slip inside the container has gelled and solidified, the inner plastic molded container is pulled out, and the outer synthetic resin container is also removed to obtain a shape-retentive silica molded body. (2) The obtained molded body is dried in a constant humidity machine with a humidity of approximately 60% at room temperature for two weeks to obtain a dry molded body. This dry molded body had a square outer shape with each side of 270 mm and a height of 270 mm. The dry molded body L obtained in this process showed no cracks or cracks at all.
Heat to 0°C and degrease for 2 hours. In this step, the water-soluble gelling agent added to the silica slip is removed. [Phase] Thereafter, it was continuously sintered in a vacuum at 1400° C. for 2 hours to obtain quartz glass. The quartz glass obtained in this process had translucency. This quartz glass had a square outer shape with one side of 240 mm and a height of 240 mm. Also, the density is 2.
The quartz glass had a purity of 5N (99,999%) or higher at 20g/cm". As a result of ICP analysis of this quartz glass, Fe was found to be 0.
OO1ppm, contained 0.5ppm of Na, 0.02ppm of Ca, and no AQ was detected. In this way, when spherical first amorphous silica powder particles are used, the density of the silica particles increases even in the dry molded product, and therefore, quartz glass with high precision and high density can be obtained. Furthermore, by mixing the second amorphous silica powder, the sintering temperature can be lowered to obtain the same quartz glass, so cristobalite is less likely to form in the obtained quartz glass. [Example 2] A silica slip was prepared in the same manner as in Example 1 using a 5% aqueous ammonium alginate solution instead of curdlan as the water-soluble gelling agent. The ammonium alginate aqueous solution is prepared by adding a dispersant to amorphous silica powder, dispersing it in pure water, and stirring the resulting mixture. A molded silica slip container having the shape shown in FIG. 2 is used. This molded container is 400mm x 400mm
A molding chamber is formed by stacking two plastic plates with a spacer of equal width in between. In the same manner as in Example 1, silica slip was injected into a molded container, degreased and dried to give an outer diameter of 36OX360mm.
The dried compact with a thickness of 5 mm was obtained. The obtained dry compact was sintered in a He atmosphere at 1500'C for 2 hours using the same heating rate and degreasing conditions as in Example 1. , quartz glass was obtained. The quartz glass obtained through this process has a density of 2°20g/
cm', and the purity was 5N (over 99,999%). In the same way, five pieces of quartz glass were prototyped, assembled into a box shape, and each side was welded with an oxygen-hydrogen burner to form a box shape. [Example 3] 3 kg of a first amorphous silica powder with a volume average particle size of 0.6μ and a second amorphous silica powder (Aerosil OX- 50) A silica slip was obtained in the same manner as in Example 1 except that 7 kg was used.This silica slip had an inner diameter of 50 mmφ and a length of 1
After pouring into a polyethylene tube of 000mm kept at 80℃, cooling to room temperature and gelling for 3 hours,
After drying for 4 days at 40°C with a relative humidity of 80%, it was formed into a film from a plastic tube and further dried at 40°C with a relative humidity of 60%.
The molded body was dried for two weeks to obtain a dry molded body. This molded body was sintered under the same conditions as in Example 2, and the outer diameter was 4.
0mmφ, total length 800mm, density 2.20g
/cm3 transparent quartz glass was obtained.

【Effect of the invention】

As described above, the method of the present invention involves adding a water-soluble gelling agent to amorphous silica powder to obtain a silica slip, molding it into a shape-retaining state, and then drying and firing the quartz slip. The glass manufacturing method allows large-sized quartz glass to be produced easily and efficiently, and in large quantities with high yields. The reason why the method of this invention can significantly improve the yield of quartz glass is that it can minimize cracking during the drying, degreasing, and sintering steps. By the way, when quartz glass is manufactured using the method of the present invention, it is possible to achieve a yield of almost 100% regardless of the size.

[Brief explanation of drawings]

1 to 3 are a sectional view and a perspective view showing a molded silica slip container.

Claims (1)

[Claims] (1) A method for producing quartz glass, which comprises adding a water-soluble gelling agent to amorphous silica powder and water to form a silica slip, shaping the slip, and then drying and firing it.