JPH03257029A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To obtain large-sized transparent quartz glass having superior light transmittance in a high yield by successively subjecting alkoxy silane to hydrolysis with an alkali catalyst, hydrolysis with an acid catalyst and specified treatment, converting the resulting sol into gel, drying and sintering this gel. CONSTITUTION:Alkoxysilane is partially hydrolyzed with an alkali catalyst, an acid catalyst is added and the unreacted alkoxysilane is hydrolyzed to prepare a sol. Alkali is further added to the sol so as to accelerate gelatinization. The resulting sol is converted into gel, this gel is dried to produce dry gel transmitting light in UV and visible regions and the dry gel is sintered to obtain porous or nonporous quartz glass. The alkoxysilane used is lower alkoxysilane represented by a formula Si(OR)4 (where R is lower alkyl), e.g. tetramethoxysilane [Si(OCH3)4] or tetraethoxysilane [Si(OC2H5)4].

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing transparent porous or non-porous quartz glass. More specifically, the present invention uses alkoxysilane as a raw material and polycondenses its hydrolysis product sol to form a gel, then dries and sinters it to produce transparent porous quartz glass or ,
The present invention relates to a method of manufacturing non-porous quartz glass.

[Prior Art] In recent years, the sol-gel method has attracted attention as a low-temperature synthesis method for quartz glass. This sol-gel method includes: 1. It can be produced at a much lower temperature (800 to 1100°C) compared to the melting method; 2. The starting material is a liquid and can be easily purified to a high degree by rectification; and 2. The gel stage. It has features such as being able to give various shapes to it. Moreover, by appropriately controlling the sintering operation of the gel in the sintering process, it is possible to produce a porous body that can be endowed with various functionalities.

In the sol-gel method, alkoxysilane S+ (OR) 4
is used as a starting material, which is hydrolyzed to form a sol, then polycondensed to form a gel, and then dried and sintered to produce the desired quartz glass. In the simplest sol-gel method, acids,
Or alkali is used alone.

The most important technical issue when manufacturing quartz glass using the sol-gel method is to prevent cracks that occur during the drying, heating, and sintering processes, and to increase the yield of the product quartz glass. . When an acid catalyst is used alone as a hydrolysis catalyst (hereinafter referred to as the acid catalyst method), the polycondensation reaction of the hydrolysis product silicic acid Sl (DH) 4 does not proceed much under these conditions, so at most four The sol exists as a low molecular weight substance, and the gel produced by gelation of the sol becomes homogeneous and strong as a whole. The gel obtained here has the characteristic that it does not easily crack during drying shrinkage, but because the pores inside the gel are small (average diameter of about 2 nm or less), the dissipation rate of water generated during sintering is slow. It has the disadvantage of being slow and prone to cracking during firing.

When an alkali catalyst is used alone as a hydrolysis catalyst (hereinafter referred to as an alkali catalyst method), the polycondensation reaction of the silicic acid product proceeds in parallel with the hydrolysis. Therefore, when the alkoxysilane concentration in the hydrolysis reaction system is high, gelation of the entire sol occurs. However, when the concentration is low, the silica fine particles grow as individual spherical silica particles, forming a dispersed system and not gelling.

When the sol-gel method is usually referred to as an alkali catalyst method, it means that the hydrolysis conditions for alkoxysilane are set such that the alkoxysilane concentration in the reaction system is high. However, even in this case, the particles constituting the sol grow into larger spherical fine particles than in the acid catalyst method, so the resulting gel is one in which these particles are weakly bonded to each other.

Therefore, this gel has relatively large pores (including many with a diameter of around 10 nm) corresponding to the large individual particles, making it difficult to crack during firing, but has the disadvantage of being susceptible to cracking during drying and shrinkage.

As mentioned above, both the acid catalyst method and the alkali catalyst method each have serious drawbacks and problems in that cracks occur during drying or firing and the yield of product quartz glass decreases. One attempt to solve this problem has been made in a two-step process, in which the alkoxysilane is completely hydrolyzed with an acid catalyst, and then an alkali is added to adjust the pH value of the system to 4 to 6 to accelerate the polycondensation reaction. A sol-gel method (hereinafter referred to as a two-step sol-gel method) has been proposed (for example, Japanese Patent Publication No. 1-24734). In this two-step sol-gel method, shrinkage of the gel is promoted to form a strong gel, so compared to the acid catalyst method, the yield during drying is improved and a large gel can be obtained. However, it is not possible to obtain a significant improvement effect in preventing cracking during firing (during non-porous formation), and it is still unsatisfactory.

As another attempt, a sol-gel method (hereinafter referred to as mixed sol-gel method, for example, 1-23420, Japanese Patent Publication No. 64-3811, Special Publication No. 64-3812) have been proposed.

The mixed sol-gel method includes a method using fine powder particles obtained by a gas phase method such as the CVD method (Japanese Patent Publication No. 1-2340), and a method using powder particles obtained by using an alkali catalyst to hydrolyze a low concentration alkoxysilane in a liquid phase. Method using a sol containing fine particles (!I [particle dispersion system])
2) is known.

However, in the method of using powder as the fine particles to be added, it is not easy to disperse the powder, especially down to the second particle.
Since it is extremely difficult to produce a homogeneous mixed sol, this method cannot be said to be optimal as an industrial implementation method. In addition, methods using sol by alkaline hydrolysis method include
Problems remain, such as that it takes an extremely long time to completely hydrolyze alkoxysilane to produce fine particles, and that it is necessary to perform a sol concentration operation to increase the concentration of fine particles.

However, in these mixed sol-gel methods, the drawback of the two-step sol-gel method, cracking during firing (making it non-porous), is solved by increasing the pore diameter by adding fine particles, and the advantage is that the cracking during drying is solved. Because it maintains a high yield,
It is also possible to manufacture larger quartz glasses.

As already detailed, in order to produce large quartz glass with a good yield using the sol-gel method, it is necessary to increase the strength of the gel to prevent cracking due to shrinkage during drying, and to increase the pore diameter of the gel and to perform firing (no firing). It is necessary to simultaneously satisfy the contradictory conditions of preventing cracking during pore formation.

The mixed sol-gel method satisfies these conditions, but because it contains relatively large fine particles (several tens of nanometers in diameter), it scatters light at the porous glass stage and is generally white and opaque. For this reason, it is difficult to use the gel's translucency to impart functions, or to put the gel into practical use as a functional member by applying its translucency itself, which is a limitation in terms of use. Although the two-step sol-gel method is superior in terms of light transmittance, it has the serious drawback of not being able to manufacture large quartz glass with a high yield as described above.

The present inventors have conducted various research experiments on the utilization of the translucency of porous quartz glass manufactured by the sol-gel method. A method of fabricating an optical waveguide by position-selectively polymerizing monomers by exposing them to ultraviolet light through a mask to close the pores, and then introducing and fixing a substance that provides a refractive index difference into the unblocked portions (Patent Application No. 1999). -78301), but in this case as well, it is an essential condition that the porous glass be transparent in the ultraviolet region. In opaque gels such as porous glass produced by the mixed sol-gel method, only the monomers near the surface of the gel are polymerized, so it is not possible to uniformly and arbitrarily close the pores. Therefore, this microfabrication technology could not be used at all, and its range of applications had to be limited.

In addition, a method that can arbitrarily control the pore distribution of porous glass is extremely useful not only for optical applications as described above, but also for applications as supports for various catalysts or immobilized enzymes. Although important, it has generally been difficult to control this pore distribution using conventional sol-gel methods.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above-mentioned problems of the prior art and provide a method for manufacturing large-sized transparent gel/quartz glass with excellent translucency with a high yield. It's about doing. Furthermore, the present invention relates to a method for controlling the pore distribution of porous glass using a simple method.

The present inventors have developed a large transparent porous glass with excellent light transmission by a simple method by improving and ameliorating the drawbacks of the sol-gel method without impairing its excellent features, or As a result of various experimental studies aimed at producing quartz glass with good yield, we found that the pore distribution of gels obtained by acid catalyst method and gels obtained by alkali catalyst method are intermediate in pore distribution. After finding out that a gel with a pore distribution is transparent and less prone to cracking during the drying process and the firing (making it non-porous) process, the inventors conducted further intensive studies and completed the present invention.

[Means for solving the problems] The present invention includes a first step of partially hydrolyzing alkoxysilane with an alkali catalyst, and a step of adding an acid catalyst to an iron solution to hydrolyze unreacted alkoxysilane in the solution. A sol is produced through a second step of decomposition and a third step of adding alkali to the sol again to promote gelation of the sol.The sol is then gelled and dried to become transparent in the ultraviolet and visible light regions. The present invention relates to a method for producing quartz glass, characterized in that porous or non-porous quartz glass is obtained through the steps of producing a gel and firing the gel.

In the present invention, alkoxysilane is defined by the general formula 5l(O
R)4 (wherein, R means a lower alkyl group) means a lower alkoxysilane represented by the following formula, and more specifically, for example, tetramethoxysilane Sl (OCH3
) a, Tetraethoxysilane SL (OC2H3)-
etc.

In the first step of hydrolyzing alkoxysilane using an alkali catalyst, the hydrolysis rate of alkoxysilane is important. This is because the mutual spacing of the fine particles produced in this step in the final sol is determined by the hydrolysis rate. If the hydrolysis weight is small, the distance between the fine particles becomes too long, resulting in a gel with the same properties as the gel produced by the acid catalyst method.
Therefore, the effects of the present invention cannot be expected. On the other hand, once the hydrolysis of the alkoxysilane is completed, the gel will have substantially the same properties as the gel produced by the alkaline catalyst method, and therefore the effects of the present invention cannot be expected. Therefore, when carrying out the present invention, it is necessary to set the hydrolysis rate within a range where the effect of the first step appears in the gel produced. As a preferable range, the hydrolysis rate in the first step is 30 to 90.
%, the effects of the present invention can be fully expected.

The hydrolysis rate of the alkoxysilane in the first step and the average particle size of the fine particles produced are determined by the concentration of the raw material alkoxysilane in water, the concentration of the alkali catalyst, the hydrolysis temperature, and the hydrolysis time (here, in the second step). By appropriately selecting and controlling the time required to start hydrolysis using an acid catalyst, etc., it is possible to continuously change the amount of water as desired (see FIGS. 1 and 2). The experimental results illustrated in Figure 1 show that by appropriately setting the hydrolysis conditions, silica glass (dry gel ) can be produced. Furthermore, the experimental results illustrated in FIG. 2 show that the pore volume and pore surface area of quartz glass (dry gel) can be controlled by controlling the hydrolysis time. Among the above-mentioned control conditions, the hydrolysis time can be controlled extremely easily and is therefore an extremely effective quality control means in industrial practice.

In addition, the concentration of alkoxysilane and the concentration of alkali catalyst,
The hydrolysis reaction rate of alkoxysilane and the polycondensation reaction rate of silicic acid, which is a hydrolysis reaction product, are also determined by the setting of the hydrolysis temperature. If these hydrolysis reaction conditions are incorrectly set, the reaction may become uncontrollable and the reaction mixture, ie, the entire sol, may turn into a gel. Therefore, it is necessary to carry out the first step by setting each concentration and temperature so as to provide a long gelation time to the extent that the operation is easy. Furthermore, if the concentration of alkoxysilane is low, the concentration of the sol will also be low, leading to increased shrinkage and deformation during drying, so care must be taken in setting this concentration within an appropriate range in actual gel production. The final sol concentration is determined by the amount of water added not only in the first step but also in the second and third steps. Ratio of numbers, [H2O
3/ The amount of water added in each step may be determined so that [alkoxide] is in the range of 20 or less, more preferably 4 or more and 10 or less.

Next, an acid catalyst is added to proceed to the second step, the purpose of which is to hydrolyze the alkoxysilane remaining in the first step under acidic conditions. The acid-catalyzed hydrolysis operation in the second step can be carried out very easily by simply adding a predetermined amount of acid solution to the reaction mixture, ie, the sol, obtained in the first step. In this step, the amount and concentration of acid are important. The amount of the acid aqueous solution to be added needs to be set so that the concentration of the final sol falls within an appropriate range, taking into account what was stated in the first step. Also, the concentration of acid is
The reaction product, i.e. the sol, is acidic, more specifically,
The concentration may be as long as it is necessary to make it acidic with a pH value of 2 or less. When the amount of acid added is small, it is necessary to set the concentration to be high, but if the concentration is too high, local gelation may occur, so an acid of about IN or less is usually appropriate.

Further, since the sol produced in this second step is stable for a long time and does not gel, it is possible to leave the sol still after this step is completed. For this reason, the second step
The interval with the third step is arbitrary as long as it is longer than the time required for complete hydrolysis.

Next, the alkali catalyst is added again to promote gelation of the entire sol and shrinkage of the gel, which is the third step.

When an alkali catalyst is added to the reaction product after the second step, gelation is promoted by the catalytic action of hydroxide ions (DH-). It is sometimes observed that the time required for gelation decreases with increasing pH value. Therefore, it is necessary to determine the pH value of the final sol by taking into consideration the time required to pour the sol into a container, and a preferable range is, for example, pH 4 to 5. The amount of alkali added to set this pH range is determined by the final sol concentration as in the first and second steps. If a high concentration of alkali is used, only a small amount is required to be added, but care must be taken because if a high concentration of alkali is rapidly added, undesirable phenomena such as local gelation will occur. The optimal concentration of alkali may vary depending on the type of alkali used, but in the case of aqueous ammonia, which is a commonly used base, it is 0.1 to I
N is mentioned as a preferable range.

The sol obtained here can be poured into a container of any shape to gel according to a known method, dried to form a dry gel, and then fired to easily form non-porous quartz glass or becomes porous quartz glass (see Figure 3). From the experimental results illustrated in FIG. 3, it is clear that the dry gel obtained by gelling and drying the sol produced by the method of the present invention can be obtained by appropriately controlling the firing temperature.
It can be seen that transparent porous glass having arbitrary pore volume and pore surface area can be obtained.

Such controllability can be said to be extremely useful when using porous quartz glass as a functional material as described above.

[Effect] At the end of the alkaline hydrolysis in the first step, a mixture of unreacted alkoxysilane and silica particles is obtained, and in the acid addition process of the second step, the unreacted alkoxysilane undergoes hydrolysis under acidic conditions. . That is, at the end of the second step, a mixed sol of a low polymer of silica and silicic acid with grain growth to some extent is obtained. The gelation of this sol is promoted by the addition of alkali in the third step. The gel produced by the gelation of the sol produced in this three-step process has a pore structure intermediate to that of alkoxysilane hydrolyzed with acid or alkali alone, so it is free from drying shrinkage, which is the advantage of both. It maintains a high yield when forming pores, and is transparent in the ultraviolet and visible light regions.

[Example] Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples.

Example 1 Tetramethoxysilane 300Cm' and methanol 15
150 Cm3 of a 0.01N ammonia aqueous solution was added to 0 cm3 of the mixed liquid, and the mixture was stirred at 0°C for 1 hour. The hydrolysis rate of tetramethoxysilane in this first stage sol (as measured by gas chromatography) was 37%.

Furthermore, 150 Cm3 of 0.05N hydrochloric acid aqueous solution was added to this sol.
was added and stirred at 0°C for 1 hour to complete the hydrolysis to obtain a second-stage sol.
A third stage sol was prepared by adding cm3 and adjusting the pH to 4.5.

This sol was poured into multiple containers with a bottom surface of 34 mm x 64 mm, covered with lids with an open area ratio of 3%, and allowed to gel. The sol was then placed in a constant temperature and humidity chamber at 40°C and 80% RH for a total of 15 days. The gel was then dried under the conditions of 40° C. and 20% RH to obtain a dry gel. This gel was highly transparent in the visible and ultraviolet regions. When the specific surface area and pore volume of the obtained dry gel were measured by N2 adsorption method, they were 68.
0 m''/g and 0.40 Cm3/g. Note that none of the samples developed cracks or cracks during the drying process.

When this dried gel was fired in an electric furnace while increasing the temperature at a rate of 100° C./h, it became non-porous quartz glass at 950° C. (non-porous temperature). The relationship between the firing temperature of the dried gel, the specific surface area of the fired silica glass, and the pore volume was measured, and the results shown in FIG. 3 were obtained. Note that none of the samples developed cracks or cracks during the firing process.

Example 2 300 cm' of tetramethoxysilane and 15 methanol
Add 60% of 0.01N ammonia aqueous solution to 0cm3 of the mixed solution.
0 cm3 was added and stirred at 0°C for 20 minutes. The hydrolysis rate of tetramethoxysilane in this first stage sol was 77%. Furthermore, 20C1llI3 of 0.5N aqueous hydrochloric acid solution was added to this sol and stirred at 0°C for 30 minutes to complete the hydrolysis to obtain the second stage sol, and 46.5cm3 of 0.15N ammonia aqueous solution was added to adjust the pH to 4. A third stage sol was prepared in which the concentration was adjusted to 3.

Using this sol, a dry gel was prepared in exactly the same manner as in Example 1. The pore distribution of the dried gel obtained was measured (N2 adsorption method) and the results shown in FIG. 1 were obtained. The specific surface area and pore volume were 710 m2/g and 0.54 cm3/g, respectively. Note that none of the samples developed cracks or cracks during the drying process.

When the obtained dried gel was fired in the same manner as in Example 1, it became non-porous quartz glass at 1030° C. (non-porous temperature). The relationship between the firing temperature of the dried gel, the specific surface area of the fired silica glass, and the pore volume was measured, and the results shown in FIG. 3 were obtained. None of the samples developed cracks or cracks during the firing process.

Example 3 In Example 1, the reaction (stirring) time in the first step was 20
A dry gel having a specific surface area of 700 m2/g and a pore volume of 0.39 cm'/g was obtained by performing the same treatment as in Example 1, except that the gel was divided into 100% by weight. In addition, the hydrolysis rate in the first stage was 23
%Met.

Moreover, the relationship between the reaction (stirring) time in the first step and the pore distribution is shown in FIG.

Example 4 In Example 1, the reaction (stirring) time of the first step was 40
A dried gel with a specific surface area of 700 m"/g and a pore volume of 0.39 cm3/g was obtained by performing the same treatment as in Example 1, except that the hydrolysis rate in the first stage was 32%.

Moreover, the relationship between the reaction (stirring) time and pore distribution in the first step is shown in FIG.

Example 5 In Example 1, the reaction (stirring) time of the first step was 80
All treatments were carried out in the same manner as in Example 1, except that the gel was heated for 1 minute, to obtain a dry gel having a specific surface area of 670 m2/g, a pore volume of 0, and 41 cm'/g. Note that the hydrolysis rate in the first stage was 40%.

Moreover, the relationship between the reaction (stirring) time in the first step and the pore distribution is shown in FIG.

Example 6 In Example 1, the reaction (stirring) time in the first step was 12
All treatments were performed in the same manner as in Example 1, except that the time was 0 minutes. Specific surface area was 650 m2/g, and pore volume was 0°39c+n3/g.
A dry gel was obtained. Note that the hydrolysis rate in the first stage was 43%. The pore distribution of the dried gel was measured and the results shown in FIG. 1 were obtained.

Moreover, the relationship between the reaction (stirring) time in the first step and the pore distribution is shown in FIG.

Comparative Example 1 (Two-step sol-gel method) Tetramethoxysilane 300cm3 and methanol 15
Add 270 cm of 0.02N hydrochloric acid aqueous solution to 0 cm3 of the mixed solution.
3 was added thereto, and the mixture was stirred at 0° C. for 60 minutes to complete hydrolysis and form a sol. Add 1 part of 0.5N ammonia aqueous solution to this sol.
A sol was prepared by adding 2.7 cm'' and adjusting the pH to 4.5.

This sol was treated in exactly the same manner as in Example 1 to produce a dry gel. The pore distribution of the obtained dry gel was measured, and the first
We obtained the results shown in the figure. The pore surface area and pore volume of the dry gel are
They were 650 m2/g and 0.34 cm3/g, respectively.

None of the samples developed cracks or cracks during the drying process.

When the obtained dried gel was fired in the same manner as in Example 1, it became non-porous quartz glass at 880° C. (non-porous temperature). The relationship between the firing temperature, the specific surface area of the fired silica glass, and the pore volume was measured, and the results shown in FIG. 3 were obtained. Note that cracks occurred in 12% of the samples during the firing process.

Comparative Example 2 (Alkali catalyst method) Tetramethoxysilane 300Cm3 and methanol 15
Add 15% of 0.01N ammonia aqueous solution to the 0cm3 mixture.
0 Cm3 was added and stirred at 0° C. for 60 minutes to form a sol.

This sol (contains unhydrolyzed tetramethoxysilane)
was treated in exactly the same manner as in Example 1 to prepare a dry gel. During the drying process, the gel broke into small pieces and no gel was obtained.

The pore distribution was measured using pieces of this dried gel, and the results shown in FIG. 1 were obtained. The specific surface area and pore volume are each 510 m
2/g and 0.66 cm3/g.

When the pieces of the dried gel were fired in the same manner as in Example 1, they became non-porous quartz glass at 1100° C. (non-porous temperature). The relationship between the firing temperature of the dried gel, the specific surface area of the fired silica glass, and the pore volume was measured, and the results shown in FIG. 3 were obtained.

[Effects of the Invention] By using the present invention, which is characterized by producing a sol in three steps, porous quartz glass and non-porous quartz glass with well-controlled pores and transparent in the ultraviolet and visible light regions can be produced. of,
It can be manufactured extremely easily, in a short period of time, and with a high yield.

The resulting transparent porous silica glass is ideal for adding functionality using light transmission, for example, and is expected to have a wide range of applications in the optoelectronics field. It also has high utility value as a carrier for the various catalysts and enzymes used.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the hydrolysis method (reaction conditions) of alkoxysilane and the pore distribution of the dried gel. FIG. 2 shows the specific surface area and pore volume of the dry gel with respect to the reaction time of the first-stage hydrolysis reaction. FIG. 3 shows the specific surface area and pore volume of fired quartz glass versus firing temperature in the dry gel firing process. 50 100 First stage hydrolysis time (-in) 2I2I Figure 1

Claims (1)

[Claims] A first step of partially hydrolyzing alkoxysilane with an alkali catalyst, a second step of adding an acid catalyst to the liquid to hydrolyze unreacted alkoxysilane in the liquid, and adding an alkali to the sol again. After producing a sol through a third step of promoting gelation of the sol, the sol is gelled and dried to produce a gel transparent in the ultraviolet and visible light regions,
A method for producing quartz glass, characterized in that porous or non-porous quartz glass is obtained by a step of then firing the gel.