JPH0735256B2 - Quartz glass manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a method for producing quartz glass, in particular, spherical silica fine particles are concentrated and settled in a silica sol solution to form a close-packed structure and then heated. Prevents cracking, foaming, and opacity that occur in the steps of gelling, drying, and sintering vitrification.
The present invention relates to a method for producing quartz glass at low cost and with good yield by the sol-gel method.

(Prior Art) High-purity synthetic quartz glass has recently begun to be used for optical and optical communication applications. Regarding the production method of this synthetic quartz, a volatile silicon compound is added to a oxyhydrogen flame in a flame A high-temperature synthesis method that decomposes or oxidatively decomposes silica in a plasma flame to accumulate silica on the target and melts and makes it transparent, and a gel is made from an alcohol solution of metal alkoxide or an inorganic silicate such as water glass. Then, there is known a low temperature synthesis method called a sol-gel method in which this is fired to produce transparent silica glass.

However, this high-temperature synthesis method requires a large amount of energy for the combustion heat of the oxyhydrogen flame, the electric power for plasma generation, etc., and since it is necessary to raise the temperature to nearly 2,000 ° C. during plastic forming, this is also a great deal. Since a high temperature process that requires energy is required, the fixed ratio of the dopant added during silica growth for controlling the refractive index is extremely low, and the fixed dopant also remains in the high temperature history process during plastic forming. It has the disadvantages of being often volatilized and being inferior in economic efficiency because it takes a long time to obtain a product.

For this low temperature synthesis method, A) alkoxysilane is hydrolyzed in an alcohol solvent in the presence of an acid catalyst such as hydrochloric acid or a basic catalyst such as ammonia, and heated to form a wet gel. A method in which the material is dried, then sintered and made into transparent glass (see Japanese Patent Publication No. 59-9497), B) 1.
An acidic or basic gelling catalyst is added to a solution in which fine silica particles of μm or less are suspended in a dispersion medium such as water to gelate the wet gel, and this is dried, sintered, or transparent glass. Or a method of volatilizing the dispersion medium in the fine silica particle suspension described above to obtain a dried silica product, which is then sintered and vitrified (Journal of American.
Ceramic Society, 66 , No. 10, p. 683, 1983), C) Alkoxysilanes are hydrolyzed in the presence of an acid catalyst or a basic catalyst to form a uniform sol.
A solution is prepared by suspending fine silica particles of μm or less in a dispersion medium such as water and mixing them, or by dispersing the powdery fine silica in the above hydrolysis sol solution to contain fine silica particles. A method of preparing a silica sol solution, adjusting the pH and temperature of the solution to gel it into a wet gel, and drying, sintering, and vitrifying it (see JP-A-61-91033). Is known, and according to this, even at the highest temperature, it is set to 1,000 to 1,500 ° C., so that energy can be largely saved compared to the above-mentioned high temperature synthesis method, and addition of dopants can be performed with various elements. The alkoxide of is added to the alkoxysilane for co-hydrolysis, or its oxide fine particles may be added, and this dopant can be immobilized at 100% yield, and the advantage is that it does not volatilize. Given by It is further in this case molded if ask performed gelation in a vessel of desired shape,
Although it is economically advantageous because it does not require processing operations such as cutting and cutting, this method A) is large in size because cracks or foaming phenomena easily occur during gel drying and sintering. However, it is difficult to obtain a large glass body due to cracks in the drying process, and the transparent vitrification temperature is 1,500 ° C or higher. Since the method of C) has the disadvantage that high temperature is required, and that the product sometimes becomes opaque due to occasional foaming during transparent vitrification, the reproducibility is poor and the yield of transparent glass bodies is high. It has the drawback of being difficult to manufacture well.

(Structure of the Invention) The present invention relates to a method for producing a transparent glass body with good reproducibility by a sol-gel method which solves such disadvantages, which is obtained by hydrolyzing an alkoxysilane in the presence of a basic catalyst. The residual basic catalyst was distilled off from the solution containing the spherical silica fine particles having a uniform and constant spherical shape obtained as described above to adjust the pH of the solution to 8 or less, and then the spherical silica fine particles were allowed to settle, and the supernatant was removed to obtain spherical particles. In the step of obtaining silica fine particles, a solution obtained by distilling alcohol and water from a liquid obtained by hydrolyzing an alkoxysilane in the presence of an acidic catalyst to dilute the silica and increasing the silica concentration is added to the spherical silica fine particles under ice cooling to adjust the pH to 2 Step of adjusting to ~ 6, stirring and mixing to redisperse the silica fine particles, the silica fine particles were allowed to settle as a close-packed structure from this solution under ice cooling, and the supernatant was removed. The wet gel obtained by gelation Chi heated, dried, sintering, step of vitrification and is characterized in that it consists of and.

That is, as a result of examining the method C) of the sol-gel method, the present inventors have found that the wet gel obtained by this method has fine silica particles present therein having a low density, weak mechanical strength, and sintering. During vitrification, the dehydration reaction of silanol on the surface of the dried gel, which is a porous body, causes the by-product water to be trapped in the glass and causes a foaming phenomenon due to the volume expansion of water vapor in the subsequent heating process. Since the silica formed from the silica sol surrounding the silica fine particle group of sinter forms vitrified glass at a temperature lower than that of the particle group, it was confirmed that this would remain scattered as an opaque portion in the glass body, and these disadvantages were confirmed. As a result of various studies on methods of solving the problem, the silica fine particles obtained by hydrolysis with a base catalyst such as ammonia have pores with a relatively large diameter. It has sintered, with flue to volatilization of by-product steam during vitrification. Therefore, it has been found that when the number density is small, the reinforcing effect is deteriorated and the vaporization of the above-mentioned by-product steam is hindered, which causes foaming.

On the other hand, if the number density of silica fine particles is small, it causes an opaque part when the silica sol part surrounding it is gelled,
It has been found that when the number density increases, the glass body has sharp sintering and vitrification temperatures, is easily vitrified at a low temperature, and is uniform and transparent without clouding. Therefore, it is preferable to make the number density of silica fine particles as high as possible before gelation.

For that purpose, it is preferable that these granular silica particles form a close-packed structure. Generally, a structure in which spheres of the same size are most densely stacked is referred to as a close-packed structure, but since the spherical silica fine particles of the present invention are composed of a uniform monodisperse system of the same size, it is possible to concentrate and precipitate the spherical spheres. It was confirmed that the silica fine particles had a close-packed structure.

In the present invention, since the spherical silica fine particles form a close-packed structure in the silica sol solution, the volumetric shrinkage in the steps of wet gel → dry gel → sintering → vitrification in the conventional sol solution is increased by conventional method. By reducing the ratio of 85% or more to 60% or less, the shrinkage strain caused by it is less likely to cause cracks. It is easy to volatilize the above-mentioned by-product water vapor, etc. It is possible to obtain a transparent glass body with no reproducibility and high yield.

Such monodisperse spherical silica fine particles having a constant particle size can be obtained by the method described in Journal of Colloid and Interface Science 2662 (1968) and Japanese Patent Application No. 61-221569. According to this, if the alkoxysilane is hydrolyzed at a constant temperature with ammonia, an organic solvent, or an aqueous system, the particle size can be controlled in the range of 0.01 to 2.0 μm by changing the addition amount and temperature of the alkoxysilane. That is, when the amount of ammonia is increased, the particle size is increased, and when it is decreased, the particle size is decreased. Water has a maximum particle size, which varies depending on the amount. The amount of solvent is large, small is large, small is large, and high is small. By selecting the above conditions, spherical silica fine particles having a uniform particle size can be obtained. The particle size is preferably 0.1 to 2.0 μm. If it is less than 0.1 μm, it takes time and is not preferable.

The alkoxysilane used in the present invention is represented by the formula (RO) ₄ Si, and when R has a carbon number of 4 or more, the sol layer obtained from the R has increased hydrophobicity and is separated into two layers. Since it is considered to be an alkyl group having 1 to 4 carbon atoms because it cannot be obtained, this includes tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, methoxytriethoxysilane, dimethoxydiethoxysilane, Examples include trimethoxyethoxysilane, but hydrolysis reactivity,
In terms of availability and price, tetramethoxysilane,
Tetraethoxysilane is preferred.

When this quartz glass is used for optical communication, it is necessary to add a dopant to it to adjust its refractive index. Therefore, when a dopant is added in the method of the present invention, phosphorus, titanium, aluminum, boron, germanium, zirconium, alkoxy compounds such as neodymium, for example PO (OR) ₃ , Ti (OR) ₄ ,
Al (OR) ₃ , B (OR) ₃ , Ge (OR) ₄ , Zr (OR) ₄ , Nd (OR) ₃
(R is an alkyl group having 1 to 4 carbon atoms) may be added to the alkoxysilane in a predetermined amount. According to this method, since the method of the present invention does not particularly require high temperature, the dopant does not evaporate, and the dopant is substantially 100%. The advantage of being able to dope with a fixed rate of

Therefore, assuming that the fine particles are formed in the above-mentioned step, the silica fine particles precipitated in the third step have a high number density of the close-packed structure, and the wet gel obtained by heating this to form a gel It was found that the glass body obtained by drying and sintering does not crack or foam, and it was confirmed that a transparent glass body can be obtained with good reproducibility and high yield. The present invention has been completed.

Hereinafter, the method of the present invention will be described in more detail according to this order of steps.

The first step in the method of the present invention is a step of obtaining a monodispersed silica fine particle suspension having a uniform particle size by hydrolysis of alkoxysilane. Ammonia water is used as a basic catalyst that is added when the alkoxysilane or a metal alkoxide as a dopant added thereto as needed is hydrolyzed, and this hydrolysis uses ammonia water as a basic catalyst. A large amount of a mixed solution of 0.1 to 10 mol and 2 to 20 mol of water and an organic solvent compatible with alkoxysilane, particularly 5 to 100 mol of an alcohol having a carbon number of 4 or less such as methanol, ethanol, propanol and butanol. While stirring at 0 to 50 ° C under atmospheric pressure or pressure, 1 mol of the above-mentioned alkoxysilane may be added dropwise together with a solvent if necessary, but this stirring aggregates the generated silica particles to aggregate. It is advisable to stir vigorously using a stirrer with high shear to avoid body buildup. By this hydrolysis, the alkoxysilane is made into a suspension containing spherical silica fine particles, but when this solution distills off the ammonia water remaining here by distillation, the pH drops, and when this pH value is 8 or higher, If so, the acidic hydrolysis homogeneous sol added in the second step to be described later is instantly gelled, so that it is required to be 8 or less. In addition, in order to adjust the pH to 8 or less, water and ammonia as a basic catalyst may be distilled off from the suspension. According to this, the SiO ₂ concentration of the suspension gradually increases. When the content exceeds 50% by weight, silica aggregates or gels easily, so if the pH does not fall below 8 even when the SiO ₂ content exceeds 50% by weight, add water to the system and continue the distillation. Is good.

The silica thus obtained is spherical and can be obtained as a monodisperse solution having a uniform and constant particle size. If this is allowed to stand, the silica fine particles will settle, but small particles with a particle size of 0.2 μm or less will not settle in a short time, so this may be settled by centrifugal sedimentation, etc. After this settling, if the supernatant liquid is removed, the silica fine particles Is obtained.

The second step of the present invention is a step of adding a sol prepared by acidic hydrolysis of alkoxysilane to the silica fine particles obtained in the first step and redispersing the silica fine particles in the sol. Acid hydrolysis of 1 × 10
^-4 to 10 ^-1 mol Mixture of acidic catalyst such as inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid or organic acid such as acetic acid and 2 to 20 mol of water and organic solvent such as alcohol added as needed While stirring the liquid under atmospheric pressure or pressure at 0 to 50 ° C., 1 mol of the alkoxysilane or a metal alkoxide as a dopant added thereto is added dropwise with an organic solvent such as an alcohol added as necessary. The hydrolyzed sol solution may be distilled off water, alcohol, etc. to increase the silica concentration, and then added to the silica fine particles obtained in the first step. The water, alcohol, etc. may be distilled off by a normal single evaporation operation or a distillation operation, but according to this, the acid is distilled off together with water and alcohol, and the pH of the sol gradually increases with this operation to become neutral. However, the closer it is to neutrality, the easier it becomes to gel by heating. Therefore, it is preferable to carry out reduced pressure single evaporation at a temperature as low as possible.

The sol solution having an increased silica concentration is then added to the silica fine particles obtained in the above-mentioned first step and mixed by stirring, which may have a pH value in the range of 2 to 6. Therefore, an inorganic acid such as hydrochloric acid or sulfuric acid or an alkaline substance such as aqueous ammonia may be appropriately added as a pH adjusting agent. Further, since this mixing and stirring is preferably carried out at a low temperature in order to prevent gelation, it is required to be carried out under ice cooling in order to keep the temperature at 0 to 20 ° C. The silica fine particles obtained in the first step by this mixing and stirring are mixed with the silica sol liquid added in this step,
The silica fine particles are redispersed in the silica sol liquid.

In the third step of the present invention, the silica fine particle-containing sol liquid obtained in the second step is gelled to obtain a wet gel, which is dried and sintered into glass. This wet gel is obtained in the second step. It can be obtained by precipitating silica fine particles redistributed in the obtained silica sol liquid under ice cooling, removing the supernatant liquid, and then gelating at elevated temperature. This settling is performed under ice cooling in order to prevent gelation of the silica fine particles before forming the closest packed structure by settling, but this temperature may be set to 0 to 20 ° C. . Further, the precipitation of the silica fine particles may be natural precipitation or centrifugal precipitation. This gelation may be carried out by heating. The higher the temperature, the faster the gelation, but if the temperature is too high, drying may proceed at the same time and cracks may occur, so it is preferable to set it to 30 to 60 ° C. .

The wet gel thus obtained is then dried and sintered to be glass, and this drying causes cracks when it is rapidly dried, so the rate of evaporation of water and residual alcohol contained in the wet gel is reduced. It is better to hold it down and to do it gradually, so this requires an aperture ratio of 0.1-5.
% Of initial wet gel at a temperature of 50-70 ° C in a container that is
It is recommended to dry to ~ 35% by weight. In addition, this sintering was performed by drying the dried gel obtained by this drying from room temperature at 1,100
It may be carried out by gradually raising the temperature to 100 ° C.
Desorption of surface adsorbed water at ℃, oxidation of residual organic matter in degassed atmosphere of argon gas at 300 to 500 ℃, decarbonization, 500 to 1,1
In order to prevent cracking due to thermal strain during dehydration bonding of surface silanol groups at 00 ° C, the heating rate is set to 10 to 10
The temperature may be 0 ° C./hour, but in order to improve the heat conduction in the substrate and prevent cracking, it is preferable to set this atmosphere as a helium gas atmosphere. In order to remove the OH group in the sintered body, sintering at 700 to 900 ° C. is performed in the presence of a Cl agent such as Cl ₂ and SOCl ₂ to perform deOH treatment, and subsequently 900 Sintering at ˜1,100 ° C. is preferably an oxidative dechlorination treatment in the presence of an oxidizing agent such as O ₂ gas.

This vitrification converts the sintered gel thus obtained into 1,10
The temperature may be raised stepwise from 0 to 1,400 ° C.
Closes pores at 1,100-1,200 ℃, 1,200-1,400 ℃
It may be made transparent glass.

The method for producing quartz glass according to the method of the present invention is carried out by treating the alkoxysilane in the above-mentioned first to third steps. According to this method, the number density of the spherical silica fine particles in the silica sol liquid is increased to obtain the closest packing. Quartz glass obtained by drying, sintering, and vitrifying the wet gel obtained by this temperature rise gelation forming a structure has a small volume shrinkage ratio of 60% or less during the process from the wet gel, and therefore cracks. Since it is obtained as a transparent material without foaming or foaming, it has an industrial advantage that quartz glass can be produced inexpensively and with high yield.

Next, examples of the present invention will be given. The volumetric shrinkage ratio in the examples is obtained by the following equation.

Example 1 A mixed solution of 321 g of water, 4,950 ml of absolute ethanol and 297 ml of ammonia water (NH ₃ concentration: 28% by weight) was placed in a glass flask equipped with a dropping funnel, a thermometer, and a turbine stirring blade, and the temperature was adjusted.
While maintaining vigorous stirring at 10 ° C, 926 g of tetraethoxysilane was added dropwise to this, and after stirring for 2 hours to hydrolyze, pure water was added intermittently to this, water, ethanol, and ammonia were added under reduced pressure. Distill off to make a silica suspension having a pH of 6.5 and a concentration of 30%, and then centrifuge this at 4,000 rpm for 20 minutes to precipitate silica fine particles, and then remove the supernatant liquid to obtain a particle size of 0.2. Uniform spherical silica microparticles with a size of μm were made.

On the other hand, 260 g of tetraethoxysilane and 10 parts of absolute ethanol
Keep the mixed solution consisting of 3 ml at 25 ℃, add 90 g of 0.02 N hydrochloric acid water to this with vigorous stirring, and stir for 2 hours to hydrolyze, then heat this to 40 to 50 ℃ under reduced pressure. Then, water and ethanol are distilled off, and the silica concentration is 30% by weight.
The silica sol liquid is prepared, and this is added to the silica fine particles obtained above, and the silica fine particles are redispersed by vigorous stirring, and then ammonia water is added while vigorously stirring under ice cooling to adjust the pH to 5. Prepared, put this in a Teflon container of 160 × 160 × 50 mm, let stand for one day under ice cooling to settle the silica fine particles, and then remove the supernatant with a dropper. When an electron micrograph was taken using an analyzer JCXA733 (trade name of JEOL Ltd.), it was confirmed that the spherical silica fine particles had a close-packed structure as shown in FIG. It was

Then, put this in a thermostat with a lid having a 1 mm hole with an opening ratio of 0.3% and heat it to 30 ° C to gel it, and make 10 gel bodies of the same size. The gel body
It was transferred to a constant temperature bath of 60 ° C. and dried at that temperature for 16 days, but the gel body did not have one crack during this time. Next, the 10 dried gel bodies were placed in a muffle furnace, heated from room temperature to 300 ° C at a heating rate of 30 ° C / hour, heated at this temperature for 5 hours, and then decarbonized at 300 ° C. To 700 ° C at a heating rate of 30 ° C / hour, and heating at this temperature for 2 hours to dehydrate and condense in the state where the pores are open. The temperature was raised to 30 ° C. at a heating rate of 30 ° C./hour, and this temperature was maintained for 10 hours to close the pores. Then from 1100 ℃ at a heating rate of 30 ℃ / hour
When heated to 1300 ° C and heated at this temperature for 5 hours to vitrify, 10 transparent quartz glass bodies with a size of 120 × 120 × 10 mm were obtained. From this wet gel, glass bodies were obtained. The volumetric shrinkage rate was 58%.

Example 2 Hydrolysis of tetraethoxysilane in the presence of a basic catalyst was performed in the same manner as in Example 1 except that 926 g of tetraethoxysilane in Example 1 was changed to a mixture of 880 g of tetraethoxysilane and 31 g of trimethyl phosphate. By performing sedimentation and removal of the supernatant, fine silica particles doped with phosphorus having an average particle size of 0.2 μm were prepared.

Also, instead of 260 g of tetraethoxysilane in Example 1, a mixture of 247 g of tetraethoxysilane and 8.8 g of trimethyl phosphate [(CH ₃ ) O] ₃ PO was used and treated in the same manner as in Example 1 to give tetra. Hydrolysis of ethoxysilane in the presence of an acidic catalyst, removal of water and ethanol were carried out to prepare a silica sol liquid doped with phosphorus and having a silica concentration of 30% by weight.

Next, the silica fine particles and the silica sol solution were mixed in the same manner as in Example 1, redispersed and settled, the supernatant was removed, and the temperature was gelated to form a wet gel, which was dried, sintered, and glass. As a result, the volumetric shrinkage rate was 58%, and in this case as well, 10 pieces of quartz glass doped with phosphorus were obtained without cracking, and the phosphorus fixation rate at this time was almost 100%.
Met.

Comparative Example 1 A mixture of 209 g of water, 3,228 ml of absolute ethanol and 194 ml of 28% by weight ammonia water was placed in the glass flask used in Example 1, and 604 g of tetraethoxysilane was added dropwise thereto.
After stirring for 2 hours to hydrolyze, water, ethanol, and ammonia were distilled off under reduced pressure while adding pure water intermittently to the solution until the pH was adjusted to 6.5, and the average particle size was 0.16 μm.
A silica fine particle suspension having a silica concentration of 30% by weight was prepared.

On the other hand, tetraethoxysilane 494g, absolute ethanol 196m
The mixture (1) was placed in the glass flask used in Example 1, 171 g of 0.02N hydrochloric acid was added, and the mixture was stirred for 2 hours for hydrolysis to produce a silica sol solution, which was mixed with the above silica fine particle suspension. After that, add ammonia water to adjust the pH.
The same electron micrograph as that of the example was taken for the one adjusted to 5.0, and it was found that the spherical silica fine particles were scattered as shown in FIG. 2 and did not have a close-packed structure. I understood.

Then, put it in a 250 x 250 x 50 mm Teflon container, and attach it to a lid with a 1 mm hole with an opening ratio of 0.3% 30
Wet gel body of the same size by gelling in a constant temperature bath at ℃ 10
10 pieces of this gel were transferred to a constant temperature bath at 60 ° C., and dried at that temperature for 16 days to give a dry gel. As a result, 2 out of 10 pieces had cracks.

Next, the remaining 8 gel bodies were sintered and vitrified in the same manner as in Example 1, and 4 of them were 12
It became a transparent glass body of 0 × 120 × 10 mm, but two of the remaining four were opaque, one was cracked, and one contained foam. At this time, the wet gel changed to a glass body. The volumetric shrinkage was 89%.

[Brief description of drawings]

FIG. 1 is an electron micrograph of the spherical silica fine particles before gelation obtained in Example 1, and FIG. 2 is an electron micrograph of the spherical silica fine particles obtained in the comparative example.

Claims (4)

[Claims] 1. A method in which the residual basic catalyst is removed by distillation from a solution containing spherical silica fine particles obtained by hydrolyzing an alkoxysilane in the presence of a basic catalyst to bring the pH of the solution to 8 or less, A step of settling the spherical silica fine particles and removing the supernatant to obtain spherical silica fine particles; 2) distilling alcohol and water from the liquid obtained by hydrolysis of the spherical silica fine particles in the presence of an acidic catalyst to obtain alkoxysilane. , A step of adding a solution having a high silica concentration under ice cooling, adjusting PH to 2 to 6 and stirring and mixing to redisperse the silica fine particles, 3) precipitating spherical silica fine particles from this solution under ice cooling, A process for producing quartz glass, which comprises the steps of drying, sintering, and vitrifying a wet gel obtained by removing the supernatant liquid and then raising the temperature to gel. 2. The method for producing quartz glass according to claim 1, wherein spherical silica fine particles are made into a close-packed structure and then heated to cause gelation. 3. The method for producing quartz glass according to claim 1 or 2, wherein the volumetric shrinkage in the step of vitrifying the wet gel into quartz glass is 60% or less. 4. The silica glass according to claim 1, 2 or 3, wherein the alkoxysilane is doped by adding a metal alkoxide other than silicon or a metal oxyalkoxide. Production method.