JP2734083B2 - Method for producing transparent quartz glass molded body - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a transparent quartz glass molded body.
More specifically, the present invention relates to a method for industrially advantageously producing a transparent quartz glass molded article using a spherical silica aggregate.

[Prior Art] Conventionally, methods for obtaining a transparent quartz glass molded article from spherical silica particles have been studied. The typical method is Sacks
(Journal of American Ceramic Society, Vol. 67, No.
8, pp. 526-537 (1984)) and Tseng et al. (Journal of Ma
terial Science, 21, p. 3615-3624 (1986)).

Sacks et al. And Tseng et al. Argued that, in order to obtain a transparent quartz glass molded body, a sharp pore distribution without coarse pores was necessary when spherical silica particles were filled, and in order to achieve this, It is recognized that a green compact in which monodisperse spherical silica particles are closest packed is necessary, and as a molding method, a slurry in which monodisperse spherical silica particles of 0.5 μm or less are well dispersed is allowed to stand for a long time to obtain particles. (Hereinafter referred to as "sedimentation molding method"). According to this method, the particles settle without agglomeration, and thus a green compact having a sharp pore distribution consisting of only pores generated between the particles with few pores due to the packing of the aggregates is obtained. The molded body is fired to produce a transparent quartz glass. The method of Sacks et al. Shows that it is important to eliminate coarse pores larger than 100 nm and sharpen the pore distribution.

[Problems to be Solved by the Invention] However, in the sedimentation molding method adopted by Sacks et al., It takes several weeks or more to obtain a molded body because submicron fine particles are sedimented by gravity, and the molded body is dried. However, there is a problem that the molded body is broken in the process of forming, and only a small piece can be obtained. Therefore, improvement of a molding method of a green molded body is desired.

[Means for Solving the Problems] As a result of intensive studies to overcome such problems of the prior art, the present inventors have spray-dried a slurry in which specific spherical silica particles are dispersed in water or an organic solvent. The present inventors have found that a green molded body without coarse pores can be obtained without employing a gravity sedimentation method by pressure-molding the obtained spherical silica aggregate, and have reached the present invention.

That is, the present invention sprays a slurry obtained by dispersing spherical silica particles having an average particle size of 0.05 to 1.5 μm and a particle size distribution of 1.5 or less in standard deviation (σ) in water or an organic solvent. A method for producing a transparent quartz glass molded body, which comprises subjecting a spherical aggregate obtained by drying to pressure molding, and firing the molded body.

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

As the silica particles used in the present invention, spherical particles having good filling properties at the time of aggregation are used. Further, in order to bake the spherical particles into quartz glass, the particles need to be amorphous.

Further, in the present invention, the average particle size in the range of 0.05 to 1.5 μm among the spherical silica particles, more preferably the average particle size
Those having a standard deviation (σ) of 1.5 or less, more preferably 1.2 or less in the range of 0.1 to 1.0 μm are used. This is the average particle size
When particles smaller than 0.05 μm are used, the surface area of the whole particles becomes large, and the particle dispersibility of the slurry is reduced, so that good spherical aggregates cannot be obtained. Therefore, high-density compacts cannot be obtained. When the diameter is larger than 1.5 μm, coarse pores of 100 nm or more are formed between the particles after molding, and the sintering and densification do not proceed sufficiently because the sinterability of the particles themselves is reduced, so that transparent quartz glass Is not obtained. The standard deviation (σ) of the particle size distribution is 1.
The use of particles larger than 5 is not preferable because the filling of the particles and the pores formed between the particles are not uniform, and the sintering and densification do not sufficiently proceed. The standard deviation (σ) is preferably set to 1.2 or less from the viewpoint of improving the packing density of the particles.

The method for producing the above-mentioned specific spherical silica particles is not particularly limited as long as spherical silica particles having the above-mentioned particle size and particle size distribution are obtained, but for example, it can be produced by the following method. it can.

In general, silica particles can be obtained by hydrolyzing and polymerizing an alkoxide of silicon in the presence of a basic catalyst. To obtain specific spherical silica particles in the present invention, for example, the following conditions are used.

Water 0.2 to 20 mol, preferably 1.0 to 10 mol, basic catalyst 0.1
~ 10 mol, preferably 0.2-5 mol, more preferably 0.2-2 mol
is dissolved in a reaction solvent to obtain 1 reaction solution. 0-60
C., preferably 5 to 40 ° C., more preferably 10 to 40 ° C., at a temperature of 0.01 to 0.01 wt.
攪拌 1 mol /, preferably 0.02-0.5 mol /, with stirring, the whole amount is added at a time and the hydrolysis / polymerization reaction is carried out.
The reaction is completed in 1 to 5 hours, and spherical silica particles satisfying the particle size and the particle size distribution in the present invention can be obtained.

The reaction solvent used includes alcohols such as methanol, ethanol, propanol, butanol and pentanol. Examples of the silicon alkoxide include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetrapentoxysilane, and the like. Examples of the basic catalyst include ammonia, amine, and caustic.

Next, in the present invention, the above-mentioned spherical silica particles are dispersed in water or an organic solvent to obtain a silica particle-dispersed slurry. Additives such as a binder and a dispersant are used as needed for the silica particle dispersion slurry.

The dispersion medium may be any water or organic solvent, but a polar dispersion medium having a hydroxyl group such as water or alcohol is preferably used. The spherical silica particles are added thereto and sufficiently dispersed by an ultrasonic disperser or the like to obtain a silica particle dispersed slurry.

The silica concentration in the slurry is not particularly limited, but is usually 5 to 50% by weight, preferably 10 to 40% by weight, based on the dispersion medium. If the slurry concentration is too high, the viscosity becomes too high to spray, whereas if the slurry concentration is too low, a large amount of slurry needs to be used, and the production efficiency tends to deteriorate.

Next, the silica particle dispersion slurry prepared as described above is spray-dried with a spray drier. As a spray dryer, a nozzle type, a disk type, and a two-fluid type are generally used, and any type may be used.

The spherical aggregate obtained by spray drying is formed into a green compact by pressure molding. As a pressure molding method, a hydraulic press, a CIP (cold isostatic press) and the like are generally used, and any type may be used. By molding under such conditions, 10
A green compact having a sharp pore distribution without coarse pores of 0 nm or more can be obtained.

The molded body thus obtained is usually 1000 to 1500 ° C,
Preferably, it is fired at a temperature of 1100 to 1300 ° C. to remove voids to obtain a transparent quartz glass molded body. At this time, baking is usually performed in an air atmosphere, but baking may be performed in a He atmosphere or under reduced pressure to facilitate the removal of voids, or may be performed after reducing the pressure to a He atmosphere. Further, a pressure molding method such as a hot press method may be used.

According to the method of the present invention, a green molded body without coarse pores can be obtained with good yield in a simple and short time, and by firing the molded body, a transparent silica glass can be produced with good yield. The obtained transparent silica glass is industrially advantageously used as a crucible for melting semiconductors and the like.

[Examples] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist.

The average particle size () and the standard deviation value (σ) are determined according to the following equations.

Further, the void volume in the dried compact was measured by a mercury intrusion method, the density of the particles was measured by a pycnometer method, and the particle filling rate in the dried compact was calculated from the following equation.

Here, V _pore (cm ³ / g) is a void volume per unit weight of a molded article measured by a mercury intrusion method.

ρ _particle is the density of silica particles, and the density of all silica particles used in the present invention was 2.2 g / cm ³ .

Example 1 A solution obtained by dissolving and mixing 200 g of distilled water and 272 g of 25% ammonia water in 3330 g of ethanol purified by distillation was put into a jacketed reactor, and thereafter, water was passed through the jacket while stirring at 800 rpm to reduce the temperature inside the reactor to 20. C.

Next, 208 g of distilled and purified tetraethoxysilane was adjusted to 20 ° C., and then the whole amount was added at once to a reactor kept at 20 ° C. The reaction was completed in 5 hours, and the average particle size in the reaction solution was
Uniform particles having a diameter of 0.40 μm and a standard deviation (σ) of 1.1 were found. The reaction solution was pressurized with a 0.45 μm membrane filter to obtain an overcake. 150 this cake
After drying at ℃, it was pulverized with a jet mill to obtain spherical silica powder. 400 g of spherical silica particles having an average particle diameter of 0.4 μm and a standard deviation value (σ) of 1.1 thus obtained were mixed with distilled water 600 g.
g, a slurry obtained by dispersing with an ultrasonic disperser for 30 minutes, 40 g of a 10 wt% aqueous solution of polyvinyl alcohol was added, and the mixture was further dispersed with an ultrasonic disperser for 30 minutes to obtain a silica particle-dispersed slurry. The slurry was supplied to a rotary disk type spray dryer at a rate of 1.5 / hr, and spray-dried under the conditions of a disk rotation speed of 20,000 rpm and a hot air inlet temperature of 250 ° C. to obtain an aggregate having a particle size of 5 to 100 μm.

A part of the aggregate was used as a sample for a scanning electron microscope (SEM). FIG. 1 shows an example of the obtained SEM photograph. From FIG. 1, it is clear that the above-mentioned aggregates are spherical particles that are closest packed with spherical silica as primary particles. After pre-forming this aggregate by hydraulic press, 2t by rubber press
By applying a pressure of / cm ² , a pellet-shaped green compact having a diameter of 2 cm and a thickness of 0.23 cm was obtained. No pores of 100 nm or more were present in the molded body, and the particle packing ratio was 62 vol%. The molded body was heated at 50 ° C./hr to 600 ° C., kept at 600 ° C. for 2 hours, subsequently heated at 60 ° C./hr to 1200 ° C., and kept at 1200 ° C. for 5 hours to obtain a 1.7 cm diameter and a thickness of 1.7 cm. A 0.2 cm clear quartz glass pellet was obtained.

Comparative Example 1 15 g of spherical silica particles having an average particle diameter of 0.4 μm and a standard deviation (σ) of 1.1 were added to 500 g of distilled water, and further adjusted to pH = 10 with aqueous ammonia, and then dispersed with an ultrasonic disperser for 30 minutes. As a result, a silica particle dispersion slurry was obtained. The slurry has an inner diameter of 6c.
The container was transferred to a container having a length of 4 m and allowed to stand for 4 weeks to form a sediment. After removing the liquid, the molded body was dried at room temperature. In the process, the molded body was broken, and only small pieces of about 1 cm square and about 0.4 cm thick were obtained.

Comparative Example 2 A pellet-shaped compact having a diameter of 2 cm and a thickness of 0.22 cm was obtained in the same manner as in Example 1 except that spherical silica particles having an average particle size of 0.54 μm and a standard deviation value (σ) of 1.6 were used. I got 30% or more of pores of 100 nm or more were present in the molded body, and the particle filling rate was 61.6 vol%. The compact was fired under the same conditions as in Example 1, but pores remained in the sintered body and remained opaque.

Comparative Example 3 The silica particle-dispersed slurry obtained in Example 1 was evaporated to dryness, and the resulting mass was thoroughly ground with a pestle to obtain silica powder. This powder was molded under the same conditions as those for forming the aggregate in Example 1, to obtain a green pellet-shaped green body having a diameter of 2 cm and a thickness of 0.2 cm. 15% or more of pores of 100 nm or more are present in the molded body, and the particle filling rate is 61.8 vol%.
Met. The molded body was fired under the same conditions as in Example 1, but pores remained in the sintered body and remained opaque.

[Effects of the Invention] According to the method of the present invention, a green molded body without coarse pores can be obtained with good yield by simple and short-time molding, and therefore, a transparent silica glass can be produced with good yield by firing the molded body. And its industrial value is great.

[Brief description of the drawings]

FIG. 1 shows an example of a scanning electron micrograph (SEM) photograph showing the particle structure of the aggregate in Example 1, and the magnification is 3000 times.

Claims (1)

(57) [Claims] A slurry obtained by dispersing spherical silica particles having an average particle diameter of 0.05 to 1.5 μm and a particle diameter distribution of 1.5 or less in standard deviation (σ) in water or an organic solvent is spray-dried. A method for producing a transparent quartz glass molded body, which comprises subjecting a spherical aggregate obtained by pressure molding to pressure molding, and then firing the molded body.