JPH06166564A - Sintered compact of fused silica and its production - Google Patents

Abstract

PURPOSE:To provide a sintered fused silica having dense texture with little open pores and exhibiting high flexural strength. CONSTITUTION:The objective sintered fused silica having a density of >=2.05g/cm<3> and a four-point flexural strength (JIS R 1601) of 9-10kg/mm<2> is composed of amorphous silica having a purity of >=99%. It can be produced through 3 steps comprising the 1st step of preparing a slurry composed mainly of fused silica powder having an average particle diameter of <=2mum and a purity of >=99%, a 2nd step of casting the slurry with a gypsum mold having an average pore diameter of 1-3.3mum and a 3rd step of baking the formed article in air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fused siliceous sintered body and a method for producing the same. More specifically, the present invention relates to a dense fused siliceous sintered body that can be suitably used as a refractory material such as a glass melting tank kiln and a metal melting furnace, an outer tube material for a heater, a lining material for a jet device of a rocket, and a manufacturing method thereof.

[0002]

Fused silica is essentially amorphous (glassy).
And has a very small coefficient of thermal expansion (0.5 × 10 ⁻⁶ /
C.). The material is about 10
When it is heated at a high temperature near 00 ° C. for a long time, it has a characteristic that it changes into a crystalline phase such as cristobalite or tridymite. These crystal phases have an extremely large coefficient of thermal expansion as compared with glassy materials, and if they are mixed in the sintered body, the strength is lowered. In order to control the amount of the crystalline phase, it is necessary to carry out sintering in consideration of the firing temperature and time.

Generally, in the production of a fused siliceous sintered body, the firing temperature is 1250 ° C. or lower, but it is difficult to obtain a dense fused siliceous sintered body under the above temperature conditions, and the density is low by the conventional method. Only the sintered body is obtained.

For example, Japanese Examined Patent Publication No. 49-27083 discloses a method of firing at 1250 to 145 by firing in a short time.
There is described a method for producing a fused siliceous sintered body which can reduce the rate of formation of the crystalline phase even at a firing temperature of 0 ° C.

In the above method, in consideration of the formation rate of the number of crystal nuclei and its growth rate, the temperature is rapidly raised to a predetermined firing temperature and the firing temperature is also 1250 ° C. or higher, while the firing time is short. It is characterized in that a fused siliceous sintered body with suppressed crystal formation can be obtained by setting the time. In addition, special fair 1
In Japanese Patent Laid-Open No. 54301, 1050 to 1050 are set in a steam atmosphere.
A method for producing a dense fused siliceous sintered body at a firing temperature of 1250 ° C. is described.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
According to the manufacturing method described in Japanese Patent Publication No. 083, the product having a large volume and a complicated shape is unevenly baked or deformed, and sometimes the temperature uniformity in the product at the time of heating becomes poor, which causes cracks and the volume is small. It has a problem that it can be applied only to a product having a simple shape.

In addition, although the manufacturing method described in Japanese Patent Publication No. 1-54301 can produce a dense fused siliceous sintered body, the bending strength test result shows that it is half that of the conventional sintered body in air. It is about 3 to 4 kg / mm ² and has a problem in terms of characteristics.

The present invention has been made to solve the above problems, and an object thereof is to provide an amorphous and dense fused siliceous sintered body and a method for producing the same.

[0009]

The present invention has a purity of 99%.
It is made of the above amorphous silica and has a density of 2.05 g /
cm ³ or more, 4-point bending strength (JIS R 1601) is 9 to 10 kg / mm ² , and a fused siliceous sintered body characterized by having an average particle size of 2 μm or less and a purity of 99% or more. The first step to prepare powder-based mud, 1-
The fused siliceous calcination, which comprises a second step of casting by using a molding die having an average pore diameter of 3.3 μm, and a third step of calcination of the molding obtained in the above step in the atmosphere. Concerning the manufacturing method of the union.

[0010]

The function of the fused siliceous sintered body of the present invention is 2.0.
Since it is as high as 5 g / cm ³ or more and has high bending strength, it can be used for applications requiring the above-mentioned properties.

In the present invention, a molded product is produced by using a gypsum mold having a purity of 99% or more and an average particle size of 2 μm or less and a pore size adjusted by a mud casting method. It is possible to produce a high-density molded body,
A dense fused siliceous sintered body can be obtained by firing this molded body at 1210-1250 ° C.

[0012]

EXAMPLE The fused siliceous sintered body of the present invention has a purity of 99.
%, It has a very small coefficient of thermal expansion (0.5 × 10 ⁻⁶ / ° C.) and is excellent in thermal shock resistance.

The density of the sintered body is 2.05 g / c.
Since it is m ³ or more, preferably 2.10 to 2.19 g / cm ³ , the porosity is low, and the dense sintered body has improved water permeability and water absorption. The four-point bending strength (JIS R 1601) of the sintered body is 9 to 10 kg / mm.
^It is as high as ² , which is a characteristic that has not been obtained in the past, and can be used in applications where the above characteristics are required.

The siliceous sintered body can have a plate-like shape with a volume of about 20 to 600 cc.

Further, it is possible to obtain a complicated shape such as a ring shape having an outer diameter of 400 mm and a thickness of 25 mm.

From the above, the siliceous sintered body can be used as, for example, a glass melting tank kiln, a refractory material such as a metal melting furnace, an outer tube material of a heater, a lining material of a jet device of a rocket, and the like.

Next, a method for producing the fused siliceous sintered body of the present invention will be described.

The method for producing the fused siliceous sintered body of the present invention was obtained by considering basically the relationship between the size of the powder particles and the sinterability derived from the sintering theory of the ceramic powder. It is a thing. However, in the case of vitreous materials, unlike powder made of crystals, the sintering mechanism is said to be mainly the mass transfer associated with the softening phenomenon at high temperature rather than atomic diffusion. Even in this case, the particle size of the powder affects the sinterability, and the smaller the particle size, the higher the sinterability. In practice, a useful particle size needs to be found, involving the conditions of the subsequent molding process. For this reason, the present invention employs the following manufacturing method.

The method for producing the fused siliceous sintered body of the present invention comprises the first step of preparing a mud powder containing an amorphous fused silica powder having an average particle size of 2 μm or less and a purity of 99% or more as a main component. A second step of casting using a molding die having an average pore diameter of 1 to 3.3 μm composed of gypsum,
It comprises a third step of firing the molded body obtained in the above step in the atmosphere.

First, in the first step, a slurry containing amorphous fused silica powder having an average particle size of 2 μm or less and a purity of 99% as a main component is prepared.

The fused silica powder used in the present invention is an amorphous powder obtained by crushing fused silica glass mainly using silica sand as a raw material. Whether or not the powder is completely amorphous is determined by fixing the crystal by X-ray diffraction and not having a diffraction peak (however, the diffraction angle 2θ =
There is a broad peak around 21.7 °).
The powder preferably has an average particle size of 2 μm or less, and more preferably 1 to 2 μm in order to enhance the sinterability at low temperature.
In the powder having the average particle diameter of 1 to 2 μm, the average pore diameter is 1 to
The yield at the time of performing cast molding using 3.3 μm gypsum is improved. Further, powders having an average particle size of 1 μm or less tend to cause molding cracks.

Regarding the purity of the fused silica powder, the purity is preferably 99% or more, and a pure one containing no other impurities or inorganic binder is preferable. Impurities such as Al, Na, and K are not preferable because they easily promote crystallization of cristobalite, tridymite, and the like during sintering.

Further, it is preferable that the shape of the particles is almost spherical and not acicular.

Next, a slurry is prepared using the above powder.

For mud, 20 to 26% (wt%, the same applies hereinafter) of water as a dispersion medium is added to the silica powder,
If necessary, it is prepared by adding a binder system such as a dispersant and a binder.

Fused silica powder can be obtained by wet-milling with water. Since silica powder originally has high reactivity with water, OH groups are incorporated into the powder surface in the pulverizing step, and OH groups are introduced. Since it forms a layer of and has an electric double layer by itself, it is possible to obtain fluid mud without a dispersant (peptizer).

However, in the above-mentioned mud, powder tends to settle, so that it is preferable to carry out wet mixing using a rotary pot mill for 4 to 8 hours to prepare mud, and then quickly perform cast molding. . Further, when the pulverized fused silica powder is dried, the effect of forming the OH group layer on the silica surface is weakened and the solid-liquid mixing property becomes poor. In this case, wet mixing is preferably performed for 12 to 16 hours.

Examples of the dispersant include polycarboxylic acid ammonium salt, and the mixing ratio thereof is 0.3 to 2.0% with respect to the fused silica powder, and further 0.3.
.About.0.5% is preferable.

Examples of the binder include acrylic acid emulsion type, and the mixing ratio thereof is 1.0 to 3.0%, more preferably 1.5 to 2.0% based on the fused silica powder. Is preferred.

After preparing the mud as described above, the mud is composed of gypsum and the particle size is 1 to 3.3 μm.
Casting is performed using a molding die having an average pore diameter of.

As described above, the average pore size of the molding tool made of gypsum is generally 1 to 3.3 μm from the viewpoint of easy availability, gypsum strength and durability.

The mold used was a mold for forming a 15 × 15 × 100 square bar. The mold can be manufactured by a usual method using gypsum powder which is usually commercially available. The cast-molding method may be a usual cast-molding method in which the slurry prepared by the above-mentioned method is poured into a gypsum mold so that the gypsum absorbs moisture and the like to produce a molded body having a desired shape. In the present invention, by adopting cast molding, the contact resistance between the powder particles becomes almost equal in the presence of the liquid medium, the smooth movement of the fused silica powder particles becomes possible, and the dense packing becomes possible. A compact having a density can be obtained. Especially when fine powder is used, the above effect is remarkable.

In molding with a die press, it is difficult to increase the compact density because the contact resistance of the powder particles during pressing is large and the movement of the powder particles in the mold is not smooth.

Due to the cast molding, the density is 1.6.
A molded body of 6 to 1.88 g / cm ³ is obtained.

The molded body obtained by the above-mentioned cast molding is fired in the atmosphere.

The calcination is usually carried out using, for example, an electric furnace or a gas furnace, and in order to make the effect of heat uniform during the calcination, coarse particles (about 300 μm to 1 mm) obtained by pulverizing the fused silica powder that has been heated once are crushed. It is preferable to cover the molded body with and perform uniform heating.

The firing conditions when using an electric furnace are 1240 to 1250 in order to prevent crystallization and obtain a dense sintered body.
It is preferable to carry out at 3 ° C. for 3 to 4 hours.

Further, the firing conditions in the case of using a gas furnace are also to prevent crystallization and to obtain a dense sintered body.
It is preferable to carry out at 1200 to 1210 ° C. for 3 to 4 hours.

In the present invention, a dense sintered body can be obtained.
Fine silica particles with an average particle size of 2 μm or less that are easy to sinter are used, and the contact resistance between particles can be reduced by the casting method to increase the density of the molded body. It is considered that this was due to the addition of factors that could improve the sinterability, such as the fact that the coordination number could be increased.

By the above sintering, amorphous silica having a purity of 99% or more is formed, and its density is 2.05 g / cm ³ or more, preferably 2.10 to 2.19 g / cm ³ , and 4-point bending strength is 9 to. A fused siliceous sinter of 10 kg / mm ² is obtained.

In the above-described production method of the present invention, the amorphous silica powder having a high SiO ₂ purity of 99% or more and an average particle diameter of 2 μm or less is used, and the pore diameter is determined by the cast casting method. Since a molded body is manufactured by the adjusted gypsum mold, a high density molded body of 1.66 to 1.88 g / cm ³ can be manufactured.
Amorphous at a temperature of 10 to 1250 ° C. and a bending strength of 9
It is as high as -10 kg / mm ² , mechanical properties do not change due to temperature changes, and a dense siliceous sintered body having a density of 2.05 g / cm ³ or more can be obtained.

Next, the present invention will be described in more detail based on examples, but the present invention is not limited to such examples.

[Examples 1 to 5 and Comparative Example 1] As a blending raw material, fused silica powder having a SiO ₂ purity of 99.6% and 99.9% was used. Each average particle size is 5 μm
And 12 μm.

This was adjusted to a value of 2 μm or less in average particle diameter shown in Table 1 by wet pot mill grinding using a polyethylene container and zirconia balls. The obtained powder is heated and dried at 100 ° C. for 6 hours and then crushed to obtain a fine powder of fused silica, which is 30% of the fused silica powder.
Water, 0.5% dispersant and 2.0% binder were added, mixed and stirred to make mud. As the dispersant, a commercially available polycarboxylic acid ammonium salt (Cerna D-305 manufactured by Chukyo Yushi Co., Ltd.) was used, and as the binder, a polyacrylic acid emulsion type (manufactured by Mitsui Toatsu Chemicals, Inc.) was used. WA-310) was used. For the cast molding, a gypsum mold having a range of pore diameters and an average pore diameter shown in Table 1 was adopted, and solid casting was performed by pouring.
The molded product obtained by the cast molding is 15 × 15 ×
It has a shape of 100 square rods. Table 1 shows the density of the molded body. The density of the molded body was measured by the Archimedes method using kerosene.

Then, using a small electric furnace or gas furnace, as shown in FIG. 1, the molded body was set so as to cover the periphery thereof with pulverized powder of fused silica which had been heat treated, and the temperature and the temperature shown in Table 1 were set. It was fired under the firing conditions. In addition, in Table 1,
Other than those described as a gas furnace, firing was performed using an electric furnace.

As a comparative example, a commercially available fused silica powder was used, and an example of a fired body obtained in the same manner as in Example 1 is shown in Table 1.

The average particle size of the fused silica powder is
Centrifugal sedimentation type particle size analyzer SA- manufactured by Shimadzu Corporation
The average pore diameter of gypsum was determined by CP3 and was determined using a mercury porosimeter. For the density measurement of the sintered body, the sintered body was immersed in boiling distilled water for about 3 hours, left overnight for cooling, the weight in water was determined, then the wet weight was determined, and then the dry treatment was performed. After that, the dry weight was obtained.

Then, the sintered body density and water absorption were calculated from the above results. Furthermore, the 4-point bending strength is JIS R 1
Measurement was performed according to 601 and the value was obtained.

[0049]

[Table 1] From Table 1, it is understood that the finer the raw material powder used is, in general, a denser sintered body can be obtained, and in the case of the powder having a high purity, the sinterability is high. That is, comparing Examples 1 and 2, the particle diameters are 0.6 and 1.13 μm.
However, the sintering conditions are the same and almost the same sintered density is obtained. When firing at 1210 ° C. using a gas furnace, a sintering density almost the same as that obtained by firing at 1250 ° C. using an electric furnace can be obtained. Further, using a mold made of gypsum having a small average pore size tends to give a sintered compact having a high density. The true density of silica is 2.2
Since it is 1 g / cm ³ , the relative density of the fused siliceous sintered body of the present invention is 95% or more, and depending on the selection of sintering conditions, a relative density of 99% or more can be obtained. In this case, the porosity is 1% or less. The water absorption rate was 0.02% or less, and the existing pores were closed pores.

The bending strength of the dense sintered body of the present invention was 9 to 10 kg / mm ² , and the strength was improved as compared with the conventional one.

[0051]

EFFECTS OF THE INVENTION The fused siliceous sinter of the present invention is a dense sinter and has a high bending strength, so that it can be used in applications requiring the above-mentioned properties, and can be used in a wider range of applications than before. .

According to the method for producing a fused siliceous sintered body of the present invention, it is possible to obtain a fused siliceous sintered body which is dense, has high bending strength, and whose mechanical properties hardly change even when the temperature changes. Moreover, as the manufacturing equipment, commercially available equipment can be used, and the manufacturing equipment can be manufactured inexpensively and easily.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a firing step of the present invention.

[Explanation of symbols]

 3 molded body

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazuo Shimoda 1-2-9 Hachiman-cho, Higashi-Kurume City, Tokyo Optec Diddy Melco Laboratory Ltd. (72) Inventor Mitsuyuki Imaizumi Hachiman, Higashi-Kurume City, Tokyo 1-2-9 Machi Incorporated Optec Diddy Melco Laboratory (72) Inventor Hiroshi Nakajo 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation Material Device Laboratory (72) Inventor Yoshio Takada Amagasaki City 8-1, 1-1 Tsukaguchihonmachi Mitsubishi Electric Corporation Material Device Research Center

Claims (2)

[Claims] 1. A non-crystalline silica having a purity of 99% or more and a density of 2.05 g / cm ³ or more and a four-point bending strength (JIS R 1601) of 9 to 10 kg / mm ^2. And a fused siliceous sintered body. 2. A first step of preparing a slurry containing amorphous fused silica powder having an average particle diameter of 2 μm or less and a purity of 99% or more as a main component, wherein the slurry is composed of gypsum.
2. The method according to claim 1, comprising a second step of casting by using a mold having an average pore diameter of 3.3 μm, and a third step of firing the molded body obtained in the step in the atmosphere. Manufacturing method of fused siliceous sintered body.