JPS61186259A - Manufacture of fused silica base sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a dense fused silica sintered body.

(Prior art) In the production of fused silica sintered bodies, the firing temperature is generally 1
The temperature is 250°C or less. This is because when the temperature exceeds 1250°C, the tissue strength decreases due to the formation of cristobalite.

Therefore, for example, Japanese Patent Publication No. 49-27083 proposes an invention for suppressing the formation of cristobalite to a small amount even at a firing temperature of 1250 to 1450°C by firing for a short time.

Additionally, hydrothermal synthesis is a method for synthesizing substances and growing crystals. High-pressure steam is effective for sintering quartz, and synthesis of quartz by hydrothermal synthesis is particularly famous.

(Problems to be Solved by the Invention) However, during firing, it is not easy to make the temperature uniform inside the fired product in a short time, and rapid heating tends to cause thermal shock and cracks. Therefore,
The invention disclosed in Publication No. 7083 is limited to relatively small fired products.

This results in limited size, inefficiency, and high costs, resulting in poor industrial productivity.

(Means for Solving the Problems) The present inventor has conducted various studies in order to obtain a dense fused silica sintered body. As a result, it has been found that the steam sintering method is preferable as a method free from the above-mentioned conventional drawbacks.

Steam sintering of UO2 is already known.

In this method, a press-molded UO2 product is formed in an atmosphere of a combination of hydrogen gas and water vapor, but it is not possible to obtain a sintered body with a porosity of 2% or less. In addition, in the case of transparent quartz glass, it is said that the presence of water promotes cristobalite formation and devitrification, and the steam sintering method is
It's not f. For these reasons, the reality is that the steam sintering method is generally not used in the production of ceramics.

However, according to experiments conducted by the present inventors, fused silica, unlike stone capsule glass, can be fired with steam, and no grease 1-palite was observed to be formed. Furthermore, by casting with a limited particle size and then steam-sintering, it was possible to obtain an extremely dense fused silica sintered body.
1 In other words, the present invention uses particles with a particle size of 0μIn or less at 10W.
A method for producing a fused silica sintered body, which comprises casting and molding a mixture using fused silica powder containing 1.1% or more as an aggregate, and firing the obtained molded body in a steam atmosphere. It is.

The fused silica used in the present invention is obtained by melting silica stone and other silica raw materials, and can also be obtained from commercial products. The silica purity is preferably flow1% or higher. This is because if there are a large amount of impurities such as Na and O, it is easy to promote the conversion of crystals into crystals.

The particle size of the fused silica powder is 10% by weight or more of particles with a particle size of 10 μm or less. The maximum particle size varies depending on the use of the sintered body, but generally it is preferably 5w11 or more, 10
If F is less than 10 wt%, the sintered body will not have sufficient density.

Although the present invention uses fused silica powder as the main aggregate,
Depending on the purpose of the sintered body, oxides other than fused silica, carbides, nitrides, ferrides, fibers, etc. may be used in combination as auxiliary raw materials.

During cast molding, approximately 15 to 25% of a solvent is added to make the molten silica powder into a slurry-like form. The solvent may be alcohols if a highly purified sintered body is required, but water is generally easy to use and works well, but if the temperature is rapidly raised and fired, it tends to cause sharpness. Therefore, in the case of a gradual temperature rise, it may be directly fired without drying.

Steam may be supplied during firing by continuously supplying steam led from a boiler or the like into the firing furnace or into a container such as a crucible or pod installed in the furnace, or by enclosing steam. Good too. Although the water vapor pressure is not particularly limited, conditions of 0.01 to IO atm (preferably 0.1 to +atm) were best. 10a
If the temperature exceeds tm, the kiln must have a considerable pressure-resistant structure, and the equipment is not 1☆f. Further, the best condition was a water vapor flow rate of 1 to 0.1-50 Q/m]nCtjf or 1-10Q/m1n).

Steam can be introduced from the beginning of firing, or at 1000°C.
It is also possible to exceed the point in time.

The figure is an explanatory diagram of an apparatus for implementing the present invention, in which 1 is a firing furnace, 2 is a sheath, 3 is a product to be fired, and 4 is a steam supply pipe.

5 is a steam exhaust pipe, and 6 is a receiving shelf. The receiving shelf 6 is provided with a large number of pores to diffuse water vapor. Although not shown in the figure, the pod may be filled with bead-shaped refractory powder, and water vapor may be introduced through the gaps between the refractory powder.

In this way, the heating temperature for the product to be fired is uniform and
This has the effect of preventing deformation of the fired product. Heat - an example, but not a limitation.

The firing temperature is preferably 1050 to 1250°C. 1050
If it is less than 1250°C, the sintering effect will be insufficient, and if it exceeds 1250°C, the structure strength will decrease due to the formation of Grease 1 to Bury 1, which is not preferable.

Firing time is usually about 0.5 to 10 hours, preferably 1 to 10 hours.
5 hours, and it may be determined within this range depending on the firing temperature, the dimensions of the molded body, etc.

(Function) In the present invention, the reason why a dense fused siliceous sintered body is obtained is presumed to be due to the following reasons.

First, it is thought that this is because fused silica itself has higher reactivity with water during steam sintering than other materials.

4.The first aspect of the present invention is cast molding. In spin molding, the compound is filled while extruding the solvent in the slurry, so fine continuous pores, which are traces of the long path of water, remain in the molded product. Then, during firing, steam is supplied through the continuous pores to promote steam sintering.

On the other hand, in other than casting molding, such as press molding,
Since the pores formed by moisture, binder, etc. are independent and not continuous, the above-mentioned effect in casting molding does not occur.

Further, by limiting the amount of particles with a particle size of 10 μm or less to 10 wt% or more, the contact area of water vapor with the particles cannot be determined.

Sin and fused silica with a purity of 99.5 wt% were used as blending raw materials. This fused silica was pulverized to a maximum particle size of 2 mm or less. The fine powder was a slip obtained by wet pulverization using a ball mill, and this was used as it was for casting molding, and the dried one was used for press molding.

Cast molding is performed using a plaster mold while applying vibration.

Cast in. For press molding, CMC (carboxymethyl cellulose) was added as a binder, and molding was performed using an oil press machine at a pressure of 500 kg and 10 J. of the molded body
In both methods, the size was 1IOX40X160 mm.

Firing was carried out using a small tli S& furnace, into which steam led from a boiler was supplied for the steam sintering process. Since the steam exhaust 1-1 was provided at one end of the electric lambda furnace, the pressure inside the furnace was kept low and safety problems were eliminated. The test method for sintered bodies is as shown below.

Bulk specific gravity/talk porosity: , +15-High compressive strength based on R2205: , 11s-R220
61: Moto-J <Appearance: Visual observation (effects of the invention) According to the present invention, as is clear from the results of Examples,
A fused siliceous sintered body with significantly superior density compared to conventional methods can be obtained.

In the present invention, since sufficient density can be obtained by firing at 1250° C. or lower, a fused siliceous sintered body with excellent structural strength can be obtained without the formation of cristobalite.

In addition, the present invention does not require particularly high pressure in the furnace and can use an existing firing furnace, so it can be carried out without any problems from the standpoint of equipment or safe operation.

The fused siliceous sintered body obtained by the present invention has an extremely wide range of uses due to its dense property, which makes it impermeable to liquids and gases, as well as its heat resistance and chemical stability, which are the characteristics of fused silica. For example, it is used in various parts and lining materials in the steel industry, cement industry, ceramic industry, electrical industry, aircraft industry, space industry, etc., as well as medical equipment, cooking utensils, various containers, laboratory equipment, incinerators, nuclear reactors, etc. can.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an example of a device implementing the present invention. ] Firing furnace 4 Steam supply pipe 2 Saya 5 Steam exhaust pipe 3 Product to be fired
6. Fence patent applicant Harima Refractory Brick Co., Ltd. = 10- Procedural amendment (voluntary)

Claims (2)

[Claims] (1) A fused silica product characterized by casting and molding a mixture whose main aggregate is fused silica powder containing 10 wt% or more of particles with a particle size of 10 μm or less, and firing the resulting molded body in a steam atmosphere. A method for producing a sintered body. (2) The method according to claim 1, wherein the firing temperature is 1050 to 1250°C.