JPS61247660A - Manufacture of porous silica 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 porous sintered silica body. Specifically, it is a method in which a porous sintered silica body is produced by molding a powder made of monodispersed amorphous silica spherical particles and then firing it under specific conditions.

(Prior Art) Silica sintered bodies are used as high-temperature materials because they have excellent chemical stability and heat resistance, and also have a very small coefficient of thermal expansion. Conventionally, the manufacturing method was
As seen in Publication No. 9-27083, the particle size is adjusted so as to obtain a dense sintered body, and this is molded.
It is fired in a temperature range of 250 to 1450°C and in a relatively short time.

(Problem to be solved by the invention) Porous sintered silica is expected to be in demand for various filters, catalyst supports, etc. used at high temperatures, but conventional methods have It was not possible to obtain a sintered body. In other words, it is known that a method for obtaining a porous member is to integrate monodisperse spherical particles through point contact, but when sintering is attempted, the particles melt and close the pores, making it impossible to obtain a porous material. . Furthermore, at a firing temperature of 1250°C or higher, the strength of the particles themselves decreases due to the formation of cristobalite.

The present invention aims to solve the above-mentioned problems in manufacturing a porous sintered body using monodispersed amorphous silica spherical particles.

(Means for Solving the Problems) The present inventor has been conducting research on firing amorphous silica for many years. We have also continued research into porous materials that can be used at high temperatures. As a result, it was found that application of the steam sintering method is preferable.

Steam sintering of UO□ is already known.

In this method, a press-molded UO2 product is subjected to an atmosphere of a combination of hydrogen gas and water vapor. Furthermore, in the case of transparent quartz glass, it is said that the presence of water promotes the formation of grease into 1-palite and causes devitrification, and the reality is that steam sintering is not generally used in the production of ceramics.

However, according to experiments conducted by the present inventors, the formation of cristobalite was not observed in amorphous silica during steam calcination. Moreover, in the case of a porous member, water vapor reaches the interstitial space through the pores, promoting sintering.

The present invention has been completed based on the following two findings. The present invention is a method for producing a porous sintered silica body, which comprises molding a powder made of monodisperse amorphous silica spherical particles with a particle size of 0.05 to 10 μm, and then firing the powder in a steam atmosphere. .

The amorphous silica used in the present invention is monodisperse spherical particles. Monodisperse here does not mean that the particle diameters are strictly uniform, but also includes particles that are approximately the same size. A polydisperse material fills the pores of the sintered body, does not promote steam sintering, and loses its porous properties.

Further, the spherical particles may have a length ratio of 1 to 1.3, and are not necessarily limited to true spheres. Particle size is 0.05~], 0μ, preferably 0.2
~2μ. If it is less than 0505μ, the porosity of the sintered body is /
During firing, water vapor does not enter sufficiently, and the efficiency of steam firing is lost. When it exceeds 10μ, the contact area between particles decreases, and the strength of the sintered body decreases.

Various methods for producing monodispersed amorphous silica spherical particles have been proposed, and the present invention is not particularly limited thereto. Here, as examples, the sol-gel method and the thermal spray method used in the examples described later will be described. In this method, ethyl silica 1 is synthesized through hydrolysis and dehydration condensation, such as W.

6.62 (1968) J, is a well-known technique in the art. First, water, ethyl alcohol, and ethyl silica 1- are mixed to create a uniform solution. Water is what hydrolyzes ethyl silicate, and ethyl alcohol is its solvent. Thereafter, when left at room temperature, hydrolysis proceeds, and amorphous spherical particles are obtained in an alkaline system such as ammonia and at a low concentration. In this process, ethyl silicate undergoes hydrolysis and dehydration condensation in the next reaction.

Sj (C2H50)4+48. O-+Si (OR)
4+4C2It, OH(↑)Si(011)4→SjO
□+21120 (↑) On the other hand, the thermal spraying method, for example,
Publication No. 7-95877.

As disclosed in JP-A-58-1.4.561.3, this is a method in which silica particles are passed through a high-temperature flame and melted to obtain spherical particles due to surface tension.

In the present invention, shaping can be performed by methods such as a casting method, a press method, and an extrusion method. In the casting method, a solvent is added to create a slurry state, and then the material is cast into a mold. The type of solvent may be alcohols if a highly purified sintered body is required, but water is generally preferred as it is easily available and economical. In the press method, extrusion method, etc., it has been found that paraffin wax, CMC (carpodium methyl cellulose), etc. are optionally preferable. In this method, for example, as shown in Japanese Patent Publication No. 48-33248, a molded body is obtained by placing the clay in a clay container and applying electricity to utilize electrophoresis. This is because the material powder used in the present invention is monodisperse, and the molded body obtained by cast molding has low strength.

Thin plate shapes are not easy to handle. In addition, press methods, extrusion methods, and the like tend to inhibit sintering between particles due to the addition of a binder. On the other hand, in electrophoresis, N
Even in the form of a plate, a molded product with high strength can be obtained without using a binder. Moreover, the molding time is short compared to methods such as casting, pressing, and extrusion. This is probably because the particles of the powder used in the present invention are monodisperse and have an extremely small particle size.

The firing temperature is usually 500 to 1250°C, preferably 7
00~1'' and 50°C. If the temperature is less than 500°C, the sintering result will be insufficient, and if it exceeds 1250°C, vitrification and formation of cristobalite 1- will become significant, reducing the strength of the sintered body.

The firing time is, for example, about 0.5 to 10 hours.

Water vapor may be supplied during firing by being introduced from a boiler or the like and sealed. Although the water vapor pressure is not particularly limited, it is 0.001-1 Oat (preferably 0
．． 05~latm) conditions were the best. 1 oat
If it exceeds m, the kiln must have a considerable pressure-resistant structure, which is undesirable. Also, the water vapor flow rate is 0
．． 1-50Q/min (preferably 0, 5-100
/ min ) conditions were the best. Steam may be introduced from the beginning of firing or at a point at which the temperature exceeds 1000°C. Further, after performing normal firing in air, further firing may be performed in a steam atmosphere.

FIG. 1 is an explanatory diagram of an apparatus for carrying out the present invention, in which 1 is a firing furnace, 2 is a sheath, 3 is a product to be fired, 4 is a steam supply pipe,
5 is a steam exhaust pipe, and 6 is a saucer. The saucer 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 refractories 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,
This has the effect of preventing deformation of the product to be fired. The heat source is a heater such as a gas burner such as heavy oil or propane, or a silicon carbide heating element. The device shown in the figure is an example and is not limited thereto.

The porous silica sintered body obtained by the present invention takes advantage of its heat resistance and fine pores to be used as a filter for gas or liquid.
Can be widely used as catalyst carriers, insulation tiles, etc.

The reason for this is, as mentioned in Section 2 below, that amorphous silica itself is easily sintered by steam.

Next, in the present invention, since a porous body made of monodisperse spherical particles is fired, water vapor penetrates into the inside of the molded body during firing, promoting steam sintering.

On the other hand, when the same amorphous silica spherical particles are used and subjected to normal firing in air, almost no sintering occurs, and a phenomenon was even observed in which the molded product once collapsed during firing.

Furthermore, polydisperse particles whose particle size is adjusted to obtain close packing, rather than monodisperse spherical particles, have a small sintering effect because water vapor permeates less during firing.

(Example) Examples of the present invention are shown in the table, but the present invention is not limited thereto.

After adjusting the particle size of the monodisperse non-luminated silica stone used in Examples 1 to 6 and Comparative Examples 1 and 2, the particles were supplied into a flame generated from an oxyhydrogen burner. Comparative examples 3 and 4
The amorphous silica pulverized particles used were wet-pulverized in a ball mill and then dried, and because they were obtained by pulverization, the particles were rounded and polydisperse.

In casting, water was added to form a slurry, and then the material was cast into a fused silica crucible. In press molding, a binder was added and molding was performed at a pressure of 200 kg/cJ.

In the electric bed T11 method, as shown in Fig. 2, a material 7 made into a slurry by adding water is placed in a container 8, and a copper pipe as a cathode 9 and an anode surrounding it are placed in the container 8. Insert a large @ made pipe as 10. Cathode 9
The material of the anode 10 is not limited to copper as long as it has the function of an electrode. Although water was used here as the solvent for forming the slurry, a higher alcohol or the like may be used in combination if a highly purified sintered body is required. The surface of the anode 100 is preferably coated with a mold release material such as cloth 2 paper to make it easier to take out the molded body 11. In addition, in the figure, the hollow molded body 1] is transferred to the cellar 1, but in order to obtain a plate-shaped molded body, it is necessary to take measures such as making the anode 10 into a plate shape. . The voltage is preferably 5 to 15 ov, but in the examples, it was within the range of 20 to 30 volts.

In an example using this electrophoresis method, steam led from a boiler was supplied into the molded body before firing.

Since the electric furnace has an exhaust port, the pressure inside the furnace is kept low.
There were no safety issues. The test method for sintered bodies is as shown below.

Compressive strength of the molded product; after molding and drying, JIS
-42205.

Compressive strength of sintered body; after firing 1. Measured based on Tl5-R2206.

Porosity: The porosity of the sintered body is Tl5-R22
Measurements were made based on 05.

JP-A-1-2476GO (4) (Effects) According to the present invention, a porous silica sintered body with high strength can be obtained. As shown in the comparative example, in the conventional sintering method, when monodisperse amorphous silica spherical particles are used, almost no sintering occurs.

Even with steam firing, polydisperse particles lose their porous properties and have a small sintering effect. In contrast, the sintered bodies obtained in the examples of the present invention are porous, and their strength is at least three times greater than that of the comparative examples.

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

[Brief explanation of drawings]

The figures show explanatory diagrams of examples of apparatus for carrying out the present invention, with FIG. 1 being a cross-sectional view of a firing apparatus, and FIG. 2 being a cross-sectional view of a molding apparatus using an electrophoresis method. 1; firing furnace 7; material 2;
Saya 8; Container 3; Product to be fired 9; Cathode 4;
Steam supply pipe 10; Anode 5; Steam exhaust pipe 11; Molded body 6; Saucer Patent applicant: Harima Refractory Brick Co., Ltd. ■! -\' Procedural amendment (voluntary) April 19, 1985 1, Indication of case 1985 Patent Application No. 5?2 F0 No. 2
Title of the invention Method for manufacturing porous silica sintered body 3 Person making the amendment 4 All drawings subject to amendment

Claims (3)

[Claims] (1) A method for producing a porous sintered silica body, which comprises molding a powder consisting of monodisperse amorphous silica spherical particles with a particle size of 0.05 to 10 μm, and then firing the powder in a steam atmosphere. (2) The method according to claim 1, wherein the firing temperature is 500 to 1250°C. (3) The method according to claim 1, wherein the molding is performed by electrophoresis.