JPS5843351B2 - Method for producing silicon carbide hollow granules - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for producing hollow granules using a silicon carbide substance as a shell.

The hollow granules according to the present invention have excellent heat resistance, chemical resistance, and thermal shock resistance, and are lightweight, so they can be advantageously used as fillers for various refractory materials.

When producing the hollow granules according to the present invention, a siliceous material containing silica as a main component is employed as the shell material.

These include kaolin clay, kaolin shale, kaolin coal slag, silica gel, silica anhydride, synthetic silica-alumina materials, and mixtures thereof.

Such substances are used in the form of powder, usually finely pulverized particles of 74 microns or less.

To show an example of manufacturing hollow granules according to the present invention, first, granules (or spherical bodies) of a desired particle size made of a material with a low melting point are produced.
Prepare.

Any material may be used as long as it has a lower melting point than the raw material for the shell, but it is usually preferable to use an organic material, especially foamed polystyrene balls because they are easily available.

Next, using this low-melting-point granular material (particle size is usually about 2 to 20 mm) as a core material, powder of the raw material for the shell is applied to the surface of the core material to an appropriate thickness (approximately 0.5 mm or more). Cover and form balls.

This ball-forming can be carried out by a conventional method, for example, by adding water, a polymeric adhesive solution, ethyl silicate, a lignin aqueous solution, or other suitable binder to the shell material powder as a binder. The balls with the above-mentioned low melting point are used as a core material and are made into balls using a dish-shaped granulator.

Next, the granules thus obtained are dried at a temperature that does not deform the core material, usually 100°C or less, and after the shell has sufficiently dried, the granules are dried at a temperature that is higher than the temperature at which the core material shrinks or decomposes. to obtain granules which are hollow inside and whose shells consist of caking of siliceous powder.

When foamed polystyrene balls are used as the core material, the heating temperature is preferably 120° C. or higher, preferably 2000° C. or higher.

Next, the hollow granules are fired to solidify or initially sinter to an extent that the granules do not break.

The firing temperature is 500°C or higher, usually 500 to 800°C.

The hollow body thus obtained has a porous shell, and the interior thereof can be impregnated with liquid through the voids of the shell.

In the present invention, after filling the hollow part of the hollow granules thus obtained with a liquid carbon material, the granules are heated and fired to convert the silica content in the shell into silicon carbide. .

In this case, the liquid carbon material may be any material as long as it can form carbon through thermal decomposition, but preferably water-soluble liquid phenol resins and solutions prepared by arbitrarily diluting the resin with water are used. .

In order to efficiently impregnate the inside of a hollow body with liquid carbon material, after placing the hollow granules in a sealed container, the inside of the container is depressurized.
Preferably, the pressure is reduced to below 1X10-'l-- to degas the hollow space, and then the liquid carbon material is injected into the container.

In this way, granules filled with liquid carbon material are obtained.

By heating and firing the granules, the silica content in the shell is converted to silicon carbide. In this case, the relationship between the treatment temperature and the change in the granules is as follows.

That is, by heating at 100°C or less, volatile components such as moisture and solvent contained in the liquid carbon material are removed, and 100°C or less is removed.
The carbon material is concentrated in the shell by heating at a temperature of ~300°C.

After this concentration, the carbon material is carbonized in the shell when it is slowly heated to a temperature of 5000C or higher, usually 500 to 1000C, in a vacuum or an inert gas atmosphere.

at higher temperatures in vacuum or inert gas atmosphere, e.g.
When heated to a high temperature of 1,400° C. or higher, preferably 1,400° C. or higher, the silica content in the shell reacts with the carbon content generated as described above to form silicon carbide in the shell.

As described above, the grain size 3 in which the shell is made of silicon carbide material is obtained.
Hollow particles of about 20 mrIL can be obtained.

The silicon carbide hollow particles according to the present invention have a small apparent specific gravity, are lightweight, and have excellent heat resistance, chemical resistance, and thermal shock resistance, as well as thermal conductivity and abrasion resistance. It can be applied to various fields by taking advantage of its unique characteristics.

A preferred application of the hollow granules of the present invention is as a filler for refractory materials, particularly as a filler for silicon carbide bricks.By filling this material into a refractory material, the weight of the refractory material can be reduced,
Moreover, the amount of refractory material raw materials can be saved.

The strength and apparent baboon cap of the hollow granules according to the present invention can be controlled within a desired range by adjusting the shell thickness and degree of sintering.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Purified kaolin clay (hydrated halloysite) was pulverized in advance to 200 mesh (7.4 microns) or less,
This was used as a shell raw material and water was used as a binder to cover and granulate foamed polystyrene beads.

Next, the shell is dried at 30°C to prevent cracks from forming in the shell, and the core material, styrene foam, is shrunk at 200°C, and then heated at 500°C for 10 minutes to make the inside hollow. The skin was hardened.

The obtained hollow granules were placed in a vacuum container and degassed at 1 x 10-1 Torr for 30 minutes, followed by a 50% aqueous solution of a resol type water-soluble phenolic resin prepared in advance (1 part phenol resin and 1 part water). The phenol resin aqueous solution was poured into this container to encapsulate the phenol resin aqueous solution inside the hollow granules.

Next, the granules were taken out of the container, heated to 1000°C to remove some of the moisture and volatile matter, and further heated to 150°C to harden the phenolic resin while condensing it into a shell. The phenol resin is heated at a rate of temperature increase of .degree. C./Tun to 600.degree. C. while removing volatile components, and heat-treated at this temperature for 30 minutes to carbonize the phenol resin.

Next, the heating rate was 6°C/min in a nitrogen atmosphere for 15 min.
The temperature was raised to 00°C, heat treated for 1 hour, and then cooled to room temperature.

The obtained silicon carbide hollow particles have an apparent specific gravity of 0.7 to 1.
．． 0.24 hour water absorption 6-8%, single grain strength 3-6'K
g, and the particle size is 7-91nr/L1 shell thickness 0.5-
It was 1.1 minutes.

Example 2 60 parts by weight of the kaolin clay (dried at 150°C) used in Example 1 was thoroughly mixed with 40 parts by weight of silicic anhydride (commercially available special grade reagent) dried at 150°C, and this was mixed to form a coating material. Then, Styrofoam beads were coated and granulated using water as a binder.

Next, it was dried at 30°C for 12 hours, and the expanded polystyrene beads as the core material were further shrunk at 200°C, and then heat treated at 500°C for 10 minutes to hollow out the inside and solidify the shell.

The obtained hollow granules were placed in a vacuum container.
After degassing for 30 minutes at 10-1 Torr, 6
A 0% aqueous solution (a mixture of 60 parts by weight of resin and 40 parts by weight of water) was poured into this container to encapsulate this phenolic resin inside the hollow granules.

Next, the granules were taken out of the container, dried at 70°C for 24 hours to remove moisture and some volatile components, and then dried at 70°C for 24 hours.
While curing the phenolic resin at ℃, it was concentrated in the shell.

Next, this granular material is placed on a magnetic boat and inserted into an electric furnace, and the inside of the furnace is replaced with nitrogen gas, and while the inside of the furnace is maintained at about 500 Torr with a vacuum pump, it is heated from room temperature to 6.
After raising the temperature to 00° C. at a rate of 1.5° C./IIuR, the resin was heat-treated at 6000° C. for 30 minutes to carbonize the resin in the shell, cooled to room temperature, and then taken out.

Next, with the hollow granules still placed on the magnetic boat, the hollow granules are buried in the fine powder using commercially available carbon black powder, and then inserted into the electric furnace. did.

Next, after purging the inside of the furnace with nitrogen gas, the pressure was reduced to approximately 500 Torr and the temperature was increased from room temperature to 1550°C at 5°C.
The temperature was raised at a rate of /-, and after a high temperature heat treatment at 1550°C for 30 minutes, it was cooled to room temperature.

The obtained silicon carbide hollow particles have a particle size of 6 to 8 mm, a shell thickness of 0.5 to 0.7 mu, and an apparent specific gravity of 0.7 to 0.7 mu.
0.9, and the single grain strength was 1 to 3k19.

Further, as a result of X-ray diffraction, the main component of the shell was β-8iC, and mullite and α-A1203 were also detected.

Example 3 The kaolin of Example 1 was coated and granulated onto a Styrofoam piece in the same manner as in Example 1, and further hollowed out in the same manner as in Example 1. The kaolin was then placed in a vacuum container and IX 10-
'Degassed with Torr for 30 minutes.

Next, a 30% aqueous solution of a resol type phenolic resin prepared in advance (a mixture of 30 parts by weight of resin and 70 parts by weight of water) was poured into this container to encapsulate this phenolic resin inside the hollow granules.

Next, the resin was concentrated into a shell under the same conditions as in Example 2, and further carbonized under the same conditions as in Example 2, followed by high temperature heat treatment and cooled to room temperature.

The obtained silicon carbide hollow particles have a particle size of 6.5 to 8 mm.
, the thickness of the shell is 0.5 mm, and the apparent specific gravity is 0.8 to 1.0.
, the single grain strength was 2 to 5 kg.

Further, as a result of X-ray diffraction, the main component of the shell was βSiC, and α-A1203 was also detected.

Claims (1)

[Claims] 1. Fill the hollow part of hollow granules with shells made of silica material with microscopic voids with liquid carbon material, and then heat and sinter the granules in a vacuum or inert gas atmosphere. A method for producing silicon carbide hollow granules, the method comprising converting the silica content in the shell into silicon carbide.