JP2003277160A - Ceramic hollow ball or porous body, and method for manufacturing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic hollow ball or a porous body having an excellent heat resistance and heat insulatability and high mechanical strengths and a method for manufacturing them by simple processes at low costs. <P>SOLUTION: The ceramic hollow ball consists of a hollow ball of a foam of an oxide ceramic composition containing silicon, calcium and/or magnesium as a core section and a foam of the oxide ceramic composition containing magnesium and silicon as essential components as a shell section and has specific gravity of ≤1.0 and a softening point of ≥1,500°C. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat insulating material having excellent heat insulating properties of molten steel in a tundish in a process of continuously casting molten steel and also having excellent insulation performance between the molten steel surface and the outside air, and various heat resistances. The present invention relates to a lightweight ceramic hollow ball or porous body that can be used as a material for a heat retaining material, and a method for producing the same.

[0002]

2. Description of the Related Art For example, in the steel manufacturing industry, when continuously casting molten steel, molten steel is poured from a ladle into a tundish, and the tundish is poured into a mold to carry out continuous casting. In the tundish, a heat insulating material is used for the purpose of blocking the surface of the molten steel from the outside air and for suppressing the decrease of the molten steel temperature as much as possible. As a heat insulating material,
Traditionally, burnt rice, towarite, charlite, vermiculite, etc. have been used.

Further, in Japanese Patent Application Laid-Open No. 7-232246, silicon dioxide (SiO ₂ ) and aluminum oxide (Al) are used as main components occupying at least 80% of the whole.
₂ O ₃ ), and magnesium oxide (MgO),
Disclosed is a granular heat insulating material in which the weight ratio of SiO ₂ and Al ₂ O _{3 is in} the range of 2/1 or less and 1/1 or more, and which contains magnesium oxide in an amount of 20% to 45% with respect to the main component. Has been done. Further, in Japanese Patent Laid-Open No. 8-33960,
CaO / Al ₂ O ₃ = 0.5 to 1.0 and MgO = 5
% To less than 30%, SiO ₂ ≦ 10% liquid phase heat retaining agent containing 5% to 90% of hollow sintered body having CaO / Al ₂ O ₃ = less than 0.5 or more than 2.0 in molten steel A surface heat retaining agent is disclosed. Moreover, in Japanese Patent Publication No. 3-48152, magnesium oxide ≧ 60% and specific surface area: 15 m ²
/ Gr~1m ² / gr, bulk specific gravity: 0.2 to 1.5, particle size: insulation, refractory particles is disclosed a 15mm from 0.5 mm.

[0004]

The conventional heat insulating material has the following problems. That is, in the case of burnt rice, the main components of burnt rice are silicon dioxide and carbon, and although silicon dioxide has a low thermal conductivity and excellent heat retention, it reacts with aluminum in molten steel and reacts with it.
₂ O ₃ ). Therefore, burned rice containing silicon dioxide as a main component is not preferable as a heat insulating material for molten steel in a tundish or the like. Further, burned rice containing a large amount of carbon changes the carbon content of molten steel and is not preferable for ultra low carbon steel and the like.

The main components of Towarite, Charlite, Vermiculite, etc. are silicon dioxide (Si).
O ₂ ). Then, as in the case of burnt rice, it reacts with aluminum in molten steel and reacts with aluminum oxide (A
It is not preferable because it is changed to 1 ₂ O ₃ ). And there is also a problem that these Towarite, Charlite, Vermiculite, etc. depend on the supply from overseas. Burned rice, Towarite, charlite, vermiculite, and the like may cause workers to have silicosis caused by dust when used.

The heat insulating material disclosed in Japanese Unexamined Patent Publication No. 7-232246 contains silicon dioxide (SiO ₂ ) and aluminum oxide (Al ₂ O ₃ ) as main components, and changes the molten steel composition to increase the temperature. In addition, there is a problem that affects the properties of the finally obtained steel material.

In the case of the heat retaining agent disclosed in Japanese Unexamined Patent Publication No. 8-33960, there is a problem that sintering between particles progresses during use and it becomes difficult to control opening / closing of a stopper for controlling supply of molten steel from a tundish to a mold. is there. In addition, Japanese Patent Publication No. 3-481
In the case of the heat insulating and refractory particles disclosed in Japanese Patent No. 52, there is a similar problem.

An object of the present invention is to solve the above problems in the prior art, and to provide a ceramic hollow ball or porous body having excellent heat resistance and heat retention and high mechanical strength, and a method for producing the same. Another object of the present invention is to use a magnesia clinker (MgO) as a raw material.
(Content ≥ 90%) Fine ceramic powder or crushed granules of waste magnesia refractory bricks are used as raw materials, and ceramic hollow balls or porous bodies not containing a large amount of silicon dioxide (SiO ₂ ) can be produced by a simple process and at a low cost. It is to provide a method that can be manufactured at low cost. At that time, it is an object of the present invention to provide a heat insulating material which does not cause a problem in controlling the opening / closing of a stopper in a tundish due to sintering between particles, which is seen in a conventional heat insulating material.

[0009]

The invention according to claim 1 for solving the above-mentioned problems comprises a hollow core of an oxide-based ceramic composition foam hollow ball containing silicon and calcium and / or magnesium. Oxide-based ceramic composition containing magnesium and a small amount of silicon A shell having a double structure having a bulk specific gravity of ≦ 1.0 and a softening point of ≧ 1500.
It is a ceramic hollow ball characterized by being at a temperature of ℃.

According to the second aspect of the present invention, a small amount of water glass (W) and a small amount of calcium carbonate (C) and / or magnesium carbonate (M), by weight, W: C and / or M = 0. After mixing and molding so as to be 0.5: 1 to 5: 1, the mixture is heated in air at a temperature range of 200 ° C. or higher for 1 minute or more to be foamed to obtain an oxide-based ceramic composition foam hollow ball core, On the outside of the core, water glass (W) and magnesium oxide (MgO), by weight, W: MgO = 1:
After kneading so as to be 0.5 to 1:25 and applying uniformly, the mixture is heated in the air at a temperature range of 200 ° C. or higher for 1 minute or more to foam, thereby forming a shell of the oxide-based ceramic composition foam. It is a method of manufacturing a double-structured ceramic hollow ball, which is characterized in that it is formed.

According to a third aspect of the present invention, there is provided an oxide-based ceramic composition foam hollow ball containing silicon and calcium and / or magnesium, wherein the bulk specific gravity is ≤0.
4. A ceramic hollow ball having a softening point ≧ 1200 ° C.

The invention according to claim 4 is a water glass (W)
And calcium carbonate (C) and / or magnesium carbonate (M), by weight, W: C and / or M = 0.
A hollow ball of an oxide-based ceramic composition, characterized in that after being mixed and molded so as to have a ratio of 5: 1 to 5: 1, it is heated in air at a temperature range of 200 ° C. or higher for 1 minute or longer to foam. Is a manufacturing method.

According to a fifth aspect of the present invention, there is provided an oxide ceramic composition foam containing silicon and magnesium,
It is a ceramic hollow ball or a ceramic porous body having a bulk specific gravity of 1.3 and a softening point of 1500 ° C.

The invention according to claim 6 is a water glass (W)
And magnesium oxide (MgO) by weight, W: MgO
= 1: 0.5 to 1:25, mixed and molded, and then heated in air at a temperature range of 200 ° C. or higher for 1 minute or more to foam, and thus foamed oxide-based ceramic composition. A method for producing a hollow body body or a porous ceramic body.

[0015]

The ceramic hollow ball or porous body of the present invention is excellent in heat resistance and heat retention and has high mechanical strength. This ceramic hollow ball or porous body can be suitably used as a heat insulating material that keeps the molten steel warm in the dandy and shuts it off from the outside air. Also, by using this ceramic hollow ball or porous body, it is possible to develop an extremely lightweight, heat-resistant insulation material, such as a building insulation material (insulation board), electric furnace or electric heating. Insulators for home appliances such as heaters, refrigerators and freezers, lightweight heat-resistant insulators for automobiles, ships, aircraft, rockets, space shuttles, incinerators (nuclear facilities), nuclear facilities, nuclear fuel reprocessing facilities, breeder reactors, nuclear fusion It is expected to be used in many fields such as furnaces.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to its preferred embodiments.

Water glass is used in the production of the ceramic hollow ball or porous body of the present invention. Water glass is a concentrated aqueous solution of alkali silicate salt obtained by melting silicon dioxide and alkali,
Na ₂ O: 1 mol: SiO ₂ : ₂ mol to 4 mo
It is a colorless and viscous liquid containing l. About 50 wt% of the water glass is water, and since it has an appropriate viscosity, calcium carbonate or magnesium carbonate is agglomerated to facilitate molding.

When the core portion of the ceramic hollow ball according to claim 1 or the ceramic hollow ball according to claim 3 is manufactured, calcium carbonate (C) or magnesium carbonate (M) is added to water glass (W). The mixing ratio by weight is preferably within the range of W: C and M = 0.5: 1 to 5: 1. If the water glass mixing ratio is lower than W: C and M = 0.5: 1, it becomes difficult to mix calcium carbonate and magnesium carbonate efficiently and easily. On the other hand, when a large amount of water glass is added in excess of W: C, M = 5: 1, it becomes difficult not only to make the mixture into a spherical shape, but also to add silicon dioxide (SiO ₂ ) to the obtained ceramic hollow ball. When the amount is large and it is used in a tundish, etc., Al in molten steel is changed to Al ₂
It causes the problem of changing to O ₃ .

By mixing water glass with calcium carbonate or magnesium carbonate and heating the molded product in a relatively low temperature range of 200 ° C. or higher in an air atmosphere for 1 to 20 minutes, the moisture in the molded product is removed. Volatilize. When water in the water glass evaporates, calcium carbonate or magnesium carbonate is thermally decomposed and carbon dioxide (CO ₂ ) is generated at the same time, so that the mixture molded body efficiently foams and becomes a hollow ball. The chemical reaction at this time is as follows.

[0020]

[Chemical 1]

Water glass (W) and calcium carbonate (C)
Mixing ratio (weight) with magnesium carbonate (M) W:
When C and M are, for example, 4: 1, 10 at 370 ° C
The hollow balls can be formed most efficiently by heating for about a minute to form hollow balls.

Mixing of water glass with calcium carbonate or magnesium carbonate and heating of the molded product are carried out in an air atmosphere at 20
It is preferably 0 ° C or higher, more preferably 250 ° C or higher, and most preferably 350 ° C or higher. The higher the heating temperature, the shorter the time required for foaming, but if the heating temperature exceeds 500 ° C, the reaction rate becomes too high, and the resulting hollow balls deviate from the spherical shape to become elliptical or burst. I will arrive. Therefore, the heating temperature is preferably 250 ° C to 500 ° C, and most preferably 350 ° C to 450 ° C. The heating time at this time is preferably 5 minutes to 20 minutes, and most preferably about 10 minutes.

The ceramic hollow ball according to claim 1 has a double structure composed of a core portion of the ceramic hollow ball and a shell portion of the ceramic foam. This ceramic hollow ball contains a small amount of silicic acid (SiO ₂ ) and calcia (CaO) and / or obtained by the above process.
Alternatively, the surface of a hollow ball made of an oxide ceramic foam made of magnesia is coated with a small amount of a mixture of water glass (W) and magnesia (MgO), and this is again in an air atmosphere at a temperature range of 200 ° C. or higher. It is obtained by heating and foaming for 5 to 20 minutes.

At that time, the mixing ratio of magnesia (MgO) to water glass (W), W: MgO = 1: 0.5 to
It is 1:25. In a system in which the ratio of magnesia is less than 0.5 and the amount of magnesia is small, the heat resistance of the shell is insufficient. On the other hand, if the ratio of magnesia exceeds 25 and becomes large, it becomes difficult to mix magnesia efficiently and easily.

The heating temperature for forming the shell portion depends on the mixing ratio of water glass and magnesia, but is, for example, W:
When MgO = 1: 3, the oxide-based ceramic composition foam made of magnesium and silicon can be efficiently fixed to the surface of the core by heating in an air atmosphere at 370 ° C. for 5 minutes to 20 minutes.

The heating temperature for forming the shell portion is preferably 250 ° C. or higher, most preferably 350 ° C. or higher. Although the time required for foaming becomes shorter as the heating temperature becomes higher, when the heating temperature exceeds 500 ° C., the reaction rate becomes excessively high, and the shell portion becomes uneven in thickness or the shell portion bursts. Therefore, the heating temperature is 250
C. to 500.degree. C. is preferable, and 350.degree. C. to 450.degree. C. is most preferable. The heating time at this time is preferably 5 minutes to 20 minutes, and most preferably about 10 minutes.

In order to obtain the ceramic hollow ball or the ceramic porous body according to claim 5, the weight ratio of water glass (W) and magnesia (MgO) is set to W: MgO.
The mixture is kneaded and molded so that = 1: 0.5 to 1:25, and heated in an air atmosphere at a temperature range of 200 ° C. or higher for 5 minutes to 20 minutes to foam. In this way, a ceramic hollow ball or a porous body of an oxide-based composition foam containing magnesium and silicon is obtained. This ceramic hollow ball or porous body has a bulk specific gravity of 1.3 or less and a softening point of 1
It has a temperature of 500 ° C or higher, and is excellent in heat resistance and heat retention and has high mechanical strength.

The heating temperature for obtaining the above-mentioned ceramic hollow ball or porous body is preferably 250 ° C. or higher, and most preferably 350 ° C. or higher. Although the time required for foaming becomes shorter as the heating temperature becomes higher, when the heating temperature exceeds 500 ° C., the reaction rate becomes excessively high, and the shell portion becomes uneven in thickness or the shell portion bursts. Therefore, the heating temperature is preferably 250 ° C to 500 ° C, and most preferably 350 ° C to 450 ° C. The heating time at this time is preferably 5 minutes to 20 minutes, and most preferably about 10 minutes.

[0029]

EXAMPLES Example 1 Water glass (W) and calcium carbonate (C) by weight,
The mixture was kneaded and molded so that W: C = 4: 1, charged into an alumina crucible, and heated in an air atmosphere at 370 ° C. for about 10 minutes. Generation of water vapor from water glass,
At the same time, carbon dioxide gas (CO ₂ ) was generated by the thermal decomposition of calcium carbonate and foamed, and a substantially spherical ceramic white hollow ball with a diameter of about 2 mm to 20 mm was obtained.
The diameter (size) of the hollow balls increased as the weight of the mixture of water glass and calcium carbonate and / or magnesium carbonate increased, or as the mixing ratio of water glass increased.

A white hollow ball, which is a foam of the oxide ceramic composition containing silicon and calcium, is used as a core, and water glass (W) and magnesia (Mg) are formed on the surface of the core.
O), which is kneaded so that the ratio of W: MgO = 1: 3 by weight, is uniformly applied, and this is again charged into an alumina crucible and heated at 370 ° C. for about 10 minutes. It was foamed to form an oxide ceramic shell made of magnesium and silicon. The shell part completely covered the core part, and had a light brown color due to the magnesia raw material. The thickness of the shell portion increased as the total weight of the mixture of magnesia and water glass increased. A thin shell having a thickness of 0.1 mm and a thick shell having a thickness of more than 2 mm could be prepared. This double-structured ceramic hollow ball had a bulk specific gravity of 0.46 and a softening point of 1570 ° C.

Example 2 Mixing ratio (weight ratio) of water glass (W) to calcium carbonate (C) and magnesium carbonate (M), W: (C +
M) = 3: 1 was kneaded and molded, charged into an alumina crucible, and heated in an air atmosphere at 370 ° C. for 10 minutes. Water vapor generation from water glass and carbon dioxide gas (CO ₂ ) generated by thermal decomposition of calcium carbonate and magnesium carbonate are simultaneously generated to foam, thereby obtaining an oxide-based ceramic hollow ball containing silicon, calcium, and magnesium as components. Was given. These are diameter: 2m
It was a substantially hollow white hollow ball of m to 20 mm. These ceramic hollow balls have a bulk specific gravity of 0.15,
The softening point was 0.18 and the softening point was 1250 ° C.

Example 3 Mixing ratio (weight ratio) of magnesia (MgO) to water glass (W), W: MgO = 1: 5, kneading and molding, and charging this into an alumina crucible, and in an air atmosphere Three
It was heated at 70 ° C. for 10 minutes for foaming to obtain an oxide-based ceramic hollow ball containing silicon and magnesium as components. This hollow ball exhibited a light brown color due to the magnesium raw material, and its size increased as the mixing ratio of water glass in the mixture of magnesia and water glass increased. These hollow balls have a bulk specific gravity of 0.7.
8. The softening point was 1550 ° C. With water glass: magnesia = 1: 0.5, a foam having a diameter of about 30 mm was obtained, but it was distorted and had a rugby ball shape. With such a composition, it was difficult to manufacture a true hollow ball, and it often foamed too much and broke. When the mixing ratio of water glass was small, for example, water glass: magnesia = 1: 20, a ceramic porous body having innumerable small holes with a diameter of about 1 mm was obtained. This porous body had a bulk specific gravity of 1.20 and a softening point of 1550 ° C.

[0033]

According to the present invention, the bulk specific gravity is 1.3 or less,
It is possible to provide a lightweight, heat-resistant, heat-insulating ceramic hollow ball or porous body having a softening point of 1500 ° C. or higher. Therefore,
It can be suitably used as a heat insulating material in a tundish in a continuous casting process of molten steel. Also, by using this hollow ball or porous body, it is possible to develop an extremely lightweight heat insulating material, such as a building insulating material (insulating board), an electric furnace, an electric heater, a refrigerator. Insulation materials for home appliances such as refrigerators and freezers, lightweight heat-resistant insulation materials for automobiles, ships, aircraft, rockets, space shuttles, etc. In addition to incinerators (facility), nuclear reactors, nuclear fuel reprocessing furnaces, breeder reactors, etc. It becomes available.

According to the present invention, the manufacturing process is simple and the power consumption is small, so that the manufacturing cost is low. Moreover,
Since waste such as refractory bricks can be used as a starting material, it also contributes to solving environmental problems.

According to the inventions of claims 3 and 4, the softening point of the extremely light weight having a bulk specific gravity of 0.4 or less:
A ceramic hollow ball at 1200 ° C. or higher can be manufactured by a simple process and with a small energy consumption.

According to the fifth and sixth aspects of the present invention, a ceramic hollow ball or ceramic porous body having a bulk specific gravity of 1.3 or less and a softening point of 1500 ° C. or more is produced by a simple process and Can be manufactured with low energy consumption.

Claims (6)

[Claims] 1. A double structure comprising a hollow ball of an oxide-based ceramic composition foam containing silicon and calcium and / or magnesium as a core portion and a shell of an oxide-based ceramic composition foam containing magnesium and silicon as a shell portion. Structural,
A ceramic hollow ball having a bulk specific gravity of 1.0 and a softening point of 1500 ° C. 2. Water glass (W) and calcium carbonate (C) and / or magnesium carbonate (M) in a weight ratio of W: C and / or M = 0.5: 1 to 5: 1. After being mixed and molded into an air, it is heated in air at a temperature range of 200 ° C. or more for 1 minute or more to be foamed to obtain an oxide-based ceramic composition foamed hollow ball core.
Water glass (W) and magnesium oxide (MgO) are kneaded by weight so that W: MgO = 1: 0.5 to 1:25 and uniformly applied, and then in air, at a temperature of 200 ° C. or higher. A method for producing a double-structured ceramic hollow ball, which comprises heating for 1 minute or more in the region to foam the oxide-based ceramic composition foam to form a shell. 3. An oxide-based ceramic composition foam hollow ball containing silicon and calcium and / or magnesium, which has a bulk specific gravity of 0.4 and a softening point of 1200 ° C. Hollow ball. 4. Water glass (W) and calcium carbonate (C) and / or magnesium carbonate (M) in a weight ratio of W: C and / or M = 0.5: 1 to 5: 1. A method for producing a hollow ball of an oxide-based ceramic composition foam, comprising: heating and blowing in air at a temperature range of 200 ° C. or more for 1 minute or more after mixing and molding. 5. A ceramic hollow ball or a ceramic porous body, which is an oxide ceramic composition foam containing silicon and magnesium and has a bulk specific gravity of 1.3 and a softening point of 1500 ° C. Body. 6. Water glass (W) and magnesium oxide (M
gO) by weight, W: MgO = 1: 0.5 to 1:25
Of the oxide-based ceramic composition foamed hollow ball or ceramic-like porous body, which is characterized by being foamed by heating in air at a temperature range of 200 ° C. or higher for 1 minute or more after mixing and molding Production method.