JPH05170571A - Porous ceramic heat-insulating material - Google Patents

Abstract

PURPOSE:To obtain the subject heat insulating material having high porosity, uniform pore diameter and excellent heat insulating characteristics by subjecting a specific gel material to leaching treatment to remove soda content from the gel material and then drying and burning the treated gel material. CONSTITUTION:10-15wt.% sodium silicate is mixed with 65-75wt.% ceramics fine powder such as mullite, 0.05-0.15wt.% surfactant such as aminosilane, 0.1-0.5wt.% aluminum powder and 10-25wt.% water to afford silicate slurry (A). Then 10-15wt.% sodium aluminate is mixed with 65-75wt.% ceramic fine powder, 0.05-0.15wt.% surfactant and 10-25wt.% water to give aluminate slurry (B). Then the component A is blended with the component B and the blend is stirred, expanded and gelled to afford a porous hydrogel material (C). The component C is leached by ion exchange, etc., dried and burned at 1200-1600 deg.C to produce the objective porous ceramic heat-insulating material >=80% closed cell ratio, 40-80% porosity and 100-800mum pore diameter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous ceramic heat insulating material, and more particularly to a porous ceramic heat insulating material having a high closed cell ratio, a uniform pore diameter and excellent moldability.

[0002]

2. Description of the Related Art In recent years,
As part of energy conservation measures, the demand for heat insulation of general construction and industrial equipment is increasing. The heat insulating material used for such a purpose is roughly classified into an organic type and an inorganic type according to the material.

[0003] Organic heat insulating materials have excellent heat insulating properties and are widely used as heat insulating materials for buildings, but they have the problems that they are easy to burn and generate harmful gas. Therefore, recently, there is an increasing demand for an inorganic heat insulating material that is nonflammable and has excellent heat resistance.

Brick has been used as an inorganic heat insulating material for a long time, but it has a large heat capacity due to its large weight, and its shape is limited because it is a press-molded product, which makes it difficult to process. Therefore, there is an increasing demand for weight reduction and easy workability. Examples of the lightweight heat insulating material include fiber aggregates such as glass wool, lightweight ceramics such as calcium silicate foam, and foam glass.

Since glass wool is lightweight and has excellent heat insulating properties in a dry state, it is widely used for general construction and the like, but since it is a fiber aggregate, it has high air permeability,
Under high-humidity conditions, the heat insulating property decreases. High temperature, high wind speed,
Under conditions such as high temperature, problems such as mold deformation and binder burnout may occur.

[0006] Further, the calcium silicate lightweight body has an excellent heat insulating property under low humidity, but it is not suitable for use under high humidity because of its high water absorption and hygroscopicity, and its use is limited. ..

On the other hand, since foam glass has closed cells, it retains excellent heat resistance for a long period of time, but due to its manufacturing method, the pore diameters vary widely and the structure is non-uniform, so only low strength products are obtained. Absent. On the contrary, if the density is increased in order to supplement the strength, only a material having a high thermal conductivity can be obtained, and not only the heat insulation becomes insufficient, but also the yield of the molded product deteriorates.

Therefore, an object of the present invention is to provide a porous ceramics heat insulating material which solves the above conventional problems.

[0009]

Means for Solving the Problems As a result of earnest research in view of the above object, the present inventor has mixed a silicate slurry and an aluminate slurry having a predetermined composition, and foamed and gelated by stirring, A porous hydrogel body is created, and after removing the soda component by leaching treatment, it is dried and fired to contain a high proportion of closed cells and have a uniform cell diameter, as well as excellent moldability. The present invention was completed by discovering that a porous ceramics heat insulating material can be obtained.

That is, the porous ceramics heat insulating material of the present invention comprises a silicate slurry containing sodium silicate, ceramics fine powder, a surfactant and aluminum metal powder as main components, sodium aluminate, ceramics fine powder and a surfactant. Is mixed with an aluminate slurry containing as a main component, foaming and gelling by stirring to create a porous hydrogel body, and after removing the soda component from the porous hydrogel body by a leaching treatment, drying,
It is characterized by being fired.

[0011]

In the present invention, silicate slurry containing sodium silicate, ceramics fine powder, surfactant and aluminum powder as main components, and aluminate slurry containing sodium aluminate, ceramics fine powder and surfactant as main components. By mixing and stirring and, foaming and gelation proceed simultaneously as exemplified in the following formula. _{2Al + 2NaOH → Na 2 O ·} Al 2 O 3 + 2H 2 ↑ [blowing] _{Na 2 O · 2SiO 2 · xH} 2 O ( _{silicate) + 1.2Na 2 O · Al 2} O 3 · yH 2 O ( aluminate) → Na ₂ O ・ Al ₂ O ₃・ SiO ₂・ zH ₂ O + NaOH [gelation] After removing the soda component from the porous hydrogel thus obtained by leaching treatment, drying and firing, the pore size It is possible to obtain a porous ceramics heat insulating material capable of controlling the pore diameter and the closed cell ratio. Specifically, it is as follows.

(1) By controlling the amount of surfactant in the silicate slurry and aluminate slurry,
It is possible to manufacture a porous ceramic having uniform closed cells over the entire area of the molded body. As a result, the heat insulating effect can be enhanced, and a uniform structure can be obtained, so that a high strength product can be obtained. Furthermore, since it is a lightweight body, it is easy to handle.

(2) By controlling the amount of the surfactant, the surface area of the aluminum powder, and the mixing ratio (weight ratio) of the silicate slurry and the aluminate slurry, the pore diameter and porosity of the porous ceramic heat insulating material are controlled. Can be uniformly controlled over the entire area of the molded body. In particular, the maximum porosity is 80%, which can be extremely high compared to conventional products. Also by this, the heat insulating effect can be enhanced as in the case of (1), and since a uniform structure is obtained, a high strength product is obtained. Furthermore, since it is a lightweight body, it is easy to handle.

The method for producing the porous ceramic heat insulating material of the present invention will be described below.

[1] Silicate Slurry As the ceramic fine powder to be added to the silicate slurry, any ceramic can be used. For example, fine powder of cordierite, kyanite, mullite, silicon carbide, silicon nitride, zirconia, etc. can be used. Can be mentioned. Particularly, in order to obtain a porous ceramics heat insulating material for use at high temperatures, it is sufficient to use ceramics fine powder having excellent heat resistance (for example, silicon carbide, mullite, alumina, etc.). Further, oxides such as Mn ₃ O ₄ and La ₂ O ₃ can be added to enhance the strength and thermal shock properties of the heat insulating material. The average particle size of the ceramic fine powder is 5 to 50.
About μm is preferable.

By using a surfactant, it becomes possible to produce a porous ceramic having uniform closed cells throughout the molded body. As the surfactant having such an action, polydimethylsiloxane, aminosilane, acrylsilane and the like are preferable.

The aluminum powder is added to cause foaming by the following reaction when mixed with the aluminate slurry. 2Al + NaOH → Na ₂ O ・ Al ₂ O ₃ ＋ 2H ₂ ↑

The diameter of the pores formed at this time is inversely proportional to the surface area of the aluminum powder. Therefore, the surface area of the aluminum powder is preferably 0.05 to 1.5 m ² / g.
The surface area is less than 0.05 m ² / g, foaming does not rise insufficient cell content, also it is difficult to exceed a bubbling 1.5 m ² / g to obtain a vigorous uniform pore structure.

Water is preferably added so that the solid content (ceramic fine powder + silicic acid + solid content in sodium silicate) in the silicate slurry is about 75 to 90% by weight.

[2] Aluminate Slurry The fine ceramic powder and the surfactant in the aluminate slurry may be the same as those in the silicate slurry.
Water has a solid content in the aluminate slurry (ceramic fine powder + solid content in sodium aluminate) of about 75-
It is preferable to add 90% by weight.

The above-mentioned silicate slurry and aluminate slurry are respectively prepared by using an air diaphragm pump or the like.
By circulating for 14 to 16 hours, a slurry having good dispersibility and containing no bubbles can be obtained.

[3] Composition Ratio of Each Component The silicate slurry and aluminate slurry having the above composition preferably have the following composition (based on solid content). Further, it is preferable to mix the mixture at a mixing ratio such that the composition (based on solid content) is as follows.

(A) Silicate slurry Sodium silicate 10-15% by weight Ceramic fine powder 65-75% by weight Surfactant 0.05-0.15% by weight Aluminum powder 0.1-0.5% by weight Water approx. 10-25% by weight

(B) Aluminate slurry Sodium aluminate 10 to 15% by weight Ceramic fine powder 65 to 75% by weight Surfactant 0.05 to 0.15% by weight Water about 10 to 25% by weight

(C) Mixing ratio of silicate slurry / aluminate slurry: 1 / 0.6 to 1 / 1.6

(D) Mixture Sodium silicate 5-8 wt% Sodium aluminate 5-9 wt% Ceramic fine powder 65-75 wt% Surfactant 0.05-0.15 wt% Aluminum powder 0.04-0.3 wt% Water About 10- 25% by weight

When the content of sodium silicate in the mixture is less than 10% by weight, aggregate (ceramic fine powder)
Adhesion between them is insufficient, and if it exceeds 15% by weight, shrinkage during sintering becomes severe and it becomes difficult to maintain the shape of pores.

If the content of the ceramic fine powder is less than 65% by weight, the gel strength is insufficient and handling is difficult, and if it exceeds 75% by weight, the viscosity sharply increases and the moldability deteriorates. ..

Further, if the content of the surfactant is less than 0.05% by weight, it is difficult to form a uniform structure over the entire molded body. On the other hand, when it exceeds 0.15% by weight, open pores having continuous pores are formed. In this range,
The pore size of the molded product is inversely proportional to the amount of the surfactant added.

Further, the content of aluminum powder is 0.04
When it is less than wt%, the foaming rate is slow and a sufficient porosity cannot be obtained before gelation of the slurry. On the other hand, if it exceeds 0.3% by weight, the foaming rate is high and it becomes difficult to control the pore structure to be uniform.

Regarding the mixing ratio of the silicate slurry and the aluminate slurry, the solid content weight ratio of both is 1 /
The range is 0.6 to 1 / 1.6. When the mixing ratio of the aluminate slurry is less than 0.6, the gelation rate is high, molding is difficult, and sufficient porosity cannot be obtained. On the other hand, if the mixing ratio of the aluminate slurry exceeds 1.6, the gelation rate is slow, the productivity is low, and sufficient gel strength cannot be obtained.

[4] Drying and Firing As described above, aluminum powder is added only to the silicate slurry, stirred, and then mixed and stirred with the aluminate slurry and poured into a mold having a desired cavity shape. As a result, the foaming / gelling reaction represented by the following formula proceeds, and a porous hydrogel is obtained. Na ₂ O ・ 2SiO ₂・ x H ₂ O (silicate) + 1.2Na ₂ O ・ Al ₂ O ₃・ yH ₂ O (sodium aluminate) → Na ₂ O ・ Al ₂ O ₃・ SiO ₂・ zH ₂ O + NaOH

The diameter of the pores formed at this time is proportional to the weight ratio of the silicate slurry / aluminate slurry to be mixed. As described above, the mixing ratio of the silicate slurry and the aluminate slurry is 1 / weight ratio of the solid content of both.
It is preferably in the range of 0.6 to 1 / 1.6.

Since a plastic mold can be used for foaming and gelling, the degree of freedom in the shape of the molded product is large and a large product can be molded.

Further, in the molding step, by applying a release agent to the mold, the surface of the resulting molded body can be made to have a membrane structure. As the mold release agent, those composed of glycerin, water and a surfactant can be used.

[4] Reaching treatment The above porous hydrogel was washed with ion-exchanged water to remove excess soda, and then 0.5 to 2% (for example, 1%).
The sodium in the hydrogel bond is ion-exchanged with ammonium ion to remove the sodium in the hydrogel bond. Further, by washing with ion-exchanged water, excess chlorine ions are removed.

[5] Drying and firing The porous hydrogel from which the soda content has been removed by the leaching treatment is dried with warm air to remove water and then oven dried. This removes adsorbed water and ammonium. Then, a high temperature firing at about 1200 to 1600 ° C. is performed to obtain a porous ceramic body.

The porous ceramics heat insulating material of the present invention obtained by the above method has a closed cell ratio of 80% or more,
In addition, the porosity is in the range of 40-80% and the pore size is 100-80.
It can be uniformly controlled in the range of 0 μm.

[0039]

The present invention will be described in more detail by the following examples.

Example 1 Various ceramic fine powders and surfactants were added to sodium silicate and sodium aluminate at the composition ratio (% by weight) shown in Table 1 below, and after stirring with a stirrer, circulation was performed overnight with an air diaphragm pump. Specific gravity of 1.9g
A slurry with a viscosity of 4000 cps (15 ° C) was obtained.

Table 1 Silicate aluminate raw material (g) Slurry Slurry Sodium silicate (solid content 44%) 600-Sodium aluminate (solid content 46%)-600 Water 202 206 Cordierite (200mesh) 560 560 Tentative Baked Kyanite (200mesh) 582 578 Surfactant ⁽¹⁾ 3 3 Note: (1) Polydimethylsiloxane

Slurry 10 only in silicate slurry
Aluminum powder (specific surface area 1.3 m ²
/ g) 1.5% by weight was added and well dispersed, and then each slurry was weighed so that the weight ratio of aluminate slurry / silicate slurry was 1.2, and after mixing and stirring, 2
It was poured into a mold of 00 mm × 200 mm × 120 mm.

50% by weight of glycerin was previously added to the mold,
A release agent consisting of 4 to 6% by weight of wetting agent and 50% by weight of water has been applied. In about 10 minutes after casting, the volume expanded to about 3 times, and a 200 mm × 200 mm × 90 mm porous hydrogel was obtained.

This porous hydrogel was washed with ion-exchanged water to remove excess soda, and then washed with a 1% ammonium chloride aqueous solution to remove sodium ions in the hydrogel bond by exchanging them with ammonium ions. Further, it was washed with ion-exchanged water to remove chlorine ions.

The porous hydrogel was dried with hot air at 50 ° C. for one day to remove water, and then dried according to the temperature program shown in FIG. 1 to remove adsorbed water and ammonium. Further, firing was performed according to the temperature program shown in FIG. Table 2 shows the physical properties of the fired product.

Example 2 Leaching, drying and firing were carried out in the same manner as in Example 1 except that aluminum powder having a specific surface area of 0.7 m ² / g was used. Table 2 shows the physical properties of the obtained fired product.

Example 3 In Example 1, the weight ratio of the silicate slurry to the aluminate slurry was aluminate / silicate = 1.5.
The resulting porous hydrogel was similarly leached, dried and fired. Table 2 shows the physical properties of the obtained fired product.

Example 4 Leaching, drying and firing were carried out in the same manner as in Example 1 except that the amount of surfactant added to each slurry was 1.5 g. Table 2 shows the physical properties of the obtained fired product.

Example 5 Example 1 except that aluminum powder having a specific surface area of 0.7 m ² / g was used and the amount of surfactant in each slurry was 1.5 g.
Leaching, drying and firing were performed in the same manner as in. Table 2 shows the physical properties of the obtained fired product. The thermal conductivity in Table 2 is the value at 1300 ° C.

Table 2 Porosity Bending strength Thermal conductivity Example No. (%) (Kg / cm ² ) (cal / m ・ h ・ ℃) 1 70 18 to 20 0.25 2 75 15 to 17 0.23 3 78 14 to 15 0.19 4 80 12 to 14 0.16 5 82 10 to 12 0.13

[0051]

The porous ceramic heat insulating material of the present invention is
Since the porosity is extremely high as described above, it exhibits excellent heat insulating properties. In addition, since the pore structure is uniform over the entire molded body, compared to conventional products that have the same heat insulation characteristics,
High bending strength. Further, since it has excellent moldability, it can be molded into heat insulating materials of various shapes without undergoing complicated processing steps as in conventional products. Such a porous ceramics heat insulating material of the present invention is an industrial heating furnace,
It can be applied to a wide range of fields such as furnace materials for various furnaces such as ceramic furnaces, steam piping, heat insulating materials for boiler rooms and drying rooms, heat insulating boards for houses, manifolds for automobile engine rooms, etc.

[Brief description of drawings]

FIG. 1 is a diagram showing a drying program executed in each example.

FIG. 2 is a diagram showing a firing program performed in each example.

Claims (2)

[Claims] 1. A silicate slurry containing sodium silicate, a ceramic fine powder, a surfactant and a metal aluminum powder as a main component, and an aluminate slurry containing sodium aluminate, a ceramic fine powder and a surfactant as a main component. A porous ceramic heat insulating material obtained by mixing and stirring to foam / gelate to prepare a porous hydrogel body, remove the soda component from the porous hydrogel body by leaching treatment, and then dry and calcine. .. 2. The porous ceramics heat insulating material according to claim 1, wherein the closed cell ratio is 80 over the entire area.
%, And the porosity can be uniformly controlled within the range of 40 to 80% and the pore diameter within the range of 100 to 800 μm.