JPH07187851A - Heat insulating member and its production - Google Patents

Abstract

PURPOSE:To easily obtain a heat insulating member having high heat insulating property and high strength by dispersing porous spheres of ceramic particles each consisting of an unsintered layer of ceramic fine powder as a core and a sintered layer of ceramic fine particles as a surface layer. CONSTITUTION:Only the surface of ceramic fine powder of oxide of Zr, Cr, etc., having <=1mum particle diameter is sintered to such a degree that the relation of 0.01<b/a<0.3 is satisfied when the outside diameter of the resulting porous spheres is expressed by (a) and the thickness of each sintered layer is expressed by (b). By this sintering, porous spheres of ceramic particles each having 20-300um outside diameter are obtd. The surfaces of the porous spheres are then coated with stearic acid and the coated porous spheres are dispersed in a heat insulating material such as ceramic particles and metal powder to produce the objective heat insulating member in which each unsintered layer in porous spheres of ceramic particles has <=1mum particle diameter and the outside diameter of the ceramic particles is 20-300mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat insulating member having a high heat insulating property and a high strength.

[0002]

2. Description of the Related Art An exhaust system device of an internal combustion engine, such as an exhaust manifold, is a part for collecting exhausted combustion gas (exhaust gas) and discharging it to an exhaust pipe. Since exhaust gas with a high temperature of 700 to 900 ° C passes through this exhaust manifold, it is required to have the ability to withstand high temperature oxidation, corrosion, thermal stress, fatigue fracture due to vibration stress, and deformation due to creep.

Ceramic coating is widely used to improve the heat insulating property of the exhaust manifold and the like. Among them, so-called slurry coating, in which a liquid material is applied and then fired to form a film, is simple and has a high degree of freedom of a coating member, and is currently widely used.

The slurry coating is composed of a solvent, a heat insulating material (ceramic or metal powder) and a binder, and is formed by curing the binder.

In recent years, in order to further enhance the heat insulating property of this film, a so-called balloon heat insulating material containing air therein has been proposed as a heat insulating material (Japanese Patent Laid-Open No. 62-212138). This film is made by bonding hollow ceramic particles with a thin wall thickness with an inorganic binder so that there is sufficient space between the particles, and improved heat insulation, fire resistance and peel resistance. It is a thing.

[0006]

The hollow ceramic particles used in this coating have a spherical structure composed of an outer skin of a sintered body having a hollow interior, and therefore have low strength. In particular, the compressive stress is low, and if the compressive stress is applied by the thermal stress, it is likely to be broken. In addition, when used as an irregular shaped refractory, etc., these refractories are mainly manufactured by press molding, and the balls are destroyed during the pressurization during this molding, and a heat insulating function is obtained. It may disappear.

Further, the reason why the hollow ceramic particles are used is that a high heat insulating property is exhibited by the heat insulating effect of the air inside. However, the air in the interior causes convection because there are no obstacles, and therefore the low thermal conductivity inherent to air cannot be fully utilized by the hollow ceramic particles.

As described above, the film using hollow ceramic particles has problems that the strength is low and the heat insulating property cannot be sufficiently exhibited. The present invention intends to solve the above-mentioned drawbacks of a heat insulating member containing hollow ceramic particles, sufficiently utilize the high heat insulating property of air, and provide a heat insulating member having high heat insulating property and high strength. It is what

[0009]

As a result of intensive studies conducted by the present inventor to solve the above-mentioned problems of the heat insulating member, the inside of the heat insulating member was formed into a porous layer of unsintered ceramic fine powder. , By using porous spheres of ceramic particles whose outside is covered with a sintered layer and dispersing them, it is possible to obtain a heat insulating member having the original heat insulating property of air and having sufficient strength. Heading, completed the present invention.

That is, the heat insulating member of the present invention is characterized in that porous spheres of ceramic particles, which are an unsintered layer of ceramic fine powder and a surface layer which is a sintered layer of ceramic fine particles, are dispersed. It is what
Further, the present invention is characterized in that, in this method for producing a heat insulating member, the water absorption of the porous spheres of the ceramic particles is suppressed by coating the surface of the porous spheres of the ceramic particles with stearic acid.

In the production of the heat insulating member of the present invention, ceramic fine powder is granulated. This ceramic powder is not particularly limited, and commonly used one may be used. For example, Mn, Ti, Zr, Cr, Fe, Co, Ni, Cu, Zn, Al,
Examples of oxides such as Si include Zr, Cr, Fe, and
Al and Si oxides are preferred. This is because these oxides are stable even at high temperatures and in the air and do not impair the durability of the film due to transformation or the like. Especially Z
Oxides of r, Cr, Fe, Al, and Si have high-temperature stability up to 1000 ° C, and have a relatively large coefficient of thermal expansion, and even when coated on an iron-based base material, the coefficient of thermal expansion does not match. This is because peeling is less likely to occur. Film formation and molding of refractories can be performed using the above-mentioned metal nitrides and carbides, but it is not preferable because of poor stability at high temperature.

The particle size of the ceramic fine powder is preferably 1 μm or less. When it exceeds 1 μm,
The pores existing between the particles after granulation become large, so that the strength of the porous spheres of the produced ceramic particles is impaired,
As a result, the strength of the coating or refractory produced using the porous spheres decreases.

Next, the granulated particles are sintered. The sintering method is not particularly limited, and a commonly used sintering method may be used. However, in this sintering, it is necessary not to completely sinter the porous spheres, but to sinter only the surface and leave the inside unsintered. The degree of sintering is preferably 0.01 <b / a <0.3, where a is the outer shape of the obtained porous sphere and b is the thickness of the sintered layer. If the ratio is 0.01 or less, the obtained porous spheres may not have sufficient strength, while if it is 0.3 or more, the heat insulating property may be low.

The porous spheres thus produced have an outer diameter of 20 to
It is preferably 300 μm. If it is smaller than 20 μm,
If the bulk density of the porous spheres in the coating or the refractory containing the porous spheres is reduced, the heat insulating property is reduced, while if it is larger than 300 μm, the strength of the coating or the refractory containing the porous spheres is reduced. Because there is. Further, it is preferable that the porous spheres are spheres from the viewpoint of strength and the like, but it is not always necessary that they are true spheres.

The porous spheres may be coated with stearic acid. Stearic acid is used because this stearic acid forms an oil film on the surface of the porous spheres by drying,
This is because it is possible to suppress the water absorption of the porous spheres. This is because with other materials, the suppressing force is too strong, so that the porous spheres are separated in the slurry, or conversely, the suppressing force is too weak and the porous spheres absorb water. This coating method is not particularly limited, and its amount is sufficient to cover the surface of the porous sphere and impart water repellency.

Next, the porous spheres are mixed with other materials such as a heat insulating material and a binder to prepare a slurry. The amount ratio of the porous spheres to the other material is not particularly limited, but it is preferable that the porous spheres are closest packed, and the porous sphere: other material =
It is preferably 7: 3. Ceramic particles and metal powder may be used as the heat insulating material. This heat insulating material preferably has a particle size smaller than that of the porous spheres. This is because if the particle size is larger than that of the porous spheres, the strength of the obtained coating or refractory material may decrease.
The binder is not particularly limited, and for example, phosphate such as monoaluminum phosphate, silicate such as aqueous solution of water glass, and sol such as silica sol can be used.

By coating the heat insulating member of the present invention thus produced on a substrate and baking it, a ceramic coating having a high heat insulating property in which porous ceramic spheres are dispersed can be obtained as shown in FIG. 1, and the heat insulating member can be obtained. Is placed in a mold to be molded, and then fired to obtain a refractory material as shown in FIG. In this figure, ceramic powder is contained in addition to the ceramic porous sphere, but it does not necessarily have to be ceramic powder, and may be a heat insulating material such as metal powder, or may not contain this. .

[0018]

The ceramic porous spheres dispersed and contained in the heat insulating member of the present invention have a higher strength than those having a hollow inside because the inside is made of unsintered fine powder. It is clear that the air content (porosity) per sphere is larger in the hollow, but the presence of this fine powder disperses the small independent pores in the interior, so in conventional hollow spheres The convection of air, which was a problem, is suppressed, and the original heat insulating property of air can be sufficiently exhibited.

It is impossible to completely densify the outer circumference of the porous spheres, so that when they are dispersed in the slurry, they absorb water and it may be difficult to prepare a slurry having an arbitrary viscosity. . There is no such problem when the amount of binder is small, but when used as a coating,
Although it is necessary to increase the amount of binder, the water absorption phenomenon can be suppressed by coating the periphery of the porous sphere with stearic acid. This stearic acid is completely absent in the subsequent firing step and, therefore, is not present in the final product.

[0020]

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the invention.

Example 1 Zirconia powder having an average particle size of 0.5 μm was granulated into particles having a particle size of 50 μm by spray drying. The particles were sintered at 1400 ° C for 1 hour to obtain porous spheres. When the cross section of the porous sphere was observed by SEM, the depth from the surface side was 2 μm.
It had been sintered, but the inside remained unsintered.

The porous spheres and a stearic acid mixed aqueous solution (Cerosol 920 manufactured by Chukyo Yushi Co., Ltd.) were sufficiently mixed, the water was evaporated at 120 ° C., and the mixture was disintegrated to obtain stearic acid-coated zirconia porous spheres. 100 parts by weight of zirconia powder (particle size 2 μm) and 50 parts by weight of the zirconia porous spheres and
80 parts by weight of a 30% by weight aqueous solution of monobasic aluminum phosphate was added and sufficiently stirred to obtain a raw material slurry. This raw material slurry was coated on an iron-based base material that had been shot-blasted in advance. By drying and firing this at 300 ° C. for 5 hours, a ceramic coating as shown in FIG. 1 was obtained. During this baking step the stearic acid was completely evaporated and was not present in the resulting coating.

Example 2 Using the porous spheres prepared in Example 1, without coating stearic acid, 100 parts by weight of zirconia powder (particle size 2 μm) and 10% by weight of the primary spheres were used per 50 parts by weight of the porous spheres. 20 parts by weight of an aqueous solution of aluminum phosphate was added and sufficiently kneaded to obtain clay. This was inserted into a molding die, and pressure of 250 kg / cm ² was applied for molding. This was baked at 800 ℃ for 2 hours, and then
A refractory material such as that shown in FIG.

Example 3 The inner surface of a cast iron exhaust manifold, which is an automobile exhaust system component, was degreased with alcohol and then shot blasted, and the raw material slurry prepared in Example 1 was poured into the inner surface of this pipe. After that, discharge the excess slurry to 100 ℃
Was dried in the drying oven for 1 hour to evaporate the water content. By firing this at 300 ° C. for 5 hours, a cast iron exhaust manifold having a ceramic coating on the inner surface was obtained.

Examples 4 to 17 Coatings and refractories were prepared in the same manner as in Examples 1 and 2 using the materials shown in Table 1 below, and their heat insulating properties and strengths were measured. As for the heat insulating property, a raw material slurry prepared in the same manner as in Example 1 was coated on a cast iron exhaust manifold for automobiles in the same manner as in Example 3, and this was coated.
It was incorporated into a 2000cc gasoline engine, operated at a rotation speed of 4000 rpm for 30 minutes, and evaluated by measuring the temperature difference between the upper and lower portions of the coating with a thermocouple. Also,
With respect to the strength, a rod-shaped test piece of 3 × 4 × 50 mm was molded in the same manner as in Example 2, and the 3-point bending strength was measured according to a conventional method. The results are shown in Table 1.

Comparative Example 1 150 parts by weight of zirconia powder having an average particle size of 0.5 μm
80 parts by weight of 30% by weight aqueous solution of monobasic aluminum phosphate was added and sufficiently stirred to obtain a raw material slurry. Using this, a coating and a refractory were manufactured according to the method described above, and their heat insulating properties and strengths were measured. The results are shown in Table 1.

Comparative Example 2 A raw material slurry was prepared in the same manner as in Example 1 except that alumina hollow spheres were used instead of zirconia porous spheres, and using this, a coating and a refractory material were produced according to the above method.
Its heat insulating property and strength were measured. The results are shown in Table 1.

[0028]

[Table 1]

As is clear from this table, the ceramic coating containing no porous spheres produced in Comparative Example 1 was inferior in heat insulation and strength as compared with the product of the present invention. Similarly, the coating produced in Comparative Example 2 was also inferior in heat insulation and strength.

[0030]

Since the heat insulating member of the present invention includes the ceramic porous spheres whose inside is formed of unsintered fine powder, the heat insulating member has higher strength than the conventional heat insulating member including the hollow spheres, and the inside of the sphere is high. Since there is no air convection, the heat insulation is also improved.
Further, the porous spheres used in the present invention are simpler to manufacture than hollow spheres and have a high degree of freedom in materials.

[Brief description of drawings]

1 is a partial sectional view of a heat insulating refractory obtained by the present invention, (2) is a sectional view of a heat insulating coating obtained by the present invention, and (3) is It is a partial enlarged view of a cross section, and (4) is a partial cross sectional view of a ceramic porous sphere included therein.

[Explanation of symbols]

 1 ... Porous ceramic sphere 2 ... Ceramic powder 3 ... Binder

Claims (4)

[Claims] 1. A heat insulating member in which porous spheres of ceramic particles are dispersed, which are composed of an inside which is an unsintered layer of ceramic fine powder and a surface layer which is a sintered layer of ceramic fine particles. 2. The heat insulation according to claim 1, wherein the unsintered layer inside the porous spheres of the ceramic particles has a particle diameter of 1 μm or less, and the outer diameter of the ceramic particles is 20 to 300 μm. Element. 3. Granulation of ceramic fine powder, sintering only the surface layer of the ceramic particles to produce porous spheres of the ceramic particles, and then dispersing the porous spheres of the ceramic particles in a heat insulating material. Characterized by,
Method for manufacturing heat insulating member. 4. The method according to claim 3, wherein after the porous spheres of ceramic particles obtained by sintering only the surface layer are produced, the surface of the porous spheres of the ceramic particles is coated with stearic acid.