JP2002029861A - Porous body and its production process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous body having enhanced performance with respect to thermal shock resistance and creep resistance. SOLUTION: In this porous body, ceramic primary particles 2, 2a,..., and their agglomerates 3, 3a,..., are subjected to fusion bonding to each other with a glass phase 4 containing boron or phosphorus, to form a mosaic microstructure, and any thermal stress and any hot load, which are applied to the porous body, are buffered by such a mosaic microstructure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic porous body useful as a refractory, such as a firing jig and a firing furnace construction member, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a porous body made of ceramics is lightweight, has a small heat capacity, and is also excellent in heat shock resistance, heat insulation and the like. It is widely used as a firing jig such as a sheath, a hearth plate, a firing furnace construction member such as a refractory block, or a refractory used for other purposes. However, in order to improve the production efficiency of ceramic products,
It is essential to shorten the baking time during product manufacturing (rapid baking), and the rapid baking increases the thermal load on the refractory. To cope with this, the thermal characteristics of the porous body must be improved. Further improvement is required. Therefore, by sintering a molded body containing a ceramic material and a flammable powder material (a volatile material) at a higher temperature than before, the volatile material is burned off at the time of sintering, and more pores are formed. A method for producing a porous body has been developed in which the raw material particles are strongly sintered at a high temperature to improve the mechanical strength of the product.

[0003]

However, in the above method, the thermal shock resistance can be increased by increasing the porosity of the porous body, but the microstructure of the porous body is not controlled. However, since the ceramic particles themselves are melted and vitrified, there is a problem that creep resistance, that is, bending strength against a hot load is reduced.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the problem that it is difficult to improve both the thermal shock resistance and the creep resistance of a ceramic porous body based on the above-mentioned prior art. The aggregate is fused and bonded with a glass phase containing boron or phosphorus to form a mosaic-like microstructure, and the mosaic-like microstructure absorbs thermal stress and hot load. The object is provided by providing a body and a method for manufacturing the same.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a microstructure of a ceramic porous body according to the present invention, and FIG. 2 is a partially enlarged view of FIG. The porous body 1 of the present invention is basically composed of ceramic primary particles 2, 2 a, and aggregates thereof (secondary particles) 3,
Are fused and bonded with a glass phase 4 containing boron or phosphorus to form a mosaic microstructure (hereinafter simply referred to as a mosaic structure) in which countless aggregates 3, 3a are three-dimensionally combined. ), The fine pores 5, 5a ... between the primary particles 2, 2a ... in the aggregates 3, 3a ..., the pores 5, 5a ... larger pores between the aggregates 3, 3a ... 6, 6a ...

Generally, the thermal shock resistance of a ceramic member is inversely proportional to the coefficient of thermal expansion and the elastic modulus of the material, and the coefficient of thermal expansion of the material cannot be changed. It is necessary to reduce the thermal stress by the glass phase 4 between the primary particles 2 and 2a and between the aggregates 3 and 3a. , Buffer the hot load, and therefore have a small elastic modulus, and therefore have excellent thermal shock resistance and creep resistance. The crystal system of the primary particles 2, 2a... May be any crystal system such as spherical, plate-like, chain-like, and acicular.
2a... For example, the porous body 1 having a mosaic microstructure formed by borate aluminate or aluminum phosphate crystals is particularly excellent in thermal shock resistance and creep resistance.

Next, a method for producing a porous body of the present invention will be described. The manufacturing method of the first embodiment is basically a ceramic raw material that reacts with boron or phosphorus during firing to produce needle-like crystals, for example, alumina, a sintering aid containing boron or phosphorus, and A porous material 1 is obtained by blending with the volatile material to be burned off, forming the mixture A, and firing the mixture. If the average particle size of the ceramic raw material is too large, the reactivity during firing is low and needle-like crystals are not easily generated,
50 μm or less is preferable, and for the same reason, 30 μm or less is more preferable.

The boron-containing sintering aid is composed of one kind of boron material or a mixture of two or more kinds of boron materials. Examples of the boron material include boron compounds such as orthoboric acid and metaboric acid, colemanite, urexite, and borax. And the like, boron-containing glass such as borosilicate glass, and boron alone. The phosphorus-containing sintering aid is composed of one kind of phosphorus raw material or a mixture of two or more kinds of phosphorus raw materials. Examples of the phosphorus raw material include phosphoric acid, aluminum phosphate, a phosphate compound such as calcium phosphate, and phosphorus alone. Is mentioned. In addition, clay minerals such as montmorillonite (bentonite), pyrophyllite (roastite), and kaolin minerals (clay, kaolin) may be mixed with the sintering aid. 2a
And the glass phase 4 between the aggregates 3 and 3a are added with an alkaline component such as sodium, potassium and calcium, and an acidic component such as silicon, so that the strength of the glass phase 4 is improved. If the addition ratio of the clay mineral is less than 0.1 in terms of the weight ratio to boron or phosphorus 1, if the content of sodium, potassium, calcium, silicon, etc. is small, the strength of the glass phase 4 is not changed, and the addition ratio exceeds 30. In this case, the content of the impurities in the porous body 1 increases, and the properties of the porous body 1 are adversely affected. Since these clay minerals also act as binders, mixing the clay minerals imparts plasticity to the composition and improves moldability.

The volatile materials are composed of flammable powdery raw materials. Examples of volatile materials include grains such as flour, barley flour, starch and rice bran, sugars such as sucrose and fructose, and carbon such as graphite, charcoal and activated carbon. And the like. Further, in addition to these, phenols such as phenol and epoxy, celluloses such as methylcellulose, fats and oils such as fatty acids, and sol-gels of alumina and silica may be added to the composition.

According to this method, alumina is fired during firing,
A chemical reaction takes place with the sintering aid containing boron or phosphorus to form needle-like crystals of borated aluminate or aluminum phosphate, and these needle-like crystals become entangled with each other and the primary particles 2, 2a of the needle-like crystals Are fused together by the glass phase 4 to form aggregates 3, 3a. In addition, since the volatile material in the molded body is burned off during firing, pores 6, 6a are formed between the aggregates 3, 3a. Are aggregated by the glass phase 4 to form a mosaic structure.

FIG. 3 is a diagram showing the weight ratio of the test pieces 1-1 to 3 (porous body 1) prepared by the manufacturing method of the first embodiment and the conventional product, and FIG. FIG. 3 is a diagram showing firing conditions, measured values of various physical properties, types of generated main crystals, creep resistance, and thermal shock resistance test results of Comparative Example 3 and a conventional product. Specimens 1-1 to 1-3 and a conventional product were prepared under the following conditions. Formulation A blended at the ratio shown in FIG.
After pressure molding at a pressure of, sintering was performed under predetermined conditions. Test pieces 1-1 to 3 (porous body 1) obtained by the method of the first embodiment
It was confirmed that each of them was superior to conventional products in creep resistance and thermal shock resistance. In addition, creep resistance and thermal shock resistance were tested by the following methods. In the creep resistance test, the temperature of the test specimen, which was horizontally supported at both ends, was increased while a constant load was applied to the center, held for 24 hours, and after cooling, the deflection of the test specimen was measured. As a thermal shock resistance test, the specimen is rapidly heated to a predetermined temperature,
This temperature was maintained for 1 hour and then allowed to cool to room temperature. This cycle was repeated five times, and the change in the state of the test specimen was visually confirmed.

The manufacturing method according to the second embodiment basically includes agglomerates 3, 3a,...
A sintering aid containing boron or phosphorus and a volatilizing material that burns off during firing are blended, and after forming such a blend B, firing is performed to obtain the porous body 1.

The ceramic raw material in this method is composed of one type of ceramic raw material or a mixture of two or more types of ceramic raw materials.
Examples thereof include oxide materials such as alumina, magnesia, silica, stabilized zirconia, cordierite, mullite, spinel, borated aluminate and aluminum phosphate, carbide materials such as silicon carbide, and nitride materials such as silicon nitride.
Also, sintering aids and volatile materials containing boron or phosphorus,
The same manufacturing method as that of the first embodiment may be used.

According to this method, since the primary particles 2, 2a... Are sintered by pre-firing the ceramic material, the primary particles 2, 2a can be used even if a ceramic material that does not produce needle-like crystals is used. Are aggregated to form aggregates 3, 3a.
Can be formed. Also, since the bonding between the primary particles 2, 2a is a bonding by sintering, that is, a bonding between solid phases, the bonding force between the primary particles 2, 2a is strong, and the robust aggregates 3, 3a. Can be formed.

FIG. 5 is a diagram showing the composition of a test body 2 (porous body 1) prepared by the manufacturing method of the second embodiment by weight ratio.
FIG. 6 is a view showing the firing conditions of the test piece 2, the measured values of various physical properties, the type of the main crystal formed, the test results of the creep resistance and the thermal shock resistance. Test body 2 was prepared under the following conditions. First, andalusite with an average particle size of 20 μm (natural mullite)
Powder material (primary particles 2, 2a ...) was heated at a rate of 100 ° C.
/ Hour, maximum temperature 1300 ° C., holding time 3 hours, pre-fired, agglomerated powder raw material and average particle diameter 40-80
μm aggregates 3, 3a... Next, a coarsely pulverized aggregate 3, 3a ... impregnated with an aqueous solution of 5% by weight of aluminum phosphate, granulated sugar, flour, and α-starch are blended, and the blend B is pressed at a pressure of 10 MPa. After the pressure molding, firing was performed under predetermined conditions. The test body 2 (porous body 1) obtained by the method of the second embodiment is the same as the porous body 1 of the first embodiment.
It showed creep resistance and thermal shock resistance equal to or higher than that of.
FIGS. 7 and 8 are scanning electron microscope photographs of the microstructures of the above-mentioned conventional product and the test piece 2, respectively.
Although pores are formed due to the burnout of the volatile material, since the α-alumina crystal particles are densely sintered, there is no other than the pores due to the burnout of the volatile material. , 2a...) Have fine pores 5, 5a... In such a state that the aggregates 3, 3a. It was confirmed that they were combined to form a mosaic configuration. still,
Creep resistance and thermal shock resistance were tested in the same manner as in the first example.

The manufacturing method according to the third embodiment is basically based on the fact that aggregates 3, 3a,... Formed by pre-firing a mixture of a ceramic raw material and a sintering aid containing boron or phosphorus The porous material 1 is obtained by mixing the volatile material to be burned off, forming the compound C, and firing the formed compound C. In addition, ceramic materials, sintering aids and volatile materials containing boron or phosphorus,
What is necessary is just to use the thing similar to the manufacturing method of 2nd Example.

FIG. 9 is a diagram showing the composition of test pieces 3-1 to 3 (porous body 1) prepared by the manufacturing method of the third embodiment by weight ratio, and FIG. 10 is the firing of test pieces 3-1 to 3-3. It is a figure which shows the conditions, the measured value of various physical properties, the kind of the produced main crystal, the test result of creep resistance, and thermal shock resistance. Specimen 3-1
No. 3 was prepared under the following conditions. A mixture of alumina powder, electrofused mullite powder, and boric acid is pre-fired under the conditions of a heating rate of 100 ° C./hour, a maximum temperature of 1350 ° C., and a holding time of 2 hours to form aggregates 3, 3a. , A coarsely pulverized product of the aggregates 3, 3a, (a), kaolin, and flour are blended, and the blend C is molded under pressure at a pressure of 10 MPa, and then calcined under predetermined conditions. -1 was obtained. The mixture of alumina powder and boric acid is pre-fired under the conditions of a heating rate of 100 ° C./hour, a maximum temperature of 1250 ° C., and a holding time of 4 hours to form aggregates 3, 3a. A coarsely pulverized product (2) of the aggregates 3, 3a ..., kaolin, silicon carbide, granule sugar, and flour are blended, and the blend C is mixed at 10 MPa.
After press-molding under the pressure described above, firing was performed under predetermined conditions to obtain a test piece 3-2. Further, a coarsely pulverized product of the aggregates 3, 3a (b), kaolin, bentonite, granule sugar, and flour are blended. After the compound C is press-molded at a pressure of 10 MPa, a predetermined pressure is applied. Calcination was performed under the conditions to obtain a test piece 3-3. Specimens 3-1 to 3 (porous body 1) obtained by the method of the third embodiment exhibited creep resistance and thermal shock resistance equivalent to those of the porous body 1 of the second embodiment. The creep resistance and thermal shock resistance were tested in the same manner as in the first embodiment.

In the manufacturing method of the fourth embodiment, a foaming material which generates gas at the time of sintering, expands and burns out is basically added to the compound A, B or C of the first, second or third embodiment. Then, after molding, firing is performed to obtain the porous body 1.

As the foam material, one prepared by the following method is used. Urea and sugar or cereal flour are mixed at a weight ratio of 1:30, and the mixture is heated and maintained in a temperature range of 150 to 250C. Then, the caramel is expanded to 10 to 20 times the volume due to the generation of ammonia gas, and the caramel is roughly pulverized to form a foam. In addition, the foaming material is not limited to the above-mentioned one, and in short, any material may be used as long as it has flammability and generates a gas when heated to expand.

According to this method, in the firing step, the foamed material in the molded body of the porous body 1 generates a gas and expands (foams), and the ceramic material around the foamed material is expanded outside the foamed material. Because the expanded foam material partially contacts each other, and the expanded foam material is burned out, and the ceramic material around the foam material is sintered, the space after the foam material burns becomes a continuous vent. .

FIG. 11 (a) is a diagram showing the composition of the foamed material of the fourth embodiment in terms of weight ratio, and FIG. 11 (b) is a sample 4-1 to 3 (porosity) prepared by the manufacturing method of the fourth embodiment. FIG. 12 is a diagram showing the composition of the powdery body 1) by weight ratio, and FIG. 12 shows the firing conditions of the test pieces 4-1 to 3, the measured values of various physical properties, the type of the main crystal formed, the creep resistance and the thermal shock resistance test results. FIG.
Specimens 4-1 to 3 were prepared under the following conditions. First, urea 30
% By weight, granulated sugar 60% by weight, boric acid 10% by weight
The mixture was heated to 200 ° C., and this temperature was maintained for 4 hours to give caramel, and then FIG.
At a ratio shown in FIG. 1 (b), the coarsely pulverized caramel and each raw material are blended, and the blend is press-molded at a pressure of 10 MPa and then fired under predetermined conditions to obtain test specimens 3-1 to 3-1. Was. Each of the test pieces 4-1 to 3 (porous body 1) obtained by the method of the fourth embodiment shows the same creep resistance and thermal shock resistance as the porous body 1 of the second and third embodiments. Was. Further, all of the test pieces 4-1 to 3-1 had continuous air holes formed of pores having an average diameter of 10 to 2000 angstroms. The creep resistance and thermal shock resistance were tested in the same manner as in the first embodiment.

Although the method for producing the porous body 1 has been described based on the embodiments, the blending and firing conditions of the porous body 1 are not limited to those shown in the respective embodiments, but may be in the following ranges. Good. When the sintering aid containing boron or phosphorus is less than 0.1% by weight in the blends A, B, and C, the glass phase 4 formed in the porous body 1 is too small. If the bonding strength is insufficient and the porous body 1 cannot be sintered uniformly and exceeds 50% by weight, the glass phase 4 contains the primary particles 2, 2a,.
Gaps, aggregates 3, 3a, etc. are filled, and pores 5, 5a ...,
.. Are not formed, the content is preferably in the range of 0.1 to 50% by weight, and more preferably 0.5 to 3% by weight for the same reason.
The range is 0% by weight. When the volatilization material is less than 1% by weight in the formulations A, B, and C, the pores 6, 6a,... Formed between the aggregates 3, 3a. Pores 6 and 6a if the mechanical properties deteriorate and exceed 50% by weight
Is excessive and the mechanical strength of the porous body 1 becomes insufficient, so that the range is preferably 1 to 50% by weight, more preferably 1 to 50% by weight for the same reason. If the foaming material is less than 5% by weight in the blends A, B and C, the foamed materials expanded at the time of firing do not come into contact with each other, so that the pores 6, 6a... Is too large, the mechanical strength of the porous body 1 becomes insufficient due to excessive pores 6, 6a..., So that the range is preferably 5 to 60% by weight, more preferably 10 to 50% by weight for the same reason. Range. or,
The firing conditions of the porous body 1 may be appropriately adjusted in the range of 1200 to 1800 ° C. depending on the type of the ceramic material mixed. The firing atmosphere is an oxidizing atmosphere or a neutral atmosphere when the compounded ceramic raw material is only an oxide raw material, and contains a non-oxide raw material. A reducing atmosphere is used.

[0023]

In summary, the present invention provides a ceramic raw material that reacts with boron or phosphorus during firing to form needle-like crystals 2, 2a, a sintering aid containing boron or phosphorus, and a volatilization that is burned off during firing. Are mixed with each other, and the mixture A is molded and then fired to form the mixture. Therefore, the generated needle-like crystals 2, 2a ... are entangled, and the needle-like crystals 2, 2a ... 4 can be fused to form aggregates 3, 3a... Since the volatile material in the compact is burned off during firing, pores 6, 6a... Are formed between the aggregates 3, 3a. Therefore, the porous body 1 having a mosaic structure can be formed. Since the porous body 1 obtained by this method can buffer thermal stress and hot load with a mosaic structure,
It is excellent in both thermal shock resistance and creep resistance, and thus can be used as a refractory capable of coping with rapid firing and various heating processes in the production of ceramic products.

An agglomerate 3, 3a,... Formed by pre-firing a ceramic raw material, a sintering aid containing boron or phosphorus, and a volatilizing material which burns off during firing are blended. Since it is formed by firing after molding, the aggregates 3, 3a ... can be formed even if a ceramic raw material which does not generate needle-like crystals is used. The porous body 1 can be formed by using the ceramic raw material of
Can be extended. Also, primary particles 2,
Are bonded by sintering, that is, by a solid-phase reaction. Therefore, the bonding force between the primary particles 2, 2a is strong, and a strong aggregate 3, 3a is formed. By further increasing the thermal shock resistance and creep resistance of the porous body 1,
Enables use at higher temperatures.

An agglomerate 3, 3a,... Formed by pre-firing a mixture of a ceramic raw material and a sintering aid containing boron or phosphorus, and a volatilizing material that burns off during firing are blended. Since it is formed by firing after molding, in this method as well, it is possible to form the aggregates 3, 3a... Using a ceramic raw material that does not generate needle-like crystals, and thus the same effect as in the above method is obtained. I can do it.

Further, since the foaming material which generates gas at the time of firing and expands after burning out is added to the composition A, B or C, the foaming material in the molded product generates gas and expands. (Foaming) and, at the same time, pushing out the ceramic raw material around the foaming material to the outside of the foaming material, the expanded foaming materials partially contact each other, and burn out the expanded foaming material, By sintering the ceramic raw material, the space after burning out of the foam material can be used as a continuous vent. The porous body 1 obtained by this method has fine interconnected pores,
Because of its excellent thermal properties, its practical effect is extremely large, for example, it can be used as a filter used at high temperatures.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a microstructure of a porous body according to the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is a diagram showing, by weight ratio, a blending example of the porous body of the first embodiment and a conventional product.

FIG. 4 is a view showing various physical properties and the like of the porous body of the first embodiment and a conventional product.

FIG. 5 is a diagram showing a composition example of a porous body according to a second embodiment by weight ratio.

FIG. 6 is a view showing various physical properties and the like of a porous body of a second embodiment.

FIG. 7 is a scanning electron micrograph of a microstructure of a conventional product.

FIG. 8 is a scanning electron microscope photograph of the microstructure of the porous body of the second example.

FIG. 9 is a diagram showing a blending example of a porous body of a third embodiment by weight ratio.

FIG. 10 is a view showing various physical properties and the like of a porous body of a third embodiment.

FIG. 11 (a) is a diagram showing the composition of the foamed material of the fourth embodiment by weight ratio, and FIG. 11 (b) is a diagram showing the composition example of the porous body by weight ratio.

FIG. 12 is a view showing various physical properties and the like of a porous body of a fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Porous body 2, 2a ... Primary particle 3, 3a ... Aggregate (secondary particle) 4 Glass phase

Claims (5)

[Claims] 1. A porous body formed by fusing and bonding primary particles of ceramics and an aggregate thereof with a glass phase containing boron or phosphorus. 2. A mixture of a ceramic raw material that reacts with boron or phosphorus to produce needle-like crystals during firing, a sintering aid containing boron or phosphorus, and a volatile material that burns off during firing. A method for producing a porous body, characterized in that it is formed by firing after forming. 3. An agglomerate formed by pre-firing a ceramic raw material, a sintering aid containing boron or phosphorus, and a volatilizing material which is burned off during firing are blended. A method for producing a porous body, characterized in that the porous body is formed. 4. An agglomerate formed by pre-firing a mixture of a ceramic raw material and a sintering aid containing boron or phosphorus, and a volatilizing material that is burned off during firing, and the resultant mixture is formed. A method for producing a porous body, characterized by being formed by firing. 5. The method for producing a porous body according to claim 2, wherein a foaming material which generates gas during sintering, expands, and burns off is added to the composition.