JPH11128639A - Ceramic filter and method of manufacturing the same - Google Patents

Abstract

[PROBLEMS] To provide a cordierite ceramics filter having high long-term reliability as a filter for high-temperature dust-containing gas. SOLUTION: Silica component 40-65% by weight, alumina component 25-45% by weight, magnesia component 10-16% by weight
Is used, and the powder is adjusted to an average particle diameter of 20 μm or less, mixed, molded, and sintered together with an organic spherical pore-imparting material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic filter comprising a cordierite single phase having excellent heat resistance and thermal shock resistance and having a predetermined uniform pore size distribution, and a method for producing the same. Cordierite ceramics have a low thermal expansion coefficient of 1 to 2 × 10 ⁻⁶ / ° C. and a Young's modulus of 150 GPa or less, which is less than half that of alumina. Taking advantage of excellent chemical stability at the time, a material having porosity is widely used as a catalyst carrier for automobile exhaust gas or a filter for removing combustion ash contained in combustion gas and the like.

[0002]

2. Description of the Related Art As an example of a conventional method for manufacturing a cordierite sintered body, silica, alumina, magnesia powder or a chloride thereof is heated to a high temperature of 1300 to 1400 ° C., and a solid phase reaction is performed. It is known to be a cordierite sintered body.

[0003] In the case of a porous body, this sintered body is pulverized and sieved to a predetermined particle size in order to obtain a target pore diameter, and is a feldspar containing lithium, aluminum, sodium silicate or the like containing Na, Ca, K or the like. A material that has a lower melting point than cordierite, such as β-spodumene or eucryptite, or generates a liquid phase at or below the melting point is used as a binder, mixed, molded, and sintered to produce a porous body with pores between particles. Is generally used.

However, in this conventional production method, cordierite is difficult to sinter, so that as a binder, β-spodumene or eucryptite, which is a lithium aluminum silicate, or feldspar containing aluminium (Na, Ca, K) is used. However, since a material that generates a liquid phase at a melting point lower than or lower than that of cordierite, such as acid salt, is used, there is a disadvantage that heat resistance is reduced.

For example, Japanese Patent Application Laid-Open No. 1-297131 discloses a method for producing a cordierite porous material having a desired pore diameter by adding lithium aluminum silicate β-spodumene and eucryptite to cordierite. . This eucryptite has a melting point of about 1400 ° C.
It is. Therefore, since the melting point (1470 ° C.) of cordierite, which is a main component, is lower, heat resistance is reduced. Further, when mixed with cordierite and sintered, 1100
There is a drawback that it cannot be used at higher temperatures because it generates and sinters the liquid phase from around ℃.

When feldspar (aluminosilicate) containing Na, Ca, and K is used as a binder, the binder has a thermal expansion coefficient of 4 to 6 × 10 ⁻⁶ / ° C., which is higher than that of cordierite. In some cases, the thermal expansion coefficient of the sintered body is improved, and the thermal shock resistance is reduced.

In JP-A-3-10365, talc, magnesite, magnesium carbonate, quartz, calcite, aluminum hydroxide, and the like are mixed, and porosity is obtained from chemical reactions such as decomposition and sublimation of magnesium salts such as magnesium hydroxide and magnesium carbonate. Discloses a method for producing a transformed cordierite porous body, but the porous body produced by this method is a porous body having a wide pore diameter distribution because pores are produced by a thermal decomposition reaction or the like, There is a disadvantage that it is difficult to obtain a uniform porous body having a desired pore size distribution.

In Japanese Patent Application Laid-Open No. 60-226416, an aluminum metal salt and a magnesium metal salt are dissolved in an alcohol solution of an alkyl silicate, and sprayed and melted in a heating zone to produce fine glass hollow spheres, which are then formed and sintered. A method for producing a cordierite porous body having fine pores having an average pore diameter of less than 1 μm to several μm by sintering is disclosed. This method has a porosity of 48% or more and a pore diameter of several μm.
m or less, which is suitable for producing a porous body having a high porosity and fine porosity. However, the production of a porous body having a porosity of less than 48% or a large pore having an average porosity of 10 μm or more, particularly 50 μm or more. There is a drawback that production of a cordierite porous body is difficult.

JP-A-57-92574 discloses the use of a glass powder having a cordierite composition and a raw material consisting of kaolin, talc, and aluminum oxide which precipitate cordierite upon firing. This method is relatively inexpensive, and suitable for certain manufacturing methods such as extrusion.However, since the raw material is a natural mineral, impurities cannot be avoided, resulting in a decrease in strength at high temperatures. Not enough.

As described above, the essential problem of the above-mentioned existing technology is that while using cordierite having an excellent coefficient of thermal expansion, other components are added to improve the sinterability and obtain a porous body. Therefore, the properties of the material are not fully utilized, and the shape of the pores forming the porous body cannot be controlled arbitrarily. Furthermore, the porosity range is not appropriate in Japanese Patent Application Laid-Open No. 60-226416, and There are problems such as insufficient mechanical strength for functioning as a high-temperature gas filter, and all of them have a problem in long-term reliability when used as a high-temperature gas filter.

[0011]

SUMMARY OF THE INVENTION The present invention is based on these prior arts, and has high heat resistance, excellent thermal shock resistance, is chemically stable, has a substantially spherical pore shape, and has a pore size distribution. An object of the present invention is to provide a ceramic filter using a uniform cordierite porous body.

[0012]

According to the present invention, there is provided an amorphous material comprising 40 to 65% by weight of a silica component, 25 to 45% by weight of an alumina component and 10 to 16% by weight of a magnesia component as a porous body forming material. Provided is a ceramics filter comprising a cordierite single phase obtained by molding and sintering glass powder alone and a porous body mainly composed of spherical pores.

Further, as the porous material forming material, only an amorphous glass powder comprising 40 to 65% by weight of a silica component, 25 to 45% by weight of an alumina component and 10 to 16% by weight of a magnesia component is used, and The powder was adjusted to a particle size of 20 μm or less, a spherical pore-imparting material was added thereto, and mixed.
Provided is a method for producing a ceramic filter comprising a single phase of cordierite, which is formed and sintered.

In a preferred embodiment of the ceramic filter of the present invention, the porous body has an apparent porosity of 25 to 50%.
In a further preferred aspect of the ceramic filter of the present invention, the porous body has an average pore diameter of 10 to 100 µm.

In a preferred embodiment of the production method of the present invention, an amorphous glass powder adjusted to a particle size of 20 μm or less is granulated,
To this, a spherical pore-imparting material is added. In another preferred embodiment of the production method of the present invention, an organic spherical body is used as a spherical pore-imparting material, and the porous body mainly comprises spherical pores.

Since cordierite is difficult to sinter as described above, the crystallized substance hardly sinters, and a porous body in which the particles are firmly bonded cannot be obtained. The present inventors have found that only amorphous glass powder is used as a precursor material for forming a porous body, and this is finely pulverized and sintered, thereby exhibiting strong bonding without adding a binder. As a desirable method, the average pore diameter is 10 to 100 μm, particularly 40 to 6 μm by utilizing spherical pores formed after the added organic spheres are burned off during firing.
It has been found that a ceramic filter composed of a cordierite single phase porous body in which spherical pores of 0 μm are uniformly dispersed can be manufactured.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The starting material of the amorphous glass used in the present invention is silica (SiO ₂ ) as a natural silica sand source, and alumina (Al ₂ O ₃ ) as a corundum or magnesia (Al ₂ O ₃ ) source. The MgO) source may be a magnesium salt such as magnesium carbonate or magnesium nitrate, or magnesium hydroxide. 95% raw material purity for all raw materials
Above, especially 98% or more is preferable. Purity 9
If it is less than 5%, the composition of the porous body made of the cordierite single phase obtained after crystallization may be shifted due to impurities contained in the raw material, and the heat resistance may decrease and the thermal expansion coefficient may increase.

The composition of the raw glass is such that the silica component is 40 to 6
5% by weight, 25 to 45% by weight of the alumina component, and 10 to 16% by weight of the magnesia component are as follows. This is because no body can be obtained, and mullite, forsterite, spinel or starting materials such as alumina, silica and magnesia are precipitated as a mixed phase.

The glass composition may contain a small amount of other components or impurities to such an extent that these objects are not impaired. Also, in the case of using alumina balls in the wet pulverization performed for the fine pulverization, the amount of alumina mixed in from the ball abrasion at the time of the pulverization may cause a composition shift by slightly reducing the amount of alumina added in the initial stage. It is preferable not to do so.

In the present invention, the cordierite single phase is xMgO.y as a cordierite crystal.
In the _{Al 2 O 3 · zSiO 2 x} : 1.5~2.6,
y: 1.5 to 2.4, and z: a crystal phase included in the range indicated by 4.1 to 6.4.

The method for producing the amorphous glass and its powder used in the present invention is as follows. The raw materials to be used are sufficiently dried and then melted at 1500 ° C. or higher in a commercially available electric furnace. 1600 ° C to obtain a dense glass body
It is preferable that the above be melted. The electric furnace is not particularly limited as long as the temperature is 1500 ° C. or higher. It is preferable that the melt obtained in the electric furnace is taken out of the electric furnace, put into water and quenched to obtain amorphous glass. It may be poured on an iron plate or a copper plate and quenched.

The thus obtained amorphous glass was made
Crush to a size of about 3 mm. Then, it is pulverized to a particle size of 150 μm or less using a device such as a vibration mill. The obtained powder is further wet-pulverized in a monomalon pot. The dispersion medium at the time of pulverization is preferably water or alcohol. When water is used, a high concentration slurry of 30 to 40% by volume can be obtained by adding an appropriate amount of an appropriate dispersant.

It is preferable that the slurry concentration, the pulverization time, and the like be set so that the particle size of the powder obtained after the pulverization is 20 μm or less. When the particle size is more than 20 μm, more than half of the glass raw material is close to the size of the organic sphere of the pore-forming agent described below, cannot form uniform spherical pores, and when those large particles are aggregated, It can be a stress concentration source that reduces the strength of the porous body.

The above crushed slurry is dried. When the alcohol is pulverized, vacuum drying using an evaporator is performed. In the case of water pulverization, granulation drying by spray drying may be used.

An organic spheroid is preferably added in order to impart spherical porosity to the thus prepared amorphous glass powder having a cordierite composition. Various organic spheres can be used, but resinous materials such as acryl, polystyrene and PMMA (polymethyl methacrylate) which burn and decompose at a relatively low temperature are desirable.

The spherical body is used because the pores obtained after combustion are made spherical to reduce the stress concentration at the tip of the crack when the porous body is broken, and the sintered body made of only amorphous glass powder is used. This is for improving the strength of the steel. Many of the imparting materials other than organic substances, such as graphite powder, which is usually used as a pore imparting material, have a relatively high temperature at which they are decomposed during sintering,
In addition, decomposition may be very difficult due to fluctuations in the oxygen partial pressure in the firing furnace, which is generally not preferable.

Although the size of the spherical body can be selected in consideration of the pore diameter of the target ceramic filter, the ceramic filter of the present invention is suitable for removing fine particles in dust-containing gas generated from coal combustion. Considering the size of the fine particles and the pressure loss characteristics at the time of using the filter, those having an average pore diameter of about 20 to 100 μm suitable for forming pores having an average pore diameter of about 10 to 100 μm are appropriate. It is.

The mixing ratio with respect to the amorphous glass powder is related to the porosity of the obtained porous body.
About 0% by weight is preferable.

In the production method of the present invention, the amorphous glass powder having a size of 20 μm or less is used as the amorphous glass powder. It is also effective to use such a fine powder having a particle size of 20 μm or less.
The granulated powder formed into granules having a size of about 100 μm is also used in the present invention.
m or less.

That is, if the shape of the granulated material can be maintained even during sintering, there is an advantage that the amount of the pore-forming material to be added can be reduced, and if the granules have the same size as the spherical pore-forming material to be added, There is also an advantage that both can be easily mixed. Further, in the present invention, the fine amorphous glass powder may be mixed with another glass powder in a state where the fine amorphous glass powder is previously attached to the periphery of the pore-forming material.

The molding and sintering methods in the present invention are not particularly limited, and the mixed powder obtained by the above method is subjected to mold molding,
What is necessary is just to shape | mold by methods, such as extrusion molding. The obtained molded body was subjected to 1000 to 1000
Sintering may be performed at 1450 ° C. It is preferable to provide a holding time at the highest temperature to promote crystallization of the glass.

By the above-mentioned method, a sintered body consisting of a cordierite single phase in which pores mainly composed of spheres having an average pore diameter substantially the same as or slightly smaller than the added organic spheres can be produced. . As described above, according to the present invention, it is possible to produce a cordierite porous body having a target pore diameter in which pore diameters are uniformly distributed without impairing heat resistance and thermal shock resistance. When the pores in the sintered body are spherical, when stress is applied as a structure, stress concentration as a defect is small, and as a result, high strength is provided.

In the present invention, the porous body mainly composed of spherical pores has a spherical shape in which many individual pores have almost no pores with sharp corners.
These pores are connected to each other by pores so as to be open pores, and a part of the porous body forms pores in which spherical pores are connected to each other.

Such a porous body of the present invention has a large apparent porosity of 25 to 50% and an average pore diameter of 10 which can be suitably used as a ceramic filter for the above-mentioned purpose.
As the pore diameter of １００100 μm, particularly 40 μm or more, a large pore diameter can be obtained as an easily controlled one.
Further, the pore size distribution is also in the range of the above-mentioned average pore size, and desirably, one having 80% or more of the total pore volume within a range of ± 20% from the average pore size can be easily obtained.

As described above, since the filter manufactured by the manufacturing method of the present invention is made of a cordierite single phase, it has a very low coefficient of thermal expansion, is chemically stable, and has a high degree of dust removal in a high-temperature gas. It is most suitable as a material of a filter for performing the above. In addition, strength is high because pore is spherical,
Excellent long-term service reliability.

[0036]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1 49.5% by weight of silica, α-
After weighing and mixing 37.2% by weight of alumina and 13.3% by weight of magnesia, a resistance heating type electric furnace was used.
After maintaining at 1600 ° C. for 5 hours and melting, it was dropped into water to obtain an amorphous glass body. The obtained glass was roughly pulverized into particles having a particle size of 150 μm or less by a dry planetary mill. The obtained coarse powder was further wet-pulverized in a monomalon pot. Alumina was used as a ball and water was used as a dispersion medium. The raw material concentration is 35% by volume, and the pulverization time is 24 hours.

The particle size after pulverization was 20 μm or less, and the average particle size was 4.8 μm. After the pulverized slurry was taken out of the pot, it was dried and granulated by a spray dryer as it was. The rotation speed of the atomizer is 8000 rpm, the inlet air temperature is 140 ° C, and the outlet air temperature is 80 ° C. The average particle size of the dried granules was 47 μm.

The obtained granules were dry-mixed with acrylic spheres (average particle size 60 μm) using a V mixer. The mixing ratio of the acrylic sphere was 30% by weight, and the mixing time was 30 minutes. The obtained powder was filled in a mold of 60 mm × 120 mm, and was molded by a press molding machine at a pressure of 200 kgf / cm ² . The obtained molded body was heated at 1350 ° C. in a resistance heating furnace.
Baking was performed for 2 hours. The obtained sintered body was a cordierite single phase, and its apparent porosity was 32%.

The distribution of pores in the sintered body is substantially uniform,
The average pore diameter was 43 μm. The pore size distribution was 83% of the total pore volume within a range of ± 10% from the average pore size, indicating high pore size controllability. In addition, the shape of the obtained pores is basically spherical, and some of the connected pores are partially formed.However, there are few sharp pores that become stress concentration sources, and from the viewpoint of the strength of the porous body. Even the desired organization was obtained.

In order to evaluate the high temperature strength and the chemical stability of the obtained porous body, the bending strength at hot (1000 ° C.) was compared. In addition, after exposing to a 900 ° C. high-temperature gas containing a sulfide having the same composition as the exhaust gas from a coal combustion plant, the strength was measured. Table 1 shows the above results.

Table 1 also shows the test results of a material having the same porosity using lithium aluminosilicate as a conventional binder (Comparative Example 1). The porous body of the present invention comprising a single cordierite phase hardly decreased in strength even under hot conditions, and did not undergo any strength decrease under corrosive gas. Therefore, if used as a filter for hot dust removal in coal power plants,
Can be used for a long time without loss of reliability. Further, the porous body of the present invention had an extremely high Weibull coefficient (measured by hot bending strength) of 25, which indicates the variation in the strength of the ceramics, showing a structural uniformity superior to 17 of Comparative Example 1 of the conventional material.

(Example 2) After weighing and mixing 52% by weight of silica, 34% by weight of α-alumina and 14% by weight of magnesia, the mixture was kept at 1600 ° C. for 5 hours using a resistance heating type electric furnace. After melting, it was dropped into water to obtain an amorphous glass body. The obtained glass was dried with a dry planetary mill to a particle size of 150.
It was coarsely pulverized into particles having a size of not more than μm. The obtained coarse powder was further wet-pulverized in a monomalon pot. Alumina was used as the ball, and alcohol was used as the dispersion medium. The raw material concentration is 35% by volume, and the pulverization time is 20 hours.

The particle size after pulverization was 20 μm or less, and the average particle size was 4.8 μm. The pulverized slurry was dried by an evaporator. The obtained dry powder was wet-kneaded with an acrylic sphere and a binder, and extruded into a plate-like material having a plurality of elliptical holes in the longitudinal direction and preferably usable as the basis of an orthogonal filter.
The average particle size of the added acrylic sphere is 60 μm, and the mixing ratio is 30% by weight.

The structure of the obtained plate, such as the shape of pores, was almost the same as in Example 1. After drying the same material 1
The plate was fired at 375 ° C. for 3 hours, and the thermal shock resistance of the fired plate was evaluated. The evaluation method is as follows.
After exposure for 0 minute, the sample was taken out and dropped into water. The temperature at which cracks were visually observed was defined as the thermal shock destruction temperature. Table 2 shows the results.

A comparison was made with a conventional system containing a binder such as kaolin or talc (Comparative Example 2). As can be seen from Table 2,
The thermal shock fracture temperature is improved by 130 ° C. as compared with the conventional material, which is considered to be due to the low coefficient of thermal expansion due to the cordierite single phase composition.

Example 3 48% by weight of silica, 40% by weight of α-alumina and 12% by weight of magnesia were weighed, mixed and then kept at 1600 ° C. for 5 hours using a resistance heating type electric furnace. After melting, it was dropped into water to obtain an amorphous glass body. The obtained glass was roughly pulverized by a jaw crusher and further pulverized by a dry planetary mill into particles having a particle size of 150 μm or less. The average particle size of the obtained powder is 35 μm
Met. The powder was further wet-pulverized in water, added with a binder, and spray-dried.

The obtained powder has a particle size of 20 μm or less and an average particle size of 8 μm, and the average particle size of the granulated granules is 40 μm.
Met. Polystyrene spheres (average particle size 60μ)
m) was added in a mixing ratio of 45% by weight, mixed with a dry V mixer, and filled in a rubber mold having a metal core. It was formed into a cylinder having a diameter of 180 mm, a thickness of 20 mm, and a length of 300 mm using a hydrostatic press at a pressure of 500 kgf / cm ² , and after releasing the mold, the outer periphery of the formed body was green-ground with a cylindrical grinder. The obtained cylinder was fired in air at 1300 ° C. for 3 hours. The apparent porosity of the obtained cylinder was 38%, and the structure such as the shape of the pores was almost the same as that of Example 1. A thermal stress fracture test of the cylinder was performed.

A high-temperature combustion gas was passed through the inside of the cylinder, and the outer surface was radiatively cooled through a water-cooled jacket. A thermocouple was embedded in the cylinder, and the inside and outside temperature difference was measured. The combustion gas was set at a predetermined temperature, held for 30 minutes, and then extinguished and released. If there was no damage to the cylinder, it was assembled again in the tester and the test was performed at a higher temperature. The temperature difference between inside and outside that led to destruction was 350 ° C. or more. None of the conventional materials shown in Comparative Example 1 could withstand a temperature difference of 250 ° C. or more.

(Examples 4 to 7 and Comparative Examples 3 and 5) Silica, α-alumina, and magnesia were weighed to have the composition shown in Table 3, mixed, and then mixed in a resistance heating type electric furnace.
After maintaining at 600 ° C. for 5 hours and melting, it was dropped into water to obtain amorphous glasses of various compositions. The obtained glass was roughly pulverized by a dry planetary mill so as to have a particle size of 150 μm or less, and further wet pulverized using alcohol. The grinding balls used were alumina and the grinding time was 18 hours. The slurry after the pulverization was dried by an evaporator to obtain a raw material. These powders having a particle size of 16 μm or less were mixed with acrylic spheres (average particle size: 60 μm). The mixing ratio of the acrylic spheres is 30% by weight.

Then, these powders were filled in a 60 × 60 mm mold and 200 kgf / cm ² by a press molding machine.
At a pressure of Then, the molded body is placed in a heating furnace for 135 minutes.
Baking was performed at 0 ° C. for 2 hours. The apparent porosity of the porous body after sintering was 34% to 36%. The shape of the pores in the porous body is mainly spherical pores as in Example 1,
Its size is about 40 which is about the same as the added acrylic sphere.
７０70 μm and the average pore diameter is 43 μm
Met. Both the porosity and the pore diameter were almost constant irrespective of the glass composition.

From the porous body thus obtained, a thermal expansion test piece (diameter 5 mm, length 20 mm) and a strength test piece (5 × 10
× 50 mm), and the mechanical properties were measured. Table 3 shows the results. As can be seen from Table 3, within the composition range of the present invention, the coefficient of thermal expansion (0 to 1000 ° C.) is 2.5 × 1.
It was as low as 0 ⁻⁶ / ° C. or less, and analysis by X-ray diffraction confirmed only a cordierite single phase.

Such a porous body is suitable as a porous body for a filter as in Examples 1 to 3.
The filter material had the required performance as a filter material comparable to that of No. 3 to No. 3.

Those prepared in the same manner but outside the composition range of the present invention are shown in Table 3 as Comparative Examples 3 to 5. These all had high coefficients of thermal expansion, and some had cracks in the sintered porous body. This is presumably because a crystal phase other than the desired cordierite composition was precipitated, and internal damage occurred due to a change in volume and a difference in thermal expansion coefficient during sintering.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

The ceramic filter of the present invention has a very low coefficient of thermal expansion and is chemically stable because it consists of a cordierite single phase. In addition, since the pores are uniform and spherical with a predetermined size, the strength is high and the long-term durability is excellent. Therefore, it is possible to provide an optimal filter for removing fine particles contained in the high-temperature gas.

Claims (6)

[Claims] (1) As a porous material forming material, a silica component is 40
６５65% by weight, 25-45% by weight of alumina component, and 10-16% by weight of magnesia component. A ceramic filter, comprising a porous body made of a ceramic material. 2. The ceramic filter according to claim 1, wherein the apparent porosity of the porous body is 25 to 50%. 3. The ceramic filter according to claim 2, wherein the average pore diameter of the porous body is 10 to 100 μm. 4. The porous body-forming material has a silica component of 40%.
Only an amorphous glass powder having a particle size of 20 to 65 μm, an alumina component of 25 to 45% by weight, and a magnesia component of 10 to 16% by weight was used. A method for producing a ceramic filter comprising a single cordierite phase, comprising adding a pore-forming material, mixing, molding and sintering. 5. The method for producing a ceramics filter according to claim 4, wherein amorphous glass powder having a particle size of 20 μm or less is granulated, and a spherical pore-imparting material is added thereto. 6. The method for producing a ceramic filter according to claim 4, wherein an organic substance spherical body is used as the spherical pore-imparting material, and the porous body mainly comprises spherical pores.