JP2023060940A - ceramic structure - Google Patents

Abstract

To provide a ceramic structure capable of improving strength without increasing a pressure loss.SOLUTION: In a ceramic structure 10 having a skeleton 2 mainly composed of Al oxide and a communication pore whose porosity is 60-97%, when taking frequency distribution of a particle size of the skeleton 2, frequency FA of peak A having the largest frequency, and frequency FB of peak B having the next largest frequency satisfy 0.05≤FB/FA≤0.35.SELECTED DRAWING: Figure 3

Description

TECHNICAL FIELD The present invention relates to a ceramic structure that can be suitably used, for example, as a filter for exhaust pipes such as drafts, pipes and ducts.

BACKGROUND ART Conventionally, porous sintered bodies using ceramic powder have been used for applications such as sound absorbing materials and catalysts (Patent Document 1). In general, such porous sintered bodies are equipped with interconnected pores having countless fine pores.

JP-A-2000-264753

However, there is a problem that the ceramic porous body is weak in strength and easily broken.
On the other hand, if the porosity of the ceramic porous body is reduced, the strength is improved, but the pressure loss of the fluid passing through the ceramic porous body increases, which is not suitable.
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a ceramic structure capable of improving strength without increasing pressure loss.

In order to solve the above problems, a ceramic structure according to a first aspect of the present invention is a ceramic structure having a skeleton containing Al oxide as a main component and having open pores and a porosity of 60 to 97%. , when the frequency distribution of the particle size of the skeleton is taken, the frequency FA of peak A with the highest frequency and the frequency FB of peak B with the second highest frequency satisfy 0.05 ≤ FB / FA ≤ 0.35. It is characterized by

According to this ceramic structure, since the number of particles with different particle diameters is appropriately different, as the Al oxide particles serving as the skeleton, when making a mixed slurry of large-diameter particles and small-diameter particles, or when forming a mixed slurry of large-diameter particles and small-diameter particles, When the is mixed to form a slurry, small-diameter particles are closely packed between large-diameter particles, promoting sintering of the skeleton. As a result, it is possible to improve the strength of the skeleton, and thus the strength of the ceramic structure, without reducing the porosity and increasing the pressure loss.

In addition, a ceramic structure according to a second aspect of the present invention is a ceramic structure having a skeleton containing Al oxide as a main component and having a porosity of 60 to 97% and having continuous pores, wherein grains of the skeleton are When the frequency distribution of the diameters is taken, the peak particle size PC of the peak C having the largest particle size and the peak particle size PD of the peak D having the next largest particle size satisfy PC ≤ 10 μm and 5 ≤ PC / PD. It is characterized by

According to this ceramic structure, since even the largest particles are fine particles of 10 μm or less, when the Al oxide particles that form the skeleton are made into a slurry as described above, the particles are closely packed and the skeleton is sintered. is promoted. As a result, it is possible to improve the strength of the skeleton, and thus the strength of the ceramic structure, without reducing the porosity and increasing the pressure loss.
In addition, since the difference in particle size between particles with the next largest particle size becomes large, when the Al oxide particles that form the skeleton are slurried as described above, small-diameter particles are densely packed between large-diameter particles. and promotes sintering of the skeleton. As a result, it is possible to improve the strength of the skeleton, and thus the strength of the ceramic structure, without reducing the porosity and increasing the pressure loss.

In the ceramic structure of the present invention, when the cross section of the skeleton is viewed, the porosity in the skeleton may be 10% or less.
According to this ceramic structure, the strength of the skeleton is further improved.

In the ceramic structure of the present invention, the skeleton may contain other elements other than the Al oxide in a total amount of 3.0% by mass or less.
According to this ceramic structure, since the total content of other elements is 3.0 mass or less, the growth of abnormal grains of Al oxide in the framework is suppressed, the strength of the framework is reduced, and the ceramic structure is improved. A decrease in strength can be suppressed.

According to the present invention, it is possible to obtain a ceramic structure whose strength can be improved without increasing pressure loss.

1 is a schematic diagram of a ceramic structure according to an embodiment of the first aspect of the present invention; FIG. 1 is a schematic cross-sectional view of a ceramic structure according to an embodiment of the first aspect of the present invention; FIG. FIG. 2 is a schematic diagram showing the frequency distribution of grain sizes of the skeleton of the ceramic structure according to the embodiment of the first aspect of the present invention; FIG. 4 is a schematic diagram showing a method for measuring the grain size of a skeleton by an intercept method. FIG. 5 is a schematic diagram showing the frequency distribution of grain sizes of the skeleton of the ceramic structure according to the embodiment of the second aspect of the present invention;

First, an embodiment of the first aspect of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a ceramic structure 10 according to an embodiment of the first aspect of the present invention, FIG. 2 is a schematic cross-sectional view of the ceramic structure 10, and FIG. It is a schematic diagram which shows frequency distribution.

As shown in FIG. 1, the ceramic structure 10 has a skeleton 2 and has communicating pores in which gaps V in the skeleton 2 are voids.
The ceramic structure 10 can be suitably used, for example, as filters for exhaust pipes such as drafts, pipes and ducts. In particular, it can be suitably used in applications where large stress is applied, and where high-temperature fluids and chemicals flow. The fluid flows through the gap V.

The ceramic structure 10 (skeleton 2) is formed by using, for example, a urethane sponge having continuous pores as a mold, impregnating the sponge with a slurry containing ceramic particles, an organic solvent, etc., drying it, and then baking it to burn off the sponge. It can be manufactured by a manufacturing template method. By burning off the sponge, it becomes a porous ceramic having a three-dimensional network structure with communicating pores having substantially the same shape as the communicating pores of the sponge.

The porosity of the ceramic structure 10 is 60-97%, more preferably 80-95%.
If the porosity of the ceramic structure 10 is less than 60%, the pressure loss increases and the fluid flow becomes insufficient. If the porosity of the ceramic structure 10 exceeds 97%, it is difficult to manufacture the ceramic structure 10, and the skeleton 2 becomes thin, which reduces the strength of the ceramic structure 10.
The porosity of the ceramic structure 10 is calculated by cutting out a part of a predetermined size (for example, 30 mm×30 mm×30 mm, but if the ceramic structure 10 is smaller than this, the size is smaller), measuring the mass, and calculating the density. and calculate the porosity. More specifically, the theoretical density is calculated by composition analysis of the ceramic structure 10 (skeleton 2), and the porosity is calculated based on the calculated theoretical density and the measured density.

The skeleton 2 is a ceramic sintered body that contains Al oxide as a main component, is formed by sintering Al oxide particles, and has a particle size distribution described later. A main component means more than 50 mass %. Further, the skeleton 2 may substantially consist of Al oxide.
Further, the skeleton 2 may contain other elements other than Al oxide in a total amount of 3.0% by mass or less. If the total content of other elements exceeds 3.0% by mass, the growth of abnormal grains of Al oxide in the skeleton 2 is promoted, the strength of the skeleton 2 is reduced, and the strength of the ceramic structure 10 is reduced. sometimes.
Other elements include, for example, one or more divalent elements selected from the group of Mg, Ca, Sr and Ba.
The total amount of other elements contained in the skeleton 2 can be measured by ICP (Inductively Coupled Plasma).

Further, as shown in FIG. 2, when the cross section of the skeleton 2 is viewed, the porosity in the skeleton 2 is preferably 10% or less, since the strength of the skeleton 2 is further improved.
The porosity in the skeleton 2 is set so that the matrix (Al oxide of the skeleton 2) and darker regions can be distinguished in a 100×100 μm field of view AR of a backscattered electron image of a cross-sectional SEM of the skeleton 2. Binarize the image. Then, the area ratio of the dark portion in the field of view is calculated and taken as the porosity. This is because portions darker than the matrix can be regarded as voids G of the skeleton 2 .

Next, with reference to FIG. 3, the characterizing portion of the first aspect of the present invention will be described.
As shown in FIG. 3, when the frequency distribution of the particle size of the skeleton 2 is taken, the frequency FA of the peak A with the highest frequency and the frequency FB of the peak B with the second highest frequency are 0.05≦FB/FA. ≦0.35 is satisfied.

FB/FA is the difference (ratio) between the number of particles with the highest frequency (large number of predetermined particle sizes) and the number of particles with the next highest frequency (large number of predetermined particle sizes). A higher ratio indicates a greater difference in the number of particles with different particle sizes.
If 0.05 ≤ FB/FA ≤ 0.35, the number of particles with different particle sizes is moderately different, so that the mixed slurry of large-diameter particles and small-diameter particles is used as the Al oxide particles that form the skeleton 2. When the large-diameter particles and the colloidal particles are mixed to form a slurry, the small-diameter particles are closely packed between the large-diameter particles, and the sintering of the skeleton 2 is promoted. As a result, the strength of the skeleton 2 and, in turn, the strength of the ceramic structure 10 are improved.

If 0.05>FB/FA, the difference in the number of particles with two different particle sizes becomes too large, reducing the effect of close-packing of small-diameter particles between large-diameter particles, resulting in a ceramic structure. 10 strength is not sufficiently improved.
When 0.35<FB/FA, the difference in the number of particles with different diameters is small, and the effect of close-packing small-diameter particles between large-diameter particles is also reduced, and the ceramic structure 10 strength is not sufficiently improved.

The grain size of skeleton 2 is the average grain size of Al oxide particles in the cross section of skeleton 2 . FIG. 4 is an explanatory diagram showing a method of calculating the average particle size of the skeleton 2. FIG. First, a cross-section of the skeleton 2 was mirror-polished and photographed with a SEM (scanning electron microscope) to obtain a square cross-sectional image of 30 μm×30 μm (also referred to as an SEM image). Here, the acceleration voltage was set to 15 kV and the magnification was set to 3000 times.
FIG. 4A is a schematic diagram showing the state of Al oxide particles observed in an SEM image. The average particle size of 200 particles was calculated by the following intercept method using such SEM images. If less than 200 particles are counted on the following diagonal lines DG1 and DG2 per cross-sectional image of 30 μm×30 μm, another cross-sectional image is further prepared to count a total of 200 particles.

In the intercept method, first, Al oxide particles that intersect at least one of two diagonal lines DG1 and DG2 (FIG. 4A) of a 30 μm×30 μm square were selected. Then, the maximum diameter Dmax of each of the selected particles CG (FIG. 4B) was determined and defined as the major diameter D1. The maximum diameter Dmax is the maximum value of the outer diameters of the particles CG measured in all directions. The outer diameter of the particle CG on a straight line passing through the middle point of the major diameter D1 and orthogonal to the major diameter D1 was defined as the minor diameter D2. Further, the average value (D1+D2)/2 of the major diameter D1 and the minor diameter D2 was defined as the assumed particle diameter Da(i) of the target particles CG. Here, "(i)" means the value of the i-th particle CG.
The average particle diameter Dave is the average value of the assumed particle diameters Da(i) of the n particles CG intersecting at least one of the diagonal lines DG1 and DG2. This average value was adopted as the average particle size.

An embodiment of the second aspect of the invention will now be described with reference to FIG. The embodiment of the second aspect of the present invention is the same as the embodiment of the first aspect except that the frequency distribution of the particle size of the skeleton 2 is different. 2) are omitted.
As shown in FIG. 5, when taking the frequency distribution of the particle size of the skeleton 2, when taking the frequency distribution of the particle size of the skeleton 2, the peak particle size PC of the peak C with the largest particle size and the particle size of The peak particle size PD of the next largest peak D satisfies PC≦10 μm and 5≦PC/PD.
PC/PD is the difference (ratio) in particle size between the largest particle and the next largest particle, the higher the ratio, the greater the difference in particle size between the two particles. show.

If PC ≤ 10 µm, the largest particle is also a fine particle of 10 µm or less. Sintering of 2 is promoted. As a result, the strength of the skeleton 2 and, in turn, the strength of the ceramic structure 10 are improved.
Also, if 5 ≤ PC/PD, the difference in particle size between the largest particle and the second largest particle becomes large, so when making the slurry for the skeleton 2, the largest particle The particles having the next largest particle size are closely packed between the two, which promotes sintering of the framework 2 and likewise improves the strength of the ceramic structure 10 .
Although the upper limit of PC/PD is not particularly limited, it is 50, for example.

If PC>10 μm, the particle size of the largest particle becomes too large, and the effect of closely packing the particles during slurrying is reduced, and the strength of the ceramic structure 10 is not sufficiently improved.
When 5>PC/PD, the difference in particle size between the largest particle and the particle with the next largest particle size is small, and the effect of close packing of small particles between the large particles is also obtained. and the strength of the ceramic structure 10 is not sufficiently improved.

It goes without saying that the present invention is not limited to the above-described embodiments, but extends to various modifications and equivalents within the spirit and scope of the present invention.
The shape of the ceramic structure is not limited, and may be a polygonal column, a polygonal cylinder, an ellipse, or an irregular shape.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these.

A urethane sponge having continuous pores is used as a mold, and this sponge is impregnated with a slurry containing ceramic particles (alumina), particles or colloidal particles containing a divalent element shown in Table 1, a complex and an organic solvent, and then baked. Burned out the sponge. As a result, a ceramic structure 10 made of an oxide ceramic having a predetermined porosity and having continuous pores was manufactured. The dimensions of the ceramic structure 10 were a rectangular parallelepiped with a thickness of 30×30×7 mm.
The porosity of the ceramic structure 10 was adjusted to the values shown in Table 1 by changing the urethane sponge. In addition, FB/FA and PC/PD were adjusted by changing the particle size of the raw material particles, and the porosity of the skeleton was changed by changing the firing conditions to produce each sample.

The porosities of the ceramic structure 10 and skeleton 2 were measured by the method described above.
The frequency distribution of the particle size of the framework was determined by the method described above.
Whether or not the divalent element forms an aluminate phase was determined by the method described above.

The compressive strength of the ceramic structure 10 was measured by compressing it in the thickness direction with an autograph (AGX-X manufactured by Shimadzu Corporation) and breaking it. If the compressive strength exceeds 0.5 MPa, it can be said that the strength is high.
The pressure loss of the ceramic structure 10 was measured as the pressure loss when room temperature air was allowed to flow at a constant flow rate (within the range of 5 to 25 L/min) into the circulating constant temperature liquid bath. If the pressure loss is less than 3.5 Pa, it can be said that the pressure loss is small.

Table 1 shows the results obtained.

As is clear from Table 1, in each example where the porosity of the ceramic structure is 60% or more and 0.05≦FB/FA≦0.35, the strength is improved without increasing the pressure loss. was made.
Further, in each example in which the ceramic structure had a porosity of 60% or more, PC≦10 μm, and 5≦PC/PD, the strength could be improved without increasing the pressure loss.
In particular, in Examples 17 to 21, in which the porosity in the skeleton was 10% or less, the strength was further improved compared to Example 15, in which other conditions were the same.

On the other hand, in the case of Comparative Example 2, which does not satisfy 0.05≤FB/FA≤0.35 or 5≤PC/PD, the strength is lower than that of each example.
In Comparative Example 2, in which the porosity of the ceramic structure was less than 60%, the pressure loss increased compared to each example.

2 skeleton 10 ceramic structure

Claims (4)

A ceramic structure having a skeleton mainly composed of Al oxide and having a porosity of 60 to 97% and having continuous pores,
When the frequency distribution of the particle size of the skeleton is taken, the frequency FA of peak A with the highest frequency and the frequency FB of peak B with the next highest frequency satisfy 0.05 ≤ FB / FA ≤ 0.35. A ceramic structure characterized by: A ceramic structure having a skeleton mainly composed of Al oxide and having a porosity of 60 to 97% and having continuous pores,
When the frequency distribution of the particle size of the skeleton is taken, the peak particle size PC of the peak C having the largest particle size and the peak particle size PD of the peak D having the next largest particle size are PC ≤ 10 μm and 5 ≤ PC A ceramic structure characterized by satisfying /PD. 3. The ceramic structure according to claim 1, wherein the cross section of the skeleton has a porosity of 10% or less in the skeleton. 4. The ceramic structure according to any one of claims 1 to 3, wherein the skeleton contains 3.0% by mass or less of elements other than the Al oxide in total.

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