JPS62182158A - Cordierite honeycom structure and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a cordierite honeycomb structure, and more specifically to a cordierite honeycomb structure that has excellent thermal shock resistance, airtightness, and heat resistance. The present invention relates to a highly airtight cordierite honeycomb structure for an exchanger and a method for manufacturing the same.

(Prior Art) With the progress of industrial technology in recent years, there has been an increasing demand for materials with excellent heat resistance and thermal shock resistance. The thermal shock resistance of ceramics is influenced by the material's properties such as coefficient of thermal expansion, thermal conductivity, strength, modulus of elasticity, and Poisson's ratio, as well as the size and shape of the product, as well as heating and cooling conditions, that is, heat transfer rate. affected.

Among these factors that affect thermal shock resistance, it is known that the contribution rate of the thermal expansion coefficient is particularly large, and in particular, when the heat transfer rate is large, it is greatly influenced only by the thermal expansion coefficient. The development of low expansion materials with excellent thermal shock resistance is strongly desired.

Cordierite is conventionally known as a relatively low-expansion ceramic material, but cordierite is generally difficult to sinter densely, and its coefficient of thermal expansion from room temperature to 800°C is particularly low at 2. For cordierite substrates that exhibit low expansion properties such as OxlO-6/"c or less, it is necessary to limit the amount of impurities that act as fluxes, such as calcia, alkali, potash, and soda, to an extremely small amount. Very few phases and porous.

Therefore, when such cordierite ceramics is applied to a rotating regenerative heat exchanger with a honeycomb structure, for example, because of its large open porosity, heating can occur through the pores on the surface of the partition wall that form the through holes of the honeycomb structure, especially through the communicating holes. Fluid leakage occurs between the fluid and the heat recovery fluid,
It has the serious disadvantage of reducing the heat exchange efficiency and the efficiency of the overall system in which the heat exchanger is used.

For these reasons, there has been a strong desire for a low-expansion, highly airtight cordierite honeycomb structure that has excellent thermal shock resistance.

It has been known that cordierite ceramics exhibit low expansion properties, for example, as described in U.S. Patent No. 3,885.977.
As disclosed in the corresponding Japanese application (Japanese Patent Application Laid-Open No. 50-75611), the coefficient of thermal expansion between 25 and 100°C is 11 x 10-' in at least one direction.
Cordierite ceramics with an orientation smaller than 7°C are known, and planar orientation caused by plate clay or laminated clay is described as the cause of this orientation, but unlike the present invention, - Using coarse talc of 20 μm, clay ranges from 0.1 to 10 μm,
Moreover, there is no mention of pores at all.

Furthermore, U.S. Pat.
At least 20% of
It is disclosed that cordierite porous ceramics having pores with a diameter larger than 0 μm can be obtained,
Unlike the present invention, the average particle size is 7 μm when the pore volume is 5 μm or more.
There is no mention of increasing airtightness by suppressing the amount to 0.04 cc/g or less using fine talc of 0.04 cc/g or less.

Furthermore, although JP-A-53-82822 describes a positive correlation between the average talc particle size and the average pore size of cordierite ceramics, 1. In order to achieve a thermal expansion coefficient of less than OxlO-6/'cc, it is necessary to make the average grain size of talc coarse particles of 10 to 50 μm. It is not easy to make an analogy.

Furthermore, in JP-A-59-122899, the porosity is 20.
A highly airtight cordierite rotary regenerative heat exchanger, characterized in that the open pores on the surface of the partition wall forming the through-holes of a honeycomb structure mainly composed of ~45% cordierite are sealed with a filling material. However, as in the present invention, by using fine talc with an average particle size of 7 μm or less and fine kaolin with an average particle size of 2 μm or less as a cordierite raw material, 5 μm
There is no description of suppressing the pore volume of m or more to 0.04 cc/g or less to improve airtightness. Also, JP-A-5
The manufacturing method of No. 9-122899 requires a step of supporting the filler material as a slurry on the fired cordierite honeycomb and then re-firing it, so compared to the present invention, the manufacturing method is more likely to cause cell clogging and is costly. It has the disadvantage of being expensive.

(Problems to be Solved by the Invention) An object of the present invention is to provide a highly airtight cordierite honeycomb structure that achieves both airtightness and low expansion, which are the problems of conventional cordierite ceramics.

(Means for solving the problem) The present inventors have solved the problem by using talc with an average particle size of 7 μm or less and kaolin with an average particle size of 2 μm or less and 173 or less of the talc average particle size. diameter is 5
The volume of the pores larger than μm is set to 0.04 cc/g or less to make it substantially airtight, and the coefficient of thermal expansion between 40 and 800°C is set to 1. The average particle diameter of talc is 7 μm or less, which is effective in reducing the pore diameter.

Furthermore, using kaolin with a diameter of 2 μm or less is effective in suppressing porosity. Furthermore, the average particle size is 7 μm.
Using the following talc in combination with kaolin with an average particle size of 1/3 or less of the talc average particle size promotes the orientation of cordierite crystals in the cell walls of the cordierite honeycomb structure, resulting in low expansion. It is something that contributes.

In addition, the present inventors have discovered that the chemical composition of the honeycomb structure is
42-56% by weight in SiO□, preferably 47-53% by weight, 30-45% by weight in ahos, preferably 32-56% by weight
38% by weight, 12-16% by weight in MgO, preferably 1
It has been found that the content is preferably 2.5 to 15% by weight. The honeycomb structure contains other components that are unavoidably mixed, for example, TtOz + CaO + KNaO + Pe2
It may contain 2.5% by weight or less of oz as a whole, but p
, o, is preferably less than 0.1%. The reason for limiting these values is to make the main component of the crystalline phase a cordierite phase and to remove a high expansion glass phase generated from impurities.

Furthermore, the present inventors have determined that when firing the dried material of the honeycomb structure body, 1100-1
It has been found that in the temperature range of 350°C, it is preferable to raise the temperature at a temperature increase rate of 20 to 150°C, and then perform firing at a firing temperature of 1350 to 1440°C. If the temperature increase rate is less than 20°C/h, the coefficient of thermal expansion will be large, and if it is more than 60°C/h, the pore diameter during firing will be large and the airtightness will be poor. Usually 30~
A suitable range is 50°C/h. Also, 1350-14
By firing at a temperature of 40° C., the main component of the crystalline phase can be made into a cordierite phase.

The cell density of the honeycomb structure was set to 62 cells/am” (400
Cell/in or more, rib thickness 203μm (8mi+
) The reason for the following is to use the honeycomb structure as a heat exchanger with high heat exchange efficiency and low pressure loss.

There is no particular limitation on the shape of the cell, but it can be of various shapes, such as triangular, square, rectangular, hexagonal, and other shapes with fins.

The general rule for pores with a diameter of 5 μm or more is 0.04 cc/
The reason why it is limited to 0.026 cc/g or less, preferably 0.026 cc/g or less, is because fluid leakage through the thin walls of such a honeycomb structure is mainly caused by pores with a diameter of 5 μm or more, as shown in FIG. be. In order to satisfy this condition, the porosity is preferably at least 30% or less.

The present invention also includes the use of calcined talc and kaolin, which are effective in suppressing the occurrence of cracks in the honeycomb structure due to shrinkage during drying and firing, when talc and kaolin are made into fine particles. If the calcining temperature of talc or kaolin is increased, it will increase the porosity and the coefficient of thermal expansion, so when using a calcined product, it is preferable to keep the calcining temperature as low as possible. The effects of the present invention cannot be obtained unless fine particles having a particle size similar to that of the raw raw material are used.

Other cordierite forming raw materials, such as alumina source raw materials such as alumina and aluminum hydroxide, and silica source raw materials such as silica and silica sand, that have been conventionally used can be used, but the amount of impurities such as alkali in the chemical composition can be used. It is necessary to optimize the grain size, such as cutting coarse particles, depending on the rib thickness of the honeycomb structure to be manufactured.

Therefore, the chemical composition of the present invention is 42 to 56% by weight of SiO2.
Preferably 47 to 53% by weight, AlzO: + is 30 to 4
5% by weight, preferably 32-38% by weight, MgO 12-38% by weight
Talc with an average particle size of 7 μm or less and an average particle size of 2 μm so that the amount is 16% by weight, preferably 12.5 to 15% by weight.
Mixing kaolin and other cordierite forming raw materials with an average particle size of 173 or less than the average particle size of talc,
A plasticizer and a binder are added to this mixture to make a plasticized deformable batch, and this plasticized batch is molded by extrusion molding and then dried. 20 in the temperature range of °C
The main component of the crystal phase is cordierite phase, the pore volume is 0.04 cc/g or less, 40 to 8
The thermal expansion coefficient between 00℃ and 1. OX 10-h/”C
The following cordierite honeycomb structure is manufactured.

Firing is usually carried out for about 0.5 to 12 hours. The main component of the honeycomb structure is cordierite with a crystalline phase of 90% or more. Other crystals are mainly mullite and spinel (including sapphirine), each of which accounts for 2.5% by weight or less. The honeycomb structure has a total pore volume of pores of 5 μm or more of 0.04 cc/g or less, especially O,,026
cc/g or less, the leakage amount at a pressure of 1.4 kg/cm" is 100 g/sec-m2 or less, especially 50 g
/sec·m2 or less, making it substantially airtight and suitable for use as a heat exchanger.

(Function) In the present invention, since the total pore volume of the pores of 5 μm or more in the honeycomb structure is 0.04 cc/g or less and the porosity is as small as 30% or less, the amount of leakage is small and the heat exchange efficiency is high. Moreover, the thermal expansion coefficient is 1. O x 10-6l℃
Because it is small, it has high thermal shock resistance. Also, increase the rib thickness to 2
Since the walls can be made as thin as 0.3 μm (8 ml) or less, pressure loss is small, and high-density cells can be achieved, making it possible to obtain a ceramic heat exchanger with high heat exchange efficiency. In addition, due to the small pore diameter and low porosity, the strength of the honeycomb structure is higher than that of conventional honeycomb structures.
It is possible to make the walls thinner.

The present invention will be described in more detail below with reference to Examples and Comparative Examples.

The raw materials with the chemical analysis values and particle sizes shown in Table 1 below are summarized in Table 2 N according to the blending ratio, talc particle size, and kaolin particle size in Table 2.
A batch of ll-1lkL30 was prepared, and 4.5 parts by weight of methyl cellulose and added water were added to 100 parts by weight of the raw material, and the mixture was kneaded to obtain an extrudable clay. The raw materials used here all passed through a sieve with a mesh size of 63 μm. Next, each batch of clay was molded using a known extrusion method to form a rectangular cell structure with a rib thickness of 120 μm, number of cells per 11 square centimeters of 167, short side/long side = 1/1.73, a diameter of 93 mm, and a height of 100 mm. A dragon cylindrical honeycomb structure was molded.

After drying, the honeycomb structure of each batch was fired under the firing conditions shown in Table 2, and the characteristics of the sintered body were 40℃~
The coefficient of thermal expansion at 800° C., porosity, total pore volume of pores of 5 μm or more, amount of leakage, amount of cordierite crystals, and thermal shock resistance were evaluated. The evaluation results are also shown in Table 3. In addition, in the chemical composition of the sintered bodies of all batches, P2O, is 0.1
%.

The batch in Table 2, No. 4, was extruded and fired using a die with a different cell structure in the same manner as in Example 1, to produce a 93-layer cellar with a diameter of 93, having the cell structure shown in Table 3. Cylindrical honeycomb structures Nt131 to l1h40 with a height of 100 dragons were manufactured. Pressure loss and leakage amount of each honeycomb structure,
The coefficient of thermal expansion (CTE) was evaluated. The evaluation results are also shown in Table 3.

Table 3 * Measured by 0.5g/ses -cm"'f amount, pressure per unit length... Loss Force rlB comb rv=b+εノ'o1, test piece A5-嘗φ×ωclear 1 evening [
As shown in Tables 2 and 3, according to the present invention, 5
General rules for pores larger than μm: The pore volume is 0.04 cc/g or less, and the thermal expansion coefficient is 1. A honeycomb structure having excellent thermal shock resistance, an extremely small amount of leakage, and an excellent heat exchange efficiency of 0×10-'/''C or less can be obtained. Therefore, the present invention is extremely useful industrially.

[Brief explanation of drawings]

Figure 1 shows the pore volume of 5μm or more and the pressurized air pressure of 1.4kg/
Figure 2 is a diagram showing the particle size distribution of talc used in the example. Figure 3 is a diagram showing the particle size distribution of kaolin used in the example. The figure is a perspective view showing one example of the honeycomb structure of the present invention. The curve A-E in FIG. 2 and the curve A-E in FIG. 3 are the values shown in Table 2, respectively. Figure 5) tyytkA upper d [L amount tcc/9) - Figure 4 Procedures Amendment February 26, 1988 Commissioner of the Japan Patent Office Black 1) Akio 1, Indication of the case 1985 Patent Application No. 293691 No. 2, Title of the invention 3, Relationship with the case of the person making the amendment Patent applicant 4, agent 1, the following sentence is added between lines 9 and 10 on page 8 of the specification. The particle sizes of talc and kaolin were determined from the average particle size based on the blended weight ratio of raw and calcined products.''2.Table 2 on pages 16 and 17 of the same document is corrected as shown in the attached sheet. 3. Add the following sentence before the 1st line of the 19th chapter. ``As an actual example, FIGS. 4 and 5 show an example of a rotating regenerative heat exchanger composed of a plurality of cordierite matrix segments.'' 4, page 19, lines 9 to 5. Correct line 19 as shown below. [Figure 1 is a diagram showing the relationship between the pore volume of 5 μm or more and the amount of test piece leakage, including the punch in Table 2 and other experimental examples. Figure 2 is the talc in Table 1 (^) ~ Figure 3 shows the particle size distribution curves of kaolin (A) to (E) in Table 1. Figures 4 and 5 show the particle size distribution curves of kaolin (A) to (E) in Table 1. FIG. 3 is a diagram showing a rotary regenerative heat exchanger composed of segments. 5. In the drawings, Figure 4 has been changed to a corrected Figure 4, and Figure 5 has been added. Figure 4 (corrected figure) Figure 5

Claims (1)

[Claims] 1. The main component of the crystal phase is cordierite phase, the total pore volume of pores with a diameter of 5 μm or more is 0.04 cc/g or less, and the coefficient of thermal expansion is between 40 and 800°C. is 1.0×10^
-^6/℃ or less, the chemical composition is 42-56% by weight of SiO_2, 30-45% by weight of Al_2O_3, and 1% by weight of MgO.
A cordierite honeycomb structure characterized by having a content of 2 to 16% by weight. 2. The total pore volume of pores with a diameter of 5 μm or more is 0.026
cc/g or less, the cordierite honeycomb structure according to claim 1. 3. Cell density is 62 cells/cm^2 (400 cells/in
^2) The cordierite honeycomb structure according to claim 1, wherein the rib thickness is 203 μm (8 mil) or less. 4. The cordierite honeycomb structure according to claim 1, wherein the cordierite honeycomb structure is a heat exchanger. 5. Chemical composition: SiO_2 is 42-56% by weight, Al_
Talc with an average particle size of 7 μm or less, kaolin with an average particle size of 2 μm or less and 1/3 or less of the talc average particle size so that 2O_3 is 30 to 45% by weight and MgO is 12 to 16% by weight. Other cordierite forming raw materials are mixed, a plasticizer and a binder are added to this mixture to make a plasticized deformable batch, this plasticized batch is molded by extrusion molding and then dried, and then this dried product is 1
A method for producing a cordierite honeycomb structure, the method comprising firing at a temperature of 350 to 1440°C. 6. The manufacturing method according to claim 5, wherein the firing is performed at an average temperature increase rate of 20 to 60°C/hour in the temperature range of 1100 to 1350°C just before reaching the firing temperature. 7. The manufacturing method according to claim 5, using talc having an average particle diameter of 5 μm or less. 8. The manufacturing method according to claim 5, using kaolin having an average particle diameter of 1 μm or less. 9. The method according to claim 5, wherein the cordierite honeycomb structure is a heat exchanger.