JPS60241917A - Purifying body of exhaust gas - Google Patents

Abstract

PURPOSE:To reduce pressure drop by mixing 5-25wt% ceramic having m.p. higher than that of cordierite into cordierite. CONSTITUTION:A porous ceramic body of three-dimensional structure is prepared by adding 5-25pts.wt. ceramic such as aluminum titanate, mullite, zircon, and silicon carbide having higher m.p. than cordierite and having 0-5X10<-6> (1/ deg.C) thermal expansion coefficient at 20-1,000 deg.C to 95-75pts.wt. cordierite. The purifying body is manufactured by adding a binder such as polyvinyl alcohol and CMC, a deflocculant such as sodium silicate, and water to said ceramic mixture to obtain a low-viscosity slurry, depositing the slurry on a foamed organic substance, and calcining the obtained material at 1,250-1,400 deg.C.

Description

Detailed Description of the Invention The present invention uses cordierite and a ceramic having a higher melting point than cordierite and a thermal expansion coefficient of 5XlO (1/''O) or less at 20°C to 1000°C as a ceramic component. The present invention relates to an exhaust gas purifying body made of a ceramic porous body having a three-dimensional network skeleton structure.

Generally, Coop Yerai l-(2MgO・2A1203・
5SiO2) has a small coefficient of thermal expansion and excellent resistance to thermal shock when a sudden temperature change is applied, making it highly useful for industrial applications where the temperature fluctuates widely.For example, it is used in automobile exhaust gas purifiers. As shown in the above, cordierite material is suitable for applications where the temperature range under usage conditions is wide, approximately 0°C to 1000°C, and the rate of temperature change is large.

However, cordierite generally has a dense structure and the preferred firing temperature range for obtaining high-strength porcelain is limited to at most 30°C, preferably within 20°C. Sintering does not proceed at lower temperatures than the preferred firing temperature range, and the resulting product strength is unsatisfactory for practical purposes; at higher temperatures, sintering progresses rapidly, but deformation occurs due to shrinkage and softening associated with sintering. Therefore, it is difficult to achieve the desired dimensional accuracy. When producing a ceramic porous body with a three-dimensional network skeleton structure, the skeleton is thin, so deformation due to shrinkage and softening accompanying sintering is particularly noticeable. Therefore, when firing a ceramic porous body having a three-dimensional network skeleton structure made of cordierite, it is necessary to control the temperature within an appropriate and extremely narrow temperature range, which is very difficult in terms of manufacturing technology.

On the other hand, in the case of an exhaust gas purifying body, especially an exhaust gas purifying body for automobiles, it is important that the pressure loss is as low as possible, and a large pressure loss not only puts a burden on the engine but also deteriorates fuel economy.

However, a ceramic porous body with a three-dimensional network skeleton structure obtained by using cordierite as a raw material and immersing a three-dimensional network structure synthetic resin foam in cordierite slurry, pulling it up, drying it, and firing it has a large pressure loss and is not suitable for ceramics. In applications such as exhaust gas purifiers in which fluid is passed through a porous body, the pressure loss remains at an unsatisfactory level.

As mentioned above, cordierite has good thermal shock resistance.In particular, a synthetic resin foam with a three-dimensional network structure is immersed in cordierite slurry, dried, and fired to form a three-dimensional network skeleton. When creating a ceramic porous body having a sintered body, it was necessary to improve the fact that the suitable firing temperature range is particularly narrow, that it is susceptible to softening and deformation at higher temperatures, and that the pressure loss is relatively large.

The inventors of the present invention have conducted various studies and have arrived at the present invention. In other words, it has a higher melting point than cordierite,
And 5 to 25 parts by weight of ceramic having a thermal expansion coefficient 6 of 0 to 5X10 (1/'O) at 20°C to 1000°C was added to 85 to 75 parts by weight of cordierite for a total of 100 parts by weight. A synthetic resin foam is immersed in a ceramic slurry prepared by adding auxiliary materials such as a binder to ceramic powder, then pulled up, the excess slurry is removed by centrifugation, dried, molded, and fired. It has been possible to obtain an exhaust gas purifying body which is made of a ceramic porous body with a three-dimensional network skeleton structure and has improved dimensional accuracy and pressure loss.

In the present invention, a ceramic raw material having a melting point higher than that of cordierite and a thermal expansion coefficient of O6 to 5X10 (1/''O) at 20°C to 1000°C is used.
By blending these parts together, it is possible to fire at higher temperatures while suppressing shrinkage and deformation than when using cordierite alone, expanding the practical firing temperature range and achieving more stable dimensional accuracy. At the same time, by enabling denser sintering and improving mechanical strength, we discovered the possibility of manufacturing with stable quality on an industrial scale.

On the other hand, accessory raw materials such as binder to cordierite powder 4
Ceramic porous bodies with a three-dimensional network structure manufactured by conventional manufacturing methods using ceramic slurry prepared by adding It is thought that the removal is incomplete and the slurry tends to remain in the communicating spaces of the three-dimensional network structure, resulting in extremely poor pressure loss in the product.

Therefore, in order to reduce the thixotropic properties of the slurry, deflocculants such as water glass, soda carbonate, and sodium birophosphate are added, but although an improvement effect is seen, the pressure loss of the product is still not at a satisfactory level.

However, a ceramic having a melting point higher than that of the above-mentioned cordierite and having a thermal expansion coefficient of 0 to 5X10 (1/''O) at 20°C to 1000°C is used for 95 to 75 parts by weight of cordierite. It was found that by adding 5 to 25 parts by weight, the thixotropy of the slurry can be reduced and the pressure loss of the product can be greatly improved.The pressure loss is greatly improved by the porous ceramic material with a three-dimensional network skeleton structure. This is thought to be due to less clogging of the communication space with ceramics, but the detailed mechanism is not clear.

In any case, as mentioned above, 5 to 25 parts by weight of a ceramic having a melting point higher than that of cordierite and a coefficient of thermal expansion of 0 to 5XIO (+/℃) at 20 to 1000 degrees Celsius, It has been found that by using a composite material system containing 95 to 75 parts by weight, pressure loss can be clearly reduced compared to the case where cordierite is used as a single material.

Here, it has a higher melting point than cordierite,
As the ceramic having a thermal expansion coefficient of 0° (3-1000°C) of o to 6 5X10 (1/'C), aluminum titanate, mullite, zircon, and silicon carbide are preferable, and one type or a mixture of two or more types can be used. The coefficient of thermal expansion at 20°C to 1000"O is 0 to 5X10.
(1/”C ceramic coach Yelite 95 ~
The coefficient of thermal expansion of the ceramic porous body with a three-dimensional network structure created by adding 5 to 25 parts by weight to 75 parts by weight is slightly lower than that of 2.0×10 (1/”O) for cordierite 6 alone. Although there are some cases where the size increases, the maximum size is only about 63.5XIO (1/'O), and in actual thermal shock resistance tests, it maintains almost the same thermal shock resistance as cordierite alone. It turns out that

Here, a suitable addition amount of the ceramic having a melting point higher than that of cordierite and a coefficient of thermal expansion of θ~5×10 (+/”O) is 95~7
5 parts by weight and 5 to 25 parts by weight, respectively.

In other words, if the amount added is less than 5 parts by weight, the above-mentioned effect of addition is not significant, and if the amount added exceeds 25 parts by weight, the temperature range of 1250°C to 1400°C, which is suitable for industrial furnace economy, will not be compatible. This is because even if sintering of eliteite occurs, sufficient sintering of the ceramic having a higher melting point than cordierite does not occur, and mechanical strength tends to decrease as the amount added increases.

The manufacturing method is to first add 5 parts by weight of a ceramic having a melting point higher than that of cordierite and a coefficient of thermal expansion of 0 to 5 X I O-'(1/''O) to 95 to 75 parts by weight of cordierite powder. Add ~25 parts by weight.To this, a binder such as polyvinyl alcohol and CMC, a deflocculant such as sodium silicate, and water were added to create a low-viscosity ceramic slurry.The viscosity of the slurry was adjusted to the desired ceramic porosity. The amount of water added was adjusted depending on the size of the body cells. An organic material foam with a three-dimensional network structure of a predetermined shape was immersed in this ceramic slurry, and the excess slurry was removed by an appropriate method such as centrifugation. Remove and dry.

This operation is repeated until a predetermined amount of ceramic adheres to the organic foam of the three-dimensional network structure.

In order to conveniently use it as an exhaust gas purifier, it is possible to spray or coat it with a ceramic slurry in order to seal the outermost part parallel to the flow direction of the exhaust gas. Place the dried molded product in a furnace at 1250°C to 14°C.
By firing at a suitable firing temperature between 00° C., an exhaust gas purifying body with low pressure loss, high strength, and excellent dimensional accuracy can be obtained. The exhaust gas purifying body of the present invention can be used as it is or by providing a catalyst on the skeleton surface to purify exhaust gas from an automobile engine, and is particularly suitable for purifying exhaust gas from a diesel engine. When used to purify exhaust gas from a diesel engine, it is preferable to coat the skeleton surface of the ceramic porous body with alumina, and then provide a catalyst layer for burning carbon particles, hydrocarbons, and carbon oxides. The porous body preferably has 5 to 50 cells per linear inch.

The present invention will be explained below using examples.

Examples 1-6. Comparative Examples 1 to 3 Ceramic mixture containing fine cordierite powder, zircon or aluminum titanate, or a mixture thereof. 100 parts of polyvinyl alcohol, 0.2 parts of sodium silicate, 2 parts of silica gel, and an appropriate amount of water. was added to create a low viscosity slurry. A polyurethane foam having a cubic cell membrane-free three-dimensional network skeleton structure with 20 cells per inch and a side of loc+w was impregnated with this slurry.

After removing the excess slurry by centrifugation or air blowing, the sampling process was repeated until an appropriate amount of sufficiently dried ceramic was deposited on the outermost part in the direction parallel to the exhaust gas flow path. It was also coated with ceramic and then dried.

A ceramic foam was obtained by firing at 1290° C. for 1 hour. When the resulting ceramic foam was fired at high temperatures, the second side of the sample showed more shrinkage and deformation than the bottom side of the sample. In order to express the degree of this deformation, we decided to use the area ratio obtained by dividing the area of the top surface of the sample by the area of the bottom surface of the sample.

Also, from the fired product, I cut a cube with a side of 5cm and cut it into a pile with a wind speed of 3.
The pressure drop in m/sec and the compressive strength were measured.

These results are shown in Table 1. A sample in which the ceramic component was cordierite alone was also created in the same manner.

These results show that cordierite alone has a high degree of deformation, but has a higher melting point than cordierite, and has a coefficient of thermal expansion of 5X10 (1/'O )
By adding 5 to 20 parts by weight of ceramic, an exhaust gas purifying body made of a ceramic porous body with a three-dimensional network skeleton structure can be obtained, which has little deformation during firing, almost the same compressive strength, and extremely improved pressure loss. I found out that it is possible.

Table 1 (Note) The degree of deformation was calculated using the formula below.

2 Examples 7 to 10, Comparative Examples 4 to 6 4.5 parts of polyvinyl alcohol, 0.2 parts of sodium silicate, 2 parts of silica gel, and appropriate amounts to 100 parts of a ceramic mixture in which silicon carbide or mullite was blended with fine cordierite powder. of wood was added to create a low viscosity slurry. One side is TOES with 13 cells per inch.
A polyurethane foam having a three-dimensional network skeleton structure without a cubic cell membrane was impregnated with this slurry, excess slurry was removed by centrifugation or air blowing, and then thoroughly dried. 1350°C
After firing for 1 hour, a ceramic form was obtained. The degree of deformation, pressure loss and compressive strength were measured in the same manner as in the previous example.

The test results are shown in Table 2. It can be seen that the mechanical strength is almost the same as that of cordierite alone, and the degree of deformation and pressure loss are significantly improved.

Table 2 Applicant: Brideston Co., Ltd. Agent Patent Attorney Hide Hisaume - Agent Patent Attorney Etsu Suzuki

Claims (2)

[Claims] (1) In an exhaust gas purifying body made of a ceramic porous body with a three-dimensional network skeleton structure having internal communication spaces, the ceramic component has a higher melting point than cordierite and a thermal expansion coefficient of 5X 10 at 20°C to 1000°C.
-6 (1/''O) or less ceramic and 95 to 75 parts by weight of cordierite, respectively. (2) Higher melting point than cordierite and 20℃~10℃
The coefficient of thermal expansion at 00°C is 5 x 10-' (1/
2. The exhaust gas purifying body according to claim 1, wherein the following ceramic is one or more selected from aluminum titanate, zircon, mullite, and silicon carbide.