KR102549690B1 - Ceramic composition for porous filter, and porous honeycomb ceramic filter and filter segment manufactured using the same - Google Patents

Abstract

The present invention relates to a novel ceramic composition using silicon carbide as a main material and having a low thermal expansion coefficient, a porous honeycomb ceramic filter manufactured using the same, and a filter segment constituting the same. The ceramic composition for a porous filter of the present invention includes silicon carbide (SiC), carbon black, impression graphite, magnesia, silica, alumina, a cellulose-based binder, a friction reducing agent and a plasticizer, and has a thermal expansion coefficient of 5.0 × 10 ^-6 / below °C. According to the present invention, since the coefficient of thermal expansion can be lowered while silicon carbide, which has excellent heat resistance, is used as the main material, it is possible to manufacture segments of a larger size than conventional ones, and accordingly, a porous honeycomb ceramic filter can be manufactured with a small number of segments. filter efficiency and productivity can be increased.

Description

Ceramic composition for porous filter, and porous honeycomb ceramic filter and filter segment manufactured using the same {Ceramic composition for porous filter, and porous honeycomb ceramic filter and filter segment manufactured using the same}

The present invention relates to a porous honeycomb ceramic filter, and more particularly, to a ceramic composition containing silicon carbide as a main material and having a low thermal expansion coefficient, a porous honeycomb ceramic filter manufactured using the same, and a filter segment constituting the same.

A diesel particulate filter (exhaust gas aftertreatment device, soot filter device, diesel particulate filter, hereinafter referred to as 'DPF'), for which SiC porous honeycomb ceramic filters are mainly used, is a particulate matter (hereinafter referred to as 'PM') in diesel engine exhaust gas. ') is a type of exhaust post-processing device that physically collects and burns to remove it.

DPF with porous honeycomb ceramic filter is essential for reducing PM and NOx exhaust gas in diesel engines. It has a structure of 100 to 300 cells/inch in the form of a square, and it must have the characteristics of high collection efficiency and low pressure loss. In addition, it should have stability against thermal shock and high temperature generated during combustion and regeneration of PM collected under diesel engine exhaust gas temperature conditions, and a low thermal expansion coefficient is required.

Conventionally, as a porous honeycomb ceramic filter, cordierite (2MgO2Al ₂ O ₃ 5SiO ₂ ), aluminum titania (Al ₂ TiO ₅ ), and silicon carbide (SiC) are largely used. While cordierite and aluminum titania have the advantage of having a low thermal expansion coefficient, they have a disadvantage of poor high-temperature heat durability, so they are not suitable for use in ceramic filters exposed to severe conditions of high temperature. Therefore, in most harsh conditions of high temperature, silicon carbide (SiC) material with high high-temperature heat durability is used.

Silicon carbide material has excellent heat resistance and corrosion resistance, high strength, and high thermal conductivity, so it is suitable as a ceramic filter used in a high temperature environment. However, since the thermal expansion rate is high, the filter may be damaged when exposed to high temperatures for a long time during actual application or when exposed to large temperature changes such as during combustion regeneration, so it may not function properly as a filter and has a short lifespan. . Therefore, the silicon carbide ceramic filter is not made as an integral type, but is made in a segmented structure and spaced between the segments to be manufactured and used. However, since the ceramic filter segment, which uses silicon carbide as the main material, has a high thermal expansion coefficient of about 5.87×10 ^-6 / ° C, segments with a maximum size of 40 * 40 mm or less are produced, so they are mainly used only for small filters. In addition, as many segments, usually about 16, are required for one ceramic honeycomb filter, there is a problem in that the filtering effect is deteriorated due to a decrease in productivity and a filtering loss at intervals.

Republic of Korea Patent Registration No. 10-1032350 Republic of Korea Patent Registration No. 10-1338068 Republic of Korea Patent Registration No. 10-1123173 Republic of Korea Patent Registration No. 10-1217169

If the thermal expansion coefficient can be lowered to a minimum of 5.0×10 ^-6 /℃ while using silicon carbide as the main material, competitiveness and productivity as a filter can be greatly improved, and it can be manufactured as a medium-large ceramic honeycomb filter.

An object of the present invention is to provide a new ceramic composition in which silicon carbide is used as a main material and the thermal expansion coefficient, which has been a problem of silicon carbide, is reduced. Another object of the present invention is to provide a porous honeycomb ceramic filter using this ceramic composition for a porous filter having excellent heat resistance and a low coefficient of thermal expansion. In particular, using the ceramic composition, a filter segment having a larger size than conventionally used silicon carbide honeycomb filter segments is provided, and a porous honeycomb ceramic filter having high filter efficiency and productivity is provided with fewer combinations using the segments. aims to do

In order to achieve the above object, in the present invention,

300-350 mesh silicon carbide 40-70 wt%, 180-220 mesh silicon carbide 4-12 wt%, carbon black 2-6 wt%, impression graphite 2-6 wt%, magnesia 4-12 wt%, silica 6- 17% by weight, 4 to 12% by weight of alumina, 4 to 12% by weight of a cellulose binder, 1 to 6% by weight of a friction reducing agent and 1 to 6% by weight of a plasticizer, having a thermal expansion coefficient of 5.0 × 10 ^-6 / ° C or less , A ceramic composition for a porous filter is provided.

In addition, the present invention provides a porous honeycomb ceramic filter segment formed by molding the ceramic composition into a honeycomb shape having a predetermined size. The filter segment may be manufactured by molding the ceramic composition into a segment having a size of 50×50 mm.

In addition, the present invention provides a porous honeycomb ceramic filter in which the honeycomb filter segments are bonded together and processed into a predetermined shape. One embodiment of the present invention provides a porous honeycomb ceramic filter in which the filter segments are bonded and processed into a cylindrical shape. In a preferred embodiment of the present invention, a porous honeycomb ceramic filter is provided in which nine 50 × 50 mm segments are bonded together to form a cylindrical shape.

Also, in the present invention,

300-350 mesh silicon carbide 40-70 wt%, 180-220 mesh silicon carbide 4-12 wt%, carbon black 2-6 wt%, impression graphite 2-6 wt%, magnesia 4-12 wt%, silica 6- 17% by weight, 4 to 12% by weight of alumina, 4 to 12% by weight of a cellulose binder, 1 to 6% by weight of a friction reducing agent and 1 to 6% by weight of a plasticizer, having a thermal expansion coefficient of 5.0 × 10 ^-6 / ° C or less , preparing a ceramic composition for a porous filter;

manufacturing a porous honeycomb ceramic filter segment comprising molding the ceramic composition;

A method for manufacturing a porous honeycomb ceramic filter is provided, which includes a filter manufacturing step of bonding a plurality of filter segments and processing them into a predetermined shape.

In the filter manufacturing step, the filter segments may be bonded and processed into a cylindrical shape. In a preferred embodiment, the ceramic composition may be molded into porous honeycomb ceramic filter segments having a size of 50 × 50 mm, and nine filter segments may be bonded to form a cylindrical shape.

The manufacturing method may further include cutting into a predetermined shape after bonding the filter segments.

In the present invention, while using silicon carbide (SiC), which has excellent heat resistance, as a main material, it is possible to provide a new ceramic composition in which the thermal expansion coefficient, which was a problem of silicon carbide, is lowered. Since the ceramic composition of the present invention has excellent heat resistance and a low coefficient of thermal expansion, a honeycomb filter and a filter segment having excellent heat resistance and a low coefficient of thermal expansion can be manufactured by using the ceramic composition. Accordingly, since the honeycomb filter segment can be manufactured in a larger size than before, filtering efficiency and productivity can be greatly improved.

Specifically, according to a preferred embodiment of the present invention, a porous honeycomb filter segment conventionally manufactured to a maximum size of 40 × 40 mm can be manufactured to a size of 50 × 50 mm. As the size of the porous honeycomb filter segments increases, at least 16 honeycomb filter segments were used in the conventional honeycomb filter, but the porous honeycomb filter of the present invention can be manufactured with 9 segments. Accordingly, since the porous honeycomb ceramic filter is manufactured with a small number of segments, productivity can be improved, and filtering loss generated at the junction can be reduced to increase the filtering effect.

1 is a prototype of a small-sized porous honeycomb ceramic filter according to the present invention.
2 is a photograph comparing a conventional porous honeycomb ceramic filter using 16 segments (left) and a porous honeycomb ceramic filter of the present invention using 9 segments (right).
3 is a photograph of a mold manufactured in one embodiment of the present invention.
4 is a photograph showing extrusion molding of a porous honeycomb ceramic filter segment in one embodiment of the present invention.
5 is a graph showing TGA-DTA data of an extruded porous honeycomb ceramic filter segment in one embodiment of the present invention.
6 is a photograph of a porous honeycomb ceramic filter segment manufactured in an embodiment of the present invention.
7 is a photograph of a porous honeycomb filter segment before and after plugging in one embodiment of the invention. The left is a segment molded body before plugging, and the right is a segment molded body after plugging.
8A and 8B are pictures of the microstructure of the porous honeycomb filter sintered body.
9 is a graph showing the pore size of the porous honeycomb ceramic filter segment.
10 is a graph showing the thermal expansion coefficient of the porous honeycomb filter segment.

1. Ceramic composition for porous filter

The ceramic composition for a porous filter of the present invention includes 40 to 70% by weight of 300 to 350 mesh silicon carbide, 4 to 12% by weight of 180 to 220 mesh silicon carbide, 2 to 6% by weight of carbon black, 2 to 6% by weight of impression graphite, 4-12 wt% of magnesia, 6-17 wt% of silica, 4-12 wt% of alumina, 4-12 wt% of cellulose-based binder, 1-6 wt% of friction reducing agent and 1-6 wt% of plasticizer, thermal expansion The coefficient is 5.0×10 ^-6 /°C or less.

In the composition of the present invention, 320 mesh silicon carbide and 200 mesh silicon carbide are the main materials.

Carbon black and impression graphite are added as pore formers to control pore formation in silicon carbide ceramic particles where porosity control acts as an important variable.

Magnesia, silica and alumina are used as oxide bond sintering for low thermal expansion.

Since ceramic powder lacks plasticity, a binder is used to impart plasticity. In the present invention, a cellulose-based binder is used as the main binder. As the cellulose-based binder, preferably methyl cellulose (MC), hydroxypropyl cellulose (HPMC), hydroxyethyl cellulose (HEMC), or carboxymethyl cellulose (CMC) may be used, and particularly preferably methyl cellulose (MC) can be used In a preferred embodiment of the present invention, a cellulosic binder is used as an organic extrusion binder for 50x50 mm honeycomb segment extrusion.

The composition of the present invention includes a friction reducing agent for reducing frictional resistance between a molding and a mold. As the friction reducing agent, general lubricating oil, grease, and the like may be used, and wax or liquid paraffin may be particularly preferably used.

The composition of the present invention includes a plasticizer for reducing the shape change of the molded article due to rapid water dehydration. Glycerin is preferably used as a plasticizer.

While the thermal expansion coefficient of the ceramic filter segment using silicon carbide as the main material is about 5.87 × 10 ^-6 / ° C, the composition of the present invention has a much lower thermal expansion coefficient of 5.0 × 10 ^-6 / ° C or less even though silicon carbide is used as the main material. . The composition of the present invention preferably has a thermal expansion coefficient of 4.0 to 5.0 × 10 ^-6 /°C, more preferably 4.3 to 4.9 × 10 ^-6 /°C.

2. Porous Honeycomb Ceramic Filter Segments

A porous honeycomb ceramic filter segment is manufactured by molding the ceramic composition into a honeycomb shape having a predetermined size. Molding is preferably carried out by an extrusion method. During extrusion molding, it is more preferable to perform extrusion molding into a porous honeycomb ceramic filter segment having a predetermined shape after performing a vacuum kneading operation to mix the raw materials to evenly disperse the raw materials.

The coefficient of thermal expansion of the porous honeycomb ceramic filter segment prepared by the composition of the present invention is 5.0 × 10 ^-6 /°C or less, preferably 4.0 to 5.0 × 10 ^-6 /°C, more preferably 4.3 to 4.9 × 10 ^{- 6} /℃. As the coefficient of thermal expansion is lowered in this way, it is possible to manufacture the segment with a size much larger than that of the conventional porous honeycomb ceramic filter segment. For example, a conventional porous honeycomb ceramic filter segment has a maximum size of 40 × 40 mm, but in the present invention, it can be manufactured in a size of 50 × 50 mm to replace the conventional segment having a size of 40 × 40 mm.

Hereinafter, a preferred embodiment of manufacturing a porous honeycomb ceramic filter segment will be described.

(1) Extrusion molding

In order to manufacture the honeycomb-shaped porous segment, the mold shown in FIG. 3 is manufactured and used. In order to reduce the wear of the mold as much as possible, the surface of the manufactured mold is heat treated to improve wear resistance.

Extrusion molding of the porous honeycomb ceramic filter segment is performed using the ceramic composition as a raw material and using an extruder in which the mold and the discharge screw are elaborately designed. An example of the extrusion process is shown in FIG. 4 .

(2) drying

The molded body is prepared by drying the extruded porous honeycomb ceramic filter segments. In order to prevent twisting or bending of segments during drying, it is preferable to make a drying jig to remove about 50% or more of moisture in the primary dryer and then completely remove the remaining moisture in secondary hot air drying. The hot air drying jig is preferably used by manufacturing a jig using a perforated iron plate and manufacturing a structure in which a molded body is fixed and dried.

(3) foundation

Cut the dried filter segment to a certain size. The size may be determined according to the size of the porous ceramic filter to be used.

(4) plugging

The cut honeycomb filter segment is plugged using a composition mixed in the same composition ratio as that used in the extrusion molding. Plugging is to close the holes in front and rear of the honeycomb in a zigzag pattern, and the molded body of the honeycomb filter segment is completed to serve as a filter by plugging.

(5) Sintering

The honeycomb filter segment molded body that has undergone the plugging is sintered at 1300 to 1500° C. to obtain a completed honeycomb filter segment. Sintering at 1400°C is more preferred.

3. Porous Honeycomb Ceramic Filter

A porous honeycomb ceramic filter is manufactured by joining the honeycomb filter segments obtained as described above and processing them into a predetermined shape. The shape of the filter is not limited, but in one embodiment it is processed into a cylindrical shape. In a preferred embodiment, a porous honeycomb ceramic filter is manufactured by bonding 9 filter segments molded into 50×50 mm segments and processing them into a cylindrical shape.

Hereinafter, a preferred embodiment of manufacturing a porous honeycomb ceramic filter using the porous honeycomb ceramic filter segment will be described.

(1) bonding

A porous honeycomb ceramic filter is manufactured by bonding the completed porous honeycomb ceramic filter segments using a bonding agent. As a bonding agent, it is preferable to use a ceramic bonding agent, and a conventional bonding method is used.

(2) cutting

The bonded porous honeycomb ceramic filter is cut into a cylindrical shape to complete the porous honeycomb ceramic filter.

[Examples and experimental examples]

Hereinafter, the present invention will be described in more detail through specific examples and experimental examples. These are illustrative of the present invention, and the scope of the present invention is not limited to these Examples and Experimental Examples.

<Example 1>

preparation of the composition

The composition of the present invention was prepared in the following ratio. As the main materials, 65 g of 320 mesh silicon carbide and 10 g of 200 mesh silicon carbide were used. To control pore formation, 5 g of carbon black and 5 g of impression graphite were added. For low thermal expansion sintering, 10 g of magnesia, 15 g of silica and 10 g of alumina were added. 10 g of methylcellulose binder was used as a binder for extrusion molding, 5 g of wax was used as a friction reducing agent, and 5 g of glycerin was used as a plasticizer.

<Example 2>

manufacture of molds

In order to manufacture honeycomb-shaped filter segments, a mold was designed and manufactured as follows.

First, the cell structure for 200 CPSI on the primary square was designed.

For mold design, an extruded composition should be prepared by adjusting the size of the silicon carbide ceramic particles to minimize the wall thickness between the cells and the frictional stress between the silicon carbide ceramic particles having excellent wear characteristics. Accordingly, the mold was designed in consideration of the extrusion speed, the shape retention and shrinkage rate of the molded body, and the relationship between the extrusion composition and the cell wall thickness. A mold for extruding a silicon carbide ceramic segment manufactured according to the design is shown in FIG. 3 .

In order to minimize the wear of the manufactured mold, the surface of the mold was heat treated to improve wear resistance before use.

<Example 3>

Manufacture of porous honeycomb ceramic filter

The composition of Example 1 was extruded into porous honeycomb filter segments using the mold shown in FIG. 3 and an extruder with elaborately designed discharge screws. The extrusion molding process is shown in FIG. 4 .

After extruding a 200CPSI class segment, a drying jig is made to prevent twisting or bending of the segment during drying, and after removing about 50% or more of the moisture in the primary dryer, the remaining moisture is completely removed in the secondary hot air drying to form a molded body. manufactured. The hot air drying jig was used by manufacturing a jig using a perforated iron plate and manufacturing a structure in which a molded body was fixed and dried. A photograph of the molded porous SiC honeycomb ceramic filter segment is shown in FIG. 6 .

The molded porous honeycomb filter segments were cut according to the number of fixtures and plugged using the same composition of Example 1 to close the holes before and after the honeycomb in a zigzag pattern to complete a molded segment body to serve as a ceramic filter. Figure 7 shows the molded segments before and after plugging. In FIG. 7, the left side is a segment molded body before plugging, and the right side is a segment molded body after plugging.

The plugged segment molded body was finally sintered at 1400° C. to obtain a completed segment.

The final sintered segments were bonded using a ceramic binder and cut into a cylindrical shape to manufacture a 5.66×6" porous honeycomb ceramic filter as a final product. The finished porous SiC honeycomb filter is shown in FIG. 1, and a conventional porous honeycomb filter is shown in FIG. 2 shows a photograph comparing the porous honeycomb filter with the porous honeycomb filter of the present invention.

As can be seen from FIG. 2, the conventional porous honeycomb ceramic filter contains at least 16 segments, whereas the porous honeycomb ceramic filter of the present invention contains only 9 segments. This is because the conventional porous honeycomb ceramic segment was manufactured to be 40 × 40 mm because of its thermal expansion coefficient, but the porous SiC honeycomb ceramic filter segment of the present invention can be manufactured to be 50 × 50 mm because of its low thermal expansion coefficient.

<Experimental Example 1>

Check sintering conditions

To establish the sintering conditions of the segment, the burn-out temperature and weight change of the additives contained in the segment were tested using TGA (Thermogravimetric Analysis). The results of observing the weight change of the segment from room temperature to 1000 ° C are shown in FIG. 5 .

As can be seen in FIG. 5, the TGA curve can be largely divided into Stage 1, Stage 2, and Stage 3 according to the change of onset and slope, and Stage 1, Stage 2, and Stage 3 are added respectively. This is the burnout section of the liquid phase, organic mixed binder, and pore former. In fact, the burnout temperature and the starting temperature of TGA on the test report of the liquid phase, binder, and hollow body in the composition did not show a large difference as ± 3 ° C.

<Experimental Example 2>

Characterization of Porous Honeycomb Ceramic Filter Segments

1. Microstructure observation

In order to confirm the degree of bonding of the porous honeycomb ceramic filter segments manufactured, the microstructure was observed by enlarging the space between the particles, and the results are shown in FIGS. 8A and 8B.

As confirmed in FIGS. 8a and 8b, the bonding form between the silicon carbide particles had a necking structure by the oxide of the second phase. It was observed that these neck materials exhibited the binding force of the entire segment, and it was confirmed that the distribution of pore channels between particles was also uniformly formed.

Since the porosity of the segment is closely related to the back pressure of the filter exhaust gas, controlling the porosity of a certain shape is one of the important variables in the ceramic filter.

2. Pore size and porosity

As a fine dust porous ceramic filter, its main function is to collect PM, so pore size and porosity are one of the important variables, and porosity or pore size affects filter efficiency.

The pore size and porosity of the prepared porous honeycomb ceramic filter segment were confirmed and shown in FIG. 9 . As can be seen from the graph of FIG. 9, the porosity of the manufactured porous honeycomb ceramic filter segment varies depending on the ratio of the pore former, but the porosity was about 46.87% while maintaining the strength of the minimum segment as a filter, and the pore size was It was about 14.47 μm.

3. Bending strength

After firing the porous honeycomb ceramic filter segment, the bending strength of the segment was measured using a universal testing machine to measure the bending strength, which is a physical property, under the condition of a descending speed of 0.2 mm/min. The measured bending strength of the porous honeycomb ceramic filter segment is shown in Table 1 below.

Thickness (t) Width (W) span (L) load (N) Strength (Mpa) One 10.35 20.25 60 808.67 33.6 2 10.31 20.23 60 596.17 25.0 3 10.31 20.29 60 682.17 28.5 4 10.35 20.26 60 723.00 30.0 5 10.36 20.25 60 747.50 31.0 6 10.35 20.26 60 749.83 31.1 7 10.32 20.23 60 786.17 32.8 8 10.28 20.24 60 711.83 30.0 9 10.29 20.24 60 725.00 30.4 10 10.32 20.25 60 665.00 27.8 average 719.53 30.00 Standard Deviation 61.26 2.49

As confirmed in Table 1, a strength value of 30 MPa was exhibited with an average load of 719.53 N.

4. Coefficient of thermal expansion

Among the thermal properties of the porous honeycomb ceramic filter segment, the coefficient of thermal expansion is important to manufacture medium-large ceramic filters.

The coefficient of thermal expansion of the manufactured porous honeycomb ceramic filter segment was confirmed and the results are shown in FIG. 10 . As can be seen from FIG. 10, the coefficient of thermal expansion of the segment of the present invention was 4.87×10 ^-6 /°C.

Claims (10)

40 to 70% by weight of 300 to 350 mesh silicon carbide and 4 to 12% by weight of 180 to 220 mesh silicon carbide; 2 to 6% by weight of carbon black and 2 to 6% by weight of impression graphite as a pore former; 4 to 12% by weight of magnesia, 6 to 17% by weight of silica and 4 to 12% by weight of alumina as an oxide sintering binder; Cellulose-based binder 4 to 12% by weight; 1 to 6% by weight of a friction reducing agent and 1 to 6% by weight of a plasticizer,
A ceramic composition for a porous filter having a thermal expansion coefficient of 4.0 to 5.0 × 10 ^-6 / ° C when sintered at 1300 to 1500 ° C. A porous honeycomb ceramic filter segment obtained by molding the ceramic composition of claim 1 into a honeycomb shape having a predetermined size. According to claim 2,
A porous honeycomb ceramic filter segment obtained by molding the ceramic composition into segments having a size of 50×50 mm. A porous honeycomb ceramic filter in which the honeycomb filter segments of claim 2 are bonded and processed into a predetermined shape. A porous honeycomb ceramic filter obtained by bonding the honeycomb filter segments of claim 2 into a cylindrical shape. A porous honeycomb ceramic filter obtained by bonding nine honeycomb filter segments according to claim 3 into a cylindrical shape. 40 to 70% by weight of 300 to 350 mesh silicon carbide and 4 to 12% by weight of 180 to 220 mesh silicon carbide; 2 to 6% by weight of carbon black and 2 to 6% by weight of impression graphite as a pore former; 4 to 12% by weight of magnesia, 6 to 17% by weight of silica and 4 to 12% by weight of alumina as an oxide sintering binder; Cellulose-based binder 4 to 12% by weight; Preparing a ceramic composition for a porous filter containing 1 to 6% by weight of a friction reducing agent and 1 to 6% by weight of a plasticizer;
forming and sintering the ceramic composition at 1300 to 1500° C. to produce a porous honeycomb ceramic filter segment having a thermal expansion coefficient of 4.0 to 5.0×10 ⁻⁶ /° C.;
A method of manufacturing a porous honeycomb ceramic filter comprising a filter manufacturing step of bonding a plurality of filter segments and processing them into a predetermined shape. According to claim 7,
The method of manufacturing a porous honeycomb ceramic filter, characterized in that in the filter manufacturing step, the filter segments are bonded and processed into a cylindrical shape. According to claim 7,
In the manufacturing step of the filter segment, the ceramic composition is molded into a porous honeycomb ceramic filter segment having a size of 50 × 50 mm,
The method of manufacturing a porous honeycomb ceramic filter, characterized in that in the filter manufacturing step, the nine filter segments are bonded and processed into a cylindrical shape. According to any one of claims 7 to 9,
The method of manufacturing a porous honeycomb ceramic filter, wherein the filter manufacturing step further includes cutting and processing the filter segments into a predetermined shape after joining the filter segments.

Images