KR100419779B1 - Fabrication method of silicon carbide ceramics filter with high strength for dust collection - Google Patents

Abstract

An object of the present invention is to provide a method for producing a silicon carbide ceramic filter for dust collection, the method of producing a silicon carbide ceramic filter for dust collection.

According to the present invention, in the method of manufacturing a high strength silicon carbide ceramic filter for dust collection, 1.0 to 15.0 wt% of a sintering aid based on the mass of the silicon carbide ceramic powder and the silicon carbide ceramic powder is 100 wt%, based on 100 wt%, respectively. And aging by mixing 1.0-5.0 wt% molding aid, 0.1-5.0 wt% alkali compound, 0.5-5.0 wt% dispersant and 5.0-15.0 wt% water, and pressing the mature raw material. There is provided a method for producing a high-strength silicon carbide ceramic filter for dust collection, comprising the steps of forming into a filter, and heating and sintering the molded filter.

Description

Fabrication method of silicon carbide ceramics filter with high strength for dust collection}

The present invention relates to a method for producing a silicon carbide ceramics filter, and more particularly, to a method for producing a silicon carbide ceramics filter having high strength by adding alkali and alkaline earth compounds.

In general, in order to form a smooth flow of combustion exhaust gas in a porous filter, the pore fraction of the filter is high and the pore size is large, so that the pressure loss must be small. However, as the pore fraction increases, the density of the filter itself decreases. Therefore, there is a disadvantage that the strength of the filter is lowered and easily broken by thermal shock and mechanical shock when the filter is used.

As described above, since the dust collecting performance and the strength characteristics of the filter have a mutually opposite relationship, there is a mutual limit in improving the mechanical characteristics of the filter.

On the other hand, as one kind of filter, silicon carbide ceramics is widely used as porous filter, refractory for various applications, pipe material of heat exchanger, and other industrial materials due to its excellent properties such as high temperature characteristics, corrosion resistance, abrasion resistance, and thermal shock resistance. In general, however, its melting point is high and its covalent bond is high, so that it is usually difficult to sinter only by itself. Therefore, in order to use such ceramics as a porous filter, various oxides such as alumina (Al ₂ O ₃ ), silica (SiO ₂ ) and clay, and nitrides including silicon oxynitride (Si ₂ ON ₂ ) and boron Non-oxide-based raw materials such as (B) or carbon (C) are added as a sintering aid to produce a silicon carbide ceramic filter in which ceramic particles are bonded to each other.

When oxides such as alumina and silica and non-oxide materials such as boron or carbon are added to the ceramic particles, the characteristics are relatively high, but the raw material is expensive and high sintering temperature is required to form a bond of particles. Therefore, there is a disadvantage of being uneconomical.

And, in the case of an oxide-added filter such as clay, the bonding of particles easily occurs, the price of clay is low, and sintering is possible at a low sintering temperature, but it is economical, but thermal shock resistance, corrosion resistance, strength, etc. ㆍ The mechanical characteristics were relatively low compared to other sintering aids.

Therefore, in order to improve the characteristics by the clay bonding method, there is a method of increasing the characteristics of the filter by adding fibers, etc., but the glass fibers used as such fibers are harmful to the human body, the manufacturing process is complicated, and the manufacturing cost is high. There is a disadvantage that increases.

The present invention is provided to solve the problems of the prior art as described above, in the method for producing a silicon carbide ceramic filter, the method of manufacturing a silicon carbide ceramic filter having a high strength characteristics by adding clay and other additives to the existing ceramic particles. The purpose is to provide.

1 is a 50 times magnified photograph of a filter manufactured by a method of manufacturing a high strength silicon carbide ceramic filter for dust collection according to an embodiment of the present invention,

FIG. 2 is an enlarged photograph 1000 times the filter illustrated in FIG. 1;

FIG. 3 is a photograph enlarged 50 times as a photograph of a silicon carbide ceramic filter to be compared to compare with the filter illustrated in FIG. 1.

According to the present invention for achieving the object as described above, in the method of manufacturing a high-strength silicon carbide ceramic filter for dust collection, the mass of the silicon carbide ceramic powder and the silicon carbide ceramic powder with respect to the 100wt% based on 100wt% Aged by mixing 1.0 ~ 15.0wt% sintering aid, 1.0 ~ 5.0wt% molding aid, 0.1 ~ 5.0wt% alkali element compound, 0.5 ~ 5.0wt% dispersant and 5.0 ~ 15.0wt% water There is provided a method of manufacturing a high strength silicon carbide ceramic filter for dust collection, comprising the steps of: pressing the aged raw material to form a filter, and heating and sintering the molded filter.

The compound of the alkaline element of the present invention may be any one of an oxide of an alkali element, a nitride of an alkali element, a carbonate compound of an alkali element, an oxide of an alkaline earth element, a nitride of an alkaline earth element, and a carbonate compound of an alkaline earth element. And the sintered plasticizer is clay.

In addition, according to the present invention, the mature material in the forming step is molded by pressing at a molding pressure of 100 ~ 800kg / cm ² by the hydrostatic pressure molding method.

Further, according to the present invention, the sintering step includes a first step of drying the molded filter at room temperature, and a second step of sintering at a temperature of 1000 ~ 1800 ℃.

In addition, according to the present invention, in the step of sintering at a temperature of 1000 ~ 1800 ℃ in order to remove the organic matter contained in the molded filter at room temperature from 800 ℃ to 800 ℃ at a rate of 1.5 ℃ / min and then maintained at 800 ℃ 6 hours After the first sintering step and a second sintering step of maintaining the temperature at a rate of 4 ℃ / min from 800 ℃ to 1400 ℃ 4 ℃ / 10 hours at 1400 ℃ 10, the filter sintered through the secondary sintering step 1400 Cool at 5 ° C / min at ° C.

Hereinafter, the gist and purpose of the present invention will be described before explaining in detail the method of manufacturing the high-strength silicon carbide ceramic filter for dust collection of the present invention.

The raw material of the filter is composed of silicon carbide ceramic powder as a main raw material, clay as a sintering aid, and an alkaline element compound, wherein the alkali element compound is an oxide of an alkali element, a nitride of an alkali element, a carbonate compound of an alkali element, or Any one of an oxide of an alkaline earth element, a nitride of an alkaline earth element, and a carbonate compound of an alkaline earth element. At the time of mixing, organic additives such as an organic binder and a dispersant may be added, mixed, and molded to form a filter molded body. Then, the filter molded body is degreased through heat treatment, and the organic additive is removed, followed by sintering at a higher temperature to produce a filter of high strength.

As described above, in order to express the strength characteristics of the manufactured sintered filter higher, silicon carbide ceramics are easily sintered and have excellent characteristics even by using an economical raw material by setting an optimum combination ratio of the elements of the filter. To get a filter.

Hereinafter, a preferred embodiment of a method of manufacturing a high strength silicon carbide ceramic filter for dust collection according to the present invention will be described in detail.

First, clay is added to the silicon carbide ceramic powder which is a main component of the filter raw material. At this time, the clay is added to increase the bonding force between the silicon carbide ceramic powder particles, the amount of the clay is added by mixing 1.0 ~ 15.0wt% with respect to the mass of the silicon carbide ceramic powder. That is, the silicon carbide ceramics filter according to one embodiment of the present invention has weak strength between particles of silicon carbide when the clay used as the sintering aid is added to less than 1.0 wt%, thereby having an unsuitable strength for use as a filter. . In addition, the silicon carbide ceramics filter does not significantly improve its strength even when the proportion of clay is added in excess of 15.0 wt%, and the pore size is also reduced.

CarboxyMethyl Cellulose (CMC), which is an organic binder, is added to the mixed silicon carbide ceramic powder and clay as a molding aid. The carboxymethyl cellulose added at this time is added and mixed 1.0 to 5.0wt% with respect to the mass of the silicon carbide ceramic powder. If the carboxymethyl cellulose is added below 1.0 wt%, the bonding strength between particles becomes weak during the molding of the silicon carbide ceramics filter, and if the carboxymethyl cellulose is added above 5.0 wt%, the inside of the silicon carbide ceramics filter is heat-treated. The mixed raw materials are then placed in a polyethylene container and dry mixed for 1 hour in a vibration pot mill to ensure uniform mixing.

In the next step, apart from the solid mixture of silicon carbide ceramic powder, clay and molding aid, water, an alkali compound or alkaline earth compound, and an organic dispersant are put together in a kneader, and then mixed evenly for 30 to 60 minutes to prepare a liquid mixture. At this time, calcium carbonate of an alkali-based element compound, which is an inorganic binder serving as a sintering aid, is added to the liquid mixture in a range corresponding to 0.1 to 5.0 wt% of the mass of the silicon carbide ceramic powder. This calcium carbonate weakens the interparticle bonds of silicon carbide when added to less than 0.1 wt% as in the case of clay, and does not improve the filter strength even if the added ratio is increased when added above 5.0 wt%. In addition, the dispersant of the liquid mixture is added 0.5 to 5.0wt% based on the mass of the silicon carbide ceramic powder for interparticle dispersion. If the dispersant is added less than 0.5wt%, the mixture of the filter is not evenly mixed, agglomeration of particles is generated a lot, and when the dispersant is added more than 5.0wt%, the inside of the filter during the heat treatment like the molding aid In addition, 5.0-15.0 wt% of water is added to the mixture used for forming the silicon carbide ceramic filter based on the mass of the silicon carbide ceramic powder to impart plasticity. If water is added below 5.0 wt%, the mixture is inadequate for molding due to lack of flexibility, and if water is added above 15.0 wt%, it is unbonded because it takes a long time to dry to make the filter mixture impossible to mold. .

The solid mixture and the liquid mixture formed as described above are mixed again and aged at room temperature for 24 hours, followed by hydrostatic pressing (CIP; Cold Isostatic Press) to form a molded body of the filter. At this time, the mixture obtained by remixing the solid and liquid mixture is filled into a hydrostatic pressure molding mold, and hydrostatically pressurized at a molding pressure of 100 to 800 kg / cm ² to form a filter. The molded product of the filter manufactured as described above is dried for 12 hours or more at room temperature or 6 hours or more when the dryer is used to remove water, followed by sintering for 1 to 10 hours at a temperature range of 1000 to 1800 ° C., according to the present invention. Prepare the filter.

Here, the molding pressure of 100kg / cm ² is the minimum pressing force capable of molding the filter in the present invention, the pores between the ceramic particles is small when molding at a molding pressure of 800kg / cm ² or more in the hydrostatic molding mold The removal effect of harmful fine dust, which is the main function of the filter, is reduced.

For this reason, when the filter molded body is molded at a molding pressure of 100 to 800 kg / cm ² and sintered at an appropriate temperature, the silicon carbide ceramic powders are particle bonded, and the pore diameter of the filter formed by particle bonding is 25 to 75. And the pore fraction is 30 to 60 vol% of the total volume of the filter.

At this time, when the pore diameter is smaller than 25 μm or the porosity is smaller than 30 vol%, the pores are not interconnected and are separated and distributed, so that the smooth flow of the combustion flue gas does not occur, resulting in large pressure loss, thereby not functioning as a filter. If the pore diameter is larger than 75 μm or the porosity is larger than 60 vol%, the strength value of the filter is very weak, and thus the performance as a filter is not exhibited.

On the other hand, the organic molding aids in the molded filter molded body is melted and vaporized and removed in advance by maintaining the filter molded body at a relatively low temperature rising rate up to about 800 ° C. for 1 to 6 hours.

Ceramics filter according to the present invention is composed of ceramic particles having a particle size of 100 ~ 300㎛ and pores having a diameter of 25 ~ 75㎛, the total volume ratio of the pores, that is porosity is composed of a volume ratio of 30 ~ 60 vol% The ceramic particles are bonded three-dimensionally to each other by clay, an alkali compound or an alkaline earth compound, which is a sintering aid.

As described above, an alkali compound or an alkaline earth compound is added to the silicon carbide ceramic filter manufactured according to the present invention as a sintering aid together with clay. As a result, the porosity and pore size of the filter and the density of the sintered compact are added only to the clay sintering aid. There is no significant difference compared to the case, and a pressure loss similar to that of a conventional ceramic filter is formed.At the same time, the bonding force between the ceramic particles is improved by clay, an alkali compound or an alkaline earth compound, thereby improving the quality of the filter compared to the conventional ceramic filter. It can manufacture.

Experimental Example

Hereinafter, as an experimental example according to the present invention, it will be described in detail by comparing a plurality of embodiments according to the present invention and their comparative examples.

As shown in Table 1 below, in Comparative Examples 1 to 5, 80g of 1wt% clay, 240g of 3wt%, 400g of 5wt% and 800g of 10wt% with respect to 8000g of silicon carbide powder having an average particle size of 180 μm 1 g of carboxymethylcellulose was added and mixed for 1 hour. An aqueous solution containing 80 g of a dispersant of 1 wt%, 160 g of calcium carbide dispersed in 2 wt% (800 g of water of 10 wt%) was added thereto, and then mixed again for 30 minutes. The mixed powders were aged at room temperature for 24 hours to spread the water evenly, and then filled in a hydrostatic molding mold and hydrostatically molded at a molding pressure of 300 kg / cm ² . After drying the molded body at room temperature for 20 hours, the temperature was raised at a rate of 1.5 ° C./min to 800 ° C. to remove the organic molding aid contained in the molded body, and then maintained at 800 ° C. for 6 hours, and then 4 ° C. to 1400 ° C. After the temperature was raised at a rate of / min and maintained at 1400 ℃ for 10 hours, a filter was prepared by cooling at a rate of 5 ℃ / min. At this time, a filter in which 80 g of clay of 1 wt% was mixed was Comparative Example 1, a filter in which 240 g of 3 g of clay was mixed in 3 wt% was Comparative Example 2, and a filter of 400 g of clay in 5 wt% was Comparative Example 3 And Comparative Example 4 are filters in which 800 g of clay having a weight of 10 wt% is mixed. In addition, Comparative Example 5 is a filter manufactured in Germany for actual combustion gas purification, and the composition composition ratio, molding pressure, etc. cannot be known due to the secret of the manufacturer regarding the composition of Comparative Example 5. Therefore, in the unknown data in the comparative example 5, it represented with "-".

Meanwhile, the filters prepared according to the present invention are Examples 1 to 8, and in Examples 1 to 8, 400 g of clay of 5 wt% and 8 g of 0.5 wt of 0.5 wt% of 8000 g of silicon carbide powder having an average particle size of 180 μm. The molded product was molded under the same conditions as the comparative examples except that 40% of calcium (1%), 80g of 1% by weight, and 160g of 2% by weight were mixed, and the molded product was subjected to 1350 ° C, 1375 ° C, 1400 ° C, 1425 ° C, 1450 Sintering was carried out at a temperature of ℃ to measure the porosity and mechanical strength.

From Table 1, the following conclusions can be drawn.

The mechanical strength of the filter increased with the addition of clay and calcium carbonate.In case of the same amount of clay, the strength increased with the addition of calcium carbonate, and the sintering temperature for the same amount of clay and calcium carbonate. The higher is, the higher the strength is. Meanwhile, among these examples, the filters of Examples 3 to 8 were shown as good examples in terms of porosity and mechanical strength.

Meanwhile, in the drawings, FIG. 1 is a 50 times magnified photograph of a filter manufactured by a method of manufacturing a high strength silicon carbide ceramic filter for dust collection according to an embodiment of the present invention, and FIG. 2 is a 1000 times magnification of the filter shown in FIG. 3 is an enlarged photograph of FIG. 3, which is a 50 times enlarged photograph of a silicon carbide ceramic filter to be compared for comparison with the filter illustrated in FIG. 1.

After crushing the filter center portion of Example 3 in Examples 1 to 8 described in Table 1, a portion was magnified and observed by a scanning electron microscope (SEM), and as a result, as shown in the photograph of FIG. The silicon particles are about 200 μm, which is not significantly different from the size of the initial starting material. However, as shown in the enlarged photograph shown in FIG. 2, the added clay and calcium carbonate are used to define the grain boundary between the silicon carbide particles. It can be seen that the connection is combined.

Meanwhile, the bending strength of the manufactured filters (Examples 1 to 8 and Comparative Examples 1 to 5) was measured to evaluate the change in strength of the filter according to the amount of calcium carbonate compound added. In order to measure the bending strength, a sintered filter was cut to a size of about 40 mm × 10 mm × 5 mm using a diamond cutter, and the plane of the cut specimen was polished by a diamond electrode wheel having a particle size of 125 μm. In addition, before measuring the cut specimens, the surface and edges subjected to tensile stress to remove the defect that is the origin of the crack at the time of fracture was polished and edge-treated with silicon carbide 1200 abrasive paper to prepare the specimen. Thereafter, the specimen was placed on a jig having a lower distance of 25 mm, and the bending strength was measured by a universal strength tester using a three-point bending strength test method. On the other hand, the density and porosity were calculated by using the Archimedes method after weighing each specimen in water for 3 hours, weighing the suspension weight, the catcher weight and the dry weight. Table 1 shows the porosity and strength values of the filters thus measured.

In Table 1, the silicon carbide ceramic filter of Example 3 has a porosity of 32 vol% and an intensity value of 28 MPa, which is relatively very high in comparison with the comparative examples.

Meanwhile, as shown in FIG. 3, in the sintered compact microstructure of Comparative Example 3, almost no connection medium connecting the silicon carbide particles was formed. As a result, as shown in Table 1, the porosity was 37 vol%, but the mechanical strength was 3.75 MPa, which was low.

Taken together these results, it can be seen that the filter produced by the present invention is improved in strength, the improvement of the very high strength only by the simple addition of a small amount of alkaline earth compounds.

On the other hand, the mechanical strength and the standard deviation according to the heat cycle recovery of the filter of Example 3 and the filter according to the prior art (Germany product; almost the same product as Comparative Example 3) in Table 1 were analyzed.

As shown in Table 2, using the filter of Example 3 and the filter according to the prior art, a heat cycle was repeatedly applied from 15 to 25 ℃ normal temperature to 800 to 850 ℃ operating temperature. In general, as the number of heat cycles increases, the strength of the filter due to thermal fatigue decreases. In Table 2, the change in strength with respect to the number of heat cycles applied to the filter according to the prior art and the filter of Example 3 according to the present invention is reduced. Indicates.

The mechanical strength of Example 3 in Table 2 shows almost the same strength, even if heated to 800-850 degreeC up to 0-200 times. Table 2 shows that the mechanical strength increases when only the mechanical strength is seen. However, since the variation range is so wide, it can be predicted to have approximately the same strength as the initial filter. However, in the case of the filter according to the prior art, the number of heat cycles is increased. It can be clearly seen that the mechanical strength decreases as time goes by.

As described in detail above, the filter manufactured by the method of manufacturing the high-strength silicon carbide ceramic filter for dust collection of the present invention is a three-dimensional clay, alkali compound or alkaline earth compound as an additive to the silicon carbide ceramic particles constituting the filter It has the advantage that its mechanical strength is excellent.

In addition, the filter produced by the method for producing a high-strength silicon carbide ceramic filter for dust collection of the present invention has the advantage that the life of the filter is long because the change in strength with respect to the heat cycle recovery is small.

Although the technical idea of the method for manufacturing the high-strength silicon carbide ceramic filter for dust collection of the present invention has been described with the accompanying drawings, this is illustrative of the best embodiment of the present invention and is not intended to limit the present invention. In addition, it is obvious that any person skilled in the art can make various modifications and imitations without departing from the scope of the technical idea of the present invention.

Claims (6)

In the manufacturing method of the high strength silicon carbide ceramic filter for dust collection, 1.0 to 15.0 wt% of sintering aid, 1.0 to 5.0 wt% of molding aid, and 0.1 to 5.0 wt% of alkali based on the mass of silicon carbide ceramic powder and silicon carbide ceramic powder based on 100 wt% Aging by mixing an elemental compound, 0.5-5.0 wt% dispersant and 5.0-15.0 wt% water; Pressing the mature raw material to form a shape of the filter; Heating and sintering the shaped filter, The mass of the sintering aid, the molding aid, the compound of the alkali-based element, the dispersant and the water is mixed in each of the set mass ratio with respect to the mass of the silicon carbide ceramic powder, the high strength silicon carbide ceramic filter for dust collection Manufacturing method. The method of claim 1, The compound of the alkaline element is any one of an oxide of an alkali element, a nitride of an alkali element, a carbonate compound of an alkaline element, or an oxide of an alkaline earth element, a nitride of an alkaline earth element, or a carbonate compound of an alkaline earth element. Manufacturing method of high strength silicon carbide ceramic filter for dust collection. The method according to claim 1 or 2, The sintered plasticizer is a method for producing a high strength silicon carbide ceramic filter for dust collection, characterized in that clay. The method of claim 1, The method of producing a high-strength silicon carbide ceramic filter for dust collection, characterized in that the raw material matured in the forming step is pressurized at a molding pressure of 100 ~ 800kg / cm ² . The method of claim 1, The sintering step comprises the first step of drying the molded filter at room temperature, and the second step of sintering at a temperature of 1000 ~ 1800 ℃ a method for producing a high-strength silicon carbide ceramic filter for dust collection. The method of claim 5, In the step of sintering at a temperature of 1000 ~ 1800 ℃ in order to remove the organic matter contained in the molded filter at room temperature from 800 ℃ to 800 ℃ at a rate of 1.5 ℃ / min and then maintained at 800 ℃ for 6 hours, After heating up at a rate of 4 ° C./min from 800 ° C. to 1400 ° C., a second sintering step is maintained at 1400 ° C. for 10 hours. A method for producing a high strength silicon carbide ceramic filter for dust collection, characterized by cooling at a speed.