JPH09234319A - Porous ceramics film, ceramics filter and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a porous ceramics film having high porosity and high strength suitable as a high strength ceramics filter wherein ceramics fibers are not individually scattered or peeled from a base material even under high filtering pressure. SOLUTION: Ceramics fibers 2 supported on a ceramics base material 1 are coated with a liquid silicon-containing polymeric compd. and the coated fibers are backed to form a ceramics coating layer composed of at least one of carbide and nitride. The individual ceramics fibers 3 are mutually bonded by the ceramics coating layer and a high strength ceramics film having a three- dimensional reticulated skeletal structure is obtained. The ceramics fibers 3 are Si3 N4 fibers and the voids of the ceramics film is 70-95% and the average pore size thereof is 0.1-100μm.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a porous ceramic membrane having high porosity and high strength, a ceramic filter using the same, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, high heat resistance and high strength,
A filter with high thermal shock resistance is required. Ceramic filters are regarded as promising as filters having such characteristics.

[0003] However, since the typical ceramics filters currently on the market are produced by sintering raw material powders, their porosity remains at a low level of about 40% by volume at the maximum. Therefore, although it depends on the average pore diameter, the permeation flow rate is generally very small and the pressure loss is large.

On the other hand, a ceramic foam is known as a ceramic filter having a high porosity. It has a skeletal structure by immersing an organic foaming material such as polyurethane foam having a three-dimensional skeleton structure in a ceramic slurry, adhering the slurry to the surface, and then burning this to eliminate the organic content. It is a ceramic filter.

However, the filter made of ceramic foam is liable to be clogged due to its manufacturing reason, a uniform product cannot be obtained, and it has many defects, so that the mechanical strength is low. is there. Of course, there is a problem that a thin film filter cannot be synthesized, and in particular, a filter having an average pore diameter of 100 μm or less causes severe clogging and cannot be manufactured.

On the other hand, as a ceramics filter having a high porosity and an excellent thermal shock resistance, the inventors of the present invention, in Japanese Patent Application No. 5-351046, propose a reticulated aggregate of silicon nitride fibers on a ceramics base material. A fixed ceramics filter was proposed. This ceramic filter has a simple skeleton structure in which Si ₃ N ₄ fibers are entangled with each other and has a porosity of 80% or more.

[0007]

[Problems to be Solved by the Invention] However, Japanese Patent Application No. 5-3
Also in the ceramic filter proposed by No. 51046, the strength is insufficient due to the small diameter of the fiber itself and the joint between the fibers and the contact between the fiber and the base material are not strong, and When it is used for filtering impurity particles, there is a phenomenon that the filter is destroyed because the filtration pressure is high, the individual fibers are scattered in pieces, or the ceramic fiber aggregate is separated from the base material.

The present invention has been made in view of such a conventional situation,
High-strength porous ceramic membrane and ceramics using the same, which has a high porosity and does not cause individual ceramic fibers to be dispersed or the fiber aggregate from peeling off from the substrate even when used at high filtration pressure. Intended to provide a filter.

[0009]

In order to achieve the above object, a porous ceramic membrane provided by the present invention is a porous ceramic membrane composed of an assembly of ceramic fibers supported by a ceramic substrate and having a core. A ceramic coating layer made of at least one type of carbide or nitride is formed on the surface of each ceramic fiber forming the matrix, and the ceramic coating layer has a three-dimensional network skeleton structure in which the ceramic fibers are bonded to each other. .

The production of the porous ceramic film of the present invention is carried out on the surface of each ceramic fiber of the ceramic fiber aggregate supported on the ceramic substrate.
After coating with a liquid silicon-containing polymer compound, baking is carried out at 600 to 2000 ° C. In this method for producing a porous ceramic film, a flat or cylindrical ceramic substrate having a through hole having a diameter of 1 to 10 mm is used, and an aggregate of ceramic fibers is synthesized from a gas phase to produce the ceramic substrate. A method of filling the through holes is preferable.

Further, the ceramic filter of the present invention comprises a flat or cylindrical ceramic substrate having a through hole having a diameter of 1 to 10 mm, and a porous ceramic of a ceramic fiber aggregate filled and held in the through hole. The porous ceramic film comprises a ceramic coating layer formed of at least one kind of carbide or nitride on the surface of each ceramic fiber forming a core, and the ceramic fibers are bonded to each other by the ceramic coating layer. It has a three-dimensional net-like skeleton structure.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a ceramic fiber-reinforced ceramic is obtained by forming a ceramic coating layer on the surface of each ceramic fiber forming a porous ceramic film as a core. At the same time, the diameter of the porous ceramic film is increased, and the fibers are firmly bonded to each other and the fiber and the substrate are firmly bonded to each other by this coating layer to form a porous ceramic film having a three-dimensional network skeleton structure.

The ceramic fiber to be used is not particularly limited and may be, for example, Si ₃ N ₄ , SiC, Al ₂ O ₃ or the like, but Si ₃ N ₄ having particularly high strength is most effective. These ceramic fibers may be commercially available, but they are preferably formed in situ on a ceramic substrate by a known method such as thermal carbon reduction of SiO ₂ or Al ₂ O ₃ or direct decomposition of amorphous Si ₃ N _4. Use the one synthesized from the gas phase.

There is no particular limitation on the material of the ceramic base material in the filter. The shape of the ceramic base material may be a flat plate shape, a cylindrical shape, or the like, and a through hole is provided in the wall portion, and the ceramic fiber is filled therein. For example, in the case of a flat plate-shaped ceramic substrate, as shown in FIGS. 1 and 2, a through hole 2 is provided in the ceramic substrate 1, and a ceramic fiber 3 is synthesized from the gas phase and filled in the through hole 2. It is preferable. In this case, if the diameter of the through hole 2 is less than 1 mm or conversely exceeds 10 mm, it becomes difficult to fill and hold the ceramic fiber, so that the range of 1 to 10 mm is preferable.

Next, a method for forming a porous ceramic film on the ceramic substrate will be described. First, an aggregate of ceramic fibers is coated on a ceramic substrate, preferably by the above-described vapor phase synthesis method, immersed in a liquid silicon-containing polymer compound, taken out, and dried. After this, 600 ~ 20
When fired at a temperature of 00 ° C., a ceramic produced by thermal decomposition of the silicon-containing polymer compound is formed around the fiber as a coating layer.

According to this method, the surface of each ceramic fiber constituting the porous ceramic film is coated with a coating layer of ceramics produced by thermal decomposition of the silicon-containing polymer compound, so-called ceramics. It becomes a fiber reinforced ceramic and its diameter becomes thicker. Then, the ceramic coating layers combine the individual ceramic fibers to form a three-dimensional net-like skeleton structure as a whole. For this reason, the porous ceramic film of the present invention has significantly higher strength than the conventional ceramic fiber alone.

At the same time, in the method of the present invention, since the individual ceramic fibers and the ceramic base material are also joined by the ceramic coating layer, the adhesion strength between the base material and the ceramic fiber is increased, and as a result, the ceramic filter is also used. Very high mechanical strength is obtained as a whole.

The silicon-containing polymer compounds used for forming the ceramic coating layer are shown in Table 1 below, and various ceramics can be coated by arbitrarily selecting them.

[0019]

TABLE 1 silicon-containing polymer compound thermal decomposition products ceramic polysilazane Si-N-C, Si- N polycarbosilane SiC polyborosiloxane SiC, B ₄ C polysilastyrene SiC polycarborane siloxane SiC, B ₄ C Porichitano Carbosilane SiC, TiC

The firing temperature for producing ceramics from the silicon-containing compound may be 600 ° C. or higher at which each silicon-containing polymer is thermally decomposed, but 1000 ° C. or higher is required for sufficient sintering. preferable. The higher the firing temperature, the higher the strength of the porous ceramic film obtained, but if the temperature exceeds 2000 ° C., the effect is saturated and it is uneconomical. Therefore, the range is usually from 200 to 2000 ° C.

As the firing atmosphere, a non-oxidizing atmosphere such as nitrogen or argon is used so that the silicon-containing polymer compound is not oxidized. The higher the pressure, the higher the strength of the obtained porous ceramic film, and when gas pressure sintering or pressure sintering such as HIP is used, the strength of the ceramic produced from the silicon-containing polymer compound becomes higher. It can withstand higher filtration pressure as a filter.

When the porous ceramic membrane of the present invention is used as a filter, the average pore diameter is preferably 0.1 to 100 μm and the porosity is preferably 70 to 95%. Average pore size is 0.
When it is less than 1 μm, the porosity is less than 70%, the pressure loss during filtration is increased, and the filtration performance is deteriorated. Further, when the average pore diameter exceeds 100 μm, the number of contact points between fibers becomes small, so that the mechanical strength is low even when formed into a network, and high filtration pressure cannot be endured.

The average pore diameter is mainly determined by the state of the ceramic fiber aggregate before coating with the silicon-containing polymer compound, but can be changed by changing the thickness of the ceramic coating layer formed on the surface of the fiber. For example, if the ceramic coating layer is thickly coated, the average pore diameter of the porous ceramic film is reduced accordingly. On the other hand, the porosity can be controlled mainly by the thickness of the ceramic coating layer on the surface of the ceramic fiber. However, when the porosity exceeds 95%, the ceramic coating layer becomes thin, so that the coating effect is not obtained, the mechanical strength becomes low, and high filtration pressure cannot be endured.

The porous ceramic membrane of the present invention is made of a ceramic fiber reinforced ceramic composite material,
This has a three-dimensional net-like skeleton structure joined to the difference,
It has high porosity and excellent strength. Therefore, when this porous ceramic membrane is used as a filter, it withstands a high filtration pressure and at the same time exhibits excellent permeation performance. Particularly, it is highly effective for filtering fine particles in gas.

[0025]

EXAMPLES Example 1 A disk of alumina having a diameter of 25 mm and a thickness of 0.5 mm with 10 through holes having a diameter of 5 mm was used as a base material, and the base material was placed in a CVD furnace. Further, a mixed powder obtained by adding 5% by weight of TiO ₂ powder to amorphous Si ₃ N ₄ powder was molded into 25 × 25 × 10 mm, and this compact was placed in the same CVD furnace. Nitrogen gas was caused to flow in the furnace and heated at a temperature of 1500 ° C. and a pressure of 1 atm for 2 hours, and Si ₃ N ₄ fiber was filled in the through holes of the substrate by gas phase synthesis to coat the fiber.

The base material in which the Si ₃ N ₄ fiber was filled in the through hole was dipped in a solution of polysilazane, which is a polymer compound composed of Si and N, diluted 5 times with xylene, and immediately pulled up at 50 ° C. After drying, 1 in nitrogen
Firing was performed at 000 ° C and 1 atm for 2 hours. By this firing,
A Si ₃ N ₄ coating layer having a thickness of about 1 μm was formed on the surface of each Si ₃ N ₄ fiber, and a porous ceramic film having a three-dimensional network skeleton structure was obtained. For the purpose of Comparative Example, a porous ceramic film of Comparative Example was produced in the same manner as above except that polysilazane was not coated.

The porous ceramic film formed on these substrates was placed as a filter 4 in the gas separator shown in FIG. 3 and attached to the sample adapter 5 via the O-ring 6. Nitrogen gas in which ceramic particles having a particle size of 0.1 μm were suspended at a concentration of 10 ppm was supplied to the filter 4 from a gas supply system 7 at a supply pressure of 5 to 20 atm, and filtered by the filter 4. The concentration of ceramic particles in the gas after filtration was measured by a concentration analyzer 8 and the gas flow rate was measured by a flow meter 9. Table 2 shows the obtained results.

[0028]

[Table 2] Polymer average porosity Porosity Filtration pressure Collection rate Permeation flow rate Sample coating diameter (μm) (%) (atm) (%) (ml / min) 1 Yes 8 80 5 99.9 5885 2 Yes 8 80 20 99.9 19985 3 * None 10 825 Peeling off- (Note) Samples marked with * in the table are comparative examples.

As can be seen from the results shown in Table 2, the filters of the examples showed high permeation performance and excellent collection performance, but the filters of the comparative examples separated the ceramic fiber aggregate from the substrate during filtration. However, some of the ceramic fibers had disappeared.

Example 2 A disk of Si ₃ N _{4 having} a diameter of 25 mm and a thickness of 0.5 mm was processed and 10 through holes having a diameter of 5 mm were used as a base material, which was placed in a CVD furnace. Moreover, a mixed powder obtained by adding 5% by weight of C powder to SiO ₂ powder is 25 × 25.
Molded to × 10 mm. The compact was placed in the same furnace. Nitrogen gas was caused to flow in the furnace and heated at a temperature of 1300 ° C. and a pressure of 1 atm for 2 hours to fill and coat the through holes of the substrate with Si ₃ N ₄ fibers.

This base material was immersed in a solution of polysilazane, which is a polymer compound composed of Si and N, diluted 5 times with xylene, immediately pulled up and dried at 50 ° C., and then 500 to 500 ° C. in nitrogen gas. 10 at a temperature of 1900 ° C
Baking at 00 atm for 2 hours, Si _{3 on} the surface of the fiber
The N ₄ coating layer was coated to a thickness of 8 μm. As a comparative example, a sample similar to the above was prepared except that polysilazane was not coated.

Using each of these samples as a filter, a gas in which ceramic particles having a particle size of 1 μm were suspended at a concentration of 10 ppm in nitrogen gas was supplied in the same manner as in Example 1 at a supply pressure of 5 to 3.
It was supplied at 0 atm and filtered, and the results are shown in Table 3.

[0033]

[Table 3] Polymer firing temperature Average pore Porosity Filtration pressure Collection rate Permeation flow rate Sample coating (℃) Diameter (μm) (%) (atm) (%) (ml / min) 4 Yes 500 25 80 5 99.9 14990 5 Yes 600 25 80 5 99.9 15001 6 Yes 1900 25 80 5 99.9 15401 7 Yes 500 25 80 20 Peel − 8 Yes 600 25 80 20 99.9 45 600 9 Yes 1900 25 80 20 99.9 51000 10 Yes 500 25 80 30 Peel − 11 Yes 600 25 80 30 Peeling-12 Yes 1900 25 80 30 99.9 76530 13 * No-35 82 5 Peeling- (Note) Samples marked with * in the table are comparative examples.

From the results in Table 3 above, it is understood that the higher the firing temperature of polysilazane, the higher the pressure resistance of the obtained ceramic filter.

Example 3 A SiC disk having a diameter of 25 mm and a thickness of 0.5 mm was processed, and 10 through holes having a diameter of 5 mm were formed as a base material, which was placed in a CVD furnace. In addition, a mixed powder obtained by adding 5% by weight of C powder to Al ₂ O ₃ powder is 25 × 25.
It was molded to × 10 mm, and the molded body was placed in the same furnace. Nitrogen gas was caused to flow in this furnace and heated at a temperature of 1800 ° C. and a pressure of 1 atm for 2 hours to fill and coat the through holes of the substrate with AlN fibers.

The obtained substrate was immersed in a solution of polycarbosilane, which is a silicon-containing polymer compound composed of Si and C, diluted 4 times with xylene, immediately pulled up, dried at 50 ° C., and then nitrogen. 1700 ° C in gas, 1-1
After firing at 000 atm for 2 hours, the surface of the AlN fiber was coated with a coating layer of SiC to a thickness of 5 μm. As a comparative example, a sample similar to the above was prepared except that polycarbosilane was not coated.

Using these samples as filters, in the same manner as in Example 1, a gas prepared by suspending ceramic particles having a particle size of 3 μm in nitrogen gas at a concentration of 6 ppm was filtered at a supply pressure of 1 to 7 atm, and the results are shown in Table 1. Shown in FIG.

[0038]

[Table 4] Polymer Firing pressure Average pore Porosity Filtration pressure Collection rate Permeation flow rate Sample coating (atm) Diameter (μm) (%) (atm) (%) (ml / min) 14 Yes 1 99 81 1 99.5 264 15 Yes 500 99 80 1 99.5 266 16 Yes 1000 99 81 1 99.6 26 300 17 Yes 1 99 81 4 Peel − 18 Yes 500 99 80 4 99.9 42500 19 Yes 1000 99 81 4 99.6 42250 20 Yes 1 99 81 7 Peel − 21 Yes 500 99 80 7 Peel-off 22 Yes 1000 99 81 7 99.6 69980 23 * None 1 99 81 1 Peel-Note: The samples marked with * in the table are comparative examples.

From the results in Table 4 above, it can be seen that, under a constant firing temperature, the higher the firing pressure is, the more excellent the pressure resistant ceramic filter can be obtained.

Example 4 A disk of SiC having a diameter of 25 mm and a thickness of 0.5 mm was machined and 10 through holes having a diameter of 5 mm were formed as a base material, which was placed in a CVD furnace. In addition, amorphous S
A mixed powder obtained by adding 5% by weight of TiO ₂ powder to i ₃ N ₄ powder was molded, and this molded body was placed in the same furnace. Nitrogen gas is flown into this furnace, and heated at a temperature of 1400 ° C to 1500 ° C at a pressure of 0.9 atm for 2 hours to produce Si ₃ N 2.
₄ fibers were filled and coated in the through holes of the substrate.

This base material is treated with polycarbosilane, which is a silicon-containing polymer compound composed of Si and C, with 4 to 4 parts of xylene.
Immerse in 1 (no dilution) times diluted solution (heated to 50 ° C.), immediately pull up and dry at 50 ° C., then bake in nitrogen gas at 1700 ° C. and 5 atm for 2 hours to obtain Si
The surface of the ₃ N ₄ fiber was coated with a SiC coating layer in various thicknesses. As a comparative example, a sample prepared in the same manner as above except that polycarbosilane is not coated,
A commercially available Al ₂ O ₃ filter having a diameter of 25 mm and a thickness of 0.5 mm was prepared.

[0042] For each of these samples, Si ₃ N ₄ and Si ₃ N ₄ fibers prior to coating the polymer compound polycarbosilane, SiC coating layer after coating is formed
The average pore size and porosity of the fiber were measured, and the results are shown in Table 5 together with the fiber synthesis temperature and the polycarbosilane concentration.

[0043]

[Table 5] Before coating Fiber after coating Fiber synthesis temperature Average pore porosity Polymer High molecular weight average polymer Porosity Sample (℃) Diameter (μm) (%) Coating solution concentration diameter (μm) (%) 24 * 1400 110 96 No-110 96 25 1400 110 96 Yes 4-fold dilution 102 92 26 1400 110 96 Yes 2-fold dilution 99 90 27 1400 110 96 Yes 1-fold dilution 85 86 28 * Commercial Al ₂ O ₃ filter − − 85 35 29 * 1500 45 90 None − 45 90 30 1500 45 90 Yes 4-fold dilution 43 88 31 1500 45 90 Yes 3-fold dilution 33 80 32 1500 45 90 Yes 2-fold dilution 27 71 33 1500 45 90 Yes 1-fold dilution 24 69 34 * Commercial Al ₂ O ₃ filter − − 25 35 35 * 1600 5 85 None − 5 85 36 1600 5 85 Yes 4-fold dilution 3 79 37 1600 5 85 Yes 3-fold dilution 0.12 72 38 1600 5 85 Yes 2-fold dilution 0.09 70 39 * Commercially available Al ₂ O ₃ filter --- 0.12 35 (Note) Samples marked with * in the table are comparative examples.

Using each of these samples as a filter, a gas in which ceramic particles having a particle size of 3 μm were suspended in nitrogen gas at a concentration of 6 ppm was filtered at a supply pressure of 7 atm as in Example 1, and the permeation flow rate and the collection amount were collected. The rate was measured. Further, the average pore size and the porosity of the filter after gas permeation were measured, and the results are shown in Table 6 together. Samples 35-39
For the above, a gas in which particles having a particle diameter of 0.01 μm were suspended at a concentration of 6 ppm as described above was filtered at a supply pressure of 7 atm, and the collection rate was measured in the same manner.

[0045]

[Table 6] Permeation flow rate Average pore Porosity collection rate (%) Sample (ml / min) Diameter (μm) (%) 3 μm Particle 0.01 μm Particle 24 * Unmeasurable Fiber peels off − − 25 68540 266 92 98.2 − 26 66410 99 90 99.2 − 27 56 200 85 86 99.3 − 28 * 6640 85 35 99.6 − 29 * Unmeasurable Fiber peels − − 30 23 300 43 88 99.6 − 31 21 100 33 80 99.7 − 32 19960 27 71 99.7 − 33 17700 24 69 99.7 − 34 * 1660 25 35 99.7 − 35 * Not measurable Fiber peels off − − 36 1300 3 79 99.99 99.9 37 65 0.12 72 99.999 99.99 38 33 0.09 70 99.999 99.99 39 * 7 0.12 35 99.999 99.99 (Note) * in the table The sample marked with is a comparative example.

From the above results, the ceramic filters of the Examples did not show fiber separation due to high pressure gas,
The filter of the comparative example, which showed a high permeation flow rate and an excellent collection rate, but did not form the SiC coating layer by the coating of the high molecular compound polysilazane, had the fibers peeled from the substrate and a commercially available Al ₂ O ₃ filter. It can be seen that is very low permeation flow rate.

[0047]

According to the present invention, the porosity is high because the structure is a three-dimensional network skeleton structure of the ceramic fiber reinforced ceramic composite material while maximizing the porosity of the ceramic fiber aggregate. Moreover, it is possible to provide a porous ceramic film having extremely high strength.

Further, this high-strength porous ceramic membrane is suitable as a filter, and it is possible to obtain a high permeation flow rate without peeling of the fiber even at a high filtration pressure.
The porous ceramics membrane is effective as a high-pressure filter such as a diesel particulate, a battery separator, a catalyst carrier, a semiconductor element cleaning filter, a fine particle filtration filter in a semiconductor element manufacturing gas, and the like.

[Brief description of drawings]

FIG. 1 is a plan view showing a specific example of a filter provided with a porous ceramic membrane of the present invention.

2 is a cross-sectional view of the filter of FIG.

FIG. 3 is a schematic explanatory view of a gas separation device used for a filter test in Examples.

[Explanation of symbols]

 1 Ceramics Base 2 Through Hole 3 Ceramics Fiber 4 Filter 5 Sample Adapter 6 O-ring 7 Gas Supply System 8 Concentration Analyzer 9 Flowmeter

Claims (6)

[Claims] 1. A porous ceramic film comprising an aggregate of ceramic fibers supported on a ceramic substrate, wherein a coating layer of ceramics made of at least one of carbide and nitride is formed on the surface of each ceramic fiber forming a core. A porous ceramic film having a three-dimensional net-like skeleton structure in which ceramic fibers are bonded to each other by the ceramic coating layer. 2. The porous ceramic film according to claim 1, wherein the ceramic fiber is a Si ₃ N ₄ fiber. 3. The porous ceramics membrane according to claim 1, which has a porosity of 70 to 95% and an average pore diameter of 0.1 to 100 μm. 4. The surface of each ceramic fiber of the ceramic fiber aggregate supported on the ceramic substrate is coated with a liquid silicon-containing polymer compound and then fired at 600 to 2000 ° C. A method for manufacturing a porous ceramic film. 5. A flat or cylindrical ceramic substrate having a through hole having a diameter of 1 to 10 mm is used, and an aggregate of ceramic fibers is synthesized from a gas phase and filled in the through hole of the ceramic substrate. The method for producing a porous ceramic film according to claim 4, characterized in that 6. A plate-shaped or cylindrical ceramic substrate having a through hole having a diameter of 1 to 10 mm, and a porous ceramic film of a ceramic fiber aggregate filled and held in the through hole. Quality ceramic film
A ceramic coating layer made of at least one of a carbide and a nitride is formed on the surface of each ceramic fiber forming a core, and the ceramic coating layer has a three-dimensional net-like skeleton structure in which the ceramic fibers are bonded to each other. And ceramics filter.