Porous ceramic with nanofiber network pore wall as well as preparation method and application of porous ceramic

Abstract

The invention belongs to the technical field of ceramic carriers, and particularly relates to porous ceramic with nanofiber network pore walls as well as a preparation method and application thereof. Silicon carbide powder and monatomic silicon powder are mixed to obtain mixed powder; mixing the mixed powder, polyisocyanate, polyether polyol and a silicone oil foam stabilizer to obtain ceramic slurry; and adding a foaming agent and a catalyst into the ceramic slurry, adjusting the slurry-NCO / -OH (R), carrying out mechanical stirring foaming and glue discharging on the obtained slurry, and then carrying out reduction heat treatment to obtain the reticular composite structure ceramic composed of nano-fiber network pore walls and a reticular porous matrix. The apparent porosity of the prepared ceramic is 50-90%, the volume density is 0.9-1.9 g / cm < 3 >, the compression strength is 1.0-15 MPa, the specific surface area is 5-25 m < 2 > / g, the ceramic has the characteristics of high open porosity, large specific surface area, high strength and the like, the preparation process is simple and convenient, the weight of a carrier material can be reduced, the mechanical property and the specific surface area of the carrier material can be improved, and the ceramic has a good application prospect in the fields of automobile exhaust purification and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic carriers, in particular to a nanofiber network pore wall porous ceramic and its preparation method and application. Background Art

[0002] With the increase in the number of automobiles, the amounts of CO, HC, NO and soot particles (PM) emitted by automobiles into the atmosphere are increasing, and the resulting environmental problems are becoming increasingly severe. At present, many countries control vehicle exhaust emissions by installing catalytic purifiers on vehicle exhausts, and their performance directly determines the exhaust gas purification effect. In the purifier, the main purification function is played by three-way or four-way catalysts, and the catalysts are attached to various carriers. The performance and form of the carriers directly affect the catalytic conversion effect. Therefore, the catalyst carrier is a key component of the vehicle exhaust purifier.

[0003] Due to its high porosity and excellent high-temperature performance, cordierite honeycomb ceramics are widely used as vehicle exhaust catalyst carriers, but they have disadvantages such as a narrow synthesis range, a low load softening temperature and poor toughness. Compared with cordierite carriers, silicon carbide porous ceramics have more excellent properties, such as acid and alkali resistance to exfoliation, high strength and excellent thermal stability, and have great application prospects in the field of vehicle exhaust filtration. The prior art records the preparation of silicon carbide honeycomb ceramics with a porosity of about 70% by the pore-forming agent method, but has the disadvantages of a small specific surface area and large pore size, resulting in a small catalyst loading amount and poor catalytic effect. There is also prior art that records the preparation of a silicon carbide porous ceramic carrier with a porosity of 55-75% using silicon carbide powder as the base material, silicon carbide fiber as the reinforcing phase, and polycarbosilane as the pore-forming agent through extrusion molding and high-temperature calcination. This method has certain limitations, specifically manifested in: 1) the porosity is relatively low and the pore structure is uncontrollable, and the specific surface area of the carrier is low; 2) the fiber reinforcing phase is unevenly dispersed, resulting in poor mechanical properties; 3) this method combines extrusion molding and the pore-forming agent method, and the preparation process is complex. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a high-performance and simple-process nanofiber network pore wall hierarchical pore ceramic. The prepared porous ceramic has the characteristics of controllable pore structure, high specific surface area, low piezoresistance and high strength, and is suitable for use as a catalyst carrier.

[0005] According to one aspect of the present invention, the present invention provides the following technical solution:

[0006] A preparation method of a nanofiber network pore wall porous ceramic, comprising the following steps:

[0007] S1. Mix silicon carbide powder and elemental silicon powder to obtain a mixed powder;

[0008] S2. Mix the mixed powder, polyisocyanate, polyether polyol, and silicone oil foam stabilizer to obtain a ceramic slurry;

[0009] S3. Add a foaming agent and a catalyst to the ceramic slurry, adjust the -NCO / -OH (R) of the slurry, and mechanically stir and foam the obtained slurry, degrease it, and then perform reduction heat treatment to obtain a reticulated composite structure ceramic composed of a "nano-fiber network pore wall - reticulated porous matrix".

[0010] As a preferred embodiment of the preparation method of the nano-fiber network pore wall porous ceramic described in the present invention, wherein: in the step S1, the mass ratio of the silicon carbide powder to the elemental silicon powder is (20 - 80):(20 - 80).

[0011] As a preferred embodiment of the preparation method of the nano-fiber network pore wall porous ceramic described in the present invention, wherein: in the step S1, the particle size of the silicon carbide powder is 0.5 - 10 μm, and the purity is SiC ≥ 99 wt%; the particle size of the elemental silicon powder is 1 - 5 μm, and the purity is Si ≥ 98 wt%.

[0012] As a preferred embodiment of the preparation method of the nano-fiber network pore wall porous ceramic described in the present invention, wherein: in the step S2, the solid content of the ceramic slurry is 50 - 70 wt%.

[0013] As a preferred embodiment of the preparation method of the nano-fiber network pore wall porous ceramic described in the present invention, wherein: in the step S2, the polyisocyanate is one of polymethylene polyphenyl isocyanate, diphenylmethane diisocyanate, and toluene diisocyanate; its -NCO content is 5 - 30 wt%; the polyether polyol is a polyfunctional polyether polyol; its molecular weight is 500 - 3000 g / mol, and the viscosity is 200 - 500 mPa·s; the silicone oil foam stabilizer is a Si-C bond hydrolysis-resistant silicone oil, and the viscosity is 200 - 400 mPa·s.

[0014] As a preferred embodiment of the preparation method of the nano-fiber network pore wall porous ceramic described in the present invention, wherein: in the step S3, add 0.1 - 0.5 wt% of the foaming agent and 0.01 - 1.0 wt% of the catalyst to the ceramic slurry.

[0015] As a preferred embodiment of the preparation method of the nano-fiber network pore wall porous ceramic described in the present invention, wherein: in the step S3, the foaming agent is deionized water; the catalyst is at least one of tin-based catalysts (stannous octoate, dibutyltin dilaurate) and amine-based catalysts (triethanolamine, triethylamine).

[0016] As a preferred embodiment of the method for preparing a nanofiber network porous ceramic wall according to the present invention, in step S3, the binder is removed at 500-700 °C for 10-50 h.

[0017] As a preferred embodiment of the method for preparing a nanofiber network porous ceramic wall according to the present invention, in step S3, a reduction heat treatment is carried out in a CO / Ar atmosphere (the volume ratio of CO to Ar is 40:60) at 1400-1600 °C.

[0018] As a preferred embodiment of the method for preparing a nanofiber network porous ceramic wall according to the present invention, in step S3, the ratio of the slurry -NCO / -OH (R) is adjusted to 0.8-1.2.

[0019] As a preferred embodiment of the method for preparing a nanofiber network porous ceramic wall according to the present invention, in step S3, the stirring speed of mechanical stirring for foaming is 1000-2000 rpm.

[0020] According to another aspect of the present invention, the present invention provides the following technical solution:

[0021] A nanofiber network porous ceramic wall, prepared by the method for preparing a nanofiber network porous ceramic wall described above, having an apparent porosity of 50.0-90.0%, a bulk density of 0.9-1.9 g / cm 3 , a compressive strength of 1.0-15 MPa, and a specific surface area of 5-25 m 2 / g.

[0022] According to another aspect of the present invention, the present invention provides the following technical solution:

[0023] An application of the above nanofiber network porous ceramic wall as a catalyst carrier.

[0024] The beneficial effects of the present invention are as follows:

[0025] The present invention provides a nanofiber network porous ceramic wall, a preparation method and an application thereof. A mixed powder is obtained by mixing silicon carbide powder and elemental silicon powder; a ceramic slurry is obtained by mixing the mixed powder, polyisocyanate, polyether polyol and silicone oil foam stabilizer; a foaming agent and a catalyst are added to the ceramic slurry, and the ratio of the slurry -NCO / -OH (R) is adjusted, and the obtained slurry is mechanically stirred for foaming, the binder is removed, and then a reduction heat treatment is carried out to obtain a network composite structure ceramic composed of a "nanofiber network porous wall - reticulated porous matrix". The apparent porosity of the ceramic prepared by the present invention is 50-90%, the bulk density is 0.9-1.9 g / cm 3 , the compressive strength is 1.0-15 MPa, and the specific surface area is 5-25 m2 / g. The ceramics prepared by the present invention have the characteristics of high open porosity, large specific surface area, high strength, etc. The preparation process is simple, which can improve the mechanical properties and specific surface area while reducing the weight of the carrier material, and has good application prospects in the fields such as automotive exhaust purification. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the structures shown in these drawings.

[0027] Figure 1 It is the micro-structure of the ceramics prepared in Example 1 of the present invention.

[0028] The realization of the object, functional characteristics and advantages of the present invention will be further described with reference to the embodiments and the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The following will clearly and completely describe the technical solutions in the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0030] The present invention provides a nano-fiber network pore-wall porous ceramic with high performance and simple process, which has the advantages of high specific surface area and many active sites, is beneficial to improving the diffusion efficiency of reaction molecules in the pores, thereby improving the catalytic efficiency. The prepared porous ceramic has the characteristics of controllable pore structure, high specific surface area, low piezoresistance and high strength, and is suitable for use as a catalyst carrier. It has the following advantages:

[0031] (1) The present invention uses silicon carbide powder and elemental silicon powder as the main raw materials, and prepares a silicon carbide ceramic carrier material with nano-fiber pore walls through configuring ceramic slurry, foaming, casting and carbonization sintering. The casting mold can be adjusted according to the size of the carrier, which is suitable for large-scale mass preparation. The slurries of silicon carbide and elemental silicon are mixed with polyurethane raw materials with different R values, and the pore structure and micro-structure of the ceramics can be regulated by controlling the R value and the solid content of the suspension.

[0032] (2) The current method for constructing pores in ceramic carrier materials is to add pore-forming agents. Although the introduction of pores can increase their specific surface area, the pores are irregular and have large sizes, resulting in a low specific surface area. Moreover, the irregular pores lead to poor mechanical properties of the carrier materials, failing to achieve the maximum catalytic effect of the catalyst carrier. In the present invention, during the carbonization process, elemental silicon reacts with CO gas to form a silicon carbide fiber network on the pore walls, which not only ensures a high specific surface area of the carrier material but also constructs a toughening layer. The unvaporized elemental silicon forms a liquid phase after reaching its melting point at 1410 °C and disperses among the silicon carbide particles, and can also promote the sintering of the silicon carbide matrix through liquid-phase mass transfer.

[0033] (3) The nano-fiber network pore wall high-efficiency multi-stage pore ceramic carrier prepared by the present invention has low cost and simple process, and is suitable for large-scale batch production. The product is tested: the apparent porosity is 50.0 - 90.0%, the bulk density is 0.9 - 1.9 g / cm 3 , the compressive strength is 1.0 - 15 MPa, and the specific surface area is 5 - 25 m 2 / g. The silicon carbide ceramic carrier material prepared by the present invention has the characteristics of high porosity, large specific surface area, high strength, and good connectivity. The preparation process is simple, which can improve the specific surface area of the carrier material while enhancing its mechanical properties, and has great application prospects in the fields such as catalyst carriers.

[0034] According to one aspect of the present invention, the present invention provides the following technical solution:

[0035] A preparation method of a nano-fiber network pore wall porous ceramic, comprising the following steps:

[0036] S1. Mix silicon carbide powder and elemental silicon powder to obtain a mixed powder;

[0037] S2. Mix the mixed powder, polyisocyanate, polyether polyol, and silicone oil foam stabilizer to obtain a ceramic slurry;

[0038] S3. Add a foaming agent and a catalyst to the ceramic slurry, adjust the slurry - NCO / -OH (R), and mechanically stir and foam the obtained slurry, degum, and then perform reduction heat treatment to obtain a reticulated composite structure ceramic composed of a "nano-fiber network pore wall - reticulated porous matrix".

[0039] Preferably, in the step S1, the mass ratio of the silicon carbide powder to the elemental silicon powder is (20 - 80):(20 - 80). The particle size of the silicon carbide powder is 0.5 - 10 μm, and the purity is SiC ≥ 99 wt%; the particle size of the elemental silicon powder is 1 - 5 μm, and the purity is Si ≥ 98 wt%.

[0040] Preferably, in step S2, the addition amounts of the polyisocyanate and the polyether polyol are defined by -NCO / -OH and the solid content of the ceramic slurry, and the solid content of the ceramic slurry is 50-70 wt%. Specifically, the addition amount of the polyisocyanate can be 15-30 wt% of the mass of the mixed powder, and the polyisocyanate is one of polymethylene polyphenyl isocyanate, diphenylmethane diisocyanate, and toluene diisocyanate; its -NCO content is 5-30 wt%; specifically, the addition amount of the polyether polyol can be 15-25 wt% of the mass of the mixed powder, and the polyether polyol is a polyfunctional polyether polyol; its molecular weight is 500-3000 g / mol, and its viscosity is 200-500 mPa·s; the addition amount of the silicone oil foam stabilizer is 0.1-1.0 wt% of the mass of the mixed powder, and the silicone oil foam stabilizer is a Si-C bond hydrolysis-resistant silicone oil with a viscosity of 200-400 mPa·s.

[0041] Preferably, in step S3, 0.1-0.5 wt% of a foaming agent and 0.01-1.0 wt% of a catalyst are added to the ceramic slurry. The foaming agent is deionized water; the catalyst is at least one of tin-based catalysts (stannous octoate, dibutyltin dilaurate) and amine-based catalysts (triethanolamine, triethylamine).

[0042] Preferably, in step S3, the debinding is carried out at 500-700 °C for 10-50 h. The reduction heat treatment is carried out at 1400-1600 °C in a CO / Ar atmosphere (the volume ratio of CO to Ar is 40:60). The slurry -NCO / -OH (R) is adjusted to 0.8-1.2. The stirring speed of mechanical stirring foaming is 1000-2000 rpm.

[0043] According to another aspect of the present invention, the present invention provides the following technical solution:

[0044] A nanofiber network pore-wall porous ceramic is prepared by using the preparation method of the nanofiber network pore-wall porous ceramic as described above, and its apparent porosity is 50.0-90.0%, and its bulk density is 0.9-1.9 g / cm 3 , and its compressive strength is 1.0-15 MPa, and its specific surface area is 5-25 m 2 / g.

[0045] According to another aspect of the present invention, the present invention provides the following technical solution:

[0046] An application of the above nanofiber network pore-wall porous ceramic as a catalyst carrier.

[0047] The technical solution of the present invention is further described below with specific examples.

[0048] Example 1

[0049] A preparation method of a porous ceramic with a nanofiber network pore wall. Mix 60 parts by weight of silicon carbide powder and 40 parts by weight of elemental silicon powder evenly to obtain a mixed powder. Then, fully mix the mixed powder, 19.8 parts by weight of polyisocyanate PM200, 20 parts by weight of polyether polyol R2305, and 0.2 parts by weight of silicone oil foam stabilizer to obtain a ceramic slurry with a solid content of 60 wt%. Subsequently, add 0.2 wt% of deionized water and 0.2 wt% of dibutyltin dilaurate to the slurry, adjust the slurry -NCO / -OH(R) to 0.9, and mechanically stir and foam the obtained slurry. Debind at 600 °C for 24 h, and then perform reduction heat treatment in a CO / Ar atmosphere (the volume ratio of CO to Ar is 40:60) at 1450 °C to obtain a reticulated composite structure ceramic composed of "nanofiber network pore wall - reticulated porous matrix". As Figure 1 shown ( Figure 1 in a), it is the microstructure of the ceramic after carbonization and firing, Figure 1 in b) and c), it is the microstructure of the nanofibers on the pore wall after further magnification), it can be seen that an interlaced nanofiber structure is formed on the surface of the ceramic pore wall after carbonization and firing, and the nanofiber network pore wall and the three-dimensional reticulated porous matrix form a double network structure.

[0050] Example 2

[0051] A preparation method of a porous ceramic with a nanofiber network pore wall. Mix 50 parts by weight of silicon carbide powder and 50 parts by weight of elemental silicon powder evenly to obtain a mixed powder. Then, fully mix the mixed powder, 23 parts by weight of polyisocyanate PM200, 22 parts by weight of polyether polyol R2305, and 0.5 parts by weight of silicone oil foam stabilizer to obtain a ceramic slurry with a solid content of 65 wt%. Subsequently, add 0.25 wt% of deionized water and 0.25 wt% of triethanolamine to the slurry, adjust the slurry -NCO / -OH(R) to 1.02, and mechanically stir and foam the obtained slurry. Debind at 600 °C for 30 h, and then perform reduction heat treatment in a CO / Ar atmosphere (the volume ratio of CO to Ar is 40:60) at 1500 °C to obtain a reticulated composite structure ceramic composed of "nanofiber network pore wall - reticulated porous matrix".

[0052] The ceramic prepared in this example was tested: the apparent porosity was 58%, the bulk density was 1.7 g / cm 3 , the compressive strength was 13.5 MPa, and the specific surface area was 9.5 m 2 / g.

[0053] Example 3

[0054] A preparation method of a porous ceramic with a nanoporous fiber network pore wall involves mixing 60 parts by weight of silicon carbide powder and 40 parts by weight of elemental silicon powder evenly to obtain a mixed powder. Then, the mixed powder, 25.6 parts by weight of polyisocyanate, 23.6 parts by weight of polyether polyol, and 1.0 part by weight of a silicone oil foam stabilizer are fully mixed to obtain a ceramic slurry with a solid content of 50 wt%. Subsequently, 0.5 wt% of deionized water and 0.8 wt% of stannous octoate are added to the slurry, and the slurry -NCO / -OH (R) is adjusted to 1.1. The obtained slurry is mechanically stirred and foamed, degassed at 600 °C for 36 h, and then subjected to reduction heat treatment in a CO / Ar atmosphere (the volume ratio of CO to Ar is 40:60) at 1500 °C to obtain a reticulated composite structure ceramic composed of a "nanofiber network - reticulated porous matrix".

[0055] The ceramic prepared in this example was tested: the apparent porosity was 88.0%, the bulk density was 0.98 g / cm 3 , the compressive strength was 2.5 MPa, and the specific surface area was 21.6 m 2 / g.

[0056] Comparative Example 1

[0057] The difference from Example 2 is that 90 parts of silicon carbide powder and 10 parts of elemental silicon powder are mixed evenly to obtain a mixed powder.

[0058] The ceramic prepared in this comparative example was tested: the apparent porosity was 45%, the bulk density was 2.2 g / cm 3 , the compressive strength was 17.8 MPa, and the specific surface area was 3.8 m 2 / g.

[0059] Comparative Example 2

[0060] The difference from Example 2 is that the solid content of the ceramic slurry is 45 wt%.

[0061] The ceramic prepared in this comparative example was tested: the apparent porosity was 93%, the bulk density was 0.82 g / cm 3 , the compressive strength was 0.7 MPa, and the specific surface area was 25.2 m 2 / g.

[0062] Comparative Example 3

[0063] The difference from Example 2 is that the slurry -NCO / -OH (R) is adjusted to 1.3.

[0064] The ceramic prepared in this comparative example was tested: the apparent porosity was 43%, the bulk density was 2.42 g / cm 3 , the compressive strength was 18.2 MPa, and the specific surface area was 2.9 m 2 / g.

[0065] Comparative Example 4

[0066] It is different from Example 2 in that a reduction heat treatment is carried out in a CO / Ar atmosphere (volume ratio of CO to Ar is 40:60) at 1200 °C.

[0067] The ceramics prepared in this comparative example were tested: the apparent porosity was 42%, and the bulk density was 2.52 g / cm 3 , the compressive strength was 15.8 MPa, and the specific surface area was 2.8 m 2 / g.

[0068] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structural transformation made by using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect application in other related technical fields are all included in the patent protection scope of the present invention.

Claims

1. A preparation method of a porous ceramic with a porous pore wall of a nanofiber network, characterized in that, It includes the following steps: S1. Mix silicon carbide powder and elemental silicon powder to obtain a mixed powder; S2. Mix the mixed powder, polyisocyanate, polyether polyol and silicone oil foam stabilizer to obtain a ceramic slurry; S3. Add a foaming agent and a catalyst to the ceramic slurry, adjust the slurry -NCO / -OH, mechanically stir and foam the obtained slurry, degum, and then perform reduction heat treatment to obtain a reticulated composite structure ceramic composed of "nano-fiber network pore walls - reticulated porous matrix".

2. The preparation method of the porous ceramic with nanoporous fiber network pore walls according to claim 1, characterized in that, In the step S1, the mass ratio of the silicon carbide powder to the elemental silicon powder is (20 - 80):(20 - 80).

3. The preparation method of the nano-fiber network pore wall porous ceramic according to claim 1, characterized in that, In the step S1, the particle size of the silicon carbide powder is 0.5 - 10 μm, and the purity is SiC≥99wt%; the particle size of the elemental silicon powder is 1 - 5 μm, and the purity is Si≥98wt%.

4. The preparation method of the nanoporous ceramic with a nanofiber network pore wall according to claim 1, wherein, In the step S2, the solid content of the ceramic slurry is 50 - 70wt%.

5. The preparation method of the nanoporous ceramic with a nanofiber network pore wall according to claim 1, characterized in that, In the step S2, the polyisocyanate is one of polymethylene polyphenyl isocyanate, diphenylmethane diisocyanate, toluene diisocyanate; its -NCO content is 5 - 30wt%; the polyether polyol is a multi-functional polyether polyol; its molecular weight is 500 - 3000 g / mol, and the viscosity is 200 - 500 mPa·s; the silicone oil foam stabilizer is a Si-C bond hydrolysis-resistant silicone oil, and the viscosity is 200 - 400 mPa·s.

6. The preparation method of the nanoporous ceramic with a nanofiber network pore wall according to claim 1, characterized in that, In the step S3, add 0.1 - 0.5wt% of a foaming agent and 0.01 - 1.0wt% of a catalyst to the ceramic slurry; the foaming agent is deionized water; the catalyst is at least one of tin-based catalysts and amine-based catalysts.

7. The preparation method of the nanoporous ceramic with a nanofiber network pore wall according to claim 1, characterized in that, In the step S3, degum at 500 - 700 °C for 10 - 50 h; perform reduction heat treatment at 1400 - 1600 °C; the stirring speed of mechanical stirring and foaming is 1000 - 2000 rpm.

8. The preparation method of the nanoporous ceramic with a nanofiber network pore wall according to claim 1, characterized in that In the step S3, adjust the slurry NCO / -OH to 0.8 - 1.

2.

9. A nanoporous ceramic with a porous wall in a nanofiber network, characterized in that, Prepared by the method for preparing a nanoporous ceramic with a porous wall of a nanofiber network according to any one of claims 1-8, having an apparent porosity of 50.0 to 90.0%, a bulk density of 0.9 to 1.9 g / cm 3 , a compressive strength of 1.0 to 15 MPa, and a specific surface area of 5 to 25 m 2 / g.

10. Application of the nano-fiber network pore wall porous ceramic as claimed in claim 9 as a catalyst carrier.

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