阅读说明：本技术 一种多级孔结构的多孔陶瓷 (Porous ceramic with hierarchical pore structure ) 是由 郭新爽 黄葳 万力 王献忠 颜嘉威 祝嘉诚 闵俊豪 胡兆龙 于 2020-06-09 设计创作，主要内容包括：本发明涉及一种多级孔结构的多孔陶瓷,属于陶瓷技术领域,解决了现有多孔陶瓷的连通性较差导致过滤或催化效果较差,现有多孔陶瓷的强度较低,适用范围较窄的问题。本发明的多级孔结构的多孔陶瓷的原料组成包括：羧甲基纤维素钠、碳纳米管、水、溶胶、盐酸、十二烷基硫酸钠和氨水,制备得到的多级孔结构的多孔陶瓷的表面和内部均分布有毫米级的一级孔、微米级的二级孔和纳米级的三级孔；所述一级孔的孔壁上分布有二级孔和三级孔。本发明的多级孔结构的多孔陶瓷能用于过滤和催化领域。(The invention relates to porous ceramic with a hierarchical pore structure, belongs to the technical field of ceramics, and solves the problems of poor filtering or catalyzing effect caused by poor connectivity of the existing porous ceramic, low strength of the existing porous ceramic and narrow application range. The porous ceramic with the hierarchical pore structure comprises the following raw materials: the surface and the interior of the porous ceramic with the hierarchical pore structure are uniformly distributed with millimeter-sized primary pores, micron-sized secondary pores and nanoscale tertiary pores; and the hole wall of the primary hole is distributed with a secondary hole and a tertiary hole. The porous ceramic with the hierarchical pore structure can be used in the fields of filtration and catalysis.)

1. A porous ceramic with a hierarchical pore structure is characterized in that the raw material composition of the porous ceramic with the hierarchical pore structure comprises: sodium carboxymethyl cellulose, carbon nano tubes, water, sol, hydrochloric acid, sodium dodecyl sulfate and ammonia water.

2. The porous ceramic with a hierarchical pore structure according to claim 1, wherein the porous ceramic with a hierarchical pore structure is prepared from the following raw materials in a mass or volume ratio: sodium carboxymethylcellulose: carbon nanotube: water: sol: hydrochloric acid: sodium lauryl sulfate: 0.03-0.06 g of ammonia water: 0.06-0.12 g: 10-20 mL: 15-28 mL: 3-8 ml: 0.15-0.3 g: 4-12 mL.

3. The porous ceramic of hierarchical pore structure according to claim 1, wherein the porous ceramic of hierarchical pore structure has primary pores (1) of millimeter level, secondary pores (2) of micrometer level and tertiary pores (3) of nanometer level distributed on both surface and inside; and the wall of the first-stage hole (1) is distributed with a second-stage hole (2) and a third-stage hole (3).

4. The porous ceramic with a hierarchical pore structure according to claim 3, wherein the pore walls of the secondary pores (2) are distributed with tertiary pores (3).

5. The porous ceramic having a hierarchical pore structure according to claim 3, wherein the pore diameter of the primary pores is in the range of 0.8 to 3mm, the pore diameter of the secondary pores is in the range of 2 to 15 μm, and the pore diameter of the tertiary pores is in the range of 30 to 100 nm.

6. The porous ceramic having a hierarchical pore structure according to claim 5, wherein the porosity of the porous ceramic having a hierarchical pore structure is 65.4% to 82.2%.

7. The porous ceramic of hierarchical pore structure according to claim 6, wherein the flexural strength of the porous ceramic of hierarchical pore structure is 7 to 13.5 MPa.

8. The multi-stage pore structure porous ceramic according to claims 1 to 7, wherein the multi-stage pore structure porous ceramic is prepared by the following method:

step 1, adding sodium carboxymethylcellulose and carbon nanotubes into water, and performing ultrasonic dispersion to obtain a uniform carbon nanotube dispersion solution;

step 2, adding the sol into the carbon nano tube dispersion liquid, sequentially adding hydrochloric acid and sodium dodecyl sulfate in sequence, stirring to obtain a mixed liquid with uniform bubbles, adding ammonia water, and stirring to obtain a gel;

and 3, drying the gel, and then sintering the dried gel in vacuum to obtain the porous ceramic with the hierarchical pore structure.

9. The porous ceramic with a hierarchical pore structure according to claim 8, wherein in the step 3, the step of sintering the dried gel body in vacuum to obtain the porous ceramic with a hierarchical pore structure comprises: and putting the dried gel into a vacuum high-temperature furnace, heating to the pyrolysis temperature of ammonium chloride, preserving heat for pre-removing, then continuously heating to the final sintering temperature, and preserving heat to obtain the porous ceramic with the hierarchical pore structure.

10. The porous ceramic having a hierarchical pore structure according to claim 9, wherein the final sintering temperature is 700 to 1500 ℃.

Technical Field

The invention relates to the technical field of porous ceramics, in particular to porous ceramics with a hierarchical pore structure.

Background

Porous ceramics have been widely used in various fields because of their excellent properties such as low density, high mechanical strength, and high temperature resistance. It can be classified into open-cell and closed-cell porous ceramics, depending on the connectivity of the pores. The pore structure of the porous ceramic includes micropores, mesopores, and macropores, etc., depending on the pore size. In recent years, with the rapid development of the environmental protection industry, the chemical industry, and the like, there has been an increasing demand for porous ceramics. The porous ceramic having a hierarchical pore structure is a porous ceramic having two or more pore structure types. The multi-stage pore structure combines the advantages of various types of pore structures, and has the advantages of low density, high porosity and large specific surface area. When it is used as water absorbing and retaining material, the macro pores are favorable to water penetration, and the meso pores and the micro pores are favorable to water adsorption; when it is used as catalyst or catalyst carrier, it is favorable for raising material diffusion capacity and reaction efficiency; when it is used as bone repairing material, macro pores are favorable to cell and tissue regeneration and nutrient transfer, and meso pores and micro pores can raise their bioactivity. Although the preparation of porous ceramics has made some progress, its pore connectivity is poor, especially for nanopores; in addition, the strength of the ceramic backbone is reduced with increased pore connectivity.

Disclosure of Invention

In view of the above analysis, the present invention aims to provide a porous ceramic having a hierarchical pore structure, which can solve at least one of the following technical problems: (1) the existing porous ceramics have poor connectivity, so that the filtering or catalyzing effect is poor; (2) the existing porous ceramics have lower strength and narrower application range.

The purpose of the invention is mainly realized by the following technical scheme:

the invention provides porous ceramic with a hierarchical pore structure, which comprises the following raw materials: sodium carboxymethyl cellulose, carbon nano tubes, water, sol, hydrochloric acid, sodium dodecyl sulfate and ammonia water.

In one possible design, the porous ceramic of the hierarchical pore structure has a raw material composition with a mass or volume ratio of: sodium carboxymethylcellulose: carbon nanotube: water: sol: hydrochloric acid: sodium lauryl sulfate: 0.03-0.06 g of ammonia water: 0.06-0.12 g: 10-20 mL: 15-28 mL: 3-8 ml: 0.15-0.3 g: 4-12 mL.

In one possible design, the surface and the inside of the porous ceramic with the hierarchical pore structure are distributed with millimeter-sized primary pores, micron-sized secondary pores and nanometer-sized tertiary pores; and the wall of the first-stage hole is distributed with a second-stage hole and a third-stage hole.

In one possible design, the wall of the secondary pores is also distributed with tertiary pores.

In one possible design, the aperture range of the primary pores is 0.8-3 mm, the aperture range of the secondary pores is 2-15 μm, and the aperture range of the tertiary pores is 30-100 nm.

In one possible design, the porosity of the porous ceramic of the hierarchical pore structure is 65.4% to 82.2%.

In one possible design, the flexural strength of the porous ceramic with the hierarchical pore structure is 7-13.5 MPa.

In one possible design, the porous ceramic with the hierarchical pore structure is prepared by the following method:

step 1, adding sodium carboxymethylcellulose and carbon nanotubes into water, and performing ultrasonic dispersion to obtain a uniform carbon nanotube dispersion solution;

step 2, adding the sol into the carbon nano tube dispersion liquid, sequentially adding hydrochloric acid and sodium dodecyl sulfate in sequence, stirring to obtain a mixed liquid with uniform bubbles, adding ammonia water, and stirring to obtain a gel;

and 3, drying the gel, and then sintering the dried gel in vacuum to obtain the porous ceramic with the hierarchical pore structure.

In one possible design, in step 3, the step of sintering the dried gel body in vacuum to obtain the porous ceramic with the hierarchical pore structure comprises: and putting the dried gel into a vacuum high-temperature furnace, heating to the pyrolysis temperature of ammonium chloride, preserving heat for pre-removing, then continuously heating to the final sintering temperature, and preserving heat to obtain the porous ceramic with the hierarchical pore structure.

In one possible design, the final sintering temperature is 700-1500 ℃.

Compared with the prior art, the invention can realize at least one of the following beneficial effects:

(1) the porous ceramic with the hierarchical pore structure provided by the invention adopts the carbon nano tubes with high toughness and high strength as the reinforcing framework, so that the strength of the porous ceramic is improved, and the carbon nano tubes are mutually lapped, so that the porosity of the porous ceramic with the hierarchical pore structure can be improved; the porous ceramic with the hierarchical pore structure has the advantages of low density, high porosity and good connectivity, the bending strength can reach 7.2-13.5 MPa, the porous ceramic with the hierarchical pore structure can be used for multilevel filtration, can be used as a carrier of a catalyst, and has a wide application range.

(2) Hydrochloric acid and ammonia water are selected as catalysts, a sol-gel method is utilized to promote sol to gel quickly, the hydrochloric acid and the ammonia water react to generate ammonium chloride and the ammonium chloride slowly crystallizes in gel, and ammonium chloride fibers are generated under the action of a surfactant, namely sodium dodecyl sulfate, and alternate growth is performed in a matrix; in the sintering process, when ammonium chloride crystallization and ammonium chloride fibers reach the decomposition temperature, holes with different pore sizes are respectively reserved in situ, and the holes obtained by foaming together construct porous ceramics with a hierarchical pore structure, so that the porosity and the specific surface area are greatly improved.

(3) According to the invention, the carbon nano tube is used as a ceramic framework, and in order to keep a multi-level pore structure, vacuum sintering is adopted, the gel is placed in an alumina crucible and then placed in a vacuum high-temperature furnace, and sintering is carried out at 700-1500 ℃ to obtain the porous ceramic.

(4) According to the invention, because ammonium chloride is crystallized and ammonium chloride fibers are generated, proper heat preservation is carried out at the pyrolysis temperature of 300-350 ℃ to fully decompose ammonium chloride, so that cracking or crushing of a matrix in the removing process is avoided, and the integrity of the matrix structure is ensured.

(5) The sol-gel method adopted by the invention has simple process, and the sol can be one or more of silica sol, aluminum sol, zirconium sol and the like, so the cost is lower and the medicine source is wide; the method has low requirement on equipment, strong universality, industrial production and wide application prospect.

In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the embodiments and instrumentalities pointed out in the specification and drawings.

Drawings

The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention.

FIG. 1 is a macroscopic view of a porous ceramic of a hierarchical pore structure according to the present invention;

FIG. 2 is a schematic view of a hierarchical pore structure of the porous ceramic of the present invention;

FIG. 3 is an SEM image of secondary pore structures present in the pore walls of a primary pore of the present invention;

fig. 4 is an SEM image of the tertiary pore structure present on the pore wall of a single pore (secondary pore) of the present invention.

Detailed Description

The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and which together with the embodiments of the invention serve to explain the principles of the invention and not to limit its scope.

The invention provides porous ceramic with a hierarchical pore structure, which comprises the following raw materials: sodium carboxymethyl cellulose, carbon nano tubes, water, sol, hydrochloric acid, sodium dodecyl sulfate and ammonia water.

In order to further improve the overall performance of the porous ceramic having a hierarchical pore structure, the raw material composition of the porous ceramic having a hierarchical pore structure may be limited. Illustratively, the raw materials comprise the following components in percentage by mass or volume: sodium carboxymethylcellulose: carbon nanotube: water: sol: hydrochloric acid: sodium lauryl sulfate: 0.03-0.06 g of ammonia water: 0.06-0.12 g: 10-20 mL: 15-28 mL: 3-8 ml: 0.15-0.3 g: 4-9 mL.

Specifically, as shown in fig. 1 to 4, the surface and the inside of the porous ceramic with the hierarchical pore structure are distributed with millimeter-sized primary pores 1, micron-sized secondary pores 2 and nanometer-sized tertiary pores 3; the wall of the first-stage hole 1 is distributed with a second-stage hole 2 and a third-stage hole 3; the porosity of the porous ceramic is 65.4% to 82.2% (e.g., 72.3% to 82%).

Specifically, the wall of the secondary hole 2 is also distributed with tertiary holes 3.

Specifically, the aperture range of the primary holes is 0.8-3 mm, the aperture range of the secondary holes is 2-15 microns, the aperture range of the tertiary holes is 30-100 nm, and the structures and sizes of the primary holes, the secondary holes and the tertiary holes are uniform.

Specifically, the bending strength of the porous ceramic is 7-13.5 MPa.

Compared with the prior art, the porous ceramic with the hierarchical pore structure provided by the invention adopts the high-toughness and high-strength carbon nano tubes as the reinforcing framework, so that the strength of the porous ceramic is improved, and the carbon nano tubes are mutually lapped, so that the porosity of the porous ceramic with the hierarchical pore structure can be improved; the porous ceramic with the multi-stage pore structure has low density and high porosity, secondary pores and tertiary pores are distributed on the walls of the primary pores, and the tertiary pores are also distributed on the walls of the secondary pores, so that the product has good connectivity, the bending strength can reach 7.2-13.5 MPa, the pore structure is uniform in size, and the porous ceramic with the multi-stage pore structure can be used for multi-stage filtration, can be used as a carrier of a catalyst, and has a wide application range.

Specifically, the porous ceramic with the hierarchical pore structure is prepared by the following method: by utilizing a sol-gel method, taking sol as a raw material, carbon nano tubes as a reinforcing material, sodium dodecyl sulfate as a foaming agent, using hydrochloric acid and ammonia water to convert the sol into gel and seal bubbles, wherein the bubbles are used as a primary pore-forming agent; and carrying out in-situ crystallization on ammonium chloride generated by hydrochloric acid and ammonia water in a gel matrix, then utilizing a foaming agent to induce the ammonium chloride to grow into fibers in the matrix to serve as a secondary pore-forming agent, taking the non-fiber ammonium chloride crystals as a tertiary pore-forming agent, and carrying out vacuum sintering to obtain the porous ceramic with the hierarchical pore structure.

Specifically, the preparation method of the porous ceramic with the hierarchical pore structure comprises the following steps:

step 1, adding sodium carboxymethylcellulose and carbon nanotubes into water, and performing ultrasonic dispersion to obtain a uniform carbon nanotube dispersion solution;

step 2, adding the sol into the carbon nano tube dispersion liquid obtained in the step 1, sequentially adding hydrochloric acid and sodium dodecyl sulfate in sequence, stirring for the first time to obtain a mixed liquid with uniform bubbles, adding ammonia water, and stirring to obtain a gel;

and 3, drying the gel, and then sintering the dried gel in vacuum to obtain the porous ceramic with the hierarchical pore structure.

Specifically, in the step 1, since tap water or water from a common source has many impurities and a part of free substances may adversely affect the dispersion of the carbon nanotubes in the present invention, and deionized water has high chemical purity and does not contain other impurities, the water in the step 1 is deionized water.

Specifically, in the step 1, the ultrasonic dispersion time is too short, and the carbon nanotube dispersion liquid is not uniform enough; the ultrasonic dispersion time is too long, the structure and length of the carbon nanotube are damaged, the enhancement effect is poor, the improvement of the dispersion effect is small, and the time is wasted. Therefore, the time of ultrasonic dispersion is controlled to be 40-120 min. The structure of the carbon nano tube can be damaged when the ultrasonic power is too high; most of the carbon nanotubes with too low ultrasonic power still agglomerate and cannot achieve the ideal dispersion effect. Therefore, the ultrasonic power is controlled to be 120-200 w.

It is noted that, in the step 1, too high concentration of the carbon nanotubes may result in poor dispersion effect and serious agglomeration; too low a concentration may result in poor mutual bridging in the matrix and failure to provide reinforcement. Therefore, the concentration of the carbon nanotubes in the carbon nanotube dispersion liquid is controlled to be 0.004-0.012 g/mL.

It should be noted that, in the step 1, too high concentration of sodium carboxymethyl cellulose may cause the carbon nanotube solution to be too viscous and to agglomerate more significantly; too small results in poor suspension of the carbon nanotubes. Therefore, the concentration of sodium carboxymethylcellulose is controlled to be 0.001 to 0.005 g/ml. Preferably, the concentration of sodium carboxymethylcellulose is 0.003 g/ml.

In step 2, the sol is one or more of silica sol, aluminum sol, zirconium sol, and the like.

Specifically, in the step 2, the volume ratio of the sol to the carbon nanotube dispersion is too large, that is, the carbon nanotubes are too few, so that the carbon nanotubes cannot substantially reinforce the matrix; too small means too little sol, resulting in an incomplete gel network. Therefore, the volume ratio of the sol to the carbon nanotube dispersion is controlled to be 1 to 3.

Specifically, in the step 2, in order to provide conditions for ammonium chloride in-situ crystallization and ammonium chloride fiber growth in the step 3, the volume ratio of hydrochloric acid to ammonia water is controlled to be 1-2.

Specifically, in the step 2, the growth of the ammonium chloride fibers is excessively promoted by the excessively high concentration of the sodium dodecyl sulfate, so that the strength and the structure of the matrix are damaged; too low results in insufficient foaming, reduced porosity and less good growth promotion of ammonium chloride fibers. Therefore, the concentration of the sodium dodecyl sulfate in the mixed solution is controlled to be 0.003 to 0.008 g/ml.

Specifically, in the step 2, in order to ensure that the mixed liquid with uniform bubbles is obtained, the stirring speed is 200 to 350r/min, and the stirring time is 10 to 60 min.

Specifically, in the step 2, hydrochloric acid and sodium dodecyl sulfate must be added in sequence, and after uniform bubbles are generated by stirring, ammonia water is added finally to gel and seal the bubbles; hydrochloric acid and ammonia water can promote sol-gel, and the lauryl sodium sulfate can also ensure the experimental safety according to the operation sequence.

Specifically, in step 3, in order to ensure complete aging of the sol and in-situ crystallization of ammonium chloride, step S3 includes, before drying the gel, the steps of: standing the gel at room temperature for 8-12 h.

Specifically, in the step 3, in order to ensure that the ammonium chloride fiber is completely grown in the gel, the drying temperature of the gel is controlled to be 60-80 ℃, and the dried gel is sintered in vacuum to obtain the porous ceramic with the hierarchical pore structure.

Specifically, in step 3, the step of obtaining the porous ceramic with the hierarchical pore structure by vacuum sintering the dried gel includes: and putting the dried gel into a vacuum high-temperature furnace, heating to the pyrolysis temperature of ammonium chloride at a speed V1, preserving the heat for t1 time (excluding ammonium chloride), then continuously heating to the final sintering temperature at a speed V2, and preserving the heat for t2 time to obtain the porous ceramic with the hierarchical pore structure.

Specifically, in the step 3, the decomposition speed of the ammonium chloride is too high due to the too high speed of V1, so that the substrate is cracked, and the requirement on the quality of the furnace is high; the velocity V1 is too low and the efficiency is low. Therefore, the control speed V1 is 2-5 ℃/min, preferably, V1 is 3 ℃/min.

Specifically, in the step 3, the pyrolysis temperature of the ammonium chloride is 300-350 ℃.

Specifically, in step 3, in order to ensure that ammonium chloride is sufficiently decomposed and removed, cracking or crushing of the matrix is not caused in the removal process, and the integrity of the matrix structure is ensured. Therefore, t1 is controlled to be 50-120 min, and t1 is preferably 60 min.

Specifically, in the step 3, the speed V2 is controlled to be 3-5 ℃/min, preferably, V2 is 4 ℃/min.

Specifically, in step 3, the final sintering temperature is too high, which may cause collapse due to excessive liquid phase generation; too low results in a porous ceramic having low strength. Therefore, the final sintering temperature is controlled to be 700-1200 ℃; too long t2 can cause a large amount of liquid phase to generate blocked pores, and reduce the porosity; too short results in low strength of the porous ceramic. Therefore, t2 is controlled to be 1-3 h, and t2 is preferably 2 h.

Compared with the prior art, the preparation method of the porous ceramic with the hierarchical pore structure takes the carbon nanotubes with high toughness and high strength as the reinforcing framework, so that a uniform carbon nanotube reinforcing network is formed in a gel body, and the strength of the porous ceramic is improved (firstly, a carbon nanotube dispersion liquid with good dispersibility is prepared and taken as the framework of the ceramic, then, the carbon nanotube dispersion liquid is uniformly mixed with sol, in the subsequent sol-gel process, the carbon nanotubes can be distributed in the ceramic in situ and taken as the reinforcing framework, the strength of the porous ceramic is improved, and secondly, the carbon nanotubes are mutually lapped, so that the porosity is also improved).

Hydrochloric acid and ammonia water are selected as catalysts, a sol-gel method is utilized to promote sol to gel rapidly, the hydrochloric acid and the ammonia water react to generate ammonium chloride, the ammonium chloride is crystallized slowly in gel, and ammonium chloride fibers are generated under the action of a surfactant, namely sodium dodecyl sulfate, and alternate growth is performed in a matrix; in the sintering process, when ammonium chloride crystallization and ammonium chloride fibers reach the pyrolysis temperature, pores with the sizes of about 30-100 nm and 2-15 microns are respectively left in situ, and the pores obtained by foaming together construct the porous ceramic with the hierarchical pore structure, so that the porosity and the specific surface area are greatly improved.

According to the invention, the carbon nano tube is used as a ceramic framework, and in order to keep a multi-level pore structure, vacuum or reduction sintering is adopted, the gel is placed in an alumina crucible and then is placed in a high-temperature furnace together for sintering at 700-1500 ℃ (exemplarily 800-1300 ℃) to obtain the porous ceramic, and the sintering method ensures that the carbon nano tube framework is not oxidized, and avoids generating a plurality of liquid phases, so that the pore structure is kept.

According to the invention, because ammonium chloride is crystallized and ammonium chloride fibers are generated, the heat is preserved for a certain time at the pyrolysis temperature of 300-350 ℃ so that ammonium chloride is fully decomposed and removed, and thus, a matrix is not cracked or broken in the removing process, and the integrity of the matrix structure is ensured.

The sol-gel method adopted by the invention has simple process, and the sol can be one or more of silica sol, aluminum sol and zirconium sol, so the cost is lower and the medicine source is wide.

The primary pores of the porous ceramic are formed by foaming agents, and the pore diameter of the primary pores is 0.8-3 mm; the secondary pores are pores formed by the ammonium chloride fibers which are inserted into the ceramic substrate and are left after the fibers are decomposed at a certain temperature, and the pore diameter of the secondary pores is 2-15 mu m; the tertiary pores are pores obtained when the pyrolysis temperature of ammonium chloride is reached, the pore diameter is 30-100 nm, the preparation method of the pore structure of the porous ceramic is simple, the requirement on equipment is low, the universality is strong, the industrial production can be realized, and the application prospect is wide.

The preparation methods of the porous ceramics of hierarchical pore structures of examples 1 to 3 below were adopted in the above-described methods, differing only in specific parameters.

Example 1

The aperture size of the primary pores of the porous ceramic is 0.9-2.5 mm; the size of the secondary pores is 4-15 mu m; the tertiary pore size is about 40-100 nm; the porosity of the porous ceramic was 78.3%, and the flexural strength was about 9.3 MPa.

The preparation method of the porous ceramic with the hierarchical pore structure comprises the following steps:

step 1, 0.06g of carbon nanotube and 0.03g of sodium carboxymethylcellulose are weighed and added into a beaker filled with 20mL of water, cells are subjected to ultrasonic dispersion for 90min, and the ultrasonic power is 130w, so that uniformly dispersed carbon nanotube dispersion liquid is obtained.

And 2, adding 20mL of silica sol into the carbon nano tube dispersion liquid obtained in the step 1, sequentially adding 5mL of hydrochloric acid and 0.15g of sodium dodecyl sulfate, stirring at a stirring speed of 200r/min for 15min, fully stirring to uniformly foam the sol, adding 7mL of ammonia water, stirring while adding until the sol is gelled and bubbles are sealed, and thus obtaining a gel.

And 3, standing the gel obtained in the step 2 at room temperature for 12h to obtain a gel block, putting the gel block into a forced air drying oven for drying at 60 ℃, growing a large amount of ammonium chloride fibers from the gel block under the induction of a surfactant sodium dodecyl sulfate, putting the gel block into a high-temperature furnace after drying, and sintering at 800 ℃ for 2h at a heating rate of 3 ℃/min V1 and 4 ℃/min V2 to obtain the porous ceramic (shown in figure 1). Wherein, ammonium chloride is decomposed at 350 ℃ and is discharged for 1 hour in advance.

Example 2

The pore size of the primary pores of the porous ceramic is 1.3-2.9 mm, the size of the secondary pores is 2-8 μm, and the size of the tertiary pores is about 30-100 nm; the porosity of the porous ceramic was about 81%, and the flexural strength was about 7.5 MPa.

The preparation method of the porous ceramic with the hierarchical pore structure comprises the following steps:

step 1, 0.06g of carbon nanotube and 0.03g of sodium carboxymethylcellulose are weighed and added into a beaker filled with 10mL of water, cells are subjected to ultrasonic dispersion for 90min, and the ultrasonic power is 180w, so that uniformly dispersed carbon nanotube dispersion liquid is obtained.

And 2, adding 20mL of silica sol into the carbon nano tube dispersion liquid obtained in the step 1, sequentially adding 5mL of hydrochloric acid and 0.3g of sodium dodecyl sulfate, stirring at a stirring speed of 225r/min for 15min, fully stirring to uniformly foam the sol, adding 5mL of ammonia water, stirring while adding until the sol is gelled and bubbles are sealed, and thus obtaining a gel.

And 3, standing the gel obtained in the step 2 at room temperature for 8 hours to obtain a gel block, putting the gel block into a forced air drying oven for drying at 60 ℃, growing a large amount of ammonium chloride fibers from the gel block under the induction of a surfactant sodium dodecyl sulfate, putting the gel block into a high-temperature furnace after drying, sintering at 700 ℃ for 2 hours, and obtaining the porous ceramic, wherein the heating rate V1 is 3 ℃/min, and the heating rate V2 is 4 ℃/min. Wherein, ammonium chloride is decomposed at 350 ℃ and is discharged for 1 hour in advance.

Example 3

The pore size of the primary pore of the porous ceramic of the embodiment is 1.1-2.7mm, the size of the secondary pore is 2-12 μm, and the size of the tertiary pore is about 30-90 nm; the porosity of the porous ceramic was 78.9%, and the flexural strength was about 9.6 MPa.

The preparation method of the porous ceramic with the hierarchical pore structure comprises the following steps:

step 1, weighing 0.08g of carbon nanotube and 0.06g of sodium carboxymethylcellulose, adding the carbon nanotube and the sodium carboxymethylcellulose into a beaker filled with 20mL of water, and ultrasonically dispersing cells for 90min at the ultrasonic power of 180w to obtain uniformly dispersed carbon nanotube dispersion liquid.

And 2, adding 22mL of alumina sol into the carbon nano tube dispersion liquid obtained in the step 1, sequentially adding 4mL of hydrochloric acid and 0.3g of sodium dodecyl sulfate, stirring at the stirring speed of 300r/min for 60min, fully stirring to uniformly foam the sol, adding 7mL of ammonia water, stirring while adding until the sol is gelled and bubbles are sealed, and thus obtaining a gel.

And 3, standing the gel obtained in the step 2 at room temperature for 10 hours to obtain a gel block, drying the gel block in a forced air drying oven at the temperature of 80 ℃, growing a large amount of ammonium chloride fibers from the gel block under the induction of a surfactant sodium dodecyl sulfate, sintering the gel block in a high-temperature furnace at the temperature of 1200 ℃ for 2 hours after drying, and obtaining the porous ceramic, wherein the heating rate V1 is 3 ℃/min, and the heating rate V2 is 4 ℃/min. Wherein, ammonium chloride is decomposed at 330 ℃ and is discharged for 1 hour in advance.

Therefore, the porous ceramic with the hierarchical pore structure has high porosity and good connectivity, the bending strength can reach 7.2-13.5 MPa, the porous ceramic with the hierarchical pore structure can be used for multilevel filtration, can be used as a carrier of a catalyst, and has a wide application range; and the preparation method is simple, has low requirements on equipment, has strong universality, can realize industrial production and has wide application prospect.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.