阅读说明：本技术 一种多孔陶瓷的制备方法 (Preparation method of porous ceramic ) 是由 郭新爽 王献忠 万力 黄葳 颜嘉威 闵俊豪 祝嘉诚 胡兆龙 于 2020-06-09 设计创作，主要内容包括：本发明涉及一种多孔陶瓷的制备方法,特别是涉及一种原位造孔技术。本发明的方法克服利用普通造孔剂法成型时,造孔剂直接添加时存在团聚和难分散问题,制备孔的不均匀等现象。本发明的制备方法以溶胶、酸和碱为原料,通过向溶胶中直接加入过量的酸和碱,以在形成凝胶体的同时,在凝胶体中产生酸碱反应生成的无机盐晶体的原位析出,无机盐晶体作为造孔剂,烧结后制得多孔陶瓷。该方法工艺简便,成型设备简单,便于工业化应用。(The invention relates to a preparation method of porous ceramic, in particular to an in-situ pore-forming technology. The method of the invention overcomes the problems of agglomeration and difficult dispersion when the pore-forming agent is directly added during the forming by using the common pore-forming agent method, and the phenomena of uneven prepared pores and the like. The preparation method of the invention takes sol, acid and alkali as raw materials, excessive acid and alkali are directly added into the sol, so that in-situ precipitation of inorganic salt crystals generated by acid-base reaction is generated in the gel while the gel is formed, the inorganic salt crystals are used as pore-forming agents, and the porous ceramic is prepared after sintering. The method has simple process and simple forming equipment, and is convenient for industrial application.)

1. The preparation method of the porous ceramic is characterized in that sol, acid and alkali are used as raw materials, excessive acid and alkali are directly added into the sol, so that inorganic salt crystals generated by acid-base reaction are precipitated in situ in the gel while the gel is formed, the inorganic salt crystals are used as a pore-forming agent, and the porous ceramic is prepared after sintering.

2. The method according to claim 1, wherein the inorganic salt produced is an inorganic salt that can be pyrolyzed into a gas.

3. The method of manufacturing according to claims 1-2, characterized in that the method of manufacturing comprises the steps of:

step 1, putting the sol into a vessel, adding a certain amount of acid, stirring, adding excessive alkali, and fully stirring to make the mixed solution gel to obtain a gel;

step 2, standing the gel obtained in the step 1 at room temperature until the gel is aged, and precipitating inorganic salt crystals generated by acid-base reaction in the gel in situ to obtain a gel block;

and 3, drying the gel block, and then sintering the dried gel block in vacuum to obtain the porous ceramic containing the nano-pores.

4. The preparation method according to claim 3, wherein in the step 1, the volume ratio of the raw materials is as follows: sol: acid: 15-28% of alkali: 3-8: 4 to 12.

5. The method of claim 4, wherein the step of sintering the dried gel block to obtain the porous ceramic in step 3 comprises: and putting the dried gel block into a high-temperature furnace, heating to the pyrolysis temperature of the inorganic salt at a first speed, then preserving heat, continuing heating to the final sintering temperature at a second speed, and preserving heat to obtain the porous ceramic containing the nano-pores.

6. The method according to claim 5, wherein the final sintering temperature is 700 to 1500 ℃.

7. The preparation method according to claim 3, wherein carbon nanotubes are further added as a reinforcing skeleton, and a foaming agent is added to realize multi-stage pore formation.

8. The method of claim 7, wherein the foaming agent is sodium lauryl sulfate.

9. The method of claim 8, wherein the inorganic salt is one of ammonium chloride, ammonium phosphate, or ammonium acetate.

10. The method of claim 9, comprising the steps of:

s1, adding sodium carboxymethyl cellulose into the weighed water, adding CNT after the sodium carboxymethyl cellulose is dissolved, and uniformly dispersing the CNT to obtain CNT dispersion liquid containing a continuous CNT three-dimensional network in the solution;

s2, adding sol into the CNT dispersion liquid, adding HCl and SDS, stirring for foaming, and dripping ammonia water into the foamed mixed liquid to promote the sol to become gel;

s3, standing the gel obtained in the step S2 at room temperature until the gel is aged and NH is formed₄Pre-crystallizing Cl to obtain gel block, drying the gel block in a drying oven, sintering in a high temperature furnace until the temperature reaches NH₄After the Cl decomposition temperature, heat preservation is carried out to obtain NH₄And after removing Cl, heating to the final sintering temperature for sintering to obtain the porous ceramic.

Technical Field

The invention relates to the technical field of porous ceramic in-situ pore forming, in particular to a preparation method of porous ceramic.

Background

Porous ceramics have attracted attention in the fields of filtration, catalyst carriers and the like because of their excellent properties of high temperature resistance, good thermal stability, low density and the like. With the increasing sharpness of environmental issues, particularly in water and atmospheric treatments, there is an increasing demand for porous ceramics, particularly those of multilevel pore structure. The porous ceramic having a hierarchical pore structure is typically characterized by two or more pore structure types, and thus it has high filtration, high flux, low density, and high specific surface area characteristics, and thus is attracting attention. The preparation process of the porous ceramic generally comprises one or more than two of a sol-gel method, a replication method, a foaming method and a pore-forming agent method, wherein the pore-forming agent method is easy, simple, convenient, wide in universality and wide in application. When the pore-forming agent method is used for preparing the porous ceramic with the nano-pore structure, the method of directly adding the nano-pore-forming agent is generally adopted, and the nano-pore-forming agent is easy to agglomerate in the preparation process, so that the pore uniformity and connectivity of the nano-pore ceramic are poor, the strength of a ceramic framework is reduced, the nano-pore structure cannot be effectively utilized, and the use efficiency is influenced.

Disclosure of Invention

In order to solve the technical problems, the invention develops a preparation method of porous ceramic, which can overcome the problem of low strength of the porous ceramic prepared by the existing preparation method, and also avoid the problems that when the nano pore-forming agent is added to prepare the porous ceramic with nano pores at present, the nano pore-forming agent is easy to agglomerate, the prepared pores are not uniform, the pore uniformity and the connectivity are poor and the like.

In order to achieve the purpose, the invention adopts the technical scheme that:

on one hand, the invention provides a preparation method of porous ceramic, which takes sol, acid and alkali as raw materials, and directly adds excessive acid and alkali into the sol to generate acid-base reaction in the gel to generate inorganic salt crystals which are precipitated in situ while forming the gel, wherein the inorganic salt crystals are used as pore-forming agents, and the porous ceramic is prepared after sintering.

Further, the inorganic salt produced is an inorganic salt that can be pyrolyzed into a gas.

Further, the preparation method comprises the following steps:

step 1, putting the sol into a vessel, adding a certain amount of acid, stirring, adding excessive alkali, and fully stirring to make the mixed solution gel to obtain a gel;

step 2, standing the gel obtained in the step 1 at room temperature until the gel is aged, and precipitating inorganic salt crystals generated by acid-base reaction in the gel in situ to obtain a gel block;

and 3, drying the gel block, and then sintering the dried gel block in vacuum to obtain the porous ceramic containing the nano-pores.

Further, in the step 1, the volume ratio of the raw materials is as follows: sol: acid: 15-28% of alkali: 3-8: 4 to 12.

Further, in step 2, the step of sintering the dried gel block to obtain the porous ceramic includes: and putting the dried gel block into a high-temperature furnace, heating to the pyrolysis temperature of the inorganic salt at a first speed, then preserving heat, continuing heating to the final sintering temperature at a second speed, and preserving heat to obtain the porous ceramic containing the nano-pores.

Furthermore, the final sintering temperature is 700-1500 ℃.

Furthermore, the preparation method can also add carbon nanotubes as a reinforced skeleton and add a foaming agent to realize multi-stage pore-forming.

Further, the foaming agent is sodium dodecyl sulfate.

Further, the inorganic salt is one of ammonium chloride, ammonium phosphate or ammonium acetate.

Further, the preparation method comprises the following steps:

s1, adding sodium carboxymethyl cellulose into the weighed water, adding CNT after the sodium carboxymethyl cellulose is dissolved, and uniformly dispersing the CNT to obtain CNT dispersion liquid containing a continuous CNT three-dimensional network in the solution;

s2, adding sol into the CNT dispersion liquid, adding HCl and SDS, stirring for foaming, and dripping ammonia water into the foamed mixed liquid to promote the sol to become gel;

s3, standing the gel obtained in the step S2 at room temperature until the gel is aged and NH is formed₄Pre-crystallizing Cl to obtain gel block, drying the gel block in a drying oven, sintering in a high temperature furnace until the temperature reaches NH₄After the Cl decomposition temperature, heat preservation is carried out to obtain NH₄And after removing Cl, heating to the final sintering temperature for sintering to obtain the porous ceramic.

Compared with the prior art, the invention has at least the following advantages:

a. the application provides a porous ceramic's preparation method adopts the sol-gel method, use sol, acid and alkali as the raw materials, through directly adding excessive acid and alkali to the sol, make it form the gel, in the ageing process of gel, inorganic salt crystal that takes place acid-base reaction in the gel and generate in situ is appeared, the crystal that the normal position was appeared evenly distributed in the gel, in sintering process, when inorganic salt crystal reached decomposition temperature, inorganic salt decomposes and gets rid of, leave the nanopore in the normal position, can obtain the porous ceramic who contains nanopore and hole intercommunication through the high temperature sintering finally. Because the reaction is carried out in the gel, the reaction is uniform, the phenomenon similar to agglomeration of the added nanospheres is basically avoided, and the prepared porous ceramic containing the nanopores has uniform pore diameter and good connectivity.

b. The application introduces the Carbon Nano Tube (CNT) with high strength and high toughness to realize the reinforcement of the ceramic skeleton, and the network is utilized to reinforce the gel and finally realize the purpose of reinforcing the strength of the porous ceramic by forming a three-dimensional network in the CNT dispersion liquid; the sol is quickly gelled by hydrochloric acid and ammonia water, the hydrochloric acid and the ammonia water slowly react in the gel and NH is separated out₄Cl crystals, NH₄The Cl is crystallized under the action of SDS to generate NH₄Cl fiber is inserted and grown in the bubbles formed under the action of the foaming agent SDS and the hole walls formed by the bubbles; sintering gel with devitrified body and fiber, NH₄After Cl is decomposed, pore structures with different pore sizes are left at the original positions, and the pore structures and pores prepared by foaming form porous ceramics with a hierarchical pore structure.

c. The preparation method of the porous ceramic is simple and convenient to implement, low in cost, simple to operate, green and environment-friendly, and simple in equipment requirement. The porous ceramic with the hierarchical pore structure prepared by the method can be used for multilevel filtration and catalyst carriers, and is suitable for large-scale popularization and application.

The technical solutions described in the present application can be combined with each other to achieve more preferable modes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be readily apparent from the description, or may be learned by practice of the invention.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, are included to provide a further understanding of the application and are not intended to be limiting of the application.

FIG. 1 is a microscopic morphology of a block-like gel body after sintering in example 1 of the present invention;

FIG. 2 is a macroscopic view of a gel used for preparing a porous ceramic in example 3 of the present invention before sintering;

FIG. 3 shows NH generated in the gel for preparing a porous ceramic in example 3 of the present invention₄The morphology of Cl fibers;

FIG. 4 is a sample morphology of the porous ceramic of example 3 of the present invention;

FIG. 5 is a three-dimensional schematic view of a hierarchical pore structure of the porous ceramic of the present invention.

Reference numerals:

1-primary pore; 2-secondary pores; 3-three-stage pore.

Detailed Description

The technical solutions of the present invention are further described in detail below with reference to specific examples and drawings, but the scope and implementation of the present invention are not limited thereto.

The invention provides a preparation method of porous ceramic, which adopts a sol-gel process, takes sol, acid and alkali as raw materials, directly adds excessive acid and alkali into the sol to form gel, the gel is aged and generates in-situ precipitation of inorganic salt crystals generated by acid-base reaction in the gel, and the inorganic salt crystals are removed by sintering to finally prepare the porous ceramic.

It is noted that the inorganic salt formed above is an inorganic salt that can be pyrolyzed into a gas, and the inorganic salt is crystallized in situ in the gel; in the sintering process, when the decomposition temperature of the inorganic salt crystal is reached, the inorganic salt crystal is decomposed into gas to be discharged, the nano-pores formed after the decomposition of the nano-crystals are left at the original inorganic salt crystal position, and the temperature is continuously increased to sinter the matrix, so that the porous ceramic containing the nano-pores can be finally obtained.

Illustratively, the inorganic salt may be NH₄Cl, ammonium phosphate, ammonium acetate, and the like.

In order to achieve the above object, the method for preparing the porous ceramic comprises the steps of:

step 1, putting the sol into a vessel, adding a certain amount of acid, stirring at a certain stirring speed and for a certain stirring time, adding excessive alkali, quickly and uniformly stirring, and gelling the mixed solution to obtain a gel;

step 2, standing the gel obtained in the step 1 at room temperature until the gel is aged, and precipitating inorganic salt crystals generated by acid-base reaction in the gel in situ to obtain a gel block;

and 3, drying the gel block obtained in the step 2, and then sintering the dried gel block in vacuum to obtain the porous ceramic containing the nano holes.

It should be noted that, in the step 1, the volume ratio of the raw materials is: sol: acid: 15-28% of alkali: 3-8: 4 to 12.

In order to provide the condition of salt in-situ crystallization in the step 2, the volume ratio of acid to alkali in the step 1 is controlled to be 1-2. When NH is generated₄When Cl is used, the excessive alkali is beneficial to the gel reaction, and unreacted ammonium ions can be left in the gel, and the ammonium ions are combined with chloride ions to generate NH in the aging process of the gel₄And (4) Cl crystals.

The sol in step 1 may be a silica sol, an aluminum sol, a zirconium sol, or the like, or a combination thereof.

In the step 1, in order to make the gel more uniform, the stirring speed is controlled to be 200 to 350r/min, and the stirring time is 10 to 60 min.

It should be noted that, in the step 1, hydrochloric acid must be added first and stirred uniformly, and then ammonia water must be added finally. If a small amount of hydrochloric acid is added after ammonia water is added, although the ammonium ions are excessive, flocculation is easily generated due to excessive alkali, and the uniformity of the gel is influenced.

And in the step 2, standing the gel for 8-24h at room temperature so as to control the inorganic salt crystal to be fully precipitated in situ.

And 3, controlling the drying temperature of the gel block body to be 60-80 ℃, and sintering the dried gel block body in vacuum to obtain the porous ceramic containing the nano holes.

In the step 3, the step of sintering the dried gel block in vacuum to obtain the porous ceramic comprises the following steps: and putting the dried gel block into a vacuum high-temperature furnace, heating to the pyrolysis temperature of salt at a first speed V1, then preserving the heat for t1 time (the stage is to ensure the decomposition and elimination of inorganic salt crystals), and then continuing heating to the final sintering temperature at a second speed V2 and preserving the heat for t2 time to obtain the porous ceramic containing the nano pores.

In the step 3, the first speed V1 is controlled to be 2-5 ℃/min, and the second speed V2 is controlled to be 3-5 ℃/min.

Specifically, in the step 3, in order to ensure that the salt is sufficiently decomposed and removed and that the base body is not cracked or broken in the removing process, the integrity of the base body structure is ensured, and the heat preservation time t1 is controlled to be 50-120 min.

In step 3, the sintering temperature greatly affects the pore structure, and finally, too high sintering temperature may cause collapse due to too much liquid phase generation; too low results in a porous ceramic having low strength. Therefore, the final sintering temperature is controlled to be 700-1500 ℃; 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.

In the step 3, the porosity of the porous ceramic containing nanopores was 71.3%.

According to the preparation method of the porous ceramic, a sol-gel method is adopted, sol, acid and alkali are used as raw materials, excessive acid and alkali are directly added into the sol to form gel, and inorganic salt crystals generated by acid-base reaction in the gel are precipitated in situ in the aging process of the gel. The crystals precipitated in situ are uniformly distributed in the gel, in the sintering process, when the inorganic salt crystals reach the decomposition temperature, the inorganic salt is decomposed and removed, the nano holes are left in situ, and the porous ceramic containing the nano holes and communicated with the holes can be obtained through high-temperature sintering. Because the reaction is carried out in the gel, the reaction is relatively uniform, the phenomenon similar to the agglomeration of an additional nano pore-forming agent is basically not generated, and the prepared porous ceramic containing nano pores has uniform pore diameter and good connectivity.

In a possible design, in order to further improve the connectivity of the pores of the porous ceramic and increase the strength of the porous ceramic, Carbon Nanotubes (CNTs) can be added as a reinforcing skeleton in the preparation method of the porous ceramic, Sodium Dodecyl Sulfate (SDS) is added to realize multi-stage pore forming, and the salt can be NH₄And (4) Cl. Specifically, the preparation method of the porous ceramic comprises the following steps:

s1, adding CNT and CMC (sodium carboxymethyl cellulose) into water to prepare CNT dispersion liquid with good dispersibility, wherein the CNT dispersion liquid contains a three-dimensional CNT network;

s2, adding sol into the CNT dispersion liquid, then adding hydrochloric acid and SDS, stirring and foaming, regulating and controlling uniform bubbles generated in the solution, and finally performing gelation by using ammonia water to prepare gel (the microstructure of the gel is shown in figure 1);

s3, standing the gel obtained in S2 at room temperature until the gel is aged and NH is formed₄And pre-crystallizing Cl to obtain a gel block, and sintering the dried gel block to obtain the porous ceramic material with the multilevel pore structure.

In S1-S3, the mass or volume ratio of the raw materials is as follows: CMC: CNT: water: sol: hydrochloric acid: SDS (sodium dodecyl sulfate): 0.03-0.06 g of ammonia water: 0.06-0.12 g: 10-20 mL: 15-35 mL: 3-8 ml: 0.15-0.3 g: 4-12 mL.

In S1, when the CNTs are ultrasonically dispersed in the solution, if the processing time is too short, the dispersibility of the CNTs is poor, and if the processing time is too long, the structure and length of the CNTs are damaged, the reinforcing effect is poor, and the efficiency is affected. Therefore, the ultrasonic dispersion time of the CNT is controlled to be 40-120 min. In addition, the structure of the carbon nano tube can be damaged when the ultrasonic power is too high; too small an agglomerated CNT cannot be uniformly dispersed. Therefore, the ultrasonic power is controlled to be 120-200 w to fully and well disperse the CNT.

In S1, the water used for the experiment was deionized water because it was chemically pure and almost free of impurity substances, avoiding the negative effect of improving CNT dispersibility.

It is noted that in S1, if the concentration of CNTs is too high, the dispersibility thereof is poor and the agglomeration is accelerated; if the concentration of the CNT is too low, the three-dimensional network of the CNT is incomplete, and the reinforcing effect on the ceramic skeleton is poor. Therefore, the concentration of the CNT in the CNT dispersion is controlled to be 0.004-0.012 g/mL to effectively play a role in enhancing.

In S1, too high a CMC concentration may result in high solution viscosity and thus in high CNT agglomeration, but too low a CNT concentration may result in poor CNT dispersibility. Therefore, the concentration of CMC is set between 0.001-0.005 g/ml to achieve better dispersion effect.

The sol in S2 may be a silica sol, an aluminum sol, a zirconium sol, or the like, or a combination thereof.

In S2, if the volume ratio of the CNT to the sol is too large, that is, the carbon nanotubes are too small, the carbon nanotubes do not substantially reinforce the matrix; too small means too little sol, resulting in an incomplete gel network. Therefore, the volume ratio of the CNT to the sol is controlled to be 1 to 3.

In the above step S2, NH in the step 3 is provided₄Cl in situ crystallization and NH₄And (3) under the condition that Cl grows out of the fiber, and the volume ratio of the hydrochloric acid to the ammonia water is properly controlled to be 1-2.

In S2, too high concentration of SDS in the mixed solution excessively promotes NH₄The growth of Cl fiber damages the strength and structure of the matrix; too low results in insufficient foaming, reduced porosity and poor promotion of NH₄Cl fiberAnd (5) growing the dimension. Therefore, it is preferable to control the concentration of SDS in the mixed solution to 0.003 to 0.008 g/ml.

Further, in the above step S2, in order to ensure that a mixed liquid having uniform bubbles is obtained, the stirring speed is 200 to 350r/min, and the stirring time is 10 to 60min, the experimental effect is the best.

It should be emphasized that, in the above S2, hydrochloric acid and SDS must be added in sequence, after uniform bubbles are generated by stirring, ammonia water is finally added to gel and seal the bubbles; the hydrochloric acid and the ammonia water can promote sol-gel, and the SDS can also ensure the experimental safety according to the operation sequence.

To ensure complete aging of the gel and NH₄Cl in-situ crystallization and ensuring complete NH growth in the gel₄Cl fiber (NH)₄SEM image of Cl fiber is shown in figure 3), and in the S3, standing the gel for 8-24h at room temperature; and controlling the drying temperature of the gel block body to be 60-80 ℃, and sintering the dried gel block body in vacuum to obtain the porous ceramic with the hierarchical pore structure.

In S3, the step of obtaining the porous ceramic with the hierarchical pore structure by vacuum sintering the dried gel block comprises the following steps: putting the dried gel block into a vacuum high-temperature furnace, and heating to NH at a first speed V1₄Incubation for t1 time after Cl pyrolysis temperature (NH excluded)₄Cl) and then continuously raising the temperature to the final sintering temperature at a second speed V2 and keeping the temperature for t2 time to obtain the porous ceramic with the hierarchical pore structure.

Too great of the first speed V1 may cause NH₄The decomposition speed of Cl is too high, so that a matrix is cracked, and the requirement on the quality of the furnace is high; the first speed V1 is too small and inefficient. Therefore, the first speed V1 is controlled to be 2-5 ℃/min.

Specifically, the second speed V2 is controlled to be 3-5 ℃/min.

In the above-mentioned S3, in order to secure NH formed in the gel₄And the Cl crystal is fully decomposed to remove the matrix, so that the cracking or crushing of the matrix in the removing process is avoided, the structural integrity of the matrix is ensured, and t1 is controlled to be 50-120 min.

In S3, too high a final sintering temperature causes excessive liquid phase formation and collapse; too low results in a porous ceramic having low strength. Therefore, the final sintering temperature is controlled to be 700-1500 ℃; too long t2 may cause a large amount of liquid phase to form a plugged cell structure and reduce 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.

The structure of the porous ceramic with the hierarchical pore structure obtained in S3 is shown in fig. 4 to 5, and 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 wall of the second-level hole 2 is also distributed with third-level holes 3; the porosity of the porous ceramic is 65% to 82% (e.g., 68.2% to 78.3%); wherein the aperture range of the primary holes is 0.8-3 mm, the aperture range of the secondary holes is 2-15 mu m, the aperture range of the tertiary holes is 30-100 nm, and the structures and the sizes of the primary holes, the secondary holes and the tertiary holes are uniform.

Specifically, the bending strength of the porous ceramic with the hierarchical pore structure is 7-13.5 MPa.

The preparation method of the porous ceramic takes sol as a raw material, CNT as a reinforcing material and SDS as a foaming agent, the sol is changed into gel by hydrochloric acid and ammonia water and bubbles are sealed, and the bubbles generated by foaming are taken as a primary pore-forming agent; and NH generated by hydrochloric acid and ammonia water₄Cl is crystallized in situ in a gel matrix, and then foaming agent is utilized to induce NH₄Cl grows into fiber in the matrix to be used as a secondary pore-forming agent, and unfiberized NH₄And (3) taking the Cl crystal as a three-level pore-forming agent, and performing vacuum sintering at 700-1500 ℃ to obtain the porous ceramic with the hierarchical pore structure.

Compared with the prior art, the preparation method of the porous ceramic provided by the invention has the advantages that the carbon nano tube CNT with high strength, high toughness and high strength is introduced to realize the reinforcement of the ceramic skeleton into the reinforced skeleton, the three-dimensional network of the CNT is formed in the CNT dispersion liquid, the network is utilized to reinforce the gel and finally the purpose of reinforcing the porous ceramic is realized, so that the uniform carbon nano tube reinforced network is formed in the gel, and the strength of the porous ceramic is improved. Secondly, the carbon nanotubes are mutually lapped, so that the porosity can be improved; by passing throughHydrochloric acid and ammonia water, and the sol-gel method is utilized to promote the sol to gel rapidly, so that the hydrochloric acid and the ammonia water react slowly in the gel and NH is precipitated₄The Cl crystals react hydrochloric acid with ammonia water to generate ammonium chloride NH₄Cl is slowly crystallized in the gel, and the crystallized liquid generates ammonium chloride NH under the action of a surfactant Sodium Dodecyl Sulfate (SDS)₄And Cl fibers are interpenetrated and grown in the foam formed bubbles and the pore walls formed by the bubbles in the matrix. After the gel with the devitrified body and the fiber thereof is sintered, NH is generated in the sintering process₄When the crystallization of Cl and the ammonium chloride fiber reach the decomposition temperature, holes with the sizes of about 30-100 nm and 2-15 microns are respectively left in situ, and the holes obtained by foaming are jointly constructed to form the porous ceramic with the hierarchical pore structure, so that the porosity and the specific surface area are greatly improved.

The invention is due to NH₄Cl crystallization and NH₄Formation of Cl fiber, therefore, it is necessary to use NH₄Keeping the Cl pyrolysis temperature at 300-350 ℃ for a certain time to ensure that NH is generated₄Cl is fully decomposed and removed, so that cracking or crushing of the matrix cannot be caused in the removing process, and the structural integrity of the matrix is ensured.

The preparation method of the porous ceramic provided by the invention is simple and convenient to implement, low in cost, simple to operate, green and environment-friendly, and simple in equipment requirement. The porous ceramic with the hierarchical pore structure prepared by the method can be used for multilevel filtration and catalyst carriers, and is suitable for large-scale popularization and application.

Example 1

Firstly, 20mL of silica sol is added into a beaker, then 5mL of hydrochloric acid is added, stirring is carried out at the stirring speed of 200r/min for 15min, 7mL of ammonia water is added, and stirring is carried out while adding until gel is formed, so as to obtain gel. And standing the obtained gel for 10h at room temperature to obtain a gel block, putting the gel block into an air-blowing drying oven for drying at 60 ℃, putting the gel block into a high-temperature furnace after drying, sintering at 700 ℃ for 2h at a heating rate V1 of 3 ℃/min and a heating rate V2 of 4 ℃/min to obtain the porous ceramic containing the nanopores. Wherein NH is reacted at 350 ℃₄Cl was decomposed and pre-drained for 1 h. The pore size of the nano-pores of the porous ceramic prepared by the embodiment is 50-100 nm; gas of porous ceramicsThe porosity was 71.6%, and the flexural strength was about 0.9 MPa.

Example 2

Firstly, 20mL of silica sol is added into a beaker, then 5mL of hydrochloric acid is added, the stirring speed is 250r/min, the stirring time is 10min, 7mL of ammonia water is added, and the stirring is carried out while adding until the gel is formed, so as to obtain the gel. Standing the obtained gel at room temperature for 24h to obtain gel block, drying the gel block in an air-blast drying oven at 50 deg.C, drying, placing the gel block in a high temperature furnace, and adding NH at 350 deg.C₄Pre-discharging Cl for 2h, and sintering at 800 ℃ for 2h to obtain the porous ceramic containing the nano-pores. The temperature rise rate V1 is 3 ℃/min, and V2 is 4 ℃/min. The pore size of the nano-pores of the porous ceramic prepared by the embodiment is 40-75 nm; the porosity of the porous ceramic was 68.2%, and the flexural strength was about 1.3 MPa.

Example 3

First, 20mL of water was added to a beaker, and then 0.06g of CNT and 0.03g of CMC were added thereto, and a uniformly dispersed CNT dispersion was obtained after sonication at a sonication power of 130w and a sonication time of 90 min. After 20mL of silica sol was added to the prepared CNT dispersion, 5mL of HCl and 0.15g of SDS were added to the mixture, and the mixture was stirred at 200r/min for 15min to generate uniform bubbles in the sol. To the sol which was uniformly foamed, 7mL of aqueous ammonia was added to turn it into a gel and the generated bubbles were sealed. Standing the gel at room temperature for 24 hr to obtain gel block, drying at 60 deg.C, and inducing with surfactant SDS to grow a large amount of NH in the gel block₄Cl fiber, drying, putting the gel block into a high-temperature furnace, keeping the temperature at 350 ℃ for 2h, and adding NH₄And (3) decomposing Cl, then heating to 800 ℃, and keeping the temperature for 2h to obtain the porous ceramic with the hierarchical pore structure (shown in figure 4), wherein the heating rate V1 is 3 ℃/min, and the heating rate V2 is 4 ℃/min. The pore size of the primary pores of the porous ceramic prepared by the embodiment 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.

Example 4

First 20mL of water was added to the beaker, thenThen 0.1g of CNT and 0.03g of CMC are weighed and added into a beaker with water, and the uniformly dispersed CNT dispersion liquid is obtained by ultrasonic treatment when the ultrasonic power is 150w and the ultrasonic time is 60 min. And adding 22mL of silica-alumina sol into the CNT dispersion, adding 3mL of hydrochloric acid and 0.15g of SDS in sequence, stirring at the speed of 350r/min for 15min, fully stirring to uniformly foam the sol, adding 12mL of ammonia water, stirring while adding until the sol is gelled and bubbles are sealed, and thus obtaining the gel. Standing the prepared gel at room temperature for 12h to obtain a gel block, drying the gel block in an air-blast drying oven at 70 ℃, and growing a large amount of NH from the gel block under the induction of a surfactant SDS₄And (3) drying the Cl fiber, putting the gel block into a high-temperature furnace, sintering for 2h at 1300 ℃, and obtaining the porous ceramic, wherein the heating rate V1 is 3 ℃/min, and the heating rate V2 is 4 ℃/min. Wherein NH is reacted at 350 ℃₄Cl was decomposed and pre-drained for 1 h. The pore size of the primary pore of the porous ceramic prepared by the embodiment is 0.8-1.6 mm; the size of the secondary pores is 2-10 mu m, and the size of the tertiary pores is 35-90 nm; the porosity of the porous ceramic was about 73.5%, and the flexural strength was about 13 MPa.

The preparation method of the porous ceramic provided by the invention is simple and convenient to implement, simple in process, low in cost, simple to operate, green and environment-friendly, and simple in equipment requirement. The porous ceramic with the hierarchical pore structure prepared by the method can be used for multilevel filtration and catalyst carriers, and is suitable for large-scale popularization and application. The above embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalents, improvements, etc. made by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention as claimed.