阅读说明：本技术 一种绳状结构莫来石基多孔陶瓷材料及其制备方法 (Mullite-based porous ceramic material with rope-shaped structure and preparation method thereof ) 是由 李翠伟 王涵 武令豪 李�昊 付梦丽 李俊文 于 2019-10-14 设计创作，主要内容包括：本发明提供了一种绳状结构莫来石基多孔陶瓷材料及其制备方法,所述制备方法包括以下步骤：步骤S10,将α-Al<Sub>2</Sub>O<Sub>3</Sub>、SiO<Sub>2</Sub>、AlF<Sub>3</Sub>·3H<Sub>2</Sub>O、CaCl<Sub>2</Sub>和去离子水球磨混合获得陶瓷悬浮液；步骤S20,向取出的悬浮液中加入没食子酸丙酯(PG)和明胶,进行发泡处理获得泡沫浆料；步骤S30,将泡沫浆料倒入模具中并置于低温环境中使其凝胶,脱模后获得坯体；步骤S40,将获得的坯体真空冷冻干燥；步骤S50,烧结干燥后的坯体,获得莫来石基多孔陶瓷材料。本发明实施例的制备方法得到一种由柱状莫来石晶粒并列、交叉紧密连接形成的有助于提高多孔陶瓷强度的绳状结构孔壁,并能通过调整工艺参数获得高气孔率、高强度和结构可控的莫来石基多孔陶瓷材料。(The invention provides a string-structure mullite-based porous ceramic material and a preparation method thereof, wherein the preparation method comprises the following steps: step S10, mixing alpha-Al 2 O 3 、SiO 2 、AlF 3 ·3H 2 O、CaCl 2 Ball-milling and mixing the ceramic suspension with deionized water to obtain ceramic suspension; step S20, adding Propyl Gallate (PG) and gelatin to the taken-out suspension, and performing a foaming process to obtain a foam slurry; step S30, pouring the foam slurry into a mold, placing the mold in a low-temperature environment to enable the foam slurry to be gelled, and obtaining a blank after demolding; step S40, freezing and drying the obtained blank in vacuum; and step S50, sintering the dried green body to obtain the mullite-based porous ceramic material. The preparation method of the embodiment of the invention obtains the columnar mullite grains which are connected in parallel and in a crossed and tight wayThe formed rope-shaped structure pore wall is beneficial to improving the strength of the porous ceramic, and the mullite-based porous ceramic material with high porosity, high strength and controllable structure can be obtained by adjusting process parameters.)

1. The string-structure mullite-based porous ceramic material is characterized by being prepared from the following main raw materials: alpha-Al₂O₃、SiO₂、AlF₃·3H₂O and CaCl₂Wherein alpha-Al₂O₃、SiO₂The molar ratio is 2.4:2, the mullite phase content of the string-structure mullite-based porous ceramic material is 94.16-94.80 wt%, the porosity is 79.11-83.39%, and the bulk density is 0.54g/cm³～0.68g/cm³The compressive strength is 2.50MPa to 10.23 MPa.

2. A preparation method of a string-structure mullite-based porous ceramic material is characterized by comprising the following steps:

step S10, mixing alpha-Al₂O₃、SiO₂、AlF₃·3H₂O、CaCl₂Ball-milling and mixing the ceramic suspension with deionized water to obtain ceramic suspension;

step S20, adding PG and gelatin into the taken suspension, and carrying out foaming treatment to obtain foam slurry;

step S30, pouring the foam slurry into a mold, placing the mold in a low-temperature environment to enable the foam slurry to be gelled, and obtaining a blank after demolding;

step S40, freezing and drying the obtained blank in vacuum;

and step S50, sintering the dried green body to obtain the mullite-based porous ceramic material.

3. The method for preparing mullite-based porous ceramic material in string-like structure as claimed in claim 2, wherein in the step S10, raw material powder α -Al is added₂O₃、SiO₂The molar ratio is 2.4:2, the volume fraction of solid particles in the suspension is 25 vol%, CaCl₂1.0-2.9 wt% of solid particles, AlF₃·3H₂O accounts for 12 wt% of the mullite proportion.

4. The method for preparing the string-structure mullite-based porous ceramic material as claimed in claim 2, wherein the step S10 is implemented by roller ball milling at 60-120 rpm for 18-24 h, and the ball-to-material mass ratio is about 1.6: 1-2.2: 1.

5. The method for preparing a string-structured mullite-based porous ceramic material as claimed in claim 2, wherein the step S20 specifically comprises:

step S21, placing the container filled with the ceramic suspension liquid in a water bath kettle, and preheating at 60 ℃;

step S22, pouring PG and gelatin into deionized water in advance, and heating the PG and the gelatin into solutions, wherein the corresponding deionized water amounts are 5mL and 25mL respectively;

step S23, pouring the solution S22 into the ceramic suspension S21, mechanically stirring at the rotation speed of 400rpm, and stirring for 5-15 min to be uniform;

step S24, increasing the rotating speed of the stirrer in the step S23 to 900rpm, stirring for 5min, then increasing to 1500rpm, and stirring for 10-20 min until the volume of the foaming slurry is stable;

wherein the gelatin accounts for 6 wt% of the solid particles, and PG accounts for alpha-Al₂O₃1 wt% of (B).

6. The method for preparing a string-structured mullite-based porous ceramic material as claimed in claim 2, wherein the step S30 includes:

step S31, pouring the foamed ceramic slurry into a paper mold;

step S32, placing the mixture in a cold trap of a freeze drying box for pre-freezing for 15-25 min, and carrying out gel forming on a gelatin system;

and step S33, demolding the block formed in the step S32 to obtain a blank.

7. The method for preparing the string-structure mullite-based porous ceramic material as claimed in claim 2, wherein in the step S40, the ceramic body is subjected to vacuum freeze drying, the body obtained in the step S30 is continuously frozen in a cold trap for 9-10 hours at a temperature of about-70 ℃, and then the body is placed in a vacuum environment with a vacuum degree of 5-10 Pa, and the drying is completed within about 24 hours.

8. The method for preparing the string-structured mullite-based porous ceramic material as claimed in claim 2, wherein in the step S50, the temperature of the green body is raised from room temperature to 100 ℃ and 550 ℃ at a rate of 1 ℃/min, the temperature is maintained for 1 hour, the temperature is raised to 1200 ℃ at a rate of 2 ℃/min, the temperature is maintained for 3 hours and 5 hours at 1500 ℃, the temperature is reduced to 300 ℃ at a rate of 5 ℃/min, and then the green body is cooled to room temperature along with the furnace.

Technical Field

The invention relates to a preparation method of a porous ceramic material, in particular to a special string-structure mullite-based porous ceramic material and a preparation method thereof.

Background

The porous ceramic is a three-dimensional solid ceramic containing a large number of air holes, and has excellent performances of low density, good permeability, low thermal conductivity, good thermal stability, corrosion resistance, high creep resistance and the like, so that the porous ceramic has important application in the aspects of filtration, heat insulation and the like. However, compared with dense ceramics, only the porous ceramics bear force on the pore wall, the strength of the material can be obviously reduced under high porosity, and the development of the material is limited by the contradiction between light and strong. Therefore, it is one of the important researches to develop a porous ceramic having both high porosity and high strength and a preparation technology thereof.

Disclosure of Invention

In view of the above, the present invention aims to provide a mullite-based porous ceramic with a special structure and a preparation method thereof, so as to obtain high strength at a higher porosity through a rope-shaped structure formed by juxtaposing and intersecting columnar mullite. With alpha-Al₂O₃、SiO₂As a raw material, AlF₃·3H₂O、CaCl₂The gelatin is used as a sintering aid, the gelatin is used as a gel system, Propyl Gallate (PG) modifies the hydrophobicity of the alumina in the raw material powder to obtain partially hydrophobic solid ceramic particles to stabilize wet foam, and meanwhile, the vacuum freeze drying technology is combined to reduce the shrinkage rate of a blank and improve the porosity of the porous material.

The invention provides a string-structure mullite-based porous ceramic material on one hand.

The invention also provides a preparation method of the string-structure mullite-based porous ceramic.

In order to solve the technical problems, the invention adopts the following technical scheme:

the string-structure mullite-based porous ceramic material according to the embodiment of the first aspect of the invention is prepared from the following raw materials:

from alpha-Al₂O₃、SiO₂Is prepared by selecting AlF₃·3H₂O and CaCl₂As an additive, a ceramic body is prepared by combining a particle stable foam method and a vacuum freeze drying process. The content of mullite phase in the string-shaped structure mullite-based porous ceramic material is 94.16-94.80 wt%, and the bulk density is 0.54g/cm³～0.68g/cm³The porosity is 79.11-83.39%, and the compressive strength is 2.50-10.23 MPa.

The method for preparing the string-structure mullite-based porous ceramic material according to the embodiment of the second aspect of the invention comprises the following steps:

step S10, mixing alpha-Al₂O₃、SiO₂、AlF₃·3H₂O、CaCl₂Ball-milling and mixing the ceramic suspension with deionized water to obtain ceramic suspension;

step S20, adding PG and gelatin into the taken suspension, and carrying out foaming treatment to obtain foam slurry;

step S30, pouring the foam slurry into a mold, placing the mold in a low-temperature environment to enable the foam slurry to be gelled, and obtaining a blank after demolding;

step S40, freezing and drying the obtained blank in vacuum;

and step S50, sintering the dried green body to obtain the mullite-based porous ceramic material.

Further, in the step S10, raw material powder α -Al is added₂O₃、SiO₂The molar ratio is 2.4:2, the volume fraction of solid particles in the suspension is 25 vol%, CaCl₂1.0-2.9 wt% of solid particles, AlF₃·3H₂O represents 12 wt% of mullite.

Further, roller ball milling is adopted in the step S10, the ball milling rotation speed and the ball milling time are respectively 60-120 rpm and 18-24 hours, and the ball material mass ratio is about 1.6: 1-2.2: 1.

Further, the step S20 specifically includes:

step S21, placing the container filled with the ceramic suspension liquid in a water bath kettle, and preheating at 60 ℃;

step S22, the PG and the gelatin are poured into deionized water in advance, and heated to form solutions, wherein the amount of the deionized water is 5mL and 25mL respectively.

Step S23, pouring the solution S22 into the ceramic suspension S21, mechanically stirring at the rotation speed of 400rpm, and stirring for 5-15 min to be uniform;

and step S24, increasing the rotating speed of the stirrer in the step S23 to 900rpm, stirring for 5min, then increasing to 1500rpm, and stirring for 10-20 min until the volume of the foaming slurry is stable.

Wherein the gelatin accounts for 6 wt% of the solid particles, and PG accounts for alpha-Al₂O₃1 wt% of (B).

Further, the step S30 includes:

step S31, pouring the foamed ceramic slurry into a paper mold;

step S32, placing the mixture in a cold trap of a freeze drying box for pre-freezing for 15-25 min, and carrying out gel forming on a gelatin system;

and step S33, demolding the block formed in the step S32 to obtain a blank.

Further, in the step S40, the ceramic body is subjected to vacuum freeze drying, the body obtained in the step S30 is continuously frozen in a cold trap for 9-10 hours at a temperature of about-70 ℃, and then the ceramic body is placed in a vacuum environment with a vacuum degree of 5-10 Pa and is dried for about 24 hours.

Further, in the step S50, the temperature of the green body is raised from room temperature to 100 ℃ and 550 ℃ at a rate of 1 ℃/min, respectively, and the temperature is maintained for 1 h. Then the temperature is raised to 1200 ℃ at the speed of 2 ℃/min, the temperature is respectively preserved for 3h and 5h at the temperature of 1500 ℃, the temperature is reduced to 300 ℃ at the speed of 5 ℃/min after the temperature preservation is finished, and then the temperature is cooled to the room temperature along with the furnace.

The technical scheme of the invention at least has one of the following beneficial effects:

1) according to the preparation method of the mullite-based porous ceramic material, the pore wall of the obtained porous ceramic material is of a rope-shaped structure formed by juxtaposing and intersecting columnar mullite grains, the rope-shaped structures growing in different directions can be mutually inserted and tightly connected, and the strength of the porous material can be obviously improved.

2) The invention adopts a particle-stabilized foam method to prepare the porous ceramic body, greatly reduces the variety and the dosage of the organic additive, and is environment-friendly.

3) The invention adopts the vacuum freeze drying technology to dry the green body, reduces the drying shrinkage rate and is beneficial to obtaining the porous ceramic with high porosity.

4) The preparation process is controllable by adjusting CaCl₂、AlF₃·3H₂Parameters such as the addition amount of O, the solid content, the Al/Si ratio and the like control the synthesis temperature, the rope-shaped structuring degree, the porosity, the compressive strength, the median pore size distribution and the like of the sample.

5) The rope-structure mullite-based porous ceramic material prepared by the invention has the mullite phase content of 94.16-94.80 wt% and the volume density of 0.54g/cm³～0.68g/cm³The porosity is 79.11-83.39%, the compressive strength is 2.50-10.23 MPa, the high porosity and the high strength are achieved, and under the condition that the porosity is high, the high compressive strength is obtained due to the special rope-shaped structure, so that the practical application of the material can be expanded to a greater extent.

Drawings

FIG. 1 is a flow chart of a method for manufacturing a string-structured mullite-based porous ceramic material according to one embodiment of the present invention;

FIG. 2 is a flow chart of a method for manufacturing a string-structured mullite-based porous ceramic material according to another embodiment of the present invention;

FIG. 3 is an X-ray diffraction pattern of a string-structured mullite-based porous ceramic material in accordance with an embodiment of the present invention;

FIG. 4 is a scanning electron microscope photograph of the microscopic pore structure of the string-structured mullite-based porous ceramic material according to the embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of the invention.

The string-structured mullite-based porous ceramic material according to an embodiment of the present invention will be described first in detail.

The string-structure mullite-based porous ceramic material is prepared from the following raw materials: from alpha-Al₂O₃、SiO₂Is prepared by selecting AlF₃·3H₂O and CaCl₂As an additive, a ceramic body is prepared by combining a particle stable foam method and a vacuum freeze drying process. The content of mullite phase in the string-shaped structure mullite-based porous ceramic material is 94.16-94.80 wt%, and the bulk density is 0.54g/cm³～0.68g/cm³The porosity is 79.11-83.39%, and the compressive strength is 2.50-10.23 MPa.

The string-structure mullite-based porous ceramic material is characterized in that the pore wall is a special string-structure formed by parallel, crossed and tightly connected columnar mullite grains, so that the porous ceramic has high strength under high porosity.

The method for manufacturing the string-structure mullite-based porous ceramic material according to the embodiment of the invention, as shown in fig. 1, comprises the following steps:

step S10, mixing alpha-Al₂O₃、SiO₂、AlF₃·3H₂O、CaCl₂Ball-milling and mixing the ceramic suspension with deionized water to obtain ceramic suspension;

step S20, adding PG and gelatin into the taken suspension, and carrying out foaming treatment to obtain foam slurry;

step S30, pouring the foam slurry into a mold, placing the mold in a low-temperature environment to enable the foam slurry to be gelled, and obtaining a blank after demolding;

step S40, freezing and drying the obtained blank in vacuum;

and step S50, sintering the dried green body to obtain the mullite-based porous ceramic material.

In other words, according to some embodiments of the invention, α -Al is used₂O₃、SiO₂Preparing mullite-based porous ceramic material by firstly mixing alpha-Al₂O₃、SiO₂、AlF₃·3H₂O and CaCl₂Adding the mixture into deionized water, ball milling and mixing to obtain a ceramic suspension, adding PG and gelatin which are dissolved in advance by heating to serve as a surface modifier and a binder respectively, and then mechanically stirring and foaming to obtain foam slurry. And (3) injecting the foam slurry into a mold, placing the mold in a low-temperature environment, performing gel demolding, and drying the blank by adopting a vacuum freeze drying process. And finally, sintering the dried green body in a sintering furnace to obtain the mullite-based porous ceramic material.

Therefore, according to the method for manufacturing the string-structure mullite-based porous ceramic material provided by the embodiment of the invention, the obtained porous ceramic pore wall is a special string-structure formed by parallel, crossed and tightly connected columnar mullite grains, and the string-structure grown in different directions can be mutually inserted and tightly connected, so that the strength of the porous material can be obviously improved.

In addition, the porous ceramic body is prepared by adopting a particle-stabilized foam method, so that the variety and the using amount of organic additives are greatly reduced, and the environment is protected. The invention adopts the vacuum freeze drying technology to dry the green body, reduces the drying shrinkage rate and is beneficial to obtaining the porous ceramic with high porosity. The string-structure mullite-based porous ceramic obtained by the preparation method of the mullite-based porous ceramic material has the mullite phase content of 94.16-94.80 wt%, the porosity of 79.11-83.39% and the compressive strength of 2.50-10.23 MPa.

According to one embodiment of the present invention, in step S10, raw material powder α -Al is added₂O₃、SiO₂The molar ratio is 2.4:2, and AlF is added₃·3H₂O and CaCl₂Two additives, the solid particles representing 25 vol% of the suspension by volume fraction. Can utilize AlF₃·3H₂O and CaCl₂Under the combined action of the components, a purer mullite phase is obtained at a lower sintering temperature, and a special columnar mullite crystal cross-linking is obtainedAnd connecting to form a rope-shaped structure.

According to an embodiment of the present invention, step S20 specifically includes:

step S21, placing the container filled with the ceramic suspension liquid in a water bath kettle, and preheating at 60 ℃;

step S22, the PG and the gelatin are poured into deionized water in advance, and heated to form solutions, wherein the amount of the deionized water is 5mL and 25mL respectively.

Step S23, pouring the solution S22 into the ceramic suspension S21, mechanically stirring at the rotation speed of 400rpm, and stirring for 5-15 min to be uniform;

and step S24, increasing the rotating speed of the stirrer in the step S23 to 900rpm, stirring for 5min, then increasing to 1500rpm, and stirring for 10-20 min until the volume of the foaming slurry is stable.

Wherein the gelatin accounts for 6 wt% of the solid particles, and PG accounts for alpha-Al₂O₃1 wt% of (B).

According to an embodiment of the present invention, as shown in fig. 2, step S30 includes:

step S31, pouring the foamed ceramic slurry into a paper mold;

step S32, placing the mixture in a cold trap of a freeze drying box for pre-freezing for 15-25 min, and carrying out gel forming on a gelatin system;

and step S33, demolding the block formed in the step S32 to obtain a blank.

That is, in steps S20 and S30, the particle-stabilized foam method and the vacuum freeze-drying process are combined, so that the type and the amount of organic substances can be reduced, the wet foam can be fixed and molded in a short time, the lower shrinkage rate is ensured, and the porous ceramic material with higher porosity is obtained.

According to an embodiment of the invention, in step S40, the ceramic body is subjected to vacuum freeze drying, the body obtained in step S30 is continuously frozen in a cold trap for 9-10 hours at a temperature of about-70 ℃, and then the body is placed in a vacuum environment with a vacuum degree of 5-10 Pa, and the drying is completed for about 24 hours.

According to one embodiment of the invention, in step S50, the temperature of the green body is raised from room temperature to 100 ℃ and 550 ℃ at a rate of 1 ℃/min respectively during the sintering process in the sintering furnace, and the temperature is kept for 1 h. Then the temperature is raised to 1200 ℃ at the speed of 2 ℃/min, the temperature is respectively preserved for 3h and 5h at the temperature of 1500 ℃, the temperature is reduced to 300 ℃ at the speed of 5 ℃/min after the temperature preservation is finished, and then the temperature is cooled to the room temperature along with the furnace. The reaction of the sintering process comprises: dehydrating the blank, cracking and removing gelatin, nucleating mullite crystals, and finally obtaining the mullite-based porous ceramic material.

The string-structure mullite-based porous ceramic obtained by the preparation method of the mullite-based porous ceramic material provided by the embodiment of the invention has the mullite phase content of 94.16-94.80 wt% and the bulk density of 0.54g/cm³～0.68g/cm³The porosity is 79.11-83.39%, and the compressive strength is 2.50-10.23 MPa. The material has high porosity and high strength, and can obtain high compressive strength due to the special rope-shaped structure under the condition of high porosity, thereby greatly expanding the practical application of the material.

The preparation method of the string-structured mullite-based porous ceramic material according to the present invention will be described with reference to the following specific examples.

In the following examples, α -Al is used₂O₃、SiO₂As a raw material, AlF₃·3H₂O and CaCl₂The sintering aid is exemplified by a particle-stabilized foam method in combination with a vacuum freeze-drying method, but the present invention is not limited thereto, and any other reagents known to those skilled in the art may be used as a gel system or other drying methods, and these modifications should be understood to fall within the scope of the present invention.