Alumina / mullite composite porous ceramic and preparation method thereof

Abstract

The invention discloses an alumina / mullite composite porous ceramic and a preparation method thereof. The preparation method first adopts a plastic forming method to prepare the alumina porous ceramic, i.e., a matrix, and then fills the aluminum silicon source into the pores by vacuum impregnation, calcining at a high temperature, and growing mullite whiskers on the surface of the alumina wafer by a gas phase reaction of the aluminum silicon source, and finally forming the alumina / mullite composite porous ceramic. The invention combines an alumina material having excellent high temperature stability and chemical stability with a mullite material, takes a porous framework constructed by an alumina wafer as a main body, and grows mullite whiskers on the alumina wafer as a secondary material to form an alumina / mullite composite porous ceramic, which has good high temperature resistance, excellent chemical stability and appropriate pore structure, and can be used as a high temperature filter material.

Description

Technical Field

[0001] The invention belongs to the technical field of porous ceramics, and in particular relates to an alumina / mullite composite porous ceramic and a preparation method thereof. Background Art

[0002] Porous ceramic materials have important applications in the fields of filtration and impurity removal. The main performance requirements for such materials usually include good temperature resistance, excellent chemical stability, high porosity, suitable pore structure and large specific surface area. Alumina porous ceramics are commonly used porous ceramic materials. The high-temperature stable crystal form of alumina is corundum phase (α-Al2O3). Corundum phase alumina can undergo anisotropic growth to form corundum phase alumina wafers (hereinafter referred to as alumina wafers) during a specific reaction process. Alumina wafers can be used to construct porous ceramic materials, for example, card house structure porous ceramic materials and wafer interlocking structure alumina porous ceramic materials constructed with alumina wafers, etc. Among them, the wafer interlocking structure alumina porous ceramic material prepared under fluorine catalysis has good high temperature stability, interconnected pore structure, large porosity and appropriate mechanical strength, and therefore has potential application value in high temperature filtration and other fields. However, since the size of the alumina wafers in the wafer interlocking structure is micron-sized, the internal pore size of the porous structure formed by it is large, which limits the filtering ability of the material for smaller impurities. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing alumina / mullite composite porous ceramics, wherein the preparation method first adopts a plastic forming method to prepare alumina porous ceramics, i.e., a matrix, and then fills the aluminum silicon source into the pores by vacuum impregnation, calcining at a high temperature, and growing mullite whiskers on the surface of the alumina wafer by the gas phase reaction of the aluminum silicon source, and finally forming an alumina / mullite composite porous ceramic. Another object of the present invention is to provide an alumina / mullite composite porous ceramic obtained by the above preparation method, wherein the alumina / mullite composite porous ceramic has good high temperature resistance and chemical stability and an appropriate pore structure, and can be used as a high temperature filter material. The present invention uses an alumina porous ceramic with an interlocking structure of wafers as a matrix, and introduces mullite whiskers to the surface and interior of the matrix by interfacial growth to enhance the material's filtering ability for tiny impurities.

[0004] The purpose of the present invention is achieved through the following technical solutions.

[0005] A method for preparing an alumina / mullite composite porous ceramic comprises the following steps:

[0006] 1) ball-milling pseudo-boehmite powder, a pore-forming agent and a catalyst, drying to obtain a mixed powder, mixing the mixed powder and a binder evenly, and then pressing them into blocks in a mold by a plastic molding method, drying, sintering at 550° C. to 650° C. for 1 to 2 hours for debinding, and then heating to 1000 to 1500° C. and sintering for 1 to 3 hours to obtain a matrix;

[0007] In the step 1), the pore-forming agent is soluble starch, the catalyst is AlF3, and the binder is a polyvinyl alcohol aqueous solution.

[0008] In the step 1), the ratio of the pseudo-boehmite powder, the pore former, the catalyst and the binder is (10-20):(1-3):(1-3):(5-10) by mass.

[0009] In the above technical solution, the concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 8-10 wt %.

[0010] In the step 1), the ball mill uses anhydrous ethanol as the liquid phase medium for wet ball milling, the rotation speed of the ball mill is 100 to 400 r / min, and the ball milling time is 1 to 6 hours.

[0011] In the step 1), the drying temperature is 60 to 80° C., and the drying time is 8 to 12 hours.

[0012] In the step 1), the drying temperature is 40 to 60° C., and the drying time is 8 to 12 hours.

[0013] 2) vacuum impregnating the substrate with a silicon source, an aluminum source and an NH4F aqueous solution, or vacuum impregnating the substrate with a silicon aluminum source and an NH4F aqueous solution, to obtain an alumina / mullite ceramic preform, sintering the alumina / mullite ceramic preform at a temperature of 1100-1500°C for 2-3h to obtain an alumina / mullite composite porous ceramic, wherein each vacuum impregnation is at least half an hour and the substrate is taken out and dried after each vacuum impregnation, the number of vacuum impregnations with the silicon source is 1 time, the number of vacuum impregnations with the aluminum source is 1-2 times, the number of vacuum impregnations with the NH4F aqueous solution is 1 time, and the number of impregnations with the aluminum silicon source is 1 time.

[0014] In the step 2), the vacuum degree of the vacuum impregnation is -0.15 to -0.09 MPa.

[0015] The concentration of NH4F in the NH4F aqueous solution is 1.5 to 3 mol / L.

[0016] The alumina / mullite composite porous ceramics obtained by the above preparation method.

[0017] In the above technical solution, the specific surface area of ​​the alumina / mullite composite porous ceramic is 1.3 to 2.6 m 2 / g.

[0018] The benefit of the present invention lies in that an alumina material having excellent high temperature stability and chemical stability is combined with a mullite material, a porous framework constructed with an alumina wafer is used as the main body, and mullite whiskers are grown as secondary materials on the alumina wafer to form an alumina / mullite composite porous ceramic, which has good high temperature resistance, excellent chemical stability and appropriate pore structure, and can be used as a high temperature filter material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The scanning electron microscope morphology of the microstructure of the alumina / mullite composite porous ceramic obtained in Example 2, wherein 1 is an alumina wafer and 2 is a mullite whisker;

[0020] Figure 2 This is a scanning electron microscope surface morphology image of the microstructure of the alumina / mullite composite porous ceramic obtained in Example 4;

[0021] Figure 3 XRD diagram of alumina / mullite composite porous ceramics obtained in Examples 1 and 2;

[0022] Figure 4 The XRD diagram of the alumina / mullite composite porous ceramic and the matrix therein obtained in Example 3;

[0023] Figure 5 The transmission electron microscope microscopic morphology and selected area electron diffraction pattern of the alumina / mullite composite porous ceramic obtained in Example 2;

[0024] Figure 6 The transmission electron microscope microscopic morphology and energy spectrum of the alumina / mullite composite porous ceramic obtained in Example 2;

[0025] Figure 7 This is a scanning electron microscope microscopic morphology image of the alumina / mullite composite porous ceramic obtained in Example 1;

[0026] Figure 8 This is a scanning electron microscope microscopic morphology image of the alumina / mullite composite porous ceramic obtained in Example 3;

[0027] Fig. 9 The surface porosity of the alumina / mullite composite porous ceramic obtained in Example 4 is estimated;

[0028] Fig.10 This is a scanning electron microscope microscopic morphology image of the substrate obtained in Example 1. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0030] Pseudo-boehmite powder was purchased from Chinalco Shandong Aluminum Company, Zibo, Shandong;

[0031] Polyvinyl alcohol was purchased from Aladdin;

[0032] Soluble starch was purchased from Sinopharm Chemical Reagent Company;

[0033] Aluminum fluoride was purchased from Fuchen (Tianjin) Chemical Reagent Company;

[0034] Silica sol and aluminum sol were purchased from Dalian Sinuo Chemical New Materials Science and Technology Co., Ltd.

[0035] The model of XRD test instrument is: ARL Equinox 3000, France

[0036] The model of SEM test instrument is: FEI Verios 460L, Germany

[0037] The model of TEM testing instrument is: FEI Talos F200X, USA

[0038] The concentration of NH4F in the NH4F aqueous solution is 1.5 mol / L.

[0039] Example 1

[0040] A method for preparing an alumina / mullite composite porous ceramic comprises the following steps:

[0041] 1) Mix pseudo-boehmite powder, pore-forming agent and catalyst, ball mill at a speed of 250r / min for 3h, dry at 60℃ for 10h to obtain a mixed powder, mix and grind the mixed powder and binder until uniform, knead into a lump powder, seal and age for 30min, take 2g of the lump powder, and then press it into blocks in a mold by plastic molding, dry at 60℃ for 12h, heat to 600℃ at a rate of 2℃ / min in a high-temperature furnace and sinter at this temperature for 1h for debinding, and then heat to 1200℃ and sinter for 2h to obtain a matrix, wherein the pore-forming agent is soluble starch, the catalyst is AlF3, the binder is a polyvinyl alcohol aqueous solution, the concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 8wt%, and the ratio of pseudo-boehmite powder, pore-forming agent, catalyst and binder is 20:2:3:9 by mass, and anhydrous ethanol is used as the liquid phase medium for wet ball milling;

[0042] 2) In a vacuum tank, the substrate is vacuum impregnated with a silicon source, an aluminum source and an NH4F aqueous solution (as a catalyst) respectively, each vacuum impregnation is performed for half an hour, and after each vacuum impregnation, the substrate is taken out and dried at 60°C for 6 hours to obtain an alumina / mullite ceramic preform, and the alumina / mullite ceramic preform is sintered at a temperature of 1100°C for 2 hours to generate mullite whiskers in the alumina / mullite ceramic preform to obtain an alumina / mullite composite porous ceramic, wherein the number of vacuum impregnations of the silicon source is 1 time, the number of vacuum impregnations of the aluminum source is 1 time, the number of vacuum impregnations of the NH4F aqueous solution is 1 time, the vacuum degree of vacuum impregnation is -0.1MPa (i.e., the substrate is placed in a vacuum tank and then the vacuum tank is pumped to the vacuum degree, and then the corresponding impregnation liquid is pumped in), the silicon source is silica sol, the aluminum source is a mixture of Al(NO3)3·9H2O and water, and the concentration of Al(NO3)3 in the aluminum source is 0.3mol / L. The concentration of NH4F in the NH4F aqueous solution is 1.5 mol / L.

[0043] The X-ray diffraction pattern of the alumina / mullite composite porous ceramic obtained in step 2) of Example 1 is as follows: Figure 3 As shown, it can be seen that alumina is generated in XRD, but the diffraction peak of mullite is not obviously seen because the content ratio of mullite in the alumina / mullite composite porous ceramic sample is relatively low. Figure 7 This is the microscopic morphology of the alumina / mullite composite porous ceramic obtained in step 2) of Example 1 under a scanning electron microscope. It can be seen that the alumina / mullite composite porous ceramic is composed of alumina wafers and mullite whiskers. At the same time, the introduction of mullite whiskers is also the main reason for the decrease in porosity of the alumina / mullite composite porous ceramic compared with the original alumina porous matrix. Fig.10 The scanning electron microscope microscopic morphology of the substrate obtained in the embodiment shows the presence of alumina wafers. After being impregnated with aluminum, silica sol and NH4F aqueous solution and calcined at high temperature, mullite material grows on the surface of alumina through gas phase reaction.

[0044] According to the test, the porosity of the matrix obtained in Example 1 is 72.35%, and the porosity of the obtained alumina / mullite composite porous ceramic is 51.08%.

[0045] Example 2

[0046] A method for preparing an alumina / mullite composite porous ceramic comprises the following steps:

[0047] 1) Mix pseudo-boehmite powder, pore-forming agent and catalyst, ball mill at a speed of 250r / min for 3h, dry at 60℃ for 10h to obtain a mixed powder, mix and grind the mixed powder and binder until uniform, knead into a lump powder, seal and age for 30min, take 2g of the lump powder, and then press it into blocks in a mold by plastic molding, dry at 60℃ for 12h, heat to 600℃ at a rate of 2℃ / min in a high-temperature furnace and sinter at this temperature for 1h for debinding, and then heat to 1200℃ and sinter for 2h to obtain a matrix, wherein the pore-forming agent is soluble starch, the catalyst is AlF3, the binder is a polyvinyl alcohol aqueous solution, the concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 8wt%, and the ratio of pseudo-boehmite powder, pore-forming agent, catalyst and binder is 20:2:3:9 by mass, and anhydrous ethanol is used as the liquid phase medium for wet ball milling;

[0048] 2) In a vacuum tank, the substrate is vacuum impregnated with a silicon source, an aluminum source and an NH4F aqueous solution respectively, each vacuum impregnation is performed for half an hour, and after each vacuum impregnation, the substrate is taken out and dried at 60°C for 6 hours to obtain an alumina / mullite ceramic preform, and the alumina / mullite ceramic preform is sintered at a temperature of 1100°C for 2 hours to generate mullite whiskers in the alumina / mullite ceramic preform to obtain an alumina / mullite composite porous ceramic, wherein the number of vacuum impregnations of the silicon source is 1 time, the number of vacuum impregnations of the aluminum source is 2 times, the number of vacuum impregnations of the NH4F aqueous solution is 1 time, the vacuum degree of the vacuum impregnation is -0.1MPa, the silicon source is silica sol, and the aluminum source is aluminum sol. The concentration of NH4F in the NH4F aqueous solution is 1.5mol / L.

[0049] Figure 1 It is the alumina / mullite composite porous ceramic obtained in step 2) of Example 2. It can be seen from the figure that some needle-shaped whisker materials grow on the chip. Based on the raw materials used and the implementation plan, it is preliminarily determined that 1 in the figure is an alumina chip and 2 is a mullite whisker material.

[0050] The X-ray diffraction pattern of the alumina / mullite composite porous ceramic obtained in step 2) of Example 2 is as follows: Figure 3 As shown, the alumina phase can be detected from the diffraction pattern, while the diffraction peak of the mullite phase is not obviously detected. This result is caused by the relatively low mass proportion of mullite in the alumina / mullite composite porous ceramic sample. Figure 5 The transmission electron microscope high-resolution microscopic morphology image and selected area electron diffraction image of the alumina / mullite composite porous ceramic obtained in step 2) of Example 2. After analysis and calibration of the data, it is concluded that the needle-shaped whisker material introduced into the matrix after composite is the mullite phase. Figure 6The transmission electron microscope microscopic morphology and energy spectrum analysis of the alumina / mullite composite porous ceramic obtained in step 2) of Example 2 show that the element composition of the introduced needle-shaped whiskers is consistent with that of the mullite material, that is, it is composed of Al, Si, and O elements.

[0051] Example 3

[0052] A method for preparing an alumina / mullite composite porous ceramic comprises the following steps:

[0053] 1) Mix pseudo-boehmite powder, pore-forming agent and catalyst, ball mill at a speed of 250r / min for 3h, dry at 60℃ for 10h to obtain a mixed powder, mix and grind the mixed powder and binder until uniform, knead into a lump powder, seal and age for 30min, take 2g of the lump powder, and then press it into blocks in a mold by plastic molding, dry at 60℃ for 12h, heat to 600℃ at a rate of 2℃ / min in a high-temperature furnace and sinter at this temperature for 1h for debinding, and then heat to 1200℃ and sinter for 2h to obtain a matrix, wherein the pore-forming agent is soluble starch, the catalyst is AlF3, the binder is a polyvinyl alcohol aqueous solution, the concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 8wt%, and the ratio of pseudo-boehmite powder, pore-forming agent, catalyst and binder is 20:2:3:9 by mass, and anhydrous ethanol is used as the liquid phase medium for wet ball milling;

[0054] 2) In a vacuum tank, the substrate is vacuum impregnated with a silicon aluminum source and an NH4F aqueous solution respectively, and the substrate is taken out half an hour after each vacuum impregnation and dried at 60°C for 6 hours to obtain an alumina / mullite ceramic preform, and the alumina / mullite ceramic preform is sintered at a temperature of 1100°C for 2 hours to generate mullite whiskers in the alumina / mullite ceramic preform to obtain an alumina / mullite composite porous ceramic, wherein the number of vacuum impregnations of the silicon aluminum source is 1 time, the number of vacuum impregnations of the NH4F aqueous solution is 1 time, the vacuum degree of vacuum impregnation is -0.1MPa, the silicon aluminum source is a mixture of silica sol and aluminum sol, and the molar ratio in the silicon aluminum source is Al:Si=3:2. The concentration of NH4F in the NH4F aqueous solution is 3mol / L.

[0055] Example 4

[0056] A method for preparing an alumina / mullite composite porous ceramic comprises the following steps:

[0057] 1) Mix pseudo-boehmite powder, pore-forming agent and catalyst, ball mill at a speed of 250r / min for 3h, dry at 60℃ for 10h to obtain a mixed powder, mix and grind the mixed powder and binder until uniform, knead into a lump powder, seal and age for 30min, take 2g of the lump powder, and then press it into blocks in a mold by plastic molding, dry at 60℃ for 12h, heat to 600℃ at a rate of 2℃ / min in a high-temperature furnace and sinter at this temperature for 1h for debinding, and then heat to 1200℃ and sinter for 2h to obtain a matrix, wherein the pore-forming agent is soluble starch, the catalyst is AlF3, the binder is a polyvinyl alcohol aqueous solution, the concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 8wt%, and the ratio of pseudo-boehmite powder, pore-forming agent, catalyst and binder is 20:2:3:9 by mass, and anhydrous ethanol is used as the liquid phase medium for wet ball milling;

[0058] 2) In a vacuum tank, the substrate is vacuum impregnated with a silicon aluminum source and an NH4F aqueous solution respectively, and the substrate is taken out after half an hour of each vacuum impregnation and after each vacuum impregnation, and then dried at 60°C for 6 hours to obtain an alumina / mullite ceramic preform, and the alumina / mullite ceramic preform is sintered at a temperature of 1300°C for 2 hours, and mullite whiskers are generated in the alumina / mullite ceramic preform to obtain an alumina / mullite composite porous ceramic, wherein the number of vacuum impregnations of the silicon aluminum source is 1 time, the number of vacuum impregnations of the NH4F aqueous solution is 1 time, the vacuum degree of vacuum impregnation is -0.1MPa, the silicon aluminum source is a mixture of silica sol and aluminum sol, and the molar ratio in the silicon aluminum source is Al:Si=3:2. The concentration of NH4F in the NH4F aqueous solution is 3mol / L.

[0059] The X-ray diffraction patterns of the alumina / mullite composite porous ceramic and the matrix obtained in step 2) of Example 3 are as follows: Figure 4 As shown, the matrix and the sample obtained in Example 3 are still similar in phase, and it can be judged that the matrix is ​​aluminum oxide. The specific surface area of ​​the sample obtained in Example 3 is 2.26m 2 / g. Figure 2 This is the surface morphology of the alumina / mullite composite porous ceramic obtained in step 2) of Example 4. It can be observed that there are many mullite whiskers on the surface of the alumina / mullite composite porous ceramic. Fig. 9 The surface pore distribution diagram of the alumina / mullite composite porous ceramic material obtained in Example 4 was obtained by analyzing the software ImageJ. In the diagram, it can be observed that the small-sized pore structure composed of mullite whiskers on the surface of the alumina / mullite composite porous ceramic is formed. After the silicon aluminum source is impregnated and combined with high-temperature calcination, the mullite whiskers and the alumina porous matrix can be composited. The obtained alumina / mullite composite porous ceramic has appropriate porosity, pore structure and specific surface area and good high temperature resistance, and is suitable for use as a high-temperature filter material.

[0060] After testing, the specific surface area of ​​the alumina / mullite composite porous ceramic prepared in Example 1 is 2.52 m 2 / g, and the porosity is 51.08%. Figure 7 The scanning electron microscope microscopic morphology of the alumina / mullite composite porous ceramic prepared in Example 1. The specific surface area of ​​the alumina / mullite composite porous ceramic prepared in Example 2 is 1.35 m 2 / g, and the porosity is 51.36%. Figure 1 This is a scanning electron microscope microscopic morphology of the alumina / mullite composite porous ceramic prepared in Example 2. The specific surface area of ​​the alumina / mullite composite porous ceramic obtained in Example 3 is 2.26 m 2 / g, porosity is 68.30%, Figure 8 This is a scanning electron microscope microscopic morphology image of the alumina / mullite composite porous ceramic prepared in Example 3.

[0061] The present invention is described above by way of example. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by those skilled in the art without inventive effort falls within the protection scope of the present invention.

Claims

1. Application of alumina / mullite composite porous ceramics as high temperature filter materials, characterized in that: The specific surface area of ​​alumina / mullite composite porous ceramics is 1.3 to 2.6 m 2 / g, the preparation method of alumina / mullite composite porous ceramic comprises the following steps: 1) ball-milling pseudo-boehmite powder, a pore-forming agent and a catalyst, drying to obtain a mixed powder, mixing the mixed powder and a binder evenly, and then pressing them into blocks in a mold by a plastic molding method, drying, sintering at 550° C. to 650° C. for 1 to 2 hours for debinding, and then heating to 1000 to 1500° C. and sintering for 1 to 3 hours to obtain a matrix; 2) vacuum impregnating the substrate with a silicon source, an aluminum source and an NH4F aqueous solution, or vacuum impregnating the substrate with a silicon aluminum source and an NH4F aqueous solution, to obtain an alumina / mullite ceramic preform, sintering the alumina / mullite ceramic preform at a temperature of 1100-1500°C for 2-3h to obtain an alumina / mullite composite porous ceramic, wherein each vacuum impregnation is at least half an hour and the substrate is taken out and dried after each vacuum impregnation, the number of vacuum impregnations with the silicon source is 1 time, the number of vacuum impregnations with the aluminum source is 1-2 times, the number of vacuum impregnations with the NH4F aqueous solution is 1 time, and the number of impregnations with the aluminum silicon source is 1 time.

2. The use according to claim 1, characterized in that: In the step 1), the pore-forming agent is soluble starch, the catalyst is AlF3, and the binder is a polyvinyl alcohol aqueous solution.

3. The use according to claim 2, characterized in that: In the step 1), the ratio of the pseudo-boehmite powder, the pore former, the catalyst and the binder is (10-20):(1-3):(1-3):(5-10) by weight.

4. The use according to claim 3, characterized in that: The concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 8-10 wt %.

5. The use according to claim 4, characterized in that: In the step 1), the ball mill uses anhydrous ethanol as the liquid phase medium for wet ball milling, the rotation speed of the ball mill is 100 to 400 r / min, and the ball milling time is 1 to 6 hours.

6. The use according to claim 5, characterized in that: In the step 1), the drying temperature is 60 to 80° C., and the drying time is 8 to 12 hours.

7. The use according to claim 6, characterized in that: In the step 1), the drying temperature is 40 to 60° C., and the drying time is 8 to 12 hours.

8. The use according to claim 7, characterized in that: In the step 2), the vacuum degree of the vacuum impregnation is -0.15 to -0.09 MPa.

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