阅读说明：本技术 以发泡硅胶和无机粉体复合物为前驱体制备泡沫陶瓷材料的方法 (Method for preparing foamed ceramic material by using foamed silica gel and inorganic powder compound as precursor ) 是由 贺祖章 张燕萍 赵志国 于 2020-06-04 设计创作，主要内容包括：本发明提供了一种以发泡硅胶-无机粉体复合物为前驱体制备泡沫陶瓷材料的方法,以发泡硅胶的发泡原理造孔,制备出泡沫陶瓷材料的多孔前驱体坯体,而后经低温裂解、高温陶瓷化烧结得到所述泡沫陶瓷材料,本发明属于无机功能陶瓷复合材料领域；其制备方法为：(1)无机粉体料的配合及表面处理；(2)液体发泡硅胶与经过配合和表面处理好的无机粉体料的均匀分散混合；(3)混合好的发泡硅胶-无机粉体料复合物的发泡硫化成型；(4)发泡硫化成型好的多孔前驱体坯体低温度段热压裂解；(5)高温度条件下低温裂解完成的产物的高温陶瓷化烧结；最终得到孔隙率高、孔径分布均匀、力学性能优良的多孔泡沫陶瓷材料。(The invention provides a method for preparing a foamed ceramic material by taking a foamed silica gel-inorganic powder composite as a precursor, which comprises the steps of forming pores by using the foaming principle of the foamed silica gel to prepare a porous precursor blank of the foamed ceramic material, and then performing low-temperature cracking and high-temperature ceramic sintering to obtain the foamed ceramic material, belonging to the field of inorganic functional ceramic composite materials; the preparation method comprises the following steps: (1) matching and surface treatment of inorganic powder materials; (2) uniformly dispersing and mixing the liquid foaming silica gel and the inorganic powder material which is well matched and subjected to surface treatment; (3) foaming and vulcanizing the mixed foaming silica gel-inorganic powder compound for molding; (4) carrying out low-temperature section hot-pressing pyrolysis on a foamed and vulcanized porous precursor body; (5) carrying out high-temperature ceramic sintering on the product subjected to low-temperature cracking at a high temperature; finally, the porous foamed ceramic material with high porosity, uniform pore size distribution and excellent mechanical properties is obtained.)

1. A method for preparing a foamed ceramic material by using a foamed silica gel and inorganic powder compound as precursors is characterized in that holes are formed by using the foaming principle of the foamed silica gel to prepare a porous precursor blank of the foamed ceramic material, and then the porous precursor blank is subjected to low-temperature cracking and high-temperature ceramic sintering to obtain the foamed ceramic material; the preparation method comprises the following steps:

step (1) matching and surface treatment of inorganic powder materials;

uniformly dispersing and mixing the liquid foaming silica gel and the inorganic powder material which is well matched and subjected to surface treatment;

step (3), hot-pressing, foaming and vulcanizing the mixed foaming silica gel-inorganic powder compound for molding;

step (4), carrying out low-temperature section hot-pressing cracking on the foamed and vulcanized porous precursor body;

and (5) carrying out high-temperature ceramic sintering on the product subjected to low-temperature cracking under a high-temperature condition to finally obtain the porous foamed ceramic material.

2. The method for preparing the foamed ceramic material by using the composite of the foaming silica gel and the inorganic powder as the precursor according to claim 1, wherein the inorganic powder in the step (1) is a solid material which stably exists at normal temperature and normal pressure, and comprises the following steps: metal oxide, non-metal oxide, metal carbide, non-metal carbide, allotrope of carbon element simple substance, metal nitride, non-metal nitride, metal boride, metal silicide.

3. The method for preparing the foamed ceramic material by taking the foamed silica gel-inorganic powder composite as the precursor as claimed in claim 1, wherein the inorganic powder material in the step (1) is prepared by the following steps: ceramic powder materials with the same or different types and different particle sizes are selected to be matched, the porosity of the matched mixture is required to be within the range of 10% -30%, and the particle size of each type of inorganic powder material is smaller than 100 um;

the surface treatment of the inorganic powder material in the step (1) comprises the following steps: dispersing a silane coupling agent without P, N, S element in 95% ethanol solution, and then placing the well-mixed inorganic powder material in the solution, wherein the mass ratio of the inorganic powder material to the coupling agent is as follows: 1000: 1-10, stirring at 2000r/min for 2hrs, and spray drying at 80-120 deg.C.

4. The method for preparing the foamed ceramic material by taking the foamed silica gel-inorganic powder compound as the precursor as claimed in claim 3, wherein the 95% ethanol solution is condensed, liquefied and collected for reuse in the spray drying process.

5. The method for preparing the foamed ceramic material by taking the foamed silica gel-inorganic powder composite as the precursor according to claim 1, wherein the foamed silica gel in the step (2) is a liquid silica gel which is prepared by mixing two components according to a mass ratio of 1:1, has a viscosity of 500-50000 mp-s, has a foaming ratio of 3-9 times, and can operate for more than 5hrs at room temperature.

6. The method for preparing foamed ceramic material using foamed silica gel-inorganic powder composite as precursor according to claim 1, wherein the uniform dispersion mixing in step (2) is performed by mixing liquid foamed silica gel and compounded and surface-treated inorganic powder material with one of kneader, planetary mixer or internal mixer under the condition of controlling the mixing temperature to be less than 40 ℃ and controlling the mixing time to be 2-5 hrs, and the mass ratio of the foamed silica gel to the inorganic powder material is controlled as follows: 1: 1-12.

7. The method for preparing the foamed ceramic material by using the foamed silica gel-inorganic powder composite as the precursor as claimed in claim 1, wherein the hot-pressing, foaming and vulcanizing formation of the mixed foamed silica gel-inorganic powder composite in the step (3) is as follows: placing the material in the step (2) in a mold with a certain shape for hot-pressing vulcanization foaming, wherein the vulcanization foaming conditions are as follows: 150 deg.C/10 MPa/2 hrs.

8. The method for preparing the foamed ceramic material by using the foamed silica gel-inorganic powder compound as the precursor as claimed in claim 1, wherein the porous precursor body formed by foaming and vulcanizing in the step (4) is subjected to hot-pressing cracking at a low temperature section: and (3) placing the porous precursor body which is vulcanized and molded in the step (3) into a vacuum hot-pressing furnace, maintaining the vacuum degree lower than-0.09 Mpa, applying pressure less than or equal to 3MPa on the surface of the body, heating to 800 ℃ under the condition that the heating rate is less than or equal to 3 ℃/min, and preserving heat for 3hrs for hot-pressing cracking.

9. The method for preparing the foamed ceramic material by using the foamed silica gel-inorganic powder composite as the precursor as claimed in claim 1, wherein the high-temperature ceramic sintering is performed on the product cracked at the low-temperature section under the high-temperature condition in the step (5): removing the pressure applied on the cracked product, continuously maintaining the vacuum degree in the high-temperature furnace to be less than-0.09 Mpa, and selecting the heating rate of 3-10 ℃/min and the temperature of 1500-2300 ℃ to carry out high-temperature ceramic sintering to finally obtain the porous foamed ceramic material.

10. The method for preparing the foamed ceramic material by using the foamed silica gel-inorganic powder composite as the precursor according to claim 1, wherein when the foaming magnification of the foamed silica gel in the step (2) is 9 times, the porous foamed ceramic material with the porosity of 80-90% and the compressive strength of more than 2Mpa can be obtained by the hot-pressing foaming vulcanization molding in the step (3), the cracking reaction in the step (4) and the ceramic sintering in the step (5).

Technical Field

The invention belongs to the field of preparation of inorganic functional ceramic composite materials, and particularly relates to a method for preparing a foamed ceramic material by taking a foamed silica gel-inorganic powder composite as a precursor.

Background

The foamed ceramic is a porous ceramic body with three-dimensional space grid structure and high porosity, and is like toughened foamed plastic or vitrified sponge foam, and because the foamed ceramic has high porosity, large specific surface area, thermal shock resistance, high temperature resistance, chemical corrosion resistance, good mechanical strength and filtering and adsorbing properties, the foamed ceramic can be widely applied to heat exchange materials, gas distribution materials, automobile exhaust devices, molten metal filtering and recovering heat energy in the purification and metallurgy industry, industrial sewage treatment, heat insulation and sound insulation materials, and also can be used as chemical catalyst carriers, electrolytic diaphragms, separation and dispersion elements and the like.

The preparation process of the existing foam ceramic material mainly comprises the following steps: the direct foaming method is characterized in that when ceramic blank slurry is prepared, a foaming agent is added into the slurry, then the slurry is dried and molded to prepare a blank, the blank containing the foaming agent is decomposed and releases gas in the high-temperature sintering process to generate pores, and thus, a foamed ceramic material is obtained, wherein the foaming agent comprises the following components in percentage by weight: the Chinese patent 'foamed ceramic material and the preparation method thereof' with application number 201610826905.3 and application publication number CN106631104A, 6-18% of foaming agent (consisting of dolomite, calcium carbonate, calcium sulfate, carbon powder, silicon powder and the like) is added in the preparation process of ceramic slurry, and then the foamed ceramic material is obtained by ceramic sintering, and the method mainly comprises the following steps: the preparation of ceramic slurry → the drying and forming of the slurry to prepare a green body → a high-temperature sintering green body, but the method has the problems that the preparation of the ceramic slurry, the ball milling and mixing of the foaming agent and the drying and forming of the green body are very time-consuming, and in addition, a large amount of impurities (foaming agent components) are introduced, so that the prepared foamed ceramic material has insufficient strength.

The sol-gel method is mainly used for preparing the microporous ceramic material with the pore diameter in the nanometer level, and meanwhile, the method can also be used for preparing the high-regularity foamed ceramic material after being improved. The foam material is prepared by using a sol-gel technology, and the viscosity of the system is rapidly increased in the conversion process from sol to gel, so that bubbles generated at the early stage are stabilized, and the foam material is favorable for foaming. Compared with other processes, the process has the unique point that the foamed ceramic film with the pore size uniformly distributed in the nanometer level can be prepared.

Such as: the Chinese patent with application number 201810196262.8 and application publication number CN108484006A, "a preparation method of a multilevel porous alumina foam ceramic with an aerogel comparable to each other", mainly comprises the following steps: preparing nano alumina sol particles → preparing alumina sol suspension → adjusting the PH of the sol → foaming in a mechanical sol stirring way → drying the sol to obtain the alumina foam ceramic material. Similarly, chinese patent application No. 201610663739.X, application publication No. CN106316456A, "a method for preparing foamed ceramics by hydrophobic flocculation". Although the alumina foam ceramic material prepared by the method has the advantages of ultrahigh porosity and specific surface area, and the preparation process is very environment-friendly, the alumina foam ceramic material prepared by the method has poor compressive strength and high shrinkage rate, so that the dimensional stability is not easy to control, and the large-scale industrial production and the actual industrial application value also have problems.

The method for adding the pore-forming agent is characterized in that the pore-forming agent is added into ceramic ingredients, the pore-forming agent occupies a certain space in a blank body, and then the ceramic ingredients are sintered to enable the pore-forming agent to leave a substrate to form pores so as to prepare the foamed ceramic. The shape and size of the pore former particles determine the shape and size of the pores of the foamed ceramic material. The forming method mainly comprises the steps of mould pressing, extrusion, isostatic pressing, rolling, injection, slurry casting and the like. The method can be used for preparing materials with complex shapes and different pore structures, but the uniformity of pore distribution is poor. Such as: chinese patent application No. 201811076373.1, application publication No. CN108821790A, "method for preparing foamed ceramic with heat-curable polycarbosilane and tungsten trioxide"; application No. 201811076386.9, Chinese patent application publication No. CN109133931A, "method for preparing silicon carbide foamed ceramic from thermocurable polycarbosilane and polyurethane", both of which are methods of adding pore-forming agent, adding pore-forming agent "polyurethane" in the preparation process of blank, then high-temperature ceramic sintering, removing pore-forming agent to obtain said foamed ceramic.

The organic precursor impregnation method is invented by Schwartzwalder in 1963, and the method utilizes the special structure of an open-cell three-dimensional reticular skeleton of an organic foam body to uniformly coat the prepared slurry on the organic foam reticular body, dries and burns off the organic foam body to obtain the mesh porous ceramic. The method can prepare the high-performance foam ceramic product by controlling the slurry performance, optimizing the inorganic binder system and strictly controlling the slurry impregnation process, and is the most ideal preparation method of the foam ceramic at present. Foamed ceramics prepared by this forming process have found a number of applications in a number of fields. Such as: the Chinese patent with application number 201710007143.9 and application publication number CN106631121A, "a calcium oxide foamed ceramic and a preparation method thereof", comprises the following steps: preparing calcium-containing ceramic slurry → polyurethane sponge dipping slurry → drying and forming to obtain a blank body → ceramic sintering to remove organic matters to obtain the calcium oxide foamed ceramic.

In the field of preparation of foamed ceramic materials, methods such as a solid-phase sintering process, an extrusion molding process, a gel casting process, a self-propagating high-temperature synthesis process, a particle accumulation pore-forming process, a freeze drying process, a pore gradient preparation process and the like are provided, which are not listed, each method has advantages and disadvantages, different methods are suitable for preparing different types of materials, but a certain method can not be suitable for all materials. It is believed that with the progress of scientific technology, more advanced, efficient and environment-friendly methods are continuously available.

Disclosure of Invention

The problems existing in the prior method for preparing the foamed ceramics are solved, such as: some methods have more preparation process flows; some methods require the use of large amounts of organic solvents; the green body prepared by some methods has poor strength and cannot be finely processed; the product prepared by some methods has large shrinkage rate and is easy to have collapse and pulverization phenomena; the mechanical strength of the product prepared by some methods is seriously insufficient, and the product can not be applied, and the like. The invention provides a method for preparing a foamed ceramic material by taking a foamed silica gel-inorganic powder compound as a precursor, which is characterized in that the core is a direct foaming method, pores are manufactured by utilizing the hot-pressing vulcanization foaming of liquid foamed silica gel, the method is a novel foaming method, the foaming and pore-forming processes are preposed, and foaming and pore-forming are carried out while a green body is prepared and formed, so that a foamed precursor green body which is easy to finely process, excellent in mechanical property and almost not shrunk is prepared, and then the green body is subjected to multi-temperature-section vacuum cracking and ceramic sintering to obtain the foamed ceramic material.

The technical scheme of the invention is as follows: a method for preparing a foamed ceramic material by using a foamed silica gel and inorganic powder compound as precursors comprises the steps of forming pores by using the foaming principle of the foamed silica gel to prepare a porous precursor blank of the foamed ceramic material, and then performing low-temperature cracking and high-temperature ceramic sintering to obtain the foamed ceramic material; the preparation method comprises the following steps:

step (1) matching and surface treatment of inorganic powder materials;

uniformly dispersing and mixing the liquid foaming silica gel and the inorganic powder material which is well matched and subjected to surface treatment;

step (3), hot-pressing, foaming and vulcanizing the mixed foaming silica gel-inorganic powder compound for molding;

step (4), carrying out low-temperature section hot-pressing cracking on the foamed and vulcanized porous precursor body;

and (5) carrying out high-temperature ceramic sintering on the product subjected to low-temperature cracking under a high-temperature condition to finally obtain the porous foamed ceramic material.

Further, the inorganic powder material in the step (1) is a solid material which stably exists at normal temperature and normal pressure, and comprises: metal oxide, non-metal oxide, metal carbide, non-metal carbide, allotrope of carbon element simple substance, metal nitride, non-metal nitride, metal boride, metal silicide.

Further, the inorganic powder material in the step (1) is prepared by the following steps: ceramic powder materials with the same or different types and different particle sizes are selected to be matched, the porosity of the matched mixture is required to be within the range of 10% -30%, and the particle size of each type of inorganic powder material is smaller than 100 um.

Preferably Al₂O₃、Si₃N₄、ZrO₂-SiC、ZrB₂-SiC、Al₂O₃-SiO₂、Al₂O₃-SiC-Y₂O₃、Al₂O₃-Si₃N₄The inorganic powder materials of several types and different grain diameters are matched according to the requirement of porosity parameter.

Further, the surface treatment of the inorganic powder material in the step (1) is as follows: dispersing a silane coupling agent without P, N, S element in 95% ethanol solution, and then placing the well-mixed inorganic powder material in the solution, wherein the mass ratio of the inorganic powder material to the coupling agent is as follows: 1000: 1-10, stirring at 2000r/min for 2hrs, and spray drying at 80-120 deg.C. And condensing and liquefying the 95% ethanol solution in the spray drying process, and collecting and recycling the ethanol solution.

Further, the foaming silica gel in the step (2) is a liquid silica gel which is prepared by mixing two components according to the mass ratio of 1:1, has the viscosity of 500-50000 mp.s, the foaming ratio of 3-9 times and the room temperature operable time of more than 5 hrs.

Four liquid foaming silica gels with 3-fold, 5-fold, 7-fold, and 9-fold expansion ratios are preferable.

Further, the step (2) of uniformly dispersing and mixing the liquid foaming silica gel and the inorganic powder material after the coordination and surface treatment are mixed by one of a kneader, a planetary mixer or an internal mixer under the conditions that the mixing temperature is controlled to be less than 40 ℃ and the mixing time is controlled to be 2-5 hrs, wherein the mass ratio of the foaming silica gel to the inorganic powder material is controlled as follows: 1: 1-12.

Further, the hot-pressing foaming vulcanization molding of the mixed foaming silica gel-inorganic powder compound in the step (3): placing the material in the step (2) in a mold with a certain shape for hot-pressing vulcanization foaming, wherein the vulcanization foaming conditions are as follows: 150 deg.C/10 MPa/2 hrs.

According to different foaming multiplying powers of the selected foaming silica gel, the preparation of the porous precursor body is carried out by preferably selecting several foaming and vulcanizing conditions of 3 times/150 ℃/10MPa/2hrs, 5 times/150 ℃/10MPa/2hrs, 7 times/150 ℃/10MPa/2hrs and 9 times/150 ℃/10MPa/2 hrs.

Further, the low-temperature section of the porous precursor body formed by foaming and vulcanizing in the step (4) is subjected to hot-pressing pyrolysis: and (3) placing the porous precursor body which is vulcanized and molded in the step (3) into a vacuum hot-pressing furnace, maintaining the vacuum degree lower than-0.09 Mpa, applying pressure less than or equal to 3MPa on the surface of the body, heating to 800 ℃ under the condition that the heating rate is less than or equal to 3 ℃/min, and preserving heat for 3hrs for hot-pressing cracking.

Further, performing high-temperature ceramic sintering on the product subjected to the cracking in the low-temperature section under the high-temperature condition in the step (5): removing the pressure applied on the cracked product, continuously maintaining the vacuum degree in the high-temperature furnace to be less than-0.09 Mpa, and selecting the heating rate of 3-10 ℃/min and the temperature of 1500-2300 ℃ to carry out high-temperature ceramic sintering, thereby finally obtaining the porous foamed ceramic material with high porosity, uniform pore size distribution and excellent mechanical property.

According to different types of the selected inorganic powder materials, different ceramic sintering temperatures are preferred: 1500 deg.C (Al)₂O₃)、1700℃(Si₃N₄)、2200℃(ZrO₂-SiC)、2300℃(ZrB₂-SiC)、1550℃(Al₂O₃-SiO₂)、1750℃(Al₂O₃-SiC-Y₂O₃)、1600℃(Al₂O₃-Si₃N₄)。

Further, when the foaming multiplying power of the foaming silica gel in the step (2) is 9 times, the porous foamed ceramic material with the porosity of 80-90% and the compressive strength of more than 2Mpa can be obtained through the hot-pressing foaming vulcanization molding in the step (3), the cracking reaction in the step (4) and the ceramic sintering in the step (5).

Different from the conventional direct foaming method for preparing foamed ceramics, the key of the batch industrial production of foamed ceramic products is to prepare a blank body which has excellent structural strength, easy batch forming, easy fine processing and no shrinkage. And removing organic groups of the foamed silica gel through multi-temperature-section cracking, and generating Si-O or Si-C bonds in the high-temperature ceramic process to form a composition phase of the main ceramic to obtain the foamed ceramic material.

The invention has the beneficial effects that:

1. the invention solves the problem that the dimensional stability is not easy to control in the traditional preparation method of the foamed ceramic material. For example, the sol-gel method for preparing the foamed ceramic uses a large amount of solvent, the influence of external factors (temperature, pressure, solvent amount, gel reaction time and the like) in the gel drying process is large, the dimensional stability of the product is difficult to control, and the mechanical property of the obtained product is poor.

2. The problems of sintering collapse and pulverization of the foamed ceramic are improved. The low-temperature vulcanization foaming process of the invention prepositions a pore-forming process. Like the preparation of foamed ceramics by a direct foaming method, the foaming agent needing high-temperature decomposition is added, so that impurity phases are easily introduced, in the high-temperature sintering process, the process of ceramic phase grain forming and strength increasing is exactly the process, and the formation of ceramic phases in the sintering process is easily hindered while pores are made by gas released by the foaming agent needing high-temperature decomposition; and a pore-forming agent is added, and the pore-forming agent is ablated at high temperature, so that gas is released, the same defects exist, and the problems of collapse and pulverization of the product are easily caused finally.

3. The invention solves the problem that the complex blank is difficult to form and finely process, the complex part of the traditional foamed ceramic material needs a specific mould for auxiliary forming and is difficult to finely polish, but the invention can be used for preparing the massive or flaky blank, has the advantages of high strength and good plasticity, and is not easy to crack during polishing and punching, so the blank can be directly polished and punched and the like.

4. The contradiction between the porosity and the structural strength of the foamed ceramic material is improved. Generally, the higher the porosity of the conventional foam ceramic material, the poorer the compressive strength. The method of the present invention can prepare foamed ceramic material with porosity similar to that of traditional foamed ceramic material (porosity of 80-90%) and high compression strength (over 2 MPa).

5. The method of the invention can also be used for preparing other foamed ceramic materials with different matrix types and different porosity requirements so as to meet different use occasions.

Detailed Description

In order to better explain the present invention, the following specific examples are further detailed to describe the method for preparing foamed ceramic material by using the foamed silica gel-inorganic powder composite as the precursor. However, this embodiment is not intended to limit the present invention, and all similar methods and similar variations using the present invention are intended to fall within the scope of the present invention.