CN110668802A - Green preparation method of light high-strength cordierite porous ceramic and filter - Google Patents

Green preparation method of light high-strength cordierite porous ceramic and filter Download PDF

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CN110668802A
CN110668802A CN201911045349.6A CN201911045349A CN110668802A CN 110668802 A CN110668802 A CN 110668802A CN 201911045349 A CN201911045349 A CN 201911045349A CN 110668802 A CN110668802 A CN 110668802A
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slurry
porous ceramic
strength
cordierite porous
deionized water
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李翠伟
李俊文
李�昊
武令豪
付梦丽
王涵
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Beijing Jiaotong University
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Beijing Jiaotong University
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Abstract

The invention provides a green preparation method of light high-strength cordierite porous ceramic and a filter, wherein the preparation method comprises the following steps: step S10, mixing magnesia, alumina and silica according to a cordierite stoichiometric ratio to obtain mixed powder, adding the mixed powder into deionized water with a certain volume, and ball-milling and mixing to prepare slurry; step S20, carrying out foaming treatment on the slurry to obtain foam slurry; step S30, injecting the foam slurry into a mould for freeze drying; and step S40, sintering the dried green body to obtain the light-weight high-strength cordierite porous ceramic. The invention has the advantages of small additive amount, environmental friendliness, and size change from injection molding to sintering ending smaller than 2% (the bus shrinkage rate range is-1.87% -0.45%), and is in line with the technical characteristics of green preparation.

Description

Green preparation method of light high-strength cordierite porous ceramic and filter
Technical Field
The invention relates to a preparation method of porous ceramic, in particular to a green preparation method of light high-strength cordierite porous ceramic and a filter.
Background
The cordierite porous ceramic has excellent performances of low thermal expansion coefficient, good thermal stability, high permeability and the like, so that the cordierite porous ceramic has wide application prospects in the aspects of molten metal filtration, high-temperature smoke filtration, automobile exhaust filtration, particle complementary collection and the like. However, it is difficult to achieve both high strength and high porosity by conventional production techniques, and it is difficult to produce a product having a complicated shape by sintering shrinkage. Although the newly developed foam-gel-casting method can solve the above problems, the gel system generally used is an acrylamide system, the polymerization of which requires the addition of a crosslinking agent (N, N-methylene-bisacrylamide) and an initiator (ammonium persulfate, potassium persulfate, etc.), and the addition of a certain amount of a catalyst (e.g., tetramethylethylenediamine) for the room-temperature polymerization. Wherein, the acrylamide has certain neurotoxicity, reproductive development toxicity and carcinogenicity; the initiators of ammonium persulfate and potassium persulfate both have strong oxidizability, combustion-supporting property and certain toxicity; tetramethylethylenediamine is also a strong oxidizing agent, which is harmful to the environment, especially to the water body. Therefore, the acrylamide system needs a plurality of types of additives and has a large addition amount, which is very unfavorable for environmental protection. In addition, in the porous ceramic preparation process, the blank body often has great drying shrinkage in the drying and sintering processes, which brings difficulty to manufacture products with complex shapes, and needs to design and prepare large dies or follow-up processing in consideration of shrinkage, which increases the manufacturing cost. In addition, large shrinkage often causes microcracks in the material or directly cracks the product, which affects the product yield and brings high manufacturing cost. Therefore, it is necessary to develop a green preparation technology of porous ceramics which combines high performance, environmental protection, high yield and is suitable for products with complex shapes.
Disclosure of Invention
In view of the above, the present invention provides a green method for producing cordierite porous ceramic, so as to obtain a cordierite porous ceramic filter having both high porosity and high strength.
The invention also aims to provide an environment-friendly preparation method to reduce environmental pollution and protect the environment.
It is yet another object of the present invention to provide a method for preparing a near net-size porous ceramic, so that articles having complex shapes can be prepared.
In order to solve the technical problems, the invention adopts the following technical scheme:
the green preparation method of the light-weight high-strength cordierite porous ceramic according to the embodiment of the first aspect of the invention comprises the following steps:
step S10, mixing magnesia, alumina and silica according to a cordierite stoichiometric ratio to obtain mixed powder, adding the mixed powder into deionized water with a certain volume, and mixing to prepare slurry;
step S20, carrying out foaming treatment on the slurry to obtain foam slurry;
step S30, injecting the foam slurry into a mould for freeze drying;
and step S40, sintering the dried green body to obtain the light-weight high-strength cordierite porous ceramic.
Further, in the step S10, the magnesium oxide has a particle size of 10nm to 500nm and a purity of 99.99%, the aluminum oxide has a particle size of 100nm to 800nm and a purity of 99.99%, the silicon dioxide has a particle size of 1 μm to 10 μm, the slurry has a solid content of 15 vol% to 25 vol%, and a certain volume of deionized water is weighed according to 55% to 75% of the total volume of the slurry;
further, the step S10 includes:
step S11, adding a dispersing agent into the slurry, mixing the slurry with agate balls, putting the mixture into a ball milling tank, controlling the mass ratio of the agate balls to the powder raw material to be 1.3-2.1, ball milling the mixture for 15-20 h on a roller ball mill (with the rotating speed of 100rpm),
wherein the dispersant is ammonium polyacrylate, and the dispersant accounts for 2-6 wt% of the total mass of the magnesium oxide, the aluminum oxide and the silicon dioxide.
Further, the step S20 specifically includes:
step S21, mixing a proper amount of deionized water with gelatin, heating and dissolving the mixture in a water bath at 60 ℃ to obtain a gelatin solution, and weighing the proper amount of deionized water according to 10-20% of the total volume of the slurry;
step S22, pouring the ball-milled slurry out, mixing and stirring the ball-milled slurry with a gelatin solution (the stirring speed is 450rpm), adding a foaming agent solution, and uniformly stirring the mixture at the stirring speed of 1200rpm to obtain the foam slurry;
wherein, in the step S21, the gelatin is a high molecular polysaccharide, which is formed by degrading collagen in connective tissues such as animal skin, bone and sarcolemma, has excellent biodegradability, is non-toxic, harmless and environment-friendly, and the addition amount of the gelatin is only 6-10 wt% of the total mass of the magnesium oxide, the aluminum oxide and the silicon dioxide; in the step S22, the foaming agent solution includes deionized water, sodium dodecyl sulfate and dodecanol, where the sodium dodecyl sulfate is 0.1 wt% of the deionized water, the dodecanol is 0.008 wt% of the deionized water, and the content of the foaming agent solution in the slurry is 2 g/L.
Further, the step S30 includes:
step S31, pouring the foam slurry into a mold (the mold is made of paper and is easy to detach), pre-freezing the foam slurry in a cold trap of a freeze dryer for 10-30 min, and demolding to obtain a green body (the actual pre-freezing time is determined by whether the green body can be easily demolded);
step S32, continuously freezing the demolded blank for 8-9 h;
and step S33, performing vacuum-pumping drying on the frozen blank on a freeze dryer with the vacuum degree of 5-10Pa for about 24h, wherein the size change range before and after freeze drying is 0.65-0.81%.
Further, the step S40 includes:
step S41, heating at 0.5 ℃/min, and keeping the temperature at 100 ℃, 350 ℃ and 420 ℃ for 1h-2h respectively to remove residual water and organic matters;
step S42, heating at 1 ℃/min, and preserving heat for 2h-3h at 975 ℃, 1270 ℃ and 1365 ℃ respectively to ensure the full progress of the reaction;
step S43, raising the temperature to 1450 ℃ at the speed of 0.5 ℃/min, and preserving the temperature for 5h to ensure that the framework achieves sufficient strength;
step S44, cooling to 300 ℃ at the speed of 2 ℃/min, and then cooling to room temperature along with the furnace;
wherein magnesia and alumina react at 975 ℃ to generate magnesia-alumina spinel, quartz is subjected to phase change at 1270 ℃ and is converted into cristobalite, magnesia-alumina spinel and quartz react at 1365 ℃ to generate cordierite, the expansion generated by the reaction counteracts partial sintering shrinkage, and the sintering line shrinkage is between-2.70% and 0.19%.
The light-weight high-strength cordierite porous ceramic filter according to the embodiment of the second aspect of the invention is manufactured by the method for manufacturing the light-weight high-strength cordierite porous ceramic according to any one of the above-mentioned methods.
Furthermore, the light-weight high-strength cordierite porous ceramic has the total shrinkage rate of-1.87-0.45%, the open porosity of 84.63-90.80% and the volume density of 0.23g/cm3～0.37g/cm3The compressive strength is 0.58MPa to 3.37 MPa. Wherein, the bus shrinkage rate is obtained by calculating the inner diameter size of the corresponding mould, the size of the dried blank and the size of the sintered sample; the open porosity and the volume density are obtained by measurement by a boiling method based on the Archimedes law; the compressive strength was measured by a universal tester (WDW-100E, Changchun, China) and the sample size was
Figure BDA0002253982710000041
The coefficient of thermal expansion was measured using a thermal analyzer (NETZSCH DIL 402PC, Germany) and the sample size was 5X 25mm3The test temperature is 25 to 1000 ℃; the permeability is measured by a porous ceramic permeameter (DSY porous ceramic permeameter, China Hunan Tan Xiang Co., Ltd.) with a sample size of
Figure BDA0002253982710000042
The technical scheme of the invention at least has one of the following beneficial effects:
1) the prepared high-purity cordierite porous ceramic has high permeability, high strength, lower thermal expansion coefficient and good thermal shock resistance, and when the obtained light high-strength cordierite porous ceramic material is used as a high-temperature filter, the filter has longer service life;
2) according to the invention, the ceramic body is prepared by adopting a foam injection-coagulation method based on an environment-friendly gel system, the adopted gelatin is green, environment-friendly and pollution-free, the addition amount is small, other additives are not needed for assisting in gelation, the body preparation process is simplified, and feasibility is provided for the green preparation technology of cordierite porous ceramic;
3) the invention adopts a freeze drying process, directly places the green body of the ceramic slurry in a low-temperature environment to freeze the moisture contained in the green body into ice, then carries out vacuum pumping and heating to sublimate and remove the ice, removes the moisture and simultaneously avoids the agglomeration of slurry particles, so that the green body can be uniformly shrunk inside and outside in the drying process, the drying shrinkage rate is smaller, the near-net shape is facilitated, the deformation and the internal cracks in the drying process can be effectively reduced, the compression strength and the thermal shock resistance of the porous ceramic are improved, and the service life of the porous ceramic is prolonged;
4) the invention controls the important process parameters (solid content, gelatin addition amount, foaming agent concentration and the like) in the whole preparation process, utilizes the synthesis of magnesium aluminate spinel, the phase change of silicon dioxide and the volume expansion caused in the generation process of cordierite of a sample in the sintering process to offset the spontaneous large shrinkage in the sintering process, and even can offset part of the shrinkage caused by drying, thereby realizing the complete near net size preparation from injection molding to sintering;
5) the light-weight high-strength cordierite porous ceramic material provided by the embodiment of the invention has the total shrinkage rate of-1.87-0.45%, the open porosity of 84.63-90.80% and the bulk density of 0.23g/cm3～0.37g/cm3The compressive strength is 0.58MPa to 3.37MPa, and the thermal expansion coefficient is 1.78843 multiplied by 10-6/℃～2.29688×10-6Permeability 0.3452X 10/deg.C-11m2～5.026×10-11m2. As a high-temperature filter material, the filter with higher porosity is obtained under the condition that the material strength is in the application range, and the mass can be reduced to a greater extent so as to improve the filtering effect.
Drawings
FIG. 1 is a process diagram of a method for preparing a lightweight high-strength cordierite porous ceramic according to one embodiment of the present invention;
FIG. 2 is an X-ray diffraction pattern of a lightweight, high strength cordierite porous ceramic according to an embodiment of the present invention;
FIG. 3 is a scanning electron microscope photograph of the micro-pore structure at the fracture site of a lightweight high-strength cordierite porous ceramic material according to an embodiment of the present invention, (a) at low magnification of 100 and (b) at high magnification of 5 k;
FIG. 4 is a photograph of a tubular cordierite porous ceramic according to example 4 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.
First, a green production method of a lightweight high-strength cordierite porous ceramic according to an embodiment of the present invention will be described in detail.
The green preparation method of the light-weight high-strength cordierite porous ceramic material according to the embodiment of the invention, as shown in FIG. 1, comprises the following steps:
step S10, mixing magnesia, alumina and silica according to a cordierite stoichiometric ratio to obtain mixed powder, adding the mixed powder into deionized water with a certain volume, and mixing to prepare slurry;
step S20, carrying out foaming treatment on the slurry to obtain foam slurry;
step S30, injecting the foam slurry into a mould for freeze drying;
and step S40, sintering the dried green body to obtain the light-weight high-strength cordierite porous ceramic.
In other words, according to some embodiments of the present invention, the lightweight high-strength cordierite porous ceramic material is prepared by using magnesia, alumina, and silica as raw materials, first, the magnesia, alumina, and silica are mixed according to a stoichiometric ratio of cordierite to obtain a mixed powder, and the mixed powder is added into deionized water of a certain volume obtained by calculation to be mixed to prepare slurry; then, combining gel injection molding and mechanical stirring foaming processes, preparing a porous ceramic blank by adopting an environment-friendly foam injection-coagulation method, namely heating gelatin and a proper amount of deionized water to form a gelatin solution, pouring the slurry out, stirring and mixing the gelatin solution, adding a foaming agent, mechanically stirring to obtain a foam slurry, pouring the foam slurry into a mold, pre-freezing to accelerate gelation to obtain a blank, and finally, adopting a freeze drying process, and sintering the dried blank in a sintering furnace to obtain the light high-strength cordierite porous ceramic material. Here, it is understood that since the gelatin is not greatly different in the temperature at which it is dissolved and solidified, it is possible to promote its gelation by freezing, increase the gel strength, and then dry it by a suitable freeze-drying technique.
Therefore, according to the green preparation method of the light-weight high-strength cordierite porous ceramic, the raw materials are high in purity and are strictly proportioned according to the stoichiometric ratio of cordierite, so that the obtained cordierite porous ceramic material is high in purity, particles in the cordierite porous ceramic material are tightly combined, and the overall strength is improved. In addition, the open porosity, compressive strength, thermal expansion coefficient and the like of the sample can be controlled by adjusting parameters such as solid content, gelatin addition amount and the like.
The thermal expansion coefficient of cordierite is lower than that of mullite and anorthite, namely the light-weight high-strength cordierite porous material has high strength and good thermal shock resistance, and when the obtained light-weight high-strength cordierite porous ceramic material is used as a filter, the service life of the material is longer when the material is filtered at high temperature.
In addition, on the basis of the foam gel injection method, a green and environment-friendly gelatin gel system is adopted to replace a toxic acrylamide system, so that substances harmful to human bodies and the environment are removed, the dosage of additives is reduced, and the environment-friendly foam gel injection method is developed; the blank can be uniformly shrunk inside and outside in the drying process by combining the freeze drying technology, and the drying shrinkage rate is greatly reduced; volume expansion generated by phase change and phase reaction in the sintering process is utilized to offset sintering and drying shrinkage, and near net size preparation is realized by regulating and controlling process parameters; effectively reduces internal cracks generated by large shrinkage in the drying and sintering processes, improves the compressive strength and the thermal shock resistance of the porous ceramic, and improves the durability of the porous ceramic. The light high-strength cordierite porous ceramic obtained by the preparation method of the light high-strength cordierite porous ceramic provided by the embodiment of the invention has the total shrinkage of-1.87-0.45%, the open porosity of 84.63-90.80% and the bulk density of 0.23g/cm3～0.37g/cm3The compressive strength is 0.58MPa to 3.37MPa, and the thermal expansion coefficient is 1.78843 multiplied by 10-6/℃～2.29688×10-6Permeability 0.3452X 10/deg.C-11m2～5.026×10-11m2. The light-weight high-strength cordierite porous ceramic material disclosed by the embodiment of the invention has the characteristics of high porosity and high strength, and a filter prepared from the light-weight high-strength cordierite porous ceramic material has higher strength, the service life of the filter is greatly prolonged, the filtering effect is also improved, and the application range is wider.
According to an embodiment of the present invention, in step S10, raw material powder with higher purity and smaller particle size is prepared, wherein the particle size of magnesium oxide is 10nm to 500nm and the purity is 99.9%, the particle size of aluminum oxide is 100nm to 800nm and the purity is 99.99%, the particle size of silicon dioxide is 1 μm to 10 μm and the purity is 99.4%, the solid content of the slurry is 15 vol% to 25 vol%, and a certain volume of deionized water is weighed according to 55% to 75% of the total volume of the slurry. Because the granularity of the raw materials is smaller, the reaction activity is higher, the combination degree between the particles is high, and the porous ceramic material with higher strength can be obtained. In addition, the strength of the green body and the final ceramic body can be controlled by adjusting the solid content.
According to an embodiment of the present invention, step S10 further includes:
step S11, adding a dispersing agent into the slurry, mixing the slurry with agate balls, putting the mixture into a ball milling tank, controlling the mass ratio of the balls to the powder raw material to be 1.3-2.1, ball milling the mixture for 15-20 h on a roller ball mill (with the rotating speed of 100rpm),
wherein the dispersant is ammonium polyacrylate, and the dispersant accounts for 2-6 wt% of the total mass of the magnesium oxide, the aluminum oxide and the silicon dioxide.
According to an embodiment of the present invention, step S20 specifically includes:
step S21, mixing a proper amount of deionized water with gelatin, heating the mixture in a water bath at 60 ℃, stirring and dissolving the mixture to obtain a gelatin solution, and weighing the proper amount of deionized water according to 10-20% of the total volume of the slurry;
step S22, pouring the slurry after ball milling, mixing and stirring the slurry with gelatin solution (the stirring speed is 450rpm), then adding foaming agent solution and stirring the mixture evenly (the stirring speed is 1200rpm) to obtain the foam slurry,
wherein, in the step S21, the gelatin is a high molecular polysaccharide, which is formed by degrading collagen in connective tissues such as animal skin, bone and sarcolemma, has excellent biodegradability, is non-toxic, harmless and environment-friendly, and is 6 wt% -10 wt% of the total mass of the magnesium oxide, the aluminum oxide and the silicon dioxide;
in the step S22, the foaming agent solution includes deionized water, sodium dodecyl sulfate and dodecanol, where the sodium dodecyl sulfate is 0.1 wt% of the deionized water, the dodecanol is 0.008 wt% of the deionized water, and the content of the foaming agent solution in the slurry is 2 g/L. The foaming volume can be adjusted by adjusting the content of the foaming agent, so that the porosity, the compressive strength, the median pore size distribution and the like of the sample are controlled.
Further, the step S30 may include:
step S31, pouring the foam slurry into a mold, then placing the mold into a cold trap of a freeze dryer for pre-freezing for 10-30 min, and then demolding to obtain a blank (the actual pre-freezing time is subject to whether the blank can be easily demolded);
step S32, continuously freezing the demolded blank for 8-9 h;
and step S33, performing vacuum-pumping drying on the frozen blank on a freeze dryer, wherein the vacuum degree is 5-10Pa, the blank is dried for about 24 hours, and the size change range before and after freeze drying is 0.65-0.81%.
In the step S31, the used mold is made of paper and is easy to detach, pre-freezing is performed to accelerate gelatin gelation, because gelatin is not greatly different in initial dissolution and solidification temperature, the gelatin is melted at about 30 ℃ and solidified at 20-25 ℃, freezing can promote the combination of particles between blanks to be firmer, the gel strength of the blanks is improved to be not lower than the strength of chemical gel reaction, so that the blanks are obtained by solidification and demolding, in the step S32, the demolded blanks are frozen for 8-9 h again, in order to enable the internal and external temperatures of the whole blanks to be consistent in a low-temperature environment, the moisture contained in the blanks is completely frozen into ice, the vacuum drying after the blanks is facilitated, in the step S33, the frozen blanks are subjected to vacuum drying on a freeze dryer, the ice is sublimated by vacuum heating, the moisture is removed, and the agglomeration of slurry particles is avoided, the blank can be uniformly shrunk inside and outside in the drying process, the drying shrinkage rate is small, the near-net forming is favorably realized, and the deformation and the internal cracks in the drying process can be effectively reduced.
Therefore, according to the green preparation method of the light high-strength cordierite porous ceramic material, which is disclosed by the embodiment of the invention, an environment-friendly foam injection-condensation method is combined with a freeze-drying technology, so that the porosity of a green body is fixed and stably existed in a short time, the breakage and polymerization of foam are reduced to the greatest extent, and the finally obtained porous ceramic material has the advantages of higher porosity, higher strength, better thermal shock resistance and higher durability.
According to an embodiment of the present invention, step S40 includes:
in the process of sintering the dried green body in a muffle furnace, the green body is respectively subjected to heat preservation for 1h-2h at 100 ℃, 350 ℃ and 420 ℃, heat preservation for 1h-3h at 975 ℃, 1270 ℃ and 1365 ℃ and heat preservation for 5h at 1450 ℃, wherein the heating rates to 100 ℃, 350 ℃, 420 ℃ and 1450 ℃ are all 0.5 ℃/min; the heating rates to 975 ℃, 1270 ℃ and 1365 ℃ are all 1 ℃/min. And then cooling to 300 ℃ at the speed of 2 ℃/min, and then cooling to room temperature along with the furnace to obtain the lightweight high-strength cordierite porous ceramic, wherein the sintering shrinkage rate of the lightweight high-strength cordierite porous ceramic is between-2.70% and 0.19%. The reaction of the sintering process comprises: removing residual water from the blank, decomposing magnesium hydroxide to generate magnesium oxide, decomposing and discharging gelatin colloid, generating intermediate-phase magnesia-alumina spinel, carrying out quartz phase transition and finally obtaining the light-weight high-strength cordierite porous ceramic material.
The light high-strength cordierite porous ceramic material prepared by the preparation method of the light high-strength cordierite porous ceramic material provided by the embodiment of the invention has the total shrinkage of-1.87-0.45%, the open porosity of 84.63-90.80% and the bulk density of 0.23g/cm3～0.37g/cm3The compression strength is 0.58MPa to 3.37MPa, and the thermal expansion coefficient is 1.78843 multiplied by 10-6/℃～2.29688×10-6Permeability 0.3452X 10/deg.C-11m2～5.026×10-11m2As a filter material for filtering molten metal at high temperature, the filter with higher porosity and better filtering performance is obtained under the condition that the material strength is in the application range, the mass of the filter can be reduced to a greater extent, the filtering effect is improved, and casting is reducedRejection rate of the piece.
The method for producing a lightweight, high-strength cordierite porous ceramic material according to the present invention will be described with reference to specific examples.
In the following examples, the green production method of an environmentally friendly gel, which is exemplified by a combination of a gelatin gel system and a freeze-drying technique, is described as an example, but the present invention is not limited thereto, and any other polysaccharide type gel known to those skilled in the art may be used. In the following examples, sodium lauryl sulfate was used as a foaming agent, but the present invention is not limited thereto, and those skilled in the art can perform foaming treatment using any other foaming agent. Such modifications are to be understood as falling within the scope of the present invention.
Example 1
15 vol.% of slurry is prepared, the total volume of the slurry is 200ml, and gelatin accounting for 8 wt% of the total mass of the raw material powder is adopted. Magnesium oxide (purity 99.9%) with a particle size of 50nm, aluminum oxide (purity 99.99%) with a particle size of 300nm, and silicon dioxide (purity 99.4%) with a particle size of 10 μm were mixed in a cordierite stoichiometric ratio (Mg)2Al4Si5O18) The materials are proportioned, then a dispersing agent (ammonium polyacrylate) accounting for 2 wt% of the total mass of the raw material powder and 140ml of deionized water are added, and the mixture is subjected to ball milling for 17 hours on a roller ball mill (the rotating speed is 100 rpm). Heating and dissolving gelatin by using 30ml of deionized water, and stirring the mixed slurry and the gelatin solution at a low speed of 450rpm to uniformly mix the slurry and the gelatin solution; then adding 2g/L foaming agent (sodium dodecyl sulfate) for foaming, gradually increasing the rotating speed to 1200rpm, stably stirring for 15min until the foaming volume is about 470ml, pouring the slurry into a paper cup mold, and injection molding. And pre-freezing the injection molded sample in a vacuum freeze dryer for 20min, taking out the sample, demolding, continuously freezing the demolded blank for 8-9 h, vacuumizing and drying the blank, wherein the vacuum degree is controlled to be 5-10Pa, and drying for about 24 h. Sintering was then carried out at 1450 ℃. A temperature rising stage: firstly, heating to 100 ℃ at the speed of 0.5 ℃/min and preserving heat for 1 h; then heating to 350 ℃ at the speed of 0.5 ℃/min and preserving heat for 1 h; then the temperature is raised to 420 ℃ at the speed of 0.5 ℃/minKeeping the temperature for 1h, then heating to 975 ℃ at the speed of 1 ℃/min and keeping the temperature for 1 h; heating to 1270 ℃ at the speed of 1 ℃/min and preserving the heat for 3 h; heating to 1365 ℃ at the speed of 1 ℃/min and preserving the heat for 3 h; finally, the temperature is raised to 1450 ℃ at the speed of 0.5 ℃/min and is preserved for 5 h. And (3) cooling: finally, the temperature is reduced to 300 ℃ at the speed of 2 ℃/min and then cooled to the room temperature along with the furnace. The cordierite porous ceramic material can be obtained through the sintering schedule. The XRD pattern of the sintered material is shown in FIG. 2, and the material can be obtained as pure cordierite porous ceramic. The scanning electron microscope photograph of the fracture surface is shown in FIG. 3, in which (a) is a photograph at 100 times and (b) is a photograph at 5k times. The obtained light high-strength cordierite porous ceramic material has the open porosity of 90.08 percent and the volume density of 0.23g/cm3The compressive strength is 0.58MPa, the total shrinkage rate is 0.45 percent, and the coefficient of thermal expansion is 1.78843 multiplied by 10-6Permeability 5.026X 10/deg.C-11m2。
Wherein the open porosity and volume density are measured by boiling method based on Archimedes' law, the compressive strength is determined by universal tester (WDW-100E, Changchun, China), and the sample size is
Figure BDA0002253982710000101
Figure BDA0002253982710000102
The coefficient of thermal expansion was measured using a thermal analyzer (NETZSCH DIL 402PC, Germany) and the sample size was 5X 25mm3The test temperature is 25 to 1000 ℃, the permeability passes through a porous ceramic permeameter (DSY porous ceramic permeameter, Hunan Tan Xiang Co., Ltd., China) and the sample size is
Figure BDA0002253982710000104
Example 2
20 vol.% of slurry is prepared, the total volume of the slurry is 200ml, and gelatin accounting for 8 wt% of the total mass of the raw material powder is adopted. Oxidizing with a particle size of 50nmMagnesium (purity 99.9%), alumina (purity 99.99%) with particle size of 300-500nm and silica (purity 99.4%) with particle size of 10 μm according to cordierite stoichiometric ratio (Mg)2Al4Si5O18) The mixture was blended, then 4 wt% of the total raw material powder mass of dispersant (ammonium polyacrylate) and 130ml of deionized water were added, and the mixture was ball milled in a roller ball mill (100 rpm) for 17 hours. Heating and dissolving gelatin by using 30ml of deionized water, and stirring the mixed slurry and the gelatin solution at a low speed of 450rpm to uniformly mix the slurry and the gelatin solution; then adding 2g/L foaming agent (sodium dodecyl sulfate) for foaming, gradually increasing the rotating speed to 1200rpm, stably stirring for 15min until the foaming volume is about 440ml, pouring the slurry into a paper cup mold, and injection molding. The injection molded sample was pre-frozen in a vacuum freeze-dryer for 15min, and the subsequent freeze-drying process was the same as in the first embodiment. The sintering system is the same as that of the first embodiment. The XRD pattern of the sintered material was the same as fig. 2 of example 1, and the scanning electron micrograph of the fracture surface was similar to fig. 3 of example 1. The obtained cordierite foamed ceramic material has an open porosity of 87.85% and a bulk density of 0.27g/cm3The compressive strength is 1.90MPa, the total shrinkage is-1.85 percent, and the coefficient of thermal expansion is 1.96332 multiplied by 10-6Permeability of 1.688 multiplied by 10 at/deg.C-11m2. The test method and the apparatus are the same as those in the first embodiment.
Example 3
25 vol.% of slurry was prepared, the total volume of which was 200ml, using gelatin in an amount of 8 wt.% of the total mass of the raw material powder. Magnesium oxide (purity 99.9%) with a particle size of 50nm, alumina (purity 99.99%) with a particle size of 300-500nm and silica (purity 99.4%) with a particle size of 10 μm were mixed in a stoichiometric ratio (Mg) of cordierite2Al4Si5O18) The materials are proportioned, then dispersant (ammonium polyacrylate) with the total mass of 6 wt% of the raw material powder and 110ml of deionized water are added, and the mixture is ball-milled for 17 hours on a roller ball mill (the rotating speed is 100 rpm). Heating and dissolving gelatin by using 40ml of deionized water, and stirring the mixed slurry and the gelatin solution at a low speed of 450rpm to uniformly mix the slurry and the gelatin solution; then 2g/L of blowing agent (dodecyl sulfur) was addedSodium) is foamed, the rotating speed is gradually increased to 1200rpm, the foaming volume is about 360ml after stable stirring for 15min, the foaming is finished, the slurry is poured into a paper cup mold, and injection molding is carried out. The injection molded sample was pre-frozen in a vacuum freeze-dryer for 10min, and the subsequent freeze-drying process was the same as in the first embodiment. The sintering system is the same as that of the first embodiment. The XRD pattern of the sintered material was the same as fig. 2 of example 1, and the scanning electron micrograph of the fracture surface was similar to fig. 3 of example 1. The obtained cordierite foamed ceramic material has an open porosity of 84.63% and a bulk density of 0.37g/cm3The compressive strength is 3.37MPa, the total shrinkage is-1.87 percent, and the coefficient of thermal expansion is 2.29688 multiplied by 10-6Permeability 0.3452X 10/deg.C-11m2. The test method and the apparatus are the same as those in the first embodiment.
Example 4
Cordierite porous ceramics having a tubular shape were obtained by using the same slurry and method steps as in example 2 except that they were poured into a tubular mold, as shown in the photograph of FIG. 4.
The performance data obtained from the literature studies of this experiment is superior to the performance of existing filters. The light-weight high-strength cordierite porous ceramic material according to the embodiment of the invention is far higher than the existing requirements, and can be completely suitable for a porous ceramic filter for filtering molten metal.
Compared with cordierite porous ceramics prepared by Lihao and the like, the preparation method is more environment-friendly, and the prepared light high-strength cordierite porous ceramic material can reach the same or even higher performance during filtration, and has wide application prospect.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (8)

1. A green preparation method and a filter of light-weight high-strength cordierite porous ceramic are characterized by comprising the following steps:
step S10, mixing magnesia, alumina and silica according to a cordierite stoichiometric ratio to obtain mixed powder, adding the mixed powder into deionized water with a certain volume, and ball-milling and mixing to prepare slurry;
step S20, carrying out foaming treatment on the slurry to obtain foam slurry;
step S30, injecting the foam slurry into a mould for freeze drying;
and step S40, sintering the dried green body to obtain the high-quality and high-strength cordierite porous ceramic.
2. The green production method of a lightweight high-strength cordierite porous ceramic according to claim 1, wherein in step S10, the magnesia has a particle size of 10nm to 500nm and a purity of 99.9%, the alumina has a particle size of 100nm to 800nm and a purity of 99.99%, the silica has a particle size of 1 μm to 10 μm and a purity of 99.4%, and the slurry has a solid content of 15 vol% to 25 vol%.
3. The green production method of a lightweight high-strength cordierite porous ceramic according to claim 1, wherein the step S10 specifically includes:
step S11, calculating the stoichiometric ratio of the cordierite to the magnesia, the alumina and the silica, weighing according to a specific solid content, and adding into deionized water with a specific volume, wherein the solid content of solid particles is controlled to be 15-25 vol%, and the deionized water with a certain volume is weighed according to 55-75% of the total volume of the calculated slurry;
step S12, adding a certain amount of dispersant into the suspension liquid obtained in the step S11, mixing the slurry and agate balls (the mass ratio of the balls to the powder raw material is controlled to be 1.3-2.1), putting the mixture into a ball milling tank, and carrying out ball milling on the mixture for 15-20 h on a roller ball mill (the rotating speed is 100 rpm);
wherein the dispersant is ammonium polyacrylate, and the dispersant accounts for 2-6 wt% of the total mass of the magnesium oxide, the aluminum oxide and the silicon dioxide.
4. The green production method of a lightweight high-strength cordierite porous ceramic according to claim 1, wherein the step S20 specifically includes:
step S21, mixing a proper amount of deionized water with gelatin, heating the mixture in a water bath at 60 ℃, stirring and dissolving the mixture to obtain a gelatin solution, and weighing the proper amount of deionized water according to 10-20% of the total volume of the slurry;
step S22, separating the ball-milled slurry balls obtained in the step S10, pouring out the ball-milled slurry balls, and uniformly mixing and stirring the ball-milled slurry balls with the gelatin solution obtained in the step S21 (the stirring speed is 450 rpm);
step S23, adding a foaming agent solution into the slurry of S22 and stirring rapidly (the rotation speed of a stirrer is 1200rpm) to obtain the foam slurry;
wherein, in the step S21, the gelatin is a high molecular polysaccharide, which is formed by degrading collagen in connective tissues such as animal skin, bone and sarcolemma, has excellent biodegradability, is non-toxic, harmless and environment-friendly, and the addition amount of the gelatin is only 6-10 wt% of the total mass of the magnesium oxide, the aluminum oxide and the silicon dioxide; in the step S22, the foaming agent solution includes deionized water, sodium dodecyl sulfate and dodecanol, where the sodium dodecyl sulfate is 0.1 wt% of the deionized water, the dodecanol is 0.008 wt% of the deionized water, and the content of the foaming agent solution in the slurry is 2 g/L.
5. The green production method of a lightweight high-strength cordierite porous ceramic according to claim 1, wherein the step S30 specifically includes:
step S31, pouring the foam slurry obtained in the step S20 into a mold, then placing the mold into a cold trap of a freeze dryer for pre-freezing for 10-30 min, and then demolding to obtain a blank;
step S32, continuously freezing the demolded blank of S31 in a cold trap for 8-9 h;
s33, taking out the blank body S32, and placing the blank body in a freeze dryer for vacuum drying, wherein the time is 20-24 hours, and the vacuum degree is 5-10 Pa;
wherein the used mould is made of paper and is easy to disassemble, and the size change range before and after freeze drying is 0.65-0.81%.
6. The green production method of light-weight high-strength cordierite porous ceramic according to claim 1, wherein in step S40, the dried green body of S33 is placed in a muffle furnace for sintering, and specifically comprises:
step S41, heating at 0.5 ℃/min, and keeping the temperature at 100 ℃, 350 ℃ and 420 ℃ for 1h-2h respectively to remove residual water and organic matters;
step S42, heating at 1 ℃/min, and preserving heat for 2h-3h at 975 ℃, 1270 ℃ and 1365 ℃ respectively to ensure the full progress of the reaction;
step S43, raising the temperature to 1450 ℃ at the speed of 0.5 ℃/min, and preserving the temperature for 5h to ensure that the framework achieves sufficient strength;
step S44, cooling to 300 ℃ at the speed of 2 ℃/min, and then cooling to room temperature along with the furnace;
wherein magnesia and alumina react at 975 ℃ to generate magnesia-alumina spinel, quartz is subjected to phase change at 1270 ℃ and is converted into cristobalite, magnesia-alumina spinel and quartz react at 1365 ℃ to generate cordierite, the expansion generated by the reaction counteracts partial sintering shrinkage, and the sintering line shrinkage is between-2.70% and 0.19%.
7. A lightweight high-strength cordierite porous ceramic filter produced by the green production method for a lightweight high-strength cordierite porous ceramic according to any one of claims 1 to 6.
8. The lightweight high-strength cordierite porous ceramic according to claim 7, having a total shrinkage of-1.87 to 0.45%, an open porosity of 84.63 to 90.80%, and a bulk density of 0.23g/cm3～0.37g/cm3The compressive strength is 0.58MPa to 3.37MPa, and the thermal expansion coefficient is 1.78843 multiplied by 10-6/℃～2.29688×10-6Permeability 0.3452X 10 ℃ C./(test temperature range 25 to 1000 ℃ C.)-11m2～5.026×10-11m2。
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CN111205074A (en) * 2020-01-13 2020-05-29 山东晟世达科技有限公司 Foamed ceramic containing cordierite framework and preparation method thereof
CN114031297A (en) * 2021-11-24 2022-02-11 中建材蚌埠玻璃工业设计研究院有限公司 Cordierite-based porous glass ceramic and preparation method thereof
CN117886625A (en) * 2024-03-15 2024-04-16 安徽大学 Preparation method of high-strength porous cordierite ceramic material

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CN114031297A (en) * 2021-11-24 2022-02-11 中建材蚌埠玻璃工业设计研究院有限公司 Cordierite-based porous glass ceramic and preparation method thereof
CN114031297B (en) * 2021-11-24 2023-08-22 中建材玻璃新材料研究院集团有限公司 Cordierite-based porous glass ceramic and preparation method thereof
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CN117886625B (en) * 2024-03-15 2024-05-24 安徽大学 Preparation method of high-strength porous cordierite ceramic material

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