A method for preparing high-strength porous zirconite ceramic by foaming gelation

Abstract

The application belongs to the technical field of zirconite porous ceramics, and discloses a method for preparing high-strength zirconite porous ceramics by a foaming gel-casting method, which uses zirconite powder, yttrium oxide powder and manganese oxide powder as raw materials, and prepares zirconite porous ceramics by the foaming gel-casting method, and the zirconite porous ceramics is obtained after the steps of preparing a sugar syrup solution, premixing ceramic powder, preparing ceramic slurry, gel injection molding and sintering treatment; the foaming gel-casting method can effectively increase the porosity of the zirconite porous ceramics and reduce the heat radiation transmission efficiency; the use of sugar instead of water as a solution medium increases the sintering surface and improves the strength of the porous ceramics; the addition of manganese oxide and yttrium oxide accelerates the merging and growing process between zirconite crystal grains, stabilizes the crystal form of zirconia at high temperature, avoids the generation of cracks caused by crystal form transformation, further improves the strength of the zirconite porous ceramics, and the prepared zirconite porous ceramics is stable in high-temperature performance, high in strength and low in thermal conductivity.

Description

Technical Field

[0001] This invention belongs to the field of zircon porous ceramics technology, specifically relating to a method for preparing high-strength zircon porous ceramics by foaming and solidification. Background Technology

[0002] In recent years, my country's high-temperature industrial system has continued to expand, and its technological capabilities have been comprehensively improved. The steel industry, while optimizing and upgrading traditional long-process smelting, has also made significant breakthroughs in cutting-edge fields such as clean steel smelting, large-scale blast furnaces, and low-carbon metallurgy. The cement industry has also made continuous progress in new dry process technologies, low environmental impact technologies, and the application of alternative fuels. These intensified high-temperature processes and stricter environmental standards have placed more stringent demands on thermal insulation materials for industrial kilns. Higher operating temperatures and longer operating cycles pose more severe challenges to the high-temperature stability and thermal shock resistance of porous insulating ceramics. Simultaneously, these materials must maintain stable performance and low thermal conductivity under high-temperature service environments to ensure the energy efficiency of thermal equipment, extend maintenance cycles, and conserve energy. Therefore, developing a type of porous insulating ceramic that combines low thermal conductivity and high strength has become a key direction in current industrial energy conservation and materials research.

[0003] Foaming is a typical method for preparing porous ceramics. Its principle involves introducing gas into a ceramic slurry through physical, chemical, or mechanical means to form stable bubbles, followed by curing, drying, and sintering to obtain a porous structure. The main advantage of this method is its ability to produce products with high porosity and three-dimensional interconnected pore structures, and its relatively simple process flow suggests good potential for large-scale production. However, this technology also has significant limitations: the mechanical strength of the resulting porous ceramics is generally low, restricting their application under load-bearing conditions. Gel casting is a near-net-shape forming technology for preparing high-performance dense ceramics. Its basic principle involves injecting a ceramic slurry containing organic monomers into a mold, initiating monomer polymerization and cross-linking under specific temperature conditions, causing the slurry to solidify in situ to form a three-dimensional network gel, thus firmly encapsulating the ceramic particles. Finally, through drying and sintering, dense ceramic parts with uniform microstructure, few defects, and excellent mechanical properties are obtained. The main advantage of this method is the good fluidity of the slurry before curing, allowing for a higher solid content, which helps reduce sintering shrinkage and improve the density of the final product. Therefore, porous ceramics prepared by combining foaming and gel casting can have both high porosity and high strength, making it an emerging method for preparing porous ceramics.

[0004] Currently, the medium used in the foaming and injection molding process for preparing porous ceramics is mostly water. For example, the porous ceramic preparation medium described in patent document "A method for self-foaming injection molding of porous ceramics" (CN104402456B) is water, and the selected foaming agent is an inorganic foaming agent, not an organic one. Patent document "A method for synthesizing calcium hexaaluminate material by gel injection molding" (CN112358291A) describes a gel injection molding method using deionized water as the medium. It is evident that the medium in the existing foaming and injection molding process for preparing porous ceramics is primarily water. Water as a medium increases the distance between powder particles, reducing sintering activity and thus decreasing strength. Therefore, how to prepare a zircon porous ceramic with a simple process, high strength, and low thermal conductivity is an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing high-strength zircon porous ceramics using a foaming and gelation process. This method is simple, energy-efficient, and low-cost. It utilizes zircon powder, yttrium oxide powder, and manganese oxide powder as raw materials, adding syrup solution, foaming agent, dispersant, monomer, crosslinking agent, initiator, and catalyst. The resulting zircon porous ceramics are obtained through injection molding, gelation, and sintering. The zircon porous ceramics prepared by this method exhibit stable high-temperature performance, high strength, and low thermal conductivity.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: a method for preparing high-strength zircon porous ceramics by foaming and solidification, comprising the following steps:

[0007] Step 1: Prepare the syrup solution: Dissolve the sugars weighed according to the specified weight at a temperature of 190-230°C to form a syrup solution;

[0008] Step 2: Premixing ceramic powders: Weigh the zircon powder, yttrium oxide powder, and manganese oxide powder according to their respective weight proportions and premix them.

[0009] Step 3: Preparation of ceramic slurry: Add the ceramic powder from Step 2 to the syrup solution from Step 1, and run at 100-200 rpm for 10-25 minutes at a temperature of 190-230℃; then add the foaming agent, foam stabilizer, and dispersant in proportion, and run at 100-200 rpm for 5-8 minutes at a temperature of 190-230℃; then add the monomer, crosslinking agent, initiator, and catalyst in proportion, and run the prepared ceramic slurry at 150-250 rpm for 10-25 minutes at a temperature of 190-230℃.

[0010] Step 4, Injection of Cement: Inject the ceramic slurry obtained in the previous step into the mold, cure at 50-70℃ for 36-48 hours, then cure at 100-110℃ for 48-60 hours, and then demold.

[0011] Step 5, sintering treatment: The demolded ceramic green body is baked at a heating rate of 1-5℃ / min to 1350-1500℃ and held for 1-3 hours to obtain high-strength zircon porous ceramic.

[0012] The zircon porous ceramic prepared by this invention has a bulk density of 0.6–0.9 g / cm³. 3 It has an apparent porosity of 75-88%, a room temperature compressive strength of 7.2-9.7 MPa, and a thermal conductivity of 0.2-0.35 (W / (m·K)) at 900℃.

[0013] Preferably, the raw material composition and weight percentages for preparing zircon porous ceramics are as follows: 25-42 parts zircon powder, 1-3 parts yttrium oxide powder, 2-5 parts manganese oxide powder, 55-70 parts syrup solution, plus 0.7-1.0% foaming agent (by weight of ceramic powder), 0.1-0.2% foam stabilizer (by weight of ceramic powder), 0.5-0.8% dispersant (by weight of ceramic powder), 4-8% monomer (by weight of ceramic powder), 10% crosslinking agent (by weight of monomer), 0.3-0.7% initiator (by weight of ceramic powder), and 0.3-0.8% catalyst (by weight of ceramic powder).

[0014] Preferably, the zircon powder contains ZrO2 content ≥ 63wt% and SiO2 content ≤ 32wt%; the zircon powder particle size is ≤ 0.074mm.

[0015] Preferably, the Y2O3 content in the yttrium oxide powder is ≥99.5wt%; and the particle size of the yttrium oxide powder is ≤0.074mm.

[0016] Preferably, the MnO2 content in the manganese oxide powder is ≥90wt%; the particle size of the manganese oxide powder is ≤0.088mm.

[0017] Preferably, the sugar is sucrose, glucose, or fructose.

[0018] Preferably, the foaming agent is sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or sodium α-olefin sulfonate.

[0019] Preferably, the foam stabilizer is polyvinyl alcohol or sodium alginate.

[0020] Preferably, the dispersant is sodium citrate, sodium tripolyphosphate, or sodium hexametaphosphate.

[0021] Preferably, the monomer is methylamide or methacrylamide.

[0022] Preferably, the crosslinking agent is N,N'-methyleneacrylamide.

[0023] Preferably, the initiator is ammonium persulfate.

[0024] Preferably, the catalyst is tetramethylethylenediamine.

[0025] This invention combines the characteristics of two ceramic preparation processes—foaming and gel casting—to prepare zircon porous ceramics. The introduction of foaming effectively controls porosity, pore size, and distribution. The resulting closed or semi-closed pore structure effectively blocks heat conduction and convection, giving the product excellent thermal insulation properties. However, the resulting ceramic products have high porosity, leading to lower strength and shorter service life. Gel casting, as an advanced ceramic forming technology, uniformly disperses ceramic powder in a monomer-containing solution, forming a three-dimensional gel network through in-situ polymerization, thus solidifying the green body. This process effectively reduces defects common in traditional forming processes, such as porosity, cracks, and uneven density, allowing the ceramic powder particles to achieve a dense and uniform packing state. This lays the foundation for forming a highly dense ceramic matrix with a uniform microstructure during subsequent sintering. Simultaneously, the encapsulation effect of the gel network prevents powder particle agglomeration, reduces porosity and impurity accumulation at grain boundaries after sintering, and significantly improves the density and structural integrity of the ceramic.

[0026] The present invention employs a foaming method to effectively increase the porosity of zircon porous ceramics. The thermal conductivity of the air or inert gas filling the pores is much lower than that of the solid matrix, which can significantly weaken the heat conduction effect. At the same time, when the pores exist in a closed or semi-closed form, the convective movement of the gas in the pores can be restricted, reducing the heat transfer caused by thermal convection. Furthermore, the scattering and absorption of thermal radiation by the pore walls can further reduce the heat radiation transfer efficiency.

[0027] In the sintering process of zircon porous ceramics, sugars were used instead of water as the solution medium during preparation. Sugar solutions have higher viscosity than water, which helps to bind the powder particles more tightly together. This increases the contact area between the powder particles during sintering, thereby increasing the sintering surface area and facilitating the formation of sintering necks, thus improving sintering activity and further enhancing the strength of the porous ceramics. Manganese oxide, due to its similar ionic radius to zircon ions, allows manganese ions to enter the zircon lattice during sintering, replacing some zircon ions and forming lattice defects. The formation of these defects alters the amplitude of thermal vibrations at high temperatures, promoting the sintering process and accelerating the merging and growth of zircon grains, thus further promoting sintering and increasing strength. Meanwhile, the zirconium ions replaced by manganese ions migrate to the surface of the grains and reach the vicinity of the pores. At this time, the introduction of yttrium oxide helps to stabilize the crystal form of zirconium oxide at high temperature and avoid the transformation of tetragonal zirconium oxide to monoclinic zirconium oxide during the cooling process, thereby avoiding the generation of cracks caused by crystal transformation. At the same time, this part of zirconium oxide exists near the pores and can play a toughening role, further improving the strength of zircon porous ceramics.

[0028] In step four of this invention, a two-stage curing method is adopted. The first curing promotes the reaction between the crosslinking agent and the catalyst, so that the monomer and the crosslinking agent react completely to form a complete three-dimensional gel structure. The second curing is to evaporate any water that may be present in the system, and at the same time improve the structure of the green body and stabilize the bubbles generated by the foaming method so that these bubbles will not be crushed by the powder.

[0029] The beneficial effects of this invention are as follows: The foamed gel casting method effectively increases the porosity of zircon porous ceramics and reduces heat radiation transfer efficiency; using sugars as a medium increases the viscosity of the ceramic slurry, bringing the powder particles closer together and increasing the contact area between them, thereby improving sintering activity; introducing sol monomers into the ceramic slurry forms molecular chains that connect the powder particles in the system, forming a high-strength green body while further improving sintering activity; the introduction of yttrium oxide and manganese oxide can both enter the zircon lattice to form lattice defects, thus improving sintering activity, and stabilize the crystal form of zircon oxide generated by the decomposition reaction of some zircon, further improving the strength of the porous ceramic; this invention uses simple raw materials, has a simple preparation process, high production efficiency, low cost, and is easy to industrialize, producing zircon porous ceramics with excellent properties such as stable high-temperature performance, high strength, and low thermal conductivity, making it a preferred material for porous thermal insulation ceramics. Attached Figure Description

[0030] Figure 1 This is a SEM image of the zircon porous ceramic prepared in Example 1 of the present invention. Detailed Implementation

[0031] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0032] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; and the reagents and materials used are commercially available unless otherwise specified.

[0033] In the examples, the zircon powder used had a ZrO2 content ≥63wt%, a SiO2 content ≤32wt%, and a particle size ≤0.074mm; the yttrium oxide powder had a Y2O3 content ≥99.5wt% and a particle size ≤0.074mm; and the manganese oxide powder had a MnO2 content ≥90wt% and a particle size ≤0.088mm.

[0034] Example 1

[0035] A method for preparing high-strength zircon porous ceramics by foaming and casting includes the following steps:

[0036] Step 1: Prepare the syrup solution: Dissolve 60 parts by weight of sucrose at 190°C to form a syrup solution;

[0037] Step 2, ceramic powder premixing: Weigh 35 parts by weight of zircon powder, 2 parts by weight of yttrium oxide powder, and 3 parts by weight of manganese oxide powder respectively, and premix the ceramic powder.

[0038] Step 3: Preparation of ceramic slurry: Add the ceramic powder from Step 2 to the syrup solution from Step 1, and run at 100 rpm for 10 minutes at 190°C; then add sodium dodecyl sulfate (0.8% by weight of ceramic powder) as a foaming agent, polyvinyl alcohol (0.1% by weight of ceramic powder) as a foam stabilizer, and sodium citrate (0.8% by weight of ceramic powder) as a dispersant, and run at 100 rpm for 5 minutes at 190°C; then add methylamide (6% by weight of ceramic powder) as a monomer, N,N'-methyleneacrylamide (10% by weight of monomer) as a crosslinking agent, ammonium persulfate (0.4% by weight of ceramic powder) as an initiator, and tetramethylethylenediamine (0.3% by weight of ceramic powder) as a catalyst, and run the prepared ceramic slurry at 150 rpm for 10 minutes at 190°C;

[0039] Step 4, Injection of Cement: Inject the ceramic slurry obtained in the previous step into the mold, cure at 50°C for 40 hours, then cure at 110°C for 48 hours, and then remove and demold.

[0040] Step 5, sintering treatment: The demolded ceramic green body is baked at a heating rate of 1℃ / min to 1350℃ and held for 2 hours to obtain high-strength zircon porous ceramic.

[0041] The zircon porous ceramic prepared in this embodiment was tested and found to have a bulk density of 0.64 g / cm³. 3 It has an apparent porosity of 87.1%, a room temperature compressive strength of 7.3 MPa, and a thermal conductivity of 0.229 (W / (m·K)) at 900℃.

[0042] The SEM image of the zircon porous ceramic prepared in this embodiment is shown below. Figure 1 In the image, the black part represents pores, the white part represents yttrium oxide, and the gray part represents zircon, which is the main phase. Yttrium oxide exists near the pores and has a toughening effect on porous ceramics. Manganese oxide forms a solid solution and enters the zircon. It can also be seen that the pores introduced by the foaming method are nearly circular.

[0043] Example 2

[0044] A method for preparing high-strength zircon porous ceramics by foaming and casting includes the following steps:

[0045] Step 1: Prepare the syrup solution: Dissolve 55 parts by weight of glucose at 215°C to form a syrup solution;

[0046] Step 2, ceramic powder premixing: Weigh 42 parts by weight of zircon powder, 1 part by weight of yttrium oxide powder, and 2 parts by weight of manganese oxide powder respectively, and premix the ceramic powder.

[0047] Step 3: Ceramic slurry preparation: Add the ceramic powder from Step 2 to the syrup solution from Step 1, and run at 225°C and 200 rpm for 25 minutes; then add sodium dodecylbenzenesulfonate (1.0% by weight of ceramic powder) as a foaming agent, sodium alginate (0.2% by weight of ceramic powder) as a foam stabilizer, and sodium tripolyphosphate (0.5% by weight of ceramic powder) as a dispersant, and run at 215°C and 200 rpm for 7 minutes; then add methacrylamide (4% by weight of ceramic powder) as a monomer, N,N'-methyleneacrylamide (10% by weight of monomer) as a crosslinking agent, ammonium persulfate (0.3% by weight of ceramic powder) as an initiator, and tetramethylethylenediamine (0.6% by weight of ceramic powder) as a catalyst, and run the prepared ceramic slurry at 215°C and 220 rpm for 15 minutes;

[0048] Step 4, Injection of Cement: Inject the ceramic slurry obtained in the previous step into the mold, cure at 70°C for 36 hours, then cure at 100°C for 60 hours, and then demold.

[0049] Step 5, sintering treatment: The demolded ceramic green body is baked at a heating rate of 4℃ / min to 1450℃ and held for 3 hours to obtain high-strength zircon porous ceramic.

[0050] The zircon porous ceramic prepared in this embodiment was tested and found to have a bulk density of 0.82 g / cm³. 3 It has an apparent porosity of 80.2%, a room temperature compressive strength of 8.5 MPa, and a thermal conductivity of 0.288 (W / (m·K)) at 900℃.

[0051] Example 3

[0052] A method for preparing high-strength zircon porous ceramics by foaming and casting includes the following steps:

[0053] Step 1: Prepare the syrup solution: Dissolve 70 parts by weight of fructose at 230°C to form a syrup solution;

[0054] Step 2, ceramic powder premixing: Weigh 25 parts by weight of zircon powder, 3 parts by weight of yttrium oxide powder, and 5 parts by weight of manganese oxide powder respectively, and premix the ceramic powder.

[0055] Step 3: Preparation of ceramic slurry: Add the ceramic powder from Step 2 to the syrup solution from Step 1, and run at 230℃ and 120 rpm for 20 minutes; then add sodium α-olefin sulfonate (0.7% by weight of ceramic powder) as a foaming agent, polyvinyl alcohol (0.15% by weight of ceramic powder) as a foam stabilizer, and sodium hexametaphosphate (0.6% by weight of ceramic powder) as a dispersant, and run at 230℃ and 120 rpm for 8 minutes; then add methylamide (8% by weight of ceramic powder) as a monomer, N,N'-methyleneacrylamide (10% by weight of monomer) as a crosslinking agent, ammonium persulfate (0.7% by weight of ceramic powder) as an initiator, and tetramethylethylenediamine (0.8% by weight of ceramic powder) as a catalyst, and run the prepared ceramic slurry at 230℃ and 230 rpm for 25 minutes;

[0056] Step 4, Injection of Cement: Inject the ceramic slurry obtained in the previous step into the mold, cure at 55°C for 48 hours, then cure at 110°C for 55 hours, and then demold.

[0057] Step 5, sintering treatment: The demolded ceramic green body is baked at a heating rate of 5℃ / min to 1500℃ and held for 3 hours to obtain high-strength zircon porous ceramic.

[0058] The zircon porous ceramic prepared in this embodiment was tested and found to have a bulk density of 0.88 g / cm³. 3 It has an apparent porosity of 76.5%, a room temperature compressive strength of 9.6 MPa, and a thermal conductivity of 0.348 (W / (m·K)) at 900℃.

[0059] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings and examples. However, this should not be construed as limiting the scope of protection of the present invention. The present invention is not limited to the above embodiments. Any changes made within the scope of protection of the claims of the present invention are within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength zircon porous ceramics by foaming and casting, characterized in that, Includes the following steps: Step 1: Prepare the syrup solution: Dissolve the sugars weighed according to the specified weight at a temperature of 190-230°C to form a syrup solution; Step 2: Premixing ceramic powders: Weigh the zircon powder, yttrium oxide powder, and manganese oxide powder according to their respective weight proportions and premix them. Step 3: Preparation of ceramic slurry: Add the ceramic powder from Step 2 to the syrup solution from Step 1, and run at 100-200 rpm for 10-25 minutes at a temperature of 190-230℃; then add the foaming agent, foam stabilizer, and dispersant in proportion, and run at 100-200 rpm for 5-8 minutes at a temperature of 190-230℃; then add the monomer, crosslinking agent, initiator, and catalyst in proportion, and run the prepared ceramic slurry at 150-250 rpm for 10-25 minutes at a temperature of 190-230℃. Step 4, Injection of Cement: Inject the ceramic slurry obtained in the previous step into the mold, cure at 50-70℃ for 36-48 hours, then cure at 100-110℃ for 48-60 hours, and then demold. Step 5, sintering treatment: The demolded ceramic green body is baked at a heating rate of 1-5℃ / min to 1350-1500℃ and held for 1-3 hours to obtain high-strength zircon porous ceramic. The sugar is sucrose; The prepared zircon porous ceramics have a bulk density of 0.6–0.9 g / cm³. 3 It has an apparent porosity of 75-88%, a room temperature compressive strength of 7.2-9.7 MPa, and a thermal conductivity of 0.2-0.35 (W / (m·K)) at 900℃.

2. The method for preparing high-strength zircon porous ceramics by foaming and solidification according to claim 1, characterized in that: The raw material composition and weight percentages for preparing zircon porous ceramics are as follows: 25-42 parts zircon powder, 1-3 parts yttrium oxide powder, 2-5 parts manganese oxide powder, 55-70 parts syrup solution, plus 0.7-1.0% foaming agent, 0.1-0.2% foam stabilizer, 0.5-0.8% dispersant, 4-8% monomer, 10% crosslinking agent, 0.3-0.7% initiator, and 0.3-0.8% catalyst.

3. The method for preparing high-strength zircon porous ceramics by foaming and solidification according to claim 1, characterized in that: The zircon powder contains ZrO2 content ≥63wt% and SiO2 content ≤32wt%; the zircon powder particle size is ≤0.074mm.

4. The method for preparing high-strength zircon porous ceramics by foaming and solidification according to claim 1, characterized in that: The Y2O3 content in the yttrium oxide powder is ≥99.5wt%; the particle size of the yttrium oxide powder is ≤0.074mm.

5. The method for preparing high-strength zircon porous ceramics by foaming and solidification according to claim 1, characterized in that: The MnO2 content in the manganese oxide powder is ≥90wt%; the particle size of the manganese oxide powder is ≤0.088mm.

6. The method for preparing high-strength zircon porous ceramics by foaming and solidification according to claim 1, characterized in that: The foaming agent is sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or sodium α-olefin sulfonate.

7. The method for preparing high-strength zircon porous ceramics by foaming and solidification according to claim 1, characterized in that: The foam stabilizer is polyvinyl alcohol or sodium alginate.

8. The method for preparing high-strength zircon porous ceramics by foaming and solidification according to claim 1, characterized in that: The dispersant is sodium citrate, sodium tripolyphosphate, or sodium hexametaphosphate.

9. The method for preparing high-strength zircon porous ceramics by foaming and solidification according to claim 1, characterized in that: The monomer is methylamide or methacrylamide; the crosslinking agent is N,N'-methyleneacrylamide; the initiator is ammonium persulfate; and the catalyst is tetramethylethylenediamine.

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