A porous zirconia ceramic for steelmaking casting

Abstract

This invention discloses a porous zirconia ceramic for steelmaking casting, belonging to the field of zirconia ceramic technology. This ceramic is prepared by introducing a catalyst-supported composite mineral powder and stabilizing zirconia to form a slurry, followed by foam impregnation, secondary impregnation molding, and gradient sintering. The composite mineral releases active components and generates gas at high temperatures, forming interconnected micropores, increasing porosity and the chemical adsorption capacity for inclusions; simultaneously, catalytically grown silicon nitride whiskers form a three-dimensional network within the framework, significantly enhancing the material's fracture toughness and erosion resistance. The porous ceramic prepared by this invention possesses high structural strength, excellent high-temperature stability, and high filtration efficiency, effectively capturing non-metallic inclusions in molten steel, improving steel purity, and extending filter lifespan.

Description

Technical Field

[0001] This invention belongs to the field of zirconia ceramics technology, and particularly relates to a porous zirconia ceramic for steelmaking casting. Background Technology

[0002] Non-metallic inclusions are a significant factor affecting steel quality, as their presence can significantly reduce fatigue life, toughness, and machinability. Removing inclusions and improving the purity of molten steel are crucial for enhancing steel quality. Especially in the smelting of ultra-low carbon steel, high-strength steel, and special alloy steel, molten steel requires deep deoxidation, desulfurization, and inclusion removal refining processes to obtain high-purity, uniformly performing, high-quality steel. Therefore, introducing highly efficient porous ceramic filters into the steel refining or casting process has become an important technical means to purify molten steel and improve steel quality.

[0003] Currently, porous ceramic materials commonly used for molten steel filtration mainly include alumina, zirconium oxide, silicon carbide, and their composite systems. Among them, zirconium oxide ceramics are considered a suitable candidate material for molten steel filtration due to their excellent high-temperature stability, good resistance to molten steel erosion, and high mechanical strength. However, existing zirconium oxide porous ceramic filters still have several prominent problems in practical applications: the skeleton strength of traditional zirconium oxide porous ceramics is generally low, making them prone to cracking and spalling under the strong scouring action of high-temperature molten steel, resulting in a short service life and difficulty in meeting the requirements of continuous and efficient filtration operations. Secondly, existing porous ceramics often have a relatively dense surface, with a pore structure mainly consisting of closed or semi-open pores, resulting in weak physical and chemical interactions with non-metallic inclusions in molten steel, limiting their ability to capture small inclusions, and requiring further improvement in filtration efficiency. In addition, some filters are prone to phase transformation or sintering densification at high temperatures, leading to a decrease in porosity and reduced air permeability, further affecting their filtration performance and service life.

[0004] Therefore, it is of great significance to develop a zirconia porous ceramic that combines high porosity, high structural strength, and strong inclusion adsorption capacity. Summary of the Invention

[0005] To address the above issues, this invention introduces composite functional mineral powder and catalytically assisted in-situ whisker growth technology to synergistically construct a zirconia porous ceramic filter with high porosity, high structural strength, and strong inclusion adsorption capacity, thereby solving the problems of low frame strength, short service life, and poor filtration effect of existing filters.

[0006] To achieve the above objectives, the following technical solution is adopted: This invention provides a porous zirconia ceramic for steelmaking casting, prepared through the following steps: (a) Preparation of composite functional mineral powder with catalyst supported: After mixing bastnaesite fine powder and dolomite fine powder, the mixture is immersed in a precursor solution containing cobalt or iron catalyst, and then dried and calcined to obtain composite functional mineral powder with catalyst supported. (b) Preparation of ceramic slurry: The composite functional mineral powder is mixed with stabilized zirconia fine powder and elemental silica powder, and then a dispersant, binder and water are added to make a uniform ceramic slurry; (c) Foam impregnation: The ceramic slurry is impregnated in a carrier, excess slurry is removed and dried to obtain a porous green body; (d) Secondary impregnation and preforming: The porous preform is impregnated twice in a precursor solution containing silicon nitride, and then dried to obtain a composite preform; (e) Gradient sintering: The composite green body is first heated to 700-800℃ and held for 1-2 hours, then heated to 1100-1300℃ and held for 1-3 hours, and finally heated to 1350-1450℃ and held for 4-10 hours. Then it is cooled to room temperature in the furnace to obtain the zirconia porous ceramic.

[0007] Further, in step (a), the mass ratio of bastnaesite fine powder to dolomite fine powder is 1:(0.5~2), and the particle size is 1~50μm; the dolomite fine powder contains MgO content ≥30wt% and CaO content ≥50wt%, and the bastnaesite fine powder contains CeO2 content ≥60wt%; the catalyst loading is 0.5~3wt% of the mass of the mixed powder.

[0008] Further, in step (a), the catalyst precursor solution is one of cobalt nitrate solution, cobalt chloride solution, ferric nitrate solution or ferric chloride solution, with a concentration of 0.05~0.2mol / L; the impregnation time of the mixed powder is 2~8h, and the liquid-solid volume-to-mass ratio is (2~5)mL:1g; Furthermore, in step (a), the drying conditions are drying at 80~120℃ for 4~12h, and the calcination conditions are calcination at 500~700℃ in air atmosphere for 2~6h.

[0009] Further, in step (b), the mass ratio of each powder is as follows: 60-80 parts of stabilized zirconia fine powder, 10-25 parts of composite functional mineral powder, and 2-8 parts of elemental silicon powder; the stabilized zirconia fine powder is doped with yttrium oxide accounting for 3-8% of the mass fraction of stabilized zirconia.

[0010] Further, in step (b), the dispersant is one of ammonium polycarboxylate, sodium tripolyphosphate, or sodium hexametaphosphate, and the amount added is 0.2 to 1.0% of the total mass of the powder.

[0011] Further, in step (b), the binder is polyvinyl alcohol, sodium carboxymethyl cellulose or hydroxypropyl methyl cellulose, and the amount added is 1 to 5% of the total mass of the powder; the amount of water added is 30 to 60% of the total mass of the powder.

[0012] Further, in step (c), the carrier is polyurethane foam with a pore size of 5~50ppi and an impregnation time of 10~60s; excess slurry is removed by extrusion with an extrusion pressure of 0.01~0.05MPa.

[0013] Furthermore, the silicon nitride substance is a solution or dispersion of at least one of silicon nitride, polysilazane, or trichlorosilane, with a mass concentration of 20-60 g / L.

[0014] Further, in step (d), the impregnation method is as follows: after evacuating the porous blank to -0.1~-0.08MPa, it is immersed in the solution or dispersion of the silicon nitride material, and the vacuum impregnation is maintained for 10~30min, and then the atmospheric pressure is restored and impregnation is continued for 1~3h.

[0015] The beneficial effects of this invention are: In this invention, bastnaesite undergoes thermal decomposition to release active CeO2, which generates gas at high temperatures, promoting micropore formation and improving pore connectivity. Simultaneously, CeO2, as a surface-active component, enhances impurity capture efficiency through chemical adsorption and reaction with oxide inclusions such as Al2O3 and SiO2 in molten steel. Dolomite provides MgO and CaO, which react with other components in the system at high temperatures, promoting liquid phase formation and whisker development. It also acts as a structural stabilizer, improving the phase stability of zirconium oxide. The supported cobalt and iron catalysts promote the decomposition and whisker growth of silicon nitride-like substances during heat treatment, reducing whisker forming temperature and shortening process time. Silicon nitride whiskers are generated in situ within the zirconia framework through impregnation and gradient sintering processes. The whiskers exhibit strong interfacial bonding with the matrix, avoiding the uneven dispersion and weak interfacial bonding problems caused by externally added whiskers. The whiskers intertwine to form a three-dimensional network within the pores, effectively bridging cracks, deflecting crack paths, and consuming fracture energy. This significantly improves the fracture toughness and thermal shock resistance of the ceramic, making it less prone to cracking and spalling under drastic temperature changes in molten steel, thus extending its service life. This network also serves as a structural framework; even if the matrix is ​​partially damaged, the whisker network can still maintain its overall shape and filtration function, improving the reliability of the filter during continuous use.

[0016] In the final product prepared by this invention, the surface of the ceramic skeleton is rich in active sites composed of cerium oxide and the like, which have a strong chemical adsorption capacity for oxide inclusions; at the same time, the microporous structure formed by the growth of whiskers and mineral decomposition gases greatly increases the specific surface area and the probability of impurity capture. Attached Figure Description

[0017] Figure 1 This is a process flow diagram illustrating the preparation steps of a porous zirconia ceramic for steelmaking casting in various embodiments of the present invention.

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0021] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all commercially available. A process flow diagram of the preparation steps of a porous zirconia ceramic for steelmaking casting is attached to each of the following embodiments. Figure 1 As shown. Example

[0022] A porous zirconia ceramic for steelmaking casting is prepared by the following steps: (a) Preparation of composite functional mineral powder with catalyst supported: Fluorocarbonate cerium ore fine powder and dolomite fine powder were mixed at a mass ratio of 1:0.5 (particle size 1 μm; MgO content ≥30wt%, CaO content ≥50wt%, CeO2 content ≥60wt% in dolomite fine powder), and then impregnated in a 0.05mol / L cobalt nitrate solution (liquid-solid volume mass ratio 2mL:1g, impregnation time 2h), dried at 80℃ for 4h, and then calcined at 500℃ for 2h in air atmosphere to obtain composite functional mineral powder with catalyst supported (the loading amount is 0.5wt% of the mass of the mixed powder); (b) Preparation of ceramic slurry: 60 parts of stabilized zirconia fine powder (which is doped with yttrium oxide accounting for 3% of the mass of stabilized zirconia), 10 parts of the composite functional mineral powder, and 2 parts of elemental silica powder are mixed, and then 0.2% of the total mass of polycarboxylate ammonium salt as a dispersant, 1% of the total mass of polyvinyl alcohol as a binder, and 30% of the total mass of water are added to prepare a uniform ceramic slurry; (c) Foam impregnation: The ceramic slurry is impregnated in a polyurethane foam carrier with a pore size of 5ppi for 10s, and the excess slurry is removed by extrusion (extrusion pressure 0.01MPa) and dried to obtain a porous preform. (d) Secondary impregnation and preforming: The porous preform is impregnated twice in a precursor solution containing silicon nitride, and then dried to obtain a composite preform. The silicon nitride is a dispersion of silicon nitride with a mass concentration of 40 g / L. The impregnation method is as follows: the porous preform is evacuated to -0.1 MPa and then immersed in the solution or dispersion of the silicon nitride. The vacuum impregnation is maintained for 10 min, and then the atmospheric pressure is restored and impregnation is continued for 1 h. (e) Gradient sintering: The composite green body is first heated to 700°C and held for 1 hour, then heated to 1100°C and held for 1 hour, and finally heated to 1350°C and held for 4 hours. Then it is cooled to room temperature in the furnace to obtain the zirconia porous ceramic. Example

[0023] A porous zirconia ceramic for steelmaking casting is prepared by the following steps: (a) Preparation of composite functional mineral powder with catalyst supported: Fluorocarbonate cerium ore fine powder and dolomite fine powder were mixed at a mass ratio of 1:2 (particle size 50 μm; MgO content ≥30 wt%, CaO content ≥50 wt%, CeO2 content ≥60 wt% in dolomite fine powder), and then impregnated in a 0.2 mol / L ferric chloride solution (liquid-solid volume mass ratio 5 mL:1 g, impregnation time 8 h), dried at 120 °C for 12 h, and then calcined at 700 °C for 6 h in air atmosphere to obtain composite functional mineral powder with catalyst supported (the loading amount is 3 wt% of the mass of the mixed powder). (b) Preparation of ceramic slurry: Mix 80 parts of stabilized zirconia fine powder (which is doped with yttrium oxide accounting for 8% of the mass of stabilized zirconia), 25 parts of the composite functional mineral powder, and 8 parts of elemental silica powder, and then add 1.0% sodium tripolyphosphate as a dispersant, 5% sodium carboxymethyl cellulose as a binder, and 60% water as a total mass of powder to prepare a uniform ceramic slurry; (c) Foam impregnation: The ceramic slurry is impregnated in a polyurethane foam carrier with a pore size of 50 ppi for 60 s, and the excess slurry is removed by extrusion (extrusion pressure 0.05 MPa) and dried to obtain a porous preform. (d) Secondary impregnation and preforming: The porous preform is impregnated twice in a precursor solution containing silicon nitride, and then dried to obtain a composite preform. The silicon nitride is a solution of polysilazane with a mass concentration of 40 g / L. The impregnation method is as follows: the porous preform is evacuated to -0.08 MPa and then immersed in the solution or dispersion of the silicon nitride. The vacuum impregnation is maintained for 30 min, and then the pressure is restored to normal and impregnation is continued for 3 h. (e) Gradient sintering: The composite green body is first heated to 800°C and held for 2 hours, then heated to 1300°C and held for 3 hours, and finally heated to 1450°C and held for 10 hours. Then it is cooled to room temperature in the furnace to obtain the zirconia porous ceramic. Example

[0024] A porous zirconia ceramic for steelmaking casting is prepared by the following steps: (a) Preparation of composite functional mineral powder with catalyst supported: Fluorocarbonate cerium ore fine powder and dolomite fine powder were mixed at a mass ratio of 1:1.2 (particle size 25 μm; MgO content ≥30wt%, CaO content ≥50wt%, CeO2 content ≥60wt% in dolomite fine powder), and then impregnated in a 0.12mol / L ferric nitrate solution (liquid-solid volume mass ratio 3.5mL:1g, impregnation time 5h), dried at 100℃ for 8h, and then calcined at 600℃ for 4h in air atmosphere to obtain composite functional mineral powder with catalyst supported (the loading amount is 1.8wt% of the mass of the mixed powder); (b) Preparation of ceramic slurry: 70 parts of stabilized zirconia fine powder (which is doped with yttrium oxide accounting for 5.5% of the mass of stabilized zirconia), 17 parts of the composite functional mineral powder, and 5 parts of elemental silica powder are mixed, and then 0.6% of sodium hexametaphosphate as a dispersant, 3% of hydroxypropyl methylcellulose as a binder and 45% of water as a total mass of powder are added to prepare a uniform ceramic slurry; (c) Foam impregnation: The ceramic slurry is impregnated in a polyurethane foam carrier with a pore size of 27ppi for 35s, and the excess slurry is removed by extrusion (extrusion pressure 0.03MPa) and dried to obtain a porous preform. (d) Secondary impregnation and preforming: The porous preform is impregnated twice in a precursor solution containing silicon nitride, and then dried to obtain a composite preform. The silicon nitride is a solution of trichlorosilane with a mass concentration of 40 g / L. The impregnation method is as follows: the porous preform is evacuated to -0.09 MPa and then immersed in the solution or dispersion of the silicon nitride. The vacuum impregnation is maintained for 20 min, and then the atmospheric pressure is restored and impregnation is continued for 2 h. (e) Gradient sintering: The composite green body is first heated to 750°C and held for 1.5 h, then heated to 1200°C and held for 2 h, and finally heated to 1400°C and held for 6 h. Then it is cooled to room temperature in the furnace to obtain the zirconia porous ceramic.

[0025] Comparative Example 1 The formulation and process of this comparative example are the same as those of Example 3, except that the addition of the composite functional mineral powder supporting the catalyst in step a is omitted. Specifically, in step b, the composite functional mineral powder is not added, the amount of stabilized zirconia fine powder is increased to 87 parts, and the amount of elemental silica powder remains 5 parts. All other steps and parameters are consistent with those of Example 3.

[0026] Comparative Example 2 The formulation and process are basically the same as in Example 3, except that the in-situ whisker growth process in step e is omitted. Specifically, after obtaining the porous blank, step d is not performed, and gradient sintering is carried out directly, with all parameters being consistent with those in Example 3.

[0027] Comparative Example 3 In this comparative example, only stabilized zirconia fine powder (doped with 5.5% yttrium oxide) was used for preparation. Specific steps: The stabilized zirconia fine powder, dispersant, binder, and water were mixed in proportion to form a slurry, using the same process as in Example 3, without adding composite functional mineral powder, elemental silicon powder, or performing whisker growth treatment.

[0028] Results Analysis The performance of the zirconia porous ceramic samples prepared according to the embodiments and comparative examples of the present invention was tested. The test items and methods are as follows: Porosity and pore size distribution: determined by the drainage method.

[0029] Compressive strength at room temperature: tested using a universal testing machine.

[0030] High-temperature flexural strength: Measure the width, thickness, and blade spacing of the sample at room temperature using vernier calipers, accurate to 0.1 mm; heat the furnace to 1400℃, hold for 10 minutes in an empty furnace, then quickly push the sample from room temperature onto the blade in the furnace via a slide rail, and hold at 1400℃ for 3 minutes; apply pressure continuously and uniformly at a rate of 0.15 MPa / s until the sample breaks, and record the maximum load F indicated. See GB / T 25139-2025 "Foamed Ceramic Filters for Foundry" for related content.

[0031] The high-temperature flexural strength of the sample is The value is expressed in MPa and is calculated using the following formula: In the formula:

[0032] The maximum load at which the sample breaks, expressed in Newtons (N). : Spacing between the lower cutting edges, in millimeters (mm); : Width of the middle part of the sample, in millimeters (mm); Thickness at the center of the sample, in millimeters (mm).

[0033] Inclusion adsorption capacity simulation experiment: The porous ceramic sample was placed in a high-temperature furnace. Under the protection of argon at 1550℃, air was blown into the molten simulated steel and stirred to allow it to pass through the sample. After filtration, the removal rate of Al2O3 in the molten steel was analyzed.

[0034] The test results are shown in Table 1.

[0035] Table 1 Comparison of Test Results for Zirconia Porous Ceramic Samples As shown in Table 1, the zirconia porous ceramics prepared in the three embodiments of this invention are superior to the comparative examples in terms of porosity, compressive strength, high-temperature flexural strength, and inclusion adsorption capacity, with Example 3 showing the most outstanding performance. Comparing the embodiments with Comparative Example 1, although Comparative Example 1 retains the whisker network, its compressive strength, high-temperature flexural strength, and Al2O3 removal rate are significantly lower than those of the embodiments. This is because it lacks the active CeO2 provided by bastnaesite, resulting in a reduction in chemisorption sites and the MgO / CaO provided by dolomite. This indicates that the composite minerals are not only functional additives but also key to optimizing the matrix microstructure, enhancing interfacial bonding, and providing chemical activity, forming the basis for toughening and functionalization together with the whisker network. In contrast, the absence of whiskers in Comparative Example 2 leads to a sharp decrease in compressive strength and high-temperature flexural strength, which are the lowest among all samples. Comparative Example 3 exhibits the lowest performance across all parameters, with low compressive strength and poor high-temperature flexural strength. This indicates that the present invention ensures the high-temperature stability of zirconium oxide by adding yttrium oxide stabilizer, stabilizing components in the composite mineral, and the supporting effect of the whisker network, while simultaneously improving porosity, strength, and functionality.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0037] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A porous zirconia ceramic for steelmaking casting, characterized in that: Prepared by the following steps: (a) Preparation of composite functional mineral powder with catalyst supported: After mixing bastnaesite fine powder and dolomite fine powder, the mixture is immersed in a precursor solution containing cobalt or iron catalyst, and then dried and calcined to obtain composite functional mineral powder with catalyst supported. (b) Preparation of ceramic slurry: The composite functional mineral powder is mixed with stabilized zirconia fine powder and elemental silica powder, and then a dispersant, binder and water are added to make a uniform ceramic slurry; (c) Foam impregnation: The ceramic slurry is impregnated in a carrier, excess slurry is removed and dried to obtain a porous green body; (d) Secondary impregnation and preforming: The porous preform is impregnated twice in a precursor solution containing silicon nitride, and then dried to obtain a composite preform; (e) Gradient sintering: The composite green body is first heated to 700-800℃ and held for 1-2 hours, then heated to 1100-1300℃ and held for 1-3 hours, and finally heated to 1350-1450℃ and held for 4-10 hours. Then it is cooled to room temperature in the furnace to obtain the zirconia porous ceramic.

2. The porous zirconia ceramic for steelmaking casting according to claim 1, characterized in that: In step (a), the mass ratio of bastnaesite fine powder to dolomite fine powder is 1:(0.5~2), and the particle size is 1~50μm; the dolomite fine powder contains MgO content ≥30wt% and CaO content ≥50wt%, and the bastnaesite fine powder contains CeO2 content ≥60wt%; the catalyst loading is 0.5~3wt% of the mass of the mixed powder.

3. The porous zirconia ceramic for steelmaking casting according to claim 2, characterized in that: In step (a), the catalyst precursor solution is one of cobalt nitrate solution, cobalt chloride solution, ferric nitrate solution or ferric chloride solution, with a concentration of 0.05~0.2mol / L; the impregnation time of the mixed powder is 2~8h, and the liquid-solid volume-to-mass ratio is (2~5)mL:1g.

4. The porous zirconia ceramic for steelmaking casting according to claim 3, characterized in that: In step (a), the drying conditions are drying at 80~120℃ for 4~12h, and the calcination conditions are calcination at 500~700℃ in air atmosphere for 2~6h.

5. The porous zirconia ceramic for steelmaking casting according to claim 4, characterized in that: In step (b), the mass ratio of each powder is as follows: 60-80 parts of stabilized zirconia fine powder, 10-25 parts of composite functional mineral powder, and 2-8 parts of elemental silicon powder; the stabilized zirconia fine powder is doped with yttrium oxide accounting for 3-8% of the mass fraction of stabilized zirconia.

6. The porous zirconia ceramic for steelmaking casting according to claim 5, characterized in that: In step (b), the dispersant is one of ammonium polycarboxylate, sodium tripolyphosphate, or sodium hexametaphosphate, and the amount added is 0.2 to 1.0% of the total mass of the powder.

7. The porous zirconia ceramic for steelmaking casting according to claim 6, characterized in that: In step (b), the binder is polyvinyl alcohol, sodium carboxymethyl cellulose, or hydroxypropyl methyl cellulose, and the amount added is 1-5% of the total mass of the powder; the amount of water added is 30-60% of the total mass of the powder.

8. The porous zirconia ceramic for steelmaking casting according to claim 7, characterized in that: In step (c), the carrier is polyurethane foam with a pore size of 5~50ppi and an impregnation time of 10~60s; excess slurry is removed by extrusion with an extrusion pressure of 0.01~0.05MPa.

9. The porous zirconia ceramic for steelmaking casting according to claim 8, characterized in that: The silicon nitride substance is a solution or dispersion of at least one of silicon nitride, polysilazane, or trichlorosilane, with a mass concentration of 20-60 g / L.

10. The porous zirconia ceramic for steelmaking casting according to claim 9, characterized in that: In step (d), the impregnation method is as follows: after evacuating the porous preform to -0.1 to -0.08 MPa, immerse it in the solution or dispersion of the silicon nitride material, maintain vacuum impregnation for 10 to 30 minutes, and then restore normal pressure to continue impregnation for 1 to 3 hours.

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