A porous ultra-high temperature carbide ceramic with high strength and stepped pore size distribution and its preparation method

Abstract

The present invention discloses a porous ultrahigh temperature carbide ceramic with a high-strength stepped pore size distribution and a preparation method thereof. N portions of a mixture are prepared, and any portion of the mixture consists of mixed powder and ultrahigh temperature metal wires; any portion of the mixed powder consists of ultrahigh temperature carbide powder, a sintering aid, a binder, and a pore-forming agent. In any two portions of the mixture, the particle sizes of the pore-forming agent are different, and only the particle sizes of the pore-forming agent are different. Then, the N portions of raw materials are laid in sequence in a mold. During the laying process, the ultrahigh temperature metal wires are controlled to form a criss-cross network structure, and the pore-forming agent is laid in the order of particle size from large to small or from small to large. After the laying is completed, the pore-forming agent is pressed and formed to obtain a compact, and the compact is sintered to obtain the product.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic material preparation, and in particular relates to a porous ultra-high temperature carbide ceramic with high-strength stepped pore size distribution and a preparation method thereof. Background Art

[0002] Ultra-high-temperature carbide ceramics, such as hafnium carbide (HfC), tantalum carbide (TaC), and zirconium carbide (ZrC), have broad application prospects in cutting-edge fields such as aerospace, energy, and national defense due to their excellent high-temperature performance, wear resistance, corrosion resistance, and oxidation resistance. With the continuous advancement of science and technology, the performance requirements for ultra-high-temperature ceramic materials are becoming increasingly stringent. Not only are they required to possess excellent high-temperature mechanical properties, but they are also expected to possess specific microstructures and porosities to meet the needs of specialized applications such as heat exchange, catalyst supports, and biomedicine.

[0003] Ultra-high temperature carbide ceramics with porous structures have the characteristics of low density and high specific surface area, and have great application prospects. However, the current methods for preparing porous ultra-high temperature carbide ceramics have some limitations. For example, traditional porous ceramics face the challenge of balancing mechanical properties and functionality: although high porosity can achieve functional requirements such as lightweight and high permeability, it will significantly reduce the strength and thermal shock resistance of the material, especially in ultra-high temperature and thermal-mechanical coupling environments. Structural failure is prone to occur. Some advanced preparation technologies, such as template method and freeze-drying method, although they can regulate the pore structure to a certain extent, are complex and costly, making it difficult to achieve large-scale production.

[0004] In addition, the existing technology for porous ultra-high temperature carbide ceramics has not been sufficiently optimized for pore size distribution, and cannot meet the refined material performance requirements of specific application scenarios. For example, in catalyst support applications, pores of different sizes are required to respectively achieve the transport of reactants and the conduct of catalytic reactions; in the biomedical field, a specific pore size distribution facilitates the attachment and growth of cells. Therefore, developing a method for preparing porous ultra-high temperature carbide ceramics with high strength and a stepped pore size distribution is of great significance for promoting the application of such materials in more fields. Summary of the Invention

[0005] In view of the problems in the prior art of porous ultra-high temperature carbide ceramics such as difficulty in precise control of pore size distribution, insufficient strength, and complex preparation process, the first object of the present invention is to provide a method for preparing porous ultra-high temperature carbide ceramics with high-strength stepped pore size distribution. The preparation method of the present invention can achieve precise control of the pore size distribution of porous ultra-high temperature carbide ceramics, forming a stepped pore structure and a continuous network structure inside the ceramics, thereby significantly improving the strength of the ceramics, achieving coordinated optimization of structural uniformity and structural stability, and at the same time simplifying the preparation process, reducing costs, and improving production efficiency, thereby meeting the needs of aerospace, energy, national defense and other fields for high-performance porous ultra-high temperature ceramic materials.

[0006] The second object of the present invention is to provide a porous ultra-high temperature carbide ceramic with high strength and stepped pore size distribution prepared by the above preparation method.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for preparing a porous ultrahigh temperature carbide ceramic with a high-strength stepped pore size distribution. The method comprises the following steps: preparing N portions of a mixture, wherein any portion of the mixture is composed of a mixed powder and an ultrahigh temperature metal wire; wherein any portion of the mixed powder is composed of an ultrahigh temperature carbide powder, a sintering aid, a binder, and a pore-forming agent; wherein the particle sizes of the pore-forming agent in any two portions of the mixture are different, and only the particle sizes of the pore-forming agent are different; then, the N portions of the mixture are sequentially laid in a mold; during the laying process, the ultrahigh temperature metal wires are controlled to form a crisscross network structure; and simultaneously, the pore-forming agent is laid in an order of particle size from large to small or from small to large; after the laying is completed, the pore-forming agent is pressed and formed into a compact; and the compact is sintered to obtain the product.

[0009] In the mixture, the mass fraction of ultrahigh temperature carbide powder is 10-90%, the mass fraction of ultrahigh temperature metal wire is 3-50%, the mass fraction of sintering aid is 1-15%, the mass fraction of binder is 1-20%, and the mass fraction of pore former is 5-30%;

[0010] The metal elements in the ultrahigh temperature carbide powder are the same as the metal elements in the ultrahigh temperature metal wire;

[0011] The ultra-high temperature carbide powder is selected from one of hafnium carbide (HfC), tantalum carbide (TaC), and zirconium carbide (ZrC);

[0012] The sintering aid is selected from at least one of nickel powder, cobalt powder, molybdenum disilicide, and tantalum disilicide;

[0013] The binder is selected from at least one of polyvinyl alcohol (PVA), polyethylene glycol (PEG), acrylic resin, and methyl cellulose (MC);

[0014] The pore-forming agent is selected from at least one of sodium chloride, potassium chloride, ammonium bicarbonate, ammonium carbonate, ammonium chloride, natural fiber, and high molecular polymer.

[0015] The preparation method of the present invention directly adopts a layering method to lay raw materials of different particle sizes in a mold in a certain order. Finally, during the sintering process, the pore-forming agent can be volatilized or decomposed and removed at high temperature to adjust the porosity and pore size, thereby obtaining a porous ultra-high temperature carbide ceramic with a stepped pore size distribution.

[0016] In the present invention, a criss-cross network structure is formed by ultra-high temperature metal wires to ultimately form a skeleton structure of a porous ultra-high temperature carbide ceramic, which not only improves the overall strength of the porous ultra-high temperature carbide ceramic, but also avoids the stratification of the porous ultra-high temperature carbide ceramic and the generation of cracks. In addition, in the present invention, ultra-high temperature carbide powder is used as the raw material of carbide, and the densification of tantalum carbide ceramics is promoted and the sintering temperature is reduced by sintering aids. By controlling the amount of sintering aids and binders within the scope of the present invention, the volume shrinkage and the volatilization of other components to generate pores can be greatly reduced, and the pores are mainly generated by the volatilization of the pore-forming agent, thereby obtaining a porous ultra-high temperature carbide ceramic with a specific pore structure in a controllable manner.

[0017] In the present invention, in any two raw materials, only the particle size of the pore former is different, and the other components are the same, thereby ensuring that the gradient porous structure is controlled by the pore former.

[0018] In a preferred embodiment, in the mixture, the mass fraction of ultrahigh temperature carbide powder is 75-85%, the mass fraction of ultrahigh temperature metal wire is 5-15%, the mass fraction of sintering aid is 1-4%, the mass fraction of binder is 1-3%, and the mass fraction of pore former is 5-8%.

[0019] In a preferred embodiment, the particle size of the ultrahigh temperature carbide powder is 0.5-500 μm. Controlling the particle size of the ultrahigh temperature carbide powder within the above range is beneficial to the spreading of the raw materials and the progress of sintering, and ultimately makes the product stronger.

[0020] In a preferred embodiment, the high molecular polymer is selected from at least one of polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), polycarbonate (PC), polyurethane (PU), polyimide (PI), and polyacrylamide (PAM).

[0021] In a preferred embodiment, the particle size of the pore-forming agent in each of the N parts of the mixture is 0.2-10 mm. In the present invention, any part of the mixture needs to be controlled within the above range. If the particle size of the pore-forming agent is smaller, it is easy to agglomerate during the mixing process, resulting in uneven pore distribution and even the formation of closed pores, which reduces the through-porosity and poor pore connectivity. If the particle size of the pore-forming agent is too large, the pore passages of the porous ceramic are too large, the mechanical strength of the material is reduced, and the excessively large pore size will lead to poor filtration effect, which will not achieve the desired results.

[0022] In a preferred embodiment, N≥2.

[0023] In a preferred embodiment, the diameter of the ultrahigh temperature metal wire is 0.3-5 mm. Experiments have found that the performance of the ultrahigh temperature metal wire is optimal within this range. If the diameter of the metal wire is too small, it is not conducive to improving the strength. If the diameter is too large, it will affect the formation of high porosity.

[0024] In a preferred embodiment, the ultrahigh-temperature metal wire is selected from ultrahigh-temperature metal short wires and / or ultrahigh-temperature metal long wires, and the length of the ultrahigh-temperature metal short wires ranges from 1 to 50 mm. Ultrahigh-temperature metal wires have excellent toughness. By forming a crisscross network of ultrahigh-temperature metal wires, the stability of the green body can be effectively enhanced, effectively preventing cracking during the sintering process of the porous ceramic and ensuring the subsequent strength of the porous ceramic.

[0025] In a preferred solution, during the laying process, the mixed powder is laid first to cover the bottom of the mold, and then the ultra-high temperature metal wire is laid, and finally the mixed powder is laid again until the mixed powder completely wraps the ultra-high temperature metal wire.

[0026] Further preferably, when the ultra-high temperature metal wire is selected from ultra-high temperature metal short wire, the ultra-high temperature metal wire is placed in a criss-cross pattern during laying; when the ultra-high temperature metal wire is selected from ultra-high temperature metal long wire, it is first woven into a criss-cross network skeleton structure and then laid; when the ultra-high temperature metal wire is selected from ultra-high temperature metal long wire and ultra-high temperature metal short wire, the ultra-high temperature metal long wire is woven into a criss-cross network skeleton structure and laid, and then the ultra-high temperature metal short wire is mixed with the mixed powder and laid together.

[0027] Experiments have found that the best reinforcement effect is achieved when the ultra-high temperature metal wire is completely wrapped with mixed powder. In addition, when the ultra-high temperature metal filaments are woven into a criss-cross network skeleton structure and laid on top of the mixed powder, ultra-high temperature metal short wires can be further added to the network skeleton structure woven from the ultra-high temperature metal filaments to jointly play a role in strengthening the structure.

[0028] In a preferred embodiment, the pressing pressure is 5-70 MPa and the holding time is 2-100 min. The ultra-high temperature metal wire is added to the green compact after pressing, and the metal wire has a toughening effect, making the green compact less likely to fall apart and the edges less likely to fall off.

[0029] A preferred solution is to place the green compact in a graphite mold. In the present invention, instead of adding additional carbon powder or the like as a carbon source, the pressed green compact is placed in a graphite mold for sintering. Firstly, some binders decompose to provide a carbon source, secondly, the graphite mold provides the carbon source, and thirdly, because the high-temperature sintering furnace itself contains a carbon atmosphere, this carbon source reacts with the ultra-high-temperature metal wire to form corresponding metal carbides. Experimental findings indicate that this can further enhance strength. Adding carbon powder as a carbon source, however, does not decompose at high temperatures and is likely to leave residues, forming impurities that reduce the strength of the product.

[0030] In a preferred embodiment, the sintering process is as follows: heating the material to 300-650°C at a heating rate of 0.5-6°C / min and holding for 0.2-2 hours, followed by heating the material to 2000-2500°C at a heating rate of 2-20°C / min and holding for 0.5-2 hours. This sintering process removes the pore-forming agent, leaving interconnected open pores and forming a porous structure. Simultaneously, the ultrahigh-temperature metal is transformed into a continuous network of ultrahigh-temperature carbides, enhancing the strength of the porous ceramic. Ultimately, a high-strength porous ultrahigh-temperature carbide ceramic with a stepped pore size distribution is formed.

[0031] The present invention also provides a porous ultra-high temperature carbide ceramic with high strength and stepped pore size distribution prepared by the above preparation method.

[0032] Principles and advantages

[0033] 1. Precise control of pore size distribution:

[0034] By using pore-forming agents of different types and particle sizes, combined with a layered design, the present invention enables precise control of the pore size distribution of porous ultrahigh-temperature carbide ceramics, creating a stepped pore structure. This precise pore size distribution can meet the specific material performance requirements of different application scenarios.

[0035] 2. Significantly improve ceramic strength:

[0036] During the manufacturing process, this invention significantly enhances the strength of porous ultrahigh-temperature carbide ceramics by optimizing mixing, molding, and sintering parameters, and by incorporating ultrahigh-temperature metal wires into the ceramic to form a network structure. This enhanced ceramic is better able to withstand mechanical loads under extreme conditions such as high temperature and high pressure.

[0037] 3. Simplify the preparation process and reduce costs:

[0038] The preparation method of the present invention is simple, easy to operate and control, and does not require complex equipment or tedious steps. Compared with some advanced preparation techniques (such as template methods and freeze-drying), the present invention significantly reduces production costs and improves production efficiency, facilitating the large-scale production and industrial application of porous ultrahigh-temperature carbide ceramics.

[0039] 4. Broad application prospects:

[0040] The porous ultrahigh temperature carbide ceramics with high strength and stepped pore size distribution prepared by the present invention have broad application prospects in the fields of aerospace, energy, biomedicine, etc. due to their excellent performance and controllable pore size structure.

[0041] 5. Reusability:

[0042] Since the preparation involves the addition of ultra-high temperature metal wire, a network structure is formed inside the ceramic, the strength of the porous ceramic is enhanced, it is not easy to crack, and it can be reused, reducing the cost of use. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The upper layer morphology of the porous tantalum carbide ceramic prepared in Example 1.

[0044] Figure 2 The lower layer morphology of the porous tantalum carbide ceramic prepared in Example 1.

[0045] Figure 3 Cross-sectional morphology of the porous hafnium carbide ceramic prepared in Example 2.

[0046] Figure 4 Surface morphology of the porous tantalum carbide ceramic in Comparative Example 1.

[0047] Figure 5 Cross-sectional morphology of the porous tantalum carbide ceramic in Comparative Example 1.

[0048] Figure 6 Surface morphology of the porous tantalum carbide ceramic in Comparative Example 2. DETAILED DESCRIPTION

[0049] Example 1

[0050] Preparation of Porous Tantalum Carbide Ceramics

[0051] 1. Raw material ratio: TaC powder (particle size 5 μm) 85wt%, PVB content 1wt%, sintering aid metal nickel powder 2wt%, NaCl pore former (layered particle size: lower layer average particle size 0.4mm, upper layer average particle size 0.7mm) 5wt%, tantalum wire (diameter 0.5mm) 7wt%.

[0052] 2. Prepare the upper and lower layer mixtures separately, depending on the size of the pore-forming agent. Thoroughly mix TaC powder, PVB, nickel metal powder, and sodium chloride pore-forming agent. Cut tantalum wire into 50mm lengths; first place a small amount of the lower layer mixture in the mold, then add the tantalum wire, crisscrossing the tantalum wires, and then add the mixture. Repeat this process until the lower layer mixture is added. Continue adding the upper layer mixture in the same manner as the lower layer mixture. Once all materials have been added, close the mold, place it in the press, and apply a pressure of 10MPa for 2 minutes.

[0053] 3. Place the prepared mold obtained in step 2 into a high-temperature furnace, and heat it to 400°C at a rate of 5°C / min under an inert atmosphere. After holding it for 30 minutes, continue to heat it to 2200°C at a rate of 5°C / min and hold it for 1 hour. The surface morphology of the porous ceramic lower layer is as follows: Figure 1 As shown, the upper surface morphology is Figure 2 As shown in the figure, the pore-forming agent used in the lower layer has a smaller particle size, resulting in a porous ceramic with widely spaced pores and small pores, with an average pore size of approximately 0.4 mm. The pore-forming agent used in the upper layer has a larger particle size than the lower layer, resulting in slightly larger pores on the ceramic surface, with smaller pore spacing and an average pore size of approximately 0.7 mm. The ceramic is relatively strong, with a compressive strength of 126 MPa, a flexural strength of 31 MPa, and an overall porosity of approximately 30%.

[0054] Example 2

[0055] Preparation of porous hafnium carbide ceramics:

[0056] 1. Raw material ratio: HfC powder (particle size 10 μm) 80wt%, PVB content 1wt%, sintering aid metal nickel powder 1wt%, sintering aid metal cobalt powder 1wt%, NaCl pore former (layered particle size: lower layer average particle size is 0.4mm, upper layer average particle size is 0.8mm) 5wt%, hafnium metal short wire (diameter 0.5mm) 5wt%, hafnium metal long wire (diameter 0.5mm) 7wt%.

[0057] 2. Prepare the mixtures for the upper and lower layers separately according to the size of the pore-forming agent: fully mix HfC powder, PVB, metal nickel powder, metal cobalt powder, NaCl pore-forming agent, and 20-35mm hafnium metal short wire.

[0058] 3. Preparation of metal wire skeleton: Weave the metal filaments into an interpenetrating network structure as a skeleton according to a certain shape and size.

[0059] 4. First place a small amount of lower layer mixture in the mold, then add the woven metal filament skeleton, continue to add the lower layer mixture, repeat this operation until the lower layer mixture is added, and then continue to add the upper layer material in the same way as adding the lower layer material. When the material is added, close the mold, put it into the press, apply a pressure of 10MPa, and maintain the pressure for 2 minutes.

[0060] 5. Place the prepared mold obtained in step 4 into a high-temperature furnace. In an inert atmosphere, heat it to 400°C at a rate of 5°C / min, keep it warm for 30 minutes, then continue to heat it to 2200°C at a rate of 5°C / min, keep it warm for 1 hour. The cross section of the porous hafnium carbide ceramic is as follows: Figure 3 As shown in the figure, the pore-forming agent used in the lower layer has a small particle size, resulting in small pores with an average pore size of approximately 0.4 mm. The pores in the upper layer are slightly larger, with an average pore size of approximately 0.8 mm. The ceramic is relatively strong, with a compressive strength of 95 MPa, a flexural strength of 41 MPa, and an overall porosity of approximately 32.5%.

[0061] Comparative Example 1

[0062] Other conditions were the same as in Example 1, except that no tantalum wire was added. The results were as follows: Figure 4 and Figure 5 As shown in the figure, cracks appear on the surface of the porous ceramic and cracks appear inside the ceramic. The reduction of metal wire increases the risk of ceramic cracking, and the ceramic flexural strength is only 8MPa.

[0063] Comparative Example 2

[0064] Preparation of porous tantalum carbide ceramics:

[0065] 1. Raw material ratio: TaC powder (particle size 80-150μm) 80wt%, PVB content 1.5wt%, sintering aid metal cobalt powder 2wt%, KCl pore former (particle size 0.6-1.5mm) 7wt%.

[0066] 2. Thoroughly mix TaC powder, PVB, metal cobalt powder, and KCl pore-forming agent. Slowly and evenly spread the mixture in the mold until all materials are added. Close the mold, place it in the press, apply a force of 10MPa, and maintain the pressure for 2 minutes.

[0067] 3. Place the prepared mold obtained in step 2 into a high temperature furnace, and heat it to 400°C at a rate of 5°C / min under an inert atmosphere. Keep it warm for 30 minutes, then continue to heat it to 2200°C at a rate of 5°C / min and keep it warm for 1 hour. The surface of the porous tantalum carbide ceramic is as follows: Figure 6 As shown in the figure, the pores of the tantalum carbide porous ceramic are uniform, but cracks appear (pointed by the arrows). This is because the tantalum carbide powder shrinks during high-temperature sintering and generates thermal stress because the ultra-high-temperature metal wire is not added to the ceramic.

Claims

1. A method for preparing porous ultrahigh temperature carbide ceramics with high strength and stepped pore size distribution, characterized by: N portions of a mixture are prepared, wherein any portion of the mixture is composed of a mixed powder and ultrahigh temperature metal wires; any portion of the mixed powder is composed of ultrahigh temperature carbide powder, a sintering aid, a binder, and a pore-forming agent; and in any two portions of the mixture, the particle sizes of the pore-forming agent are different, and only the particle sizes of the pore-forming agent are different. Then, the N portions of the mixture are laid in sequence in a mold. During the laying process, the ultrahigh temperature metal wires are controlled to form a criss-cross network structure, and the pore-forming agent is laid in an order of particle size from large to small or from small to large. After the laying is completed, the green compact is obtained by pressing and forming, and the green compact is sintered. In the mixture, the mass fraction of ultrahigh temperature carbide powder is 10-90%, the mass fraction of ultrahigh temperature metal wire is 3-50%, the mass fraction of sintering aid is 1-15%, the mass fraction of binder is 1-20%, and the mass fraction of pore former is 5-30%; The metal elements in the ultrahigh temperature carbide powder are the same as the metal elements in the ultrahigh temperature metal wire; The ultra-high temperature carbide powder is selected from one of hafnium carbide, tantalum carbide and zirconium carbide; The sintering aid is selected from at least one of nickel powder, cobalt powder, molybdenum disilicide, and tantalum disilicide; The binder is selected from at least one of polyvinyl alcohol, polyethylene glycol, acrylic resin, and methyl cellulose; The pore-forming agent is selected from at least one of sodium chloride, potassium chloride, ammonium bicarbonate, ammonium carbonate, ammonium chloride, natural fiber, and high molecular polymer.

2. The method for preparing a porous ultrahigh temperature carbide ceramic with high strength and stepped pore size distribution according to claim 1, characterized in that: The particle size of the ultra-high temperature carbide powder is 0.5-500 μm.

3. The method for preparing a porous ultrahigh temperature carbide ceramic with high strength and stepped pore size distribution according to claim 1, characterized in that: The high molecular polymer is selected from at least one of polyethylene terephthalate, polymethyl methacrylate, polyvinyl chloride, polyethylene, polypropylene, polystyrene, polyamide, polycarbonate, polyurethane, polyimide, and polyacrylamide.

4. The method for preparing a porous ultrahigh temperature carbide ceramic with high strength and stepped pore size distribution according to claim 1, characterized in that: The particle size of the pore-forming agent in the N parts of the mixture is 0.2-10 mm; Said N≥2.

5. The method for preparing a porous ultrahigh temperature carbide ceramic with high strength and stepped pore size distribution according to claim 1, characterized in that: The diameter of the ultra-high temperature metal wire is 0.3-5 mm; The ultrahigh temperature metal wire is selected from ultrahigh temperature metal short wire and / or ultrahigh temperature metal long wire, and the length of the ultrahigh temperature metal short wire is 1-50 mm; During the laying process, the mixed powder is laid first to cover the bottom of the mold, and then the ultra-high temperature metal wire is laid, and finally the mixed powder is laid again until the mixed powder completely wraps the ultra-high temperature metal wire.

6. The method for preparing a porous ultrahigh temperature carbide ceramic with high strength and stepped pore size distribution according to claim 5, characterized in that: When the ultra-high temperature metal wire is selected from ultra-high temperature metal short wire, the ultra-high temperature metal wire is placed in a crisscross pattern during laying. When the ultra-high temperature metal wire is selected from ultra-high temperature metal long wire, it is first woven into a crisscross network skeleton structure before laying. When the ultra-high temperature metal wire is selected from ultra-high temperature metal long wire and ultra-high temperature metal short wire, the ultra-high temperature metal long wire is woven into a crisscross network skeleton structure and laid, and then the ultra-high temperature metal short wire is mixed with the mixed powder and laid together.

7. The method for preparing a porous ultrahigh temperature carbide ceramic with high strength and stepped pore size distribution according to claim 1, characterized in that: The compression molding pressure is 5-70 MPa, and the holding time is 2-100 min.

8. The method for preparing a porous ultrahigh temperature carbide ceramic with high strength and stepped pore size distribution according to claim 1, characterized in that: The compact was placed in a graphite mold.

9. The method for preparing a porous ultrahigh temperature carbide ceramic with high strength and stepped pore size distribution according to claim 1, characterized in that: The sintering process is: heating to 300-650° C. at a heating rate of 0.5-6° C. / min and keeping the temperature for 0.2-2 h, then heating to 2000-2500° C. at a heating rate of 2-20° C. / min and keeping the temperature for 0.5-2 h.

10. A porous ultrahigh temperature carbide ceramic with high strength and stepped pore size distribution prepared by the preparation method according to any one of claims 1 to 9.

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