Large-aperture high-porosity porous silicon nitride ceramic material and preparation method thereof

Abstract

The invention belongs to the technical field of precise ceramic material preparation, and discloses a large-aperture high-porosity porous silicon nitride ceramic and a preparation method thereof. The preparation method comprises the following steps: carrying out ball milling on alpha-Si3N4 and a sintering aid, and uniformly mixing to obtain premixed powder; the preparation method comprises the following steps: by taking polymethyl methacrylate microspheres as a pore-forming agent and taking an alcoholic solution of phenolic resin as a binder, uniformly coating a layer of binder on the surface of the pore-forming agent, then adding premixed powder, uniformly coating the premixed powder on the binder layer on the surface of the pore-forming agent by adopting a sweet dumpling rolling type forming method, repeatedly coating a layer of binder, then coating a layer of premixed powder, and finally, carrying out drying, so as to obtain the porous material. The pre-mixed powder is completely coated, such that composite microspheres are obtained; and carrying out pressure forming on the composite microspheres to obtain a green body, and sequentially curing, carbonizing, dumping and sintering to obtain the large-aperture high-porosity porous silicon nitride ceramic material. According to the preparation method disclosed by the invention, the porous silicon nitride ceramic material with large aperture and high porosity can be prepared by controlling the size and the addition amount of the pore forming agent.

Description

Technical Field

[0001] The present invention relates to the technical field of precision ceramic material preparation, and in particular to a large-pore-diameter, high-porosity porous silicon nitride ceramic and a preparation method thereof. Background Art

[0002] Silicon nitride ceramics are considered to be one of the most promising bone implant materials due to their good antibacterial properties, excellent bone ingrowth ability, good bone imaging performance, excellent wear resistance and mechanical properties. The main process for preparing silicon nitride ceramic bone implants is 3D printing technology. The high cost limits its large-scale application, so how to reduce production costs and select a reasonable preparation process is the key to solving the problem. Ceramic artificial joint prostheses such as hip joints and ankle joints also require a composite of a porous layer and a dense layer to meet the requirements of tissue growth and wear resistance. At the same time, rapid batch preparation is also a basic requirement for reducing costs. The dry pressing process has the advantages of a simple molding process and freely adjustable material pore size and porosity. After the process matures, it can be mass-produced.

[0003] At present, most of the porous silicon nitride ceramics in the prior art have a single pore structure, which is quite different from natural bone and is difficult to meet the actual needs of bone transplantation. In order to solve the above technical problems, technicians in this field have proposed that porous silicon nitride ceramics with pore size gradient can be prepared. By forming a composite structure with pore size gradient, the force transmission between the implant and the surrounding tissue can be effectively dispersed and balanced, and the stress shielding phenomenon of the implant material in the human body can be reduced, which can meet the actual needs of bone transplantation.

[0004] However, the preparation method of the pore gradient porous structure bone implant material currently provided by the prior art has cumbersome preparation steps, and there is uneven distribution of the pore former and the ceramic matrix, resulting in poor bonding effect between the ceramic matrix powder, which in turn leads to poor mechanical properties of the prepared porous ceramic material, and it is difficult to effectively disperse and balance the load transfer between the implant and the surrounding tissue, which limits the application of porous ceramic materials in the field of bone transplantation. In addition, in order to improve the mechanical properties of porous ceramic materials, the pore size of the porous layer in the pore gradient porous structure can only be controlled to be <300μm, and it is difficult to obtain a porous silicon nitride ceramic material with a large pore size and high porosity. For example, the prior art CN202310959547.3 provides a method for preparing a porous / dense composite structure silicon nitride material for an artificial hip joint, the prior art first bonds the pore former into a porous green body, prepares silicon nitride and a sintering aid into a slurry, and obtains a porous-dense composite structure by gel injection molding for the preparation of a hip prosthesis. However, the prior art requires the pre-bonding of the pore-forming agent particles. If the strength of the bonding body is too high, it will affect the solidification shrinkage of the slurry and cause the final green body to crack. At the same time, it is also necessary to configure a suitable slurry so that the slurry can fully enter the gaps between the pore-forming agent particles. The prior art CN200920072364.5 provides a method for preparing a porous bone transplant carrier with a pore size gradient including macropores with a pore size of 100 μm to 300 μm and micropores with a pore size of 1 μm to 10 μm based on β-tricalcium phosphate, but the relatively low mechanical properties of the β-tricalcium phosphate material itself limit its application in bone transplantation. Prior art CN200810097865.9 provides a method for obtaining ordered large-aperture porous ceramics by coating a slurry containing a ceramic premixed powder, an adhesive, a dispersant and a regulator on the surface of a pore former, removing the pore former and sintering at high temperature. The prior art requires that the prepared slurry be slowly poured on a screen with monodispersed polystyrene microspheres, stirred evenly with a glass rod, and applied repeatedly as needed to naturally cover the surface of the pore former particles with a layer of slurry, and the water content of the slurry on the surface of the pore former particles be controlled by evaporation of water, and then the pore former particles coated with the ceramic premixed powder are introduced into a mold and pressed into shape. However, this method may have problems such as uneven coating of the slurry on the surface of the pore former and difficulty in accurately controlling the amount of coating. In addition, if the binder of the premixed powder and the pore former are decomposed simultaneously during the carbonization process of preparing porous ceramics using a pore former, cracking will occur if there is stress inside the green body. Summary of the invention

[0005] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a porous silicon nitride ceramic material with large pore size and high porosity and a preparation method thereof. The present invention uses α-Si3N4 as a matrix, uniformly mixes it with a sintering aid to obtain a premixed powder; then uses polymethyl methacrylate microspheres as a pore-forming agent, and after covering the surface of the polymethyl methacrylate microspheres with a layer of ethanol solution of phenolic resin as a binder layer, the premixed powder is adhered and coated on the surface of the pore-forming agent by the "rolling Yuanxiao" method, and then after pressure molding, it is successively cured, carbonized, debinded and sintered at high temperature. By controlling the size of the pore-forming agent and the amount of addition, a porous silicon nitride ceramic material with large pore size and high porosity can be prepared. The porous silicon nitride ceramic material prepared by the preparation method of the present invention has excellent mechanical properties and has a pore gradient composite structure of a dense ceramic matrix layer formed by a premixed powder and a porous layer formed by a pore-forming agent. The formed pore gradient composite structure is similar to the tissue structure of natural bone, and can effectively disperse and balance the load transfer between the implant and the surrounding tissue, which is beneficial to its application in the field of bone transplantation.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: The first object of the present invention is to provide a method for preparing a porous silicon nitride ceramic material with large pore size and high porosity, comprising the following steps: Step 1, preparation of premixed powder: α-Si3N4 is used as a matrix and is mixed with a sintering aid by ball milling to obtain a premixed powder.

[0007] Step 2, preparation of composite microspheres: Polymethyl methacrylate microspheres are used as pore-forming agents, and an alcohol solution of phenolic resin is used as a binder. After a layer of the binder is uniformly coated on the surface of the pore-forming agent, the premixed powder is added, and a rolling-lantern-shaped molding method is adopted to uniformly coat a layer of the premixed powder on the binder layer on the surface of the pore-forming agent. A layer of the binder is coated repeatedly, and then a layer of the premixed powder is coated until all the premixed powder is coated to obtain composite microspheres.

[0008] Step 3, pressure molding: The composite microspheres are press-formed to obtain green compacts.

[0009] Step 4, curing: The green compact is subjected to a curing treatment to cure the phenolic resin in the binder, thereby obtaining a cured green compact.

[0010] Step 5, carbonization treatment and debinding treatment: The solidified green body is subjected to a carbonization treatment and a binder removal treatment in sequence to obtain a porous silicon nitride green body; Step 6, sintering treatment: The porous silicon nitride green body is sintered to obtain a porous silicon nitride ceramic material with large pore size and high porosity.

[0011] It should be noted that the present invention uses α-Si3N4 as a matrix, and forms a premixed powder by premixing α-Si3N4 and a sintering aid. Polymethyl methacrylate microspheres are used as a pore-forming agent, and an alcohol solution of a phenolic resin is used as a binder. A layer of the binder is first sprayed on the surface of the polymethyl methacrylate microspheres, and then the premixed powder is added. The premixed powder is evenly bonded to the surface of the pore-forming agent particles by repeated rolling and wrapping using a rolling lantern molding method to form a composite microsphere. The composite microspheres are then pressurized to compact the premixed powder, and the ceramic powder mud between the pore-forming agents is pressed and fused to form a dense ceramic matrix layer, so as to obtain a green body with a compacted ceramic matrix, uniform distribution of pore-forming agents, and tight bonding between the premixed powders of each component. Then, the obtained green body is successively cured, carbonized, debinded, and sintered to remove the polymethyl methacrylate microspheres, thereby preparing a high-performance large-pore porous silicon nitride ceramic with large pore size, high porosity, no obvious internal defects, and excellent mechanical properties, which greatly reduces the production cost. And the porous silicon nitride ceramic material prepared by the preparation method of the present invention has a dense ceramic matrix layer formed by the premixed powder and an aperture gradient composite structure formed by the pore-forming agent, and the formed aperture gradient composite structure is similar to the tissue structure of natural bone, which can effectively disperse and balance the load transfer between the implant and the surrounding tissue, which is beneficial to its application in the field of bone transplantation.

[0012] The present invention uses an alcohol solution of a phenolic resin as a binder. In some more preferred embodiments of the present invention, the ethanol solution of a phenolic resin is used as a binder, which not only improves the strength of the porous silicon nitride green body, but also effectively inhibits the cracking phenomenon caused by the cracking of the green body due to insufficient green body strength during the carbonization process of the sample prepared using a traditional binder, because the carbonization cracking temperature of the phenolic resin is higher than that of the polymethyl methacrylate microspheres, and the green body strength can be maintained during the carbonization process.

[0013] In some preferred embodiments of the present invention, the sintering aid is one or both of Al2O3 and Y2O3, and the sintering aid accounts for 10wt%~11wt% of the total mass of the premixed powder to ensure that the matrix is ​​dense after sintering.

[0014] In some more preferred embodiments of the present invention, Al2O3 and Y2O3 are used together as sintering aids, and the mass ratio of Al2O3 to Y2O3 is 2:4-6, so as to ensure that the sintered body has excellent mechanical properties.

[0015] In some preferred embodiments of the present invention, the premixed powder accounts for 65% to 80% of the total mass of the composite microspheres, so that the added premixed powder can promote the subsequent pressurization molding process, and the premixed powder can be filled in the pores of the polymethyl methacrylate microspheres, which helps to form a tightly compacted green body.

[0016] In some preferred embodiments of the present invention, when preparing the premixed powder, wet ball milling is used for ball milling and mixing, and the ball milling medium used in the wet ball milling is ethanol, the ball-to-material mass ratio is 2~4:1, the ball mill speed is 150r / min~250r / min, and the ball milling time is 16h~32h.

[0017] During the research process, the present invention found that too little phenolic resin content will cause the viscosity of the binder to be low, resulting in poor fluidity of the premixed powder and low strength of the green body. Increasing the amount of phenolic resin is beneficial to improving the above conditions. Too much phenolic resin will make the powder wrapped by the polymethyl methacrylate microspheres difficult to compact, and the matrix pores are too large, affecting the densification of the matrix. Therefore, in some preferred embodiments of the present invention, the mass concentration of the phenolic resin in the binder is 50%~70%, and the amount of phenolic resin added to the binder is 15%~20% of the mass of the premixed powder.

[0018] In some preferred embodiments of the present invention, when preparing the composite microspheres, the amount of binder applied each time is 8% to 12% of the total amount of the binder.

[0019] It should also be noted that the present invention preferably uses polymethyl methacrylate microspheres as pore-forming agents, and the mass ratio of the pore-forming agent to the premixed powder is 2-5:5-8, so that the pore-forming agent used can form pores in the matrix during subsequent carbonization and debinding treatments.

[0020] In some preferred embodiments of the present invention, the particle size of the pore former is 100 μm to 500 μm. In some more preferred embodiments of the present invention, the pore former is composed of polymethyl methacrylate microspheres with a particle size of 100 μm to 200 μm and polymethyl methacrylate microspheres with a particle size of 400 μm to 500 μm, so as to ensure that the maximum pore size of the porous silicon nitride ceramic exceeds 400 μm and can form a porous structure with different pore sizes.

[0021] During the research process, the present invention found that during the pressure forming process, too little pressure will cause the matrix of the green body to not be compacted, and cracks will be generated during the carbonization and debinding process. Too much pressure will cause the green body to be too compact, resulting in excessive stress rebound effect due to the difference in elastic modulus between the pore-forming agent and the silicon nitride matrix, causing cracking of the green body after demolding. Therefore, in some preferred embodiments of the present invention, the pressure of the pressure forming is 60MPa~100MPa.

[0022] In some preferred embodiments of the present invention, the curing treatment temperature is 80°C~150°C, and the treatment time is 8h~12h to ensure that the phenolic resin is completely cured to improve the green body strength and prevent the green body from cracking due to thermal expansion and cracking exhaust of the pore-forming agent during the carbonization process.

[0023] In some preferred embodiments of the present invention, the carbonization treatment is carried out by the following steps: In an Ar atmosphere, the solidified green body is heated from room temperature to 350°C at a rate of 1°C / min~2°C / min, then heated to 600°C at a rate of 0.25°C / min~0.5°C / min, kept at that temperature for 2h~4h, and finally cooled to room temperature with the furnace to obtain a carbonized green body.

[0024] In some preferred embodiments of the present invention, the debinding process is performed by the following steps: In an air atmosphere, the carbonized green body is heated from room temperature to 350°C at a rate of 1°C / min~2°C / min, then heated to 600°C at a rate of 0.25°C / min~0.5°C / min, kept at that temperature for 2h~4h, and finally cooled to room temperature in the furnace to obtain a porous silicon nitride green body.

[0025] In some preferred embodiments of the present invention, the average particle size of α-Si3N4 is 0.1 μm to 1 μm, and the sphericity is good to achieve the purpose of matrix densification.

[0026] In some preferred embodiments of the present invention, the sintering process is carried out by the following steps: The porous silicon nitride green body is placed in a graphite crucible buried with Si3N4-BN powder, and then heated from room temperature to 1100°C at 5°C / min~15°C / min in a nitrogen atmosphere, and then heated to 1800°C at 4°C / min~6°C / min, and kept warm for 2h~4h. Finally, it is cooled to room temperature in the furnace to obtain the large-pore and high-porosity porous silicon nitride ceramic material.

[0027] The second object of the present invention is to provide a porous silicon nitride ceramic material with large pore size and high porosity prepared by the above preparation method.

[0028] It should be noted that the porosity of the sintered body in the large-aperture and high-porosity porous silicon nitride ceramic material prepared by the present invention is 28% to 68%, and the maximum pore diameter exceeds 400 μm.

[0029] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses α-Si3N4 as a matrix, premixes α-Si3N4 and a sintering aid to form a premixed powder, uses polymethyl methacrylate microspheres as a pore former, uses an alcohol solution of a phenolic resin as a binder, sprays a layer of binder on the surface of the polymethyl methacrylate microspheres, and then adds the premixed powder, and uses a rolling lantern-shaped molding method to uniformly bond the premixed powder to the surface of the pore former particles by repeated rolling and wrapping to form a composite microsphere. The composite microsphere is then pressurized to compact the premixed powder, and the ceramic powder mud between the pore formers is pressed and fused to obtain a green body with a compacted ceramic matrix, uniformly distributed pore formers, and tightly bonded premixed powders of each component. Then, the obtained green body is sequentially cured, carbonized, debinded, and sintered to prepare a high-performance large-aperture porous silicon nitride ceramic with controllable porosity and pore diameter, no obvious internal defects, and excellent mechanical properties, thereby greatly reducing production costs. The porous silicon nitride ceramic material prepared by the preparation method of the present invention has a double-layer or higher pore size gradient composite structure, which is similar to the tissue structure of natural bone, can effectively disperse and balance the load transfer between the implant and the surrounding tissue, and is beneficial to its application in the field of bone transplantation.

[0030] The present invention adopts a dry pressing molding process to effectively prepare large-pore and high-porosity porous silicon nitride ceramics with good mechanical properties. It can also prepare porous silicon nitride ceramics with composite structures of different pore sizes. The layers are tightly combined by the fusion of mud under pressure. There is no problem of decreased mechanical properties of the material due to poor interface bonding, which simplifies the preparation process and reduces costs.

[0031] The present invention uses an alcohol solution of phenolic resin as a binder, and can evenly coat the premixed powder on the surface of the pore-forming agent particles, thereby solving the problem of uneven distribution of the pore-forming agent inside the matrix. At the same time, the phenolic resin can effectively improve the strength of the green body after thermal curing, and its decomposition lags behind the pore-forming agent, thereby effectively solving the green body cracking phenomenon caused by thermal expansion of the pore-forming agent.

[0032] The preparation method of the present invention can effectively regulate the porosity and pore diameter of the porous material according to the size of the pore-forming agent and the amount of the pore-forming agent added, thereby meeting the needs of different bone transplant materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a microscopic morphology of the pore-forming agent used in Example 3.

[0034] Figure 2 This is a surface microscopic morphology of the composite microspheres in Example 3 at a scale of 500 μm; Figure 2 The inset is a surface microscopic morphology of the composite microspheres in Example 3 at a scale of 300 μm.

[0035] Figure 3This is a surface microscopic morphology of the porous silicon nitride green body in Example 3.

[0036] Figure 4 This is a surface microscopic morphology of the porous silicon nitride ceramic in Example 3.

[0037] Figure 5 This is the surface micromorphology of the porous silicon nitride green body in Comparative Example 7.

[0038] Figure 6 This is the surface micromorphology of the porous silicon nitride ceramic in Comparative Example 7.

[0039] Figure 7 This is the surface micromorphology of the porous silicon nitride green body in Comparative Example 8.

[0040] Figure 8 This is the surface micromorphology of the porous silicon nitride ceramic in Comparative Example 9.

[0041] Fig. 9 This is the surface micromorphology of the porous silicon nitride ceramic of Example 12.

[0042] Fig.10 This is the surface micromorphology of the porous silicon nitride ceramic of Example 13.

[0043] Fig.11 This is the surface micromorphology of the porous silicon nitride ceramic of Example 14.

[0044] Fig.12 This is the surface micromorphology of the porous silicon nitride ceramic in Example 15.

[0045] Fig.13 This is the surface micromorphology of the porous silicon nitride green body of Example 8.

[0046] Fig.14 This is the surface micromorphology of the porous silicon nitride green body of Comparative Example 11.

[0047] Fig.15 This is the surface micromorphology of the porous silicon nitride green body of Comparative Example 12.

[0048] Fig.16 This is the surface micromorphology of the porous silicon nitride ceramic of Example 8.

[0049] Fig.17 This is the surface micromorphology of the porous silicon nitride ceramic of Comparative Example 11.

[0050] Fig.18 This is the surface micromorphology of the porous silicon nitride ceramic of Comparative Example 12. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the present invention will be described clearly and completely below.

[0052] In order to explore the effect of the concentration of the ethanol solution of phenolic resin on the porous silicon nitride ceramic material with large pore size and high porosity, the present invention provides the following embodiments and comparative examples.

[0053] Example 1 This embodiment provides a large-pore-diameter, high-porosity porous silicon nitride ceramic material, which is prepared by the following steps: In this embodiment, α-Si3N4 with an average particle size of 0.5 μm is used as the matrix, Al2O3 and Y2O3 are used as sintering aids, and polymethyl methacrylate microspheres with a particle size of 500 μm are used as pore-forming agents. According to the mass ratio of 58.2:2:4.8:35, the corresponding masses of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres are weighed respectively and set aside.

[0054] Step 1, preparation of premixed powder: After mixing α-Si3N4 with the sintering aid, ethanol is used as the ball milling medium and wet ball milling is used to mix them. The ball-to-material mass ratio of the wet ball milling is 3:1, the ball mill speed is 200r / min, the ball milling time is 24h, and then dried to obtain a premixed powder.

[0055] Step 2, preparation of composite microspheres: An ethanol solution of phenolic resin with a mass concentration of 50% is used as a binder, and the amount of phenolic resin added in the binder is controlled to be 15% to 20% of the mass of the premixed powder. After a layer of binder is evenly coated on the surface of the polymethyl methacrylate microsphere, the premixed powder prepared in step 1 is added, and a rolling lantern molding method is adopted to evenly coat a layer of premixed powder on the binder layer on the surface of the pore-forming agent, and then a layer of binder is repeatedly coated and then a layer of the premixed powder is coated, and the amount of the binder coated each time is controlled to be 10% of the total amount of the binder, until all the added premixed powders are completely coated to obtain composite microspheres.

[0056] In this embodiment, the volume proportion of the pore-forming agent is 56%.

[0057] Step 3, pressure molding: The composite microspheres are introduced into a mold and subjected to bidirectional pressure of 80 MPa to obtain a green body.

[0058] Step 4, curing: The green compact was cured at 80° C. for 12 hours to cure the phenolic resin in the binder, thereby obtaining a cured green compact.

[0059] Step 5, carbonization treatment and debinding treatment: 5.1) Carbonization treatment: In an Ar atmosphere, the solidified green body was heated from room temperature to 350°C at a rate of 1°C / min~2°C / min, then heated to 600°C at a rate of 0.25°C / min~0.5°C / min, kept at that temperature for 3 hours, and finally cooled to room temperature with the furnace to obtain a carbonized green body.

[0060] 5.2) Debinding treatment: In an air atmosphere, the carbonized green body is heated from room temperature to 350°C at a rate of 1°C / min~2°C / min, then heated to 600°C at a rate of 0.25°C / min~0.5°C / min, kept at that temperature for 3 hours, and finally cooled to room temperature in the furnace to obtain a porous silicon nitride green body.

[0061] Step 6, sintering treatment: The porous silicon nitride green body is placed in a graphite crucible buried with Si3N4-BN powder, and then heated from room temperature to 1100°C at 10°C / min in a nitrogen atmosphere, and then heated to 1800°C at 5°C / min, and kept warm for 3 hours. Finally, it is cooled to room temperature in the furnace to obtain the large-pore and high-porosity porous silicon nitride ceramic material.

[0062] Example 2 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 1 is only that: In this embodiment, the binder used is an ethanol solution of phenolic resin with a mass concentration of 60%.

[0063] Example 3 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 1 is only that: In this embodiment, the binder used is an ethanol solution of phenolic resin with a mass concentration of 70%.

[0064] Comparative Example 1 This comparative example provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this example and Example 1 is only that: In this comparative example, the binder in Example 1 was replaced by an equal volume of an ethanol solution of a phenolic resin having a mass concentration of 10%.

[0065] Comparative Example 2 This comparative example provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this example and Example 1 is only that: In this comparative example, the binder in Example 1 was replaced by an equal volume of an ethanol solution of a phenolic resin having a mass concentration of 20%.

[0066] Comparative Example 3 This comparative example provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this example and Example 1 is only that: In this comparative example, the binder in Example 1 was replaced by an equal volume of an ethanol solution of a phenolic resin having a mass concentration of 30%.

[0067] Comparative Example 4 This comparative example provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this example and Example 1 is only that: In this comparative example, the binder in Example 1 was replaced by an equal volume of an ethanol solution of a phenolic resin having a mass concentration of 40%.

[0068] Comparative Example 5 This comparative example provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this example and Example 1 is only that: In this comparative example, the binder in Example 1 was replaced by an equal volume of an ethanol solution of a phenolic resin having a mass concentration of 80%.

[0069] Comparative Example 6 This comparative example provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this example and Example 1 is only that: In this comparative example, the binder in Example 1 was replaced by an equal volume of an ethanol solution of a phenolic resin having a mass concentration of 90%.

[0070] In order to explore the influence of the pressure of press molding on the porous silicon nitride ceramic material with large pore size and high porosity, the present invention provides the following embodiments and comparative examples.

[0071] Example 4 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: In this embodiment, the pressure used for pressurization is 60 MPa.

[0072] Example 5 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: In this embodiment, the pressure used for press molding is 100 MPa.

[0073] Comparative Example 7 This comparative example provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this example and Example 3 is only that: In this comparative example, the pressure used for the press molding was 40 MPa.

[0074] Comparative Example 8 This comparative example provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this example and Example 3 is only that: In this comparative example, the pressure used for the press molding was 120 MPa.

[0075] Comparative Example 9 This comparative example provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this example and Example 3 is only that: In this comparative example, the pressure used for the press molding was 160 MPa.

[0076] In order to explore the effects of different amounts of pore-forming agents added on large-pore-diameter and high-porosity porous silicon nitride ceramic materials, the present invention provides the following comparative examples.

[0077] Example 6 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 71.6:2.4:6:20.

[0078] In this embodiment, the volume proportion of the pore-forming agent is 32%.

[0079] Example 7 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 67.1:2.3:5.6:25.

[0080] In this embodiment, the volume proportion of the pore-forming agent is 40%.

[0081] Example 8 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 62.7:2.1:5.3:30.

[0082] In this embodiment, the volume proportion of the pore-forming agent is 47%.

[0083] Example 9 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 53.7:1.8:4.5:40.

[0084] In this embodiment, the volume proportion of the pore-forming agent is 61%.

[0085] Example 10 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 49.2:1.7:4.1:45.

[0086] In this embodiment, the volume proportion of the pore-forming agent is 66%.

[0087] Embodiment 11 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 44.8:1.5:3.7:50.

[0088] In this embodiment, the volume proportion of the pore-forming agent is 74%.

[0089] Comparative Example 10 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 40.3:1.3:3.4:55.

[0090] In this embodiment, the volume proportion of the pore-forming agent is 79%.

[0091] In order to explore the influence of the particle sizes of different pore formers on large-pore-diameter and high-porosity porous silicon nitride ceramic materials, the present invention provides the following comparative examples.

[0092] Example 12 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: in this embodiment, the particle size of the polymethyl methacrylate microspheres is 200 μm.

[0093] Embodiment 13 This embodiment provides a porous silicon nitride ceramic material with a large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: in this embodiment, the particle size of the polymethyl methacrylate microspheres is 100 μm.

[0094] Embodiment 14 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: In this embodiment, the pore-forming agent used in the present invention is obtained by mixing polymethyl methacrylate microspheres with a particle size of 100 μm and polymethyl methacrylate microspheres with a particle size of 500 μm in equal mass ratio.

[0095] Embodiment 15 This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this embodiment and embodiment 3 is only that: In this embodiment, the pore-forming agent used in the present invention is obtained by mixing polymethyl methacrylate microspheres with a particle size of 200 μm and polymethyl methacrylate microspheres with a particle size of 500 μm in equal mass ratio.

[0096] In order to explore the effects of different types of binders on large-pore and high-porosity porous silicon nitride ceramic materials, the present invention provides the following comparative examples.

[0097] Comparative Example 11 This comparative example provides a porous silicon nitride ceramic material with a large pore size and high porosity, and the difference between this example and Example 8 is only that the binder used in this comparative example is a polyvinyl alcohol solution with a mass concentration of 5%.

[0098] Comparative Example 12 This comparative example provides a porous silicon nitride ceramic material with large pore size and high porosity, and the difference between this example and Example 8 is only that the binder in this comparative example is a polyvinyl alcohol solution with a mass concentration of 10%.

[0099] Experimental Section It should be noted that, for the sake of convenience, the present invention hereinafter refers to the large-pore-diameter and high-porosity porous silicon nitride ceramics as porous silicon nitride ceramics.

[0100] 1) Effect of the concentration of phenolic resin ethanol solution on the properties of porous silicon nitride ceramic materials Since the pore-forming agents and the composite microspheres formed in Examples 1 to 3 of the present invention have similar microscopic morphologies, in order to avoid redundant description, the present invention takes Example 3 as an example, and tests are conducted on the surface microscopic morphologies of the pore-forming agents and the composite microspheres formed in Example 3. The test results are as follows: Figure 1 and Figure 2 shown.

[0101] Figure 1 is a microscopic morphology of the pore-forming agent used in Example 3. Figure 1 It can be seen that the pore former used in the present invention has good sphericity, uniform size, and a diameter of 500 μm.

[0102] Figure 2 This is a surface microscopic morphology of the composite microspheres in Example 3 at a scale of 500 μm. Figure 2 The inset in the figure is the surface microscopic morphology of the composite microspheres in Example 3 at a scale of 300 μm. Figure 2 As can be seen from the illustration, the premixed powder is evenly distributed on the surface of the pore-forming agent, which indicates that the rolling lantern molding method can evenly coat the premixed powder on the surface of the pore-forming agent.

[0103] The present invention also tests the surface micromorphology of the porous silicon nitride green body and the porous silicon nitride ceramic in Example 3, and the test results are as follows: Figure 3 and Figure 4 shown. Figure 3 This is a surface microscopic morphology of the porous silicon nitride green body in Example 3. Figure 4 Surface microscopic morphology of the porous silicon nitride ceramic in Example 3. Figure 3 and Figure 4 It can be seen that there are no cracks on the surface of the porous silicon nitride green body, and the internal microstructure of the porous silicon nitride ceramic is that the matrix has no cracks.

[0104] The present invention also uses the Archimedes drainage method to test the porosity and porosity of the porous silicon nitride ceramic materials in Examples 1 to 3 and Comparative Examples 1 to 6, uses a universal testing machine to measure the compressive strength, and organizes the above test results and the analysis results of the microstructure morphology as shown in Table 1.

[0105] Table 1 Performance test results of Example 1 to Example 3 and Comparative Example 1 to Comparative Example 6

[0106] It can be seen from the test results in Table 1 that when the mass concentration of phenolic resin in the binder is 50%~70%, the phenolic resin in the binder can account for 15%~20% of the mass of the premixed powder. At this time, the premixed powder can be wrapped on the surface of the pore-forming agent polymethyl methacrylate microspheres, and the pressed green body has high strength and no cracks.

[0107] When the mass concentration of phenolic resin in the binder is lower than 50%, the amount of phenolic resin added is small, and the viscosity of the binder is low at this time, so that the premixed powder cannot be effectively coated on the surface of the microspheres, and the green body has low strength and cracks.

[0108] When the mass concentration of phenolic resin in the binder is higher than 70%, the amount of phenolic resin added is too high relative to the premixed powder, which leads to agglomeration of the phenolic resin and reduces the strength of the green body.

[0109] 2) Effect of pressure during press forming on the properties of porous silicon nitride ceramic materials The present invention further tests the surface micromorphology of the porous silicon nitride green bodies and porous silicon nitride ceramics in Examples 4 to 5 and Comparative Examples 7 to 9. The results show that the morphologies of the porous silicon nitride green bodies and porous silicon nitride ceramics in Examples 4 and 5 are similar to those in Example 3, so they are not described again here.

[0110] Figure 5 The surface microstructure of the porous silicon nitride green body in Comparative Example 7 is shown in FIG. Figure 6 The surface microstructure of the porous silicon nitride ceramic in Comparative Example 7 is shown in FIG. Figure 7 The surface microstructure of the porous silicon nitride green body in Comparative Example 8 is shown in FIG. Figure 8 This is the surface micromorphology of the porous silicon nitride ceramic in Comparative Example 9.

[0111] Compared to Figure 3 and Figure 4 In terms of Figure 5~Figure 8 It can be seen that when the molding pressure is 40 MPa, there are still gaps on the surface of the green body, and the powder between the pores is not compacted. When the molding pressure is 80 MPa, there are no obvious gaps on the surface of the green body. When the molding pressure is 120 MPa, cracks appear in the green body along the pore-forming agent due to the stress rebound of the pore-forming agent.

[0112] And by Figure 5~Figure 8 It can also be seen that as the molding pressure increases from 40MPa to 80MPa, the state of the porous silicon nitride ceramic changes from premixed powder not tightly bonded to completely tightly bonded, and when the molding pressure further increases to 120MPa, cracks exist in the matrix between the pores. Among them, the morphology of comparative example 9 is similar to that of comparative example 8, so it will not be repeated here.

[0113] The present invention also uses the Archimedes drainage method to test the porosity and porosity of the porous silicon nitride ceramic materials in Examples 3 to 5 and Comparative Examples 7 to 8, respectively, and uses a universal testing machine to measure the compressive strength. The test results are summarized with the analysis results of the microstructure morphology obtained from the above tests as shown in Table 2.

[0114] Table 2 Performance test results of Examples 3 to 5 and Comparative Examples 7 to 9

[0115] It can be seen from the test results in Table 2 that when the molding pressure is low, the premixed powder and the pore-forming agent are not yet compacted, and when the molding pressure is high, the stress rebound effect of the green body is large and cracks are easily generated. Therefore, the pressure of the press molding in the present invention is preferably within the range of 60 MPa to 100 MPa.

[0116] 3) Effect of different pore-forming agent addition amounts on the properties of porous silicon nitride ceramic materials The present invention further tests the surface micromorphology of the porous silicon nitride green body and the porous silicon nitride ceramic in Examples 6 to 11 and Comparative Example 10. The results show that the morphology of the porous silicon nitride green body and the porous silicon nitride ceramic in Examples 6 to 11 is similar to that in Example 3, so it is not repeated here. The present invention also uses the Archimedes drainage method to test the porosity and porosity of the porous silicon nitride ceramic materials in Examples 6 to 11 and Comparative Example 10, and uses a universal testing machine to measure the compressive strength, and the test results are collated with the analysis results of the microstructure morphology obtained by the above test as shown in Table 3.

[0117] Table 3 Performance test results of Example 3, Example 6 to Example 11 and Comparative Example 10

[0118] It can be seen from the test results in Table 3 that when the amount of pore former added is too high, the volume of the pore former accounts for a high proportion, so that the added premixed powder is relatively small, and it is difficult to fill the pores between the pores, resulting in poor performance of the prepared sample. Therefore, when adding the pore former, the present invention adds 20g~50g of the polymethyl methacrylate microspheres for every 50g~80g of the premixed powder, so that the volume of the added pore former accounts for 32%~74%, and the porous silicon nitride ceramic material prepared within this range has good mechanical properties.

[0119] 4) Effect of particle size of different pore-forming agents on the properties of porous silicon nitride ceramic materials The present invention further tests the surface micromorphology of the porous silicon nitride green body and the porous silicon nitride ceramic prepared in Examples 12 to 15, and the test results are as follows: Figure 9~Figure 12 shown.

[0120] Fig. 9 The surface microstructure of the porous silicon nitride ceramic of Example 12 is shown in FIG. Fig.10 is the surface microstructure of the porous silicon nitride ceramic of Example 13, and compared with Example 3, Fig. 9 and Fig.10 It can be seen that as the pore size of the pore-forming agent changes, the pore size of the porous silicon nitride also changes accordingly. The sample has no obvious cracking phenomenon and has good performance.

[0121] Fig.11 The surface microstructure of the porous silicon nitride ceramic of Example 14 is shown in FIG. Fig.12 The surface microstructure of the porous silicon nitride ceramic of Example 15 is shown in FIG. Fig.11 and Fig.12 It can be seen that the middle layer and the interlayer separation of the porous silicon nitride ceramics are obvious, and the interface bonding is good, which effectively ensures the strength of the porous silicon nitride ceramics.

[0122] The present invention uses the Archimedes drainage method to test the porosity and porosity of the porous silicon nitride ceramic materials in Examples 12 to 15, respectively, and uses a universal testing machine to measure the compressive strength. The test results and the analysis results of the microstructure morphology obtained by the above tests are summarized as shown in Table 4.

[0123] Table 4 Performance test results of Example 3, Example 12 to Example 15

[0124] From the test results in Table 4, it can be seen that the porous silicon nitride ceramics with different pore sizes and their composite structures prepared by this process have controllable pore size and porosity and excellent mechanical properties.

[0125] 5) Effects of different binders on the properties of porous silicon nitride ceramic materials The present invention also takes Example 8 and Comparative Examples 11 and 12 as examples, and tests the surface micromorphology of the porous silicon nitride ceramics prepared therefrom, and the test results are as follows: Figure 13~Figure 18 shown.

[0126] Fig.13 The surface microstructure of the porous silicon nitride green body of Example 8 is shown in FIG. Fig.14 The surface microstructure of the porous silicon nitride green body of Comparative Example 11 is shown in FIG. Fig.15 The surface microstructure of the porous silicon nitride green body of Comparative Example 12 is shown in FIG. Fig.16 The surface microstructure of the porous silicon nitride ceramic of Example 8 is shown in FIG. Fig.17 The surface microstructure of the porous silicon nitride ceramic of Comparative Example 11 is shown in FIG. Fig.18 This is the surface micromorphology of the porous silicon nitride ceramic of Comparative Example 12.

[0127] Depend on Figure 13~Figure 15 It can be seen from the test results that there are many cracks on the surface of the green body prepared with polyvinyl alcohol solution as the binder. This is because the green body strength is not high enough to resist the stress rebound caused by the difference in elastic modulus between polymethyl methacrylate microspheres and silicon nitride premixed powder. Using ethanol solution of phenolic resin as a binder can greatly improve the green body strength and reduce green body cracks.

[0128] Depend on Figure 16~Figure 18It can be seen from the test results that there are also a large number of cracks inside the sample prepared with polyvinyl alcohol solution as the binder, and these cracks greatly affect the strength of the sintered body.

[0129] The present invention uses the Archimedes drainage method to test the porosity and porosity of the porous silicon nitride ceramic materials in Example 8, Comparative Examples 11 and 12, respectively, and uses a universal testing machine to measure the compressive strength. The test results are summarized with the analysis results of the microstructure morphology obtained from the above tests as shown in Table 5.

[0130] Table 5 Performance test results of Example 8 and Comparative Examples 11 to 12

[0131] It can be seen from the test results in Table 5 that when the traditional polyvinyl alcohol solution is used as a binder to adhere the premixed powder, the green body strength is not high, which causes the green body to crack during the carbonization process.

[0132] In summary, the present invention uses α-Si3N4 as a matrix, Al2O3 and Y2O3 as sintering aids, polymethyl methacrylate microspheres as a pore former, and a phenolic resin solution as a binder. The phenolic resin binder is sprayed on the surface of the polymethyl methacrylate microspheres, ceramic premixed powder is sprinkled in, and the premixed powder is evenly bonded to the surface of the pore former particles by rolling and wrapping. The operation is repeated to coat all the premixed powders on the surface of the pore former particles. By controlling the particle size and addition amount of the pore former, the content of the phenolic resin binder, the molding pressure, etc., a green body in which the premixed powders are tightly bonded between the pore former particles is obtained. After curing, carbonization, debinding, and sintering, high-performance large-aperture porous silicon nitride ceramics with controllable porosity and pore size, no obvious internal defects, and excellent mechanical properties can be prepared, thereby greatly reducing the production cost. The present invention uses an ethanol solution of phenolic resin as a binder, which not only improves the strength of the porous silicon nitride green body, but also effectively inhibits the cracking phenomenon caused by insufficient green body strength cracking during the carbonization process of the sample prepared using a traditional binder due to the carbonization cracking temperature of the phenolic resin being higher than that of polymethyl methacrylate microspheres. The process is also easy to prepare a double-layer or higher pore gradient composite structure, which is similar to the tissue structure of natural bone. The pore gradient composite structure can effectively disperse and balance the load transfer between the implant and the surrounding tissue, which is beneficial to its application in the field of bone transplantation.

[0133] Obviously, the above embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing a porous silicon nitride ceramic material with large pore size and high porosity, characterized in that: The following steps are involved: Taking α-Si3N4 as the matrix, it is ball-milled and mixed with a sintering aid to obtain a premixed powder; Using polymethyl methacrylate microspheres as a pore former and an alcohol solution of phenolic resin as a binder, after uniformly coating a layer of the binder on the surface of the pore former, adding the premixed powder, and using a rolling lantern-shaped molding method to uniformly coat a layer of the premixed powder on the binder layer on the surface of the pore former, repeatedly coating a layer of the binder and then coating a layer of the premixed powder until the premixed powder is completely coated to obtain composite microspheres; Pressing and molding the composite microspheres to obtain green compacts; Performing a curing treatment on the green compact to cure the phenolic resin in the binder to obtain a cured green compact; The solidified green body is subjected to a carbonization treatment and a binder removal treatment in sequence to obtain a porous silicon nitride green body; The porous silicon nitride green body is sintered to obtain a porous silicon nitride ceramic material with large pore size and high porosity.

2. The method for preparing a porous silicon nitride ceramic material with large pore size and high porosity as claimed in claim 1, characterized in that: The addition amount of the premixed powder is 65% to 80% of the total mass of the composite microspheres.

3. The method for preparing the large-pore-diameter, high-porosity porous silicon nitride ceramic material according to claim 1, characterized in that: The mass concentration of phenolic resin in the binder is 50% to 70%; The amount of phenolic resin added to the binder is 15% to 20% of the mass of the premixed powder.

4. The method for preparing a porous silicon nitride ceramic material with large pore size and high porosity according to claim 1, characterized in that: The mass ratio of the pore former to the premixed powder is 2-5:5-8.

5. The method for preparing the porous silicon nitride ceramic material with large pore size and high porosity according to claim 1, characterized in that: The sintering aid is one or two of Al2O3 and Y2O3; The sintering aid accounts for 10wt% to 11wt% of the total mass of the premixed powder.

6. The method for preparing a porous silicon nitride ceramic material with large pore size and high porosity according to claim 1, characterized in that: The particle size of the pore-forming agent is 100 μm to 500 μm.

7. The method for preparing a porous silicon nitride ceramic material with large pore size and high porosity according to claim 1, characterized in that: The average particle size of the α-Si3N4 is 0.1 μm~1 μm.

8. The method for preparing a porous silicon nitride ceramic material with large pore size and high porosity as claimed in claim 1, characterized in that: The pressure of the press molding is 60MPa~100MPa.

9. The method for preparing a porous silicon nitride ceramic material with large pore size and high porosity according to claim 1, characterized in that: The sintering process is carried out by the following steps: The porous silicon nitride green body is placed in a graphite crucible buried with Si3N4-BN powder, and then heated from room temperature to 1100°C at 5°C / min~15°C / min in a nitrogen atmosphere, and then heated to 1800°C at 4°C / min~6°C / min, and kept warm for 2h~4h. Finally, it is cooled to room temperature in the furnace to obtain the large-pore and high-porosity porous silicon nitride ceramic material.

10. A porous silicon nitride ceramic material with large pore size and high porosity prepared by the preparation method according to any one of claims 1 to 9.

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