A large-aperture and high-porosity porous silicon nitride ceramic material and its preparation method

Abstract

The present invention belongs to the technical field of the preparation of precision ceramic materials, and discloses a porous silicon nitride ceramic with large pore diameter and high porosity and a preparation method thereof. The preparation method is as follows: α-Si3N4 and a sintering aid are ball-milled and mixed evenly to obtain a premixed powder; polymethyl methacrylate microspheres are used as pore-forming agents, and an alcoholic solution of phenolic resin is used as a binder. After a layer of binder is evenly coated on the surface of the pore-forming agent, the premixed powder is added, and the premixed powder is evenly coated on the binder layer on the surface of the pore-forming agent by using a rolling-snowball type forming method. After repeating the coating of a layer of binder and coating a layer of premixed powder until all the premixed powder is coated, composite microspheres are obtained; after the composite microspheres are pressure-molded into green bodies, they are successively cured, carbonized, debound and sintered to obtain a porous silicon nitride ceramic material with large pore diameter and high porosity. The preparation method of the present invention can prepare a porous silicon nitride ceramic material with large pore diameter and high porosity by controlling the size and 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 particularly relates to a large-aperture and 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 at present is 3D printing technology, and the high cost limits its large-scale application. Therefore, how to reduce the production cost and select a reasonable preparation process is the key to solving the problem. Hip joints, ankle joints and other artificial joint prostheses made of ceramics also require the combination of a porous layer and a dense layer to meet the requirements of tissue growth and wear resistance, and rapid batch preparation is also a basic requirement for cost reduction. The dry pressing forming process has the advantages of simple forming process, free regulation of the pore diameter and porosity of the material, etc. After the process is mature, large-scale production can be achieved.

[0003] At present, most of the porous silicon nitride ceramics in the prior art are porous silicon nitride ceramics with a single pore structure, and there is a large difference between the single pore structure and natural bone, which is difficult to meet the actual bone transplantation needs. To solve the above technical problems, those skilled in the art have proposed that porous silicon nitride ceramics with a pore size gradient can be prepared. By forming a pore size gradient composite structure, the force transmission between the implant and the surrounding tissues can be effectively dispersed and balanced, the stress shielding phenomenon of the implant material in the human body can be slowed down, and the actual bone transplantation needs can be met.

[0004] However, the preparation methods of pore-gradient porous structure bone implant materials provided by the current prior art have cumbersome preparation steps, and there are uneven distributions of pore-forming agents and ceramic matrices, resulting in poor bonding effects between ceramic matrix powders, and further resulting in poor mechanical properties of the prepared porous ceramic materials. It is difficult to effectively disperse and balance the load transfer between the implant and the surrounding tissues, 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, it is only possible to control the pore size of the porous layer in the pore-gradient porous structure to be <300 μm, and it is difficult to obtain porous silicon nitride ceramic materials with large pore sizes and high porosity. For example, the prior art CN202310959547.3 provides a preparation method of a porous / dense composite structure silicon nitride material for artificial hip joints. In this prior art, the pore-forming agent is first bonded into a porous green body, silicon nitride and sintering aids are formulated into a slurry, and a porous-dense composite structure is obtained through gel casting for the preparation of hip joint prostheses. However, this prior art requires the pre-bonding and forming of pore-forming agent particles. Excessive strength of the bonded body will affect the curing shrinkage of the slurry and cause cracking of the final green body. At the same time, it is also necessary to prepare a suitable slurry so that the slurry can fully enter the voids between the pore-forming agent particles. The prior art CN200920072364.5 provides a method for preparing a pore-gradient porous bone graft carrier based on β-tricalcium phosphate, including macropores with a pore size of 100 μm to 300 μm and micropores with a pore size of 1 μm to 10 μm. However, the relatively low mechanical properties of β-tricalcium phosphate materials themselves limit their application in bone transplantation. The prior art CN200810097865.9 provides a method for obtaining ordered large-pore porous ceramics by wrapping a slurry containing ceramic premixed powder, adhesive, dispersant, and regulator around the surface of a pore-forming agent and then removing the pore-forming agent and performing high-temperature sintering. This prior art requires slowly pouring the prepared slurry onto a sieve with monodisperse polystyrene microspheres, stirring evenly with a glass rod, and repeatedly coating as needed to naturally cover a layer of slurry on the surface of the pore-forming agent particles. By controlling the water content of the slurry on the surface of the pore-forming agent particles through water evaporation, and then introducing the pore-forming agent particles wrapped with ceramic premixed powder into a mold and pressing them into shape. However, this method may have problems such as uneven wrapping of the slurry on the surface of the pore-forming agent and difficulty in accurately controlling the wrapping amount. In addition, during the carbonization process of preparing porous ceramics using a pore-forming agent, if the binder of the premixed powder and the pore-forming agent decompose simultaneously and there is stress inside the green body, it will cause cracking. Summary of the Invention

[0005] To overcome the defects of the above-mentioned existing technologies, 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 the matrix, and uniformly mixes it with a sintering aid to obtain a premixed powder; then uses polymethyl methacrylate microspheres as the pore-forming agent, and by covering a layer of ethanol solution of phenolic resin on the surface of the polymethyl methacrylate microspheres as the binder layer, through the method of "rolling glutinous rice balls", the premixed powder is adhered and coated on the surface of the pore-forming agent, and then after pressure molding, it is successively subjected to curing, carbonization, debinding and high-temperature sintering. By controlling the size and addition amount of the pore-forming agent, a porous silicon nitride ceramic material with large pore size and high porosity can be prepared. Moreover, the porous silicon nitride ceramic material prepared by the preparation method of the present invention has excellent mechanical properties, and has a pore size gradient composite structure of a dense ceramic matrix layer formed by the premixed powder and a porous layer formed by the pore-forming agent. The formed pore size gradient composite structure is similar to the tissue structure of natural bone, can effectively disperse and balance the load transfer between the implant and the surrounding tissues, and is beneficial to its application in the field of bone transplantation.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The first object of the present invention is to provide a preparation method of a porous silicon nitride ceramic material with large pore size and high porosity, comprising the following steps:

[0008] Step 1, preparation of the premixed powder:

[0009] Using α-Si3N4 as the matrix, ball-milling and mixing it with a sintering aid to obtain a premixed powder.

[0010] Step 2, preparation of the composite microspheres:

[0011] Using polymethyl methacrylate microspheres as the pore-forming agent and an alcohol solution of phenolic resin as the binder, after uniformly coating a layer of the binder on the surface of the pore-forming agent, adding the premixed powder, and adopting the rolling glutinous rice ball molding method, uniformly coating a layer of the premixed powder on the binder layer on the surface of the pore-forming agent, repeating the coating of a layer of the binder and then coating a layer of the premixed powder until all the premixed powder is coated to obtain composite microspheres.

[0012] Step 3, pressure molding:

[0013] Pressing the composite microspheres into a green body.

[0014] Step 4, curing treatment:

[0015] Performing curing treatment on the green body to cure the phenolic resin in the binder to obtain a cured green body.

[0016] Step 5, carbonization treatment and debinding treatment:

[0017] The solidified green body is subjected to carbonization treatment and debinding treatment in sequence to obtain a porous silicon nitride green body;

[0018] Step 6, sintering treatment:

[0019] The porous silicon nitride green body is subjected to sintering treatment to obtain a porous silicon nitride ceramic material with large pore diameter and high porosity.

[0020] It should be noted that the present invention uses α-Si3N4 as the matrix. After premixing α-Si3N4 and a sintering aid to form a premixed powder, polymethyl methacrylate microspheres are used as the pore-forming agent, and an alcohol solution of phenolic resin is used as the binder. After spraying a layer of binder on the surface of the polymethyl methacrylate microspheres first, the premixed powder is added. By adopting the method of making yuanxiao (a kind of Chinese traditional sweet dumpling), that is, using the way of repeated rolling and wrapping, the premixed powder is evenly bonded on the surface of the pore-forming agent particles to form composite microspheres. Then, the composite microspheres are pressed into shape to compact the premixed powder. At the same time, the ceramic powder mud between the pore-forming agents is pressed and fused to form a dense ceramic matrix layer, obtaining a green body with a compacted ceramic matrix, uniform distribution of pore-forming agents, and tight combination between the premixed powder of each component. Then, the obtained green body is subjected to curing, carbonization, debinding, and sintering in sequence to remove the polymethyl methacrylate microspheres, thereby preparing a high-performance large-pore-diameter porous silicon nitride ceramic with large pore diameter, high porosity, no obvious internal defects, and excellent mechanical properties, greatly reducing the production cost. Moreover, 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 a pore size gradient composite structure formed by the pore-forming agent. The formed pore size gradient composite structure is similar to the tissue structure of natural bone, can effectively disperse and balance the load transfer between the implant and the surrounding tissues, and is beneficial to its application in the field of bone transplantation.

[0021] The present invention uses an alcohol solution of phenolic resin as the binder. In some more preferred embodiments of the present invention, an ethanol solution of phenolic resin is used as the 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 during carbonization when preparing samples using traditional binders according to the characteristic that the carbonization cracking temperature of phenolic resin is higher than that of polymethyl methacrylate microspheres and the green body strength can still be maintained during the carbonization process.

[0022] In some preferred embodiments of the present invention, the sintering aid is one or two of Al2O3 and Y2O3, and the sintering aid accounts for 10wt% - 11wt% of the total mass of the premixed powder to ensure the denseness of the matrix after sintering.

[0023] In some more preferred embodiments of the present invention, Al2O3 and Y2O3 are used together as the sintering aid, and the mass ratio of Al2O3 and Y2O3 is 2:4 - 6 to ensure excellent mechanical properties of the sintered body.

[0024] In some preferred embodiments of the present invention, the premixed powder accounts for 65% - 80% of the total mass of the composite microspheres, so that the added premixed powder can promote the filling of the premixed powder between the pores of the polymethyl methacrylate microspheres during the subsequent pressure molding process, which helps to form a tightly compacted green body.

[0025] 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 wet ball milling is ethanol, the mass ratio of balls to materials is 2 - 4:1, the rotational speed of the ball mill is 150 r / min - 250 r / min, and the ball milling time is 16 h - 32 h.

[0026] During the exploration of the present invention, it is found that too little phenolic resin content will cause the viscosity of the binder to be not high enough, resulting in poor fluidity of the premixed powder and low strength of the green body. Increasing the dosage of phenolic resin is beneficial to improving the above situation. Too much phenolic resin will cause the powder wrapped by the polymethyl methacrylate microspheres to be difficult to compact, and the pores of the matrix are too large, affecting the densification of the matrix. Therefore, in some preferred embodiments of the present invention, the mass concentration of phenolic resin in the binder is 50% - 70%, and the addition amount of phenolic resin in the binder is 15% - 20% of the mass of the premixed powder.

[0027] In some preferred embodiments of the present invention, when preparing the composite microspheres, the dosage of the binder applied each time is 8% - 12% of the total dosage of the binder.

[0028] It should also be noted that the present invention preferably uses polymethyl methacrylate microspheres as the pore-forming agent, and the mass ratio of the pore-forming agent to the premixed powder is 2 - 5:5 - 8, so that the used pore-forming agent can form pores in the matrix during the subsequent carbonization treatment and debinding treatment.

[0029] In some preferred embodiments of the present invention, the particle size of the pore-forming agent is 100 μm - 500 μm. Among them, in some more preferred embodiments of the present invention, the pore-forming agent is composed of polymethyl methacrylate microspheres with a particle size of 100 μm - 200 μm and polymethyl methacrylate microspheres with a particle size of 400 μm - 500 μm, so as to ensure that the maximum pore size of the porous silicon nitride ceramic exceeds 400 μm and a porous structure with different pore sizes can be formed.

[0030] In the exploration process of the present invention, it is found that during the pressure forming process, if the pressure is too small, the matrix of the green body cannot be pressed tightly, resulting in cracks during the carbonization and debinding processes. If the pressure is too large, the green body will be too tight, and the large stress rebound effect caused by the difference in elastic modulus between the pore-forming agent and the silicon nitride matrix will cause the green body to crack after demolding. Therefore, in some preferred embodiments of the present invention, the pressure for pressure forming is 60 MPa to 100 MPa.

[0031] In some preferred embodiments of the present invention, the temperature for curing treatment is 80 °C to 150 °C, and the treatment time is 8 h to 12 h, to ensure complete curing of the phenolic resin, improve the strength of the green body, and prevent the green body from cracking due to the thermal expansion and cracking exhaust of the pore-forming agent during the carbonization process.

[0032] In some preferred embodiments of the present invention, the carbonization treatment is carried out through the following steps:

[0033] In an Ar gas atmosphere, the cured green body is heated from room temperature to 350 °C at a rate of 1 °C / min to 2 °C / min, and then heated to 600 °C at a rate of 0.25 °C / min to 0.5 °C / min, held for 2 h to 4 h, and finally cooled to room temperature with the furnace to obtain the carbonized green body.

[0034] In some preferred embodiments of the present invention, the debinding treatment is carried out through the following steps:

[0035] In an air atmosphere, the carbonized green body is heated from room temperature to 350 °C at a rate of 1 °C / min to 2 °C / min, and then heated to 600 °C at a rate of 0.25 °C / min to 0.5 °C / min, held for 2 h to 4 h, and finally cooled to room temperature with the furnace to obtain the porous silicon nitride green body.

[0036] 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.

[0037] In some preferred embodiments of the present invention, the sintering treatment is carried out through the following steps:

[0038] The porous silicon nitride green body is placed in a graphite crucible buried with Si3N4-BN powder, and then in a nitrogen atmosphere, it is heated from room temperature to 1100 °C at a rate of 5 °C / min to 15 °C / min, and then heated to 1800 °C at a rate of 4 °C / min to 6 °C / min, held for 2 h to 4 h, and finally cooled to room temperature with the furnace to obtain the large-pore high-porosity porous silicon nitride ceramic material.

[0039] The second object of the present invention is to provide a large-pore high-porosity porous silicon nitride ceramic material prepared by the above preparation method.

[0040] It should be noted that the porosity of the sintered body in the macroporous high-porosity porous silicon nitride ceramic material prepared by the present invention is 28% - 68%, and the maximum pore diameter exceeds 400 μm.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention uses α-Si3N4 as the matrix. By premixing α-Si3N4 and sintering aids to form a premixed powder, using polymethyl methacrylate microspheres as pore-forming agents, and using an alcohol solution of phenolic resin as a binder. After spraying a layer of binder on the surface of the polymethyl methacrylate microspheres first, then adding the premixed powder, and by adopting the method of making yuanxiao (a kind of Chinese traditional sweet dumpling), that is, using the way of repeated rolling and wrapping to uniformly bond the premixed powder on the surface of the pore-forming agent particles to form composite microspheres. Then, the composite microspheres are pressure-molded to compact the premixed powder. At the same time, the ceramic powder mud between the pore-forming agents is pressed and fused to obtain a green body with a compacted ceramic matrix, uniform distribution of pore-forming agents, and tight combination between the premixed powder of each component. Then, the obtained green body is successively subjected to curing, carbonization, debinding, and sintering to prepare a high-performance macroporous silicon nitride ceramic with controllable porosity and pore diameter, no obvious internal defects, and excellent mechanical properties, greatly reducing the production cost. Moreover, the porous silicon nitride ceramic material prepared by the preparation method of the present invention has a double-layer or more 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 tissues, and is beneficial to its application in the field of bone transplantation.

[0043] The present invention adopts a dry pressing forming process to effectively prepare macroporous high-porosity porous silicon nitride ceramics with good mechanical properties. It can also prepare porous silicon nitride ceramics with different pore size composite structures. The layers are tightly combined through the fusion of the mud under pressure, and there are no problems such as the decline of the mechanical properties of the material caused by poor interfacial bonding, simplifying the preparation process and reducing the cost.

[0044] The present invention uses an alcohol solution of phenolic resin as a binder, which can uniformly coat the premixed powder on the surface of the pore-forming agent particles, solves the problem of uneven distribution of the pore-forming agent in the matrix, and at the same time, the phenolic resin can effectively improve the strength of the green body after thermal curing and decomposes later than the pore-forming agent, so it effectively solves the phenomenon of green body cracking caused by the thermal expansion of the pore-forming agent.

[0045] The preparation method of the present invention can effectively regulate the porosity and pore diameter of the porous material according to the size and addition amount of the pore-forming agent, meeting the requirements of different bone transplantation materials. Description of the Drawings

[0046] Figure 1 It is the microscopic morphology diagram of the pore-forming agent used in Example 3.

[0047] Figure 2It is the surface microscopic morphology diagram of the composite microspheres in Example 3 at a scale of 500 μm; Figure 2 The inset in it is the surface microscopic morphology diagram of the composite microspheres in Example 3 at a scale of 300 μm.

[0048] Figure 3 It is the surface microscopic morphology diagram of the green body of porous silicon nitride in Example 3.

[0049] Figure 4 It is the surface microscopic morphology diagram of the porous silicon nitride ceramic in Example 3.

[0050] Figure 5 It is the surface microscopic morphology of the green body of porous silicon nitride in Comparative Example 7.

[0051] Figure 6 It is the surface microscopic morphology of the porous silicon nitride ceramic in Comparative Example 7.

[0052] Figure 7 It is the surface microscopic morphology of the green body of porous silicon nitride in Comparative Example 8.

[0053] Figure 8 It is the surface microscopic morphology of the porous silicon nitride ceramic in Comparative Example 9.

[0054] Figure 9 It is the surface microscopic morphology of the porous silicon nitride ceramic in Example 12.

[0055] Figure 10 It is the surface microscopic morphology of the porous silicon nitride ceramic in Example 13.

[0056] Figure 11 It is the surface microscopic morphology of the porous silicon nitride ceramic in Example 14.

[0057] Figure 12 It is the surface microscopic morphology of the porous silicon nitride ceramic in Example 15.

[0058] Figure 13 It is the surface microscopic morphology of the green body of porous silicon nitride in Example 8.

[0059] Figure 14 It is the surface microscopic morphology of the green body of porous silicon nitride in Comparative Example 11.

[0060] Figure 15 It is the surface microscopic morphology of the green body of porous silicon nitride in Comparative Example 12.

[0061] Figure 16 It is the surface microscopic morphology of the porous silicon nitride ceramic in Example 8.

[0062] Figure 17 It is the surface microscopic morphology of the porous silicon nitride ceramic in Comparative Example 11.

[0063] Figure 18 It is the surface microscopic morphology of the porous silicon nitride ceramic of Comparative Example 12. Specific embodiments

[0064] The technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0065] In order to explore the influence of the concentration of the ethanol solution of phenolic resin on the large-pore high-porosity porous silicon nitride ceramic material, the present invention provides the following several examples and comparative examples.

[0066] Example 1

[0067] This example provides a large-pore high-porosity porous silicon nitride ceramic material, which is prepared by the following steps:

[0068] In this example, α-Si3N4 with an average particle size of 0.5 μm is used as the matrix, Al2O3 and Y2O3 are used together 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 reserved.

[0069] Step 1, preparation of premixed powder:

[0070] After mixing α-Si3N4 with the sintering aid, ethanol is used as the ball milling medium, and wet ball milling is used to mix evenly. The mass ratio of the balls to the materials in wet ball milling is 3:1, the rotation speed of the ball mill is 200 r / min, the ball milling time is 24 h, and then it is dried to obtain the premixed powder.

[0071] Step 2, preparation of composite microspheres:

[0072] Using an ethanol solution of phenolic resin with a mass concentration of 50% as the binder, controlling the addition amount of phenolic resin in the binder to be 15% - 20% of the mass of the premixed powder. After evenly coating a layer of binder on the surface of the polymethyl methacrylate microspheres, the premixed powder prepared in Step 1 is added. The rolling method is used to evenly coat a layer of premixed powder on the binder layer on the surface of the pore-forming agent, and then the way of coating a layer of binder and then coating a layer of the premixed powder is repeated. The amount of the binder used for each coating is controlled to be 10% of the total amount of the binder until all the added premixed powder is completely coated to obtain the composite microspheres.

[0073] In this example, the volume ratio of the pore-forming agent is 56%.

[0074] Step 3, pressure molding:

[0075] Introduce the composite microspheres into a mold and apply bi-directional pressure of 80 MPa to obtain a green body.

[0076] Step 4, curing treatment:

[0077] Cure the above-mentioned green body at 80 °C for 12 h to cure the phenolic resin in the binder, obtaining a cured green body.

[0078] Step 5, carbonization treatment and debinding treatment:

[0079] 5.1) Carbonization treatment:

[0080] Under an Ar gas atmosphere, heat the cured green body from room temperature to 350 °C at a rate of 1 °C / min to 2 °C / min, then heat it to 600 °C at a rate of 0.25 °C / min to 0.5 °C / min, hold for 3 h, and finally cool it to room temperature with the furnace to obtain a carbonized green body.

[0081] 5.2) Debinding treatment:

[0082] Under an air atmosphere, heat the carbonized green body from room temperature to 350 °C at a rate of 1 °C / min to 2 °C / min, then heat it to 600 °C at a rate of 0.25 °C / min to 0.5 °C / min, hold for 3 h, and finally cool it to room temperature with the furnace to obtain a porous silicon nitride green body.

[0083] Step 6, sintering treatment:

[0084] Place the porous silicon nitride green body into a graphite crucible buried with Si3N4-BN powder. Subsequently, under a nitrogen atmosphere, heat it from room temperature to 1100 °C at a rate of 10 °C / min, then heat it to 1800 °C at a rate of 5 °C / min, hold for 3 h, and finally cool it to room temperature with the furnace to obtain the large-pore-diameter and high-porosity porous silicon nitride ceramic material.

[0085] Example 2

[0086] This example provides a large-pore-diameter and high-porosity porous silicon nitride ceramic material, and the difference between this example and Example 1 is only that:

[0087] In this example, the binder used is an ethanol solution of phenolic resin with a mass concentration of 60%.

[0088] Example 3

[0089] This example provides a large-pore-diameter and high-porosity porous silicon nitride ceramic material, and the difference between this example and Example 1 is only that:

[0090] In this example, the binder used is an ethanol solution of phenolic resin with a mass concentration of 70%.

[0091] Comparative Example 1

[0092] 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:

[0093] In this comparative example, the binder in Example 1 was replaced with an equal volume of an ethanol solution of phenolic resin with a mass concentration of 10%.

[0094] Comparative Example 2

[0095] 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:

[0096] In this comparative example, the binder in Example 1 was replaced with an equal volume of an ethanol solution of phenolic resin with a mass concentration of 20%.

[0097] Comparative Example 3

[0098] 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:

[0099] In this comparative example, the binder in Example 1 was replaced with an equal volume of an ethanol solution of phenolic resin with a mass concentration of 30%.

[0100] Comparative Example 4

[0101] 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:

[0102] In this comparative example, the binder in Example 1 was replaced with an equal volume of an ethanol solution of phenolic resin with a mass concentration of 40%.

[0103] Comparative Example 5

[0104] 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:

[0105] In this comparative example, the binder in Example 1 was replaced with an equal volume of an ethanol solution of phenolic resin with a mass concentration of 80%.

[0106] Comparative Example 6

[0107] 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:

[0108] In this comparative example, the binder in Example 1 was replaced with an equal volume of an ethanol solution of phenolic resin with a mass concentration of 90%.

[0109] In order to explore the influence of the pressure in pressure molding on the large-pore high-porosity porous silicon nitride ceramic material, the present invention provides the following several examples and comparative examples.

[0110] Example 4

[0111] This example provides a large-pore high-porosity porous silicon nitride ceramic material, and the difference between this example and Example 3 is only that:

[0112] In this example, the pressure used in pressure molding is 60 MPa.

[0113] Example 5

[0114] This example provides a large-pore high-porosity porous silicon nitride ceramic material, and the difference between this example and Example 3 is only that:

[0115] In this example, the pressure used in pressure molding is 100 MPa.

[0116] Comparative Example 7

[0117] This comparative example provides a large-pore high-porosity porous silicon nitride ceramic material, and the difference between this example and Example 3 is only that:

[0118] In this comparative example, the pressure used in pressure molding is 40 MPa.

[0119] Comparative Example 8

[0120] This comparative example provides a large-pore high-porosity porous silicon nitride ceramic material, and the difference between this example and Example 3 is only that:

[0121] In this comparative example, the pressure used in pressure molding is 120 MPa.

[0122] Comparative Example 9

[0123] This comparative example provides a large-pore high-porosity porous silicon nitride ceramic material, and the difference between this example and Example 3 is only that:

[0124] In this comparative example, the pressure used in pressure molding is 160 MPa.

[0125] In order to explore the influence of the addition amount of different pore-forming agents on the large-pore high-porosity porous silicon nitride ceramic material, the present invention provides the following several comparative examples.

[0126] Example 6

[0127] This example provides a large-pore high-porosity porous silicon nitride ceramic material, and the difference between this example and Example 3 is only that:

[0128] In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 71.6:2.4:6:20.

[0129] Moreover, in this embodiment, the volume proportion of the pore former is 32%.

[0130] Example 7

[0131] This embodiment provides a porous silicon nitride ceramic material with large pore diameter and high porosity, and the difference between this embodiment and Example 3 is only that:

[0132] In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 67.1:2.3:5.6:25.

[0133] Moreover, in this embodiment, the volume proportion of the pore former is 40%.

[0134] Example 8

[0135] This embodiment provides a porous silicon nitride ceramic material with large pore diameter and high porosity, and the difference between this embodiment and Example 3 is only that:

[0136] In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 62.7:2.1:5.3:30.

[0137] Moreover, in this embodiment, the volume proportion of the pore former is 47%.

[0138] Example 9

[0139] This embodiment provides a porous silicon nitride ceramic material with large pore diameter and high porosity, and the difference between this embodiment and Example 3 is only that:

[0140] In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 53.7:1.8:4.5:40.

[0141] Moreover, in this embodiment, the volume proportion of the pore former is 61%.

[0142] Example 10

[0143] This embodiment provides a porous silicon nitride ceramic material with large pore diameter and high porosity, and the difference between this embodiment and Example 3 is only that:

[0144] In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 49.2:1.7:4.1:45.

[0145] In this embodiment, the volume fraction of the pore former is 66%.

[0146] Example 11

[0147] This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity. The difference between this embodiment and Example 3 is only that:

[0148] In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 44.8:1.5:3.7:50.

[0149] In this embodiment, the volume fraction of the pore former is 74%.

[0150] Comparative Example 10

[0151] This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity. The difference between this embodiment and Example 3 is only that:

[0152] In this embodiment, the mass ratio of α-Si3N4, Al2O3, Y2O3 and polymethyl methacrylate microspheres is 40.3:1.3:3.4:55.

[0153] In this embodiment, the volume fraction of the pore former is 79%.

[0154] In order to explore the influence of the particle size of different pore formers on the porous silicon nitride ceramic material with large pore size and high porosity, the present invention provides the following comparative examples.

[0155] Example 12

[0156] This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity. The difference between this embodiment and Example 3 is only that: in this embodiment, the particle size of the polymethyl methacrylate microspheres is 200 μm.

[0157] Example 13

[0158] This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity. The difference between this embodiment and Example 3 is only that: in this embodiment, the particle size of the polymethyl methacrylate microspheres is 100 μm.

[0159] Example 14

[0160] This embodiment provides a porous silicon nitride ceramic material with large pore size and high porosity. The difference between this embodiment and Example 3 is only that:

[0161] In this embodiment, the pore former 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 an equal mass ratio.

[0162] Example 15

[0163] This example provides a porous silicon nitride ceramic material with a large pore diameter and high porosity, and the difference between this example and Example 3 is only that:

[0164] In this example, 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 an equal mass ratio.

[0165] In order to explore the influence of different types of binders on the porous silicon nitride ceramic material with a large pore diameter and high porosity, the present invention provides the following comparative examples.

[0166] Comparative Example 11

[0167] This comparative example provides a porous silicon nitride ceramic material with a large pore diameter 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%.

[0168] Comparative Example 12

[0169] This comparative example provides a porous silicon nitride ceramic material with a large pore diameter 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%.

[0170] Experimental part

[0171] It should be noted that for the convenience of description, the porous silicon nitride ceramic with a large pore diameter and high porosity will be hereinafter simply referred to as porous silicon nitride ceramic in the present invention.

[0172] 1) Influence of the concentration of the ethanol solution of phenolic resin on the properties of the porous silicon nitride ceramic material

[0173] Since the pore-forming agents and the formed composite microspheres used in Examples 1 to 3 of the present invention have similar microscopic morphologies, in order to avoid unnecessary repetition, the present invention takes Example 3 as an example here, and the surface microscopic morphologies of both the pore-forming agent and the formed composite microspheres used in Example 3 are tested, and the test results are respectively as Figure 1 and Figure 2 shown.

[0174] Figure 1 is the microscopic morphology diagram of the pore-forming agent used in Example 3. It can be seen from Figure 1 that the pore-forming agent adopted by the present invention has a good sphericity, uniform size, and a diameter of 500 μm.

[0175] Figure 2 is the surface microscopic morphology diagram of the composite microspheres in Example 3 at a scale of 500 μm. Figure 2The illustration in [Example 3] shows the surface micro-topography of the composite microspheres in Example 3 at a scale of 300 μm. As can be seen from Figure 2 and its illustration, the premixed powder is evenly distributed on the surface of the pore-forming agent, indicating that the premixed powder can be evenly coated on the surface of the pore-forming agent by the rolling method.

[0176] The present invention also tested the surface micro-topography of the green body of porous silicon nitride and porous silicon nitride ceramics in Example 3, and the test results are as shown in Figure 3 and Figure 4 respectively. Figure 3 is the surface micro-topography diagram of the green body of porous silicon nitride in Example 3, Figure 4 is the surface micro-topography diagram of the porous silicon nitride ceramic in Example 3. As can be seen from Figure 3 and Figure 4 , there are no cracks on the surface of the green body of porous silicon nitride, and the internal micro-topography of the porous silicon nitride ceramic is that the matrix has no cracks.

[0177] The present invention also used the Archimedes drainage method to test the porosity and air porosity of the porous silicon nitride ceramic materials in Examples 1 to 3 and Comparative Examples 1 to 6, and used a universal testing machine to measure the compressive strength. The above test results and the analysis results of the microstructural morphology are summarized in Table 1 as follows.

[0178] Table 1 Performance test results of Examples 1 to 3 and Comparative Examples 1 to 6

[0179]

[0180] As can be seen from the test results in Table 1, when the mass concentration of phenolic resin in the binder is 50% - 70%, the phenolic resin in the binder accounts for 15% - 20% of the mass of the premixed powder. At this time, the premixed powder can be evenly wrapped on the surface of the pore-forming agent polymethyl methacrylate microspheres, and the strength of the pressed green body is high and there are no cracks.

[0181] When the mass concentration of phenolic resin in the binder is less than 50%, the addition amount of phenolic resin 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 strength of the green body is low and there are cracks.

[0182] When the mass concentration of phenolic resin in the binder is higher than 70%, at this time, the addition amount of phenolic resin is too high relative to the premixed powder, which leads to agglomeration of phenolic resin, thus reducing the strength of the green body.

[0183] 2) Influence of the pressure of pressure molding on the properties of porous silicon nitride ceramic materials

[0184] The present invention further tested the surface microtopographies of the porous silicon nitride green compacts and porous silicon nitride ceramics in Examples 4 to 5 and Comparative Examples 7 to 9. The results showed that the morphologies of the porous silicon nitride green compacts and porous silicon nitride ceramics in Examples 4 and 5 were similar to those in Example 3, so they will not be elaborated here.

[0185] Figure 5 The surface microtopography of the porous silicon nitride green compact in Comparative Example 7 Figure 6 The surface microtopography of the porous silicon nitride ceramic in Comparative Example 7 Figure 7 The surface microtopography of the porous silicon nitride green compact in Comparative Example 8 Figure 8 The surface microtopography of the porous silicon nitride ceramic in Comparative Example 9

[0186] Compared with Figure 3 and Figure 4 it can be seen that when the molding pressure is 40 MPa, there are still gaps on the surface of the green compact, 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 compact. When the molding pressure is 120 MPa, cracks appear along the pore-forming agent in the green compact due to the stress rebound of the pore-forming agent. Figures 5 - 8

[0187] And it can also be seen from Figures 5 - 8 that as the molding pressure increases from 40 MPa to 80 MPa, the state of the porous silicon nitride ceramic changes from the pre-mixed powder not being tightly bonded to being completely tightly bonded. When the molding pressure further rises to 120 MPa, there are cracks 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 elaborated here.

[0188] The present invention also used the Archimedes drainage method to test the porosity and air porosity of the porous silicon nitride ceramic materials in Examples 3 to 5 and Comparative Examples 7 to 8, and used a universal testing machine to measure the compressive strength. The test results were sorted out and shown in Table 2 together with the analysis results of the microstructural morphologies obtained from the above tests.

[0189] Table 2 Performance test results of Examples 3 to 5 and Comparative Examples 7 to 9

[0190]

[0191] It can be seen from the test results in Table 2 that when the molding pressure is low, the pre-mixed powder and the pore-forming agent are not yet compacted. When the molding pressure is high, the stress rebound effect of the green body is large and cracks are easily generated. Therefore, the present invention preferably selects the pressure for pressure forming in the range of 60 MPa to 100 MPa.

[0192] 3) Influence of the addition amount of different pore formers on the properties of porous silicon nitride ceramic materials

[0193] The present invention further tested the surface microtopographies of the porous silicon nitride green bodies and porous silicon nitride ceramics in Examples 6 to 11 and Comparative Example 10. The results showed that the morphologies of the porous silicon nitride green bodies and porous silicon nitride ceramics in Examples 6 to 11 were similar to those in Example 3, so they will not be elaborated here. The present invention also used the Archimedes drainage method to test the porosity and air porosity of the porous silicon nitride ceramic materials in Examples 6 to 11 and Comparative Example 10 respectively, and used a universal testing machine to measure the compressive strength. The test results were sorted out and shown in Table 3 together with the analysis results of the microstructural morphologies obtained from the above tests.

[0194] Table 3 Performance test results of Example 3, Examples 6 to 11 and Comparative Example 10

[0195]

[0196] It can be seen from the test results in Table 3 that when the addition amount of the pore former is too high, the volume proportion of the pore former is relatively high, and the added premixed powder is relatively less, making it difficult to fill the pores and inter-pore voids, resulting in poor performance of the prepared samples. Therefore, when adding the pore former in the present invention, for every 50 g to 80 g of the premixed powder, 20 g to 50 g of the polymethyl methacrylate microspheres are added, so that the volume of the added pore former accounts for 32% to 74%. The porous silicon nitride ceramic materials prepared within this range have good mechanical properties.

[0197] 4) Influence of the particle size of different pore formers on the properties of porous silicon nitride ceramic materials

[0198] The present invention further tested the surface microtopographies of the prepared porous silicon nitride green bodies and porous silicon nitride ceramics in Examples 12 to 15, and the test results are respectively as Figures 9 - 12 shown.

[0199] Figure 9 is the surface microtopography of the porous silicon nitride ceramic in Example 12, Figure 10 is the surface microtopography of the porous silicon nitride ceramic in Example 13, and compared with Example 3, it can be seen from Figure 9 and Figure 10 that as the pore size of the pore former changes, the pore size of the porous silicon nitride also changes accordingly, and there is no obvious cracking phenomenon in the sample, and the performance is good.

[0200] Figure 11 is the surface microtopography of the porous silicon nitride ceramic in Example 14, Figure 12 is the surface microtopography of the porous silicon nitride ceramic in Example 15. It can be seen from Figure 11 andFigure 12 It can be seen that the layers of the porous silicon nitride ceramic are clearly separated from each other, and the interface bonding is good, effectively ensuring the strength of the porous silicon nitride ceramic.

[0201] In this invention, the Archimedes drainage method was used to test the porosity and air porosity of the porous silicon nitride ceramic materials in Examples 12 to 15 respectively, and a universal testing machine was used to measure the compressive strength. The test results were sorted out and shown in Table 4 together with the analysis results of the microstructural morphology obtained from the above tests.

[0202] Table 4 Performance test results of Example 3 and Examples 12 to 15

[0203]

[0204] It can be seen from the test results in Table 4 that for the porous silicon nitride ceramics with different pore diameters and their composite structures prepared by this process, the pore diameter and air porosity are controllable, and the mechanical properties are excellent.

[0205] 5) Influence of different binders on the properties of porous silicon nitride ceramic materials

[0206] In this invention, taking Example 8 and Comparative Examples 11 and 12 as examples, the surface micro-morphologies of the porous silicon nitride ceramics prepared were tested respectively, and the test results are shown as follows Figures 13 - 18 shown.

[0207] Figure 13 is the surface micro-morphology of the green body of the porous silicon nitride in Example 8, Figure 14 is the surface micro-morphology of the green body of the porous silicon nitride in Comparative Example 11, Figure 15 is the surface micro-morphology of the green body of the porous silicon nitride in Comparative Example 12, Figure 16 is the surface micro-morphology of the porous silicon nitride ceramic in Example 8, Figure 17 is the surface micro-morphology of the porous silicon nitride ceramic in Comparative Example 11, Figure 18 is the surface micro-morphology of the porous silicon nitride ceramic in Comparative Example 12.

[0208] From Figures 13 - 15 the test results, it can be seen that there are many cracks on the surface of the green body prepared with the polyvinyl alcohol solution as the binder. This is because the strength of the green body is not high enough to resist the stress rebound caused by the difference in elastic modulus between the polymethyl methacrylate microspheres and the silicon nitride premixed powder. Using the ethanol solution of phenolic resin as the binder can greatly improve the strength of the green body and reduce the cracks on the green body.

[0209] From Figures 16 - 18 the test results, it can be seen that there are also a large number of cracks inside the sample prepared with the polyvinyl alcohol solution as the binder. These cracks greatly affect the strength of the sintered body.

[0210] The present invention uses the Archimedes drainage method to test the porosity and pore rate of the porous silicon nitride ceramic materials in Example 8, Comparative Example 11 and Comparative Example 12 respectively, measures the compressive strength using a universal testing machine, and organizes the test results and the analysis results of the microstructure morphology obtained from the above tests as shown in Table 5.

[0211] Table 5 Performance test results of Example 8 and Comparative Examples 11 - 12

[0212]

[0213] It can be seen from the test results in Table 5 that when using the traditional polyvinyl alcohol solution as the binder to adhere the premixed powder, the strength of the green body is not high, resulting in cracking of the green body during the carbonization process.

[0214] In summary, the present invention uses α-Si3N4 as the matrix, Al2O3 and Y2O3 as sintering aids, polymethyl methacrylate microspheres as pore-forming agents, and phenolic resin solution as the binder. By spraying the phenolic resin binder on the surface of the polymethyl methacrylate microspheres, sprinkling the ceramic premixed powder, and rolling and wrapping to evenly bond the premixed powder on the surface of the pore-forming agent particles, repeating the operation to coat all the premixed powder on the surface of the pore-forming agent particles, and controlling the particle size and addition amount of the pore-forming agent, the content of the phenolic resin binder, the molding pressure, etc., a green body with a tightly bonded premixed powder between the pore-forming agent particles is obtained. Through curing, carbonization, debinding, and sintering, a high-performance large-pore porous silicon nitride ceramic with controllable porosity and pore diameter, no obvious internal defects, and excellent mechanical properties can be prepared, greatly reducing the production cost. The present invention uses an ethanol solution of phenolic resin as the binder, which not only improves the strength of the green body of porous silicon nitride, but also, according to the characteristic that the carbonization cracking temperature of phenolic resin is higher than that of polymethyl methacrylate microspheres and the green body strength can still be maintained during the carbonization process, effectively inhibits the cracking phenomenon caused by the insufficient strength of the green body during the carbonization process when using traditional binders to prepare samples. This process is also easy to prepare a double-layer or more pore size gradient composite structure, which is similar to the tissue structure of natural bone. The pore size gradient composite structure can effectively disperse and balance the load transfer between the implant and the surrounding tissues, which is beneficial to its application in the field of bone transplantation.

[0215] Obviously, the above embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A preparation method of a porous silicon nitride ceramic material with large pore diameter and high porosity, characterized in that, It includes the following steps: Using α-Si3N4 as the matrix, ball-milling and mixing it with a sintering aid to obtain a premixed powder; Using polymethyl methacrylate microspheres as the pore-forming agent and an ethanol solution of phenolic resin as the binder. After uniformly coating a layer of the binder on the surface of the pore-forming agent, adding the premixed powder, and adopting the rolling dumpling method to uniformly coat a layer of the premixed powder on the binder layer on the surface of the pore-forming agent. Repeat coating a layer of the binder and then coating a layer of the premixed powder until all the premixed powder is coated to obtain composite microspheres; the mass concentration of phenolic resin in the binder is 50% - 70%; the addition amount of phenolic resin in the binder is 15% - 20% of the mass of the premixed powder; Pressing the composite microspheres into a green body; Performing a curing treatment on the green body, where the temperature of the curing treatment is 80°C - 150°C and the treatment time is 8h - 12h to cure the phenolic resin in the binder and obtain a cured green body; Successively performing carbonization treatment and debinding treatment on the cured green body to obtain a porous silicon nitride green body; Performing a sintering treatment on the porous silicon nitride green body to obtain a large-pore-diameter and high-porosity porous silicon nitride ceramic material; Among them, the addition amount of the premixed powder is 65% - 80% of the total mass of the composite microspheres; The mass ratio of the pore-forming agent to the premixed powder is 2 - 5:5 - 8; The particle size of the pore-forming agent is 100μm - 500μm.

2. The preparation method of the large-aperture and high-porosity porous silicon nitride ceramic material according to claim 1, characterized in that, The sintering aid is one or both of Al2O3 and Y2O3; The sintering aid accounts for 10wt% - 11wt% of the total mass of the premixed powder.

3. The preparation method of the large-aperture and high-porosity porous silicon nitride ceramic material according to claim 1, characterized in that, The average particle size of the α-Si3N4 is 0.1μm - 1μm.

4. The preparation method of the large-aperture and high-porosity porous silicon nitride ceramic material according to claim 1, characterized in that, The pressure of the pressing is 60MPa - 100MPa.

5. The preparation method of the large-aperture and high-porosity porous silicon nitride ceramic material according to claim 1, characterized in that, The sintering treatment is carried out through the following steps: Putting the porous silicon nitride green body into a graphite crucible buried with Si3N4 - BN powder, and then under a nitrogen atmosphere, heating from room temperature to 1100°C at a rate of 5°C / min - 15°C / min, and then heating to 1800°C at a rate of 4°C / min - 6°C / min, holding for 2h - 4h, and finally cooling to room temperature with the furnace to obtain the large-pore-diameter and high-porosity porous silicon nitride ceramic material.

6. A large-pore-diameter and high-porosity porous silicon nitride ceramic material prepared by the preparation method according to any one of claims 1 - 5.

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