A ceramic material, a ceramic and a method for producing the same

Abstract

In order to improve the conductivity and mechanical strength of silicon carbide ceramics, the application provides a ceramic material, a ceramic and a preparation method thereof, the ceramic material comprising silicon carbide and multi-stage coated graphene; the multi-stage coated graphene comprises graphene particles, a metal layer and a soft carbon layer, the metal layer is coated on the surface of the graphene particles, and the soft carbon layer is coated on the surface of the metal layer.

Description

Technical Field

[0001] This invention relates to the field of ceramic technology, and in particular to a ceramic material, ceramic, and a method for preparing the same. Background Technology

[0002] Silicon carbide ceramics are widely used in high-temperature, corrosive, and abrasive environments due to their excellent high-temperature stability, wear resistance, and chemical inertness. To enhance their conductivity, existing technologies typically employ a method of directly blending carbon materials such as graphene, carbon nanotubes, or conductive carbon black with silicon carbide powder followed by sintering. However, this method has significant limitations: First, physical blending makes it difficult to uniformly disperse carbon materials within the ceramic matrix and form a complete and continuous conductive network, resulting in limited improvement in the conductivity of the composite material. Second, when increasing the amount of carbon materials added to achieve higher conductivity, the interfacial bonding between these carbon materials and the silicon carbide matrix is ​​weak and may hinder the sintering and densification process of ceramic particles, thereby severely degrading the mechanical properties of the material, such as a significant decrease in flexural strength.

[0003] Therefore, there is an urgent need for a ceramic material and its preparation method that synergistically enhances both high electrical conductivity and high mechanical strength. Summary of the Invention

[0004] The purpose of this invention is to provide a ceramic material, a ceramic, and a method for preparing the same, in order to solve the problems of poor electrical conductivity and reduced flexural strength of silicon carbide ceramics in the prior art.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0006] In a first aspect, the present invention provides a ceramic material comprising silicon carbide and multi-level coated graphene;

[0007] The multi-level coated graphene includes graphene particles, a metal layer, and a soft carbon layer. The metal layer coats the surface of the graphene particles, and the soft carbon layer coats the surface of the metal layer.

[0008] Optionally, the metal layer includes at least one of iron, nickel, cobalt, and manganese.

[0009] Optionally, the mass ratio of the metal layer to the soft carbon layer is 1:(0.5~2.5);

[0010] And / or, the mass ratio of the graphene particles to the metal layer is 1:(0.05~0.25).

[0011] Optionally, the thickness of the graphene particles is 1-3 nm, and the diameter of the graphene particles is 10-100 μm.

[0012] Optionally, the ceramic material further includes a sintering aid, and based on 100% of the mass of the ceramic material, the ceramic material comprises the following components by mass:

[0013] Silicon carbide 80%-90%, multi-level coated graphene 5%-15%, sintering aid 1%-5%, and binder 1%-5%.

[0014] Secondly, the present invention provides a ceramic prepared from the above-mentioned ceramic material.

[0015] Thirdly, the present invention provides a method for preparing the above-mentioned ceramic, comprising the following steps:

[0016] Graphene particles and metal chlorides are dispersed in a solvent, and an acidic solution is added to react and obtain a primary coated product.

[0017] A solution of a water-soluble polymer is added to a solution containing the primary coated product, dispersed, and dried to obtain precursor powder.

[0018] The precursor powder was subjected to a first heat treatment at 100-200℃, and then a second heat treatment was performed at 400-600℃ under oxygen-free conditions to obtain multi-level coated graphene.

[0019] Silicon carbide powder, the multi-level coated graphene, sintering aid and binder are mixed to form a preform;

[0020] The preform is subjected to gradient sintering under a protective atmosphere, and the soft carbon layer of the multi-level graphene coating is converted into graphitized carbon to obtain ceramic; the gradient sintering includes a first sintering, a second sintering and a third sintering, and the temperature of the first sintering, the second sintering and the third sintering are increased sequentially.

[0021] Optionally, the temperature of the first sintering is 500-800℃;

[0022] The second sintering temperature is 900-1500℃;

[0023] The temperature of the third sintering is 1500-2000℃.

[0024] Optionally, the metal chloride is selected from one or more of ferric chloride, nickel chloride, cobalt chloride, and manganese chloride;

[0025] And / or, the water-soluble polymer is selected from one or more of chitosan, starch, sodium alginate, lignin sulfonate, and water-soluble phenolic resin prepolymer.

[0026] Optionally, the mass ratio of the graphene particles to the metal chloride is 1:0.1~0.5;

[0027] And / or, the mass concentration of the solution of the water-soluble polymer is 5%-10%.

[0028] The multi-level coated graphene of this invention uses graphene particles as the conductive core, with a metal layer and a soft carbon layer constructed on the surface. The metal layer acts as a catalyst during subsequent sintering, promoting the transformation of the outermost soft carbon into highly ordered graphitized carbon. This forms a highly conductive shell layer around the graphene particles that is tightly bonded to the core, significantly enhancing the intrinsic conductivity and structural stability of a single graphene particle. When the multi-level coated graphene is combined with silicon carbide powder and sintered, the outer soft carbon and the catalytically transformed carbon shell can form a tighter interfacial bond with the silicon carbide particles at high temperatures. This effectively alleviates the problem of weak interfacial bonding between carbon materials and ceramic matrices caused by large differences in physical properties in traditional physical blending. The multi-level coated graphene of this invention not only constitutes a highly efficient conductive unit but also improves the compatibility and bonding force between the conductive phase and the ceramic matrix, laying a material foundation for achieving a synergistic improvement in high conductivity and high mechanical strength. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a SEM image of the multi-level coated graphene of Embodiment 1 of the present invention, wherein the soft carbon layer is semi-transparent under SEM.

[0031] Figure 2 This is a SEM image of the ceramic of Embodiment 1 of the present invention;

[0032] Figure 3 This is a SEM image of the metal oxides attached to graphene particles in Example 1 of the present invention, wherein the metal oxides are distributed in a dotted pattern.

[0033] Figure 4 This is a SEM image of the graphene particles of the present invention. Detailed Implementation

[0034] To make the technical problems solved, technical solutions, and beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0035] One embodiment of the present invention provides a ceramic material comprising silicon carbide and multi-level coated graphene;

[0036] The multi-level coated graphene includes graphene particles, a metal layer, and a soft carbon layer. The metal layer coats the surface of the graphene particles, and the soft carbon layer coats the surface of the metal layer.

[0037] Specifically, the multi-level coated graphene uses graphene particles as the conductive core, with a metal layer and a soft carbon layer constructed on the surface. The metal layer acts as a catalyst during subsequent sintering, promoting the transformation of the outermost soft carbon into highly ordered graphitized carbon. This forms a highly conductive shell layer around the graphene particles that is tightly bonded to the core, significantly enhancing the intrinsic conductivity and structural stability of a single graphene particle. When the multi-level coated graphene is combined with silicon carbide powder and sintered, the outer soft carbon and the catalytically transformed carbon shell can form a tighter interfacial bond with the silicon carbide particles at high temperatures. This effectively alleviates the problem of weak interfacial bonding between carbon materials and ceramic matrices caused by large differences in physical properties in traditional physical blending. The multi-level coated graphene of this invention not only constitutes a highly efficient conductive unit but also improves the compatibility and bonding force between the conductive phase and the ceramic matrix, laying a material foundation for achieving a synergistic improvement in high conductivity networks and high mechanical strength.

[0038] In some embodiments, the metal layer includes at least one of iron, nickel, cobalt, and manganese.

[0039] Specifically, the metallic element can effectively reduce the energy barrier of carbon atom rearrangement at a suitable temperature, guiding the disordered carbon structure in the outer soft carbon layer to transform into a graphite-like microcrystalline structure. This catalytic transformation not only improves the conductivity of the coating layer itself, enabling it to carry current more efficiently in conjunction with the core graphene, but also the generated graphite-like carbon structure has a better lattice matching degree with silicon carbide, thereby further strengthening the chemical bonding and physical anchoring between the conductive phase and the ceramic matrix, ensuring that the conductive network is not prone to failure under stress.

[0040] It is understandable that the metal layer can be formed by different metals sequentially through atomic deposition or electroplating, or by a mixture of multiple metals uniformly dispersed on the surface of graphene particles to form a metal layer.

[0041] In some embodiments, the mass ratio of the metal layer to the soft carbon layer is 1:(0.5~2.5);

[0042] And / or, the mass ratio of the graphene particles to the metal layer is 1:(0.05~0.25).

[0043] Specifically, the mass ratio of the metal layer to the soft carbon layer includes, but is not limited to, 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.7, 1:2, 1:2.3, and 1:2.5; the mass ratio of the graphene particles to the metal layer includes, but is not limited to, 1:0.05, 1:0.08, 1:0.1, 1:0.12, 1:0.15, 1:0.17, 1:0.2, 1:0.23, and 1:0.25. If the metal layer is too thin, there will be insufficient catalytic sites, making it difficult to fully graphitize all the soft carbon layers; if it is too thick, it may affect the uniformity of coating and the overall conductivity due to self-agglomeration or excessive reaction, affecting the soft carbon layer. The thickness needs to provide sufficient carbon source to form a continuous and complete reinforced conductive shell, but it should not be too thick to generate excessive internal stress or hinder the mass transfer process of the catalyst during heat treatment. The mass ratio of graphene particles to metal layers determines the density of catalytic sites available per unit graphene surface. This ratio needs to ensure that the metal is sufficient to form a continuous or uniformly distributed catalytic layer on the graphene surface to achieve complete and effective catalytic graphitization of the soft carbon layer, avoiding uneven coating quality due to insufficient catalyst. By limiting a reasonable ratio range, it is possible to ensure that a composite shell with a coordinated ratio and complementary functions is formed after heat treatment, thereby achieving the best balance between enhanced conductivity and interface strengthening.

[0044] In some embodiments, the thickness of the graphene particles is 1-3 nm, and the diameter of the graphene particles is 10-100 μm.

[0045] Specifically, the thickness of the graphene particles includes, but is not limited to, 1nm, 1.3nm, 1.5nm, 2nm, 2.5nm, 2.7nm, and 3nm; the sheet diameter of the graphene particles includes, but is not limited to, 10μm, 30μm, 50μm, 70μm, 90μm, and 100μm; and the number of graphene particles is 3-10 layers. A suitable graphene particle sheet diameter is beneficial for its dispersion in the solvent and the final ceramic body, avoiding sedimentation due to excessively large particles or agglomeration due to excessively small particles.

[0046] In some embodiments, the ceramic material further includes a sintering aid, and the ceramic material comprises the following components by weight, based on 100% of the ceramic material:

[0047] Silicon carbide 80%-90%, multi-level coated graphene 5%-15%, sintering aid 1%-5%, and binder 1%-5%.

[0048] Specifically, the mass composition of the silicon carbide includes, but is not limited to, 80%, 82%, 85%, 88%, and 90%; the mass composition of the multi-level coated graphene includes, but is not limited to, 5%, 8%, 10%, 12%, and 15%; the mass composition of the sintering aid includes, but is not limited to, 1%, 2%, 3%, 4%, and 5%; and the mass composition of the binder includes, but is not limited to, 1%, 2%, 3%, 4%, and 5%. Silicon carbide, as the matrix, provides the main mechanical properties and chemical stability. The multi-level coated graphene, within the stated proportions, can form a percolating conductive network without disrupting the matrix continuity due to excessive addition. The addition of the sintering aid can promote the densification of silicon carbide particles at lower temperatures, reduce sintering defects, and improve the overall mechanical strength of the ceramic. The binder ensures the strength and integrity of the green body during the forming stage. These mass components are the structural guarantee for achieving both high electrical conductivity and high mechanical strength in the final ceramic product.

[0049] The sintering aid includes one or both of alumina and yttrium oxide.

[0050] The adhesive is carboxymethyl cellulose.

[0051] An embodiment of the present invention also provides a ceramic, which is prepared from the above-described ceramic material.

[0052] Specifically, such as Figure 2 The SEM image of the ceramic product shows that the graphene structure-metal particles are firmly bonded to the silicon carbide matrix. The ceramic has formed a stable and continuous conductive pathway constructed by high-performance multi-level coated graphene. At the same time, the ceramic matrix has achieved high densification and is firmly bonded to the conductive phase interface. Thus, at the product level, it synergistically achieves conductivity and mechanical properties far exceeding those of traditional blended composite materials.

[0053] An embodiment of the present invention also provides a method for preparing the above-mentioned ceramic, comprising the following steps:

[0054] Graphene particles and metal chlorides are dispersed in a solvent, and an acidic solution is added to react and obtain a primary coated product.

[0055] A solution of a water-soluble polymer is added to a solution containing the primary coated product, dispersed, and dried to obtain precursor powder.

[0056] The precursor powder was subjected to a first heat treatment at 100-200℃, and then a second heat treatment was performed at 400-600℃ under oxygen-free conditions to obtain multi-level coated graphene.

[0057] Silicon carbide powder, the multi-level coated graphene, sintering aid and binder are mixed to form a preform;

[0058] The preform is subjected to gradient sintering under a protective atmosphere, and the soft carbon layer of the multi-level graphene coating is converted into graphitized carbon to obtain ceramic; the gradient sintering includes a first sintering, a second sintering and a third sintering, and the temperature of the first sintering, the second sintering and the third sintering are increased sequentially.

[0059] Specifically, graphene particles (such as...) Figure 4 The graphene oxide (as shown in Figure 3) is dispersed with metal chlorides and reacted with an acidic solution, such as oxalic acid solution. The metal chlorides react with the acidic solution to form oxalate precipitate. The oxalate precipitate is then subjected to a first heat treatment to form metal oxides (as shown in Figure 3, the metal oxides are distributed in a dotted pattern), achieving uniform deposition of metal oxides on the graphene surface. Subsequently, a water-soluble polymer solution is added, using the polymer as a soft carbon precursor to coat the primary coating product. After subsequent drying and staged heat treatment, these metal oxides are reduced to elemental metals during subsequent oxygen-free heat treatment and sintering. The polymer carbonization forms a soft carbon layer, and during gradient sintering, the metal element catalyzes the graphitization of the soft carbon layer, thereby precisely constructing multi-level coated graphene. Cylindrical, plate-like, and sheet-like preforms can be formed through pressing, injection, extrusion, etc., and the preforms are then gradient sintered. By gradually increasing the temperature, the binder is gently removed, promoting the action of the sintering aid, and ultimately achieving full densification of the silicon carbide matrix and a firm bond with the multi-level coated graphene at high temperature. The ceramic preparation method of this invention ensures the controllable preparation of the multi-level coated structure and its full utilization of its effectiveness in the ceramic matrix.

[0060] The protective atmosphere is nitrogen or argon.

[0061] In some embodiments, the temperature of the first sintering is 500-800°C;

[0062] The second sintering temperature is 900-1500℃;

[0063] The temperature of the third sintering is 1500-2000℃.

[0064] Specifically, the first sintering temperature includes, but is not limited to, 500℃, 600℃, 700℃, and 800℃; the first sintering is carried out at 500-800℃, and its main purpose is to allow the binder to decompose and be removed slowly, avoiding cracking of the green body due to gas generated by rapid pyrolysis; the second sintering temperature includes, but is not limited to, 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, and 1500℃; the second sintering is carried out at 900-1500℃, during which the sintering aid begins to activate, promoting the rearrangement and initial densification of silicon carbide particles, while simultaneously multi-level coating of the metal elements in the graphene. The catalytic effect is significant, and the soft carbon layer begins to transform into a graphite-like structure with better conductivity. The third sintering temperature includes, but is not limited to, 1500℃, 1600℃, 1700℃, 1800℃, 1900℃, and 2000℃. The third sintering is carried out at a high temperature of 1500-2000℃, during which silicon carbide gradually sinterstens and densifies. Furthermore, the silica on the surface of the silicon carbide particles can remove the ungraphitized soft carbon layer at high temperature, resulting in silicon carbide ceramics containing a high-quality graphene conductive network. The temperature control of gradient sintering is the core process guarantee for balancing the removal of organic components, the catalytic reaction, and the high-quality sintering of the ceramic matrix.

[0065] In some embodiments, the metal chloride is selected from one or more of ferric chloride, nickel chloride, cobalt chloride, and manganese chloride;

[0066] And / or, the water-soluble polymer is selected from one or more of chitosan, starch, sodium alginate, lignin sulfonate, and water-soluble phenolic resin prepolymer.

[0067] Specifically, the metal ions of the selected metal chlorides are readily hydrolyzed or react with hydroxide ions under acidic conditions to generate precipitates of the corresponding metal oxides, thereby efficiently and uniformly coating the graphene surface and providing a reliable precursor for subsequent catalytic activity. Water-soluble polymers such as chitosan, starch, and water-soluble phenolic resin prepolymers not only have good water dispersibility to ensure uniform coating, but also have a high carbon residue rate in subsequent heat treatment, which can be effectively converted into the desired soft carbon layer.

[0068] In some embodiments, the mass ratio of the graphene particles to the metal chloride is 1:0.1~0.5;

[0069] And / or, the mass concentration of the solution of the water-soluble polymer is 5%-10%.

[0070] Specifically, the mass ratio of graphene particles to the metal chloride includes, but is not limited to, 1:0.1, 1:0.2, 1:0.3, 1:0.4, and 1:0.5, ensuring that an appropriate amount of metal ions are available for deposition during the reaction stage, thus guaranteeing subsequent catalytic activity. The mass concentration of the water-soluble polymer solution includes, but is not limited to, 5%, 6%, 7%, 8%, 9%, and 10%. Within this mass concentration range, the viscosity and molecular chain extension of the water-soluble polymer solution are most suitable, which can achieve sufficient and uniform coating of the primary coating product, providing a uniform precursor for the soft carbon layer, while avoiding the problems of excessively thick coating or agglomeration due to excessively high concentration, and incomplete coating due to excessively low concentration.

[0071] In some embodiments, the method for preparing ceramics includes the following steps:

[0072] (1) Preparation of multi-level coated graphene:

[0073] Graphene powder is dispersed in water, and one or more of ferric chloride, nickel chloride, cobalt chloride, and manganese chloride are added. The ratio of graphene to metal chloride is 1:0.1~0.5, and the mass percentage of graphene in water is 0.5-2wt%. After mixing evenly, 0.1mol / L oxalic acid solution is added dropwise. When the molar amount of oxalic acid solution reaches 1.2 times the excess, the addition of oxalic acid is stopped. 5-10wt% of water-soluble polymer solution is added. Water-soluble polymers include one or more of chitosan, starch, sodium alginate, lignin sulfonate, and phenolic resin (water-soluble prepolymer). After mixing evenly, the precursor powder is obtained by spray drying.

[0074] The precursor powder heat treatment consists of two steps: the first step is at a temperature of 100-200℃, and the second step is at a temperature of 400-600℃ in an oxygen-free environment, which decomposes the polymer coating on the graphene surface into a soft carbon structure, resulting in multi-level coated graphene powder.

[0075] (2) Making the ceramic body:

[0076] Silicon carbide powder, multi-level coated graphene powder, sintering aid, and binder are mixed and water is added to prepare silicon carbide ceramic slurry. The slurry consists of 80%-90% silicon carbide powder, 5%-15% multi-level coated graphene powder, 1%-5% sintering aid, and 1%-5% binder, based on the mass of the ceramic material (100%). The slurry is then formed into cylindrical, plate-shaped, or sheet-shaped preforms by pressing, injection, or extrusion.

[0077] (3) Gradient sintering:

[0078] Gradient sintering is performed under a protective atmosphere:

[0079] First sintering (500-800℃): Degreasing and removal of binder;

[0080] Second sintering (900-1500℃), soft carbon graphitization;

[0081] The third sintering (1500-2000℃) yields ceramics.

[0082] The present invention will be further illustrated by the following examples.

[0083] Example 1

[0084] (1) Preparation of multi-level coated graphene:

[0085] Graphene powder with a sheet diameter of 50 μm and a thickness of 2 nm was dispersed in water and nickel chloride was added. The ratio of graphene to nickel chloride was 1:0.25, and the mass percentage of graphene in water was 0.5 wt%. After mixing evenly, 0.1 mol / L oxalic acid solution was added dropwise. When the molar amount of oxalic acid solution reached 1.2 times the excess, the addition of oxalic acid was stopped. 8 wt% water-soluble polymer solution (chitosan aqueous solution) was added, mixed evenly, and then spray-dried to obtain the precursor powder.

[0086] The precursor powder heat treatment consists of two steps: the first step is at 150℃ and the second step is at 500℃ in an oxygen-free environment, which decomposes the polymer coating on the graphene surface into a soft carbon structure, resulting in multi-level coated graphene powder. The mass ratio of graphene particles to metal layers is 1:0.1, and the mass ratio of metal layers to soft carbon layers is 1:1.

[0087] (2) Making the ceramic body:

[0088] Silicon carbide powder, multi-level coated graphene powder, sintering aid (alumina), and binder (carboxymethyl cellulose) are mixed and water is added to prepare a silicon carbide ceramic slurry. The slurry comprises, based on the mass of the ceramic material as 100%, 85% silicon carbide powder, 10% multi-level coated graphene powder, 3% sintering aid, and 2% binder. The slurry is then formed into a plate-shaped preform by injection molding.

[0089] (3) Gradient sintering:

[0090] Gradient sintering was performed under a nitrogen atmosphere.

[0091] First sintering (600℃), degreasing and removal of binder;

[0092] Second sintering (1200℃), soft carbon graphitization;

[0093] The third sintering (2000℃) yields ceramics.

[0094] Example 2-13

[0095] Examples 2-13 are mostly the same as those in Example 1, with the differences shown in Table 1.

[0096] Table 1 Preparation parameters for Examples 1-13

[0097]

[0098] Example 14

[0099] Example 14 is the same as Example 1 in most steps, except that the temperature of the second heat treatment is 400°C.

[0100] Example 15

[0101] Example 15 is the same as Example 1 in most steps, except that the temperature of the second heat treatment is 600°C.

[0102] Example 16

[0103] Example 16 is the same as Example 1 in most steps, except that the temperature of the second heat treatment is 300°C.

[0104] Example 17

[0105] Example 17 is similar to Example 1 in most steps, except that the temperature of the second heat treatment is 700°C.

[0106] Example 18

[0107] Example 18 is similar to Example 1 in most steps, except that the second sintering temperature is 900°C.

[0108] Example 19

[0109] Example 19 is similar to Example 1 in most steps, except that the second sintering temperature is 1500°C.

[0110] Example 20

[0111] Example 20 is the same as Example 1 in most steps, except that the second sintering temperature is 700°C.

[0112] Example 21

[0113] Example 21 is similar to Example 1 in most steps, except that the second sintering temperature is 1700°C.

[0114] Comparative Example 1

[0115] Comparative Example 1 is the same as Example 1 in most steps, except that ordinary graphene is used instead of multi-level coated graphene.

[0116] Comparative Example 2

[0117] Comparative Example 2 is similar to Example 1 in most steps, except that the ceramic material does not contain a metal layer.

[0118] Comparative Example 3

[0119] Comparative Example 3 is similar to Example 1 in most steps, except that the ceramic material does not contain a soft carbon layer.

[0120] Performance testing

[0121] The ceramics prepared in the above examples and comparative examples were subjected to the following tests:

[0122] (1) Conductivity test: Four-probe method, test method SJ / T 11637-2016 "Method for testing resistivity of semiconductor ceramic materials", four equally spaced probes are arranged in a straight line and pressed on the sample surface. A constant DC current is applied through the two outer probes, and the voltage drop between the two inner probes is measured with a high-precision voltmeter. Based on the measured current I and voltage V, combined with the sample thickness W and geometric correction coefficient η, the bulk resistivity of the material is calculated according to the formula ρ=η·W·(V / I).

[0123] (2) Bending strength test: Three-point bending method, GB / T 6569-2006 "Test method for bending strength of fine ceramics", measure the sample size, place it stably on two support points, align the force application point with the center of the sample, load at a constant speed until the sample breaks, record the maximum load and the fracture location, test at least 5 valid samples (fracture point located in the middle area of ​​the span), calculate the bending strength based on the load and size and take the average value.

[0124] The ceramic test results of the above embodiments and comparative examples are shown in Table 2.

[0125] Table 2. Ceramic test results of the examples and comparative examples.

[0126]

[0127] As shown in Table 2, when the mass ratio of the metal layer to the soft carbon layer is 1:(0.5~2.5), the diameter of the graphene particles is 10-100μm, the mass ratio of the graphene particles to the metal layer is 1:(0.05~0.25), and the mass ratio of the graphene particles to the metal chloride is 1:0.1~0.5, and the mass composition of silicon carbide is 80%-90%, the mass composition of multi-level coated graphene is 5%-15%, the mass composition of sintering aid is 1%-5%, and the mass composition of binder is 1%-5%, the multi-level coated graphene forms a continuous conductive network and is firmly bonded to the SiC matrix interface. The prepared ceramic sample has high conductivity and strong bending strength.

[0128] The test results of Examples 1-5 show that when the mass ratio of the metal layer to the soft carbon layer is too low (e.g., 1:0.2, Example 5), the soft carbon layer is too thin, which not only fails to fully connect the graphene particles to build a complete conductive network, but also weakens the interfacial bonding because it fails to completely cover the metal layer. At the same time, it leads to an increase in the porosity of the matrix, resulting in a double decrease in conductivity and mechanical properties. Conversely, when this ratio is too high (e.g., 1:3.5, Example 4), the proportion of the metal layer is too low, the catalytic sites are severely insufficient, the soft carbon layer cannot be fully graphitized, the quality of the formed conductive network is poor and there are a lot of defects, which also leads to a significant deterioration in both properties.

[0129] As can be seen from the test results of Examples 6-9, when the graphene particle size is too small and the mass ratio of graphene particles to metal layers is too high (Example 8), the formed metal layer is too thick and uneven, and some metal may even detach from the graphene surface, destroying the compactness of the matrix and causing a simultaneous decrease in conductivity and mechanical properties. Conversely, when the mass ratio of graphene to metal layers is too low (Example 9), a continuous catalytic layer cannot be formed on the graphene surface, causing most of the soft carbon layer to fail to be catalyzed into highly conductive graphitic carbon, resulting in the failure of the entire multi-level coating structure.

[0130] The test results of Examples 10-13 show that when the proportion of multi-level coated graphene is too high (18%, Example 12) and the sintering aid is excessive, the continuity of the silicon carbide matrix is ​​severely damaged, resulting in a loose structure and the formation of through pores. The conductive network matrix fails and the strength drops sharply. Conversely, when the proportion of multi-level coated graphene is too low (4%, Example 13), an effective percolation conductive network cannot be formed in the matrix, and the conductivity is severely insufficient.

[0131] The test results of Examples 14-17 show that when the second heat treatment temperature is within the optimized range of 400-600℃, a good soft carbon layer is formed (Examples 14 and 15). When the temperature is too low (300℃, Example 16), the polymer precursor cannot be completely pyrolyzed and transformed into a dense soft carbon layer, resulting in the failure of the coating structure and a significant decrease in performance. Conversely, when the temperature is too high (700℃, Example 17), the soft carbon layer undergoes premature decomposition or over-carbonization, introducing defects on the graphene surface and impairing its function as a conductive unit and interface transition layer.

[0132] The test results from Examples 18-21 show that when the second sintering temperature is within the optimized range of 900-1500℃, the graphitization of the soft carbon layer and the densification of the matrix can proceed synergistically (Examples 18 and 19). When the temperature is too low (700℃, Example 20), the soft carbon layer cannot be effectively graphitized, and the silicon carbide matrix also fails to densify, resulting in a decrease in electrical conductivity and mechanical properties. Conversely, when the temperature is too high (1700℃, Example 21), abnormal growth of silicon carbide grains is triggered, which reacts adversely with the carbon layer, destroying the integrity of the conductive network and severely impairing the electrical conductivity.

[0133] A comparison of the test results of Comparative Example 1 and the Examples shows that when ordinary graphene is used instead of multi-level coated graphene, the lack of a catalytic metal layer and soft carbon transition layer on the graphene surface results in weak interfacial bonding with the silicon carbide matrix. Furthermore, a continuous and efficient conductive network cannot be constructed during sintering. Therefore, the conductivity and flexural strength of the material are significantly lower than those of the Examples of the Present Invention. A comparison of the test results of Comparative Example 2 and the Examples shows that when the ceramic material does not contain a metal layer, the soft carbon layer lacks the driving force for catalytic graphitization, remaining a disordered carbon structure with low conductivity, and thus failing to effectively improve overall conductivity. Although the soft carbon layer provides some interfacial bonding, the effect is limited, resulting in minimal improvement in the material's conductivity and low mechanical strength. Comparison of the test results of Comparative Example 3 and the Example shows that when the ceramic material does not contain a soft carbon layer, there is a lack of a flexible carbon transition layer between the graphene directly coated by the metal layer and the silicon carbide matrix, which can participate in the interface bonding. This results in extremely poor interface bonding between the two phases, which is prone to becoming a crack source under stress, severely degrading the mechanical properties of the material. At the same time, it is also difficult for the metal-graphene units to form a continuous network, resulting in limited improvement in conductivity.

[0134] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A ceramic material, characterized in that, Including silicon carbide and multi-level coated graphene; The multi-level coated graphene includes graphene particles, a metal layer, and a soft carbon layer, wherein the metal layer coats the surface of the graphene particles, and the soft carbon layer coats the surface of the metal layer. The metal layer includes at least one of iron, nickel, cobalt, and manganese; The preparation method of the multi-level coated graphene includes the following steps: The graphene particles and metal chlorides are dispersed in a solvent, and an acidic solution, including oxalic acid, is added to react and a primary coated product is obtained. A solution of a water-soluble polymer is added to a solution containing the primary coated product, dispersed, and dried to obtain precursor powder. The precursor powder is subjected to a first heat treatment at 100-200℃, and then a second heat treatment is performed under oxygen-free conditions at 400-600℃ to obtain multi-level coated graphene.

2. The ceramic material according to claim 1, characterized in that, The mass ratio of the metal layer to the soft carbon layer is 1:(0.5~2.5); And / or, the mass ratio of the graphene particles to the metal layer is 1:(0.05~0.25).

3. The ceramic material according to claim 1, characterized in that, The graphene particles have a thickness of 1-3 nm and a sheet diameter of 10-100 μm.

4. The ceramic material according to claim 1, characterized in that, The ceramic material also includes a sintering aid, and based on 100% of the mass of the ceramic material, the ceramic material comprises the following components by mass: Silicon carbide 80%-90%, multi-level coated graphene 5%-15%, sintering aid 1%-5%, and binder 1%-5%.

5. A ceramic, characterized in that, It is prepared from the ceramic material described in any one of claims 1-4.

6. The method for preparing ceramics as described in claim 5, characterized in that, Includes the following steps: Silicon carbide powder, multi-level coated graphene, sintering aid and binder are mixed to form a preform; The preform is subjected to gradient sintering under a protective atmosphere, and the soft carbon layer of the multi-level graphene coating is converted into graphitized carbon to obtain ceramic; the gradient sintering includes a first sintering, a second sintering and a third sintering, and the temperature of the first sintering, the second sintering and the third sintering are increased sequentially.

7. The preparation method according to claim 6, characterized in that, The first sintering temperature is 500-800℃; The second sintering temperature is 900-1500℃; The temperature of the third sintering is 1500-2000℃.

8. The preparation method according to claim 6, characterized in that, The metal chloride is selected from one or more of ferric chloride, nickel chloride, cobalt chloride, and manganese chloride; And / or, the water-soluble polymer is selected from one or more of chitosan, starch, sodium alginate, lignin sulfonate, and water-soluble phenolic resin prepolymer.

9. The preparation method according to claim 6, characterized in that, The mass ratio of the graphene particles to the metal chloride is 1:0.1~0.5; And / or, the mass concentration of the solution of the water-soluble polymer is 5%-10%.

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