A method for preparing conductive ceramics, the resulting product, and its applications.

Abstract

This invention discloses a method for preparing conductive ceramics, the resulting products, and their applications. The invention uses alumina powder, coal gangue powder, fly ash powder, and organic carbon source as matrix raw materials, and polyvinyl alcohol as a binder, employing a rapid hot-pressing, high-temperature sintering, carbothermal reduction process to prepare conductive ceramics. This invention features a simple process, low cost, low energy consumption, high production efficiency, and good environmental performance, making it easy for industrial production. The resulting conductive ceramics exhibit high mechanical properties, good conductivity, and low resistance, making them a preferred material for indoor heaters, electromagnetic shielding devices, high-temperature sensors, aerospace thermal protection systems, and aero-engine applications.

Description

Technical Field

[0001] This invention relates to a method for preparing conductive ceramics, specifically a method for preparing conductive ceramics that is simple, environmentally friendly, and low in cost. It also relates to conductive ceramics prepared according to this method, which have good conductivity and can be used in electromagnetic shielding devices, high-temperature sensors, aerospace thermal protection systems, and aero-engines, belonging to the field of functional ceramics technology. Background Technology

[0002] Coal gangue and fly ash are industrial solid wastes generated during coal mining and combustion. Coal gangue, in particular, is a significant solid waste produced during coal mining and washing. Its main use is in producing low-value-added products, and its comprehensive utilization rate is not high. Fly ash consists of fine solid particles collected by dust collection devices after pulverized coal is burned in boilers of coal-fired power plants, carried out of the furnace with the flue gas. Fly ash is mainly used as concrete filler, in new building materials, and in roadbed engineering, with a comprehensive utilization rate reaching 70%, but the added value of the products produced is low. Existing research indicates that coal gangue and fly ash are rich in aluminum and silicon, making them potential candidate raw materials for ceramic production. They have great application prospects in adsorption materials, building insulation materials, kilns, high-temperature waste heat recovery, and solar thermal storage. Using coal gangue and fly ash in the field of functional ceramics can significantly improve their product added value and recycling efficiency.

[0003] Conductive ceramics, with their excellent high-temperature stability, good chemical inertness, and outstanding mechanical properties, have demonstrated significant application value in scenarios such as indoor heaters, electromagnetic shielding devices, high-temperature sensors, aerospace thermal protection systems, and key components of aero-engines. However, their inherent poor conductivity remains a key bottleneck restricting their further expansion in high-power electronic devices, precision sensing, and other high-end fields. Patent CN106187084 discloses a method for preparing stable conductive ceramics, using barium carbonate, polyvinyl butyral, yttrium oxide, mullite, polyethylene wax, boron oxide, coal gangue, and ethylene glycol as raw materials to prepare stable conductive ceramics. Patent CN118754674A discloses a zirconium boride-based conductive ceramic material and its preparation process, using zirconium silicate, boron carbide, and phenolic resin as raw materials. A carbothermic / borothermic reduction method is used to react at high temperature to obtain zirconium boride / silicon carbide mixed ceramic powder. The resulting mixed powder is then formulated into a slurry, dried, crushed, and formed into a blank, and sintered using a pressureless sintering method. Patent CN108821757A discloses a method for preparing composite conductive ceramics, using glyceryl monostearate, xanthan gum, nano-silicon carbide, silicon dioxide, aluminum titanate, titanium nitride, glass microspheres, lanthanum oxide, and plant starch as raw materials to prepare stable conductive ceramics. Patent CN120483765A discloses a simplified method for preparing conductive alumina ceramics, using wheat starch and corn starch as main raw materials. These are converted into volatile carbon sources through a high-temperature carbonization process under inert gas protection. The alumina ceramics are then subjected to surface deposition and carburizing treatment to obtain alumina conductive ceramics with a certain conductivity.

[0004] Although the above-mentioned existing technologies have certain advantages, they still have the following problems: (1) There are many types of raw materials, and it is difficult to mix them during the preparation process; (2) The raw material cost is high, the preparation process is complicated, and the production cycle is long; (3) Ordinary sintering temperature can easily cause abnormal growth of alumina grains. Excessively large alumina particles will push carbon to the grain boundary and accumulate, making it difficult to form a continuous and fine nanoscale conductive network, which is not conducive to improving the conductivity of ceramics.

[0005] Therefore, developing a conductive ceramic that is simple to process, environmentally friendly, low in cost, and has good conductivity has become a research focus. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing conductive ceramics and the resulting product. This invention uses alumina powder, coal gangue powder, fly ash powder, and organic carbon source as matrix raw materials, resulting in fewer raw material types and lower costs. Polyvinyl alcohol is used as a binder, and the conductive ceramics are prepared using a rapid hot-pressing, high-temperature sintering, carbothermal reduction process. The process is simple, environmentally friendly, and suitable for large-scale production. The resulting conductive ceramics exhibit good conductivity, high mechanical properties, and low resistance, solving the problems of high raw material costs, complex processes, and difficulty in large-scale industrial production in current conductive ceramic preparation methods.

[0007] The specific technical solution of this invention is as follows:

[0008] A method for preparing conductive ceramics, the method comprising the following steps:

[0009] (1) Alumina powder, silicon source, organic carbon source and polyvinyl alcohol solution are mixed and ball-milled to obtain mixed powder;

[0010] (2) Press the mixed powder into a ceramic blank;

[0011] (3) The ceramic blank is dried, and then subjected to rapid hot pressing, high-temperature sintering, and carbothermic reduction to obtain conductive ceramic.

[0012] Further, in step (1), the silicon source is coal gangue powder or fly ash powder. Coal gangue powder is a solid waste with silicon dioxide, aluminum oxide, and feldspar as the main mineral phases. The Al2O3 content in coal gangue powder is 15~25wt%, and the SiO2 content is 50~60wt%. The particle size of coal gangue powder is preferably 2~30μm. Fly ash powder is a solid waste with silicon dioxide, aluminum oxide, and feldspar as the main mineral phases. The Al2O3 content in fly ash powder is 15~25wt%, the SiO2 content is 45~55wt%, and the CaO content is 5~20wt%. The particle size of fly ash powder is preferably 2~120μm.

[0013] Furthermore, in step (1), the alumina powder is one or both of α-alumina and tabular corundum. The alumina powder contains Al2O3 content ≥99wt% and Na2O content ≤0.1wt%. The average particle size of the alumina powder is preferably 1~20μm.

[0014] Furthermore, in step (1), the organic carbon source is one or more of phenolic resin, corn starch, dextrin, and lignin fiber.

[0015] Furthermore, in step (1), the polyvinyl alcohol solution is a solution formed by polyvinyl alcohol and ethanol, with a concentration of 4-8 wt%. The molecular weight of polyvinyl alcohol is 120,000-150,000.

[0016] Furthermore, in step (1), when the silicon source is coal gangue powder, the amount of alumina powder used is 49-62 parts by weight, for example, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, 60 parts, 61 parts, or 62 parts; the amount of coal gangue powder used is 25-33 parts by weight, for example, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts, 30 parts, 31 parts, 32 parts, or 33 parts; the amount of organic carbon source used is 5-25 parts by weight, for example, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, or 20 parts. 21, 22, 23, 24, and 25 parts. The amount of polyvinyl alcohol solution used is 3-8 wt% of the total mass of the matrix raw materials (i.e., coal gangue powder, alumina powder, and organic carbon source), for example, 3%, 4%, 5%, 6%, 7%, and 8%.

[0017] Furthermore, in step (1), when the silicon source is fly ash powder, the amount of alumina powder used is 60-70 parts by weight, for example, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, or 70 parts; the amount of fly ash powder used is 15-20 parts by weight, for example, 15, 16, 17, 18, 19, or 20 parts; and the amount of organic carbon source used is 10-20 parts by weight, for example, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 parts. The amount of polyvinyl alcohol used is 3-8 wt% of the total mass of the matrix raw materials (i.e., the sum of fly ash powder, alumina powder, and organic carbon source), for example, 3%, 4%, 5%, 6%, 7%, or 8%.

[0018] Furthermore, in step (1), the ball milling time is 3 to 5 hours, for example 3h, 3.5h, 4h, 4.5h, 5h.

[0019] Furthermore, in step (2), the molding pressure is 20~40MPa, for example 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa. The pressing time is 3~10min, for example 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min.

[0020] Furthermore, in step (3), the drying is vacuum drying. The drying temperature is 100~120℃, for example 100℃, 105℃, 110℃, 115℃, 120℃, and the drying time is 3~5 hours, for example 3h, 3.5h, 4h, 4.5h, 5h.

[0021] Furthermore, in step (3), the present invention performs carbothermic reduction and hot-pressing high-temperature sintering simultaneously. When the silicon source is coal gangue powder, the rapid hot-pressing high-temperature sintering carbothermic reduction is carried out under an inert atmosphere. First, the temperature is raised from room temperature to 1200℃ at a heating rate of 100-110℃ / min, with a pressure of 5-10 MPa, for example, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, or 10 MPa. Then, the temperature is raised to 1300-1500℃ at a heating rate of 50-60℃ / min, for example, 1300℃, 1350℃, 1400℃, 1450℃, or 1500℃, with a pressure of 11-30 MPa, for example, 11 MPa, 15 MPa, 20 MPa, 25 MPa, or 30 MPa. The temperature is then held at this temperature for 10-30 minutes, for example, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes.

[0022] Furthermore, in step (3), when the silicon source is fly ash powder, the rapid hot pressing high-temperature sintering carbothermic reduction is carried out under an inert atmosphere. First, the temperature is raised from room temperature to 1000℃ at a heating rate of 100-110℃ / min, and the pressure is 5~10MPa, for example, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa, 10MPa. Then, the temperature is raised to 1200~1400℃ at a heating rate of 50-60℃ / min, for example, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, and the pressure is 11~20 MPa, for example, 11MPa, 15MPa, 20MPa, and held at this temperature for 10~30min, for example, 10 min, 15 min, 20 min, 25 min, 30 min.

[0023] Lower pressure was used in the early stage of sintering to ensure the continuity of the circuit and the stability of the system, while higher pressure was used in the later stage of sintering to ensure the densification of the ceramic.

[0024] Furthermore, in step (3), the inert atmosphere is preferably a nitrogen atmosphere, wherein the nitrogen purity is ≥99% and the flow rate is 4-6 L / min.

[0025] Furthermore, the conductive ceramic obtained by this invention exhibits stable performance. When the silicon source is coal gangue powder, the resulting conductive ceramic is a mullite-alumina-based conductive ceramic with a porosity of 32%~58% and a bulk density of 1.62~2.12 g / cm³. 3 The dielectric strength is 60MPa~98MPa, and the resistivity is 4.1~18.2Ω. When the silicon source is fly ash powder, the resulting conductive ceramic is an alumina-mullite-calcium feldspar-based conductive ceramic with a porosity of 39%~60% and a bulk density of 1.58~2.05 g / cm³. 3Withstand pressure strength 47 MPa~89 MPa, resistance 7.2~20.4Ω.

[0026] The conductive ceramic obtained by this invention can be used as a preferred material in electromagnetic shielding devices, high-temperature sensors, aerospace thermal protection systems, and aero-engines.

[0027] The present invention has the following beneficial effects:

[0028] 1. This invention uses waste materials such as coal gangue and fly ash as raw materials to prepare conductive ceramics, which can accelerate the consumption of coal gangue and fly ash and improve the recycling efficiency and added value of coal gangue and fly ash.

[0029] 2. This invention simultaneously performs hot pressing, high-temperature sintering, and carbothermic reduction, obtaining conductive ceramics in a single reaction step. Carbothermic reduction is carried out in an inert atmosphere, ensuring the decomposition of the organic carbon source during high-temperature heat treatment, forming a three-dimensional carbon network that endows the ceramic with excellent electrical conductivity. Compared to traditional high-temperature sintering, the extremely rapid heating rate allows for instantaneous carbonization of the carbon source, shortening the reaction time between impurity components. This effectively reduces the excessive development of the low-melting-point glass phase, maintains the connectivity of the conductive phase, and tightly "locks" the carbon layer at the interface between alumina and mullite particles, enabling the achievement of the conductivity threshold with a lower carbon content. Furthermore, the application of axial pressure during heating provides additional driving force, causing plastic flow and rearrangement of the powder particles. This allows for achieving a density close to the theoretical density at a lower temperature and in a very short time, resulting in smaller and more uniform grain sizes and a finer carbon network distribution. This contributes to obtaining conductive ceramics with more stable resistivity and lower anisotropy.

[0030] 4. The sintering process of the present invention can ensure that during the sintering process of coal gangue and fly ash, the trace metal oxides in their composition react with alumina to generate a small amount of transition liquid phase. The generation of this liquid phase can accelerate the diffusion of aluminum ions and silicon ions, form needle-like mullite in situ, and improve the strength of conductive ceramics.

[0031] 5. This invention improves the conductivity and strength of conductive ceramics through a combination of raw material selection and sintering processes. The process is simple, low-cost, low-energy, highly efficient, environmentally friendly, and easy to industrialize. The resulting conductive ceramics exhibit high mechanical properties, excellent conductivity, and low resistance, making them a preferred material for indoor heaters, electromagnetic shielding devices, high-temperature sensors, aerospace thermal protection systems, and aero-engine applications. Attached Figure Description

[0032] Figure 1 The image shows the XRD pattern of the conductive ceramic obtained in Example 1. Detailed Implementation

[0033] The following description illustrates exemplary embodiments of the present invention, including various details to aid understanding, and should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the invention. Similarly, for clarity and brevity, descriptions of well-known functions, operations, and structures are omitted in the following description.

[0034] Unless otherwise defined, the technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art. While similar or identical methods and materials may be applied in experimental or practical applications, the present invention describes materials and methods hereinafter. In case of conflict, the definitions included herein shall prevail.

[0035] In the following examples and comparative examples, all raw materials used were commercially available products. Specifically: the alumina powder contained ≥99wt% Al2O3, ≤0.1wt% Na2O, and had a particle size distribution of 1-10μm. The coal gangue powder contained 15-25wt% Al2O3, 50-60wt% SiO2, and had a particle size of 2-30μm. The fly ash powder contained 15-25wt% Al2O3, 45-55wt% SiO2, 5-20wt% CaO, and had a particle size of 2-120μm. The polyvinyl alcohol solution had a mass fraction of 5wt%, used ethanol as the solvent, and had a molecular weight of 120,000-150,000.

[0036] Example 1

[0037] A mullite-alumina-based conductive ceramic material, the raw materials of which are composed of the following parts by weight: 55 parts α-alumina powder, 30 parts coal gangue powder, 15 parts phenolic resin (molecular weight 320), and 5 parts polyvinyl alcohol solution.

[0038] The preparation method is as follows:

[0039] 1. According to the above raw material composition, α-alumina powder, coal gangue powder, and phenolic resin are placed in a ball mill jar, and then polyvinyl alcohol solution is added. The mixture is ball milled for 3 hours to obtain a uniform mixed powder.

[0040] 2. Press the mixed powder into a ceramic body using a press at a pressure of 20 MPa.

[0041] 3. Transfer the ceramic green body to a vacuum drying oven and dry it at a temperature of 100~110℃ for 4 hours;

[0042] 4. Place the dried ceramic blank in a rapid hot pressing sintering furnace, and raise the temperature from room temperature to 1200℃ at a rate of 100℃ / min under a nitrogen atmosphere, while maintaining a pressure of 10MPa. Then raise the temperature from 1200℃ to 1400℃ at a rate of 50℃ / min, while maintaining a pressure of 30MPa. Finally, hold the temperature at 1400℃ for 20 min to obtain the mullite-alumina based conductive ceramic material.

[0043] Figure 1 The image shows the XRD pattern of the product. It can be seen from the image that the reaction formed a mullite-alumina phase, resulting in a mullite-alumina conductive ceramic.

[0044] Example 2

[0045] A mullite-alumina-based conductive ceramic material, the raw materials of which are composed of the following parts by weight: 62 parts of tabular corundum, 33 parts of coal gangue powder, 5 parts of corn starch, and 5 parts of polyvinyl alcohol solution.

[0046] The preparation method is the same as in Example 1.

[0047] Example 3

[0048] A mullite-alumina-based conductive ceramic material, the raw materials of which are composed of the following parts by weight: 49 parts of α-alumina powder, 26 parts of coal gangue powder, 25 parts of white dextrin, and 5 parts of polyvinyl alcohol solution.

[0049] The preparation method is the same as in Example 1.

[0050] Example 4

[0051] A mullite-alumina-based conductive ceramic material, the raw material composition by weight is the same as in Example 1. The preparation method is as follows:

[0052] 1. Same as Example 1;

[0053] 2. Same as Example 1;

[0054] 3. Same as Example 1;

[0055] 4. Place the dried ceramic blank in a rapid hot pressing sintering furnace, and raise the temperature from room temperature to 1200℃ at a rate of 100℃ / min under a nitrogen atmosphere, while maintaining a pressure of 5 MPa; then raise the temperature from 1200℃ to 1300℃ at a rate of 50℃ / min, and then hold at 1300℃ for 10 min while maintaining a pressure of 25 MPa to obtain mullite-alumina based conductive ceramic material.

[0056] Example 5

[0057] A mullite-alumina-based conductive ceramic material, the raw material composition by weight is the same as in Example 1. The preparation method is as follows:

[0058] 1. Same as Example 1;

[0059] 2. Same as Example 1;

[0060] 3. Same as Example 1;

[0061] 4. Place the dried ceramic blank in a rapid hot pressing sintering furnace, and raise the temperature from room temperature to 1200℃ at a rate of 100℃ / min under a nitrogen atmosphere, while maintaining a pressure of 10 MPa. Then raise the temperature from 1200℃ to 1500℃ at a rate of 50℃ / min, and hold at 1500℃ for 30 min while maintaining a pressure of 30 MPa to obtain mullite-alumina based conductive ceramic material.

[0062] Example 6

[0063] An alumina-mullite-calcium feldspar-based conductive ceramic material has the following raw material composition by weight: 70 parts α-alumina powder, 15 parts fly ash powder, 15 parts phenolic resin (molecular weight 320), and 5 parts polyvinyl alcohol solution.

[0064] The preparation method is as follows:

[0065] 1. According to the above raw material composition, place α-alumina powder, fly ash powder, and phenolic resin in a ball mill jar, then add polyvinyl alcohol solution, and ball mill for 3 hours to obtain a uniform mixed powder;

[0066] 2. Press the mixed powder into a ceramic body using a press at a pressure of 20 MPa.

[0067] 3. Transfer the ceramic green body to a vacuum drying oven and dry it at a temperature of 100~110℃ for 4 hours;

[0068] 4. The dried ceramic green body is placed in a rapid hot-pressing sintering furnace and heated from room temperature to 1000℃ at a rate of 100℃ / min under a nitrogen atmosphere, while maintaining a pressure of 10 MPa. Then, the temperature is increased from 1000℃ to 1300℃ at a rate of 50℃ / min, and held at 1300℃ for 20 min, while maintaining a pressure of 15 MPa. This yields an alumina-mullite-calcium feldspar-based conductive ceramic material.

[0069] Example 7

[0070] An alumina-mullite-calcium feldspar-based conductive ceramic material, the raw materials of which are composed of the following parts by weight: 70 parts of tabular corundum, 20 parts of fly ash powder, 10 parts of corn starch, and 5 parts of polyvinyl alcohol solution.

[0071] The preparation method is the same as in Example 6.

[0072] Example 8

[0073] An alumina-mullite-calcium feldspar-based conductive ceramic material has the following raw material composition by weight: 60 parts α-alumina powder, 20 parts fly ash powder, 20 parts white dextrin, and 5 parts polyvinyl alcohol solution.

[0074] The preparation method is the same as in Example 6.

[0075] Example 9

[0076] An alumina-mullite-calcium feldspar-based conductive ceramic material, the raw material composition by weight is the same as in Example 6. The preparation method is as follows:

[0077] 1. Same as Example 6;

[0078] 2. Same as Example 6;

[0079] 3. Same as Example 6;

[0080] 4. The dried ceramic green body is placed in a rapid hot-pressing sintering furnace and heated from room temperature to 1000℃ at a rate of 100℃ / min under a nitrogen atmosphere, while maintaining a pressure of 5 MPa. Then, the temperature is increased from 1000℃ to 1200℃ at a rate of 50℃ / min, and held at 1200℃ for 10 min, while maintaining a pressure of 10 MPa. This yields an alumina-mullite-calcium feldspar-based conductive ceramic material.

[0081] Example 10

[0082] An alumina-mullite-calcium feldspar-based conductive ceramic material, the raw material composition by weight is the same as in Example 1. The preparation method is as follows:

[0083] 1. Same as Example 6;

[0084] 2. Same as Example 6;

[0085] 3. Same as Example 6;

[0086] 4. The dried ceramic green body is placed in a rapid hot-pressing sintering furnace and heated from room temperature to 1000℃ at a rate of 100℃ / min under a nitrogen atmosphere, while maintaining a pressure of 10 MPa. Then, the temperature is increased from 1000℃ to 1400℃ at a rate of 50℃ / min, and held at 1400℃ for 30 min, while maintaining a pressure of 20 MPa. This yields an alumina-mullite-calcium feldspar-based conductive ceramic material.

[0087] Comparative Example 1

[0088] A mullite-alumina-based conductive ceramic material, the raw material composition by weight is the same as in Example 1. The preparation method is as follows:

[0089] 1. Same as Example 1;

[0090] 2. Same as Example 1;

[0091] 3. Same as Example 1;

[0092] 4. The dried ceramic green body was placed in a hot-press sintering furnace and heated from room temperature to 1200℃ at a rate of 10℃ / min under a nitrogen atmosphere, while maintaining a pressure of 20 MPa. Then, the temperature was increased from 1200℃ to 1400℃ at a rate of 5℃ / min, and held at 1400℃ for 2 hours at a pressure of 20 MPa. This yielded a mullite-alumina-based conductive ceramic material.

[0093] Comparative Example 2

[0094] A mullite-alumina-based conductive ceramic material, the raw materials of which are composed of the following parts by weight: 44 parts of α-alumina powder, 21 parts of coal gangue powder, 35 parts of corn starch, and 5 parts of polyvinyl alcohol solution.

[0095] The preparation method is the same as in Example 1.

[0096] Comparative Example 3

[0097] A mullite-alumina-based conductive ceramic material, the raw materials of which are composed of the following parts by weight: 63 parts α-alumina powder, 34 parts coal gangue powder, 3 parts white dextrin, and 5 parts polyvinyl alcohol solution.

[0098] The preparation method is the same as in Example 1.

[0099] Comparative Example 4

[0100] A mullite-alumina-based conductive ceramic material, the raw material composition by weight is the same as in Example 1. The preparation method is as follows:

[0101] 1. Same as Example 1;

[0102] 2. Same as Example 1;

[0103] 3. Same as Example 1;

[0104] 4. Place the dried ceramic green body in a rapid hot pressing sintering furnace, and heat it from room temperature to 1200℃ at a rate of 100℃ / min under a nitrogen atmosphere. Then, hold it at 1200℃ for 30 min at a pressure of 10 MPa to obtain mullite-alumina based conductive ceramic material.

[0105] Comparative Example 5

[0106] A mullite-alumina-based conductive ceramic material, the raw material composition by weight is the same as in Example 1. The preparation method is as follows:

[0107] 1. Same as Example 1;

[0108] 2. Same as Example 1;

[0109] 3. Same as Example 1;

[0110] 4. Place the dried ceramic blank in a rapid hot pressing sintering furnace, ensuring a pressure of 20 MPa. Under a nitrogen atmosphere, raise the temperature from room temperature to 1400℃ at a heating rate of 100℃ / min, and then hold at 1400℃ for 10 min to obtain mullite-alumina based conductive ceramic material.

[0111] Comparative Example 6

[0112] A mullite-alumina-based conductive ceramic material, the raw material composition by weight is the same as in Example 1. The preparation method is as follows:

[0113] 1. Same as Example 1;

[0114] 2. Same as Example 1;

[0115] 3. Same as Example 1;

[0116] 4. The dried ceramic body is first subjected to carbothermic reduction. The steps are as follows: the ceramic body is placed in a conventional vacuum furnace and heated from room temperature to 700℃ at a heating rate of 10℃ / min under a nitrogen atmosphere. Then it is kept at this temperature for 3 hours to ensure that the organic carbon source decomposes in situ to form a carbon network. Then it is cooled to room temperature.

[0117] 5. The carbothermic reduction preform is hot-pressed and sintered under nitrogen atmosphere at a heating rate of 100℃ / min from room temperature to 1200℃ and a pressure of 10MPa. Then, the heating rate is increased from 1200℃ to 1400℃ at a heating rate of 50℃ / min and a pressure of 30MPa. The preform is then held at 1400℃ for 20 min to obtain mullite-alumina based conductive ceramic material.

[0118] Comparative Example 7

[0119] An alumina-mullite-calcium feldspar-based conductive ceramic material, the raw material composition by weight is the same as in Example 6. The preparation method is as follows:

[0120] 1. Same as Example 6;

[0121] 2. Same as Example 6;

[0122] 3. Same as Example 6;

[0123] 4. Place the dried ceramic blank in a hot-press sintering furnace and heat it from room temperature to 1000℃ at a rate of 50℃ / min under a nitrogen atmosphere, with a pressure of 5MPa. Then heat it from 1000℃ to 1300℃ at a rate of 25℃ / min, and hold it at 1300℃ for 20 min at a pressure of 15MPa to obtain an alumina-mullite-calcium feldspar based conductive ceramic material.

[0124] Comparative Example 8

[0125] An alumina-mullite-calcium feldspar-based conductive ceramic material has the following raw material composition by weight: 44 parts α-alumina powder, 21 parts fly ash powder, 35 parts corn starch, and 5 parts polyvinyl alcohol solution.

[0126] The preparation method is the same as in Example 6.

[0127] Comparative Example 9

[0128] An alumina-mullite-calcium feldspar-based conductive ceramic material has the following raw material composition by weight: 80 parts α-alumina powder, 15 parts fly ash powder, 5 parts corn starch, and 5 parts polyvinyl alcohol solution.

[0129] The preparation method is the same as in Example 6.

[0130] Comparative Example 10

[0131] An alumina-mullite-calcium feldspar-based conductive ceramic material, the raw material composition by weight is the same as in Example 1. The preparation method is as follows:

[0132] 1. Same as Example 6;

[0133] 2. Same as Example 6;

[0134] 3. Same as Example 6;

[0135] 4. Place the dried ceramic blank in a rapid hot pressing sintering furnace, and raise the temperature from room temperature to 1000℃ at a rate of 50℃ / min under a nitrogen atmosphere, with a pressure of 5MPa. Then raise the temperature from 1000℃ to 1300℃ at a rate of 100℃ / min, and hold at 1300℃ for 20 min with a pressure of 15MPa to obtain an alumina-mullite-calcium feldspar based conductive ceramic material.

[0136] Comparative Example 11

[0137] An alumina-mullite-calcium feldspar-based conductive ceramic material, the raw material composition by weight is the same as in Example 1. The preparation method is as follows:

[0138] 1. Same as Example 6;

[0139] 2. Same as Example 6;

[0140] 3. Same as Example 6;

[0141] 4. Place the dried ceramic blank in a rapid hot pressing sintering furnace, and heat it from room temperature to 1000℃ at a rate of 100℃ / min under a nitrogen atmosphere, with a pressure of 5MPa. Then heat it from 1000℃ to 1500℃ at a rate of 50℃ / min, and hold it at 1500℃ for 10 min with a pressure of 15MPa to obtain an alumina-mullite-calcium feldspar based conductive ceramic material.

[0142] The bulk density, apparent porosity, room temperature withstand voltage, and electrical resistance of the conductive ceramics prepared in the above embodiments and comparative examples were tested. The bulk density and apparent porosity were tested using the Archimedes' displacement method (GB / T 1966-2024), the room temperature withstand voltage was tested using the method in GB / T 1964-2023, and the electrical resistance was tested using a high and low temperature Hall effect testing system.

[0143] The test results of Examples 1-5 and Comparative Examples 1-6 are shown in Table 1 below.

[0144] Table 1

[0145]

[0146] The test results of Examples 6-10 and Comparative Examples 7-11 are shown in Table 2 below.

[0147] Table 2

[0148]

[0149] As can be seen from Tables 1 and 2, the conductive ceramics disclosed in the embodiments of the present invention have better strength and conductivity compared with the comparative products. This is the result of the synergistic effect of the raw materials and the rapid hot pressing sintering preparation.

[0150] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method of making an electrically conductive ceramic, characterized by The method comprises the following steps: (1) mixing alumina powder, silicon source, organic carbon source and polyvinyl alcohol solution and ball milling to obtain mixed powder; (2) pressing the mixed powder to obtain ceramic green body; (3) drying the ceramic green body, and then performing rapid hot-pressing high-temperature sintering and carbothermic reduction to obtain conductive ceramic; In step (1), the silicon source is coal gangue powder or fly ash powder; In step (1), the organic carbon source is one or more of phenolic resin, corn starch, white dextrin and lignin fiber; In step (3), when the silicon source is coal gangue powder, the rapid hot-pressing high-temperature sintering and carbothermic reduction is performed in an inert atmosphere, first increasing the temperature from room temperature to 1200℃ at a rate of 100-110℃ / min under a pressure of 5-10 MPa; then increasing the temperature to 1300-1500℃ at a rate of 50-60℃ / min under a pressure of 11-30 MPa, and maintaining the temperature for 10-30 min; when the silicon source is fly ash powder, the rapid hot-pressing high-temperature sintering and carbothermic reduction is performed in an inert atmosphere, first increasing the temperature from room temperature to 1000℃ at a rate of 100-110℃ / min under a pressure of 5-10 MPa; then increasing the temperature to 1200-1400℃ at a rate of 50-60℃ / min under a pressure of 11-20 MPa, and maintaining the temperature for 10-30 min.

2. The method of claim 1, wherein: In step (1), at least one of the following conditions is included: Condition 1: the polyvinyl alcohol solution is an ethanol solution of polyvinyl alcohol with a concentration of 4-8wt%; Condition 2: the alumina powder is one or both of α-alumina and tabular corundum; Condition 3: the average particle size of the alumina powder is 1-20μm.

3. The method of claim 1 wherein: In step (1), at least one of the following conditions is included: Condition 1: the Al2O3 content in the coal gangue powder is 15-25wt%, and the SiO2 content is 50-60wt%; Condition 2: the particle size of the coal gangue powder is 2-30μm; Condition 3: the Al2O3 content in the fly ash powder is 15-25wt%, the SiO2 content is 45-55wt%, and the CaO content is 5-20wt%; Condition 4: the particle size of the fly ash powder is 2-120μm.

4. The method of claim 1, 2 or 3, wherein: In step (1), when the silicon source is coal gangue powder, the amount of alumina powder is 49-62 parts by weight, the amount of coal gangue powder is 25-33 parts by weight, the amount of organic carbon source is 5-25 parts by weight, and the amount of polyvinyl alcohol solution is 3-8wt% of the total mass of the coal gangue powder, alumina powder and organic carbon source; when the silicon source is fly ash powder, the amount of alumina powder is 60-70 parts by weight, the amount of fly ash powder is 15-20 parts by weight, the amount of organic carbon source is 10-20 parts by weight, and the amount of polyvinyl alcohol is 3-8wt% of the total mass of the fly ash powder, alumina powder and organic carbon source.

5. The method of claim 1 wherein: In step (1), the ball milling time is 3-5 hours.

6. The method of claim 1 wherein: In step (2), the forming pressure is 20-40 MPa, and the pressing time is 3-10 min.

7. The method of claim 1 wherein: In step (3), the drying is vacuum drying, and the drying temperature is 100-120℃.

8. The electrically conductive ceramic prepared according to the method of any one of claims 1-7.

9. Use of the electrically conductive ceramic of claim 8 in electromagnetic shielding devices, high temperature sensors, aerospace thermal protection systems, and aircraft engines.

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