Semiconductor-dielectric-conductor type attenuating porcelain and preparation method

Abstract

The application discloses a semiconductor-dielectric-conductor type attenuation porcelain and a preparation method thereof, and relates to the technical field of electromagnetic wave absorption and attenuation materials. The attenuation porcelain is composed of a semiconductor phase, a dielectric phase, a conductor phase, a sintering aid and a binder; the conductor phase has a core-shell structure of a nickel-cobalt-cerium alloy solid solution inner core, a nitrogen-doped amorphous carbon intermediate layer and a silicon dioxide shell, and cerium atoms are doped in the nickel-cobalt alloy solid solution lattice in the form of lattice distortion. The preparation method comprises the following steps: preparation of a precursor solution, limited silicon dioxide coating, limited in-situ reduction and defect construction, mixing and forming, and high-temperature sintering. Through the synergistic effect of the semiconductor phase, the dielectric phase and the core-shell conductor phase, the application realizes comprehensive enhancement of impedance matching, interface polarization, conductive loss and multiple scattering attenuation, and can improve the high-temperature stability and electromagnetic wave attenuation performance of the attenuation porcelain.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorption and attenuation materials, and more specifically, to a semiconductor-dielectric-conductor type attenuating ceramic and its preparation method. Background Technology

[0002] With the rapid development of modern communication and microwave technologies, electromagnetic interference and radiation problems are becoming increasingly serious, leading to a sharp increase in demand for high-performance attenuating ceramics and absorbing materials. Semiconductor-dielectric-conductor type attenuating ceramics can integrate the electromagnetic properties of different materials, showing broad application prospects in the field of electromagnetic wave absorption and attenuation. Existing semiconductor-dielectric-conductor type attenuating ceramics typically consist of 20-40 parts by mass of a semiconductor phase, 30-55 parts by mass of a dielectric phase, 5-20 parts by mass of a conductor phase, 2-10 parts by mass of a sintering aid, and 1-5 parts by mass of a binder. However, with the increasing complexity of application scenarios, this traditional attenuating ceramic has revealed many technical defects in its preparation and practical application.

[0003] Existing attenuation ceramics suffer from high-temperature stability issues due to the easy oxidation and agglomeration of the metallic conductor phase during high-temperature sintering. Traditional metallic or alloy conductor phases, when co-fired with dielectric or semiconductor phases at high temperatures to prepare ceramics, readily react with oxygen, leading to severe oxidation and loss of their original conductive and magnetic properties. Simultaneously, nanoscale metal particles readily agglomerate and grow at high temperatures, severely damaging the material's microstructure and resulting in a significant decrease in electromagnetic attenuation performance.

[0004] Traditional attenuating ceramics suffer from a single electromagnetic loss mechanism and insufficient attenuation efficiency in their conductor phase. Conventional conductor phases often rely solely on conductivity or magnetic loss to absorb electromagnetic waves, resulting in a narrow attenuation bandwidth that fails to meet the practical requirements of broadband wave absorption. Consequently, their overall electromagnetic wave absorption and attenuation performance is extremely limited.

[0005] Existing conductive phases in ceramic matrices readily lead to macroscopic compatibility problems such as impedance mismatch and uncontrollable percolation. In multiphase composite ceramic systems, even a slightly large amount of conductive phase can easily form a macroscopically interconnected network, causing abrupt changes in conductivity and exceeding the percolation threshold. This phenomenon results in a large number of electromagnetic waves being directly reflected at the material surface, unable to penetrate the material for deep attenuation, leading to severe impedance mismatch and significantly reducing the efficiency of attenuating ceramics.

[0006] In summary, there is an urgent need in this field to develop a novel semiconductor-dielectric-conductor type attenuating ceramic and its preparation method, so as to effectively solve the technical problems of poor temperature resistance and oxidation resistance of the metal conductor phase in existing attenuating ceramics, the single electromagnetic loss mechanism, and the easy occurrence of impedance mismatch, so as to obtain a composite attenuating ceramic material with excellent high-temperature stability, wide attenuation bandwidth and high wave absorption efficiency. Summary of the Invention

[0007] To address the technical shortcomings of existing attenuating ceramics, such as the easy oxidation and agglomeration of the metallic conductor phase during high-temperature sintering, the narrow absorption bandwidth due to a single electromagnetic loss mechanism, and the high likelihood of macroscopic impedance mismatch, this invention aims to provide a semiconductor-dielectric-conductor type attenuating ceramic and its preparation method. This invention aims to obtain attenuating ceramic materials with excellent high-temperature stability, wide attenuation bandwidth, high absorption efficiency, and good macroscopic impedance matching through microscopic core-shell structure design and multiphase composite synergistic mechanism.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A semiconductor-dielectric-conductor type attenuating ceramic is composed of the following components in parts by weight:

[0010] Semiconductor phase 20-40 parts;

[0011] 30-55 parts of medium phase;

[0012] 5-20 parts of the conductor phase, wherein the conductor phase has a core-shell structure, including a nickel-cobalt-cerium alloy solid solution core, a nitrogen-doped amorphous carbon intermediate layer covering the surface of the core, and a silicon dioxide shell covering the outside of the intermediate layer, wherein cerium atoms are doped in the lattice of the nickel-cobalt alloy solid solution in the form of lattice distortion.

[0013] 2-10 parts of sintering aid;

[0014] 1-5 parts adhesive.

[0015] As a preferred embodiment of the present invention, the semiconductor phase is selected from one or more of silicon carbide, zinc oxide, and vanadium oxide.

[0016] As a preferred embodiment of the present invention, the medium phase is selected from one or more of barium titanate, aluminum oxide, and aluminum nitride.

[0017] As a preferred embodiment of the present invention, the sintering aid is selected from one or more of bismuth oxide, boron oxide, and copper oxide.

[0018] As a preferred embodiment of the present invention, the adhesive is selected from one or more of polyvinyl alcohol, polyethylene glycol, and polyvinyl butyral.

[0019] As a preferred embodiment of the present invention, the preparation method of the above-mentioned semiconductor-dielectric-conductor type attenuating ceramic includes the following steps:

[0020] (1) Preparation of precursor solution: According to the molar ratio Ni:Co:Ce=1:1:0.05, nickel nitrate hexahydrate, cobalt nitrate hexahydrate and cerium nitrate hexahydrate are dissolved in deionized water, citric acid with a molar amount equal to the total molar amount of metal ions and melamine with a molar amount equivalent to twice the total molar amount of metal ions are added, and the reaction is carried out under magnetic stirring at 60℃-80℃ for 2-4 hours to obtain a uniform transparent sol.

[0021] (2) Silica confinement coating: Dilute the above sol with anhydrous ethanol, add ammonia to adjust the pH of the system to 8.5-9.0, add ethanol solution of tetraethyl orthosilicate at a dropping rate of 0.5-1.0 mL / min under ultrasonic conditions, wherein the molar amount of silicon in tetraethyl orthosilicate is 0.5-0.8 times the total molar amount of metal ions in step (1). After the addition is complete, continue stirring for 6-8 hours, centrifuge, wash with anhydrous ethanol and deionized water, and dry to obtain precursor powder.

[0022] (3) Confined in-situ reduction and defect construction: The precursor powder is placed in a tube furnace and heated to 850℃-950℃ at a heating rate of 2-5℃ / min under an argon atmosphere, and held for 4-6 hours; after natural cooling with the furnace, the conductor phase is obtained.

[0023] (4) Mixing and molding: Mix the semiconductor phase, dielectric phase, conductor phase obtained in step (3) and sintering aid, add anhydrous ethanol as ball milling medium, ball mill for 12-24 hours, then dry the mixture at 80℃-100℃, add the aqueous solution of the binder for granulation, sieve and dry press at 100-200MPa to obtain ceramic green body.

[0024] (5) High-temperature sintering: The ceramic green body is placed in a sintering furnace and heated to 1000℃-1200℃ at a heating rate of 3-5℃ / min. The temperature is held for 2-4 hours and then cooled to room temperature with the furnace to obtain the semiconductor-dielectric-conductor type attenuating ceramic.

[0025] As a preferred embodiment of the present invention, the concentration of the ethanol solution of tetraethyl orthosilicate in step (2) is 0.05-0.20 mol / L.

[0026] As a preferred embodiment of the present invention, the heating rate in step (3) is 2-3℃ / min, the holding temperature is 850℃-900℃, and the holding time is 4-5 hours.

[0027] As a preferred embodiment of the present invention, the ball milling time in step (4) is 18-24 hours and the dry pressing pressure is 150-200 MPa.

[0028] As a preferred embodiment of the present invention, the heating rate in step (5) is 4-5℃ / min, the sintering temperature is 1100℃-1200℃, and the holding time is 3-4 hours.

[0029] A semiconductor-dielectric-conductor type attenuating ceramic can be used in the manufacture of special ceramic products such as ceramic cylinder valve plates, and in the preparation of piezoelectric, thermoelectric and other functional ceramics.

[0030] The semiconductor phase, dielectric phase, and conductor phase of this invention constitute a multiphase composite attenuation system. The semiconductor phase is used to adjust the overall conductivity and dielectric constant of the material. The dielectric phase provides a stable dielectric matrix and improves impedance matching, making it easier for incident electromagnetic waves to enter the interior of the attenuation ceramic rather than being directly reflected on the surface. The conductor phase adopts a core-shell structure of a nickel-cobalt-cerium alloy solid solution core, a nitrogen-doped amorphous carbon intermediate layer, and a silicon dioxide shell. The nickel-cobalt-cerium alloy solid solution core provides a conductive channel and generates conductive losses. Cerium atoms are doped into the nickel-cobalt alloy solid solution lattice in the form of lattice distortion, which can introduce defects and local polarization centers, enhancing dipole polarization losses. The nitrogen-doped amorphous carbon intermediate layer further constructs continuous or semi-continuous electron migration paths, improving the efficiency of electromagnetic energy to thermal energy conversion. The silicon dioxide shell forms an isolation interface between the conductor phase and the semiconductor and dielectric phases, avoiding direct agglomeration of the conductor phase that leads to impedance mismatch. At the same time, it extends the electromagnetic wave propagation path through structure, inducing multiple scattering and interface polarization. Thus, the material achieves effective absorption and attenuation of electromagnetic wave energy through the synergistic effects of impedance matching, multiple interface polarization loss, conductivity loss, and multiple scattering attenuation; the sintering aid promotes sintering densification, and the binder ensures molding stability, thereby improving the structural stability and comprehensive wave absorption performance of the attenuating ceramic.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1. This invention achieves crucial physical isolation and protection by constructing an in-situ confined silica coating layer and transforming it into a silica shell during high-temperature processing. This shell not only spatially restricts the high-temperature growth of the internal alloy, preventing abnormal grain growth and agglomeration, but also effectively blocks external oxygen from penetrating inward, completely avoiding oxidation failure of the internal alloy under high-temperature conditions. This allows the material to maintain excellent structural and performance stability in harsh high-temperature preparation and application environments.

[0033] 2. This invention significantly enhances the dipole polarization and defect polarization loss capabilities of the system by introducing trace amounts of cerium atoms into the crystal lattice to induce lattice distortion. Simultaneously, the nitrogen-doped amorphous carbon layer generated during high-temperature in-situ carbonization not only improves the local conductivity of the micro-region but also constructs abundant heterogeneous interfaces between the carbon layer and the metal core, and between the carbon layer and the silicon dioxide shell, triggering a strong multi-interface polarization effect. This deep synergy of multiple loss mechanisms effectively solves the technical problem of the single loss mechanism in traditional attenuating ceramics, comprehensively improving the material's overall attenuation capability for electromagnetic waves.

[0034] 3. The outermost layer of the conductive phase prepared in this invention is coated with an insulating silica shell with excellent wave transmission properties, tightly encapsulating the internal core with high conductivity and high magnetism, achieving excellent microscopic spatial isolation within a multiphase composite ceramic matrix. This mechanism fundamentally prevents direct contact between conductive phase particles, thus avoiding macroscopic short circuits and effectively suppressing conductivity abrupt changes caused by premature over-percolation threshold. This allows incident electromagnetic waves to penetrate the material interior to the maximum extent without reflection for deep loss attenuation, overcoming the technical defect of traditional conductive phases that easily lead to impedance mismatch. Attached Figure Description

[0035] Figure 1 This is a SEM image of a semiconductor-dielectric-conductor type attenuating ceramic prepared in Example 1 of the present invention. Detailed Implementation

[0036] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1

[0038] Fabrication of a semiconductor-dielectric-conductor type attenuating ceramic:

[0039] 1. Raw material components by weight:

[0040] The semiconductor phase comprises 30 parts, wherein the semiconductor phase is silicon carbide powder, the D50 particle size of the silicon carbide powder is 1.5 μm, and the purity is not less than 99%.

[0041] The medium phase consists of 45 parts, wherein the medium phase is barium titanate powder, the D50 particle size of the barium titanate powder is 0.8 μm, and the purity is not less than 99%;

[0042] 12 parts of the conductor phase;

[0043] Five parts of sintering aid, wherein the sintering aid is composed of three parts of bismuth oxide and two parts of boron oxide, and the purity of both bismuth oxide and boron oxide is not less than 99%;

[0044] Three parts of adhesive, wherein the adhesive is polyvinyl alcohol and the degree of alcoholysis of the polyvinyl alcohol is 87% to 89%.

[0045] In this embodiment, 1 part by mass equals 1g, namely 30g silicon carbide, 45g barium titanate, 12g conductor phase, 3g bismuth oxide, 2g boron oxide, and 3g polyvinyl alcohol.

[0046] 2. Preparation method:

[0047] (1) Preparation of precursor solution:

[0048] Weigh out 7.09 g of nickel nitrate hexahydrate, 7.10 g of cobalt nitrate hexahydrate, and 0.53 g of cerium nitrate hexahydrate according to a molar ratio of Ni:Co:Ce = 1:1:0.05, so that the total molar amount of metal ions is 0.05 mol. Add the above nickel nitrate hexahydrate, cobalt nitrate hexahydrate, and cerium nitrate hexahydrate to 150 mL of deionized water, and magnetically stir at 500 rpm for 30 min at room temperature to disperse them evenly, thus obtaining a metal salt mixed solution. Add 9.61 g of citric acid to the metal salt mixed solution, the molar amount of which is equal to the total molar amount of metal ions; then add 12.61 g of melamine, the molar amount of which is twice the total molar amount of metal ions. Subsequently, heat the system to 70 °C and magnetically stir at 600 rpm for 3 h at 70 °C to allow the metal ions, citric acid, and melamine to fully complex and form a homogeneous sol.

[0049] (2) Silica confinement coating:

[0050] After cooling the uniform transparent sol obtained in step (1) to room temperature, 300 mL of anhydrous ethanol was added for dilution, and the mixture was stirred at 500 r / min for 20 min at 25 °C. Then, 25% ammonia solution was added dropwise to adjust the pH of the system to 8.8. The system was then subjected to an ultrasonic reaction at a frequency of 40 kHz and a power of 300 W. Separately, 6.77 g of tetraethyl orthosilicate was added to anhydrous ethanol and diluted to 250 mL to prepare a 0.13 mol / L tetraethyl orthosilicate ethanol solution; wherein the molar amount of silicon in the tetraethyl orthosilicate was 0.65 times the total molar amount of metal ions in step (1). Under continuous ultrasonic and stirring conditions, the tetraethyl orthosilicate ethanol solution was added dropwise to the sol system at a rate of 0.8 mL / min. After the addition was complete, the reaction was continued at 25℃ with ultrasonic stirring for 7 hours to allow tetraethyl orthosilicate to fully hydrolyze and condense, forming a silica-confined coating layer on the surface of the precursor particles. After the reaction was completed, the reaction solution was centrifuged at 8000 r / min for 10 min, and the supernatant was discarded. The resulting precipitate was washed three times with anhydrous ethanol and three times with deionized water, centrifuged at 8000 r / min for 10 min after each wash. The washed precipitate was then dried in a vacuum drying oven at 80℃ for 12 hours to obtain the precursor powder.

[0051] (3) Confined in-situ restoration and defect construction:

[0052] The precursor powder obtained in step (2) was uniformly spread in an alumina crucible, and then the alumina crucible was placed in the constant temperature zone of a tube furnace. Argon gas with a purity of 99.999% was introduced at a flow rate of 150 mL / min, and the gas was first purged for 30 min to remove air from the furnace tube. Then, under the condition of continuous argon gas introduction, the temperature was increased from room temperature to 900℃ at a heating rate of 3℃ / min, and held at 900℃ for 5 h. During the holding process, the nickel source, cobalt source and cerium source were reduced in situ in the confined space and formed a nickel-cobalt-cerium alloy solid solution core. Cerium atoms entered the nickel-cobalt alloy solid solution lattice and formed lattice distortion. At the same time, melamine and citric acid were pyrolyzed and carbonized, forming a nitrogen-doped amorphous carbon intermediate layer on the surface of the nickel-cobalt-cerium alloy solid solution core. The external silicon dioxide confined coating layer was transformed into a silicon dioxide shell. After the heat preservation was completed, the powder was naturally cooled to room temperature in the furnace under an argon atmosphere. The powder was then removed, gently ground, and passed through a 200-mesh sieve to obtain a conductor phase with a core-shell structure of nickel-cobalt-cerium alloy solid solution core, nitrogen-doped amorphous carbon intermediate layer, and silicon dioxide outer shell.

[0053] (4) Mixing and molding:

[0054] Weigh 30g of silicon carbide, 45g of barium titanate, 12g of the conductor phase obtained in step (3), 3g of bismuth oxide, and 2g of boron oxide, and add them to a zirconia ball mill jar. Add 120mL of anhydrous ethanol to the ball mill jar as the milling medium, and add 276g of zirconia balls to make the ball-to-material mass ratio 3:1. Then, ball mill at 300r / min for 20h to ensure that the semiconductor phase, dielectric phase, conductor phase, and sintering aid are fully and uniformly mixed. After ball milling, remove the slurry and dry it in a 90℃ oven for 12h to obtain a dried mixture. Grind the dried mixture and pass it through a 100-mesh sieve to obtain a uniformly mixed powder. Add 3g of polyvinyl alcohol to 27g of deionized water and stir at 90℃ for 1h to completely dissolve it to obtain a 10% polyvinyl alcohol aqueous solution. Spray the polyvinyl alcohol aqueous solution evenly onto the above mixed powder while stirring to ensure that the binder is evenly distributed on the surface of the mixed powder. The wet powder was then granulated by passing it through a 60-mesh sieve and dried in a 60°C oven for 4 hours to obtain granulated powder. The granulated powder was then added to a 20mm diameter stainless steel mold and dry-pressed under 180MPa pressure for 2 minutes. After demolding, a circular ceramic green body with a diameter of 20mm and a thickness of 2.0mm was obtained.

[0055] (5) High-temperature sintering:

[0056] The ceramic green body obtained in step (4) was placed on an alumina sintering plate and then placed in a high-temperature sintering furnace. Argon gas with a purity of 99.999% was introduced at a flow rate of 100 mL / min for purging for 30 min. Then, under the argon atmosphere, the temperature was increased from room temperature to 550℃ at a heating rate of 2℃ / min and held at 550℃ for 1 h to remove the polyvinyl alcohol binder in the ceramic green body. Then, the temperature was increased to 1150℃ at a heating rate of 4℃ / min and held at 1150℃ for 3 h to complete the sintering and densification of the ceramic green body. After the holding period, the ceramic green body was cooled to room temperature with the furnace to obtain a semiconductor-dielectric-conductor type attenuating ceramic.

[0057] Example 2

[0058] The preparation of a semiconductor-dielectric-conductor type attenuating ceramic is carried out by referring to the preparation method of Example 1, except that 30 parts of semiconductor phase silicon carbide powder are replaced with 30 parts of zinc oxide powder. The D50 particle size of the zinc oxide powder is 1.2 μm and the purity is not less than 99%. The rest is the same as in Example 1.

[0059] Example 3

[0060] The preparation of a semiconductor-dielectric-conductor type attenuating ceramic is carried out by referring to the preparation method of Example 1, except that 45 parts of the dielectric phase barium titanate powder are replaced with 45 parts of alumina powder. The alumina powder has a D50 particle size of 0.8 μm and a purity of not less than 99%. The rest is the same as in Example 1.

[0061] Example 4

[0062] The preparation of a semiconductor-dielectric-conductor type attenuating ceramic is carried out according to the preparation method of Example 1, except that the sintering aid is replaced by 5 parts of copper oxide instead of 3 parts of bismuth oxide and 2 parts of boron oxide, wherein the purity of the copper oxide is not less than 99%, and the rest is the same as in Example 1.

[0063] Comparative Example 1

[0064] The preparation of a semiconductor-dielectric-conductor type attenuating ceramic is carried out by referring to the preparation method of Example 1, except that the molar ratio of Ni:Co:Ce=1:1:0.05 is replaced with Ni:Co:Ce=1:1:0.1, and the rest is the same as in Example 1.

[0065] Comparative Example 2

[0066] The preparation of a semiconductor-dielectric-conductor type attenuating ceramic is carried out by referring to the preparation method of Example 1, except that the molar ratio of Ni:Co:Ce=1:1:0.05 is replaced with Ni:Co:Ce=1:1:0.01, and the rest is the same as in Example 1.

[0067] Comparative Example 3

[0068] The preparation of a semiconductor-dielectric-conductor type attenuating ceramic is carried out by referring to the preparation method of Example 1, except that cerium nitrate hexahydrate is replaced with an equimolar amount of lanthanum nitrate hexahydrate, and the rest is the same as in Example 1.

[0069] Comparative Example 4

[0070] The preparation of a semiconductor-dielectric-conductor type attenuating ceramic is carried out by referring to the preparation method of Example 1, except that the silicon dioxide confinement coating step is omitted and step (3) is carried out directly, and the rest is the same as in Example 1.

[0071] Comparative Example 5

[0072] The preparation of a semiconductor-dielectric-conductor type attenuating ceramic is carried out by referring to the preparation method of Example 1, except that the tetraethyl orthosilicate in step (2) is replaced with an equimolar amount of tetrabutyl titanate, and the rest is the same as in Example 1.

[0073] Performance testing:

[0074] 1. Sample Pretreatment: The semiconductor-dielectric-conductor type attenuating ceramics prepared in Examples 1-4 and Comparative Examples 1-5 were subjected to mechanical grinding and polishing to ensure a smooth surface free of obvious cracks and chipping. Samples used for electromagnetic parameter testing were processed into coaxial ring-shaped specimens with an outer diameter of 7.00±0.02 mm, an inner diameter of 3.04±0.02 mm, and a thickness of 2.00±0.05 mm. Samples used for mechanical property testing were processed into elongated strip-shaped specimens with dimensions of 36 mm × 4 mm × 3 mm. Samples used for bulk density, open porosity, and high-temperature stability testing were processed into circular disc-shaped specimens with a diameter of 20 mm and a thickness of 2.00±0.05 mm. Before testing, all samples were dried in an 80℃ vacuum drying oven for 12 hours and then cooled to room temperature for later use.

[0075] 2. Bulk density and open porosity testing

[0076] The Archimedes displacement method was used to test the bulk density and open porosity of semiconductor-dielectric-conductor type attenuating ceramics. The dried sample was weighed to obtain a dry mass m0. The sample was then vacuum-immersed in deionized water for 2 hours to allow the open pores to fully absorb water. After removal, the surface moisture was wiped off, and the saturated mass m1 was measured. Finally, the sample was suspended in deionized water, and the suspended mass m2 was measured. The bulk density ρ and open porosity P were calculated using the following formulas:

[0077] ρ=m0ρ w / (m1-m2);

[0078] P = (m1 - m0) / (m1 - m2) × 100%;

[0079] Wherein, ρw is the density of deionized water at the test temperature, and the data are shown in Table 1.

[0080] 3. Volume resistivity test:

[0081] A circular sample with a diameter of 20 mm and a thickness of 2.00 ± 0.05 mm was polished on both sides, and then a conductive silver paste was uniformly coated on both surfaces. The sample was then dried at 120 °C for 30 min to allow the conductive silver paste to form a stable electrode layer. The volume resistivity of the sample was measured using a high-resistivity meter at an ambient temperature of 25 ± 2 °C, a relative humidity of 50 ± 5%, a test voltage of 100 V, and a stabilization time of 60 s. The volume resistivity ρv was calculated using the following formula:

[0082] ρv = Rv × S / d;

[0083] Where Rv is the sample volume resistivity, S is the effective area of ​​the electrode, and d is the sample thickness, the data are shown in Table 1.

[0084] 4. Thermal cycling stability test:

[0085] The sample was placed in a high-temperature furnace and heated from room temperature to 600°C in an air atmosphere. After holding at this temperature for 30 minutes, the sample was removed and allowed to cool naturally to room temperature. This was recorded as one thermal cycle. After repeating the thermal cycle 20 times, the sample was observed for cracking, peeling, or pulverization. The change rate of volume resistivity before and after the thermal cycle was calculated. The data are shown in Table 1.

[0086] Table 1 - Performance test data of examples and comparative examples

[0087] Example 1 4.38 2.8 <![CDATA[3.80×10 5 ]]> No cracking, no peeling, no powdering 3.2 Example 2 4.86 2.6 <![CDATA[5.40×10 5 ]]> No cracking, no peeling, no powdering 3.8 Example 3 3.56 3.5 <![CDATA[9.10×10 5 ]]> No cracking, no peeling, no powdering 4.9 Example 4 4.31 3.1 <![CDATA[2.70×10 5 ]]> No cracking, no peeling, no powdering 4.5 Comparative Example 1 4.18 5.7 <![CDATA[1.26×10 6 ]]> The surface is slightly roughened, with no obvious cracks. 14.8 Comparative Example 2 4.32 4.4 <![CDATA[1.85×10 5 ]]> Slight surface oxidation and discoloration, with no obvious peeling. 9.6 Comparative Example 3 4.29 4.9 <![CDATA[7.40×10 5 ]]> The surface is slightly roughened, with no obvious cracks. 12.1 Comparative Example 4 4.06 9.3 <![CDATA[6.80×10 3 ]]> Fine cracks appeared, and localized powdering occurred. 68.7 Comparative Example 5 4.45 5.2 <![CDATA[1.32×10 5 ]]> Slight peeling at the edges, surface oxidation and discoloration 20.6

[0088] As shown in Table 1, Examples 1-4 exhibited low open porosity, moderate volume resistivity, and good thermal cycling stability, indicating that a reasonable multiphase synergistic structure was formed between the semiconductor phase, the dielectric phase, and the conductor phase with a nickel-cobalt-cerium alloy solid solution core, a nitrogen-doped amorphous carbon interlayer, and a silicon dioxide shell. The semiconductor phase was used to regulate the overall conductivity level, the dielectric phase maintained the insulation support and impedance matching of the ceramic matrix, the nickel-cobalt-cerium alloy solid solution core in the conductor phase provided conductive loss, cerium doping induced lattice distortion and defect polarization, the nitrogen-doped amorphous carbon interlayer provided local electron migration paths, and the silicon dioxide shell effectively isolated the conductor phase particles, inhibiting oxidation, agglomeration, and percolation during high-temperature sintering and thermal cycling. Therefore, the samples maintained excellent levels in terms of densification, resistivity stability, and thermal stability. In contrast, excessive cerium content in the comparative example disrupts solid solution stability and weakens the continuity of conductive paths, while insufficient cerium content makes it difficult to fully achieve defect polarization and lattice distortion control. Replacing cerium with lanthanum weakens the control effect on lattice distortion and defect centers. Removing the silica-confined shell eliminates the protective outer shell of the conductor phase, making it prone to agglomeration, oxidation, and direct contact, leading to increased porosity, abnormally low resistivity, and significantly poor thermal cycling stability. While using a titanium-based shell to replace the silica shell provides some coating, its insulation, oxidation resistance, and interface stability are inferior to those of the silica shell, resulting in a significant decrease in overall performance. Overall, the data indicate that the synergistic construction of appropriate cerium doping and the silica-confined core-shell structure is key to achieving good density, suitable resistance control, and high-temperature stability in the attenuation ceramic of this invention.

[0089] SEM image of a semiconductor-dielectric-conductor type attenuating ceramic prepared in Example 1, as shown below. Figure 1As shown, the ceramic surface is formed by a large number of micron- and submicron-sized particles that are tightly packed together. The particles are well bonded together, and the overall structure is continuous and dense. No obvious through cracks, large-sized pores, or severe sintering collapse were observed, indicating that the semiconductor phase, dielectric phase, conductor phase, and sintering aid can achieve good sintering densification under the sintering condition of 1150℃. The particle morphology in the figure is mainly irregular blocky and near-spherical particles with a wide particle size distribution. Small particles fill the spaces between larger particles, which helps to reduce porosity and improve the compactness of the ceramic skeleton. At the same time, a small number of bright fine particles or clusters are visible locally, which are presumably enriched regions related to the conductor phase or sintering aid. They are dispersed in the ceramic matrix and do not form an obvious continuous conductive network, indicating that the silica shell plays a good role in isolating and confining the conductor phase. This microstructure helps to construct multiphase interfaces and micro-polarization centers while maintaining the stability of the material structure, providing a structural basis for multiple scattering of electromagnetic waves inside the material, interface polarization loss and conductivity loss, thereby supporting its good attenuation performance and thermal cycling stability.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A semiconductor-dielectric-conductor type attenuating ceramic, characterized in that, It consists of the following components in parts by weight: Semiconductor phase 20-40 parts; 30-55 parts of medium phase; 5-20 parts of the conductor phase, wherein the conductor phase has a core-shell structure, including a nickel-cobalt-cerium alloy solid solution core, a nitrogen-doped amorphous carbon intermediate layer covering the surface of the core, and a silicon dioxide shell covering the outside of the intermediate layer, wherein cerium atoms are doped in the lattice of the nickel-cobalt alloy solid solution in the form of lattice distortion. 2-10 parts of sintering aid; 1-5 parts adhesive.

2. The semiconductor-dielectric-conductor type attenuator ceramic according to claim 1, characterized in that, The semiconductor phase is selected from one or more of silicon carbide, zinc oxide, and vanadium oxide.

3. The semiconductor-dielectric-conductor type attenuating ceramic according to claim 1, characterized in that, The medium phase is selected from one or more of barium titanate, aluminum oxide, and aluminum nitride.

4. The semiconductor-dielectric-conductor type attenuator ceramic according to claim 1, characterized in that, The sintering aid is selected from one or more of bismuth oxide, boron oxide, and copper oxide.

5. The semiconductor-dielectric-conductor type attenuator ceramic according to claim 1, characterized in that, The adhesive is selected from one or more of polyvinyl alcohol, polyethylene glycol, and polyvinyl butyral.

6. A method for preparing a semiconductor-dielectric-conductor type attenuating ceramic as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Preparation of precursor solution: According to the molar ratio Ni:Co:Ce=1:1:0.05, nickel nitrate hexahydrate, cobalt nitrate hexahydrate and cerium nitrate hexahydrate are dissolved in deionized water, citric acid with a molar amount equal to the total molar amount of metal ions and melamine with a molar amount equivalent to twice the total molar amount of metal ions are added, and the reaction is carried out under magnetic stirring at 60℃-80℃ for 2-4 hours to obtain a uniform transparent sol; (2) Silica confinement coating: Dilute the above sol with anhydrous ethanol, add ammonia to adjust the pH of the system to 8.5-9.0, add ethanol solution of tetraethyl orthosilicate at a dropping rate of 0.5-1.0 mL / min under ultrasonic conditions, wherein the molar amount of silicon in tetraethyl orthosilicate is 0.5-0.8 times the total molar amount of metal ions in step (1). After the addition is completed, continue stirring the reaction for 6-8 hours, centrifuge, wash with anhydrous ethanol and deionized water, and dry to obtain precursor powder; (3) Confined in-situ reduction and defect construction: The precursor powder is placed in a tube furnace and heated to 850℃-950℃ at a heating rate of 2-5℃ / min under an argon atmosphere, and held for 4-6 hours; after natural cooling in the furnace, the conductor phase is obtained. (4) Mixing and molding: Mix the semiconductor phase, dielectric phase, conductor phase obtained in step (3) and sintering aid, add anhydrous ethanol as ball milling medium, ball mill for 12-24 hours, then dry the mixture at 80℃-100℃, add the aqueous solution of the binder for granulation, sieve and dry press at 100-200MPa to obtain ceramic green body; (5) High-temperature sintering: The ceramic green body is placed in a sintering furnace and heated to 1000℃-1200℃ at a heating rate of 3-5℃ / min. The temperature is held for 2-4 hours and then cooled to room temperature with the furnace to obtain the semiconductor-dielectric-conductor type attenuating ceramic.

7. The preparation method according to claim 6, characterized in that, The concentration of the ethanol solution of tetraethyl orthosilicate in step (2) is 0.05-0.20 mol / L.

8. The preparation method according to claim 6, characterized in that, The heating rate in step (3) is 2-3℃ / min, the holding temperature is 850℃-900℃, and the holding time is 4-5 hours.

9. The preparation method according to claim 6, characterized in that, The ball milling time in step (4) is 18-24 hours, and the dry pressing pressure is 150-200 MPa.

10. The preparation method according to claim 6, characterized in that, The heating rate in step (5) is 4-5℃ / min, the sintering temperature is 1100℃-1200℃, and the holding time is 3-4 hours.

Images