Raw material composition for attenuating ceramic material, attenuating ceramic material and method for its production and use

Abstract

The application relates to the technical field of microwave attenuation materials, and discloses a raw material composition for an attenuation ceramic material, the attenuation ceramic material, and a preparation method and application thereof. The raw material composition comprises a medium phase, an attenuation phase and a sintering aid, the medium phase is silicon nitride, and the attenuation phase is a nanometer carbon tube. The attenuation ceramic material has mechanical properties, thermal, electrical properties and chemical stability, silicon nitride is used as the medium phase for the first time, and the nanometer carbon tube is used as the attenuation phase, and the prepared attenuation ceramic material can be used under high-frequency conditions, especially under W-waveband and Y-waveband conditions, and has high attenuation performance, high thermal conductivity and high strength.

Description

Technical Field

[0001] This invention relates to the field of microwave attenuation materials technology, specifically to a raw material composition for attenuation ceramic materials, attenuation ceramic materials, their preparation methods, and applications. Background Technology

[0002] In the field of microwave vacuum electronic device manufacturing technology, microwave attenuation materials are important functional materials in devices. Their main function is to achieve full absorption of signals, reduce reflection, and selectively suppress various modes of clutter, thereby ensuring given high-frequency parameters and improving device stability. Attenuation ceramics are one of the key functional materials required for the development of microwave tubes. Attenuation ceramics used as concentrated attenuators must first have a sufficiently large attenuation, i.e., a sufficiently large dielectric loss tangent tanδ and good frequency matching characteristics. At the same time, since the attenuation material usually converts the absorbed microwave energy into heat energy, the attenuation material must also have sufficient thermal conductivity to conduct away the heat generated by the absorbed microwaves in a timely manner, so as to maintain the normal operating temperature of the attenuator.

[0003] With the development of microwave tubes towards higher frequencies, higher power, and miniaturization, the performance requirements for internal attenuation materials have become increasingly prominent. Currently, the main microwave attenuation materials under research include alumina-based composite attenuation ceramics, aluminum nitride-based composite attenuation ceramics, and beryllium oxide-based composite attenuation ceramics. Alumina-based composite attenuation ceramics have low thermal conductivity, making them prone to burnout in high-power devices. Beryllium oxide is gradually being restricted due to its toxicity. While aluminum nitride-based composite attenuation ceramics show a significant improvement in thermal conductivity, the solid solution properties during sintering result in a lower thermal conductivity compared to foreign attenuation ceramics. Furthermore, these attenuation ceramics are relatively brittle, posing challenges in the machining of miniaturized microwave attenuators, thus limiting their use in high-power devices. Therefore, currently researched microwave attenuation materials are only well-suited for low-frequency or mid-to-high-frequency microwave vacuum electronic devices, such as those in the X-band and K-band. However, when used in high-frequency, especially microwave, attenuation materials exhibit weak attenuation performance, poor thermal conductivity, and low material strength in the W-band (75GHz-110GHz) and Y-band (170GHz-260GHz) conditions.

[0004] Therefore, the development of microwave attenuation ceramic materials with strong attenuation performance, high strength, and good thermal conductivity is of great significance for the development of high-power high-frequency devices. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of weak attenuation performance, poor thermal conductivity, and low material strength of microwave attenuating materials when used in the W-band (75GHz-110GHz) and Y-band (170GHz-260GHz) conditions, and to provide a raw material composition for attenuating ceramic materials, attenuating ceramic materials, their preparation methods, and applications.

[0006] To achieve the above objectives, the first aspect of the present invention provides a raw material composition for attenuating ceramic materials, wherein the raw material composition comprises a dielectric phase, an attenuating phase, and a sintering aid, wherein the dielectric phase is silicon nitride, and the attenuating phase is carbon nanotubes.

[0007] A second aspect of the present invention provides a method for preparing a decay ceramic material, comprising: hot pressing and sintering silicon nitride, carbon nanotubes and sintering aids to obtain the decay ceramic material.

[0008] A third aspect of the present invention provides a method for preparing attenuating ceramic materials.

[0009] The fourth aspect of the present invention provides an application of the aforementioned attenuating ceramic material in improving the high-frequency microwave attenuation performance of attenuating ceramic materials.

[0010] Through the above technical solution, the present invention provides an attenuation ceramic material that combines mechanical properties, thermal and electrical properties and chemical stability. For the first time, silicon nitride is used as the dielectric phase and carbon nanotubes are used as the attenuation phase. The prepared attenuation ceramic material can be used at high frequencies, especially in the W and Y bands, and has high attenuation performance, high thermal conductivity and high strength. Attached Figure Description

[0011] Figure 1 It is the microstructure of α-phase silicon nitride;

[0012] Figure 2 It is the microstructure of carbon nanotubes;

[0013] Figure 3 This is a process flow diagram of the preparation process of attenuation ceramic material according to a preferred embodiment of the present invention;

[0014] Figure 4 These are comparison charts of the XRD test results of the attenuated ceramic materials in Examples 1-3;

[0015] Figure 5 This is a dielectric property diagram of Example 1 in the W-band;

[0016] Figure 6 These are the S-parameter test results in the Y-band of Example 1, where Figure a shows the S11 parameter test results and Figure b shows the S21 parameter test results.

[0017] Figure 7 These are XRD comparison images of Example 1 and Examples 4-5. Detailed Implementation

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] The first aspect of the present invention provides a raw material composition for attenuating ceramic materials, wherein the raw material composition comprises a dielectric phase, an attenuating phase and a sintering aid, wherein the dielectric phase is silicon nitride and the attenuating phase is carbon nanotubes (CNTs).

[0020] In this invention, silicon nitride is used as the dielectric phase for the first time, and carbon nanotubes are used as the attenuation phase. Through the combination of silicon nitride and carbon nanotubes, and the sintering aid, the resulting silicon nitride-based attenuation ceramic material has mechanical properties, thermal and electrical properties, and chemical stability. It is suitable for use at high frequencies, especially in the W and Y bands, and has high attenuation, good thermal conductivity, and high temperature stability.

[0021] Attenuating ceramic materials consist of a dielectric phase and an attenuating phase. The dielectric phase acts as a carrier, while the attenuating phase is uniformly dispersed within it. The attenuating and dielectric phases together determine the electromagnetic and thermal properties of the composite material. The design focus of attenuating materials is on the rational allocation and utilization of various dielectric and attenuating phases to adjust the material's microwave absorption and heat dissipation properties.

[0022] In some preferred embodiments of the present invention, the aspect ratio of the carbon nanotubes can reach 100-1000, exhibiting excellent electrical and thermal conductivity, outstanding hardness and strength, good toughness capable of withstanding considerable deformation without fracture, and unusual deformation recovery ability. Furthermore, the diameter of the carbon nanotubes is on the nanometer scale, much smaller than microwave wavelengths (centimeter waves or millimeter waves). Rayleigh scattering generated by the interaction of carbon nanotubes with microwaves causes the incident wave to be absorbed by the matrix in all directions. Therefore, carbon nanotubes are excellent high thermal conductivity microwave attenuators, and their microstructure is as follows: Figure 1 As shown.

[0023] In some preferred embodiments of the present invention, the sintering aid is selected from metal oxides, preferably one or more oxides of Group IIA, Group IIIA and Group IIB metals, and more preferably one or more of magnesium oxide, yttrium oxide and aluminum oxide.

[0024] The present invention does not have any particular requirements on the amount of the dielectric phase, the attenuation phase and the sintering aid. In some preferred embodiments of the present invention, the content of silicon nitride is 85-98 wt%, the content of carbon nanotubes is 0.8-4 wt%, and the content of sintering aid is 1-12 wt%, based on the total amount of the raw material composition.

[0025] In some preferred embodiments of the present invention, preferably, based on the total amount of the raw material composition, the content of silicon nitride is 87-95 wt%, the content of carbon nanotubes is 1-3 wt%, and the content of sintering aid is 4-10 wt%. Within this preferred range, the obtained silicon nitride-based attenuation ceramic material possesses high attenuation performance, high thermal conductivity, and high strength.

[0026] In some preferred embodiments of the present invention, preferably, the weight ratio of silicon nitride to carbon nanotubes is 20-98:1, more preferably 29-95:1. When the weight ratio of silicon nitride to carbon nanotubes is within the above range, the attenuation performance, thermal conductivity and strength of silicon nitride-based attenuating ceramic materials can be further improved.

[0027] In some preferred embodiments of the present invention, preferably, the particle size of the raw material composition is 0.1-5 μm. The attenuating ceramic material prepared within this particle size range has a uniform structure.

[0028] A second aspect of the present invention provides a method for preparing a decay ceramic material, comprising: hot pressing and sintering silicon nitride, carbon nanotubes and sintering aids to obtain the decay ceramic material.

[0029] In some preferred embodiments of the present invention, in order to make the raw materials more uniformly mixed, the method may further include ball milling to make the particle size of silicon nitride, carbon nanotubes and sintering aids 0.1-5 μm, as described above. The ball milling medium can be a low-carbon alcohol, such as ethanol, and the ball milling conditions include: a material-to-ball mass ratio of 1:2.5-4 and a ball milling time of 18-24 h.

[0030] For example, the specific process flow includes: batching, ball milling, drying, sieving, sintering, and grinding, and its preparation process flow diagram is as follows: Figure 3 As shown.

[0031] In some preferred embodiments of the present invention, the content of silicon nitride is 85-98 wt%, the content of carbon nanotubes is 0.8-4 wt%, and the content of sintering aid is 1-12 wt%, based on the total amount of silicon nitride, carbon nanotubes, and sintering aid; preferably, the content of silicon nitride is 87-95 wt%, the content of carbon nanotubes is 1-3 wt%, and the content of sintering aid is 4-10 wt%, based on the total amount of silicon nitride, carbon nanotubes, and sintering aid.

[0032] In some preferred embodiments of the present invention, the hot-pressing sintering temperature is 1650-1800℃, preferably 1700-1780℃, and the hot-pressing sintering time is 3-6 hours. The hot-pressing sintering temperature being within the preferred range results in a dense sintered ceramic material with excellent overall properties such as low porosity. The hot-pressing sintering is carried out under an inert atmosphere, which is selected from one or more of nitrogen, helium, and argon.

[0033] A third aspect of the present invention provides a method for preparing a decaying ceramic material, the decaying ceramic material comprising a dielectric phase, a decaying phase and a sintering aid, wherein the dielectric phase is α-phase silicon nitride and the decaying phase is carbon nanotubes.

[0034] In some preferred embodiments of the present invention, the silicon nitride is a low-temperature stable α-phase silicon nitride, which has a bending strength of up to 700 MPa and very good thermal shock resistance. The thermal conductivity of the reaction sintered ceramic can reach 40 W / (m·K), making it a very good heat-resistant insulating material.

[0035] In some preferred embodiments of the present invention, the density of the attenuating ceramic material is 3.148-3.255 g / cm³. 3 The thermal conductivity is 32.227-47.53 W / (m·K), and the flexural strength is 470.569-590.189 MPa; the dielectric constant of the W band is 8-21, and the dielectric loss is 0.31-0.98; the S11 of the Y band is less than -15 dB, and the S21 is -75 dB to -90 dB.

[0036] The fourth aspect of the present invention provides an application of the aforementioned attenuating ceramic material in improving the high-frequency microwave attenuation performance of attenuating ceramic materials.

[0037] The present invention will be described in detail below through embodiments.

[0038] The method for testing flexural strength is as follows: The flexural strength of the sample is tested using the three-point bending test method. During the test, a long strip sample is supported at both ends, and a force is applied to its central part, causing it to bend downwards. The load (force) during bending and the deformation after bending (usually the bending angle) are recorded. The flexural strength of the sample is calculated based on the test results and the sample's geometry.

[0039] Density testing method: The density is measured using Archimedes' method of displacement.

[0040] The thermal conductivity test method is as follows: The thermal conductivity of the material is tested and calculated using the laser flare method. The thermal diffusivity and specific heat capacity of the material are directly measured using a laser thermal conductivity meter, and the thermal conductivity can be obtained by the following formula: λ=αρCp;

[0041] In the formula: Cp is the specific heat capacity of the sample (unit: J / g·K), and α is the thermal diffusivity of the sample (unit: mm). 2 / sec), ρ is the sample density (unit: g / cm³) 3 ).

[0042] The dielectric properties testing method employs a waveguide reflection-transmission method to measure the high-frequency electromagnetic parameters of microwave loss ceramics. This method requires placing the material within a partially enclosed transmission line, which is a rectangular waveguide or coaxial air line. The measurement system consists of a vector network analyzer, a coaxial air line or waveguide, and software. An external computer controls the network analyzer, and the two are connected via LAN, USB, and GP-IB interfaces. The testing principle involves measuring the S-parameters at various frequency points within the test band in reflection-transmission mode. Based on the test results of the reflected signal (S11) and the transmitted signal (S21), the dielectric constant and dielectric loss tangent of the material are calculated using the scattering coefficient method for measuring the electromagnetic properties of microwave materials. This invention tests the range values ​​of dielectric constant and dielectric loss tangent in the W-band (75GHz-110GHz) and the range values ​​of S11 and S21 in the Y-band (170GHz-260GHz).

[0043] Unless otherwise specified in the following examples and comparative examples, all conditions were performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0044] Example 1

[0045] Silicon nitride, CNTs (with an aspect ratio of 500:1), and sintering aid (Y2O3-MgO-Al2O3) were mixed at a mass ratio of 92:2:6. The raw powder was mixed in a planetary ball mill with anhydrous ethanol as the grinding medium in a polyurethane container and agate balls for 24 hours at a mass ratio of 1:3. The mixture was dried at 80°C and passed through a 100-mesh sieve. The powder was then hot-pressed and sintered at 1720°C for 5 hours in a nitrogen atmosphere to obtain the attenuated ceramic material.

[0046] The comparison of XRD test results for the attenuating ceramic material is shown in the figure below. Figure 4 As shown in the figure, only the β-phase Si3N4 and C are formed. Furthermore, the composite ceramic phase analysis shows no formation of the α-phase Si3N4, which is beneficial for improving the thermal conductivity of the Si3N4-CNT composite microwave attenuation ceramic.

[0047] Example 2

[0048] Silicon nitride, CNTs (with an aspect ratio of 300:1), and sintering aid (Y2O3-MgO-Al2O3) were mixed at a mass ratio of 93:1:6. The raw powder was mixed in a planetary ball mill with anhydrous ethanol as the grinding medium in a polyurethane container and agate balls for 24 hours at a mass ratio of 1:3. The mixture was dried at 80°C and passed through a 100-mesh sieve. The powder was then hot-pressed and sintered at 1720°C for 5 hours in a nitrogen atmosphere to obtain the attenuated ceramic material.

[0049] The comparison of XRD test results for the attenuating ceramic material is shown in the figure below. Figure 4 As shown in the figure, when the amount of CNT added is small, MgSiN2 impurity phase is formed in the composite ceramic.

[0050] Example 3

[0051] Silicon nitride, CNTs (with an aspect ratio of 800:1), and sintering aid (Y2O3-MgO-Al2O3) were mixed in a mass ratio of 91:3:6. The raw powder was mixed in a planetary ball mill with anhydrous ethanol as the grinding medium in a polyurethane container and agate balls for 24 hours at a mass ratio of 1:3. The mixture was dried at 80°C and passed through a 100-mesh sieve. The powder was then hot-pressed and sintered at 1720°C for 5 hours in a nitrogen atmosphere to obtain the attenuated ceramic material.

[0052] The comparison of XRD test results for the attenuating ceramic material is shown in the figure below. Figure 4 As shown in the figure, only the β phase Si3N4 and C are formed. Furthermore, no α phase Si3N4 is formed in the composite ceramic phase analysis.

[0053] Example 4

[0054] Example 1 was repeated, except that the sintering temperature was 1650℃, while all other conditions remained the same. Attenuated ceramic materials were prepared, and the XRD test results are shown in the comparison diagram. Figure 7 As shown in the figure, the decay ceramic sintered at this temperature only contains the β-phase Si3N4 and C. Furthermore, in the composite ceramic phase analysis, no α-phase Si3N4 is formed.

[0055] Example 5

[0056] Example 1 was repeated, except that the sintering temperature was 1800℃, while all other conditions remained the same. Attenuated ceramic materials were prepared, and the XRD test results are shown in the comparison diagram. Figure 7 As shown in the figure, SiC impurity phases are formed in the composite ceramic sintered at this temperature.

[0057] Example 6

[0058] Example 1 was repeated, except that silicon nitride, CNT (with an aspect ratio of 500:1), and sintering aid (Y2O3-MgO-Al2O3) were mixed in a mass ratio of 90:4:6, while the other conditions remained unchanged, and the attenuation ceramic material was prepared.

[0059] Example 7

[0060] Example 1 was repeated, except that silicon nitride, CNT (with an aspect ratio of 500:1), and sintering aid (Y2O3-MgO-Al2O3) were mixed in a mass ratio of 96:1:3, while the other conditions remained unchanged, and the attenuation ceramic material was prepared.

[0061] Example 8

[0062] Example 1 was repeated, except that the aspect ratio of the CNT was 80:1, and the other conditions remained the same, to prepare the attenuating ceramic material.

[0063] Comparative Example 1

[0064] Compared with Example 1, the difference lies in the selection of aluminum nitride as the medium phase, while keeping other conditions unchanged, to prepare a decay ceramic material.

[0065] Test Example 1

[0066] The thermal conductivity, density, and flexural strength of the attenuated ceramic materials obtained in the above embodiments and comparative examples were measured, and the results are shown in Table 1.

[0067] Table 1

[0068]

[0069] Table 1 (continued)

[0070] parameter Example 6 Example 7 Example 8 Comparative Example 1 <![CDATA[Density (g / cm 3 )]]> 3.148 3.164 3.204 3.158 Thermal conductivity (W / (m·K)) 32.547 40.425 43.253 42.363 Flexural strength (MPa) 532.529 470.569 573.64 270.532

[0071] As shown in Table 1, the silicon nitride-based attenuation ceramic material prepared by this invention not only has a high thermal conductivity but also high flexural strength, exhibiting excellent mechanical properties. Compared with aluminum nitride-based attenuation ceramic materials, the high flexural strength of the silicon nitride-based attenuation ceramic material helps retain the wedge shape during the processing of attenuators for high-power traveling wave tubes, thus improving the yield rate. Examples 1-8 of this invention all show better results than Comparative Example 1, with Examples 1-3 showing significantly better performance.

[0072] Using a vector network analyzer, the dielectric properties of Example 1 in the W-band are as follows: Figure 5 As shown, its dielectric constant in the W-band is measured to be 12-18, and its dielectric loss is 0.78-0.96. Figure 6 The graph shows the S11 and S21 results for the test samples. As can be seen, near the 220GHz frequency band, S11 is below -15dB, and S21 is between -75dB and -90dB. This indicates that the Si3N4-CNT composite attenuator samples exhibit good absorption and matching characteristics. However, the S11 fluctuation among the three Si3N4-CNT attenuator samples is slightly larger than that of the Si3N4-SiC attenuator.

[0073] Test Example 2

[0074] The dielectric properties of the attenuation ceramic materials obtained in the above embodiments and comparative examples were measured, and the results are shown in Table 2.

[0075] Table 2

[0076]

[0077] Table 2 (continued)

[0078]

[0079]

[0080] As can be seen from the results in Table 2, the silicon nitride-based attenuating ceramic material prepared by the present invention, through the study of the dielectric constant and dielectric loss in the W-band and the S-parameters in the Y-band, shows that Examples 1-6 of the present invention are better than Comparative Example 1, and Examples 1-3 show significantly better results. This indicates that the silicon nitride-based attenuating ceramic material prepared by the present invention has both good electrical properties and high thermal conductivity and flexural strength. The material has excellent comprehensive performance and can be used at high frequencies, especially in the W-band and Y-band, where it has high attenuation, good thermal conductivity, and high-temperature stability.

[0081] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a decaying ceramic material, characterized in that, include: The attenuation ceramic material is obtained by hot pressing and sintering silicon nitride, carbon nanotubes and sintering aids. The sintering aids are magnesium oxide, yttrium oxide, and aluminum oxide. Based on the total amount of silicon nitride, carbon nanotubes, and sintering aids, the content of silicon nitride is 85-98 wt%, the content of carbon nanotubes is 0.8-4 wt%, and the content of sintering aids is 1-12 wt%. The weight ratio of silicon nitride to carbon nanotubes is 29-95:

1. The hot pressing sintering temperature is 1650-1720℃; the hot pressing sintering time is 3-6 hours; and the hot pressing sintering is carried out under an inert atmosphere.

2. The preparation method according to claim 1, wherein, Based on the total amount of silicon nitride, carbon nanotubes and sintering aids, the content of silicon nitride is 87-95 wt%, the content of carbon nanotubes is 1-3 wt%, and the content of sintering aids is 4-10 wt%.

3. The preparation method according to claim 1, wherein, The aspect ratio of the carbon nanotubes is 100-1000:

1.

4. The attenuation ceramic material obtained by the preparation method according to any one of claims 1-3.

5. The attenuating ceramic material according to claim 4, wherein, The attenuation ceramic material includes a dielectric phase, an attenuation phase, and a sintering aid, wherein the dielectric phase is β-phase silicon nitride, and the attenuation phase is carbon nanotubes. The density of the attenuating ceramic material is 3.148-3.255 g / cm³. 3 The thermal conductivity is 32.227-47.53 W / (m•K), and the flexural strength is 470.569-590.189 MPa; the dielectric constant of the W band is 8-21, and the dielectric loss is 0.31-0.98; the S11 of the Y band is less than -15 dB, and the S21 is -75 dB to -90 dB.

6. The application of the attenuating ceramic material according to claim 4 or 5 in improving the high-frequency microwave attenuation performance of attenuating ceramic materials.

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