Microwave body composite attenuation ceramic material as well as preparation method and application thereof

Abstract

The invention discloses a microwave composite attenuation ceramic material as well as a preparation method and application thereof. The material comprises the following components in percentage by mass: a matrix phase which is selected from beta-phase silicon nitride; an attenuation phase selected from silicon carbide; and a sintering aid phase, which is selected from the group consisting of Y2O3-MgO-Al2O3; wherein the mass ratio of the beta-phase silicon nitride to the silicon carbide to the Y2O3-MgO-Al2O3 is (60 to 90): (10 to 40): (3 to 10). The microwave body composite attenuation ceramic material has the characteristics of high strength, high toughness, high thermal conductivity, good thermal stability and the like, and the overall performance level and reliability of a high-frequency high-power microwave tube can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave vacuum electronic devices. More specifically, it relates to a microwave bulk composite attenuation ceramic material, a preparation method thereof, and an application thereof. Background Art

[0002] Microwave attenuation ceramics, also known as microwave loss ceramics, are widely used in microwave vacuum electronic devices to suppress competing modes, prevent self-excitation oscillation, reduce reflection, and increase bandwidth, so as to improve the stability of the devices. Otherwise, many microwave electro-vacuum devices will not work properly or even be scrapped. Therefore, attenuation materials are indispensable in microwave electro-vacuum devices, especially high-power devices. This requires that the attenuation materials have the following advantages: within a certain frequency band range, they play a corresponding attenuation function (that is, the tangent value of the dielectric loss angle tgδ is large enough); they have good vacuum performance and process plasticity; during use, the basic properties (attenuation amount, vacuum performance, etc.) of the attenuation materials are not damaged, that is, they have high temperature and chemical stability; they have good thermal conductivity and good matching with the cavity; the preparation process is simple, easy to control, has good repeatability, and a high yield, etc.

[0003] With the development of microwave tubes towards high frequency, high power, and miniaturization, the characteristic dimensions of the attenuators used are also getting smaller and smaller. At the same time, in order to meet the frequency matching requirements, the attenuator structure design also tends to be more complex. Taking the design of W-band and Q-band traveling wave tubes as an example, there are attenuators with special-shaped structures such as U-shaped and wedge-shaped. The characteristic dimensions of the U-shaped and wedge-shaped parts are only about 0.05 mm or even smaller, which poses greater challenges to machining and also puts forward higher requirements for the mechanical strength of microwave attenuation materials. Microwave attenuation ceramics must have higher strength and toughness to withstand the impact brought by machining without being damaged. At present, the attenuation materials applied in the high-frequency band are mainly aluminum nitride-silicon carbide composite attenuation ceramics, but this material is relatively brittle and has a low fracture toughness (4.3 MPa·m 1 / 2 ) and a low flexural strength (287 MPa). Therefore, during the process of machining micro-miniature attenuators, it is easy to cause chipping of this material, and it is not easy to maintain the integrity of the attenuator, resulting in a low machining yield; during the test assembly process, the wedge is also easily damaged, resulting in large differences in testing. Summary of the Invention

[0004] Aiming at the above problems, the present invention provides a microwave bulk composite attenuation ceramic material, a preparation method thereof, and an application thereof. The microwave bulk composite attenuation ceramic material has the characteristics of high strength, high toughness, high thermal conductivity, and good thermal stability, and can effectively improve the overall performance level and reliability of high-frequency high-power microwave tubes.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] On the one hand, the present invention provides a microwave bulk composite attenuation ceramic material, which contains, by mass percentage:

[0007] A matrix phase, selected from β-phase silicon nitride;

[0008] An attenuation phase, selected from silicon carbide; and

[0009] A sintering aid phase, selected from Y2O3-MgO-Al2O3;

[0010] Wherein, the mass ratio of the β-phase silicon nitride, silicon carbide and Y2O3-MgO-Al2O3 is (60-90):(10-40):(3-10).

[0011] Further, the attenuation phase is uniformly distributed at the grain boundaries of the matrix phase.

[0012] Further, in the microwave bulk composite attenuation ceramic material, the sintering aid phase exists at the grain boundaries of the matrix phase and the attenuation phase.

[0013] Further, the Y2O3-MgO-Al2O3 is a mixture of Y2O3, MgO and Al2O3 in a mass ratio of (2-3):(2-3):1. This sintering aid can well promote the formation of liquid phase, improve the liquid phase viscosity, increase the softening temperature and high-temperature performance, increase the sintering driving force, and realize the densification sintering of the microwave bulk composite attenuation ceramic material; and the addition of Y2O3 in this sintering aid can adsorb the lattice oxygen in silicon nitride, increase the phonon mean free path, thereby improving the thermal conductivity of the material; MgO can interact with SiO2 on the surface of silicon nitride to form a eutectic liquid phase at low temperature, promote the formation of liquid phase, fully fill the pores and accelerate the mass transfer process, and promote the phase transformation of α-Si3N4→β-Si3N4, and it is easy to obtain a ceramic with high density.

[0014] Further, the silicon carbide is α-phase silicon carbide.

[0015] On the second hand, the present invention provides a preparation method of the microwave bulk composite attenuation ceramic material as described in the first aspect above. The preparation method includes the following steps:

[0016] Weigh and mix powders of silicon nitride, silicon carbide and sintering aid to obtain a mixed powder;

[0017] Ball mill the mixed powder to obtain a uniformly dispersed slurry;

[0018] Dry the slurry and pass it through an 80-mesh sieve to obtain a powder material;

[0019] Sinter the powder material to obtain the microwave bulk composite attenuation ceramic material.

[0020] Further, in the preparation method, the silicon nitride used as the raw material is α-phase silicon nitride.

[0021] Further, in the mixed powder, the mass ratio of silicon nitride, silicon carbide and sintering aid is (60-90):(10-40):(3-10).

[0022] Further, the ball milling method is: mixing the mixed powder, ethanol and agate balls in a mass ratio of 1.7:1:2.7, and mixing in a planetary ball mill for 12-24 hours, preferably 16 hours.

[0023] Further, the drying temperature is 80°C.

[0024] Further, the calcination is carried out in a nitrogen atmosphere, the calcination temperature is 1600-1800°C, the calcination pressure is 20-30 MPa, and the calcination time is 3-5 hours.

[0025] In some examples, the calcination temperature includes but is not limited to 1600-1700°C, 1600-1650°C, 1650-1780°C, 1650-1700°C, 1700°C, etc. In some examples, the calcination pressure is 20-25 MPa, 25-30 MPa, 20 MPa, 25 MPa, 30 MPa, etc.

[0026] Further, the calcination is carried out in a graphite mold.

[0027] In a third aspect, the present invention provides the application of the microwave bulk composite attenuation ceramic material as described in the first aspect above in the preparation of microwave vacuum electronic devices.

[0028] Further, the microwave vacuum electronic device is a high-frequency high-power microwave tube.

[0029] Further, the wave vacuum electronic device is a W-band microwave tube.

[0030] Further, the frequency of the W-band is 75 GHz - 110 GHz.

[0031] The beneficial effects of the present invention are as follows:

[0032] In the microwave bulk composite attenuation ceramic material provided by the present invention, with β-phase silicon nitride as the matrix phase, silicon carbide as the attenuation phase, and Y2O3-MgO-Al2O3 as the sintering aid phase, it endows the ceramic material with excellent mechanical properties, thermal, electrical properties and chemical stability, and this attenuation ceramic material can be well applied to high-frequency high-power microwave electro-vacuum devices, and it has excellent properties such as high strength, high toughness, high thermal conductivity, and large attenuation. Description of the Drawings

[0033] The following further elaborates on the specific embodiments of the present invention in conjunction with the accompanying drawings.

[0034] Figure 1 The SEM image of the raw material silicon carbide used in Example 1 is shown.

[0035] Figure 2 The XRD patterns of the attenuation ceramic materials prepared in Example 1, Example 2, and Example 3 are shown.

[0036] Figure 3 The SEM image of the attenuation ceramic material prepared in Example 1 is shown.

[0037] Figure 4 The dielectric property diagram of the attenuation ceramic material prepared in Example 1 in the W band is shown. Specific Embodiments

[0038] To more clearly illustrate the present invention, the following further describes the present invention in conjunction with preferred embodiments and the accompanying drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0039] Example 1

[0040] A microwave bulk composite attenuation ceramic material, and its preparation method includes the following steps:

[0041] Take powders of α-phase silicon nitride, silicon carbide (whose SEM image is as Figure 1 shown) and a sintering aid (the sintering aid is a mixture of Y2O3, MgO, and Al2O3 in a mass ratio of 2:3:1), and proportion them according to a mass ratio of 70:25:5. Place the proportioned powders in a polyurethane tank, use agate balls as grinding balls, and anhydrous ethanol as a grinding medium. Mix the materials on a planetary ball mill for 16 hours according to a ratio of material: solvent: ball mass ratio of 1.7:1:2.7 to obtain a uniform slurry;

[0042] Place the slurry in an 80°C oven for drying, and then pass it through an 80-mesh sieve to obtain powders with uniform particle size;

[0043] Weigh the powders and place them in a graphite mold. Sinter at 1700°C and a hot pressing pressure of 25 MPa for 3 h in a nitrogen atmosphere to obtain the microwave bulk composite attenuation ceramic material.

[0044] The XRD pattern of the attenuation ceramic material is as Figure 2 shown. It can be seen from the figure that only the generation of β-phase Si3N4 and α-phase SiC. This indicates that during the sintering process, all of the α-phase Si3N4 has been converted into β-phase Si3N4, and there is no solid solution between the matrix phase and the attenuation phase.

[0045] The SEM image of the attenuation ceramic material is as follows Figure 3 shown. Figure 3 In the figure, the black long rod-shaped grains are silicon nitride grains, the gray grains are silicon carbide grains, and the white ones are sintering aid phases. The grain distribution areas of the two main crystal phases are obvious, the grain boundaries are clear, and there are fewer pores. The presence of long rod-shaped β-phase Si3N4 grains is conducive to the improvement of the mechanical properties and thermal conductivity of Si3N4-SiC composite microwave attenuation ceramics.

[0046] The flexural strength of the Si3N4-SiC composite attenuation ceramic material was tested by the three-point method, and its flexural strength value was 884.514MPa. The fracture toughness of the Si3N4-SiC composite attenuation ceramic was tested by the single-side notched beam method, and its fracture toughness value was 11.1MPa·m 1 / 2 ; The thermal conductivity at room temperature was measured by laser thermal conductivity meter to be 70.898W / (m·K); the dielectric constant in W band was measured by vector network analyzer to be 17-24, and the dielectric loss was 0.4-0.59. The test results are as follows Figure 4 shown.

[0047] Example 2

[0048] A microwave composite attenuation ceramic material, the preparation method of which comprises the following steps:

[0049] α-phase silicon nitride, silicon carbide and a sintering aid (the sintering aid is a mixture of Y2O3, MgO and Al2O3 in a mass ratio of 2:3:1) are taken as powders, and the ingredients are prepared in a mass ratio of 70:25:5. The prepared powders are placed in a polyurethane tank, and agate balls are used as grinding balls, and anhydrous ethanol is used as a grinding medium. The materials are mixed on a planetary ball mill for 16 hours according to a material, solvent, and ball mass ratio of 1.7:1:2.7 to obtain a uniform slurry;

[0050] The slurry was placed in an oven at 80°C for drying, and then passed through an 80-mesh sieve to obtain a powder with uniform particle size;

[0051] The powder is weighed and placed in a graphite mold, and sintered for 3 hours in a nitrogen atmosphere at a temperature of 1700° C. and a hot pressing pressure of 20 MPa to obtain the microwave body composite attenuation ceramic material.

[0052] The XRD spectrum of the attenuation ceramic material is as follows Figure 2 As shown in the figure, only β-phase Si3N4 and α-phase SiC are generated.

[0053] The flexural strength of the Si3N4-SiC composite attenuation ceramic was tested by the three-point method, and the flexural strength value was 770.089 MPa; the fracture toughness of the Si3N4-SiC composite attenuation ceramic was tested by the single-edge notched beam method, and the fracture toughness value was 9.3 MPa·m 1 / 2 ; The thermal conductivity at room temperature was measured by a laser thermal conductivity meter to be 64.208 W / (m·K); by a vector network analyzer, the dielectric constant in the W band was measured to be 24 - 30, and the dielectric loss was 0.30 - 0.40.

[0054] Example 3

[0055] A microwave bulk composite attenuation ceramic material, and its preparation method includes the following steps:

[0056] Take powders of α-phase silicon nitride, silicon carbide and sintering aids (the sintering aids are a mixture of Y2O3, MgO and Al2O3 in a mass ratio of 2:3:1), and proportion them according to a mass ratio of 70:25:5. Place the proportioned powders in a polyurethane tank, use agate balls as grinding balls, and anhydrous ethanol as the grinding medium. Mix the materials on a planetary ball mill for 16 hours according to the ratio of material:solvent:ball mass of 1.7:1:2.7 to obtain a uniform slurry;

[0057] Place the slurry in an 80°C oven for drying, and then pass it through an 80-mesh sieve to obtain powders with uniform particle size;

[0058] Weigh the powders and place them in a graphite mold. Sinter at 1700°C under a hot pressing pressure of 30 MPa for 3 h in a nitrogen atmosphere to obtain the microwave bulk composite attenuation ceramic material.

[0059] The XRD pattern of the attenuation ceramic material is as Figure 2 shown. It can be seen from the figure that only the generation of β-phase Si3N4 and α-phase SiC.

[0060] The flexural strength of the Si3N4-SiC composite attenuation ceramic was tested by the three-point method, and the flexural strength value was 872.671 MPa; the fracture toughness of the Si3N4-SiC composite attenuation ceramic was tested by the single-edge notched beam method, and the fracture toughness value was 10.1 MPa·m 1 / 2 ; The thermal conductivity at room temperature was measured by a laser thermal conductivity meter to be 55.081 W / (m·K); by a vector network analyzer, the dielectric constant in the W band was measured to be 19 - 25, and the dielectric loss was 0.30 - 0.39.

[0061] Example 4

[0062] Repeat Example 1, with the difference that the sintering temperature is 1600°C and the other conditions remain unchanged to prepare the attenuation ceramic material.

[0063] The flexural strength of the Si3N4-SiC composite attenuation ceramic was tested by the three-point method, and its flexural strength value was 841.991 MPa; the fracture toughness of the Si3N4-SiC composite attenuation ceramic was tested by the single-edge notched beam method, and its fracture toughness value was 8.6 MPa·m 1 / 2 ; Its thermal conductivity at room temperature was measured by a laser thermal conductivity meter to be 50.736 W / (m·K); by a vector network analyzer, its dielectric constant in the W band was measured to be 23 - 28, and the dielectric loss was 0.31 - 0.43.

[0064] Example 5

[0065] Repeat Example 1, except that the sintering temperature was 1650 °C and the other conditions remained unchanged, to prepare an attenuation ceramic material.

[0066] The flexural strength of the Si3N4-SiC composite attenuation ceramic was tested by the three-point method, and its flexural strength value was 865.188 MPa; the fracture toughness of the Si3N4-SiC composite attenuation ceramic was tested by the single-edge notched beam method, and its fracture toughness value was 9.1 MPa·m 1 / 2 ; Its thermal conductivity at room temperature was measured by a laser thermal conductivity meter to be 52.352 W / (m·K); by a vector network analyzer, its dielectric constant in the W band was measured to be 21 - 27, and the dielectric loss was 0.28 - 0.39.

[0067] Example 6

[0068] Repeat Example 1, except that the sintering temperature was 1780 °C and the other conditions remained unchanged, to prepare an attenuation ceramic material.

[0069] The flexural strength of the Si3N4-SiC composite attenuation ceramic was tested by the three-point method, and its flexural strength value was 741.199 MPa; the fracture toughness of the Si3N4-SiC composite attenuation ceramic was tested by the single-edge notched beam method, and its fracture toughness value was 7.7 MPa·m 1 / 2 ; Its thermal conductivity at room temperature was measured by a laser thermal conductivity meter to be 56.785 W / (m·K); by a vector network analyzer, its dielectric constant in the W band was measured to be 17 - 25, and the dielectric loss was 0.38 - 0.51.

[0070] Comparative Example 1

[0071] Compared with Example 1, the difference was that α-phase silicon nitride was replaced with aluminum nitride, that is, aluminum nitride was used as the dielectric phase, and the other conditions remained unchanged, to prepare an attenuation ceramic material.

[0072] The flexural strength of the AlN-SiC composite attenuation ceramic was tested by the three-point method, and its flexural strength value was 315.637 MPa; the fracture toughness of the Si3N4-SiC composite attenuation ceramic was tested by the single-edge notched beam method, and its fracture toughness value was 4.4 MPa·m 1 / 2 ; Its thermal conductivity at room temperature was measured to be 48.618 W / (m·K) by a laser thermal conductivity meter; its dielectric constant in the W band was measured to be 9-13 and the dielectric loss was 0.25 - 0.37 by a vector network analyzer.

[0073] Comparative Example 2

[0074] Repeat Example 1, except that silicon carbide was replaced with carbon nanotubes and the other conditions remained unchanged, to prepare an attenuation ceramic material.

[0075] The flexural strength of the AlN-SiC composite attenuation ceramic was tested by the three-point method, and its flexural strength value was 670.361 MPa; the fracture toughness of the Si3N4-SiC composite attenuation ceramic was tested by the single-edge notched beam method, and its fracture toughness value was 6.3 MPa·m 1 / 2 ; Its thermal conductivity at room temperature was measured to be 44.568 W / (m·K) by a laser thermal conductivity meter; its dielectric constant in the W band was measured to be 13-20 and the dielectric loss was 0.75 - 0.97 by a vector network analyzer.

[0076] Comparative Example 3

[0077] Repeat Example 1, except that the sintering aid Y2O3-MgO-Al2O3 was replaced with yttrium oxide and the other conditions remained unchanged. During the preparation of the attenuation ceramic material, the growth of silicon nitride grains was too coarse, resulting in significantly worse mechanical properties (flexural strength and fracture toughness) of the obtained attenuation ceramic material than the corresponding effects of each example.

[0078] The density, flexural strength, fracture toughness, and thermal conductivity results of the attenuation ceramic materials obtained in the above examples and comparative examples are shown in Table 1 below.

[0079] Table 1

[0080]

[0081] Obviously, the above examples of the present invention are merely examples for clearly illustrating the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A microwave bulk composite attenuation ceramic material, characterized in that, By mass percentage, the material contains: A matrix phase selected from β-phase silicon nitride; A decay phase selected from silicon carbide; and A sintering aid phase selected from Y2O3-MgO-Al2O3; wherein, the mass ratio of the β-phase silicon nitride, silicon carbide and Y2O3-MgO-Al2O3 is (60-90):(10-40):(3-10).

2. The microwave bulk composite attenuation ceramic material according to claim 1, characterized in that The Y2O3-MgO-Al2O3 is a mixture of Y2O3, MgO and Al2O3 in a mass ratio of (2-3):(2-3):

1.

3. The preparation method of the microwave bulk composite attenuation ceramic material according to claim 1, characterized in that, It includes the following steps: Weigh and mix powders of silicon nitride, silicon carbide and sintering aid to obtain a mixed powder; Ball-mill the mixed powder to obtain a uniformly dispersed slurry; Dry the slurry and then pass it through an 80-mesh sieve to obtain a powder material; Sinter the powder material to obtain the microwave bulk composite decay ceramic material.

4. The preparation method according to claim 3, characterized in that, In the mixed powder, the mass ratio of silicon nitride, silicon carbide and sintering aid is (60-90):(10-40):(3-10).

5. The preparation method according to claim 3, characterized in that, The way of ball-milling is: mix the mixed powder, ethanol and agate balls in a mass ratio of 1.7:1:2.7, and mix them in a planetary ball mill for 12-24 hours.

6. The preparation method according to claim 3, characterized in that, The sintering is carried out in a nitrogen atmosphere, the sintering temperature is 1600-1800 °C, the sintering pressure is 20-30 MPa, and the sintering time is 3-5 hours.

7. The preparation method according to claim 6, characterized in that, The sintering temperature is 1650-1700 °C, and the sintering pressure is 25-30 MPa.

8. The preparation method according to claim 6, characterized in that, The sintering temperature is 1700 °C, and the sintering pressure is 25-30 MPa.

9. The application of the microwave bulk composite decay ceramic material according to claim 1 in the preparation of microwave vacuum electronic devices.

10. The application according to claim 9, wherein The microwave vacuum electronic device is a microwave tube in the W band.

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