CN102978500A - High thermal conductivity microwave attenuation AlN-based composite material and preparation method thereof - Google Patents

Abstract

A high thermal conductivity microwave attenuation AlN-based composite material and a preparation method thereof belong to the field of microwave electronic vacuum technology. The present invention selects CNTs and W as the metal phase, and AlN as the dielectric phase, including CNTs: (0.1-2.0) vol.%, W: (1.0-20.0) vol.% and AlN: (100-CNTs-W) vol.% . CNTs, W powder and AlN powder are mixed according to a certain volume ratio to obtain a mixture; the mixture is formed and sintered to obtain a CNTs/W/AlN composite microwave absorbing material. The relative density of the material is >98%, the dielectric constant is 17~25, and the dielectric loss tangent is >0.04. It has good microwave absorption performance in the range of 70kHz~1MHz, and is especially suitable for the preparation of microwave electric vacuum devices, which are used in passive electronic countermeasures and Microwave measurement system.

Description

A high thermal conductivity microwave attenuation AlN-based composite material and its preparation method

technical field

The present invention relates to a microwave attenuator material and its preparation method, in particular to a green environment-friendly microwave attenuator material and its preparation technology applied under vacuum conditions, specifically a carbon nanotube/tungsten/aluminum nitride (CNTs /W/AlN) composite phase microwave absorbing material and belongs to the field of microwave electron vacuum technology.

Background technique

Microwave attenuation materials are widely used in microwave electric vacuum devices. They load high-frequency interaction circuits such as resonant cavities and slow-wave structures to broaden the frequency band, suppress oscillation and eliminate other non-design modes. In addition, microwave attenuating materials are widely used in passive electronic countermeasures. Important facilities on the ground, aircraft in the air, and the construction of confidential microwave isolation rooms all require a large amount of microwave attenuating materials to prevent the opponent from discovering, tracking, and attacking. Microwave attenuating materials are widely used in microwave measurement systems as attenuators and loads in waveguides and coaxial cables, and are known as the "heart" of electronic systems.

At present, the bulk absorber materials of electric vacuum devices used in China are mainly carburized porous alumina attenuating ceramics and BeO-based composite attenuating ceramics. Carburized porous alumina attenuation ceramics have a large amount of outgassing, low strength, uneven distribution of attenuation phases, low carburizing yield, and low thermal conductivity due to porous structure, which has caused certain obstacles to the use of high-power tubes; BeO The toxicity of BeO-based composite attenuating ceramics is difficult to meet the safety requirements.

People turn their attention to AlN, which is non-toxic, and its thermal conductivity can reach 320 Wm ^-1 .K ^-1 theoretically, which is close to the thermal conductivity of BeO, which is about 8 times that of Al ₂ O ₃ . Moreover, AlN has moderate dielectric coefficient, good chemical and thermal stability, and high resistivity. Using AlN as the dielectric phase not only helps to improve the thermal conductivity of the attenuating material, but also helps to improve the microwave attenuating performance of the material. Therefore, the AlN-based attenuation material has a low outgassing rate in a high vacuum environment, has good compatibility with oxide cathodes, and has good thermal stability and mechanical properties at high temperatures above 1000 ° C. Creates an airtight seal. Therefore, the development of AlN-based microwave attenuating materials, especially the improvement of their attenuation performance and thermal conductivity, is the development trend of microwave attenuating materials in microwave electric vacuum devices, especially in the application of high-power microwave tubes.

In high-power microwave electric vacuum devices, one of the basic requirements for attenuating materials is high dielectric constant and controllable imaginary part, which is the key to realize high attenuation of attenuating materials. However, pure aluminum nitride ceramics have the characteristics of low dielectric constant, low dielectric loss and high resistivity, so some conductive phases are often added to it for adjustment. Since the sintering temperature of AlN is about 1700°C, adding a conductive phase with too low melting point will form a liquid during the sintering process, and the desired result cannot be obtained. Cheng Jigui of Hefei University of Technology added 34%-40% (mass fraction) of Mo to AlN to obtain a material with good wave-absorbing properties in the range of 2.2-2.5GHz. Yang Zhimin of Beijing Nonferrous Metals Research Institute added Mo to AlN. 1.65%-2.01% of W or Mo obtains a reflection attenuation of 20.0dB in a wide frequency band. The conductive particle W is used as a microwave attenuator, which has a thermal expansion coefficient matched with AlN and a high thermal conductivity.

A large number of studies have shown that carbon nanotubes have excellent electrical conductivity, excellent thermal conductivity and microwave absorption performance, and are the most promising new generation of microwave absorbing materials. In the experiment of direct compounding of CNT and ceramic matrix to prepare dense ceramics, when the sintering temperature is higher than 1400 °C, the CNT composite attenuation ceramics after high temperature sintering have good attenuation performance, but when the sintering temperature reaches 1600 °C, the attenuation is very low. Small, at this temperature, the ceramic matrix and CNT react and escape, so it does not reflect the microwave absorption effect it should have. It is necessary to add metal materials. According to the design principle of complementary advantages of composite materials, conductive particles are added to the AlN matrix. It is evenly distributed in the insulating and high thermal conductivity AlN matrix material, which can increase the dielectric constant and loss of the material, and realize a new type of attenuation material with excellent comprehensive performance.

Carbon nanotubes have a large specific surface area, aspect ratio, small size and other special structures, as well as their special electromagnetic properties, so that the application of carbon nanotubes in stealth materials and wave-absorbing materials has great potential . Compared with traditional microwave attenuation, carbon nanotubes have the advantages of wide absorption frequency band, large attenuation, less dosage, high stability, oxidation resistance, light weight, etc., which make CNTs composite ceramics exhibit extraordinary microwave absorption properties . Bu Wenbo of Nanjing University of Technology added an appropriate amount of graphite powder to the AlN matrix to prepare an AlN-C composite material with excellent microwave attenuation properties, and developed an AlN-C dielectric resonant loss cavity in the research of AlN-C composite materials. Yu Liang and others from China Iron and Steel Research and Technology Group Corporation studied the preparation of AlN-SiC composite attenuation materials and their microwave attenuation properties. range of use.

Contents of the invention

The present invention aims at the defects of hot-pressing preparation of existing cermet-based microwave absorbing materials, and aims to provide a high-density, high-loss microwave attenuating sintered body obtained by rapid sintering of SPS. Electrical loss tangent>0.04, good absorbing performance in the range of 70kHz~1MHz,

For above-mentioned purpose, the technical scheme that the present invention takes is as follows:

A high thermal conductivity microwave attenuator material, select CNTs and W as the metal phase, AlN as the dielectric phase, including CNTs: (0.1-2.0) vol.%, W: (1.0-20.0) vol.% and AlN: (100- CNTs-W) vol.%.

Another object of the present invention is to provide a preparation method of the above-mentioned high thermal conductivity microwave attenuator material, the specific implementation steps are:

(1) Mix CNTs powder, W powder and AlN powder according to the volume ratio of (0.1-2.0): (1.0-20.0): (78.0-98.9) and mix them evenly. Use stainless steel balls as grinding balls, and use absolute ethanol As the grinding medium, the mass ratio of the grinding ball to the raw material powder is (4-6):1, and the ball milling time is 10-40min to obtain a mixed powder slurry.

(2) The mixed powder slurry is placed in a vacuum drying oven, and vacuum-dried at 70-90° C. for 2-4 hours to obtain a mixed powder.

(3) Put the mixed powder in a graphite mold for SPS sintering to prepare a composite ceramic sample. The sintering temperature is 1400-1700°C, the holding time is 2-10min, the sintering pressure is 30-40MPa, and the heating rate is 100-150°C/ min, the CNTs-W-AlN composite bulk material was obtained.

(4) Process the composite block material according to the shape and size of the specific use, and obtain the CNTs-W-AlN composite block material for the microwave attenuator.

The mixing methods include rolling ball milling, high-energy ball milling, magnetic stirring, and ultrasonic dispersion.

In the CNTs/W/AlN composite microwave absorbing material of the present invention, the content of W and CNTs has a direct impact on the performance of the composite ceramics. When the CNTs content is too much, the number of pores in the composite ceramics increases, and W effectively improves the sintered body. Density; adding CNTs to AlN/W increases the dielectric loss of the composite ceramic. The composite ceramic prepared by adding 1vol.%CNTs to AlN-10vol.%W has excellent dielectric properties, dielectric loss at 70kHz~1MHz frequency, tanδ>0.04, dielectric constant: ε<17.5, especially suitable for preparing microwave Electro-vacuum devices are used in passive electronic countermeasures and microwave measurement systems.

specific implementation

The present invention will be described in detail below in conjunction with specific embodiments.

Example 1

(1) Mix CNTs powder, W powder and AlN powder according to the volume ratio of 1:5:94, use stainless steel balls as grinding balls, use absolute ethanol as grinding media, and the mass ratio of grinding balls to raw material powder The ratio is 4:1, and the ball milling time is 20 minutes.

(2) Put the mixed powder slurry described in step (1) in a vacuum drying oven, and vacuum dry at 70° C. for 2 hours to obtain a mixed powder.

(3) Put the mixed powder described in step (2) in a graphite mold for SPS sintering to prepare a composite ceramic sample, the sintering temperature is 1600°C, the holding time is 10min, the sintering pressure is 30MPa, and the heating rate is 100°C/min .

(4) Process the composite block material described in step (3) according to the specific shape and size when used, to obtain the CNTs-W-AlN composite block material for microwave attenuator. Its relative density is 98%, dielectric constant is 17, dielectric loss tangent is 0.035, and it has good wave-absorbing performance in the range of 70kHz~1MHz.

the

Example 2

(1) Mix CNTs powder, W powder and AlN powder according to the volume ratio of 1:10:89 and mix them evenly. Stainless steel balls are used as grinding balls, absolute ethanol is used as grinding medium, and the mass ratio of grinding balls to raw material powder The ratio is 4:1, and the ball milling time is 20 minutes.

(2) Put the mixed powder slurry described in step (1) in a vacuum drying oven, and vacuum dry at 70° C. for 2 hours to obtain a mixed powder.

(3) Put the mixed powder described in step (2) in a graphite mold for SPS sintering to prepare a composite ceramic sample, the sintering temperature is 1600°C, the holding time is 5min, the sintering pressure is 30MPa, and the heating rate is 100°C/min .

(4) Process the composite block material described in step (3) according to the specific shape and size when used, to obtain the CNTs-W-AlN composite block material for microwave attenuator. Its relative density is 98%, the dielectric constant is 17.5, the dielectric loss tangent is 0.04, and it has good wave-absorbing performance in the range of 70kHz~1MHz.

the

Example 3

(1) Mix CNTs powder, W powder and AlN powder according to the volume ratio of 1:20:79, use stainless steel balls as grinding balls, use absolute ethanol as grinding media, and the mass ratio of grinding balls to raw material powder The ratio is 4:1, and the ball milling time is 20 minutes.

(2) Put the mixed powder slurry described in step (1) in a vacuum drying oven, and vacuum dry at 70° C. for 2 hours to obtain a mixed powder.

(3) Put the mixed powder described in step (2) in a graphite mold for SPS sintering to prepare a composite ceramic sample, the sintering temperature is 1400°C, the holding time is 5min, the sintering pressure is 30MPa, and the heating rate is 100°C/min .

(4) Process the composite block material described in step (3) according to the specific shape and size when used, to obtain the CNTs-W-AlN composite block material for microwave attenuator. Its relative density is 98%, dielectric constant is 17.3, dielectric loss tangent is 0.032, and it has good wave-absorbing performance in the range of 70kHz~1MHz.

the

Example 4

(1) Mix CNTs powder, W powder and AlN powder according to the volume ratio of 0.1:1:98.9 and mix them evenly. Using stainless steel balls as grinding balls and absolute ethanol as grinding media, the mass ratio of grinding balls to raw material powder The ratio is 4:1, and the ball milling time is 20 minutes.

(2) Put the mixed powder slurry described in step (1) in a vacuum drying oven, and vacuum dry at 70° C. for 2 hours to obtain a mixed powder.

(3) Put the mixed powder described in step (2) in a graphite mold for SPS sintering to prepare a composite ceramic sample, the sintering temperature is 1600°C, the holding time is 5min, the sintering pressure is 30MPa, and the heating rate is 100°C/min .

(4) Process the composite block material described in step (3) according to the specific shape and size when used, to obtain the CNTs-W-AlN composite block material for microwave attenuator. Its relative density is 99%, dielectric constant is 19, dielectric loss tangent is 0.05, and it has good wave-absorbing performance in the range of 70kHz~1MHz.

the

Example 5

(1) Mix CNTs powder, W powder and AlN powder according to the volume ratio of 0.1:10:89.9 and mix them evenly. Using stainless steel balls as grinding balls and absolute ethanol as grinding media, the mass ratio of grinding balls to raw material powder The ratio is 4:1, and the ball milling time is 20 minutes.

(2) Put the mixed powder slurry described in step (1) in a vacuum drying oven, and vacuum dry at 70° C. for 2 hours to obtain a mixed powder.

(3) Put the mixed powder described in step (2) in a graphite mold for SPS sintering to prepare a composite ceramic sample, the sintering temperature is 1600°C, the holding time is 5min, the sintering pressure is 30MPa, and the heating rate is 100°C/min .

(4) Process the composite block material described in step (3) according to the specific shape and size when used, to obtain the CNTs-W-AlN composite block material for microwave attenuator. Its relative density is 98.5%, dielectric constant is 20, dielectric loss tangent is 0.045, and it has good wave-absorbing performance in the range of 70kHz~1MHz.

the

Example 6

(1) Mix CNTs powder, W powder and AlN powder according to the volume ratio of 0.1:20:79.9 and mix them evenly. Using stainless steel balls as grinding balls and absolute ethanol as grinding media, the mass ratio of grinding balls to raw material powder The ratio is 4:1, and the ball milling time is 20 minutes.

(2) Put the mixed powder slurry described in step (1) in a vacuum drying oven, and vacuum dry at 70° C. for 2 hours to obtain a mixed powder.

(3) Put the mixed powder described in step (2) in a graphite mold for SPS sintering to prepare a composite ceramic sample, the sintering temperature is 1600°C, the holding time is 5min, the sintering pressure is 30MPa, and the heating rate is 100°C/min .

(4) Process the composite block material described in step (3) according to the specific shape and size when used, to obtain the CNTs-W-AlN composite block material for microwave attenuator. Its relative density is 97.5%, dielectric constant is 21, dielectric loss tangent is 0.056, and it has good wave-absorbing performance in the range of 70kHz~1MHz.

the

Example 7

(1) Mix CNTs powder, W powder and AlN powder according to the volume ratio of 2:1:97, use stainless steel balls as grinding balls, use absolute ethanol as grinding media, and the mass ratio of grinding balls to raw material powder The ratio is 5:1, and the ball milling time is 40 minutes.

(2) Put the mixed powder slurry described in step (1) in a vacuum drying oven, and vacuum dry at 70° C. for 2 hours to obtain a mixed powder.

(3) Put the mixed powder described in step (2) in a graphite mold for SPS sintering to prepare a composite ceramic sample, the sintering temperature is 1600°C, the holding time is 10min, the sintering pressure is 30MPa, and the heating rate is 100°C/min .

(4) Process the composite block material described in step (3) according to the specific shape and size when used, to obtain the CNTs-W-AlN composite block material for microwave attenuator. Its relative density is 96.5%, dielectric constant is 22, dielectric loss tangent is 0.06, and it has good wave-absorbing performance in the range of 70kHz~1MHz.

the

Example 8

(1) Mix CNTs powder, W powder and AlN powder according to the volume ratio of 2:10:88 and mix them evenly. Using stainless steel balls as grinding balls and absolute ethanol as grinding media, the mass ratio of grinding balls to raw material powder The ratio is 6:1, and the ball milling time is 50 minutes.

(2) The mixed powder slurry described in step (1) was placed in a vacuum drying oven, and vacuum-dried at 90° C. for 2 hours to obtain a mixed powder.

(3) Put the mixed powder described in step (2) in a graphite mold for SPS sintering to prepare a composite ceramic sample, the sintering temperature is 1700°C, the holding time is 10min, the sintering pressure is 40MPa, and the heating rate is 140°C/min .

(4) Process the composite block material described in step (3) according to the specific shape and size when used, to obtain the CNTs-W-AlN composite block material for microwave attenuator. Its relative density is 96.8%, dielectric constant is 23.5, dielectric loss tangent is 0.055, and it has good wave-absorbing performance in the range of 70kHz~1MHz.

Example 9

(1) Mix CNTs powder, W powder and AlN powder according to the volume ratio of 2:20:78 and mix them evenly. Using stainless steel balls as grinding balls and absolute ethanol as grinding media, the mass ratio of grinding balls to raw material powder The ratio is 4:1, and the ball milling time is 20 minutes.

(2) The mixed powder slurry described in step (1) was placed in a vacuum drying oven, and vacuum-dried at 90° C. for 2 hours to obtain a mixed powder.

(3) Put the mixed powder described in step (2) in a graphite mold for SPS sintering to prepare a composite ceramic sample, the sintering temperature is 1700°C, the holding time is 10min, the sintering pressure is 40MPa, and the heating rate is 150°C/min .

(4) Process the composite block material described in step (3) according to the specific shape and size when used, to obtain the CNTs-W-AlN composite block material for microwave attenuator. Its relative density is 96.7%, dielectric constant is 25, dielectric loss tangent is 0.065, and it has good wave-absorbing performance in the range of 70kHz~1MHz.

Claims (3)

1. one kind high heat conduction microwave attenuation AlN based composites, it is characterized in that: choose CNTs and W as metallographic phase, AlN is the medium phase, comprises CNTs:(0.1-2.0) vol.%, W:(1.0-20.0) vol.% and AlN:(100-CNTs-W) vol.%.

2. the preparation method of the described high heat conduction microwave attenuation AlN based composites of claim 1, it is characterized in that: implementation step is:

1) CNTs powder, W powder and AlN powder are pressed (0.1-2.0): (1.0-20.0): mix after the volume ratio proportioning (78.0-98.9), the employing Stainless Steel Ball is mill ball, take dehydrated alcohol as grinding medium, the mass ratio of mill ball and raw material powder is (4-6): 1, Ball-milling Time is 10 ~ 40min, obtains the mixed powder slurry;

2) the mixed powder slurry is placed vacuum drying oven, obtain mixed powder at 70-90 ℃ of lower vacuum-drying 2-4h;

3) mixed powder is placed graphite jig carry out the SPS sintering and prepare the composite ceramics sample, its sintering temperature is 1400 ~ 1700 ℃, and soaking time is 2 ~ 10min, and sintering pressure is 30-40MPa, temperature rise rate is 100-150 ℃/min, obtains the CNTs-W-AlN composite block material.

3. such as right preparation method claimed in claim 2, it is characterized in that: mix rolling ball milling, high-energy ball milling, magnetic agitation, the ultrasonic wave dispersing and mixing mode of comprising described in the step 1).