High-temperature-resistant carbon-based wave absorbing agent as well as preparation method and application thereof

Abstract

The invention belongs to the field of wave-absorbing materials, and particularly relates to a high-temperature-resistant carbon-based wave-absorbing agent as well as a preparation method and application thereof. According to the invention, the molten composite powder (ceramic powder and / or glass powder) is coated on the surface of the carbon-based wave-absorbing agent by adopting the low-melting-point composite powder in a state that the carbon-based wave-absorbing agent is not oxidized, so that the contact surface of the carbon-based wave-absorbing agent and air is isolated, and the high-temperature oxidation resistance and high-temperature electromagnetic wave-absorbing capacity of the carbon-based wave-absorbing agent are improved. The invention further provides an application of preparing a high-temperature-resistant darkroom wave-absorbing device with cement, and an application of covering the surface of a target object in a coating manner to realize radiation control. The carbon-based wave-absorbing agent with relatively low cost is adopted, the preparation process is simple and easy to control, and industrial preparation is easy.

Description

Technical Field

[0001] The present invention belongs to the field of wave absorbing materials, and specifically relates to a high temperature resistant carbon-based wave absorbing agent and a preparation method and application thereof. Background Art

[0002] In recent years, with the rapid development of hypersonic weapons and equipment, high-power radar antenna equipment, and high-power satellites, the demand for power-resistant absorbing devices and high-power testing has become increasingly high. Among them, carbon-based materials (including carbon powder, carbon fiber, and carbon nanotubes) have excellent absorbing properties due to their high electrical conductivity and are widely used in the field of absorbing materials. However, since carbon materials are very easy to oxidize at high temperatures, the application of carbon materials in the field of high-temperature absorbing is limited.

[0003] Microwave darkrooms are necessary facilities in microwave testing, so high-power testing places higher demands on the high-temperature resistance of absorbing materials in microwave darkrooms. At present, the absorbing cones used in microwave darkrooms are mainly made of polyurethane sponges impregnated with carbon powder. As an absorber, carbon powder plays a vital role in darkroom absorbing materials. However, since carbon powder is easily oxidized at high temperatures, high-temperature testing faces huge challenges. In addition, in high-power testing, the polyurethane sponge material as the base material cannot withstand high-power irradiation. It is easy to burn in the high-temperature environment generated by high-power testing, thus causing safety hazards.

[0004] In the field of electromagnetic stealth coatings, carbon-based materials are also widely used. This type of coating is usually made by mixing carbon-based materials with organic adhesives such as epoxy resin and then applying them to the target surface. For example, the Chinese patent with publication number CN115948071B mixes epoxy resin, spiral carbon nanotubes and various additives to prepare an absorbing coating. However, in this process, neither carbon-based materials nor organic adhesives can withstand high temperatures and will oxidize rapidly after reaching a certain temperature.

[0005] In order to solve the problem of absorbing materials withstanding high temperatures, Chinese patent No. CN116240646A discloses a SiCN ceramic fiber high-temperature absorbing material. The material is a high-performance high-temperature absorbing material obtained by synthesizing ceramic fibers of SiC and SiN. The material can work in an environment exceeding 1000°C. Chinese patent No. CN118598640A discloses a La x Sr 2-x MgMoO 6-δA ceramic absorbing material that can resist oxidation and effectively absorb electromagnetic waves from room temperature to 800°C. A Chinese patent with publication number CN117510207A discloses a high-temperature absorbing material based on perovskite structure modification, which can maintain good absorbing performance at 900°C. A Chinese patent with publication number CN118290173A discloses a high-temperature absorbing material containing a dendritic nickel ceramic matrix, which can still absorb with high performance at 800°C. However, these materials all have complex processes and high costs, and are particularly unsuitable for use in the field of microwave darkrooms.

[0006] The Chinese patent CN114315366A discloses a 3D-printed silicon carbide ceramic absorbing pyramid, which can still maintain good chemical stability and absorbing performance at 1000°C, but the silicon carbide material is too expensive and is not suitable for use in large-scale darkroom construction. In order to reduce costs, a report with publication number CN115321926A discloses a high-power absorbing material of aluminate-based hybrid carbon fiber, which can still maintain good mechanical strength and absorbing performance at 500°C and avoid safety hazards caused by high-temperature combustion, but the carbon fiber will still oxidize when the temperature is higher than 600°C. The patent with publication number CN116904960B discloses a core-shell high-temperature absorbing material of alumina-coated graphene, but this material will completely decompose at 650°C.

[0007] In summary, the existing high-temperature resistant absorbing materials for microwave darkrooms have various problems such as complex processes, high costs, or poor upper limit of high temperature tolerance, and there is no relatively good solution. Summary of the invention

[0008] In view of the above-mentioned problems or shortcomings, in order to solve the problem of easy oxidation and attenuation of electromagnetic absorbing ability of carbon-based absorbing materials under high temperature environment, the present invention provides a high temperature resistant carbon-based absorber and a preparation method and application thereof, wherein a low melting point composite powder (such as ceramic powder, glass powder) is used to coat the molten composite powder on the surface of the carbon-based absorber when the carbon-based absorber is not oxidized, thereby isolating the contact surface between the carbon-based absorber and the air, thereby improving the high temperature oxidation resistance of the carbon-based absorber and the high temperature electromagnetic absorbing ability of the device; and the process is simple, easy to control, and easy to prepare industrially.

[0009] A method for preparing a high temperature resistant carbon-based absorber comprises the following steps:

[0010] Step 1: Evenly mix the carbon-based absorber and the composite powder, wherein the mass ratio of the carbon-based absorber to the composite powder is 15-60%; wherein the composite powder is ceramic powder and / or glass powder having a melting point lower than the oxidation temperature of the carbon-based absorber.

[0011] Step 2: sinter the mixed powder obtained in step 1 in an air atmosphere and keep it warm. The sintering and keeping warm temperature is the melting point of the composite powder to 600°C, the heating rate is 5-10°C / min, and the keeping warm time is 0.5-3h.

[0012] Step 3: ball-milling the sintered product obtained in step 2 to obtain a carbon-based absorber powder coated with a composite powder.

[0013] Furthermore, the carbon-based absorber is at least one of carbon powder, carbon fiber and carbon nanotube.

[0014] Furthermore, the composite powder is a low melting point powder with a melting point lower than 330° C., so as to improve the melt coating effect, reduce energy consumption and production equipment requirements.

[0015] Furthermore, the ball milling speed in step 3 is 65-180 R / min and the time is 10-25 min. This is because the material is in a block after sintering in step 2, and the ball milling speed is very critical to minimize the physical morphology of the absorbing medium coating when grinding into powder, so the coating effect is maintained by controlling the ball milling speed.

[0016] A high temperature resistant carbon-based absorber is prepared by the method.

[0017] Applications of the above-mentioned high temperature resistant carbon-based absorbers:

[0018] The powder of the high temperature resistant carbon-based absorber is mixed with cement, with the powder accounting for 1-20 vol% of the total volume of the two, and conventionally molded to produce a high temperature resistant darkroom absorber.

[0019] Alternatively, a high temperature resistant carbon-based absorber is used as an absorber to make a coating and apply it to the surface of a target object to achieve radiation control.

[0020] Furthermore, the cement is aluminate cement.

[0021] Furthermore, the darkroom absorbing device is in the shape of a flat plate or a pyramid, wherein the volume fraction of the carbon-based absorbing agent powder after treatment is controlled to be 1-20 vol%.

[0022] In summary, the present invention uses a composite powder (ceramic powder and / or glass powder) with a melting point lower than the oxidation temperature of the carbon-based absorber. At a temperature where the carbon-based absorber (such as carbon powder / carbon fiber) is not oxidized, the composite powder is melted and coated on the surface of the carbon-based absorber before the carbon-based absorber is oxidized by controlling the ratio of the composite powder to the carbon-based absorber and the sintering temperature; the composite powder (ceramic powder and / or glass powder) with stable chemical properties on the surface of the carbon-based absorber will isolate the contact surface between the carbon-based absorber and the air, thereby improving the oxidation resistance of the carbon-based absorber; after sintering, it is ground into powder to obtain a high-temperature resistant carbon-based absorber with a carbon-based absorber / composite powder structure. It further provides the application of the composite powder and cement to make a high-temperature resistant darkroom absorber, and the application of coating the surface of the target object in a coating manner to achieve radiation control. In addition, the carbon-based absorber has a relatively low cost, a simple preparation process, and is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The flat plate absorbing device prepared in Example 1;

[0024] Figure 2 The pointed cone-shaped absorbing device prepared in Example 4;

[0025] Figure 3 The reflectivity test results of the flat absorber made of untreated carbon fiber at room temperature and 700℃;

[0026] Figure 4 The reflectivity test results of the flat-plate absorbing device made in Example 1 after being treated at room temperature and 700°C;

[0027] Figure 5 The reflectivity test results of the pyramid absorbing device made in Example 4 after being treated at room temperature and 700°C. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0029] A high temperature resistant carbon-based absorber, the preparation method is as follows:

[0030] Step 1: Weigh the carbon-based absorber and glass powder in a mass ratio of 15-60% of the carbon-based absorber to the glass powder, and grind until mixed. The composite powder used in this embodiment is a low-melting-point glass powder of 330°C.

[0031] Step 2: Put the mixed powder obtained in step 1 into an Al2O3 ceramic crucible, cover it with a lid and leave a small gap, and then put it into a muffle furnace for sintering directly in an air atmosphere. The muffle furnace is heated from room temperature to 400-600°C at a heating rate of 8°C / min, and kept at this sintering temperature for 0.5-4h.

[0032] Step 3: After sintering, take out the product from the crucible, put it into a ball mill, and mill it at a speed of 65-180R / min for 25 minutes to obtain carbon fiber particles coated with glass powder.

[0033] Step 4: Mix the absorbing particles (carbon fiber particles coated with glass powder) obtained in step 3 with aluminate cement, the absorbing particles accounting for 1-20 vol% of the total volume, and conventionally mold them into a flat-type device. The flat-type device is a square sample with a thickness of 10 mm and a side length of 200×200 mm. The specific physical picture is as follows Figure 1 The pyramid is a square with a base of 6×6 mm and a height of 20 mm. The specific physical picture is as follows Figure 2 shown.

[0034] The specific synthesis conditions are shown in the following table

[0035] Table 1 Specific implementation of high temperature absorber synthesis

[0036]

[0037] Table 2. Results of reflectivity at room temperature

[0038]

[0039] Table 3 Reflectivity results after 700℃ treatment

[0040]

[0041] Table 4 Reflectivity results after 800℃ treatment

[0042]

[0043] Figure 3 The reflectivity test results of the flat-plate absorber made of carbon fiber without glass powder coating at room temperature and 700℃. Figure 3 It can be seen that although the untreated carbon fiber has relatively stable wave-absorbing properties at room temperature, its wave-absorbing properties are basically lost after being treated at 700°C.

[0044] Figure 4 The reflectivity test results of the flat-plate absorber made of coated carbon fiber in Example 1 after being treated at room temperature and 700°C; Figure 5 The reflectivity test results of the pyramid absorber made of coated carbon fiber in Example 4 after being treated at room temperature and 700°C. Figure 4 It can be seen that after the carbon fiber is coated and treated at 700℃, although the wave absorption performance is weakened to a certain extent, it still has wave absorption performance. Figure 5It can be seen that the prepared pyramidal device has excellent wave absorbing performance before and after high temperature treatment.

[0045] It can be seen from the above examples and comparative examples that the present invention uses low melting point composite powders to coat the surface of the carbon-based absorber with molten composite powders (ceramic powders and / or glass powders) when the carbon-based absorber is not oxidized, thereby isolating the contact surface between the carbon-based absorber and the air, thereby improving the high temperature oxidation resistance and high temperature electromagnetic absorption capacity of the carbon-based absorber. When the carbon-based absorber is made into a high temperature resistant darkroom absorber with cement, or is coated on the surface of a target object in a coating manner to achieve radiation control, the high temperature resistance of the carbon-based absorber will be better, which can improve its application scenarios; and the carbon-based absorber has a relatively low cost, a simple preparation process, is easy to control, and is easy to prepare industrially.

Claims

1. A method for preparing a high temperature resistant carbon-based absorber, characterized in that: The following steps are involved: Step 1, mixing the carbon-based absorber and the composite powder, wherein the mass ratio of the carbon-based absorber to the composite powder is 15-60%; wherein the composite powder is a ceramic powder and / or a glass powder having a melting point lower than the oxidation temperature of the carbon-based absorber; Step 2, sintering and keeping the mixed powder after mixing in step 1 in an air atmosphere, the sintering and keeping temperature is the melting point of the composite powder to 600°C, the heating rate is 5-10°C / min, and the keeping time is 0.5-3h; Step 3: ball-milling the sintered product obtained in step 2 to obtain carbon-based absorber powder coated with composite powder.

2. The method for preparing the high temperature resistant carbon-based absorber according to claim 1, characterized in that: The carbon-based absorber is at least one of carbon powder, carbon fiber and carbon nanotube.

3. The method for preparing the high temperature resistant carbon-based absorber according to claim 1, characterized in that: The composite powder is a low melting point powder with a melting point lower than 330°C.

4. The method for preparing the high temperature resistant carbon-based absorber according to claim 1, characterized in that: The ball milling speed in step 3 is 65-180R / min, and the time is 10-25min.

5. A high temperature resistant carbon-based absorber, characterized in that: Prepared by any method of claims 1-4.

6. The use of the high temperature resistant carbon-based absorber as claimed in claim 5, characterized in that: The powder of the high temperature resistant carbon-based absorber is mixed with cement, with the powder accounting for 1-20 vol% of the total volume of the two, and conventionally molded to produce a high temperature resistant darkroom absorber.

7. The use of the high temperature resistant carbon-based absorber as claimed in claim 6, characterized in that: The cement is aluminate cement.

8. The use of the high temperature resistant carbon-based absorber as claimed in claim 6, characterized in that: The darkroom absorbing device is in the shape of a flat plate or a pyramid, wherein the volume fraction of the carbon-based absorbing agent powder after treatment is controlled to be 1-20 vol%.

9. The use of the high temperature resistant carbon-based absorber as claimed in claim 5, characterized in that: A high temperature resistant carbon-based absorber is used as an absorber to make a coating and is applied to the surface of a target object to achieve radiation control.

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