High-temperature-resistant foam ceramic wave-absorbing material and preparation method thereof

Abstract

The application belongs to the technical field of wave-absorbing stealth materials, and particularly relates to a high-temperature-resistant foam ceramic wave-absorbing material and a preparation method thereof. The high-temperature-resistant foam ceramic wave-absorbing material is composed of foam ceramic small balls and a foam ceramic matrix, the foam ceramic small balls are uniformly distributed in the foam ceramic matrix, the foam ceramic matrix is prepared from quartz, sodium carbonate, manganese dioxide and a zirconium nitride blank, and sintered at 860-900 DEG C, and the foam ceramic small balls are prepared by cutting, ball milling, surface loading of nickel powder and calcium carbonate powder. The application can overcome the difficulties of oxidation of a wave-absorbing agent during high-temperature sintering of the foam ceramic wave-absorbing material, influence of the wave-absorbing agent on foaming performance of the foam ceramic, and reduction of the wave-absorbing effect after cutting, and has lower reflectivity and better wave-absorbing effect.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing stealth materials technology, specifically relating to a high-temperature resistant foam ceramic microwave absorbing material and its preparation method. Background Technology

[0002] Microwave-absorbing materials are key foundational materials for technologies such as electromagnetic shielding, preventing interference with communication equipment, preventing information leakage, and building radiation protection. Since microwave-absorbing materials are typically made by introducing an absorbing agent into a microwave-transparent matrix, their temperature resistance is determined by both the matrix and the absorbing agent. Using polymer matrices to prepare microwave-absorbing materials offers advantages such as simple molding, high design freedom, and easy achievement of absorption effects; however, it also has the fatal flaw of poor temperature resistance, making it unsuitable for high-temperature environments.

[0003] Ceramic materials with low dielectric constants can also serve as the transparent matrix for microwave absorbing materials, and they possess excellent temperature resistance, allowing them to operate for extended periods in high-temperature environments. Foam ceramics, in particular, with their low dielectric constant, offer advantages such as lightweight, temperature resistance, water resistance, and sound insulation, making them an ideal choice for preparing multifunctional microwave absorbing materials. However, the preparation of foam ceramic microwave absorbing materials is very challenging. First, the preparation of foam ceramics requires high-temperature sintering, and the preparation of foam ceramic microwave absorbing materials necessitates the addition of an absorbing agent to the green body before high-temperature sintering. Regardless of whether the added absorbing agent is of electrical or magnetic loss type, it will undergo severe oxidation during the sintering process, causing the foam ceramic to lose its intended microwave absorbing performance. Second, the introduction of an absorbing agent alters the raw material composition of the green body, affecting the foaming performance of the foam ceramic and severely reducing its physical and mechanical properties.

[0004] To address the aforementioned issues, patent CN118561621A provides a solution: preparing a microwave-absorbing coating on the surface of foam ceramics to give the foam ceramics microwave-absorbing properties. This solution has two drawbacks: (1) Since the microwave-absorbing effect of the foam ceramics is due to the surface microwave-absorbing coating, if the foam ceramics are cut for use, the cut components will lose their microwave-absorbing effect due to damage to the surface microwave-absorbing coating. (2) This solution is only suitable for preparing small-sized components, because large-sized foam ceramic components require large sintering furnaces to complete the preparation process, making industrial production difficult. Summary of the Invention

[0005] This invention addresses the prominent challenges of "oxidation of the absorbing agent during high-temperature sintering of foam ceramic microwave absorbing materials", "the introduction of the absorbing agent affecting the foaming performance of foam ceramics", and "the microwave absorption effect of the material is brought about by the surface microwave absorbing coating, and the microwave absorption effect is severely reduced or even disappeared after cutting". It provides a high-temperature resistant foam ceramic microwave absorbing material and its preparation method.

[0006] The specific plan is as follows:

[0007] A high-temperature resistant foam ceramic microwave absorbing material is composed of foam ceramic microspheres and a foam ceramic matrix, wherein the foam ceramic microspheres are uniformly distributed in the foam ceramic matrix.

[0008] The foam ceramic matrix is ​​obtained by preparing a blank from quartz, sodium carbonate, manganese dioxide and zirconium nitride, and sintering it at 860~900℃;

[0009] The foam ceramic microspheres are prepared by cutting and ball milling closed-cell foam ceramics, and loading nickel powder and calcium carbonate powder onto the surface.

[0010] The closed-cell foam ceramic is prepared using the technical solution described in patent CN 108911715 B, specifically as follows:

[0011] S1.1 Preparation of mixed powder

[0012] The raw materials are added by weight as follows: 5-15g calcium carbonate, 2-10g silicon carbide, 5-8g talc powder, 6-9g sodium feldspar or 7-10g potassium feldspar to every 100g of quartz sand. The above raw materials are then mixed to obtain the mixture.

[0013] The mixture is poured into a zirconia ball mill jar, and 20-25 zirconia balls with a diameter of 10-15 mm are added to every 100 g of the mixture. Then, the mixture is ball-milled at high speed for 1-3 hours using a planetary ball mill to obtain a mixed powder with a particle size of less than 5 μm. During ball milling, the revolution speed of the ball mill is 150-200 rpm and the rotation speed is 120-180 rpm.

[0014] S1.2 Mixed powder filling

[0015] Add water to the mixed powder at a ratio of 10-15 grams per 100 grams of the mixed powder, then mix it evenly using a mixer and fill it into the alumina mold. When filling, the filling volume of the mixed powder occupies 45-55% of the mold cavity volume.

[0016] S1.3 Sintering

[0017] Place the alumina mold filled with the mixed powder in a high-temperature furnace, heat it at 1150-1250℃ for 10-30 minutes at a heating rate of 5-20℃ / minute, and then cool it to room temperature with the furnace. Open the mold and take out the fired closed-cell foam ceramic with a hard and dense outer shell.

[0018] The closed-cell foam ceramic with a hard and dense outer shell obtained by firing has a foam structure inside and a hard and dense outer shell of 1-2 mm on the surface. The hard and dense outer shell completely seals the internal pores, making them all closed pores.

[0019] Preferably, the quartz sand has a particle size of 2 mm and a silica content of more than 98%, the calcium carbonate has a particle size of 80 μm, the silicon carbide has a particle size of 20 μm, the talc has a particle size of 20 μm, the albite has a particle size of 30 μm, and the potassium feldspar has a particle size of 50 μm.

[0020] A method for preparing a high-temperature resistant foam ceramic microwave absorbing material includes the following steps:

[0021] S1. The closed-cell foam ceramic is cut and ball-milled to obtain foam ceramic spheres;

[0022] S2 is prepared as a suspension using water, nickel powder, calcium carbonate powder, polyvinyl alcohol, and sodium carboxymethyl cellulose.

[0023] S3 Immerse the foam ceramic microspheres obtained in step S1 in the suspension prepared in step S2;

[0024] S4 uses quartz, sodium carbonate, manganese dioxide and zirconium nitride to prepare a mixture;

[0025] S5. The foam ceramic microspheres obtained in step S3 are mixed with the mixture prepared in step S4, and then the mixture is molded and pressed into a blank. The mixture is then sintered at a temperature of 20~40℃ / min to 860~900℃ to obtain a high-temperature resistant foam ceramic microwave absorbing material.

[0026] Preferably, in step S1, the diameter of the foam ceramic microspheres is 7~9mm;

[0027] Preferably, in step S2, the average particle size of the nickel powder is 0.5~0.8μm, and the average particle size of the calcium carbonate powder is 0.3~0.6μm.

[0028] Preferably, in step S2, the weight ratio of water, nickel powder, calcium carbonate powder, polyvinyl alcohol, and sodium carboxymethyl cellulose is 100:(5~10):(0.8~1.2):(0.4~0.6):(0.3~0.5).

[0029] Preferably, in step S3, the weight ratio of the foam ceramic microspheres to the suspension is 100:(250~350).

[0030] Preferably, in step S3, the soaking conditions are: vacuum degree of -0.08 to -0.09 MPa, and time of 10 to 15 min.

[0031] Preferably, in step S4, the weight ratio of quartz, sodium carbonate, manganese dioxide and zirconium nitride is (80~82):(15~17):2:1, and the average particle size of the mixture is 1~3μm.

[0032] Preferably, in step S5, 50-80 foam ceramic balls are mixed with every 100 grams of the mixture; the sintering time is 12-18 minutes.

[0033] Preferably, in step S5, the molding pressure is 3~5MPa.

[0034] Compared with existing technologies, the beneficial effects are as follows:

[0035] (1) Since the current foam ceramic absorbing materials are only prepared by preparing a absorbing coating on the surface of foam ceramic, the absorbing effect is only brought about by the absorbing coating on the surface. Therefore, the absorbing effect will be severely reduced or even disappeared after cutting in actual use. However, the foam ceramic prepared by the technical solution of the present invention has a absorbing performance brought about by the foam ceramic microspheres that are uniformly distributed in the foam ceramic matrix. Therefore, the foam ceramic prepared by the technology of the present invention has a lower reflectivity and a better absorbing effect. At the same time, the absorbing effect is not affected after the prepared foam ceramic is cut.

[0036] (2) The foam ceramic microspheres used in this invention are taken from foam ceramic plates fired at 1150~1250℃, while the sintering temperature of the green body in this invention is 860~900℃. This means that the foam ceramic microspheres are sintered twice at 860~900℃. Since 860~900℃ is much lower than the sintering temperature of the foam ceramic microspheres, the second sintering will not change the intrinsic morphology and physical and mechanical properties of the foam ceramic microspheres. At the same time, the foam ceramic microspheres in the green body are only in simple physical contact with the mixture, and the addition of foam ceramic microspheres does not affect the raw material composition of the mixture. In addition, since the physical and mechanical properties of the foam ceramic microspheres do not change at 860~900℃, the presence or absence of foam ceramic microspheres in the green body will not change the foaming properties of the mixture, and naturally will not affect the physical and mechanical properties of the foam ceramic produced.

[0037] (3) Theoretically, nickel powder will undergo severe oxidation in air at 860~900℃, losing its conductivity and magnetism, and thus losing its absorption of electromagnetic waves. The preparation method of the present invention has the beneficial effect of preventing the high-temperature oxidation of nickel powder. Its principle is as follows: the mixture is in a molten state at 800℃, and the ceramic matrix in the molten state can prevent the nickel powder from contacting the air; at the same time, the zirconium nitride in the mixture begins to oxidize at around 800℃ to generate nitrogen gas, so that the green body is filled with nitrogen gas, thereby forming an atmosphere to protect the nickel powder.

[0038] (4) Calcium carbonate powder and nickel powder adhere together to the surface of foam ceramic balls. During the heating process of the green body, the carbon dioxide generated by the decomposition of calcium carbonate above 600°C will form an atmosphere to protect the nickel powder, thereby avoiding the oxidation of nickel powder in the medium temperature stage of 600~800°C. At the same time, the oxidation rate of nickel powder below 600°C is very low. The present invention uses a heating rate of 20~40°C / min to reduce the contact time between nickel powder and air below 600°C, thereby further slowing down the oxidation of nickel powder in the low temperature stage. Attached Figure Description

[0039] Figure 1 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0040] The embodiments of the present invention will be described in further detail below. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention. Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. Example 1

[0041] A method for preparing a high-temperature resistant foam ceramic microwave absorbing material includes the following steps:

[0042] S1 Obtaining Closed-Cell Foam Ceramics: The closed-cell foam ceramics were prepared using Example 1 of patent CN108911715B, specifically as follows: 5g of calcium carbonate, 2g of silicon carbide, 5g of talc powder, and 6g of albite were added to 100g of quartz sand. The mixture was poured into a zirconia ball mill jar, and 25 zirconia balls with a diameter of 10mm were added per 100g of the mixture. The mixture was then ball-milled at high speed for 1 hour using a planetary ball mill. During ball milling, the revolution speed of the ball mill was 200 rpm and the rotation speed was 180 rpm, resulting in a uniform mixed powder. 10g of water was added to each 100g of the mixed powder, and the mixture was stirred evenly using a mixer before being filled into an alumina mold. During filling, the volume of the mixed powder occupied 55% of the volume of the mold cavity. The mold filled with the mixed powder was placed in a high-temperature furnace and sintered at 1250℃ for 10 minutes using a heating rate of 5℃ / min to obtain closed-cell foam ceramics with a hard and dense outer shell.

[0043] Closed-cell foam ceramics are cut into a large number of small foam ceramic blocks with a side length of 9mm. These small foam ceramic blocks are then rolled into small foam ceramic balls with a diameter of 8mm using a horizontal ball mill. At the same time, the small foam ceramic balls are washed and dried using an ultrasonic cleaner.

[0044] S2 High-speed ball milling was performed using a planetary ball mill to obtain nickel powder with an average particle size of 0.7 μm and calcium carbonate powder with an average particle size of 0.4 μm; water, nickel powder, calcium carbonate powder, polyvinyl alcohol and sodium carboxymethyl cellulose were mixed and stirred evenly in a weight ratio of 100:8:1.0:0.5:0.4 to prepare a suspension.

[0045] S3 According to the weight ratio of foam ceramic microspheres to suspension of 100:300, immerse the foam ceramic microspheres obtained in step S1 into the suspension prepared in step S2, keep the suspension under a vacuum of -0.09MPa for 10min, then restore to normal pressure, take out the foam ceramic microspheres from the suspension and dry them.

[0046] S4. Quartz, sodium carbonate, manganese dioxide and zirconium nitride are mixed in a weight ratio of 81:16:2:1 and ball-milled to prepare a mixture with an average particle size of 2μm.

[0047] S5. According to the ratio of 60 foam ceramic balls per 100 grams of mixture, the mixture prepared in step S4 is mixed evenly with the foam ceramic balls obtained in step S3, and then the mixture is molded into a green body under a pressure of 4 MPa. The green body is placed in a high-temperature furnace and heated to 880°C at a rate of 30°C / min and held for 16 minutes to complete sintering, thus obtaining the final high-temperature resistant foam ceramic microwave absorbing material. Example 2

[0048] A method for preparing a high-temperature resistant foam ceramic microwave absorbing material includes the following steps:

[0049] S1 Obtaining Closed-Cell Foam Ceramics: The closed-cell foam ceramics were prepared using Example 2 of Patent CN108911715B, specifically as follows: 15g of calcium carbonate, 10g of silicon carbide, 8g of talc powder, and 9g of albite were added to 100g of quartz sand. The mixture was poured into a zirconia ball mill jar, and 20 zirconia balls with a diameter of 15mm were added for every 100g of the mixture. The mixture was then ball-milled at high speed using a planetary ball mill for 3 hours. During the ball milling, the revolution speed of the ball mill was 150 rpm and the rotation speed was 120 rpm, resulting in a uniform mixed powder. Add 15g of water to every 100g of mixed powder, mix evenly using a mixer, and then fill the alumina mold. When filling, the volume of the mixed powder should be 45% of the volume of the mold cavity. Place the mold filled with the mixed powder in a high-temperature furnace and sinter at 1200℃ for 20 minutes at a heating rate of 20℃ / min to obtain closed-cell foam ceramic with a hard and dense outer shell.

[0050] The closed-cell foam ceramic is cut into a large number of small foam ceramic pieces with a side length of 9mm. These small foam ceramic pieces are then rolled into small foam ceramic balls with a diameter of 8mm using a horizontal ball mill. The small foam ceramic balls are then washed and dried using an ultrasonic cleaner to obtain small foam ceramic balls.

[0051] S2 High-speed ball milling was performed using a planetary ball mill to obtain nickel powder with an average particle size of 0.6 μm and calcium carbonate powder with an average particle size of 0.5 μm; water, nickel powder, calcium carbonate powder, polyvinyl alcohol and sodium carboxymethyl cellulose were mixed and stirred evenly in a weight ratio of 100:10:1.2:0.6:0.5 to prepare a suspension.

[0052] S3 According to the weight ratio of foam ceramic microspheres to suspension of 100:300, immerse the foam ceramic microspheres obtained in step S1 into the suspension prepared in step S2, keep the suspension under a vacuum of -0.09MPa for 12min, then restore to normal pressure, take out the foam ceramic microspheres from the suspension and dry them.

[0053] S4. Quartz, sodium carbonate, manganese dioxide and zirconium nitride are mixed in a weight ratio of 81:16:2:1 and ball-milled to prepare a mixture with an average particle size of 2μm.

[0054] S5. According to the ratio of 70 foam ceramic balls per 100 grams of mixture, the mixture prepared in step S4 is mixed evenly with the foam ceramic balls obtained in step S3. Then, it is molded into a green body under a pressure of 4 MPa. The green body is placed in a high-temperature furnace and heated to 880°C at a rate of 30°C / min and held for 14 minutes to complete sintering, thus obtaining the final high-temperature resistant foam ceramic microwave absorbing material. Example 3

[0055] A method for preparing a high-temperature resistant foam ceramic microwave absorbing material includes the following steps:

[0056] S1 Obtaining closed-cell foam ceramics: The closed-cell foam ceramics were prepared using Example 3 of patent CN108911715B, specifically by adding 10g of calcium carbonate, 5g of silicon carbide, 6g of talc, and 7g of potassium feldspar to 100g of quartz sand. The mixture was poured into a zirconia ball mill jar, and 25 zirconia balls with a diameter of 10 mm were added for every 100 g of the mixture. The mixture was then ball-milled at high speed for 2 hours using a planetary ball mill. During the ball milling, the revolution speed of the ball mill was 200 rpm and the rotation speed was 180 rpm, resulting in a uniform mixed powder. 12 g of water was added to every 100 g of the mixed powder, and the mixture was stirred evenly using a mixer before being filled into an alumina mold. During filling, the volume of the mixed powder occupied 50% of the volume of the mold cavity. The mold filled with the mixed powder was placed in a high-temperature furnace and sintered at 1150°C for 30 minutes at a heating rate of 10°C / min to obtain a closed-cell foam ceramic with a hard and dense outer shell.

[0057] The closed-cell foam ceramic is cut into a large number of small foam ceramic pieces with a side length of 10 mm. These small foam ceramic pieces are then rolled into small foam ceramic balls with a diameter of 9 mm using a horizontal ball mill. The small foam ceramic balls are then washed and dried using an ultrasonic cleaner.

[0058] S2 High-speed ball milling was performed using a planetary ball mill to obtain nickel powder with an average particle size of 0.8 μm and calcium carbonate powder with an average particle size of 0.6 μm; water, nickel powder, calcium carbonate powder, polyvinyl alcohol and sodium carboxymethyl cellulose were mixed and stirred evenly in a weight ratio of 100:7:0.9:0.4:0.3 to prepare a suspension.

[0059] S3 According to the weight ratio of foam ceramic microspheres to suspension of 100:250, immerse the foam ceramic microspheres obtained in step S1 into the suspension prepared in step S2, keep the suspension under vacuum of -0.08MPa for 14min, then restore to normal pressure, take out the foam ceramic microspheres from the suspension and dry them.

[0060] S4. Quartz, sodium carbonate, manganese dioxide and zirconium nitride are mixed in a weight ratio of 80:17:2:1 and ball-milled to prepare a mixture with an average particle size of 3μm.

[0061] S5. According to the ratio of 50 foam ceramic balls per 100 grams of mixture, the mixture prepared in step S4 is mixed evenly with the foam ceramic balls obtained in step S3. Then, the mixture is molded into a green body under a pressure of 5 MPa. The green body is placed in a high-temperature furnace and heated to 860°C at a rate of 20°C / min and held for 18 minutes to complete sintering, thus obtaining the final high-temperature resistant foam ceramic microwave absorbing material. Example 4

[0062] A method for preparing a high-temperature resistant foam ceramic microwave absorbing material includes the following steps:

[0063] S1 Obtaining Closed-Cell Foam Ceramics: The closed-cell foam ceramics were prepared using Example 4 of patent CN108911715B, specifically as follows: 12g of calcium carbonate, 8g of silicon carbide, 7g of talc powder, and 10g of potassium feldspar were added to 100g of quartz sand. The mixture was poured into a zirconia ball mill jar, and 20 zirconia balls with a diameter of 15mm were added per 100g of mixture. The mixture was then ball-milled at high speed using a planetary ball mill for 3 hours, with the ball mill's revolution speed being 15 km / h during the milling process. The mixture was prepared by rotating at 0 rpm and 120 rpm to obtain a uniform powder. 15g of water was added to every 100g of the powder and stirred evenly using a mixer. The mixture was then filled into an alumina mold. During filling, the volume of the powder was 45% of the volume of the mold cavity. The mold filled with the powder was placed in a high-temperature furnace and sintered at 1200℃ for 10 minutes at a heating rate of 10℃ / min to obtain a closed-cell foam ceramic with a hard and dense outer shell.

[0064] The closed-cell foam ceramic is cut into a large number of small foam ceramic pieces with a side length of 8mm. These small foam ceramic pieces are then rolled into small foam ceramic balls with a diameter of 7mm using a horizontal ball mill. The small foam ceramic balls are then washed and dried using an ultrasonic cleaner.

[0065] S2 High-speed ball milling was performed using a planetary ball mill to obtain nickel powder with an average particle size of 0.5 μm and calcium carbonate powder with an average particle size of 0.3 μm; water, nickel powder, calcium carbonate powder, polyvinyl alcohol and sodium carboxymethyl cellulose were mixed and stirred evenly in a weight ratio of 100:5:0.8:0.4:0.3 to prepare a suspension.

[0066] S3 According to the weight ratio of foam ceramic microspheres to suspension of 100:350, immerse the foam ceramic microspheres obtained in step S1 into the suspension prepared in step S2, keep the suspension under a vacuum of -0.08MPa for 15min, then restore to normal pressure, take out the foam ceramic microspheres from the suspension and dry them.

[0067] S4. Quartz, sodium carbonate, manganese dioxide and zirconium nitride are mixed in a weight ratio of 82:15:2:1 and ball-milled to prepare a mixture with an average particle size of 1μm.

[0068] S5. According to the ratio of 80 foam ceramic balls per 100 grams of mixture, the mixture prepared in step S4 is mixed evenly with the foam ceramic balls obtained in step S3. Then, the mixture is molded into a green body under a pressure of 3 MPa. The green body is placed in a high-temperature furnace and heated to 900°C at a rate of 40°C / min and held for 12 minutes to complete sintering, thus obtaining the final high-temperature resistant foam ceramic microwave absorbing material. Comparative Example 1

[0069] Quartz, sodium carbonate, manganese dioxide, and zirconium nitride were mixed in a weight ratio of 81:16:2:1 and ball-milled to prepare a mixture with an average particle size of 2 μm. The mixture was then molded into a green body under a pressure of 4 MPa. The green body was then placed in a high-temperature furnace and heated to 880°C at a rate of 30°C / min and held for 16 min to complete sintering, thus obtaining the final foam ceramic microwave absorbing material. Comparative Example 2

[0070] Referring to Example 1, the difference is that steps S2 and S3 are omitted, and the foam ceramic microspheres obtained in step S1 are directly mixed with the mixture prepared in step S4, while the remaining steps and parameters remain unchanged.

[0071] Performance testing

[0072] The porosity, compressive strength, and reflectivity of the foam ceramics prepared in Examples 1-4 and Comparative Examples 1-2 were tested. Porosity was determined using the bulk density method according to national standard GB / T25995-2010. Compressive strength was determined using the compression test method according to national standard GB / T4740-1999. Reflectivity was tested using the arcuate reflection method at a frequency of 8-18 GHz, with sample dimensions of 180 mm × 180 mm × 8 mm. The test results are shown in Table 1.

[0073] Table 1 Performance Parameters

[0074]

[0075] After sintering at 860-900℃, both the foam ceramic microspheres and the foam ceramic matrix exhibit a uniform porous structure. Furthermore, as shown in Table 1, the foam ceramics prepared in Examples 1-4 have similar porosity and compressive strength. This indicates that the preparation method of this invention has good process tolerance, and the prepared foam ceramic microwave absorbing material has high structural stability and yield.

[0076] The foam ceramics prepared in Comparative Examples 1 and 2 have the same porosity and compressive strength, indicating that adding foam ceramic microspheres to the green body does not affect the intrinsic physical and mechanical properties of the foam ceramics. Furthermore, based on the average reflectivity of -0.4 dB and -0.3 dB for the foam ceramics prepared in Comparative Examples 1 and 2, respectively, it can be concluded that the foam ceramics do not possess electromagnetic wave absorption properties regardless of whether foam ceramic microspheres are added.

[0077] Further comparing Examples 1-4 with Comparative Examples 1-2, after impregnating the foam ceramic microspheres with water, nickel powder, calcium carbonate powder, polyvinyl alcohol, and sodium carboxymethyl cellulose using the preparation method of the present invention, the porosity and compressive strength of the prepared foam ceramics remained unchanged, but the average reflectivity was significantly reduced. This indicates that the preparation method of the present invention can impart excellent electromagnetic wave absorption properties to foam ceramics without affecting their intrinsic physical and mechanical properties.

[0078] As shown in Table 1, the total porosity and closed-cell ratio of the foam ceramics prepared in Examples 1-4 are all greater than 80%, and the closed-cell ratio is only 1% lower than the total porosity. This indicates that the foam ceramics prepared by the method described in this invention not only have excellent physical, mechanical and wave-absorbing properties, but also have the characteristics of being lightweight, heat-insulating, and waterproof.

[0079] The porous structure of the foam ceramic prepared in this invention is closed-cell, which provides excellent protection for the nickel powder on the surface of the internal foam ceramic microspheres. After the foam ceramic prepared in this invention was kept in air at 700°C for 100 hours, all its performance indicators remained unchanged. This indicates that the foam ceramic prepared in this invention has excellent high-temperature resistance.

[0080] In practice, the foam ceramic microspheres in the preparation method described in this invention can be processed from the scraps of foam ceramic boards. This not only enables the high-value reuse of foam ceramic scraps but also reduces the amount of raw materials used in the foam ceramics produced by this invention, thus achieving a win-win effect.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-temperature resistant foam ceramic microwave absorbing material, characterized in that, It is composed of foam ceramic microspheres and a foam ceramic matrix, wherein the foam ceramic microspheres are uniformly distributed within the foam ceramic matrix; The foam ceramic matrix is ​​obtained by preparing a blank from quartz, sodium carbonate, manganese dioxide and zirconium nitride, and sintering it at 860~900℃; The foam ceramic microspheres are prepared by cutting and ball milling closed-cell foam ceramics, and loading nickel powder and calcium carbonate powder onto the surface. The method for preparing the closed-cell foam ceramic is as follows: S1.1 Preparation of mixed powder The raw materials are added by weight as follows: 5-15g calcium carbonate, 2-10g silicon carbide, 5-8g talc powder, 6-9g sodium feldspar or 7-10g potassium feldspar to every 100g of quartz sand. The above raw materials are then mixed to obtain the mixture. The mixture is poured into a zirconia ball mill jar, and 20-25 zirconia balls with a diameter of 10-15 mm are added to every 100 g of the mixture. Then, the mixture is ball-milled at high speed for 1-3 hours using a planetary ball mill to obtain a mixed powder with a particle size of less than 5 μm. During ball milling, the revolution speed of the ball mill is 150-200 rpm and the rotation speed is 120-180 rpm. S1.2 Mixed powder filling Add water to the mixed powder at a ratio of 10-15 grams per 100 grams of the mixed powder, then mix it evenly using a mixer and fill it into the alumina mold. When filling, the filling volume of the mixed powder occupies 45-55% of the mold cavity volume. S1.3 Sintering Place the alumina mold filled with the mixed powder in a high-temperature furnace, heat it at 1150-1250℃ for 10-30 minutes at a heating rate of 5-20℃ / minute, and then cool it to room temperature with the furnace. Open the mold and take out the fired closed-cell foam ceramic with a hard and dense outer shell. The preparation method of the high-temperature resistant foam ceramic microwave absorbing material includes the following steps: S1. The closed-cell foam ceramic is cut and ball-milled to obtain foam ceramic spheres; S2 is prepared as a suspension using water, nickel powder, calcium carbonate powder, polyvinyl alcohol, and sodium carboxymethyl cellulose. S3 Immerse the foam ceramic microspheres obtained in step S1 in the suspension prepared in step S2; S4 uses quartz, sodium carbonate, manganese dioxide and zirconium nitride to prepare a mixture; wherein the weight ratio of quartz, sodium carbonate, manganese dioxide and zirconium nitride is (80~82):(15~17):2:1; S5. The foam ceramic microspheres obtained in step S3 are mixed with the mixture prepared in step S4, and then the mixture is molded and pressed into a blank. The mixture is then sintered at a temperature of 20~40℃ / min to 860~900℃ to obtain a high-temperature resistant foam ceramic microwave absorbing material.

2. The preparation method of a high-temperature resistant foam ceramic microwave absorbing material as described in claim 1, characterized in that, Includes the following steps: S1. The closed-cell foam ceramic is cut and ball-milled to obtain foam ceramic spheres; S2 is prepared as a suspension using water, nickel powder, calcium carbonate powder, polyvinyl alcohol, and sodium carboxymethyl cellulose. S3 Immerse the foam ceramic microspheres obtained in step S1 in the suspension prepared in step S2; S4 uses quartz, sodium carbonate, manganese dioxide and zirconium nitride to prepare a mixture; S5. The foam ceramic microspheres obtained in step S3 are mixed with the mixture prepared in step S4, and then the mixture is molded and pressed into a blank. The mixture is then sintered at a temperature of 20~40℃ / min to 860~900℃ to obtain a high-temperature resistant foam ceramic microwave absorbing material.

3. The preparation method according to claim 2, characterized in that, In step S1, the diameter of the foam ceramic spheres is 7~9mm.

4. The preparation method according to claim 2, characterized in that, In step S2, the average particle size of the nickel powder is 0.5~0.8μm, and the average particle size of the calcium carbonate powder is 0.3~0.6μm.

5. The preparation method according to claim 2, characterized in that, In step S2, the weight ratio of water, nickel powder, calcium carbonate powder, polyvinyl alcohol, and sodium carboxymethyl cellulose is 100:(5~10):(0.8~1.2):(0.4~0.6):(0.3~0.5).

6. The preparation method according to claim 2, characterized in that, In step S3, the weight ratio of the foam ceramic microspheres to the suspension is 100:(250~350).

7. The preparation method according to claim 2, characterized in that, In step S3, the soaking conditions are: vacuum degree of -0.08 to -0.09 MPa, and time of 10 to 15 min.

8. The preparation method according to claim 2, characterized in that, In step S4, the average particle size of the mixture is 1~3μm.

9. The preparation method according to claim 2, characterized in that, In step S5, 50-80 foam ceramic balls are mixed with every 100 grams of the mixture; the sintering time is 12-18 minutes.

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