Surface metallization method of low-dielectric porous silicon nitride ceramic material

Abstract

The invention provides a surface metallization method of a low-dielectric porous silicon nitride ceramic material, and belongs to the field of ceramic metallization. The method comprises the steps of porous silicon nitride ceramic material preparation, hole sealing treatment and metallization. The hole sealing treatment comprises the following steps: heating aluminum sol to 36-40 DEG C, then spraying the aluminum sol on the surface of the porous silicon nitride ceramic material, drying, and preserving heat at 556-565 DEG C for 1.2-1.4 hours to obtain hole-sealed silicon nitride ceramic; by adopting the method disclosed by the invention, a firm and uniform metallization layer can be formed on the surface of the porous silicon nitride ceramic, and the high-temperature resistance is good.

Description

Technical Field

[0001] The present invention belongs to the fields of silicon nitride-based ceramic materials and ceramic metallization, and particularly relates to a method for surface metallization of a low-dielectric porous silicon nitride ceramic material. Background Art

[0002] Facing the complex battlefield environment, high-speed flight, precise strike, stealth penetration, etc. have become the basic requirements for a new generation of weaponry. This poses performance requirements of high temperature resistance, wideband wave transmission, and stealth for aircraft radar radomes, which not only need to achieve normal reception and transmission of signals of their own working radars, but also effectively reduce the RCS in front of the aircraft in non-working frequency bands.

[0003] Currently, the frequency band of conventional wave-transmitting materials is limited. A ceramic material with a dielectric constant of 3.0 can at most expand a bandwidth of 1.5 GHz and cannot achieve stealth. Conventional stealth measures, such as aircraft shape stealth, radar absorbing materials, etc., cannot achieve wave transmission. Existing materials cannot effectively solve this problem.

[0004] Using frequency selective surfaces (FSS) to prepare wave-transmitting / stealth ceramic radomes has become the best technical choice at present. Leaving aside the specific FSS structure design, high-temperature resistant FSS wave-transmitting materials can be abstracted as a type of high-temperature resistant dielectric material with specific metal patterns on the surface or inside. The most important core process technology is to prepare a high-temperature resistant metal coating inside or on the surface of the ceramic wave-transmitting material.

[0005] Currently, quartz ceramics and quartz fiber reinforced composite materials have developed into one of the most mature and widely used radome materials at home and abroad, but their long-term use temperature does not exceed 1200 °C, and their mechanical properties decline severely at high temperatures, unable to meet the high-temperature environment requirements faced by radomes during flight in the aerospace field.

[0006] As a high-performance ceramic material, silicon nitride ceramics have excellent high-temperature resistance, can still maintain good mechanical properties and dielectric properties at high temperatures, can withstand a relatively high temperature environment, effectively solve the problem of insufficient temperature resistance of quartz ceramics, and can better adapt to complex working environments.

[0007] However, for the porous silicon nitride ceramics prepared by the existing technology, although they have a certain porosity, the dielectric constant of the material is reduced. The dielectric constant is only 2.9, which can expand the frequency band width to 1.5 GHz, but still cannot meet the wideband wave transmission requirements above 2 GHz. At the same time, due to the large number of pores and the porosity reaching 40%-50%, when preparing a high-temperature resistant metal coating on its surface, a large amount of the metal coating penetrates into the pores, and it is difficult for the metal coating to adhere evenly to the ceramic surface. Problems such as poor bonding of the ceramic layer and uneven metal penetration at the pores are likely to occur. Especially in a high-temperature environment, the bonding force between the metal layer and the ceramic matrix drops sharply, easily leading to the shedding of the metal layer, thus affecting the comprehensive stability of the stealth / wave transmission performance of the radome and shortening the service life of the radome.

[0008] Therefore, a surface metallization method for a low-dielectric porous silicon nitride ceramic material is provided. The pores of the porous silicon nitride ceramic are uniform, the mechanical properties are excellent, the frequency band width can be expanded, and a firm and uniform metallization layer can be formed on the surface of the porous silicon nitride ceramic, with good high-temperature resistance. Summary of the Invention

[0009] In order to solve the technical problems existing in the prior art, the present invention provides a surface metallization method for a low-dielectric porous silicon nitride ceramic material. The pores of the porous silicon nitride ceramic material are uniform, the mechanical properties are excellent, the frequency band width can be expanded, and a firm and uniform metallization layer can be formed on the surface of the porous silicon nitride ceramic material, with good high-temperature resistance.

[0010] For the above technical problems, the present invention adopts the following technical solutions: A surface metallization method for a low-dielectric porous silicon nitride ceramic material includes steps of preparing the porous silicon nitride ceramic material, hole sealing treatment, and metallization, and the specific operations are as follows: 1. Preparation of the porous silicon nitride ceramic material (1) Preparation of activated graphene oxide Graphene oxide is treated with oxygen plasma. The oxygen flow rate of the oxygen plasma treatment is controlled to be 30-35 sccm, the discharge power is 100-108 W, the vacuum pressure is 1.4-1.6 Kpa, and the treatment time is 5.0-7.0 min to obtain activated graphene oxide; The particle size of the graphene oxide is 130-160 nm; (2) Preparation of epoxy alumina fibers Mix alumina fibers with 4 - 6 times the mass of 20 - 25 wt% hydrochloric acid solution, raise the temperature to 56 - 62 °C, keep warm and stir for 3.8 - 4.2 h, then filter, wash and dry to obtain pickled alumina fibers; put the pickled alumina fibers into toluene, after dispersing evenly, add 2 - bromoisobutyryl bromide and triethylamine, raise the temperature to 56 - 60 °C, keep warm and react for 4.8 - 5.2 h under a nitrogen atmosphere, then add allyl glycidyl ether and azobisisobutyronitrile, keep warm and react for 7.8 - 8.2 h under a nitrogen atmosphere. After the reaction ends, centrifuge, wash and dry to obtain epoxidized alumina fibers; The diameter of the alumina fibers is 55 - 65 nm and the length is 0.1 - 0.3 μm; The mass ratio of the pickled alumina fibers, toluene, 2 - bromoisobutyryl bromide, triethylamine, allyl glycidyl ether, azobisisobutyronitrile is 9.5 - 10.6:500:1.2 - 1.5:0.82 - 0.88:6.2 - 6.6:2.5 - 3.2; (3)Mixing Add epoxidized alumina fibers to toluene, after dispersing evenly, add activated graphene oxide, ultrasonically disperse for 26 - 35 min, the ultrasonic power is 115 - 125 W, the ultrasonic frequency is 28 - 32 kHz. After the ultrasonic dispersion ends, add 4 - dimethylaminopyridine, stir evenly, raise the temperature to 86 - 90 °C, keep warm and react for 7.0 - 7.5 h. After the reaction ends, add polyimide solution and stir evenly, raise the temperature to 112 - 117 °C, keep warm and react for 8.2 - 8.7 h. After the reaction ends, filter, wash and dry to obtain the preliminary mixture; mix α - silicon nitride particles with absolute ethanol, stir evenly, add polyvinylpyrrolidone and sodium dodecyl sulfate, continue to stir evenly, add the preliminary mixture, pore - forming agent, yttrium oxide, mix evenly, then filter, wash and dry to obtain the composite material; The mass ratio of the toluene, epoxidized alumina fibers, activated graphene oxide, 4 - dimethylaminopyridine, polyimide solution is 280 - 320:7.2 - 7.6:2.0 - 2.5:0.28 - 0.32:102 - 108; The polyimide solution is a mixed solution of polyimide and N, N - dimethylformamide, and the mass ratio of polyimide and N, N - dimethylformamide is 4.0 - 6.0:100; The pore - forming agent is polymethyl methacrylate with a particle size of 240 - 260 nm; The particle size of the yttrium oxide is 160 - 200 nm; The mass ratio of the α-silicon nitride particles, absolute ethanol, polyvinylpyrrolidone, sodium dodecyl sulfate, premixed material, pore-forming agent, and yttrium oxide is 88-93:600:2.0-2.5:1.0-1.5:10.2-10.8:42-48:11.6-12.4; (4)Preparation of green body Place the composite material in a mold for molding, and then, in an air atmosphere, raise the temperature to 636-642 °C and keep it warm for 2.4-2.6 h to obtain a green body; (5)Calcination Place the green body in a calcination furnace, under a nitrogen atmosphere, control the pressure to be 0.2-0.5 MPa, raise the temperature to 1650-1750 °C, and keep it warm for 2.0-3.0 h to obtain a porous silicon nitride ceramic material.

[0011] 2. Sealing treatment Heat the aluminum sol to 36-40 °C, then spray the aluminum sol on the surface of the porous silicon nitride ceramic material, control the spraying pressure to be 0.1-0.3 MPa, the spraying distance to be 10-14 cm, the spraying thickness to be 18-22 μm. After spraying, dry it at room temperature for 13-18 min, then put it in an oven and dry it for 28-32 min. Finally, raise the temperature to 556-565 °C at a rate of 1.3-1.6 °C / min and keep it warm for 1.2-1.4 h to obtain a sealed silicon nitride ceramic; The preparation method of the aluminum sol is as follows: Add aluminum nitrate to absolute ethanol and stir until completely dissolved, then add deionized water and continue stirring. After stirring evenly, add an 8-12 wt% sodium hydroxide solution to adjust the pH value to 5.2-5.7, and then add 0.8-1.2 g of polyethylene glycol 400 and stir for 55-65 min to obtain the aluminum sol; The mass ratio of the absolute ethanol, aluminum nitrate, and deionized water is 200:18-23:2.0-2.5.

[0012] 3. Metallization (1)Preparation of metallization paste Mix platinum powder, chromium powder, nickel powder, silicon dioxide, aluminum oxide, and titanium powder evenly, add ethyl cellulose, terpineol, and polyvinyl alcohol, and stir evenly to obtain a metallization paste; The mass-volume ratio of the platinum powder, chromium powder, nickel powder, silicon dioxide, aluminum oxide, titanium powder, ethyl cellulose, terpineol, and polyvinyl alcohol is 47.0-48.0 g:11.8-12.3 g:1.2-1.5 g:2.6-3.0 g:3.0-3.4 g:8.0-8.5 g:13-16 mL:195-206 mL:1.2-1.7 g; (2)Spraying Spray a metallization slurry on the surface of the sealed silicon nitride ceramic, control the spraying pressure to be 0.2 - 0.4 MPa, the spraying distance to be 15 - 20 cm, and the wet weight of the coating after spraying to be 0.008 - 0.012 g / cm 3 , after spraying, dry it at 70 - 80 °C for 10 - 15 min, then place it in a high-temperature furnace. Under an air atmosphere, raise the temperature to 680 - 720 °C at a rate of 4.0 - 6.0 °C / min, hold for 18 - 22 min, then switch to a nitrogen atmosphere, control the pressure to be 90 - 110 Pa, raise the temperature to 850 - 900 °C at a rate of 1.2 - 1.7 °C / min, hold for 28 - 35 min, cool the furnace temperature to 680 - 720 °C, stop introducing nitrogen, and wait for it to naturally cool to room temperature to obtain the metallized ceramic.

[0013] The present invention conducts surface metallization treatment on porous silicon nitride ceramics. The technical route is to first prepare porous silicon nitride ceramics, and after sealing treatment, perform surface metallization; the specific operation is to first perform oxygen plasma treatment on graphene oxide to activate it, and oxygen-containing groups such as carboxyl groups can be introduced on the surface of graphene oxide, then introduce alumina fibers. After pickling, add 2-bromo-2-methylpropionyl bromide to react with the hydroxyl groups on the fiber surface to introduce bromine atoms as the initiation sites for free radical polymerization. Allyl glycidyl ether undergoes free polymerization under the action of an initiator, thereby introducing epoxy groups on the surface of alumina fibers; in the mixing step, the epoxidized alumina fibers react with the activated graphene oxide under the action of a catalyst, and then react with the amino groups of polyimide, thereby realizing the strong combination of alumina fibers and graphene oxide, improving the interfacial bonding strength of the initial mixture, and at the same time improving the mixing uniformity with other components, ensuring the homogeneity of the composite material, making the pores of the ceramic uniform, and further enhancing the mechanical properties and stability of the ceramic, ensuring the wave-transmitting performance and dielectric properties; then perform sealing treatment on the porous silicon nitride ceramics, reducing the surface porosity of the porous silicon nitride ceramics. The surface of the sealed silicon nitride ceramic is more conducive to the attachment of metal particles and the formation of a continuous conductive network, laying a foundation for the subsequent full metallization. And the treatment with aluminum sol can improve the mechanical strength and stability of the ceramic. In the metallization step, a specific metallization slurry is used to form a uniform and dense metal layer on the ceramic surface, and the bonding force between the metal layer and the ceramic is strong. The finally obtained metallized ceramic has a good conductivity of the metallized layer, low resistance, and excellent high-temperature stability.

[0014] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. Using the method of the present invention to obtain porous silicon nitride ceramic materials, the pores are uniform, and the density is 0.9 - 1.2 g / cm 3 ; 2. The porous silicon nitride ceramic material obtained by the method of the present invention has a flexural strength of 58 - 64 MPa and a linear expansion coefficient (RT - 1200 °C) of 4.5 - 5.5×10 -6 / °C; 3. The porous silicon nitride ceramic material obtained by the method of the present invention has a dielectric constant of 2.2 - 2.6 and a loss tangent value of 0.001 - 0.008; 4. The porous silicon nitride ceramic material obtained by the method of the present invention, and the radome made of this material can achieve a wave transmission rate of 65 - 85% within 3 GHz; 5. The metallized ceramic obtained by the method of the present invention has a resistance of 45 - 60 Ω; 6. For the metallized ceramic obtained by the method of the present invention, the adhesion between the metal and the porous silicon nitride ceramic material of the material after metallization treatment is tested by the cross - cut method and is grade 0. After being examined by a quartz lamp at 1200 °C for 1000 s, the coating does not show phenomena such as peeling and cracking, and the adhesion remains grade 0. Detailed Embodiments

[0015] For a clearer understanding of the technical features, objectives, and effects of the present invention, the detailed embodiments of the present invention are now described.

[0016] Example 1 A method for surface metallization of a low - dielectric porous silicon nitride ceramic material 1. Preparation of porous silicon nitride ceramic material (1) Preparation of activated graphene oxide Graphene oxide is treated with oxygen plasma. The oxygen flow rate of the oxygen plasma treatment is controlled at 30 sccm, the discharge power is 100 W, the vacuum pressure is 1.4 Kpa, and the treatment time is 5.0 min to obtain activated graphene oxide; The particle size of the graphene oxide is 130 nm; (2) Preparation of epoxidized alumina fiber Alumina fiber is mixed with 4 times its mass of 20 wt% hydrochloric acid solution, the temperature is raised to 56 °C, and it is kept warm and stirred for 4.2 h. After filtration, washing, and drying, pickled alumina fiber is obtained; 9.5 g of pickled alumina fiber is put into 500 g of toluene, dispersed evenly, then 1.2 g of 2 - bromoisobutyryl bromide and 0.82 g of triethylamine are added, the temperature is raised to 56 °C, and it is kept warm and reacted for 4.8 h under a nitrogen atmosphere. Then 6.2 g of allyl glycidyl ether and 2.5 g of azobisisobutyronitrile are added, and it is kept warm and reacted for 8.2 h under a nitrogen atmosphere. After the reaction ends, it is centrifuged, washed, and dried to obtain epoxidized alumina fiber; The diameter of the alumina fiber is 55 nm and the length is 0.1 μm; (3) Mixing Add 7.2 g of epoxy alumina fiber to 280 g of toluene. After uniform dispersion, add 2.0 g of activated graphene oxide and ultrasonically disperse for 26 min with an ultrasonic power of 115 W and an ultrasonic frequency of 28 kHz. After the ultrasonic dispersion is completed, add 0.28 g of 4-dimethylaminopyridine, stir evenly, raise the temperature to 86 °C, and keep the temperature for 7.0 h. After the reaction is completed, add 102 g of polyimide solution and stir evenly. Raise the temperature to 112 °C and keep the temperature for 8.2 h. After the reaction is completed, filter, wash, and dry to obtain a preliminary mixture; Mix 88 g of α-silicon nitride particles with 600 g of absolute ethanol, stir evenly, add 2.0 g of polyvinylpyrrolidone and 1.0 g of sodium dodecyl sulfate, continue to stir evenly, add 10.2 g of the preliminary mixture, 42 g of pore-forming agent, and 11.6 g of yttrium oxide. After mixing evenly, filter, wash, and dry to obtain a composite material; The polyimide solution is a mixed solution of 4.0 g of polyimide and 100 g of N,N-dimethylformamide; The pore-forming agent is polymethyl methacrylate with a particle size of 240 nm; The particle size of the yttrium oxide is 160 nm; (4)Prepare a green body Place the composite material in a mold for molding, and then, in an air atmosphere, raise the temperature to 636 °C and keep the temperature for 2.6 h to obtain a green body; (5)Calcination Place the green body in a calcination furnace, in a nitrogen atmosphere, control the pressure to 0.2 MPa, raise the temperature to 1650 °C, and keep the temperature for 3.0 h to obtain a porous silicon nitride ceramic material.

[0017] 2. Sealing treatment Heat the aluminum sol to 36 °C, then spray the aluminum sol on the surface of the porous silicon nitride ceramic material, control the spraying pressure to 0.1 MPa, the spraying distance to 14 cm, and the spraying thickness to 18 μm. After spraying, dry at room temperature for 13 min, then put it in an oven and dry for 28 min. Finally, raise the temperature to 556 °C at a rate of 1.3 °C / min and keep the temperature for 1.2 h to obtain a sealed silicon nitride ceramic; The preparation method of the aluminum sol is as follows: Add 18 g of aluminum nitrate to 200 g of absolute ethanol and stir until completely dissolved, then add 2.0 g of deionized water and continue stirring. After stirring evenly, add an 8 wt% sodium hydroxide solution to adjust the pH value to 5.2, and then add 0.8 g of polyethylene glycol 400 and stir for 55 min to obtain the aluminum sol.

[0018] 3. Metallization (1)Prepare a metallization paste Mix 47.0 g of platinum powder, 11.8 g of chromium powder, 1.2 g of nickel powder, 2.6 g of silicon dioxide, 3.0 g of aluminum oxide, and 8.0 g of titanium powder evenly, add 13 mL of ethyl cellulose, 195 mL of terpineol, and 1.2 g of polyvinyl alcohol, and stir evenly to obtain a metallization paste; (2)Spraying Spray the metallization paste on the surface of the sealed-hole silicon nitride ceramic, control the spraying pressure to be 0.2 MPa, the spraying distance to be 15 cm, and the wet weight of the coating after spraying to be 0.008 g / cm 3 After spraying, dry it at 70 °C for 15 min, then place it in a high-temperature furnace. Under an air atmosphere, raise the temperature to 680 °C at a rate of 4.0 °C / min, hold for 22 min, then switch to a nitrogen atmosphere, control the pressure to be 90 Pa, raise the temperature to 850 °C at a rate of 1.2 °C / min, hold for 35 min, cool the furnace temperature to 680 °C, stop introducing nitrogen, and wait for it to naturally cool to room temperature to obtain a metallized ceramic.

[0019] Use the method of Example 1 to obtain a porous silicon nitride ceramic material with a density of 1.2 g / cm 3 The flexural strength is 58 MPa, the linear expansion coefficient (RT - 1200 °C) is 5.5×10 -6 / °C, the dielectric constant is 2.6, and the loss tangent value is 0.001; the radome made of this material can achieve a wave transmission rate of 65% within 3 GHz.

[0020] The resistance of the metallized ceramic obtained by the method of Example 1 is 60 Ω. The adhesion between the metal and the porous silicon nitride ceramic material of the metallized material is tested by the cross-cut method and is grade 0. After being tested by a quartz lamp at 1200 °C / 1000 s, the coating does not show phenomena such as peeling and cracking, and the adhesion remains grade 0.

[0021] Example 2 A method for surface metallization of a low-dielectric porous silicon nitride ceramic material 1. Preparation of porous silicon nitride ceramic material (1)Preparation of activated graphene oxide Treat graphene oxide with oxygen plasma, control the oxygen flow rate of the oxygen plasma treatment to be 32 sccm, the discharge power to be 105 W, the vacuum pressure to be 1.5 Kpa, and the treatment time to be 6.0 min to obtain activated graphene oxide; The particle size of the graphene oxide is 150 nm; (2)Preparation of epoxidized alumina fiber Mix alumina fibers with 5 times the mass of a 22 wt% hydrochloric acid solution, raise the temperature to 60 °C, keep warm and stir for 4.0 h, filter, wash and dry to obtain pickled alumina fibers; Put 10.0 g of pickled alumina fibers into 500 g of toluene, disperse evenly, add 1.3 g of 2-bromoisobutyryl bromide and 0.85 g of triethylamine, raise the temperature to 58 °C, keep warm and react for 5.0 h under a nitrogen atmosphere, then add 6.4 g of allyl glycidyl ether and 2.8 g of azobisisobutyronitrile, keep warm and react for 8.0 h under a nitrogen atmosphere. After the reaction, centrifuge, wash and dry to obtain epoxidized alumina fibers; The diameter of the alumina fibers is 60 nm and the length is 0.2 μm; (3)Mixing Add 7.4 g of epoxidized alumina fibers to 300 g of toluene, disperse evenly, add 2.3 g of activated graphene oxide, ultrasonically disperse for 30 min, the ultrasonic power is 120 W, the ultrasonic frequency is 30 kHz. After the ultrasonic dispersion, add 0.30 g of 4-dimethylaminopyridine, stir evenly, raise the temperature to 88 °C, keep warm and react for 7.2 h. After the reaction, add 105 g of polyimide solution and stir evenly, raise the temperature to 115 °C, keep warm and react for 8.5 h. After the reaction, filter, wash and dry to obtain a preliminary mixture; Mix 90 g of α-silicon nitride particles with 600 g of absolute ethanol, stir evenly, add 2.2 g of polyvinylpyrrolidone and 1.3 g of sodium dodecyl sulfate, continue to stir evenly, add 10.5 g of the preliminary mixture, 45 g of pore-forming agent, and 12.0 g of yttrium oxide, mix evenly, and then filter, wash and dry to obtain a composite material; The polyimide solution is a mixed solution of 5.0 g of polyimide and 100 g of N,N-dimethylformamide; The pore-forming agent is polymethyl methacrylate with a particle size of 250 nm; The particle size of the yttrium oxide is 180 nm; (4)Preparing green body Place the composite material in a mold for molding, then in an air atmosphere, raise the temperature to 640 °C, keep warm for 2.5 h to obtain a green body; (5)Calcination Place the green body in a calcination furnace, under a nitrogen atmosphere, control the pressure to 0.3 MPa, raise the temperature to 1700 °C, keep warm for 2.5 h to obtain a porous silicon nitride ceramic material.

[0022] 2. Sealing hole treatment Heat the aluminum sol to 38 °C, then spray the aluminum sol on the surface of the porous silicon nitride ceramic material, control the spraying pressure to be 0.2 MPa, the spraying distance to be 12 cm, the spraying thickness to be 20 μm, dry it at room temperature for 15 min after spraying, then put it into an oven and dry it for 30 min, and finally raise the temperature to 560 °C at a rate of 1.5 °C / min, and keep it warm for 1.3 h to obtain the sealed silicon nitride ceramic; The preparation method of the aluminum sol is as follows: add 20 g of aluminum nitrate to 200 g of absolute ethanol, stir until completely dissolved, then add 2.3 g of deionized water and continue stirring. After stirring evenly, add 10 wt% sodium hydroxide solution to adjust the pH value to 5.4, then add 1.0 g of polyethylene glycol 400, and stir for 60 min to obtain the aluminum sol.

[0023] 3. Metallization (1)Prepare the metallization paste Mix 47.5 g of platinum powder, 12.0 g of chromium powder, 1.4 g of nickel powder, 2.8 g of silicon dioxide, 3.2 g of alumina, and 8.2 g of titanium powder evenly, add 14 mL of ethyl cellulose, 200 mL of terpineol, and 1.4 g of polyvinyl alcohol, and stir evenly to obtain the metallization paste; (2)Spraying Spray the metallization paste on the surface of the sealed silicon nitride ceramic, control the spraying pressure to be 0.3 MPa, the spraying distance to be 18 cm, and the wet weight of the coating after spraying to be 0.010 g / cm 3 , after spraying, dry it at 75 °C for 12 min, then put it into a high-temperature furnace, in an air atmosphere, raise the temperature to 700 °C at a rate of 5.0 °C / min, keep it warm for 20 min, then switch to a nitrogen atmosphere, control the pressure to be 100 Pa, raise the temperature to 880 °C at a rate of 1.5 °C / min, keep it warm for 30 min, reduce the temperature with the furnace to 700 °C, stop introducing nitrogen, and wait for it to naturally cool to room temperature to obtain the metallized ceramic.

[0024] The porous silicon nitride ceramic material obtained by the method of Example 2 has a density of 0.9 g / cm 3 , a flexural strength of 64 MPa, a linear expansion coefficient (RT - 1200 °C) of 4.5×10 -6 / °C, a dielectric constant of 2.2, and a loss tangent value of 0.003; the radome made of this material can achieve a wave transmission rate of 85% within 3 GHz.

[0025] The metallized ceramic obtained by the method of Example 2 has a resistance of 45 Ω. The adhesion between the metal and the porous silicon nitride ceramic material of the material after metallization treatment is tested by the cross-cut method and is grade 0. After being tested by a quartz lamp at 1200 °C / 1000 s, the coating does not show phenomena such as peeling and cracking, and the adhesion remains grade 0.

[0026] Example 3 A method for surface metallization of a low-dielectric porous silicon nitride ceramic material 1. Preparation of a porous silicon nitride ceramic material (1)Preparation of activated graphene oxide Treat graphene oxide with oxygen plasma, control the oxygen flow rate of the oxygen plasma treatment to be 35 sccm, the discharge power to be 108 W, the vacuum pressure to be 1.6 Kpa, and the treatment time to be 7.0 min to obtain activated graphene oxide; The particle size of the graphene oxide is 160 nm; (2)Preparation of epoxidized alumina fibers Mix alumina fibers with 6 times the mass of 25 wt% hydrochloric acid solution, raise the temperature to 62 °C, keep warm and stir for 3.8 h, filter, wash and dry to obtain pickled alumina fibers; Put 10.6 g of pickled alumina fibers into 500 g of toluene, disperse evenly, add 1.5 g of 2-bromoisobutyryl bromide and 0.88 g of triethylamine, raise the temperature to 60 °C, keep warm and react for 5.2 h under a nitrogen atmosphere, then add 6.6 g of allyl glycidyl ether and 3.2 g of azobisisobutyronitrile, keep warm and react for 7.8 h under a nitrogen atmosphere. After the reaction is completed, centrifuge, wash and dry to obtain epoxidized alumina fibers; The diameter of the alumina fibers is 65 nm and the length is 0.3 μm; (3)Mixing Add 7.6 g of epoxidized alumina fibers to 320 g of toluene, disperse evenly, add 2.5 g of activated graphene oxide, ultrasonically disperse for 35 min, the ultrasonic power is 125 W, the ultrasonic frequency is 32 kHz. After the ultrasonic dispersion is completed, add 0.32 g of 4-dimethylaminopyridine, stir evenly, raise the temperature to 90 °C, keep warm and react for 7.5 h. After the reaction is completed, add 108 g of polyimide solution and stir evenly, raise the temperature to 117 °C, keep warm and react for 8.7 h. After the reaction is completed, filter, wash and dry to obtain a preliminary mixture; Mix 93 g of α-silicon nitride particles with 600 g of absolute ethanol, stir evenly, add 2.5 g of polyvinylpyrrolidone and 1.5 g of sodium dodecyl sulfate, continue to stir evenly, add 10.8 g of the preliminary mixture, 48 g of pore-forming agent, and 12.4 g of yttrium oxide, mix evenly, and filter, wash and dry to obtain a composite material; The polyimide solution is a mixed solution of 6.0 g of polyimide and 100 g of N, N-dimethylformamide; The pore-forming agent is polymethyl methacrylate with a particle size of 260 nm; The particle size of the yttrium oxide is 200 nm; (4)Preparation of a green body Place the composite material in a mold for forming, and then, under an air atmosphere, raise the temperature to 642 °C and hold for 2.4 h to obtain a green body; (5)Calcination Place the green body in a calcination furnace. Under a nitrogen atmosphere, control the pressure to be 0.5 MPa, raise the temperature to 1750 °C, and hold for 2.0 h to obtain a porous silicon nitride ceramic material.

[0027] 2. Sealing treatment Heat the aluminum sol to 40 °C, then spray the aluminum sol on the surface of the porous silicon nitride ceramic material. Control the spraying pressure to be 0.3 MPa, the spraying distance to be 10 cm, and the spraying thickness to be 22 μm. After spraying, dry at room temperature for 18 min, then place in an oven and dry for 32 min. Finally, raise the temperature to 565 °C at a rate of 1.6 °C / min and hold for 1.4 h to obtain a sealed silicon nitride ceramic; The preparation method of the aluminum sol is as follows: Add 23 g of aluminum nitrate to 200 g of absolute ethanol and stir until completely dissolved. Then add 2.5 g of deionized water and continue stirring. After stirring evenly, add a 12 wt% sodium hydroxide solution to adjust the pH value to 5.7. Then add 1.2 g of polyethylene glycol 400 and stir for 65 min to obtain the aluminum sol.

[0028] 3. Metallization (1)Prepare the metallization paste Mix 48.0 g of platinum powder, 12.3 g of chromium powder, 1.5 g of nickel powder, 3.0 g of silicon dioxide, 3.4 g of aluminum oxide, and 8.5 g of titanium powder evenly. Add 16 mL of ethyl cellulose, 206 mL of terpineol, and 1.7 g of polyvinyl alcohol, and stir evenly to obtain the metallization paste; (2)Spraying Spray the metallization paste on the surface of the sealed silicon nitride ceramic. Control the spraying pressure to be 0.4 MPa, the spraying distance to be 20 cm, and the wet weight of the coating after spraying to be 0.012 g / cm 3 , after spraying, dry at 80 °C for 10 min, then place in a high-temperature furnace. Under an air atmosphere, raise the temperature to 720 °C at a rate of 6.0 °C / min and hold for 18 min. Then switch to a nitrogen atmosphere, control the pressure to be 110 Pa, raise the temperature to 900 °C at a rate of 1.7 °C / min, and hold for 28 min. Reduce the temperature with the furnace to 720 °C, stop introducing nitrogen, and wait for it to naturally cool to room temperature to obtain a metallized ceramic.

[0029] The porous silicon nitride ceramic material obtained by the method of Example 3 has a density of 1.1 g / cm 3 , a flexural strength of 60 MPa, and a linear expansion coefficient (RT - 1200 °C) of 4.7×10 -6 / °C, the dielectric constant is 2.4, and the tangent value of the loss angle is 0.008; the radome made of this material can achieve a wave transmission rate of 78% within 3 GHz.

[0030] The metallized ceramic obtained by the method of Example 3 has a resistance of 50 Ω. After the metallization treatment, the bonding strength between the metal and the porous silicon nitride ceramic material is tested by the cross-cut method and is grade 0. After being tested by a quartz lamp at 1200 °C for 1000 s, there is no peeling, cracking or other phenomena in the coating, and the bonding strength remains grade 0.

[0031] Comparative Example 2.1 Based on Example 2, the following changes are made: (1) In the process of preparing the porous silicon nitride ceramic material, the step of preparing epoxy alumina fiber is omitted; (2) The mixing step is as follows: Add 7.4 g of alumina fiber to 300 g of toluene, disperse evenly, then add 2.3 g of activated graphene oxide, and ultrasonically disperse for 30 min. The ultrasonic power is 120 W, and the ultrasonic frequency is 30 kHz. After the ultrasonic dispersion is completed, filter, wash and dry to obtain a preliminary mixture; Mix 90 g of α-silicon nitride particles with 600 g of absolute ethanol, stir evenly, then add 2.2 g of polyvinylpyrrolidone and 1.3 g of sodium dodecyl sulfate, continue to stir evenly, add 10.5 g of the preliminary mixture, 45 g of pore-forming agent, and 12.0 g of yttrium oxide, mix evenly, and then filter, wash and dry to obtain a composite material; The diameter of the alumina fiber is 60 nm and the length is 0.2 μm; The pore-forming agent is polymethyl methacrylate with a particle size of 250 nm; The particle size of the yttrium oxide is 180 nm; (3) The rest of the operations are the same.

[0032] The porous silicon nitride ceramic material obtained by the method of Comparative Example 2.1 has a density of 1.3 g / cm 3 , a flexural strength of 48 MPa, and a linear expansion coefficient (RT - 1200 °C) of 7.4×10 -6 / °C, the dielectric constant is 3.1, and the tangent value of the loss angle is 0.016; the radome made of this material can achieve a wave transmission rate of 52% within 3 GHz.

[0033] Comparative Example 2.1 omitted the epoxy treatment step of alumina fibers and omitted the polyimide component in the mixing step. For the obtained porous silicon nitride ceramic material, the interfacial bonding force between alumina fibers and graphene oxide is poor, and the mixing uniformity with other components in the mixing step is poor, thus affecting the homogeneity of the ceramic, reducing the mechanical properties, the interaction between alumina fibers and other components is weak, the polarization phenomenon inside the material is obvious, the dielectric constant is high, the dielectric loss is large, and the wave transmittance is low, which affects the comprehensive performance of the porous silicon nitride ceramic material.

[0034] Comparative Example 2.2 Based on Example 2, the following changes were made: (1) The hole sealing treatment step was omitted; in the spraying step of the metallization process, the hole-sealed silicon nitride ceramic was replaced with the porous silicon nitride ceramic material; (2) The remaining operations were the same.

[0035] For the metallized ceramic obtained by the method of Comparative Example 2.2, the resistance was 72 Ω. After the material after metallization treatment was tested for the bonding force between the metal and the porous silicon nitride ceramic material by the cross-cut method, the bonding force was Grade 2. After being examined by a quartz lamp at 1200 °C for 1000 s, large-area peeling and cracking occurred on the coating, and the bonding force was Grade 4.

[0036] Comparative Example 2.2 omitted the hole sealing treatment step. There were many unfilled pores in the porous silicon nitride ceramic material. When spraying the metallization slurry, it was difficult for metal particles to form good connections at the pores, resulting in discontinuous conductive paths and many regions with large resistances. Moreover, the existence of pores reduced the contact area between the metallization layer and the porous silicon nitride ceramic material, weakened the bonding force, and reduced the stability of the metallization layer.

[0037] Unless otherwise specified, the ratios described in the present invention are all mass ratios, and the percentages are all mass percentages.

[0038] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for surface metallization of a low-dielectric porous silicon nitride ceramic material, characterized in that, It includes steps of preparing porous silicon nitride ceramic material, hole sealing treatment and metallization; The preparation of the porous silicon nitride ceramic material includes steps of preparing activated graphene oxide, preparing epoxy alumina fiber, mixing, preparing green body and calcination; The step of preparing epoxy alumina fiber is as follows: putting pickled alumina fiber into toluene, dispersing evenly, adding 2-bromoisobutyryl bromide and triethylamine, raising the temperature to 56 - 60 °C, keeping the temperature for reaction for 4.8 - 5.2 h under nitrogen atmosphere, then adding allyl glycidyl ether and azobisisobutyronitrile, and keeping the temperature for reaction for 7.8 - 8.2 h under nitrogen atmosphere to obtain epoxy alumina fiber; The step of hole sealing treatment is as follows: heating aluminum sol to 36 - 40 °C, then spraying aluminum sol on the surface of the porous silicon nitride ceramic material, drying, and keeping the temperature at 556 - 565 °C for 1.2 - 1.4 h to obtain hole-sealed silicon nitride ceramic.

2. The surface metallization method of a low-dielectric porous silicon nitride ceramic material according to claim 1, characterized in that The step of preparing activated graphene oxide is as follows: treating graphene oxide with oxygen plasma, controlling the oxygen flow rate of the oxygen plasma treatment to be 30 - 35 sccm, the discharge power to be 100 - 108 W, the vacuum pressure to be 1.4 - 1.6 Kpa, and the treatment time to be 5.0 - 7.0 min to obtain activated graphene oxide; The particle size of the graphene oxide is 130 - 160 nm.

3. The surface metallization method of a low-dielectric porous silicon nitride ceramic material according to claim 1, characterized in that In the step of preparing epoxy alumina fiber, the mass ratio of the pickled alumina fiber, toluene, 2-bromoisobutyryl bromide, triethylamine, allyl glycidyl ether, and azobisisobutyronitrile is 9.5 - 10.6:500:1.2 - 1.5:0.82 - 0.88:6.2 - 6.6:2.5 - 3.2; The preparation method of the pickled alumina fiber is as follows: mixing alumina fiber with 4 - 6 times the mass of 20 - 25 wt% hydrochloric acid solution, raising the temperature to 56 - 62 °C, keeping the temperature and stirring for 3.8 - 4.2 h, and obtaining pickled alumina fiber through filtration, washing, and drying; The diameter of the alumina fiber is 55 - 65 nm, and the length is 0.1 - 0.3 μm.

4. The surface metallization method of a low-dielectric porous silicon nitride ceramic material according to claim 1, characterized in that The mixing step is as follows: Add alumina fiber epoxide to toluene, and after dispersing evenly, add activated graphene oxide, and perform ultrasonic dispersion for 26 - 35 min, with the ultrasonic power being 115 - 125 W and the ultrasonic frequency being 28 - 32 kHz. After the ultrasonic dispersion ends, add 4 - dimethylaminopyridine, stir evenly, raise the temperature to 86 - 90 °C, and keep the temperature for reaction for 7.0 - 7.5 h. After the reaction ends, add polyimide solution and stir evenly, raise the temperature to 112 - 117 °C, and keep the temperature for reaction for 8.2 - 8.7 h. After the reaction ends, filter, wash, and dry to obtain a preliminary mixture; Mix α - silicon nitride particles with absolute ethanol, stir evenly, add polyvinylpyrrolidone and sodium dodecyl sulfate, continue to stir evenly, add the preliminary mixture, pore - forming agent, and yttrium oxide, mix evenly, and then filter, wash, and dry to obtain a composite material.

5. According to the method for surface metallization of a low - dielectric porous silicon nitride ceramic material described in claim 4, characterized in that The mass ratio of the toluene, alumina fiber epoxide, activated graphene oxide, 4 - dimethylaminopyridine, and polyimide solution is 280 - 320:7.2 - 7.6:2.0 - 2.5:0.28 - 0.32:102 - 108; The polyimide solution is a mixed solution of polyimide and N, N - dimethylformamide, and the mass ratio of the polyimide and N, N - dimethylformamide is 4.0 - 6.0:100; The pore - forming agent is polymethyl methacrylate, and the particle size is 240 - 260 nm; The particle size of the yttrium oxide is 160 - 200 nm; The mass ratio of the α - silicon nitride particles, absolute ethanol, polyvinylpyrrolidone, sodium dodecyl sulfate, preliminary mixture, pore - forming agent, and yttrium oxide is 88 - 93:600:2.0 - 2.5:1.0 - 1.5:10.2 - 10.8:42 - 48:11.6 - 12.

4.

6. According to the method for surface metallization of a low - dielectric porous silicon nitride ceramic material described in claim 1, characterized in that The step of preparing the green body is as follows: Place the composite material in a mold for forming, and then in an air atmosphere, raise the temperature to 636 - 642 °C, and keep the temperature for 2.4 - 2.6 h to obtain a green body; The calcination step is as follows: Place the green body in a calcination furnace, under a nitrogen atmosphere, control the pressure to be 0.2 - 0.5 MPa, raise the temperature to 1650 - 1750 °C, and keep the temperature for 2.0 - 3.0 h to obtain a porous silicon nitride ceramic material.

7. According to the method for surface metallization of a low - dielectric porous silicon nitride ceramic material described in claim 1, characterized in that In the step of hole - sealing treatment, when spraying aluminum sol, control the spraying pressure to be 0.1 - 0.3 MPa, the spraying distance to be 10 - 14 cm, and the spraying thickness to be 18 - 22 μm; The preparation method of the aluminum sol is as follows: aluminum nitrate is added to absolute ethanol and stirred until completely dissolved, then deionized water is added and stirring continues. After stirring evenly, an 8-12 wt% sodium hydroxide solution is added to adjust the pH value to 5.2-5.7, and then 0.8-1.2 g of polyethylene glycol 400 is added and stirred for 55-65 min to obtain the aluminum sol; The mass ratio of the absolute ethanol, aluminum nitrate, and deionized water is 200:18-23:2.0-2.

5.

8. A method for surface metallization of a low-dielectric porous silicon nitride ceramic material according to claim 1, characterized in that The metallization step includes a step of preparing a metallization paste and a spraying step; The step of preparing the metallization paste is as follows: platinum powder, chromium powder, nickel powder, silicon dioxide, alumina, and titanium powder are mixed evenly, and ethyl cellulose, terpineol, and polyvinyl alcohol are added and stirred evenly to obtain the metallization paste; The mass-volume ratio of the platinum powder, chromium powder, nickel powder, silicon dioxide, alumina, titanium powder, ethyl cellulose, terpineol, and polyvinyl alcohol is 47.0-48.0 g:11.8-12.3 g:1.2-1.5 g:2.6-3.0 g:3.0-3.4 g:8.0-8.5 g:13-16 mL:195-206 mL:1.2-1.7 g.

9. A method for surface metallization of a low-dielectric porous silicon nitride ceramic material according to claim 8, characterized in that The spraying step is to spray metallization slurry on the surface of the sealed silicon nitride ceramic, control the spraying pressure to be 0.2 - 0.4 MPa, the spraying distance to be 15 - 20 cm, and the wet weight of the coating after spraying to be 0.008 - 0.012 g / cm 3 , after spraying, dry at 70 - 80 °C for 10 - 15 min, then place it in a high-temperature furnace. Under an air atmosphere, raise the temperature at a rate of 4.0 - 6.0 °C / min to 680 - 720 °C, hold for 18 - 22 min, then switch to a nitrogen atmosphere, control the pressure to be 90 - 110 Pa, raise the temperature at a rate of 1.2 - 1.7 °C / min to 850 - 900 °C, carry out heat preservation treatment for 28 - 35 min, reduce the temperature in the furnace to 680 - 720 °C, stop introducing nitrogen, and wait for it to naturally cool to room temperature to obtain metallized ceramics.