A surface metallization method for low-dielectric porous silicon nitride ceramic material

Abstract

The present invention provides a surface metallization method for a low-dielectric porous silicon nitride ceramic material, belonging to the field of ceramic metallization. The method comprises the steps of preparing the porous silicon nitride ceramic material, sealing the pores, and metallizing the material. The sealing step comprises heating an aluminum sol to 36-40°C, spraying the aluminum sol onto the surface of the porous silicon nitride ceramic material, drying the material, and then maintaining the temperature at 556-565°C for 1.2-1.4 hours to obtain the sealed silicon nitride ceramic. The method can form a firm and uniform metallization layer on the surface of the porous silicon nitride ceramic with excellent high-temperature resistance.

Description

Technical Field

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

[0002] Faced with complex battlefield environments, high-speed flight, precision strikes, stealth penetration, etc. have become the basic requirements of the new generation of weapons and equipment. This puts forward performance requirements for the aircraft radar antenna cover to be resistant to high temperatures, have wide-band wave transmission, and have stealth. It must not only achieve normal reception and transmission of signals from its own working radar, but also effectively reduce the RCS directly in front of the aircraft in the non-working band.

[0003] Currently, conventional wave-transmitting materials have limited bandwidth expansion. Ceramic materials with a dielectric constant of 3.0 can only expand the bandwidth to 1.5GHz at most and cannot achieve stealth. Conventional stealth measures, such as aircraft shape stealth and radar absorbing materials, cannot achieve wave transmission. Existing materials cannot effectively solve this problem.

[0004] The use of frequency selective surfaces (FSS) to prepare wave-transmitting / stealth ceramic radomes has become the best technical option at present; putting aside the specific FSS structural design scheme, high-temperature resistant FSS wave-transmitting materials can be abstracted as a class of high-temperature resistant dielectric materials 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] At present, 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. However, the long-term use temperature does not exceed 1200℃, and the mechanical properties degrade severely at high temperatures, which cannot meet the high-temperature environment requirements faced by radomes in the aerospace field during flight.

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

[0007] However, the porous silicon nitride ceramics prepared by existing technology, although having a certain porosity, have reduced the dielectric constant of the material, and the dielectric constant is only 2.9. The bandwidth can be expanded to 1.5GHz, but it still cannot meet the broadband wave transmission requirements above 2GHz. 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, the metal coating penetrates into the holes in large quantities, and the metal coating is difficult to adhere evenly to the ceramic surface, which easily leads to problems such as loose bonding of the ceramic layer and uneven metal penetration in the holes. Especially in a high-temperature environment, the bonding force between the metal layer and the ceramic substrate drops sharply, which easily causes the metal layer to fall off, thereby affecting the comprehensive stability performance of the stealth / wave transmission of the antenna cover and shortening the service life of the antenna cover.

[0008] Therefore, a surface metallization method for a low-dielectric porous silicon nitride ceramic material is provided. The porous silicon nitride ceramic has uniform pores, excellent mechanical properties, can expand the frequency bandwidth, and can form a firm and uniform metallization layer 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 low-dielectric porous silicon nitride ceramic materials. The porous silicon nitride ceramic materials have uniform pores and excellent mechanical properties. They can expand the frequency bandwidth and form a firm and uniform metallization layer on the surface of the porous silicon nitride ceramic materials with good high-temperature resistance.

[0010] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0011] A method for surface metallization of a low-dielectric porous silicon nitride ceramic material includes the steps of preparing the porous silicon nitride ceramic material, sealing the pores, and metallizing the material. The specific operations are as follows:

[0012] 1. Preparation of porous silicon nitride ceramic materials

[0013] (1) Preparation of activated graphene oxide

[0014] Graphene oxide is treated with oxygen plasma, with the oxygen flow rate of the oxygen plasma treatment controlled 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;

[0015] The particle size of the graphene oxide is 130-160 nm;

[0016] (2) Preparation of epoxidized alumina fibers

[0017] Alumina fiber is mixed with 4-6 times the mass of a 20-25wt% hydrochloric acid solution, the temperature is increased to 56-62°C, the mixture is stirred at this temperature for 3.8-4.2 hours, and the mixture is filtered, washed, and dried to obtain acid-washed alumina fiber; the acid-washed alumina fiber is added into toluene, and after uniform dispersion, 2-bromoisobutyryl bromide and triethylamine are added, the temperature is increased to 56-60°C, the mixture is stirred at this temperature for 4.8-5.2 hours under a nitrogen atmosphere, and then allyl glycidyl ether and azobisisobutyronitrile are added, the mixture is stirred at this temperature for 7.8-8.2 hours under a nitrogen atmosphere, and after the reaction is completed, the mixture is centrifuged, washed, and dried to obtain epoxidized alumina fiber;

[0018] The diameter of the alumina fiber is 55-65 nm and the length is 0.1-0.3 μm;

[0019] The mass ratio of the acid-washed 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;

[0020] (3) Mixing

[0021] Add epoxidized alumina fiber to toluene, disperse evenly, add activated graphene oxide, and ultrasonically disperse for 26-35 minutes, with an ultrasonic power of 115-125W and an ultrasonic frequency of 28-32kHz. After the ultrasonic dispersion is completed, add 4-dimethylaminopyridine, stir evenly, increase the temperature to 86-90°C, and keep the reaction for 7.0-7.5 hours. After the reaction is completed, add polyimide solution and stir evenly, increase the temperature to 112-117°C, and keep the reaction for 8.2-8.7 hours. After the reaction is completed, filter, wash, and dry to obtain a primary mixture; mix α-silicon nitride particles with anhydrous ethanol, stir evenly, add polyvinyl pyrrolidone and sodium lauryl sulfate, continue to stir evenly, add the primary mixture, a pore-forming agent, and yttrium oxide, mix evenly, filter, wash, and dry to obtain a composite material;

[0022] The mass ratio of the toluene, epoxidized alumina fiber, 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;

[0023] The polyimide solution is a mixture of polyimide and N,N-dimethylformamide, and the mass ratio of the polyimide to N,N-dimethylformamide is 4.0-6.0:100;

[0024] The pore-forming agent is polymethyl methacrylate with a particle size of 240-260 nm;

[0025] The particle size of the yttrium oxide is 160-200 nm;

[0026] The mass ratio of the α-silicon nitride particles, anhydrous ethanol, polyvinyl pyrrolidone, sodium lauryl sulfate, primary mixed 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;

[0027] (4) Preparation of green body

[0028] The composite material is placed in a mold for forming, and then the temperature is raised to 636-642° C. in an air atmosphere and kept at this temperature for 2.4-2.6 hours to obtain a green body;

[0029] (5) Calcination

[0030] The green body is placed in a calcining furnace, under a nitrogen atmosphere, the pressure is controlled to be 0.2-0.5 MPa, the temperature is increased to 1650-1750° C., and the heat treatment is carried out for 2.0-3.0 hours to obtain a porous silicon nitride ceramic material.

[0031] 2. Sealing treatment

[0032] The aluminum sol is heated to 36-40° C., and then the aluminum sol is sprayed on the surface of the porous silicon nitride ceramic material, the spraying pressure is controlled to be 0.1-0.3 MPa, the spraying distance is 10-14 cm, and the spraying thickness is 18-22 μm. After the spraying, the material is dried at room temperature for 13-18 minutes, and then placed in an oven for drying for 28-32 minutes. Finally, the temperature is increased to 556-565° C. at a rate of 1.3-1.6° C. / min, and the material is kept warm for 1.2-1.4 hours to obtain a sealed silicon nitride ceramic.

[0033] The aluminum sol is prepared by adding aluminum nitrate to anhydrous ethanol and stirring until completely dissolved, adding deionized water and continuing to stir, stirring evenly, adding 8-12 wt % sodium hydroxide solution to adjust the pH value to 5.2-5.7, and then adding 0.8-1.2 g of polyethylene glycol 400 and stirring for 55-65 minutes to obtain the aluminum sol;

[0034] The mass ratio of the anhydrous ethanol, aluminum nitrate and deionized water is 200:18-23:2.0-2.5.

[0035] 3. Metallization

[0036] (1) Preparation of metallization slurry

[0037] Platinum powder, chromium powder, nickel powder, silicon dioxide, aluminum oxide, and titanium powder are mixed evenly, and ethyl cellulose, terpineol, and polyvinyl alcohol are added and stirred evenly to obtain a metallization slurry;

[0038] 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 47.0-48.0g:11.8-12.3g:1.2-1.5g:2.6-3.0g:3.0-3.4g:8.0-8.5g:13-16mL:195-206mL:1.2-1.7g;

[0039] (2) Spraying

[0040] Spray metallization slurry on the surface of sealed silicon nitride ceramics, control the spraying pressure to 0.2-0.4MPa, spray distance to 15-20cm, and the wet weight of the coating after spraying is 0.008-0.012g / cm 3 After spraying, dry it at 70-80℃ for 10-15min, then put it in a high-temperature furnace, and in an air atmosphere, increase the temperature to 680-720℃ at a rate of 4.0-6.0℃ / min, keep it warm for 18-22min, then switch to a nitrogen atmosphere, control the pressure to 90-110Pa, increase the temperature to 850-900℃ at a rate of 1.2-1.7℃ / min, keep it warm for 28-35min, and then reduce the temperature to 680-720℃ with the furnace, stop introducing nitrogen, and wait for it to naturally decrease to room temperature to obtain metallized ceramics.

[0041] The present invention performs surface metallization treatment on porous silicon nitride ceramics. The technical route is to first prepare porous silicon nitride ceramics, and then perform surface metallization after sealing treatment. 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 the graphene oxide, and then introduce alumina fiber. After acid washing, 2-bromoisobutyryl bromide is added to react with hydroxyl groups on the fiber surface, introducing bromine atoms as initiation sites for free radical polymerization. Allyl glycidyl ether is freely polymerized under the action of the initiator, thereby introducing epoxy groups on the surface of the alumina fiber. In the mixing step, the epoxidized alumina fiber reacts with the activated graphene oxide under the action of a catalyst, and then reacts with the amino group of the polyimide, thereby achieving a strong combination of the alumina fiber and the graphene oxide. The interfacial bonding strength of the primary mixture is improved, and the mixing uniformity with other components is also improved, ensuring the homogeneity of the composite material, making the pores of the ceramic uniform, thereby enhancing the mechanical properties and stability of the ceramic, and ensuring the wave transmission performance and dielectric properties; then the porous silicon nitride ceramic is sealed to reduce the surface porosity of the porous silicon nitride ceramic. The surface of the sealed silicon nitride ceramic is more conducive to the adhesion of metal particles and the formation of a continuous conductive network, laying the foundation for the next step of full metallization. In addition, 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 resulting metallized ceramic metallization layer has good conductivity, low resistance, and excellent high-temperature stability.

[0042] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0043] 1. The porous silicon nitride ceramic material obtained by the method of the present invention has uniform pores and a density of 0.9-1.2g / cm 3 ;

[0044] 2. The porous silicon nitride ceramic material obtained by the method of the present invention has a bending strength of 58-64 MPa and a linear expansion coefficient (RT 1200℃) of 4.5-5.5×10 -6 / ℃;

[0045] 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 of 0.001-0.008;

[0046] 4. The porous silicon nitride ceramic material obtained by the method of the present invention can achieve a wave transmittance of 65-85% within 3 GHz for a radome made of the material;

[0047] 5. The metallized ceramic obtained by the method of the present invention has a resistance of 45-60Ω;

[0048] 6. The metallized ceramic obtained by the method of the present invention has a bonding strength of level 0 between the metal and the porous silicon nitride ceramic material tested by the cross-hatch method after metallization treatment. After testing with a quartz lamp at 1200°C / 1000s, the coating showed no signs of falling off or cracking, and the bonding strength remained at level 0. DETAILED DESCRIPTION

[0049] In order to more clearly understand the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described.

[0050] Example 1 A method for surface metallization of a low dielectric porous silicon nitride ceramic material

[0051] 1. Preparation of porous silicon nitride ceramic materials

[0052] (1) Preparation of activated graphene oxide

[0053] The graphene oxide was treated with oxygen plasma, and the oxygen flow rate of the oxygen plasma treatment was controlled to be 30 sccm, the discharge power was 100 W, the vacuum pressure was 1.4 KPa, and the treatment time was 5.0 min to obtain activated graphene oxide;

[0054] The particle size of the graphene oxide is 130 nm;

[0055] (2) Preparation of epoxidized alumina fibers

[0056] Alumina fiber was mixed with 4 times its mass of 20wt% hydrochloric acid solution, the temperature was increased to 56°C, the mixture was stirred at this temperature for 4.2 hours, and the mixture was filtered, washed, and dried to obtain acid-washed alumina fiber. 9.5g of the acid-washed alumina fiber was added to 500g of toluene and uniformly dispersed. 1.2g of 2-bromoisobutyryl bromide and 0.82g of triethylamine were added, the temperature was increased to 56°C, and the mixture was stirred at this temperature for 4.8 hours under a nitrogen atmosphere. 6.2g of allyl glycidyl ether and 2.5g of azobisisobutyronitrile were added, and the mixture was stirred at this temperature for 8.2 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain epoxidized alumina fiber.

[0057] The diameter of the alumina fiber is 55 nm and the length is 0.1 μm;

[0058] (3) Mixing

[0059] 7.2 g of epoxidized alumina fiber was added to 280 g of toluene, and after uniform dispersion, 2.0 g of activated graphene oxide was added, and ultrasonic dispersion was performed for 26 min at an ultrasonic power of 115 W and an ultrasonic frequency of 28 kHz. After the ultrasonic dispersion was completed, 0.28 g of 4-dimethylaminopyridine was added, stirred evenly, the temperature was raised to 86 ° C, and the reaction was kept warm for 7.0 h. After the reaction was completed, 102 g of polyimide solution was added and stirred evenly, the temperature was raised to 112 ° C, and the reaction was kept warm for 8.2 h. After the reaction was completed, it was filtered, washed, and dried to obtain a primary mixture; 88 g of α-silicon nitride particles were mixed with 600 g of anhydrous ethanol, stirred evenly, 2.0 g of polyvinyl pyrrolidone and 1.0 g of sodium lauryl sulfate were added, and stirring was continued. 10.2 g of the primary mixture, 42 g of a pore-forming agent, and 11.6 g of yttrium oxide were added, mixed evenly, and filtered, washed, and dried to obtain a composite material;

[0060] The polyimide solution is a mixture of 4.0 g of polyimide and 100 g of N,N-dimethylformamide;

[0061] The pore-forming agent is polymethyl methacrylate with a particle size of 240 nm;

[0062] The particle size of the yttrium oxide is 160 nm;

[0063] (4) Preparation of green body

[0064] The composite material was placed in a mold for forming, and then the temperature was raised to 636°C in an air atmosphere and kept at this temperature for 2.6 hours to obtain a green body;

[0065] (5) Calcination

[0066] The green body was placed in a calcining furnace, under a nitrogen atmosphere, the pressure was controlled to 0.2 MPa, the temperature was increased to 1650° C., and the heat preservation treatment was carried out for 3.0 hours to obtain a porous silicon nitride ceramic material.

[0067] 2. Sealing treatment

[0068] The aluminum sol was heated to 36°C, and then sprayed on the surface of the porous silicon nitride ceramic material. The spraying pressure was controlled to be 0.1 MPa, the spraying distance was 14 cm, and the spraying thickness was 18 μm. After the spraying, the material was dried at room temperature for 13 minutes, then placed in an oven for drying for 28 minutes, and finally the temperature was increased to 556°C at a rate of 1.3°C / min and kept warm for 1.2 hours to obtain a sealed silicon nitride ceramic.

[0069] The aluminum sol is prepared by adding 18 g of aluminum nitrate to 200 g of anhydrous ethanol and stirring until completely dissolved, then adding 2.0 g of deionized water and continuing to stir. After stirring evenly, 8 wt % sodium hydroxide solution is added to adjust the pH value to 5.2, and then 0.8 g of polyethylene glycol 400 is added and stirred for 55 minutes to obtain the aluminum sol.

[0070] 3. Metallization

[0071] (1) Preparation of metallization slurry

[0072] 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 were mixed evenly, and 13 mL of ethyl cellulose, 195 mL of terpineol, and 1.2 g of polyvinyl alcohol were added and stirred evenly to obtain a metallization slurry;

[0073] (2) Spraying

[0074] The metallization slurry was sprayed on the surface of the sealed silicon nitride ceramic. The spraying pressure was controlled to 0.2 MPa and the spraying distance was 15 cm. The wet weight of the coating after spraying was 0.008 g / cm 3 After spraying, dry it at 70℃ for 15min, then put it in a high-temperature furnace, raise the temperature to 680℃ at a rate of 4.0℃ / min in an air atmosphere, keep it warm for 22min, then switch to a nitrogen atmosphere, control the pressure to 90Pa, raise the temperature to 850℃ at a rate of 1.2℃ / min, keep it warm for 35min, lower the temperature to 680℃ with the furnace, stop introducing nitrogen, and wait for it to naturally cool to room temperature to obtain metallized ceramics.

[0075] The porous silicon nitride ceramic material was obtained by the method of Example 1, and the density was 1.2 g / cm 3 , bending strength is 58MPa, linear expansion coefficient (RT 1200℃) is 5.5×10 -6 / ℃, the dielectric constant is 2.6, and the loss tangent is 0.001; the antenna cover made of this material can achieve a wave transmittance of 65% within 3GHz.

[0076] The metallized ceramic obtained by the method of Example 1 has a resistance of 60Ω. The bonding strength between the metal and the porous silicon nitride ceramic material after the metallization treatment is tested by the cross-hatch method and is level 0. After testing with a quartz lamp at 1200°C / 1000s, the coating does not show any signs of falling off or cracking, and the bonding strength remains at level 0.

[0077] Example 2 A method for surface metallization of a low dielectric porous silicon nitride ceramic material

[0078] 1. Preparation of porous silicon nitride ceramic materials

[0079] (1) Preparation of activated graphene oxide

[0080] The graphene oxide was treated with oxygen plasma, and the oxygen flow rate of the oxygen plasma treatment was controlled to be 32 sccm, the discharge power was 105 W, the vacuum pressure was 1.5 KPa, and the treatment time was 6.0 min to obtain activated graphene oxide;

[0081] The particle size of the graphene oxide is 150 nm;

[0082] (2) Preparation of epoxidized alumina fibers

[0083] Alumina fiber was mixed with 5 times its mass of 22wt% hydrochloric acid solution, the temperature was increased to 60°C, the mixture was stirred at this temperature for 4.0 hours, and the mixture was filtered, washed, and dried to obtain acid-washed alumina fiber. 10.0g of the acid-washed alumina fiber was added to 500g of toluene and uniformly dispersed. 1.3g of 2-bromoisobutyryl bromide and 0.85g of triethylamine were added, the temperature was increased to 58°C, and the mixture was stirred at this temperature for 5.0 hours under a nitrogen atmosphere. 6.4g of allyl glycidyl ether and 2.8g of azobisisobutyronitrile were added, and the mixture was stirred at this temperature for 8.0 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain epoxidized alumina fiber.

[0084] The diameter of the alumina fiber is 60 nm and the length is 0.2 μm;

[0085] (3) Mixing

[0086] 7.4 g of epoxidized alumina fiber was added to 300 g of toluene, and after uniform dispersion, 2.3 g of activated graphene oxide was added, and ultrasonic dispersion was carried out for 30 min at an ultrasonic power of 120 W and an ultrasonic frequency of 30 kHz. After the ultrasonic dispersion was completed, 0.30 g of 4-dimethylaminopyridine was added, stirred evenly, and the temperature was raised to 88 ° C. and the reaction was kept warm for 7.2 h. After the reaction was completed, 105 g of polyimide solution was added and stirred evenly, the temperature was raised to 115 ° C. and the reaction was kept warm for 8.5 h. After the reaction was completed, it was filtered, washed, and dried to obtain a primary mixture; 90 g of α-silicon nitride particles were mixed with 600 g of anhydrous ethanol, stirred evenly, 2.2 g of polyvinyl pyrrolidone and 1.3 g of sodium lauryl sulfate were added, and stirring was continued. 10.5 g of the primary mixture, 45 g of a pore-forming agent, and 12.0 g of yttrium oxide were added, mixed evenly, and filtered, washed, and dried to obtain a composite material;

[0087] The polyimide solution is a mixture of 5.0 g of polyimide and 100 g of N,N-dimethylformamide;

[0088] The pore-forming agent is polymethyl methacrylate with a particle size of 250 nm;

[0089] The particle size of the yttrium oxide is 180 nm;

[0090] (4) Preparation of green body

[0091] The composite material was placed in a mold for forming, and then the temperature was raised to 640°C in an air atmosphere and kept at this temperature for 2.5 hours to obtain a green body;

[0092] (5) Calcination

[0093] The green body was placed in a calcining furnace, under a nitrogen atmosphere, the pressure was controlled at 0.3 MPa, the temperature was raised to 1700° C., and the heat treatment was carried out for 2.5 hours to obtain a porous silicon nitride ceramic material.

[0094] 2. Sealing treatment

[0095] The aluminum sol was heated to 38°C, and then sprayed on the surface of the porous silicon nitride ceramic material with the aluminum sol. The spraying pressure was controlled to be 0.2 MPa, the spraying distance was 12 cm, and the spraying thickness was 20 μm. After the spraying, the material was dried at room temperature for 15 minutes, then placed in an oven for drying for 30 minutes, and finally the temperature was increased to 560°C at a rate of 1.5°C / min and kept warm for 1.3 hours to obtain a sealed silicon nitride ceramic.

[0096] The aluminum sol is prepared by adding 20 g of aluminum nitrate to 200 g of anhydrous ethanol and stirring until completely dissolved, then adding 2.3 g of deionized water and continuing to stir. After stirring evenly, 10 wt % sodium hydroxide solution is added to adjust the pH value to 5.4, and then 1.0 g of polyethylene glycol 400 is added and stirred for 60 minutes to obtain the aluminum sol.

[0097] 3. Metallization

[0098] (1) Preparation of metallization slurry

[0099] 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 aluminum oxide, and 8.2 g of titanium powder were mixed evenly, and 14 mL of ethyl cellulose, 200 mL of terpineol, and 1.4 g of polyvinyl alcohol were added and stirred evenly to obtain a metallization slurry;

[0100] (2) Spraying

[0101] The metallization slurry was sprayed on the surface of the sealed silicon nitride ceramic. The spraying pressure was controlled to 0.3 MPa and the spraying distance was 18 cm. The wet weight of the coating after spraying was 0.010 g / cm 3After spraying, dry it at 75℃ for 12 minutes, then put it in a high-temperature furnace, increase the temperature to 700℃ at a rate of 5.0℃ / min in an air atmosphere, keep it warm for 20 minutes, then switch to a nitrogen atmosphere, control the pressure to 100Pa, increase the temperature to 880℃ at a rate of 1.5℃ / min, keep it warm for 30 minutes, lower the temperature to 700℃ with the furnace, stop introducing nitrogen, and wait for it to naturally drop to room temperature to obtain metallized ceramics.

[0102] The porous silicon nitride ceramic material was obtained by the method of Example 2, and the density was 0.9 g / cm 3 , bending strength is 64MPa, linear expansion coefficient (RT 1200℃) is 4.5×10 -6 / ℃, the dielectric constant is 2.2, and the loss tangent is 0.003; the antenna cover made of this material can achieve a wave transmittance of 85% within 3GHz.

[0103] The metallized ceramic obtained by the method of Example 2 has a resistance of 45Ω. The bonding strength between the metal and the porous silicon nitride ceramic material after the metallization treatment is tested by the cross-hatch method and is level 0. After testing with a quartz lamp at 1200°C / 1000s, the coating does not show any signs of falling off or cracking, and the bonding strength remains at level 0.

[0104] Example 3 A method for surface metallization of a low dielectric porous silicon nitride ceramic material

[0105] 1. Preparation of porous silicon nitride ceramic materials

[0106] (1) Preparation of activated graphene oxide

[0107] The graphene oxide was treated with oxygen plasma, and the oxygen flow rate of the oxygen plasma treatment was controlled to be 35 sccm, the discharge power was 108 W, the vacuum pressure was 1.6 KPa, and the treatment time was 7.0 min to obtain activated graphene oxide;

[0108] The particle size of the graphene oxide is 160 nm;

[0109] (2) Preparation of epoxidized alumina fibers

[0110] Alumina fiber was mixed with 6 times its mass of 25wt% hydrochloric acid solution, the temperature was increased to 62°C, the mixture was stirred at this temperature for 3.8 hours, and the mixture was filtered, washed, and dried to obtain acid-washed alumina fiber. 10.6g of the acid-washed alumina fiber was added to 500g of toluene and uniformly dispersed. 1.5g of 2-bromoisobutyryl bromide and 0.88g of triethylamine were added, the temperature was increased to 60°C, and the mixture was stirred at this temperature for 5.2 hours under a nitrogen atmosphere. 6.6g of allyl glycidyl ether and 3.2g of azobisisobutyronitrile were added, and the mixture was stirred at this temperature for 7.8 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain epoxidized alumina fiber.

[0111] The diameter of the alumina fiber is 65 nm and the length is 0.3 μm;

[0112] (3) Mixing

[0113] 7.6 g of epoxidized alumina fiber was added to 320 g of toluene, and after uniform dispersion, 2.5 g of activated graphene oxide was added, and ultrasonic dispersion was carried out for 35 min at an ultrasonic power of 125 W and an ultrasonic frequency of 32 kHz. After the ultrasonic dispersion was completed, 0.32 g of 4-dimethylaminopyridine was added, stirred evenly, and the temperature was raised to 90 ° C. and the reaction was kept warm for 7.5 h. After the reaction was completed, 108 g of polyimide solution was added and stirred evenly, the temperature was raised to 117 ° C. and the reaction was kept warm for 8.7 h. After the reaction was completed, it was filtered, washed, and dried to obtain a primary mixture; 93 g of α-silicon nitride particles were mixed with 600 g of anhydrous ethanol, stirred evenly, 2.5 g of polyvinyl pyrrolidone and 1.5 g of sodium lauryl sulfate were added, and stirring was continued. 10.8 g of the primary mixture, 48 g of a pore-forming agent, and 12.4 g of yttrium oxide were added, mixed evenly, and filtered, washed, and dried to obtain a composite material;

[0114] The polyimide solution is a mixture of 6.0 g of polyimide and 100 g of N,N-dimethylformamide;

[0115] The pore-forming agent is polymethyl methacrylate with a particle size of 260 nm;

[0116] The particle size of the yttrium oxide is 200 nm;

[0117] (4) Preparation of green body

[0118] The composite material was placed in a mold for forming, and then the temperature was raised to 642°C in an air atmosphere and kept at this temperature for 2.4 hours to obtain a green body;

[0119] (5) Calcination

[0120] The green body was placed in a calcining furnace, under a nitrogen atmosphere, the pressure was controlled to 0.5 MPa, the temperature was increased to 1750° C., and the heat preservation treatment was carried out for 2.0 hours to obtain a porous silicon nitride ceramic material.

[0121] 2. Sealing treatment

[0122] The aluminum sol was heated to 40°C, and then sprayed on the surface of the porous silicon nitride ceramic material with the aluminum sol. The spraying pressure was controlled to be 0.3 MPa, the spraying distance was 10 cm, and the spraying thickness was 22 μm. After the spraying, the material was dried at room temperature for 18 minutes, then placed in an oven for drying for 32 minutes, and finally the temperature was increased to 565°C at a rate of 1.6°C / min and kept warm for 1.4 hours to obtain a sealed silicon nitride ceramic.

[0123] The aluminum sol is prepared by adding 23 g of aluminum nitrate to 200 g of anhydrous ethanol and stirring until completely dissolved, then adding 2.5 g of deionized water and continuing to stir. After stirring evenly, 12 wt % sodium hydroxide solution is added to adjust the pH value to 5.7, and then 1.2 g of polyethylene glycol 400 is added and stirred for 65 minutes to obtain the aluminum sol.

[0124] 3. Metallization

[0125] (1) Preparation of metallization slurry

[0126] 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 were mixed evenly, and 16 mL of ethyl cellulose, 206 mL of terpineol, and 1.7 g of polyvinyl alcohol were added and stirred evenly to obtain a metallization slurry;

[0127] (2) Spraying

[0128] The metallization slurry was sprayed on the surface of the sealed silicon nitride ceramic. The spraying pressure was controlled at 0.4 MPa and the spraying distance was 20 cm. The wet weight of the coating after spraying was 0.012 g / cm 3 After spraying, dry it at 80℃ for 10 minutes, then put it in a high-temperature furnace, and in an air atmosphere, increase the temperature to 720℃ at a rate of 6.0℃ / min, keep it warm for 18 minutes, then switch to a nitrogen atmosphere, control the pressure to 110Pa, increase the temperature to 900℃ at a rate of 1.7℃ / min, keep it warm for 28 minutes, lower the temperature to 720℃ with the furnace, stop introducing nitrogen, and wait for it to naturally cool to room temperature to obtain metallized ceramics.

[0129] The porous silicon nitride ceramic material was obtained by the method of Example 3, and the density was 1.1 g / cm 3 , bending strength is 60MPa, linear expansion coefficient (RT 1200℃) is 4.7×10 -6 / ℃, the dielectric constant is 2.4, and the loss tangent is 0.008; the antenna cover made of this material can achieve a wave transmittance of 78% within 3GHz.

[0130] The metallized ceramic obtained by the method of Example 3 has a resistance of 50Ω. The bonding strength between the metal and the porous silicon nitride ceramic material after the metallization treatment is tested by the cross-hatch method and is level 0. After testing with a quartz lamp at 1200°C / 1000s, the coating does not show any signs of falling off or cracking, and the bonding strength remains at level 0.

[0131] Comparative Example 2.1

[0132] The following changes are made based on Example 2:

[0133] (1) In the process of preparing porous silicon nitride ceramic material, the step of preparing epoxidized alumina fiber is omitted;

[0134] (2) The mixing step is as follows: add 7.4g of alumina fiber to 300g of toluene, disperse evenly, add 2.3g of activated graphene oxide, and ultrasonically disperse for 30min at an ultrasonic power of 120W and an ultrasonic frequency of 30kHz. After the ultrasonic dispersion is completed, filter, wash, and dry to obtain a primary mixed material; mix 90g of α-silicon nitride particles with 600g of anhydrous ethanol, stir evenly, add 2.2g of polyvinyl pyrrolidone and 1.3g of sodium lauryl sulfate, continue to stir evenly, add 10.5g of the primary mixed material, 45g of a pore-forming agent, and 12.0g of yttrium oxide, mix evenly, filter, wash, and dry to obtain a composite material;

[0135] The diameter of the alumina fiber is 60 nm and the length is 0.2 μm;

[0136] The pore-forming agent is polymethyl methacrylate with a particle size of 250 nm;

[0137] The particle size of the yttrium oxide is 180 nm;

[0138] (3) The rest of the operations are the same.

[0139] The porous silicon nitride ceramic material was obtained by the method of comparative example 2.1, and the density was 1.3 g / cm 3 , bending strength is 48MPa, linear expansion coefficient (RT 1200℃) is 7.4×10 -6 / ℃, the dielectric constant is 3.1, and the loss tangent is 0.016; the antenna cover made of this material can achieve a wave transmittance of 52% within 3GHz.

[0140] Comparative Example 2.1 omitted the epoxidation treatment step of the alumina fiber, and omitted the polyimide component in the mixing step. The porous silicon nitride ceramic material obtained had poor interfacial bonding between the alumina fiber and graphene oxide, and poor mixing uniformity with other components in the mixing step, which affected the homogeneity of the ceramic and reduced the mechanical properties. The interaction between the alumina fiber and other components was weak, the internal polarization phenomenon of the material was obvious, the dielectric constant was high, the dielectric loss was large, and the wave transmittance was low, which affected the comprehensive performance of the porous silicon nitride ceramic material.

[0141] Comparative Example 2.2

[0142] The following changes are made based on Example 2:

[0143] (1) Omit the sealing step; replace the sealed silicon nitride ceramic with porous silicon nitride ceramic material in the spraying step of the metallization process;

[0144] (2) The rest of the operations are the same.

[0145] The metallized ceramic obtained by the method of Comparative Example 2.2 has a resistance of 72Ω. The bonding strength between the metal and the porous silicon nitride ceramic material after metallization treatment is tested by the cross-hatch method and is level 2. After testing with a quartz lamp at 1200℃ / 1000s, the coating shows large-scale shedding and cracking, and the bonding strength is level 4.

[0146] Comparative Example 2.2 omits the sealing step, and there are many unfilled pores in the porous silicon nitride ceramic material. When spraying the metallization slurry, it is difficult for the metal particles to form a good connection at the pores, resulting in a discontinuous conductive path and the presence of many areas with high resistance. In addition, the presence of pores reduces the contact area between the metallization layer and the porous silicon nitride ceramic material, weakens the bonding force, and reduces the stability of the metallization layer.

[0147] Unless otherwise specified, all ratios and percentages described in the present invention are by mass.

[0148] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for surface metallization of a low dielectric porous silicon nitride ceramic material, characterized in that: The method comprises the steps of preparing porous silicon nitride ceramic material, sealing pores and metallization; The preparation of the porous silicon nitride ceramic material includes the steps of preparing activated graphene oxide, preparing epoxidized alumina fibers, mixing materials, preparing green compacts, and calcining; The steps of preparing the epoxidized alumina fiber are as follows: adding the acid-washed alumina fiber into toluene, uniformly dispersing the alumina fiber, adding 2-bromoisobutyryl bromide and triethylamine, raising the temperature to 56-60° C., and keeping the temperature under a nitrogen atmosphere for a reaction of 4.8-5.2 hours; then adding allyl glycidyl ether and azobisisobutyronitrile, and keeping the temperature under a nitrogen atmosphere for a reaction of 7.8-8.2 hours to obtain the epoxidized alumina fiber; The sealing treatment step is to heat the aluminum sol to 36-40° C., then spray the aluminum sol on the surface of the porous silicon nitride ceramic material, dry it, and then keep it at 556-565° C. for 1.2-1.4 hours to obtain the sealed silicon nitride ceramic.

2. The method for surface metallization of a low dielectric porous silicon nitride ceramic material according to claim 1, characterized in that: The step of preparing activated graphene oxide comprises 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 method for surface metallization of a low dielectric porous silicon nitride ceramic material according to claim 1, characterized in that: In the step of preparing the epoxidized alumina fiber, the mass ratio of the acid-washed 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 acid-washed alumina fiber comprises mixing the alumina fiber with 4-6 times the mass of a 20-25wt% hydrochloric acid solution, raising the temperature to 56-62°C, keeping the temperature and stirring for 3.8-4.2 hours, filtering, washing, and drying to obtain the acid-washed alumina fiber; The diameter of the alumina fiber is 55-65 nm, and the length is 0.1-0.3 μm.

4. The method for surface metallization of a low dielectric porous silicon nitride ceramic material according to claim 1, characterized in that: The mixing step comprises the following steps: adding epoxidized alumina fiber to toluene, dispersing the fiber uniformly, adding activated graphene oxide, performing ultrasonic dispersion for 26-35 minutes, with an ultrasonic power of 115-125 W and an ultrasonic frequency of 28-32 kHz; adding 4-dimethylaminopyridine after the ultrasonic dispersion is completed, stirring uniformly, increasing the temperature to 86-90° C., and keeping the temperature for reaction for 7.0-7.5 hours; adding polyimide solution after the reaction is completed, stirring uniformly, increasing the temperature to 112-117° C., and keeping the temperature for reaction for 8.2-8.7 hours; filtering, washing, and drying after the reaction is completed to obtain a primary mixture; and mixing α-silicon nitride particles with anhydrous ethanol, stirring uniformly, adding polyvinyl pyrrolidone and sodium lauryl sulfate, continuing to stir uniformly, adding the primary mixture, a pore-forming agent, and yttrium oxide, mixing uniformly, and filtering, washing, and drying to obtain a composite material.

5. The method for surface metallization of a low dielectric porous silicon nitride ceramic material according to claim 4, characterized in that: The mass ratio of the toluene, epoxidized alumina fiber, 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 mixture of polyimide and N,N-dimethylformamide, and the mass ratio of the polyimide to 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, anhydrous ethanol, polyvinyl pyrrolidone, sodium lauryl sulfate, primary mixed 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.

6. The method for surface metallization of a low dielectric porous silicon nitride ceramic material according to claim 1, characterized in that: The green body preparation step comprises placing the composite material in a mold for forming, then raising the temperature to 636-642° C. in an air atmosphere, and heat-treating for 2.4-2.6 hours to obtain a green body; The calcination step comprises placing the green body in a calcination furnace, controlling the pressure at 0.2-0.5 MPa under a nitrogen atmosphere, raising the temperature to 1650-1750° C., and maintaining the temperature for 2.0-3.0 hours to obtain a porous silicon nitride ceramic material.

7. The method for surface metallization of a low dielectric porous silicon nitride ceramic material according to claim 1, characterized in that: In the sealing treatment step, the aluminum sol is sprayed, and the spraying pressure is controlled to be 0.1-0.3 MPa, the spraying distance is 10-14 cm, and the spraying thickness is 18-22 μm; The aluminum sol is prepared by adding aluminum nitrate to anhydrous ethanol and stirring until completely dissolved, adding deionized water and continuing to stir, stirring evenly, adding 8-12 wt % sodium hydroxide solution to adjust the pH value to 5.2-5.7, and then adding 0.8-1.2 g of polyethylene glycol 400 and stirring for 55-65 minutes to obtain the aluminum sol; The mass ratio of the anhydrous ethanol, aluminum nitrate and deionized water is 200:18-23:2.0-2.

5.

8. The method for surface metallization of a low dielectric porous silicon nitride ceramic material according to claim 1, characterized in that: The metallization step includes preparing metallization slurry and spraying steps; The step of preparing the metallization slurry is to mix platinum powder, chromium powder, nickel powder, silicon dioxide, aluminum oxide, and titanium powder uniformly, add ethyl cellulose, terpineol, and polyvinyl alcohol, and stir uniformly to obtain the metallization slurry; 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 47.0-48.0g:11.8-12.3g:1.2-1.5g:2.6-3.0g:3.0-3.4g:8.0-8.5g:13-16mL:195-206mL:1.2-1.7g.

9. The 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 the metallization slurry on the surface of the sealed silicon nitride ceramic, control the spraying pressure to 0.2-0.4 MPa, spray distance to 15-20 cm, and the wet weight of the coating after spraying is 0.008-0.012 g / cm 3 After spraying, dry it at 70-80℃ for 10-15min, then put it in a high-temperature furnace, and in an air atmosphere, increase the temperature to 680-720℃ at a rate of 4.0-6.0℃ / min, keep it warm for 18-22min, then switch to a nitrogen atmosphere, control the pressure to 90-110Pa, increase the temperature to 850-900℃ at a rate of 1.2-1.7℃ / min, keep it warm for 28-35min, and then reduce the temperature to 680-720℃ with the furnace, stop introducing nitrogen, and wait for it to naturally decrease to room temperature to obtain metallized ceramics.