Core-shell structure composite ceramic substrate and preparation method thereof

Abstract

The application relates to a core-shell structure composite ceramic substrate and a preparation method thereof. The preparation method comprises the following steps: ball milling, drying, high-temperature molten salt reaction of a metal oxide, TiO2, anhydrous ethanol and a NaCl-KCl molten salt to synthesize titanate precursor powder; cleaning the titanate precursor powder and adding deionized water to obtain a titanate aqueous solution; uniformly mixing a surfactant, a co-surfactant, an oil phase and the titanate aqueous solution to obtain a first microemulsion; dropping ammonia water into the first microemulsion to obtain a second microemulsion; adding isopropyl alcohol salt into the second microemulsion to obtain core-shell structure powder; demulsifying the core-shell structure powder with a demulsifier, drying and calcining the core-shell structure powder, and ball milling the core-shell structure powder with zirconium balls, a solvent, a defoaming agent and a dispersing agent to obtain slurry; arranging glue of the slurry green body, sintering the slurry green body, and finally preparing a ceramic substrate with a core-shell structure. The core-shell structure composite ceramic substrate prepared by the application has the advantages of low dielectric loss, high breakdown strength and low sintering temperature.

Description

Technical Field

[0001] The invention belongs to the field of microwave dielectric ceramics for the electronics industry and relates to a core-shell structured composite ceramic substrate and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of modern communication technologies such as mobile communications, satellite communications, the Global Positioning System (GPS), Bluetooth, and wireless local area networks (WLAN), microwave technology is moving towards higher frequencies, namely millimeter and submillimeter waves. The operating frequencies of microwave communication devices are also continuously expanding towards higher frequencies, placing higher demands on the performance of microwave dielectric materials. Miniaturization and integration have become new themes in the development of wireless communication systems and terminals. This requires microwave dielectric materials to have low dielectric loss and high breakdown strength.

[0003] Microwave dielectric ceramics have large dielectric loss and low breakdown strength, which limits their practical application. In order to expand their application areas, the dielectric properties of microwave dielectric ceramics are regulated by compounding them with materials with low dielectric constant and negative temperature coefficient. However, due to the influence of intrinsic loss in the composite ceramic lattice and non-intrinsic loss such as grain size, second phase, impurities, defects, and pores inside the material, the dielectric loss of the composite ceramics is high and the breakdown strength is low, which affects the expansion of the application areas of the composite ceramics. Therefore, reducing the dielectric loss of composite ceramics and improving the breakdown strength is an urgent and significant topic.

[0004] Existing methods for preparing composite ceramics rely primarily on solid-phase processes. Most current research employs this process, which involves ball-milling and mixing multiphase ceramic powders in a predetermined ratio before sintering. However, traditional solid-phase processes suffer from high sintering temperatures, uneven mixing, potential segregation after sintering, high porosity, large grain size, and the susceptibility to impurities. This makes it difficult to meet the demands of miniaturization, micro-scaling, and high performance in electronic components. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for preparing a core-shell structured composite ceramic substrate with low dielectric loss and improved breakdown strength.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a core-shell structure composite ceramic substrate comprises the following steps:

[0008] (1) Using metal oxide and TiO2 as raw materials, using anhydrous ethanol as a medium, and using NaCl-KCl as a molten salt for the first ball milling, drying the slurry, and reacting the molten salt at a first preset temperature to synthesize titanate precursor powder;

[0009] (2) ultrasonically cleaning the titanate precursor powder with deionized water to remove NaCl and KCl, washing until no precipitation is found after titration with AgNO3 solution, and then drying to obtain titanate powder; stirring and mixing the titanate powder with deionized water to form a titanate aqueous solution;

[0010] (3) uniformly mixing the surfactant, the co-surfactant, the oil phase and the titanate aqueous solution to obtain a first microemulsion;

[0011] (4) adding ammonia water dropwise into the first microemulsion to obtain a second microemulsion;

[0012] (5) adding metal isopropylate to the second microemulsion, and performing ultrasonic dispersion at a second preset temperature for a first preset time to generate a core-shell structure powder having a metal hydroxide shell, thereby obtaining a third microemulsion;

[0013] (6) Demulsifying the third microemulsion containing the core-shell structure powder with a demulsifier at a third preset temperature, ultrasonically dispersing the powder to produce a precipitate, and centrifuging and washing the powder to remove the active agent on the particle surface to obtain a composite powder. The composite powder is dried and placed in a tubular furnace, and calcined under an inert gas atmosphere to obtain a core-shell structure ceramic powder.

[0014] (7) Ceramic powder, zirconium balls, solvent, defoamer, dispersant and binder are added to a ball mill in proportion, and the mixture is sieved after a certain period of time after the second ball milling, and vacuum defoamed to obtain a slurry;

[0015] (8) After the slurry is tape-cast, it is cut into green bodies of certain specifications and sizes. The green bodies are debinded and microwave sintered to form ceramic substrates with a core-shell structure.

[0016] The metal oxide is selected from at least one of calcium oxide, barium oxide, magnesium oxide and strontium oxide; the first preset temperature is 900-1100° C., and the high-temperature molten salt reaction time is 1-2 hours.

[0017] The molar ratio of the metal oxide to TiO2 is 1:(0.5-4.5), the time for the first ball milling is 6-10 hours, and the speed of the first ball milling is 200-400 r / min; the volume mass ratio of the anhydrous ethanol to the raw material is (2-3):1, the mass ratio of the molten salt to the raw material is (3-10):1, and the mass ratio of NaCl to KCl is (1-2:1). The time for drying the slurry is 16-24 hours, and the temperature of the drying slurry is 50-60°C.

[0018] The drying time in step (2) is 16 to 24 hours, the drying temperature is 50 to 60° C., the ultrasonic cleaning of the titanate precursor powder is carried out at a temperature of 25 to 35° C., a time of 20 to 30 minutes, a frequency of 20 to 40 kHz, and a power of 120 to 300 W, and the concentration of the AgNO 3 solution is 0.01 to 1 mol / L;

[0019] The molar concentration of the titanate aqueous solution is 0.5 to 1 mol / L.

[0020] The surfactant is selected from at least one of sodium lauryl sulfonate, hexadecyltrimethylammonium bromide, sorbitan monostearate, octadecenoic acid, polyoxyethylene sorbitan monooleate and nonylphenol polyoxyethylene ether; the co-surfactant is selected from at least one of n-hexanol, n-pentanol and n-octanol; the oil phase is selected from at least one of cyclohexane, n-heptane and isooctane, the mass ratio of the surfactant to the oil phase is 3:7, 4:6, 5:5, 6:4 or 7:3, the mass ratio of the surfactant to the co-surfactant is 1:4, 2:3, 3:2 or 4:1, and the mass ratio of the surfactant to the titanate aqueous solution is 3:7, 4:6, 5:5, 6:4 or 7:3;

[0021] The surfactant, co-surfactant, oil phase and titanate aqueous solution are uniformly mixed by ultrasonication;

[0022] The ammonia solution is dripped into the first microemulsion under ultrasonic dispersion at a temperature of 25-35°C, a time of 20-30 minutes, a frequency of 20-40 KHz, and a power of 120-300 W;

[0023] The pH value of the second microemulsion is 8-9.

[0024] The metal isopropoxide is samarium isopropoxide, cerium isopropoxide, copper isopropoxide, neodymium isopropoxide, aluminum isopropoxide or zinc isopropoxide; the molar ratio of the metal isopropoxide to the titanate solution is 7:4, 6:5, 5:6, 4:7 or 3:8;

[0025] The first preset time is 10 to 16 hours, and the second preset temperature is 20 to 100°C.

[0026] The frequency of ultrasonic dispersion at the second preset temperature is 20-40 KHz, and the power is 120-300 W.

[0027] The demulsifier is selected from at least one of acetone, ethyl cellulose, chitosan, α-amylase and β-cyclodextrin; the mass ratio of the demulsifier to the third microemulsion is (0.4-2):1, and the third preset temperature is 20-80°C;

[0028] The ultrasonic dispersion is performed at a third preset temperature for 10 to 30 minutes, at a frequency of 20 to 40 kHz, and at a power of 120 to 300 W;

[0029] The centrifugal speed is 5000-10000 r / min, and the centrifugal time is 5-15 min;

[0030] The composite powder is dried at a temperature of 50 to 60° C. and for a time of 4 to 8 hours.

[0031] The calcination temperature is 500-1000°C, and the calcination time is 1-2 hours;

[0032] The inert gas is Ar gas or nitrogen gas.

[0033] The mass fraction of the ceramic powder is 35-50%, the mass fraction of the solvent is 20-25%, the mass fraction of the defoaming agent is 0-5%, the mass fraction of the dispersant is 14-16%, and the mass fraction of the binder is 15-28%;

[0034] The solvent is methyl ethyl ketone, toluene, xylene, isopropyl alcohol, ethanol, acetone or ethyl acetate;

[0035] The defoaming agent is emulsified silicone oil, n-butanol, tributyl phosphate or n-octanol;

[0036] The dispersant is triethanolamine, ammonium citrate, polyvinyl pyrrolidone or polyacrylate;

[0037] The binder is carboxyethyl cellulose, polyvinyl alcohol, latex or methyl cellulose;

[0038] The mass ratio of the ceramic powder to the zirconium balls is 1:(2-3), the rotation speed of the second ball milling is 150-200 r / min, the time of the second ball milling is 14-24 hours, and the sieve mesh number is 300-500 meshes.

[0039] The binder removal curve of the green body of the ceramic substrate is:

[0040]

[0041] RT is the room temperature during debinding; T1 is 200-400℃; T2 is 900-1000℃.

[0042] The microwave sintering temperature rise curve of the debinded green body is:

[0043]

[0044] Among them, RT is the room temperature during microwave sintering; T3 is the relatively low temperature section temperature; T4 is the microwave sintering temperature; T3 is 200°C-400°C, and T4 is 1100°C-1150°C.

[0045] The green bodies are stacked in piles of 1 to 2 pieces, zirconium oxide powder is spread between the pieces, and they are placed on a support plate in a flat manner for debinding. After debinding, the green bodies are stacked in piles of 1 to 5 pieces, zirconium oxide powder is spread between the pieces, and they are placed on a support plate in a flat manner with a load of 300 to 500 g for sintering.

[0046] The ceramic powder and the composite ceramic substrate have a core-shell structure after debinding and sintering, wherein the shell of the core-shell structure is samarium oxide, cerium oxide, copper oxide, neodymium oxide, aluminum oxide or zinc oxide, the shell thickness is 5 to 20 nm, and the crystal core is at least one of calcium titanate, magnesium titanate, barium titanate and strontium titanate crystals, with an average grain size of 1 to 2 μm;

[0047] The size of the cut green body is (50.8±0.2)×(50.8±0.2)×(0.9±0.1 mm).

[0048] The present invention also provides a core-shell structured composite ceramic substrate, which is prepared according to the preparation method.

[0049] By means of the above technical solution, the present invention has at least the following advantages:

[0050] 1. The composite ceramic substrate prepared by the present invention has low dielectric loss and a high quality factor. The core-shell process can significantly improve the dielectric properties of high-dielectric-constant composite ceramic substrates. The core particles are surrounded by a shell to form a barrier layer. The shell localizes the charge carriers, reducing the loss tangent and conductivity, thereby reducing the dielectric loss of the composite ceramic substrate. The dielectric loss of the sample was tested using a resonant cavity method. For example, using a calcium titanate ceramic substrate at a frequency of 1 kHz, the dielectric loss was reduced from 2% to approximately 0.2%.

[0051] 2. The composite ceramic substrate prepared by the present invention has high breakdown strength. In view of the core-shell structure characteristics of the composite ceramic substrate, the present invention can effectively control the thickness and composition of the shell, the size and uniformity of the crystal nucleus, and the dispersion of the powder by controlling the molar ratio of pure metal oxide and TiO2, the reaction temperature of the titanate molten salt, the composition and ratio of the surfactant, co-surfactant, oil phase, and water phase during the reaction process, the composition and addition amount of the metal isopropoxide, the synthesis temperature and holding time of the shell oxide, the composition and ratio of the demulsifier, the sintering temperature and other parameters, thereby reducing the pores and the probability of containing impurities in the ceramic material, thereby improving the breakdown strength of the composite ceramic substrate after microwave sintering. Taking the calcium titanate ceramic substrate as an example, the breakdown strength is increased from the original 300kV / cm to about 500kV / cm.

[0052] 3. The composite ceramic substrate prepared by the present invention has a low sintering temperature. To address the high sintering temperature of composite ceramic substrates, a wet chemical core-shell process is used to synthesize ceramic powder with high surface activity. The ceramic substrate is then prepared using microwave sintering, maintaining the crystal morphology of the ceramic substrate and thereby reducing the sintering temperature. For example, for a calcium titanate ceramic substrate, the sintering temperature was reduced from 1200°C to 1150°C.

[0053] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention. DETAILED DESCRIPTION

[0054] To further illustrate the technical means and effects employed by the present invention to achieve its intended objectives, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention is provided in conjunction with preferred embodiments. In the following description, different references to "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0055] Example 1

[0056] A method for preparing a core-shell structure composite ceramic substrate comprises the following steps:

[0057] (1) Using analytically pure calcium oxide and TiO2 as raw materials, anhydrous ethanol as a medium, and NaCl-KCl as a molten salt, ball milling at 300 r / min for 8 hours, drying at a temperature of 50°C for 16 hours, drying the slurry, and reacting in a high-temperature molten salt at 1000°C for 1.5 hours to synthesize calcium titanate precursor powder; the molar ratio of calcium oxide to TiO2 is 1:1, the volume mass ratio of the anhydrous ethanol to the raw materials is 2:1, the mass ratio of the molten salt to the raw materials is 3:1, and the mass ratio of NaCl to KCl in the molten salt is 1:1;

[0058] (2) ultrasonically cleaning the calcium titanate precursor powder with deionized water at a temperature of 25° C., a time of 20 min, a frequency of 20 kHz, and a power of 120 W to remove NaCl and KCl, and washing until no precipitation is observed after titration with a 0.02 mol / L AgNO3 solution, and then drying at a temperature of 50° C. for 24 h to obtain calcium titanate powder; stirring and mixing the calcium titanate powder with deionized water to form a calcium titanate aqueous solution with a concentration of 0.5 mol / L;

[0059] (3) uniformly mixing the surfactant sodium dodecyl sulfate, the co-surfactant n-hexanol, the oil phase cyclohexane and the calcium titanate aqueous solution by ultrasonic dispersion to obtain a first microemulsion; wherein the mass ratio of the surfactant sodium dodecyl sulfate to the co-surfactant n-hexanol is 1:4, the mass ratio of sodium dodecyl sulfate to cyclohexane is 3:7, and the mass ratio of sodium dodecyl sulfate to the titanate aqueous solution is 3:7, and the ultrasonic dispersion is carried out at a temperature of 25°C, a time of 20 minutes, a frequency of 20 kHz, and a power of 120 W;

[0060] In this step, the hydrophilic end of the surfactant combines with water, while the lipophilic end of the surfactant combines with the solvent oil. Under the action of the co-surfactant, the surfactant forms spherical micelles with an oil-enclosed water phase, and the water phase of the spherical micelles contains a titanate core.

[0061] (4) adding ammonia water dropwise into the first microemulsion, and performing ultrasonic dispersion at a temperature of 25°C, a time of 20 min, a frequency of 20 kHz, and a power of 120 W to obtain a second microemulsion with a pH value of 8;

[0062] (5) adding samarium isopropoxide to the second microemulsion and performing ultrasonic dispersion at a temperature of 60°C, a time of 13 hours, a frequency of 20 kHz, and a power of 120 W to obtain a third microemulsion containing a core-shell structure;

[0063] In this step, samarium isopropoxide has a high solubility in the oil phase, and can be fully dispersed in the microemulsion oil phase and fully contacted with the dispersed micelles. The samarium isopropoxide molecules pass through the surfactant membrane layer from the oil phase and diffuse into the aqueous phase. Under the catalysis of ammonia in the aqueous phase, they are fully hydrolyzed and polycondensed, and finally wrapped on the surface of the calcium titanate core, forming a core-shell structure powder with a samarium hydroxide shell.

[0064] The molar ratio of samarium isopropoxide to calcium titanate aqueous solution is 7:4;

[0065] (6) The third microemulsion containing the core-shell structure was demulsified with acetone as a demulsifier at 60°C, with the mass ratio of acetone to the third microemulsion being 0.4:1. Ultrasonic dispersion was performed at a frequency of 20 kHz and a power of 120 W for 10 minutes. After ultrasonic dispersion, a precipitate was precipitated to obtain a mixed solution. The solution was centrifuged at a speed of 5000 r / min for 5 minutes. The mixed solution was washed with ethanol to remove the active agent on the particle surface to obtain a composite powder. The composite powder was dried at 60°C for 4 hours, placed in a tubular furnace, and calcined at 800°C for 1.5 hours under an Ar atmosphere to obtain a ceramic powder with a core-shell structure.

[0066] (7) Ceramic powder, zirconium balls, solvent, defoamer, dispersant, and binder are added to a ball mill in a proportionate manner, with the mass ratio of ceramic powder to zirconium balls being 1:2. The mixture is ball milled at 150 r / min for 16 h, passed through a 400-mesh sieve, and vacuum-defoamed to obtain a slurry.

[0067] The mass fraction of the ceramic powder is 35%, the mass fraction of the solvent methyl ethyl ketone is 25%, the mass fraction of the defoaming agent emulsified silicone oil is 5%, the mass fraction of the dispersant triethanolamine is 15%, and the mass fraction of the binder carboxyethyl cellulose is 20%;

[0068] (8) After the slurry is tape-cast, it is cut into green pieces with a specification size of 50.8×50.8×0.9 mm.

[0069] Two green sheets are stacked in a stack, zirconium oxide powder is spread between the sheets, and the sheets are laid flat on a setter for debinding. After debinding, three green sheets are stacked in a stack, zirconium oxide powder is spread between the sheets, and the sheets are laid flat on a setter with a load of 300 to 500 grams. The green sheets are then sintered on a setter. After debinding and microwave sintering, the green sheets are made into a ceramic substrate with a core-shell structure. The shell of the core-shell structure is samarium oxide with a shell thickness of 20 nm, and the crystal core is calcium titanate crystal with an average grain size of 1 μm.

[0070] The binder removal curve of the green compact is:

[0071] Temperature rising rate holding time

[0072] RT~T1 5℃ / min /

[0073]

[0074] RT is the room temperature during debinding; T1 is 300℃; T2 is 950℃;

[0075] The sintering temperature rise curve of the debinded green body is:

[0076]

[0077] Among them, RT is the room temperature during sintering; T3 is the relatively low temperature section temperature; T4 is the sintering temperature; T3 is 300°C, and T4 is 1100°C.

[0078] Example 2

[0079] A method for preparing a core-shell structure composite ceramic substrate comprises the following steps:

[0080] (1) Using analytically pure strontium oxide and TiO2 as raw materials, anhydrous ethanol as a medium, and NaCl-KCl as a molten salt, ball milling at 400 r / min for 10 hours, drying the slurry at 55°C for 20 hours, and reacting the molten salt at 1100°C for 1 hour to synthesize strontium titanate precursor powder; the molar ratio of strontium oxide to TiO2 is 1:2, the volume mass ratio of the anhydrous ethanol to the raw materials is 2.5:1, the mass ratio of the molten salt to the raw materials is 5:1, and the mass ratio of NaCl to KCl in the molten salt is 1.5:1;

[0081] (2) ultrasonically cleaning the strontium titanate precursor powder with deionized water at a temperature of 30°C, a time of 25 min, a frequency of 25 kHz, and a power of 180 W to remove NaCl and KCl, and cleaning until no precipitation is observed after titration with a 0.05 mol / L AgNO3 solution, drying at a temperature of 55°C for 20 h, and drying to obtain strontium titanate powder; stirring and mixing the strontium titanate powder with deionized water to form a 0.8 mol / L strontium titanate aqueous solution;

[0082] (3) uniformly mixing the surfactant, the co-surfactant, the oil phase and the strontium titanate aqueous solution by ultrasonic dispersion to obtain a first emulsion; wherein the mass ratio of the surfactant to the co-surfactant is 2:3, the mass ratio of the surfactant to the oil phase is 5:5, and the mass ratio of the surfactant to the titanate aqueous solution is 5:5; the ultrasonic dispersion is carried out at a temperature of 30°C, a time of 25 minutes, a frequency of 25 kHz, and a power of 180 W;

[0083] The surfactant is a mixture of cetyltrimethylammonium bromide and nonylphenol polyoxyethylene ether in any proportion;

[0084] The co-surfactant is a mixture of n-pentanol and n-octanol in any proportion;

[0085] The oil phase is isooctane;

[0086] (4) adding ammonia water to the first microemulsion under ultrasonic dispersion at a temperature of 30°C, a time of 25 min, a frequency of 25 kHz, and a power of 180 W to obtain a second microemulsion with a pH value of 9;

[0087] (5) adding copper isopropoxide to the second microemulsion, and performing ultrasonic dispersion at a temperature of 100° C., a frequency of 30 kHz, and a power of 200 W for 10 h to obtain a third microemulsion containing a core-shell structure;

[0088] In this step, copper isopropoxide has a high solubility in the oil phase, and can be fully dispersed in the microemulsion oil phase and fully contacted with the dispersed micelles. The copper isopropoxide molecules pass through the surfactant membrane layer from the oil phase and diffuse into the aqueous phase. Under the catalysis of ammonia in the aqueous phase, they are fully hydrolyzed and polycondensed, and finally coated on the surface of the strontium titanate core, forming a core-shell structure powder with a copper hydroxide shell.

[0089] The molar ratio of the copper isopropoxide to the strontium titanate aqueous solution is 6:5;

[0090] (6) The third microemulsion containing a core-shell structure was demulsified with chitosan as a demulsifier at 80°C, and ultrasonically dispersed at a frequency of 25 kHz and a power of 180 W for 20 minutes. After ultrasonic dispersion, a precipitate was precipitated to obtain a mixed solution, which was centrifuged at a speed of 7000 r / min for 10 minutes. The mixed solution was washed with ethanol to remove the active agent on the surface of the particles to obtain a composite powder. The composite powder was dried at a temperature of 55°C for 6 hours, placed in a tubular furnace, and calcined at 500°C for 2 hours under a nitrogen atmosphere to obtain a ceramic powder with a core-shell structure; the mass ratio of chitosan to the third microemulsion was 1:1;

[0091] (7) Ceramic powder, zirconium balls, solvent, defoamer, dispersant, and binder are added to a ball mill in proportion, with the mass ratio of ceramic powder to zirconium balls being 1:2.5. The mixture is ball milled at 180 r / min for 20 h, passed through a 300-mesh sieve, and vacuum-defoamed to obtain a slurry.

[0092] The mass fraction of the ceramic powder is 40%, the mass fraction of the solvent methyl ethyl ketone is 22%, the mass fraction of the defoaming agent emulsified silicone oil is 1%, the mass fraction of the dispersant triethanolamine is 16%, and the mass fraction of the binder carboxyethyl cellulose is 21%;

[0093] The solvent is isopropyl alcohol;

[0094] The defoaming agent is n-butanol;

[0095] The dispersant is polyacrylate;

[0096] The binder is methyl cellulose;

[0097] (8) After the slurry is tape-cast, it is cut into green pieces with a specification size of 50.6×50.6×0.8 mm.

[0098] The green bodies are stacked one piece at a time and laid flat on a setter for debinding. After debinding, the green bodies are stacked five pieces at a time, zirconium oxide powder is spread between the pieces, and the green bodies are laid flat on a setter with a load of 300 to 500 grams. The green bodies are sintered after debinding and microwave sintering to produce a ceramic substrate with a core-shell structure. The shell of the core-shell structure is copper oxide with a thickness of 15 nm, and the crystal core is strontium titanate crystal with an average grain size of 1.5 μm.

[0099] The binder removal curve of the green compact is:

[0100]

[0101] RT is the room temperature during debinding; T1 is 200℃; T2 is 900℃;

[0102] The sintering temperature rise curve of the debinded green body is:

[0103]

[0104] Among them, RT is the room temperature during sintering; T3 is the relatively low temperature section temperature; T4 is the sintering temperature; T3 is 400°C, and T4 is 1125°C.

[0105] Example 3

[0106] A method for preparing a core-shell structure composite ceramic substrate comprises the following steps:

[0107] (1) Using the analyzed metal oxides and TiO2 as raw materials, anhydrous ethanol as the medium, and NaCl-KCl as the molten salt with a mass ratio of 2:1, the mixture was ball-milled at 200 r / min for 6 h, dried at a temperature of 60°C for 24 h, and reacted in a high-temperature molten salt at 900°C for 2 h to synthesize titanate precursor powder; the molar ratio of the metal oxide to TiO2 was 1:4, the volume mass ratio of the anhydrous ethanol to the raw materials was 3:1, the mass ratio of the molten salt to the raw materials was 10:1, and the mass ratio of NaCl to KCl in the molten salt was 2:1;

[0108] The metal oxide is a mixture of barium oxide and magnesium oxide in any proportion;

[0109] (2) ultrasonically cleaning the titanate precursor powder with deionized water. The ultrasonic cleaning temperature of the strontium titanate precursor is 35°C, the time is 30 minutes, the frequency is 40 kHz, and the power is 300 W to remove NaCl and KCl. The powder is cleaned until no precipitation is observed after titration with a 1.0 mol / L AgNO3 solution. The powder is then dried at 60°C for 24 hours to obtain a titanate powder. The titanate powder is stirred and mixed with deionized water to form a 1.0 mol / L titanate aqueous solution.

[0110] (3) The surfactant sodium dodecylsulfonate, the co-surfactant, the oil phase and the titanate aqueous solution were uniformly mixed by ultrasonic dispersion to obtain a first microemulsion; the mass ratio of the surfactant to the co-surfactant was 4:1, the mass ratio of the surfactant to the oil phase was 7:3, and the mass ratio of the surfactant to the titanate aqueous solution was 7:3. The ultrasonic dispersion temperature was 35°C, the time was 30 minutes, the frequency was 40 kHz, and the power was 300 W.

[0111] The surfactant is a mixture of octadecenoic acid, sorbitan monostearate and sodium lauryl sulfonate in any proportion;

[0112] The co-surfactant is a mixture of n-hexanol, n-pentanol and n-octanol in any proportion;

[0113] The oil phase is a mixture of cyclohexane and n-heptane in any proportion;

[0114] (4) ultrasonically dispersing the solution at a temperature of 35°C, a time of 30 min, a frequency of 40 kHz, and a power of 300 W, by dripping ammonia water into the first microemulsion to obtain a second microemulsion with a pH value of 8;

[0115] (5) Aluminum isopropoxide is added to the second microemulsion and ultrasonically dispersed for 16 hours at a temperature of 20°C, a frequency of 40 kHz, and a power of 300 W. Aluminum isopropoxide has a large solubility in the oil phase and can be fully dispersed in the oil phase of the microemulsion and fully contacted with the dispersed micelles. Aluminum isopropoxide molecules pass through the surfactant membrane layer from the oil phase and diffuse into the aqueous phase. Under the catalysis of ammonia in the aqueous phase, they are fully hydrolyzed and polycondensed, and finally wrapped on the surface of the titanate core to generate a core-shell structure powder with a metal aluminum hydroxide shell, forming a third microemulsion;

[0116] The molar ratio of the aluminum isopropoxide to the titanate aqueous solution is 3:8;

[0117] (6) The third microemulsion containing the core-shell structure is demulsified with a demulsifier at 20°C, and ultrasonically dispersed at a frequency of 40KHz and a power of 300W for 30 minutes, until a precipitate is precipitated to obtain a mixed solution, which is centrifuged at 10,000 r / min for 15 minutes, and the mixed solution is washed with ethanol to remove the active agent on the particle surface to obtain a composite powder. The composite powder is dried at 60°C for 8 hours, placed in a tube furnace, and calcined at 1000°C for 1 hour under an Ar atmosphere to obtain a ceramic powder with a core-shell structure; the demulsifier is a mixture of ethyl cellulose, α-amylase and β-cyclodextrin in any proportion; the mass ratio of the demulsifier mixture to the third microemulsion is 2:1;

[0118] (7) Ceramic powder, zirconium balls, solvent, defoamer, dispersant, and binder are added to a ball mill in a proportionate manner, with the mass ratio of ceramic powder to zirconium balls being 1:3. The mixture is ball milled at 200 r / min for 24 h, passed through a 500-mesh sieve, and vacuum-defoamed to obtain a slurry.

[0119] The mass fraction of the ceramic powder is 50%, the mass fraction of the solvent methyl ethyl ketone is 20%, the mass fraction of the defoaming agent emulsified silicone oil is 1%, the mass fraction of the dispersant triethanolamine is 14%, and the mass fraction of the binder carboxyethyl cellulose is 15%;

[0120] The solvent is toluene;

[0121] The defoaming agent is n-octanol;

[0122] The dispersant is ammonium citrate;

[0123] The binder is polyvinyl alcohol;

[0124] (8) After the slurry is tape-cast, it is cut into green pieces with a size of 60×60×1 mm.

[0125] Two green sheets are stacked in a stack, zirconium oxide powder is spread between the sheets, and the sheets are laid flat on a setter for debinding. After debinding, four green sheets are stacked in a stack, zirconium oxide powder is spread between the sheets, and the sheets are laid flat on a setter with a load of 300 to 500 grams. The green sheets are then sintered. After debinding and microwave sintering, the green sheets are made into a ceramic substrate with a core-shell structure. The shell of the core-shell structure is aluminum oxide with a thickness of 10 nm, and the crystal core is barium titanate and magnesium titanate crystals with an average grain size of 2 μm.

[0126] The binder removal curve of the green compact is:

[0127]

[0128] RT is the room temperature during debinding; T1 is 400℃; T2 is 1000℃;

[0129] The sintering temperature rise curve of the debinded green body is:

[0130]

[0131]

[0132] Among them, RT is the room temperature during sintering; T3 is the temperature of the relatively low temperature section; T4 is the sintering temperature; T3 is 200°C, and T4 is 1150°C.

[0133] Table 1 Performance comparison between each embodiment and existing magnesium titanate ceramic base

[0134] Project Name Dielectric loss% Breakdown strength kV / cm Sintering temperature ℃ Example 1 0.2 500 1100 Example 2 0.7 389 1125 Example 3 1.0 355 1150 Existing calcium titanate ceramic substrate 2 300 1200

[0135] Among them, the dielectric loss is tested at a frequency of 1kHz, and the insulation resistivity is tested at 500V.

[0136] It can be seen from the performance test indicators in Table 1 that the various performance indicators of Example 1 are the best. The shell thickness of the core-shell structure powder synthesized in Example 1 is the largest. The shell surrounds the core particles to form a barrier layer. The shell localizes the charge carriers, reduces the loss tangent and reduces the electrical conductivity, thereby reducing the dielectric loss of the composite ceramic substrate; at the same time, it reduces the pores and the probability of containing impurities in the ceramic material, thereby improving the breakdown strength of the composite ceramic substrate after sintering; Example 1 synthesizes ceramic powder with high surface activity through a core-shell process using a wet chemical method, and prepares the ceramic substrate by microwave sintering, maintaining the crystal morphology of the ceramic substrate, thereby reducing the sintering temperature.

[0137] The formation mechanism of the core-shell structure composite ceramic substrate of the present invention is as follows: titanium dioxide and metal oxides after ball milling are mixed and titanate powder is synthesized under NaCl-KCl molten salt conditions, and the molten salt acts as a flux and reaction medium. The surfactant, co-surfactant, oil phase and titanate aqueous solution are uniformly mixed, the hydrophilic end of the surfactant is combined with water, and the lipophilic end of the surfactant is combined with the solvent oil. Under the action of the co-surfactant, the surfactant forms oil-in-water spherical micelles, and the aqueous phase of the spherical micelles contains the titanate core; due to the gaps in the surfactant layer surrounding the aqueous dispersed phase and the rapid molecular exchange between the aqueous phase and the oil phase, when ammonia water is dripped into the microemulsion, the ammonia water collides with the spherical micelles and enters the aqueous phase of the micelles, the solubility of isopropyl alcohol salt in the oil phase is relatively large, and the solubility of isopropyl alcohol salt in the microemulsion oil phase is relatively high. The isopropyl alcohol salt molecules are fully dispersed in the phase and in full contact with the dispersed micelles. Under certain conditions, the isopropyl alcohol salt molecules will pass through the surfactant membrane layer from the oil phase and diffuse into the water core. Under the catalysis of ammonia water, they will fully hydrolyze and condense, and finally wrap around the surface of the titanate core to form a metal hydroxide as the shell of the core-shell structure. Subsequently, a demulsifier is added to destroy the surfactant micelle structure. After centrifugal washing, a composite powder is obtained. After calcination, the metal hydroxide on the surface of the crystal core in the composite powder forms a core-shell structure with metal oxide as the shell and titanate as the core. The structure is maintained after subsequent debinding and microwave sintering.

[0138] This invention utilizes a liquid-phase method and a core-shell process to synthesize a composite ceramic substrate with a core-shell structure. This process, performed in the liquid phase, achieves uniform mixing at the atomic / molecular level. It also allows for better distribution of additives within the composite ceramic using low amounts of additives, thereby better controlling grain boundaries and grain size. Furthermore, precise control of the chemical composition and lowering of the sintering temperature ultimately reduce the substrate's dielectric loss and improve its breakdown strength, resulting in a composite ceramic substrate with low dielectric loss, high breakdown strength, and low sintering temperature.

[0139] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present profession can make slight changes or modifications to equivalent embodiments using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a core-shell structure composite ceramic substrate, characterized in that: The following steps are involved: (1) Using metal oxide and TiO2 as raw materials, using anhydrous ethanol as a medium, and using NaCl-KCl as a molten salt for the first ball milling, drying the slurry, and reacting the molten salt at a first preset temperature to synthesize a titanate precursor powder; the metal oxide is selected from at least one of calcium oxide, barium oxide, magnesium oxide, and strontium oxide; (2) ultrasonically cleaning the titanate precursor powder with deionized water to remove NaCl and KCl, washing until no precipitation is found after titration with AgNO3 solution, and then drying to obtain titanate powder; stirring and mixing the titanate powder with deionized water to form a titanate aqueous solution; (3) uniformly mixing the surfactant, the co-surfactant, the oil phase and the titanate aqueous solution to obtain a first microemulsion; the co-surfactant is selected from at least one of n-hexanol, n-pentanol and n-octanol; (4) adding ammonia water dropwise into the first microemulsion to obtain a second microemulsion; (5) adding a metal isopropoxide to the second microemulsion, and performing ultrasonic dispersion at a second preset temperature for a first preset time to generate a core-shell structure powder having a metal hydroxide shell, thereby obtaining a third microemulsion; wherein the metal isopropoxide is samarium isopropoxide, cerium isopropoxide, copper isopropoxide, neodymium isopropoxide, aluminum isopropoxide, or zinc isopropoxide; (6) Demulsifying the third microemulsion containing the core-shell structure powder with a demulsifier at a third preset temperature, ultrasonically dispersing the powder to produce a precipitate, and centrifugally washing the powder to remove the active agent on the particle surface to obtain a composite powder. The composite powder is dried and placed in a tubular furnace, and calcined under an inert gas atmosphere to obtain a core-shell structure ceramic powder. (7) Ceramic powder, zirconium balls, solvent, defoamer, dispersant and binder are added to a ball mill in proportion, and the mixture is sieved after a certain period of time after the second ball milling, and vacuum defoamed to obtain a slurry; (8) After the slurry is tape-cast, it is cut into green bodies of certain specifications and sizes. The green bodies are debinded and microwave sintered to form ceramic substrates with a core-shell structure.

2. The preparation method according to claim 1, characterized in that The first preset temperature is 900-1100° C., and the high-temperature molten salt reaction time is 1-2 hours.

3. The preparation method according to claim 2, characterized in that The molar ratio of the metal oxide to TiO2 is 1:(0.5-4.5), the time for the first ball milling is 6-10 hours, and the speed of the first ball milling is 200-400 r / min; the volume mass ratio of the anhydrous ethanol to the raw material is 2-3:1, the mass ratio of the molten salt to the raw material is (3-10):1, and the mass ratio of NaCl to KCl is (1-2:1). The time for drying the slurry is 16-24 hours, and the temperature of the drying slurry is 50-60°C. The drying time in step (2) is 16 to 24 hours, the drying temperature is 50 to 60° C., the ultrasonic cleaning of the titanate precursor powder is carried out at a temperature of 25 to 35° C., a time of 20 to 30 minutes, a frequency of 20 to 40 kHz, and a power of 120 to 300 W, and the molar concentration of the AgNO 3 solution is 0.01 to 1 mol / L; The molar concentration of the titanate aqueous solution is 0.5 to 1 mol / L.

4. The preparation method according to claim 3, characterized in that The surfactant is selected from at least one of sodium lauryl sulfonate, hexadecyltrimethylammonium bromide, sorbitan monostearate, octadecenoic acid, polyoxyethylene sorbitan monooleate and nonylphenol polyoxyethylene ether; the oil phase is selected from at least one of cyclohexane, n-heptane and isooctane, the mass ratio of the surfactant to the oil phase is 3:7, 4:6, 5:5, 6:4 or 7:3, the mass ratio of the surfactant to the co-surfactant is 1:4, 2:3, 3:2 or 4:1, and the mass ratio of the surfactant to the titanate aqueous solution is 3:7, 4:6, 5:5, 6:4 or 7:3; The surfactant, co-surfactant, oil phase and titanate aqueous solution are uniformly mixed by ultrasonication; The ammonia solution is dripped into the first microemulsion under ultrasonic dispersion at a temperature of 25-35°C, a time of 20-30 minutes, a frequency of 20-40 KHz, and a power of 120-300 W; The pH value of the second microemulsion is 8-9.

5. The preparation method according to claim 4, characterized in that The molar ratio of the metal isopropoxide to the titanate solution is 7:4, 6:5, 5:6, 4:7 or 3:8; The first preset time is 10 to 16 hours, and the second preset temperature is 20 to 100°C; The frequency of ultrasonic dispersion at the second preset temperature is 20-40 KHz, and the power is 120-300 W.

6. The preparation method according to claim 5, characterized in that The demulsifier is selected from at least one of acetone, ethyl cellulose, chitosan, α-amylase and β-cyclodextrin; the mass ratio of the demulsifier to the third microemulsion is (0.4-2):1, and the third preset temperature is 20-80°C; The ultrasonic dispersion is performed at a third preset temperature for 10 to 30 minutes, at a frequency of 20 to 40 kHz, and at a power of 120 to 300 W; The centrifugal speed is 5000-10000 r / min, and the centrifugal time is 5-15 min; The composite powder is dried at a temperature of 50 to 60° C. and for a time of 4 to 8 hours. The calcination temperature is 500-1000°C, and the calcination time is 1-2 hours; The inert gas is Ar gas or nitrogen gas.

7. The preparation method according to any one of claims 1 to 6, characterized in that In step (7), the mass fraction of the ceramic powder is 35-50%, the mass fraction of the solvent is 20-25%, the mass fraction of the defoaming agent is 0-5%, the mass fraction of the dispersant is 14-16%, and the mass fraction of the binder is 15-28%; The solvent is methyl ethyl ketone, toluene, xylene, isopropyl alcohol, ethanol, acetone or ethyl acetate; The defoaming agent is emulsified silicone oil, n-butanol, tributyl phosphate or n-octanol; The dispersant is triethanolamine, ammonium citrate, polyvinyl pyrrolidone or polyacrylate; The binder is carboxyethyl cellulose, polyvinyl alcohol, latex or methyl cellulose; The mass ratio of the ceramic powder to the zirconium balls is 1:(2-3), the rotation speed of the second ball milling is 150-200 r / min, the time of the second ball milling is 14-24 hours, and the sieve mesh number is 300-500 meshes.

8. The preparation method according to claim 7, characterized in that The binder removal curve of the green body of the ceramic substrate is: RT is the room temperature during debinding; T1 is 200-400℃; T2 is 900-1000℃; The microwave sintering temperature rise curve of the debinded green body is: Among them, RT is the room temperature during microwave sintering; T3 is the relatively low temperature section temperature; T4 is the microwave sintering temperature; T3 is 200°C-400°C, and T4 is 1100°C-1150°C.

9. The preparation method according to claim 8, characterized in that The green bodies are stacked in a stack of 1 to 2 pieces, zirconium oxide powder is spread between the pieces, and the green bodies are placed on a setter in a flat manner for debinding. After debinding, the green bodies are stacked in a stack of 1 to 5 pieces, zirconium oxide powder is spread between the pieces, and the green bodies are placed on a setter in a flat manner with a load of 300 to 500 g. The composite ceramic substrate has a core-shell structure after debinding and sintering, wherein the shell of the core-shell structure is samarium oxide, cerium oxide, copper oxide, neodymium oxide, aluminum oxide or zinc oxide, the shell thickness is 5 to 20 nm, and the crystal core is at least one of calcium titanate, magnesium titanate, barium titanate and strontium titanate crystals, with an average grain size of 1 to 2 μm; The size of the cut green body is (50.8±0.2)×(50.8±0.2)×(0.9±0.1 mm).

10. A core-shell structure composite ceramic substrate, characterized in that: It is prepared according to the preparation method according to any one of claims 1 to 9.

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