A broadband transparent sandwich structure silicon nitride-based ceramic material and its preparation method

Abstract

This invention discloses a broadband transparent silicon nitride-based ceramic material with a sandwich structure and its preparation method. The broadband transparent silicon nitride-based ceramic material includes an upper surface layer, a lower surface layer, and a silicon nitride core layer located between the upper and lower surface layers, connecting them. The microstructure of the silicon nitride core layer, the upper surface layer, and the lower surface layer is a β-Si3N4 columnar grain overlap network and intergranular micropores. The porosity of the upper and lower surface layers is lower than that of the silicon nitride core layer. The dielectric constant of the upper and lower surface layers is 3.8–4.6, and the thickness is 0.8–2.2 mm. The dielectric constant of the silicon nitride core layer is 2.0–3.0. The interfacial bonding strength between the upper and lower surface layers and the silicon nitride core layer is ≥20 MPa. This invention achieves high-temperature resistance and broadband transparentness of a single ceramic material, with a long-term temperature resistance of up to 1400℃ and a dual-band transmittance of ≥80%.

Description

Technical Field

[0001] This invention relates to the field of ceramic wave-transparent materials, specifically to a broadband wave-transparent sandwich structure silicon nitride-based ceramic material and its preparation method. Background Technology

[0002] Ceramic wave-transparent materials are widely used in radar seekers for high-speed aircraft, but their single-layer structure is limited to narrowband wave transmission and cannot meet the new requirements for dual-band / wideband wave transmission development.

[0003] Single-material ceramic wave-transparent materials with adjustable electromagnetic parameters have advantages such as good thermal shock resistance and high load-bearing strength, making them a preferred solution to the above problems. However, due to the difficulty in preparation, an effective solution has not yet been found. Summary of the Invention

[0004] The purpose of this invention is to provide a broadband transparent sandwich structure silicon nitride-based ceramic material and its preparation method, which realizes high temperature resistance and broadband wave transmission of a single ceramic material, with long-term temperature resistance up to 1400℃ and dual-band wave transmittance ≥80%.

[0005] In one aspect, the present invention provides a broadband transparent sandwich structure silicon nitride-based ceramic material, including an upper surface layer, a lower surface layer, and a silicon nitride core layer located between the upper surface layer and the lower surface layer to connect the upper surface layer and the lower surface layer;

[0006] The silicon nitride core layer, upper surface layer, and lower surface layer microstructures are all β-Si3N4 columnar grain overlapping network and intergranular micropores.

[0007] The porosity of both the upper and lower surface layers is lower than that of the silicon nitride core layer;

[0008] The dielectric constant of both the upper and lower surface layers is 3.8–4.6, and the thickness is 0.8–2.2 mm.

[0009] The dielectric constant of the silicon nitride core layer is 2.0 to 3.0;

[0010] The interfacial bonding strength between the upper and lower surface layers and the silicon nitride core layer is ≥20MPa; preferably, the broadband transparent sandwich structure silicon nitride-based ceramic material, after being tested for thermal shock at 1400℃ by air cooling, has a complete structure without brittleness, peeling, or edge chipping; achieving a bandwidth expansion of up to 3GHz and a dual-frequency transmittance of ≥80% for the broadband transparent sandwich structure silicon nitride-based ceramic material.

[0011] The advantages of this invention over the prior art are that, by including β-Si3N4 columnar grains in the silicon nitride core layer, upper surface layer, and lower surface layer, the silicon nitride-based ceramic material in the overall broadband wave-transparent sandwich structure is made of the same type of ceramic material, and the β-Si3N4 ceramic has good wave transmission performance and high temperature resistance; and the staggered arrangement of β-Si3N4 columnar grains at the junctions of the silicon core layer, upper surface layer, and lower surface layer is beneficial to achieving high bonding strength between the silicon nitride core layer and the upper surface layer, and between the silicon nitride core layer and the lower surface layer.

[0012] By ensuring that the porosity of both the upper and lower surface layers is lower than that of the silicon nitride core layer, the dielectric constants of the upper and lower surface layers and the silicon nitride core layer are different. The dielectric constant of the silicon nitride core layer is 2.0 to 3.0, and the dielectric constants of the upper and lower surface layers are 3.8 to 4.6. This results in different wave transmission frequencies between the upper or lower surface layer and the silicon nitride core layer, thereby achieving bandwidth broadening of the silicon nitride-based ceramic material with a broadband wave transmission sandwich structure.

[0013] Ultimately, a broadband transparent sandwich structure silicon nitride-based ceramic material was achieved with a bandwidth of up to 3GHz and a dual-frequency transmittance of ≥80%.

[0014] Furthermore, the density of the upper and lower surface layers is 1.8–2.2 g / cm³. 3 The porosity is 32-45%; the density of the silicon nitride core layer is 0.9-1.6 g / cm³. 3 The porosity is 51-72%.

[0015] Another aspect of the present invention provides a method for preparing a broadband transparent sandwich structure silicon nitride-based ceramic material, comprising the following steps:

[0016] Fabrication of core layer silicon nitride particles;

[0017] The core layer blank is obtained by cold isostatic pressing of the silicon nitride particles;

[0018] Prepare an upper surface slurry and a lower surface slurry; the upper surface slurry includes silicon nitride powder and silicon powder, and the lower surface slurry includes silicon nitride powder and silicon powder;

[0019] An upper surface preform is prepared on the surface of the core preform by 3D printing using an upper surface slurry, resulting in an upper surface-core preform.

[0020] A lower surface blank is prepared by 3D printing using a lower surface slurry on the surface of the core layer blank away from the upper surface blank, thereby obtaining a broadband transparent sandwich structure silicon nitride-based ceramic blank.

[0021] The broadband transparent sandwich structure silicon nitride-based ceramic preform is debinded and then sintered at high temperature under nitrogen atmosphere pressure to obtain a broadband transparent sandwich structure silicon nitride-based ceramic material.

[0022] The advantages of this invention over the prior art are as follows: by fabricating core silicon nitride particles and then isostatically pressing these particles to obtain a core blank, it is beneficial to achieve high internal porosity and through-holes in the core silicon nitride particles. Since the core blank is obtained through cold isostatic pressing, the porosity between the silicon nitride particles in the core blank is reduced, resulting in high internal porosity and high strength in the silicon nitride core layer. Furthermore, the interface does not shrink or shrinks only slightly during sintering, which facilitates uniform interface distribution between the upper and lower surfaces and the silicon nitride core layer, reducing diffuse reflection of light at the interface and avoiding insufficient bandwidth broadening due to diffuse reflection. Simultaneously, the lack of interface shrinkage or minimal shrinkage increases the interlayer bonding strength on both sides of the interface, ultimately contributing to both bandwidth broadening and improved interlayer bonding strength in the finished material.

[0023] The upper and lower surface slurries include silicon nitride powder and silicon powder, which is beneficial to the bonding strength with the silicon nitride core layer. At the same time, the main reason is that the addition of silicon powder will cause the silicon powder to react into silicon nitride during sintering. The molecular weight of silicon powder is relatively increased, which helps to offset the shrinkage phenomenon that occurs during the sintering process.

[0024] The upper and lower surface blanks are prepared on the surface of the core blank using 3D printing technology, so that the porosity and dielectric constant of the upper and lower surface layers are different from those of the silicon nitride core layer, and the internal pores and structure of the upper and lower surface layers are uniform.

[0025] By removing the binder from the broadband transparent sandwich structure silicon nitride-based ceramic preform and then sintering it at high temperature under nitrogen atmosphere pressure, problems such as cracking or damage can be avoided during the sintering process. Most importantly, the removal of binder first creates a large number of pores in the preform, which allows nitrogen to enter the interior of the preform, especially the interlayer interface, during the sintering process. This enables the silicon powder to react with nitrogen to generate silicon nitride during the sintering process, which significantly reduces interface shrinkage and improves the bonding strength between the layers on both sides of the interface.

[0026] Furthermore, the process of preparing the core layer silicon nitride particles includes the following steps: mixing silicon nitride powder, sintering aid, pore-forming agent, polymer monomer, peroxide, NN-methylenebisacrylamide, solvent, and liquid paraffin in a mass ratio of (90-97):(3-10):(5-30):(30-50):(0.05-0.5):(0.015-0.03):(30-50):(3-5) to obtain core layer silicon nitride particle slurry;

[0027] The core layer silicon nitride particle slurry is granulated at 60-80℃, and then heated once to obtain the core layer silicon nitride particles.

[0028] The pore-forming agent includes one of starch, polypropylene microspheres, and polymethyl methacrylate microspheres, with an average particle size of 1μm-5μm.

[0029] The sintering aid includes yttrium oxide and / or lanthanum oxide; the solvent is ethanol and / or methanol; the polymerization monomer includes one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, tetrahydrofuran acrylate, and isobornyl methacrylate.

[0030] The heating process is as follows: under negative pressure, the temperature is raised from room temperature to 80-100℃ at a rate of 7-8℃ / min; from 80-100℃ to 180-220℃ at a rate of 9-10℃ / min; from 180-220℃ to 280-320℃ at a rate of 4-5℃ / min; and from 280-320℃ to 610-650℃ at a rate of 2-3℃ / min.

[0031] The beneficial effects of the previous step are that the core layer silicon nitride particle slurry includes α-silicon nitride powder and sintering aids, wherein the sintering aids include yttrium oxide and / or lanthanum oxide; the silicon nitride core layer includes β-Si3N4 columnar grains with a content greater than or equal to 90%; the polymerizing monomers include one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, tetrahydrofuran acrylate, and isobornyl methacrylate, wherein the polymerizing monomers are monofunctional, resulting in more uniform polymerization, lower crosslinking degree, smaller molecular weight after polymerization, and lower volume shrinkage during granulation, thus facilitating subsequent glue removal, and the obtained core layer silicon nitride particles have high porosity and are through-pores. Simultaneously, the polymerizing monomers do not volatilize or have extremely low volatilization at 60-80℃, thus achieving a uniform internal structure of the obtained particles; however, the polymerizing monomers have a slow curing rate and low viscosity, which is solved by the liquid paraffin, without affecting granulation molding;

[0032] By heating once, the volatiles inside the silicon nitride particles in the core layer volatilize in an orderly manner according to the molecular weight gradient as the temperature increases, thus achieving full volatilization while avoiding problems such as particle cracking or damage.

[0033] By raising the temperature from room temperature to 80-100℃ under negative pressure at a rate of 7-8℃ / min, the heating rate is controlled to be not too fast. This is beneficial for polymerizing a small amount of unpolymerized monomers to improve particle strength and avoid cracking or damage during the subsequent release of large molecular volatiles, while also facilitating the rapid volatilization of small molecules. Raising the temperature from 80-100℃ to 180-220℃ at a rate of 9-10℃ / min allows for rapid volatilization of small and medium-sized molecular volatiles, resulting in numerous open pores and preventing blockage. The process involves several steps: First, the temperature is raised from 180-220℃ to 280-320℃ at a rate of 4-5℃ / min, allowing medium-sized organic molecules to slowly volatilize through the channels created by the volatilization of small molecules, while also facilitating the slow decomposition of larger molecules. Second, the temperature is raised from 280-320℃ to 610-650℃ at a rate of 2-3℃ / min, with further slow heating, allowing large-molecule volatiles to slowly volatilize through the channels created by the volatilization of medium-sized volatiles. This results in core layer silica particles with high porosity, uniform structure, and through-hole pores, while also exhibiting high strength.

[0034] Meanwhile, by not sintering at high temperatures, the silicon dioxide particles in the core layer are made active, which helps to improve the bonding strength between layers when sintered together with the upper and lower surface layers.

[0035] The further steps in preparing the upper surface slurry include the following:

[0036] Silicon nitride powder and silicon powder are mixed at a mass ratio of (20-80):(80-20) to obtain the first mixed powder.

[0037] The first mixed powder, sintering aid, photocurable resin and photoinitiator are mixed in a mass ratio of (90-95):(5-10):(80-100):(1.5-3) to obtain the upper surface slurry;

[0038] The photoinitiator includes: 2-hydroxy-2-methyl-1-phenylpropanone or methyl benzoate;

[0039] The photocurable resin includes a first photocurable resin and a second photocurable resin; preferably, the mass ratio of the first photocurable resin to the second photocurable resin is (50-80):(20-50).

[0040] The beneficial effects of the previous step are that by including silicon powder in the upper surface slurry, the upper surface blank in the subsequent upper surface-core blank contains silicon powder, which helps to avoid shrinkage during sintering and also helps to achieve high bonding strength between the upper surface layer and the silicon nitride core layer; the porosity of the upper surface layer is lower than that of the silicon nitride core layer by the addition ratio of the first mixed powder.

[0041] Furthermore, the first photocurable resin includes one or more of dipropylene glycol diacrylate, tricyclodecanediethanol diacrylate, and 1,6-hexanediol diacrylate;

[0042] The second photocurable resin comprises propoxyglycerol triacrylate and / or ethoxytrimethylolpropane acrylate.

[0043] The advantages of using the first photocurable monomer are as follows: the first photocurable monomer facilitates a faster polymerization rate and better dispersion, and the molecular weight after polymerization is not very large, which is beneficial for subsequent glue removal. At the same time, it produces large pores and low viscosity, which is beneficial for dispersion. The second photocurable monomer has a very fast polymerization rate, which is beneficial for achieving a uniform interface between the obtained upper surface layer and the silicon nitride core layer. It is also beneficial for high bonding strength of the upper surface layer. However, the degree of cross-linking of the organic matter after polymerization is not high, which is beneficial for glue removal. However, the viscosity is relatively high. But by mixing it with the first photocurable monomer, it is beneficial to avoid the problem of uneven dispersion of the upper surface slurry caused by the high viscosity of the second monomer.

[0044] Furthermore, the preparation process of the upper surface slurry also includes the following steps: mixing silicon nitride powder, silicon powder, and sintering aid to obtain a second mixed powder; adding the second mixed powder to a first modification solution, filtering, and drying to obtain a modified second mixed powder;

[0045] The modified second mixed powder, photocurable resin, and photoinitiator are mixed at a mass ratio of 100:(80-100):(1.5-3) to obtain the upper surface slurry.

[0046] The first modified solution comprises a modifier, a second photocurable resin, and a solvent in a mass ratio of (0.1-2):(0.17-0.36):(1-20); the modifier is vinyltriethoxysilane and / or vinyltrimethoxysilane; the solvent is methanol or ethanol.

[0047] The beneficial effect of the previous step is that the α-silicon nitride, silicon powder, and sintering aid are modified first, so that vinyltriethoxysilane and / or vinyltrimethoxysilane are attached to the surface, making it easier for the powder to mix with organic solutions. At the same time, silicon oxide or silicon nitride is sintered. During the modification, a second photocurable resin with high viscosity is attached to the surface, which is beneficial to the uniform mixing when it is mixed with the photocurable resin and photoinitiator in a certain mass ratio. Moreover, the upper surface slurry does not contain solvent, avoiding the problem of high porosity of the upper surface layer.

[0048] Furthermore, before preparing the upper and lower surface blanks on the surface of the core layer blank, the core layer blank is sintered at a final temperature of 1650–1750°C under a nitrogen pressure of 0.3–2 MPa.

[0049] Then, a second modification solution is coated on both surfaces of the core layer blank. The second modification solution comprises silicon powder, sintering aid, pore-forming agent, polymer monomer, peroxide, N,N-methylenebisacrylamide, solvent, and liquid paraffin mixed in a mass ratio of (90-95):(5-10):(30-50):(0.05-0.5):(0.015-0.03):(30-50):(3-5).

[0050] Then, a second heating process is carried out, in which the temperature is raised from room temperature to 60-80℃ at a rate of 9-10℃ / min; and from 60-80℃ to 180-220℃ at a rate of 6-8℃ / min.

[0051] The beneficial effect of the previous step is that by sintering the core layer preform first, it is more conducive to achieving a more uniform interface between the silicon nitride core layer and the upper or lower surface layer, thereby avoiding the phenomenon of diffuse reflection when waves pass through the interface, thus achieving bandwidth broadening of the finished material; by coating the two surfaces of the core layer preform with a second modification solution, even coating with a very thin layer of the second modification solution can achieve uniform coating, and at the same time achieve uniform adhesion of silicon powder to the surface of the silicon nitride core layer, so that when the upper and lower surface preforms are subsequently attached and sintered, the attached carbon powder reacts to form silicon nitride with high bonding strength to the upper and lower surface layers;

[0052] The secondary heating process involves raising the temperature from room temperature to 60-80℃ at a rate of 9-10℃ / min. This process allows the polymerization of monomers to adhere silicon powder and sintering aids to the surface of the silicon nitride core layer. The resulting organic molecules have a relatively low molecular weight, which is beneficial for subsequent debinding. The temperature is then raised from 60-80℃ to 180-220℃ at a rate of 6-8℃ / min, which allows the evaporation of small molecule solvents and unreacted monomers.

[0053] Furthermore, the upper surface-core layer blank is heated three times; the upper surface-core layer blank includes the upper surface blank surface and the core layer blank surface;

[0054] The three heating processes are as follows: the upper surface layer blank is under negative pressure, and the heating temperature of one side of the upper surface layer blank is 50-100℃ lower than that of the core layer blank; the heating process of one side of the upper surface layer blank is as follows: from room temperature to 60-80℃, the heating rate is 4-5℃ / min; from 60-80℃ to 180-220℃, the heating rate is 7-8℃ / min; from 180-220℃ to 280-320℃, the heating rate is 3-4℃ / min; and from 280-320℃ to 510-580℃, the heating rate is 2-3℃ / min.

[0055] The debinding process of the broadband transparent sandwich structure silicon nitride-based ceramic green body is as follows: the broadband transparent sandwich structure silicon nitride-based ceramic green body includes an upper surface green body surface and a lower surface green body surface; the lower surface green body is under negative pressure environment, and the heating temperature of the lower surface green body surface is 50-100℃ lower than the heating temperature of the upper surface green body surface; the heating process of the upper surface green body surface is as follows: from room temperature to 60-80℃, the heating rate is 4-5℃ / min; from 60-80℃ to 180-220℃, the heating rate is 5-6℃ / min; from 180-220℃ to 280-320℃, the heating rate is 2-3℃ / min; from 280-320℃ to 510-580℃, the heating rate is 2-3℃ / min.

[0056] The beneficial effect of the previous step is that, by heating one side of the upper surface blank at a temperature 50-100°C lower than that of the core blank, the outer surface of the upper surface blank and the contact surface with the silicon nitride core layer are heated evenly, avoiding cracking during glue removal. Furthermore, by placing the upper surface blank under negative pressure, it is more conducive to the glue being discharged from the outer surface of the upper surface blank, and the resistance during the discharge process is relatively small, which is conducive to achieving uniform glue discharge.

[0057] The heating process on one side of the upper surface preform involves raising the temperature from room temperature to 60-80℃ at a rate of 4-5℃ / min. This allows unreacted monomers in the upper surface preform to undergo further reaction, increasing its strength. The resulting organic compound has a low molecular weight, which facilitates its volatilization and prevents cracking or damage during this process. The temperature is then raised from 60-80℃ to 180-220℃ at a rate of 7-8℃ / min, which facilitates the release of medium and small molecule volatiles. Rapid evaporation forms through-pores; heating from 180-220℃ to 280-320℃ at a rate of 3-4℃ / min allows larger volatile molecules to slowly evaporate through channels that allow smaller volatile molecules to evaporate, while also facilitating the slow decomposition of large organic molecules; heating from 280-320℃ to 510-580℃ at a rate of 2-3℃ / min allows the decomposed organic matter to evaporate through channels that allow larger volatile molecules to evaporate; thus, it facilitates the formation of uniform through-pores without cracking.

[0058] Furthermore, the debinding process of the broadband transparent sandwich structure silicon nitride-based ceramic preform is as follows: under negative pressure, the temperature is raised from room temperature to 60-80℃ at a rate of 4-5℃ / min; from 60-80℃ to 180-220℃ at a rate of 5-6℃ / min; from 180-220℃ to 280-320℃ at a rate of 2-3℃ / min; and from 280-320℃ to 510-580℃ at a rate of 2-3℃ / min.

[0059] After the binder is removed from the broadband transparent sandwich structure silicon nitride-based ceramic preform, the high-temperature sintering process is as follows: sintering is carried out under a nitrogen atmosphere, with the temperature rising from 1150-1200℃ to 1380-1420℃ at a rate of 0.5-1.5℃ / min, and holding at 1380-1420℃ for 3-5 hours, with a nitrogen pressure of 0.15-0.3MPa; then the temperature is raised from 1380-1420℃ to 1600-1700℃ at a rate of 0.75-1℃ / min, and held at 1600-1700℃ for 1-2 hours, with a nitrogen pressure of 0.3-2.0MPa.

[0060] The beneficial effect of the previous step is that by sintering under nitrogen pressure, at a temperature of 1150-1200℃ and a nitrogen pressure of 0.15-0.3MPa, the silicon powder in the surface material reacts completely with nitrogen to form silicon nitride. The increased micro-volume of the 21.2% nitrided silicon powder fills the material pores, achieving an increase in surface material density while maintaining macroscopic dimensions, thereby improving its dielectric constant. By heating from 1380-1420℃ to 1600-1700℃ at a heating rate of 0.75-1℃ / min, holding at 1600-1700℃ for 1-2 hours, and maintaining a nitrogen pressure of 0.3-2MPa, it is beneficial to achieve the growth of the silicon nitride core layer, upper surface layer, and lower surface layer into a β-Si3N4 columnar grain overlapping network structure, strengthening the interlayer bonding between the core layer and the surface layer, while avoiding the decomposition of silicon nitride at high temperatures. Detailed Implementation

[0061] To better understand the technical solution of the present invention, the present invention will be further described below with reference to specific embodiments.

[0062] Example 1:

[0063] One aspect of this embodiment provides a broadband transparent sandwich structure silicon nitride-based ceramic material, including an upper surface layer, a lower surface layer, and a silicon nitride core layer located between the upper surface layer and the lower surface layer, connecting the upper surface layer and the lower surface layer;

[0064] The silicon nitride core layer, upper surface layer, and lower surface layer all have a β-Si3N4 columnar grain overlap network and intergranular micropores; the thickness of the upper surface layer and the lower surface layer is 1.5 mm.

[0065] The porosity of both the upper and lower surface layers is lower than that of the silicon nitride core layer; the porosity of the silicon nitride core layer is 61.5%, and the porosity of the upper and lower surface layers is 38%; the density of the silicon nitride core layer is 1.25 g / cm³. 3 The density of the upper and lower surface layers is 2 g / cm³. 3 ;

[0066] The dielectric constant of the silicon nitride core layer is 2.6, and the dielectric constants of the upper and lower surface layers are 4.3. The interfacial bonding compressive shear strength between the upper and lower surface layers and the silicon nitride core layer is 26 MPa. After the broadband transparent sandwich structure silicon nitride-based ceramic material is tested at 1400℃ with air cooling thermal shock, the sandwich structure is intact without brittleness, peeling, or edge chipping.

[0067] Another aspect of this embodiment provides a method for preparing a broadband transparent sandwich structure silicon nitride-based ceramic material, including the following steps:

[0068] The process of preparing the core layer silicon nitride particles includes the following steps: mixing silicon nitride powder, sintering aid, pore-forming agent, polymer monomer, peroxide, NN-methylenebisacrylamide, solvent, and liquid paraffin in a mass ratio of 93:7:18:40:0.28:0.22:40:4 to obtain core layer silicon nitride particle slurry.

[0069] The core layer silicon nitride particle slurry is granulated at 70°C and then heated once to obtain the core layer silicon nitride particles.

[0070] The pore-forming agent includes polypropylene microspheres with an average particle size of 3 μm.

[0071] The sintering aid includes yttrium oxide; the solvent is ethanol; the polymerization monomer includes hydroxyethyl acrylate.

[0072] The heating process is as follows: under negative pressure, the temperature rises from room temperature to 90°C at a rate of 7.5°C / min; from 90°C to 200°C at a rate of 9.5°C / min; from 200°C to 300°C at a rate of 4.5°C / min; and from 300°C to 630°C at a rate of 2.5°C / min.

[0073] The core blank is obtained by cold isostatic pressing of the silicon nitride particles, and the forming pressure is 35 MPa.

[0074] Prepare an upper surface slurry and a lower surface slurry; the upper surface slurry includes silicon nitride powder and silicon powder, and the lower surface slurry includes silicon nitride powder and silicon powder; the preparation process of the upper surface slurry includes the following steps:

[0075] Silicon nitride powder and silicon powder are mixed at a mass ratio of 50:50 to obtain the first mixed powder.

[0076] The first mixed powder, sintering aid, photocurable resin, and photoinitiator are mixed in a mass ratio of 93:7:90:2.4 to obtain the upper surface slurry;

[0077] Photoinitiators include: 2-hydroxy-2-methyl-1-phenylpropanone;

[0078] The photocurable resin includes a first photocurable resin and a second photocurable resin; the mass ratio of the first photocurable resin to the second photocurable resin is 65:35; the first photocurable resin includes dipropylene glycol diacrylate and tricyclodecanediethanol diacrylate; the second photocurable resin includes propoxyglycerol triacrylate.

[0079] The method for preparing the lower surface slurry is the same as that for preparing the upper surface slurry.

[0080] An upper surface preform is prepared on the surface of the core preform by 3D printing using an upper surface slurry, resulting in an upper surface-core preform.

[0081] A lower surface blank is prepared by 3D printing using a lower surface slurry on the surface of the core blank away from the upper surface blank, resulting in a broadband transparent sandwich structure silicon nitride-based ceramic blank.

[0082] The broadband transparent silicon nitride-based ceramic preform is debinded and then sintered at high temperature under nitrogen atmosphere pressure to obtain a broadband transparent silicon nitride-based ceramic material. The debinding process of the broadband transparent silicon nitride-based ceramic preform is as follows: under negative pressure, the temperature is increased from room temperature to 70°C at a rate of 4.5°C / min; from 70°C to 200°C at a rate of 5.5°C / min; from 200°C to 300°C at a rate of 2.5°C / min; and from 300°C to 545°C at a rate of 2.5°C / min.

[0083] After the binder is removed from the broadband transparent sandwich structure silicon nitride-based ceramic preform, the high-temperature sintering process is as follows: sintering is carried out under nitrogen pressure, with the temperature rising from 1180℃ to 1400℃ at a rate of 0.8℃ / min and holding for 4 hours at a nitrogen pressure of 0.24MPa; and then rising from 1400℃ to 1650℃ at a rate of 0.85℃ / min and holding at 1650℃ for 1.5 hours at a nitrogen pressure of 1.3MPa.

[0084] Example 2:

[0085] The contents that are the same as in Example 1 will not be repeated here; the different aspects of this embodiment compared to Example 1 are as follows:

[0086] One aspect of this embodiment provides a broadband transparent sandwich structure silicon nitride-based ceramic material, wherein the thickness of both the upper and lower surface layers is 2.1 mm; the porosity of the silicon nitride core layer is 70%, and the porosity of the upper and lower surface layers is 43%; the density of the silicon nitride core layer is 0.97 g / cm³. 3 The density of the upper and lower surface layers is 1.9 g / cm³. 3 ;

[0087] The dielectric constant of the silicon nitride core layer is 2.1, and the dielectric constants of the upper and lower surface layers are 3.9; the interfacial bonding compressive shear strength between the upper and lower surface layers and the silicon nitride core layer is 22 MPa.

[0088] Another aspect of this embodiment provides a method for preparing a broadband transparent sandwich structure silicon nitride-based ceramic material, which further includes the following steps: the preparation process of the upper surface slurry further includes the following steps: mixing silicon nitride powder, silicon powder, and sintering aid in a mass ratio of 70:30:6 to obtain a second mixed powder; adding the second mixed powder to a first modified solution, filtering, and drying to obtain a modified second mixed powder;

[0089] The modified second mixed powder, photocurable resin, and photoinitiator were mixed at a mass ratio of 100:85:1.8 to obtain the upper surface slurry.

[0090] The first modified solution comprises a modifier, a second photocurable resin, and a solvent in a mass ratio of 1.5:0.34:18; the modifier is vinyltriethoxysilane; and the solvent is ethanol.

[0091] The process of making the core layer silicon nitride particles includes the following steps: mixing silicon nitride powder, sintering aid, pore-forming agent, polymer monomer, peroxide, NN-methylenebisacrylamide, solvent, and liquid paraffin in a mass ratio of 91:9:28:35:0.08:0.018:45:3.5 to obtain core layer silicon nitride particle slurry.

[0092] The silicon nitride core granule slurry is granulated at 65°C and then heated once to obtain the silicon nitride core granules.

[0093] The pore-forming agent includes starch, and the average particle size of the pore-forming agent is 4 μm.

[0094] The sintering aid includes lanthanum oxide; the solvent is ethanol; the polymerization monomer includes hydroxypropyl acrylate.

[0095] The heating process is as follows: under negative pressure, the temperature rises from room temperature to 95°C at a rate of 7.8°C / min; from 95°C to 210°C at a rate of 9.8°C / min; from 210°C to 3100°C at a rate of 4.8°C / min; and from 310°C to 640°C at a rate of 2.8°C / min.

[0096] The core blank is obtained by cold isostatic pressing of the silicon nitride particles, and the forming pressure is 40 MPa.

[0097] Photoinitiators include: methyl benzoate;

[0098] The photocurable resin includes a first photocurable resin and a second photocurable resin; the mass ratio of the first photocurable resin to the second photocurable resin is 70:30; the first photocurable resin includes tricyclodecanediethanol diacrylate and 1,6-hexanediol diacrylate; the second photocurable resin includes ethoxytrimethylolpropane acrylate.

[0099] The broadband transparent silicon nitride-based ceramic preform is debinded and then sintered at high temperature under nitrogen atmosphere pressure to obtain a broadband transparent silicon nitride-based ceramic material. The debinding process of the broadband transparent silicon nitride-based ceramic preform is as follows: under negative pressure, the temperature is raised from room temperature to 78°C at a rate of 4.8°C / min; from 78°C to 210°C at a rate of 5.8°C / min; from 210°C to 310°C at a rate of 2.8°C / min; and from 310°C to 570°C at a rate of 2.8°C / min.

[0100] After the binder is removed from the broadband transparent sandwich structure silicon nitride-based ceramic preform, the high-temperature sintering process is as follows: sintering is carried out under nitrogen pressure, with the temperature rising from 1200℃ to 1420℃ at a rate of 1.4℃ / min, held for 3.5h, and the nitrogen pressure being 0.18MPa; then the temperature is raised from 1420℃ to 1680℃ at a rate of 0.95℃ / min, held at 1650℃ for 1h, and the nitrogen pressure being 0.5MPa.

[0101] Example 3:

[0102] The contents that are the same as in Example 1 will not be repeated here; the different aspects of this embodiment compared to Example 1 are as follows:

[0103] One aspect of this embodiment provides a broadband transparent sandwich structure silicon nitride-based ceramic material, wherein the thickness of the upper and lower surface layers is 1.0 mm.

[0104] The porosity of the silicon nitride core layer is 54%, and the porosity of the upper and lower surface layers is 35%; the density of the silicon nitride core layer is 1.5 g / cm³. 3 The density of the upper and lower surface layers is 2.1 g / cm³. 3 ;

[0105] The dielectric constant of the silicon nitride core layer is 2.8, and the dielectric constants of the upper and lower surface layers are 4.5; the interfacial bonding compressive shear strength between the upper and lower surface layers and the silicon nitride core layer is 20 MPa.

[0106] Another aspect of this embodiment provides a method for preparing a broadband transparent sandwich structure silicon nitride-based ceramic material, which further includes the following steps: before preparing an upper surface blank and a lower surface blank on the surface of the core layer blank, the core layer blank is sintered at a final temperature of 1700°C under a nitrogen pressure of 1.5 MPa.

[0107] Then, a second modification solution is coated on both surfaces of the core layer blank. The second modification solution comprises silicon powder, sintering aid, pore-forming agent, polymer monomer, peroxide, NN-methylenebisacrylamide, solvent, and liquid paraffin mixed in a mass ratio of 92.5:7.5:40:0.27:0.22:40:4.

[0108] Then, a second heating process is carried out, in which the temperature is raised from room temperature to 70°C at a rate of 9.5°C / min, and from 70°C to 200°C at a rate of 7°C / min.

[0109] The preparation process of the upper surface slurry also includes the following steps: mixing silicon nitride powder, silicon powder, and sintering aid in a mass ratio of 30:70:8 to obtain a second mixed powder; adding the second mixed powder to the first modified solution, filtering, and drying to obtain a modified second mixed powder;

[0110] The modified second mixed powder, photocurable resin, and photoinitiator were mixed at a mass ratio of 100:80:1.5 to obtain the upper surface slurry.

[0111] The first modified solution comprises a modifier, a second photocurable resin, and a solvent in a mass ratio of 0.5:0.2:8; the modifier is vinyltrimethoxysilane; and the solvent is methanol.

[0112] The upper surface-core layer blank is heated three times; the upper surface-core layer blank includes the upper surface blank surface and the core layer blank surface.

[0113] The three heating processes are as follows: the upper surface blank is under negative pressure, and the heating temperature of one side of the upper surface blank is 80°C lower than that of the core blank; the heating process of one side of the upper surface blank is as follows: from room temperature to 65°C, the heating rate is 4.3°C / min; from 65°C to 190°C, the heating rate is 7.2°C / min; from 190°C to 290°C, the heating rate is 3.2°C / min; and from 290°C to 520°C, the heating rate is 2.2°C / min.

[0114] The debinding process of the broadband transparent sandwich structure silicon nitride-based ceramic green body is as follows: the broadband transparent sandwich structure silicon nitride-based ceramic green body includes an upper surface green body surface and a lower surface green body surface; the lower surface green body is under negative pressure environment, and the heating temperature of the lower surface green body surface is 75°C lower than that of the upper surface green body surface; the heating process of the upper surface green body surface is as follows: from room temperature to 62°C, the heating rate is 4.2°C / min; from 62°C to 185°C, the heating rate is 5.5°C / min; from 1850°C to 285°C, the heating rate is 2.5°C / min; from 285°C to 515°C, the heating rate is 2.2°C / min.

[0115] The process of preparing the core layer silicon nitride particles includes the following steps: mixing silicon nitride powder, sintering aid, pore-forming agent, polymer monomer, peroxide, NN-methylenebisacrylamide, solvent, and liquid paraffin in a mass ratio of 96:8:10:35:0.3:0.028:35:3.8 to obtain the core layer silicon nitride particle slurry.

[0116] The silicon nitride core layer granules are granulated at 75°C and then heated once to obtain the silicon nitride core layer granules.

[0117] The pore-forming agent includes one of starch, polypropylene microspheres, and polymethyl methacrylate microspheres, with an average particle size of 2.5 μm.

[0118] The sintering aid includes yttrium oxide and lanthanum oxide; the solvent is methanol; the polymerization monomer includes isobornyl methacrylate.

[0119] The heating process is as follows: under negative pressure, the temperature rises from room temperature to 85°C at a rate of 7.2°C / min; from 85°C to 185°C at a rate of 9.2°C / min; from 185°C to 285°C at a rate of 4.3°C / min; and from 285°C to 620°C at a rate of 2.2°C / min.

[0120] The core blank is obtained by isostatic pressing of the silicon nitride particles, and the pressing pressure is 35 MPa.

[0121] The photoinitiator includes methyl benzoylformate; the photocurable resin includes a first photocurable resin and a second photocurable resin; the mass ratio of the first photocurable resin and the second photocurable resin is 55:45; the first photocurable resin includes dipropylene glycol diacrylate and 1,6-hexanediol diacrylate.

[0122] The second photocurable resin comprises propoxyglycerol triacrylate and ethoxytrimethylolpropane acrylate.

[0123] After the binder is removed from the broadband transparent sandwich structure silicon nitride-based ceramic green body, the high-temperature sintering process is carried out under nitrogen pressure. When the temperature is ≥1000℃, the nitrogen pressure is 0.95MPa. The temperature is increased from 1410℃ to 1690℃ at a rate of 0.98℃ / min, and held at 1690℃ for 1.8h.

[0124] After the binder is removed from the broadband transparent sandwich structure silicon nitride-based ceramic preform, the high-temperature sintering process is as follows: sintering is carried out under nitrogen pressure, with the temperature rising from 1160℃ to 1390℃ at a rate of 0.6℃ / min and holding for 4.5h at a nitrogen pressure of 0.26MPa; then the temperature is raised from 1390℃ to 1630℃ at a rate of 0.8℃ / min and held at 1650℃ for 2h at a nitrogen pressure of 1.8MPa.

[0125] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, the above-described features have similar functions to (but are not limited to) those disclosed in this application.

Claims

1. A broadband wave-transparent sandwich structure silicon nitride-based ceramic material, characterized in that, It includes an upper surface layer, a lower surface layer, and a silicon nitride core layer located between the upper surface layer and the lower surface layer, connecting the upper surface layer and the lower surface layer; The silicon nitride core layer, upper surface layer, and lower surface layer microstructures are all β-Si3N4 columnar grain overlapping network and intergranular micropores. The porosity of both the upper and lower surface layers is lower than that of the silicon nitride core layer; The dielectric constant of both the upper and lower surface layers is 3.8~4.6, and the thickness is 0.8-2.2mm. The dielectric constant of the silicon nitride core layer is 2.0~3.0; The interfacial bonding strength between the upper and lower surface layers and the silicon nitride core layer is ≥20 MPa; The aforementioned broadband transparent sandwich structure silicon nitride-based ceramic material is prepared by this method: Fabrication of core layer silicon nitride particles; The core layer blank is obtained by cold isostatic pressing of the silicon nitride particles; Prepare an upper surface slurry and a lower surface slurry; the upper surface slurry includes silicon nitride powder and silicon powder, and the lower surface slurry includes silicon nitride powder and silicon powder; An upper surface preform is prepared on the surface of the core preform by 3D printing using an upper surface slurry, resulting in an upper surface-core preform. A lower surface blank is prepared by 3D printing using a lower surface slurry on the surface of the core layer blank away from the upper surface blank, thereby obtaining a broadband transparent sandwich structure silicon nitride-based ceramic blank. The broadband transparent sandwich structure silicon nitride-based ceramic preform is debonded and then sintered at high temperature under nitrogen atmosphere pressure to obtain a broadband transparent sandwich structure silicon nitride-based ceramic material. The process of preparing the core layer silicon nitride particles includes the following steps: mixing silicon nitride powder, sintering aid, pore-forming agent, polymer monomer, peroxide, NN-methylenebisacrylamide, solvent, and liquid paraffin in a mass ratio of (90-97):(3-10):(5-30):(30-50):(0.05-0.5):(0.015-0.03):(30-50):(3-5) to obtain the core layer silicon nitride particle slurry. The silicon nitride core layer granules are granulated at 60-80°C and then heated once to obtain the silicon nitride core layer granules.

2. The broadband transparent sandwich structure silicon nitride-based ceramic material according to claim 1, characterized in that, The density of both the upper and lower surface layers is 1.8~2.2 g / cm³. 3 The porosity is 32-45%; The density of the silicon nitride core layer is 0.9~1.6 g / cm³. 3 The porosity is 51-72%.

3. A method for preparing a broadband transparent sandwich structure silicon nitride-based ceramic material, characterized in that, Includes the following steps: Fabrication of core layer silicon nitride particles; The core layer blank is obtained by cold isostatic pressing of the silicon nitride particles; Prepare an upper surface slurry and a lower surface slurry; the upper surface slurry includes silicon nitride powder and silicon powder, and the lower surface slurry includes silicon nitride powder and silicon powder; An upper surface preform is prepared on the surface of the core preform by 3D printing using an upper surface slurry, resulting in an upper surface-core preform. A lower surface blank is prepared by 3D printing using a lower surface slurry on the surface of the core layer blank away from the upper surface blank, thereby obtaining a broadband transparent sandwich structure silicon nitride-based ceramic blank. The broadband transparent sandwich structure silicon nitride-based ceramic preform is debonded and then sintered at high temperature under nitrogen atmosphere pressure to obtain a broadband transparent sandwich structure silicon nitride-based ceramic material. The process of preparing the core layer silicon nitride particles includes the following steps: mixing silicon nitride powder, sintering aid, pore-forming agent, polymer monomer, peroxide, NN-methylenebisacrylamide, solvent, and liquid paraffin in a mass ratio of (90-97):(3-10):(5-30):(30-50):(0.05-0.5):(0.015-0.03):(30-50):(3-5) to obtain the core layer silicon nitride particle slurry. The silicon nitride core layer granules are granulated at 60-80°C and then heated once to obtain the silicon nitride core layer granules.

4. The method for preparing the broadband transparent sandwich structure silicon nitride-based ceramic material according to claim 3, characterized in that, The pore-forming agent includes one of starch, polypropylene microspheres, and polymethyl methacrylate microspheres, and the average particle size of the pore-forming agent is 1μm-5μm. The sintering aid includes yttrium oxide and / or lanthanum oxide; the solvent is ethanol and / or methanol; the polymerization monomer includes one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, tetrahydrofuran acrylate, and isobornyl methacrylate. The heating process is as follows: under negative pressure, the temperature is raised from room temperature to 80-100℃ at a rate of 7-8℃ / min; from 80-100℃ to 180-220℃ at a rate of 9-10℃ / min; from 180-220℃ to 280-320℃ at a rate of 4-5℃ / min; and from 280-320℃ to 610-650℃ at a rate of 2-3℃ / min.

5. The method for preparing the broadband transparent sandwich structure silicon nitride-based ceramic material according to claim 3, characterized in that, The preparation process of the upper surface slurry includes the following steps: Silicon nitride powder and silicon powder are mixed at a mass ratio of (20-80):(80-20) to obtain the first mixed powder. The first mixed powder, sintering aid, photocurable resin and photoinitiator are mixed in a mass ratio of (90-95):(5-10):(80-100):(1.5-3) to obtain the upper surface slurry; The photoinitiator includes: 2-hydroxy-2-methyl-1-phenylpropanone or methyl benzoate; The photocurable resin includes a first photocurable resin and a second photocurable resin.

6. The method for preparing the broadband transparent sandwich structure silicon nitride-based ceramic material according to claim 5, characterized in that, The first photocurable resin includes one or more of dipropylene glycol diacrylate, tricyclodecanediethanol diacrylate, and 1,6-hexanediol diacrylate; The second photocurable resin comprises propoxyglycerol triacrylate and / or ethoxytrimethylolpropane acrylate.

7. The method for preparing the broadband transparent sandwich structure silicon nitride-based ceramic material according to claim 6, characterized in that, The preparation process of the upper surface slurry also includes the following steps: mixing silicon nitride powder, silicon powder, and sintering aid to obtain a second mixed powder; adding the second mixed powder to a first modified solution, filtering, and drying to obtain a modified second mixed powder; The modified second mixed powder, photocurable resin, and photoinitiator are mixed at a mass ratio of 100:(80-100):(1.5-3) to obtain the upper surface slurry; The first modified solution comprises a modifier, a second photocurable resin, and a solvent in a mass ratio of (0.1-2):(0.17-0.36):(1-20); the modifier is vinyltriethoxysilane and / or vinyltrimethoxysilane; the solvent is methanol or ethanol.

8. The method for preparing the broadband transparent sandwich structure silicon nitride-based ceramic material according to claim 3, characterized in that, Before preparing the upper and lower surface blanks on the surface of the core layer blank, the core layer blank is sintered at a final temperature of 1650-1750°C under a nitrogen pressure of 0.3-2 MPa. Then, a second modification solution is coated on both surfaces of the core layer blank. The second modification solution comprises silicon powder, sintering aid, pore-forming agent, polymer monomer, peroxide, N,N-methylenebisacrylamide, solvent, and liquid paraffin in a mass ratio of (90-95):(5-10):(30-50):(0.05-0.5):(0.015-0.03):(30-50):(3-5). Then, a second heating process is carried out, in which the temperature is raised from room temperature to 60-80℃ at a rate of 9-10℃ / min; and from 60-80℃ to 180-220℃ at a rate of 6-8℃ / min.

9. The method for preparing the broadband transparent sandwich structure silicon nitride-based ceramic material according to claim 3, characterized in that, The upper surface-core layer blank is heated three times; the upper surface-core layer blank includes the upper surface blank surface and the core layer blank surface. The three heating processes are as follows: the upper surface layer blank is under negative pressure, and the heating temperature of one side of the upper surface layer blank is 50-100℃ lower than that of the core layer blank; the heating process of one side of the upper surface layer blank is as follows: from room temperature to 60-80℃, the heating rate is 4-5℃ / min; from 60-80℃ to 180-220℃, the heating rate is 7-8℃ / min; from 180-220℃ to 280-320℃, the heating rate is 3-4℃ / min; and from 280-320℃ to 510-580℃, the heating rate is 2-3℃ / min. The debinding process of the broadband transparent sandwich structure silicon nitride-based ceramic green body is as follows: the broadband transparent sandwich structure silicon nitride-based ceramic green body includes an upper surface green body surface and a lower surface green body surface; the lower surface green body is under negative pressure environment, and the heating temperature of the lower surface green body surface is 50-100℃ lower than the heating temperature of the upper surface green body surface; the heating process of the upper surface green body surface is as follows: from room temperature to 60-80℃, the heating rate is 4-5℃ / min; from 60-80℃ to 180-220℃, the heating rate is 5-6℃ / min; from 180-220℃ to 280-320℃, the heating rate is 2-3℃ / min; from 280-320℃ to 510-580℃, the heating rate is 2-3℃ / min.

10. The method for preparing the broadband transparent sandwich structure silicon nitride-based ceramic material according to claim 4, characterized in that, The debinding process for the broadband transparent sandwich structure silicon nitride-based ceramic preform is as follows: under negative pressure, the temperature is raised from room temperature to 60-80℃ at a rate of 4-5℃ / min; from 60-80℃ to 180-220℃ at a rate of 5-6℃ / min; from 180-220℃ to 280-320℃ at a rate of 2-3℃ / min; and from 280-320℃ to 510-580℃ at a rate of 2-3℃ / min. After the binder is removed from the broadband transparent sandwich structure silicon nitride-based ceramic preform, the high-temperature sintering process is as follows: sintering is carried out under a nitrogen atmosphere, with the temperature rising from 1150-1200℃ to 1380-1420℃ at a rate of 0.5-1.5℃ / min, and holding at 1380-1420℃ for 3-5 hours, with a nitrogen pressure of 0.15-0.3MPa; then the temperature is raised from 1380-1420℃ to 1600-1700℃ at a rate of 0.75-1℃ / min, and held at 1600-1700℃ for 1-2 hours, with a nitrogen pressure of 0.3-2.0MPa.