High-temperature radar infrared stealth SiBCN ceramic foam as well as preparation method and application thereof

Abstract

The invention relates to the technical field of polymer conversion ceramics and stealth functional materials, in particular to high-temperature radar infrared stealth SiBCN ceramic foam as well as a preparation method and application thereof. The specific preparation method comprises the following steps: carrying out polymerization reaction on boron haloalkane, vinyl halogenosilane, diphenyl halogenosilane and disilazane to prepare vinyl-containing polyborosilazane; the preparation method comprises the following steps: carrying out sulfydryl-vinyl photocuring click reaction on vinyl-containing polyborosilazane and dithiol under the action of a photoinitiator to form polyborosilazane wet gel; and performing freeze drying treatment, and performing pyrolysis under a protective atmosphere. The method provided by the invention can solve the problems of high production cost and safety risk of the existing SiBCN ceramic foam preparation process. The SiBCN ceramic foam provided by the invention can keep stable wave-absorbing performance in a wide temperature range, has the characteristic of low thermal conductivity, and can effectively block heat and reduce the surface temperature of a hot end component, thereby effectively inhibiting infrared thermal radiation energy.

Description

Technical Field

[0001] The present invention relates to the technical fields of polymer conversion ceramics and radar / infrared compatible stealth materials, and particularly relates to high-temperature radar infrared stealth SiBCN ceramic foams and a preparation method and application thereof. Background Art

[0002] The core contradiction in realizing the radar / infrared compatible stealth of materials lies in that radar stealth requires high wave absorption performance, such as low reflection at 2 GHz to 18 GHz, while infrared stealth requires low emissivity, such as high reflection at 3 μm to 5 μm / 8 μm to 14 μm, and a high-temperature environment of 400 °C to 800 °C will exacerbate the oxidation of materials and the degradation of electromagnetic properties, resulting in impedance mismatch and a sharp increase in infrared radiation. Based on the Stefan-Boltzmann law, the characteristic that the thermal radiation energy is proportional to the fourth power of the temperature, actively reducing the surface temperature of the material can significantly suppress infrared radiation, but it is necessary to synchronously regulate the temperature-dependent electromagnetic parameters, such as the real part of the dielectric constant or the imaginary part of the dielectric constant, to maintain impedance matching, so as to achieve radar-compatible infrared stealth in a high-temperature environment and solve the problem of multi-spectrum stealth compatibility.

[0003] Ceramic materials, as high-temperature resistant materials, have the characteristics of good high-temperature stability and are widely used in high-temperature environments. They are the preferred materials for preparing high-temperature stealth materials. However, traditional oxide ceramics are limited in their application in the field of high-temperature stealth materials due to disadvantages such as poor dielectric tunability and cumbersome preparation processes. Non-oxide ceramics can withstand extremely high temperatures and usually maintain stable structures and properties at temperatures up to 1000 °C or even higher, and have high hardness and compressive strength. However, the wave absorption performance of non-oxide ceramics may change at high temperatures, and the defects of narrow effective absorption bandwidth and poor dielectric tunability limit the practical application of these materials under high-temperature conditions, especially in environments that require continuous and efficient stealth. Therefore, it is of great significance to develop a non-oxide ceramic that is easy to prepare and has high-efficiency stealth performance in a high-temperature environment.

[0004] As a multiphase system composed of a matrix phase and a gas phase, the internal three-dimensional interconnected pores of the foam material can achieve electromagnetic energy dissipation through multiple scattering of electromagnetic waves and relaxation polarization effects induced by heterogeneous interfaces, significantly improving the broadband radar stealth performance. At the same time, the hierarchical pore topology structure inside the material can construct a low thermal conductivity barrier, effectively suppressing the heat conduction path, thereby weakening the temperature rise on the surface of the hot-end components, and thus suppressing the infrared radiation energy, showing the unique advantage of the synergistic effect of electromagnetic wave absorption and thermal management. However, it is difficult for polymer foams and carbon foams to meet the application requirements in extreme environments such as high temperature. Ceramic foams, with the characteristics of light weight, porosity, and high temperature resistance of the ceramic matrix, have become ideal candidates for the thermal protection-stealth integrated materials of hypersonic aircraft. However, traditional preparation methods, such as the template method and the foaming method, are difficult to achieve molecular-scale structure regulation, resulting in insufficient coordination between the pore structure and the electromagnetic / thermal insulation performance. Polymer-derived ceramics, with the English name Polymer-Derived Ceramics, abbreviated as PDCs, have the characteristics of flexible dielectric tunability and diverse preparation processes. In particular, polymer-derived SiBCN ceramic materials have excellent high-temperature resistance and flexible dielectric tunability. Combining with the porous foam structure, they provide a new idea for solving the problem of insufficient coordination between the pore structure and the electromagnetic / thermal insulation performance.

[0005] Currently, PDCs-SiBCN ceramic foams are mainly obtained by using polyborosilazane as a ceramic precursor, divinylbenzene as a crosslinking agent, and adding Karstedt catalyst through solvothermal reaction, drying, and high-temperature pyrolysis. The Chinese name of Karstedt catalyst is Kast catalyst. Among them, the way to obtain the wet gel depends on the hydrosilylation reaction, and Karstedt catalyst is usually expensive and limited in resources. In the process of large-scale production, the use of Karstedt catalyst will significantly increase the production cost, which will become an important factor restricting the large-scale application of SiBCN ceramic foams. And the solvothermal reaction usually requires high-temperature and high-pressure conditions, which is relatively complex to control and has certain safety risks. In addition, most of the research in the field of PDCs-SiBCN ceramic foams focuses on the study of single properties such as wave absorption or thermal insulation. The research on the integration of wave absorption and thermal insulation properties needs to be explored deeply. Especially in the field of high-temperature radar-compatible infrared stealth, the relevant research is still in its infancy. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a high-temperature radar and infrared stealth SiBCN ceramic foam, a preparation method thereof, and an application. The preparation method of the present invention can significantly shorten the preparation time, improve production efficiency, reduce production costs, and solve the problems of high production costs and complex operation processes existing in the existing preparation process of SiBCN ceramic foam. Moreover, the high-temperature radar and infrared stealth SiBCN ceramic foam prepared by the present invention can break through the limitation of the high intrinsic thermal conductivity of SiBCN ceramic foam, achieve lightweight heat insulation with low thermal conductivity, and thus break through the functional compatibility bottleneck of radar wave absorption and infrared radiation suppression of high-temperature stealth materials.

[0007] To achieve the above object, the technical solution of the present invention is as follows.

[0008] The first aspect of the present invention provides a preparation method of a high-temperature radar and infrared stealth SiBCN ceramic foam, comprising the following steps: Under a solvent system, borane halide, vinyl halosilane, diphenyl halosilane, and disilazane are subjected to a polymerization reaction to obtain vinyl-containing polyborosilazane; under a solvent system, the vinyl-containing polyborosilazane and dithiol are subjected to a thiol-vinyl photocuring click reaction under the action of a photoinitiator to form a crosslinked polyborosilazane wet gel; the polyborosilazane wet gel is subjected to freeze-drying treatment to be converted into a polyborosilazane dry gel, and then pyrolyzed under a protective atmosphere to obtain a high-temperature radar and infrared stealth SiBCN ceramic foam.

[0009] The preparation method of the present invention adopts a thiol-vinyl photocuring click reaction, which can quickly achieve the characteristics of polymer crosslinking. Combining with the freeze-drying technology, through pyrolysis, a high-temperature radar and infrared stealth SiBCN ceramic foam with good structure is formed in a short time. The preparation method of the present invention has the characteristics of rapid reaction and simple operation. Compared with the existing preparation process, it can significantly shorten the preparation time, improve production efficiency, reduce energy consumption, reduce production costs, and the required raw material costs are low, which is suitable for large-scale production, and solves the problems of high production costs and complex operation processes existing in the existing preparation process of SiBCN ceramic foam.

[0010] Preferably, the molar ratio of borane halide, vinyl halosilane, diphenyl halosilane, and disilazane is 1:0.4:0.08 - 0.1:0.748 - 0.77. For example, 1:0.4:0.08:0.748, 1:0.4:0.09:0.759, 1:0.4:0.1:0.77, etc.

[0011] In the present invention, by using vinyl-containing polyborosilazane as a ceramic precursor and adjusting the content of diphenylhalosilane in the ceramic precursor and the ratio of dithiol to the ceramic precursor, the dielectric properties of the SiBCN ceramic foam can be precisely controlled, and thus the wave absorption performance can be regulated. It has good customization ability and can be optimized according to different requirements.

[0012] Preferably, the boron halide alkane is boron trichloride; the vinyl halosilane is at least one of vinyltrichlorosilane and dichloromethylvinylsilane; the diphenylhalosilane is dichlorodiphenylsilane; and the disilazane is hexamethyldisilazane.

[0013] Preferably, the reaction temperature of the polymerization reaction is 170 °C to 200 °C, and the reaction time is 1 h to 3 h; the pyrolysis temperature is 1400 °C. In the present invention, vinyl-containing polyborosilazane is used as a ceramic precursor, and the molecular weight and topological structure of the ceramic precursor are regulated by controlling the reaction temperature and reaction time.

[0014] Preferably, the mass ratio of vinyl-containing polyborosilazane to dithiol is 1.6 to 2:1; for example, 2:1, 5:3, etc.; the mass percentage of the photoinitiator in the total solution of the thiol-vinyl photocuring click reaction is 0.8% to 1%.

[0015] In the present invention, by adjusting the molar ratio of boron halide alkane, vinyl halosilane, diphenylhalosilane and disilazane, as well as the mass ratio of vinyl-containing polyborosilazane to dithiol, the prepared high-temperature radar infrared stealth SiBCN ceramic foam has appropriate dielectric properties, and thus has excellent wave absorption performance. In particular, the regulation of the addition amount of diphenylhalosilane can be used to adjust the dielectric constant of the prepared high-temperature radar infrared stealth SiBCN ceramic foam, and further regulate its wave absorption performance. Preferably, the dithiol is any one of 1,5-pentanedithiol, 1,2-ethanedithiol and 1,6-hexanedithiol; the photoinitiator is trimethylbenzoyl-diphenylphosphine oxide.

[0016] Preferably, the solvent used in the polymerization reaction is cyclohexane or n-hexane; the solvent used in the thiol-vinyl photocuring click reaction is cyclohexane or n-hexane.

[0017] In the second aspect of the present invention, a high-temperature radar infrared stealth SiBCN ceramic foam is provided, which is prepared by using the preparation method of the high-temperature radar infrared stealth SiBCN ceramic foam described in the first aspect.

[0018] In the third aspect of the present invention, an application of the high-temperature radar infrared stealth SiBCN ceramic foam described in the second aspect as a stealth material is provided.

[0019] Preferably, the stealth material is a wide-temperature-range wave-absorbing material, and the temperature range of the wide-temperature-range wave-absorbing material is 25°C to 600°C; the thermal conductivity of the stealth material is <0.1 W / mK. Thus, the stealth material of the present invention has a good heat insulation effect.

[0020] Advantages of the present invention: 1. The preparation method of the present invention adopts a thiol-vinyl photocuring click reaction, which can quickly achieve a crosslinking reaction and form a high-temperature radar and infrared stealth SiBCN ceramic foam with a good structure in a short time. It has the characteristics of fast reaction and simple operation. Compared with the existing preparation process, it can significantly shorten the preparation time, improve production efficiency, reduce energy consumption, lower production costs, and the required raw material costs are low, suitable for large-scale production, solving the problems of high production costs and complex operation processes existing in the existing preparation process of SiBCN ceramic foam.

[0021] 2. Through the pore structure and component design of the present invention, the prepared high-temperature radar and infrared stealth SiBCN ceramic foam can maintain stable wave-absorbing performance in the temperature range of 25°C to 600°C. Especially at high temperatures, the wave-absorbing effect of the high-temperature radar and infrared stealth SiBCN ceramic foam is still prominent, significantly superior to the existing high-temperature wave-absorbing materials, and its wide-temperature-range applicability enables it to be widely used in the demand for high-temperature wave-absorbing materials in fields such as aerospace and national defense.

[0022] 3. The high-temperature radar and infrared stealth SiBCN ceramic foam prepared by the present invention has the characteristic of low thermal conductivity, can effectively block heat, reduce the surface temperature of the hot-end components, and thus effectively inhibit the infrared thermal radiation energy, and is suitable for ultra-high-temperature working conditions such as the thermal protection-stealth integrated skin of hypersonic aircraft and the combustion chamber lining of aero engines.

[0023] 4. The high-temperature radar and infrared stealth SiBCN ceramic foam prepared by the present invention has a high porosity and a suitable pore diameter, can significantly reduce the thermal conductivity, its thermal conductivity is <0.1 W / mK, and the pores form a good isolation effect on heat conduction, thereby improving the heat insulation effect, and effectively inhibiting the infrared radiation energy by controlling the surface temperature, so as to achieve the effect of infrared stealth. Description of the drawings

[0024] Figure 1 It is the reaction equation for preparing vinyl-containing polyborosilazane in the embodiment of the present invention.

[0025] Figure 2 It is the 1H NMR spectrum of the vinyl-containing polyborosilazane prepared in Example 1.

[0026] Figure 3 It is the 11B NMR spectrum of the vinyl-containing polyborosilazane prepared in Example 1.

[0027] Figure 4 X-ray diffraction curves of the high-temperature radar and infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6.

[0028] Figure 5 High-resolution transmission electron micrograph of the high-temperature radar and infrared stealth SiBCN ceramic foam of Example 4.

[0029] Figure 6 Scanning electron micrograph of the high-temperature radar and infrared stealth SiBCN ceramic foam of Example 6.

[0030] Figure 7 Curves of the reflection coefficient varying with frequency at different thicknesses of the high-temperature radar and infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6 at room temperature.

[0031] Figure 8 3D graph of the reflection coefficient of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 4 varying with thickness and frequency.

[0032] Figure 9 2D graph of the reflection coefficient of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 4 varying with thickness and frequency.

[0033] Figure 10 RC curve graph of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 4 at test temperatures from 100 °C to 600 °C.

[0034] Figure 11 Thermal conductivity graphs of the high-temperature radar and infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6.

[0035] Figure 12 Curve graph of the surface temperature detected over time of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 2 at the set temperature of the hot plate. Detailed implementation manners

[0036] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0038] The present invention aims to reduce costs, improve the reaction process, and enhance the microwave absorption performance and infrared stealth performance of the prepared high-temperature radar and infrared stealth SiBCN ceramic foam over a wide temperature range. The present invention provides a method for preparing high-temperature radar and infrared stealth SiBCN ceramic foam using thiol-vinyl photocurable click reaction. Through rapid photocuring reaction, ceramic foam with good pore structure is formed, and SiBCN ceramic foam with excellent microwave absorption performance is obtained through subsequent pyrolysis and sintering processes. The high-temperature radar and infrared stealth SiBCN ceramic foam prepared by the present invention exhibits stable microwave absorption performance over a wide temperature range from 25°C to 600°C and has good heat insulation effect, being particularly suitable for stealth applications in high-temperature and extreme environments.

[0039] The porous structure inside the high-temperature radar and infrared stealth SiBCN ceramic foam prepared by the present invention contributes to the attenuation of electromagnetic waves. The prepared high-temperature radar and infrared stealth SiBCN ceramic foam shows good dielectric temperature stability. The six high-temperature radar and infrared stealth SiBCN ceramic foams prepared in the following examples of the present invention all have certain high-temperature microwave absorption performance. Among them, two prepared high-temperature radar and infrared stealth SiBCN ceramic foams have microwave absorption performance at both room temperature and high temperature, respectively in the range of 300°C - 600°C and 25°C - 400°C, and the effective absorption bandwidth can cover the entire X-band, with the minimum reflection losses being -28.6 dB and -18.7 dB respectively.

[0040] The infrared radiation energy is quartically proportional to the surface temperature of the material. The high-temperature radar and infrared stealth SiBCN ceramic foam prepared by the present invention significantly reduces the heat transfer from high-temperature components to the material surface through a low thermal conductivity of <0.1 W / m·K, thereby reducing the surface temperature and fundamentally reducing the infrared radiation intensity.

[0041] Compared with bulk ceramics, under the same volume, the mass of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared by the present invention is significantly lower than that of bulk ceramics, and the density is reduced by about 70%. This is beneficial to reducing the weight of the high-temperature radar and infrared stealth SiBCN ceramic foam and meeting the industry's requirement for "lightweight" of microwave absorption materials.

[0042] The technical solution of the present invention will be further described below through specific examples.

[0043] In the following examples, unless otherwise specified, the methods are all conventional methods; the reagents and materials, unless otherwise specified, can all be purchased on the market.

[0044] In the following examples, polyborosilazane, with the English name Polyborosilazane, is abbreviated as PBSZ.

[0045] Vinyl polyborosilazane, with the English name Vinyl Polyborosilazane, abbreviated as Vi-PBSZ.

[0046] Hydrogel-polyborosilazane, with the English name Hydrogel-Polyborosilazane, abbreviated as HG-PBSZ.

[0047] Xerogel-polyborosilazane, with the English name Xerogel-Polyborosilazane, abbreviated as X-PBSZ.

[0048] In the following examples, the temperature of the ice-water bath is 0°C ± 2°C, and the normal temperature is 25°C ± 5°C.

[0049] In the following examples, the entire process of preparing the vinyl polyborosilazane solution adopts the double-tube operation technique. The reaction equation is as Figure 1 shown. During the process of preparing the vinyl polyborosilazane solution, the reaction temperature of the polymerization reaction is 170°C to 200°C, and the reaction time is 1 h to 3 h. In the present invention, vinyl polyborosilazane is used as a ceramic precursor, and the molecular weight and topological structure of the ceramic precursor are regulated by controlling the reaction temperature and reaction time. Here, taking the reaction temperature of the polymerization reaction being 190°C and the reaction time being 2 h as an example, the effects of different molar ratios of boron halosilane, vinyl halosilane, diphenyl halosilane, and disilazane on the properties of the prepared high-temperature radar infrared stealth SiBCN ceramic foam are explored.

[0050] Example 1 A preparation method of a high-temperature radar infrared stealth SiBCN ceramic foam includes the following steps: Step 1, preparing a vinyl polyborosilazane solution: After performing three cycles of inert gas on a 500 mL reaction flask, it is placed in an ice-water bath. 100 mL of a 1.0 mol / L boron trichloride-n-hexane solution, 0.1 mol of vinyltrichlorosilane, 0.3 mol of dichloromethylvinylsilane, 0.08 mol of dichlorodiphenylsilane, and 0.748 mol of hexamethyldisilazane are successively added to the reaction flask, so that the molar ratio of boron trichloride, vinyltrichlorosilane, and dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.08:0.748; stir and mix, then raise the reaction temperature to 190°C, keep it for 2 h, then remove the heating device and seal the reaction flask to obtain a vinyl polyborosilazane solution, denoted as Vi-PBSZ solution.

[0051] Step 2, preparing SiBCN hydrogel by thiol-ene click reaction: According to the mass ratio of Vi-PBSZ to 1,5-pentanedithiol of 2:1, place the Vi-PBSZ solution and 1,5-pentanedithiol in a brown glass bottle, and then add trimethylbenzoyl-diphenylphosphine oxide and cyclohexane to obtain a mixed solution. Among them, the mass percentage of trimethylbenzoyl-diphenylphosphine oxide in the mixed solution is 1%, and the mass percentage of cyclohexane in the mixed solution is 79%.

[0052] After mixing well, quickly pour it into a square mold made of polytetrafluoroethylene and cover it with a transparent lid. Place the square mold in an ultraviolet curing box for curing to obtain a polyborosilazane wet gel, denoted as HG-PBSZ.

[0053] Step 3, prepare a high-temperature radar infrared stealth SiBCN ceramic foam: Place HG-PBSZ in a freeze dryer for freeze drying. At this time, HG-PBSZ is converted into a polyborosilazane xerogel, denoted as X-PBSZ.

[0054] Place X-PBSZ in a corundum crucible, and then place the corundum crucible in the center of a tube furnace. Under an argon atmosphere, keep it at 1400 °C for 4 h, set the cooling rate to 2 °C / min, and after cooling to 500 °C, naturally cool to room temperature to obtain a high-temperature radar infrared stealth SiBCN ceramic foam.

[0055] Example 2 A preparation method of a high-temperature radar infrared stealth SiBCN ceramic foam, which is different from Example 1 in that in Step 2, the mass ratio of Vi-PBSZ to 1,5-pentanedithiol is 5:3. The specific preparation method includes the following steps: Step 1, prepare a vinyl-containing polyborosilazane solution: Carry out according to the method of Example 1.

[0056] Step 2, prepare SiBCN wet gel by thiol-ene click reaction: According to the mass ratio of Vi-PBSZ to 1,5-pentanedithiol of 5:3, place the Vi-PBSZ solution and 1,5-pentanedithiol in a brown glass bottle, and then add trimethylbenzoyl-diphenylphosphine oxide and cyclohexane to obtain a mixed solution. Among them, the mass percentage of trimethylbenzoyl-diphenylphosphine oxide in the mixed solution is 1%, and the mass percentage of cyclohexane in the mixed solution is 79%.

[0057] After mixing well, quickly pour it into a square mold made of polytetrafluoroethylene and cover it with a transparent lid. Place the square mold in an ultraviolet curing box for curing to obtain a polyborosilazane wet gel, denoted as HG-PBSZ.

[0058] Step 3, prepare a high-temperature radar infrared stealth SiBCN ceramic foam: Place HG-PBSZ in a freeze dryer for freeze drying. At this time, HG-PBSZ is converted into polyborosilazane xerogel, denoted as X-PBSZ.

[0059] Place X-PBSZ in a corundum crucible, and then place the corundum crucible in the center of a tube furnace. Under an argon atmosphere, keep it at 1400 °C for 4 h, set the cooling rate to 2 °C / min. After cooling to 500 °C, let it cool naturally to room temperature to obtain high-temperature radar and infrared stealth SiBCN ceramic foam.

[0060] Example 3 A method for preparing high-temperature radar and infrared stealth SiBCN ceramic foam, which is different from Example 1 in that in step 1, the molar ratio of boron trichloride, vinyltrichlorosilane, dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.09:0.759. The specific preparation method includes the following steps: Step 1, prepare a vinyl-containing polyborosilazane solution: After subjecting a 500 mL reaction flask to three cycles of inert gas, place it in an ice-water bath. Add 100 mL of a 1.0 mol / L boron trichloride-n-hexane solution, 0.1 mol of vinyltrichlorosilane, 0.3 mol of dichloromethylvinylsilane, 0.09 mol of dichlorodiphenylsilane, and 0.759 mol of hexamethyldisilazane to the reaction flask in sequence, so that the molar ratio of boron trichloride, vinyltrichlorosilane, dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.09:0.759. Stir and mix, then raise the reaction temperature to 190 °C, keep it for 2 h, then remove the heating device and seal the reaction flask to obtain a vinyl-containing polyborosilazane solution, denoted as Vi-PBSZ solution.

[0061] Step 2, prepare SiBCN wet gel by thiol-ene click reaction: According to the mass ratio of Vi-PBSZ to 1,5-pentanedithiol of 2:1, place the Vi-PBSZ solution and 1,5-pentanedithiol in a brown glass bottle, and then add trimethylbenzoyl-diphenylphosphine oxide and cyclohexane to obtain a mixed solution, wherein trimethylbenzoyl-diphenylphosphine oxide accounts for 1% of the mass of the mixed solution, and cyclohexane accounts for 79% of the mass of the mixed solution.

[0062] After mixing well, quickly pour it into a square mold made of tetrafluoroethylene material and cover it with a transparent lid. Place the square mold in an ultraviolet curing box for curing to obtain polyborosilazane wet gel, denoted as HG-PBSZ.

[0063] Step 3, prepare high-temperature radar and infrared stealth SiBCN ceramic foam: The HG-PBSZ was placed in a freeze dryer for freeze drying. At this time, HG-PBSZ was converted into polyborosilazane xerogel, denoted as X-PBSZ.

[0064] The X-PBSZ was placed in a corundum crucible, and then the corundum crucible was placed in the center of a tube furnace. Under an argon atmosphere, it was held at 1400 °C for 4 h, the cooling rate was set at 2 °C / min. After cooling to 500 °C, it was naturally cooled to room temperature to obtain a high-temperature radar and infrared stealth SiBCN ceramic foam.

[0065] Example 4 A preparation method of a high-temperature radar and infrared stealth SiBCN ceramic foam, which is different from Example 1 in that in Step 1, the molar ratio of boron trichloride, vinyltrichlorosilane, dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.09:0.759; in Step 2, the mass ratio of Vi-PBSZ to 1,5-pentanedithiol is 5:3. The specific preparation method includes the following steps: Step 1, preparation of vinyl-containing polyborosilazane solution: After the 500 mL reaction flask was subjected to three cycles of inert gas, it was placed in an ice-water bath. 100 mL of a 1.0 mol / L boron trichloride-n-hexane solution, 0.1 mol of vinyltrichlorosilane, 0.3 mol of dichloromethylvinylsilane, 0.09 mol of dichlorodiphenylsilane, and 0.759 mol of hexamethyldisilazane were successively added to the reaction flask, so that the molar ratio of boron trichloride, vinyltrichlorosilane, dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane was 1:0.4:0.09:0.759. Stir and mix, then raise the reaction temperature to 190 °C, keep it for 2 h, then remove the heating device and seal the reaction flask to obtain a vinyl-containing polyborosilazane solution, denoted as Vi-PBSZ solution.

[0066] Step 2, thiol-ene click reaction to prepare SiBCN wet gel: According to the mass ratio of Vi-PBSZ to 1,5-pentanedithiol of 5:3, the Vi-PBSZ solution and 1,5-pentanedithiol were placed in a brown glass bottle, and then trimethylbenzoyl-diphenylphosphine oxide and cyclohexane were added to obtain a mixed solution, wherein the mass percentage of trimethylbenzoyl-diphenylphosphine oxide in the mixed solution was 1%, and the mass percentage of cyclohexane in the mixed solution was 79%.

[0067] After being fully mixed evenly, it was quickly poured into a square mold made of polytetrafluoroethylene and covered with a transparent lid. The square mold was placed in an ultraviolet curing box for curing to obtain a polyborosilazane wet gel, denoted as HG-PBSZ.

[0068] Step 3, preparation of high-temperature radar and infrared stealth SiBCN ceramic foam: Place HG-PBSZ in a freeze dryer for freeze drying. At this time, HG-PBSZ is converted into polyborosilazane xerogel, denoted as X-PBSZ.

[0069] Place X-PBSZ in a corundum crucible, and then place the corundum crucible in the center of a tube furnace. Under an argon atmosphere, keep it at 1400 °C for 4 h, set the cooling rate to 2 °C / min, and after cooling to 500 °C, cool it naturally to room temperature to obtain high-temperature radar and infrared stealth SiBCN ceramic foam.

[0070] Example 5 A preparation method of high-temperature radar and infrared stealth SiBCN ceramic foam, which is different from Example 1 in that in Step 1, the molar ratio of boron trichloride, vinyltrichlorosilane, dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.1:0.77. The specific preparation method includes the following steps: Step 1, preparation of vinyl-containing polyborosilazane solution: After performing three cycles of inert gas on a 500 mL reaction flask, place it in an ice-water bath. Add 100 mL of 1.0 mol / L boron trichloride-n-hexane solution, 0.1 mol of vinyltrichlorosilane, 0.3 mol of dichloromethylvinylsilane, 0.1 mol of dichlorodiphenylsilane, and 0.77 mol of hexamethyldisilazane to the reaction flask in sequence, so that the molar ratio of boron trichloride, vinyltrichlorosilane, dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.1:0.77. Stir and mix, then raise the reaction temperature to 190 °C, keep it for 2 h, then remove the heating device and seal the reaction flask to obtain a vinyl-containing polyborosilazane solution, denoted as Vi-PBSZ solution.

[0071] Step 2, preparation of SiBCN wet gel by thiol-ene click reaction: According to the mass ratio of Vi-PBSZ to 1,5-pentanedithiol of 2:1, place the Vi-PBSZ solution and 1,5-pentanedithiol in a brown glass bottle, and then add trimethylbenzoyl-diphenylphosphine oxide and cyclohexane to obtain a mixed solution, wherein the mass percentage of trimethylbenzoyl-diphenylphosphine oxide in the mixed solution is 1%, and the mass percentage of cyclohexane in the mixed solution is 79%.

[0072] Step 3, preparation of high-temperature radar and infrared stealth SiBCN ceramic foam: Place HG-PBSZ in a freeze dryer for freeze drying. At this time, HG-PBSZ is converted into polyborosilazane xerogel, denoted as X-PBSZ.

[0073] Place X-PBSZ in a corundum crucible, and then place the corundum crucible in the center of a tube furnace. Under an argon atmosphere, hold at 1400 °C for 4 h, set the cooling rate to 2 °C / min, and after cooling to 500 °C, cool naturally to room temperature to obtain a high-temperature radar and infrared stealth SiBCN ceramic foam.

[0074] Example 6 A method for preparing a high-temperature radar and infrared stealth SiBCN ceramic foam, which is different from Example 1 in that in Step 1, the molar ratio of boron trichloride, vinyltrichlorosilane, dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.1:0.77; in Step 2, the mass ratio of Vi-PBSZ to 1,5-pentanedithiol is 5:3. The specific preparation method includes the following steps: Step 1, prepare a vinyl-containing polyborosilazane solution: After performing three cycles of inert gas on a 500 mL reaction flask, place it in an ice-water bath. Add 100 mL of a 1.0 mol / L boron trichloride-n-hexane solution, 0.1 mol of vinyltrichlorosilane, 0.3 mol of dichloromethylvinylsilane, 0.1 mol of dichlorodiphenylsilane, and 0.77 mol of hexamethyldisilazane to the reaction flask in sequence, so that the molar ratio of boron trichloride, vinyltrichlorosilane, dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.1:0.77. Stir and mix, then raise the reaction temperature to 190 °C, hold for 2 h, remove the heating device and seal the reaction flask to obtain a vinyl-containing polyborosilazane solution, denoted as Vi-PBSZ solution.

[0075] Step 2, prepare a SiBCN wet gel by thiol-ene click reaction: According to the mass ratio of Vi-PBSZ to 1,5-pentanedithiol of 5:3, place the Vi-PBSZ solution and 1,5-pentanedithiol in a brown glass bottle, and then add trimethylbenzoyl-diphenylphosphine oxide and cyclohexane to obtain a mixed solution, where the mass percentage of trimethylbenzoyl-diphenylphosphine oxide in the mixed solution is 1%, and the mass percentage of cyclohexane in the mixed solution is 79%.

[0076] After mixing evenly, quickly pour it into a square mold made of polytetrafluoroethylene and cover it with a transparent lid. Place the square mold in an ultraviolet curing box for curing to obtain a polyborosilazane wet gel, denoted as HG-PBSZ.

[0077] Step 3, prepare a high-temperature radar and infrared stealth SiBCN ceramic foam: Place HG-PBSZ in a freeze dryer for freeze-drying. At this time, HG-PBSZ is converted into a polyborosilazane xerogel, denoted as X-PBSZ.

[0078] Place X-PBSZ in a corundum crucible, then place the corundum crucible in the center of a tubular furnace. Under an argon atmosphere, hold at 1400 °C for 4 h, set the cooling rate to 2 °C / min, and after cooling to 500 °C, naturally cool to room temperature to obtain a high-temperature radar and infrared stealth SiBCN ceramic foam.

[0079] Next, perform performance tests on the high-temperature radar and infrared stealth SiBCN ceramic foams prepared by the preparation methods of Examples 1 to 6.

[0080] Test 1: Using Vi-PBSZ as the ceramic precursor, perform 1H and 11B spectrum tests on the ceramic precursor prepared in Example 1. The results are as Figure 2 and Figure 3 shown.

[0081] The nuclear magnetic resonance hydrogen spectrum and nuclear magnetic resonance boron spectrum of the ceramic precursor in Example 1 indicate that the target structure of the ceramic precursor prepared in Example 1 is consistent with the molecular formula, indicating that the vinyl polyborosilazane was successfully prepared in Example 1 of the present invention.

[0082] Test 2: Perform crystallization behavior tests on the high-temperature radar and infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6 by X-ray diffraction. The results are as Figure 4 shown.

[0083] From Figure 4 the X-ray diffraction curve, it can be seen that obvious broad peaks appear at 2θ = 24° for the high-temperature radar and infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6, corresponding to the graphite lattice plane (002); while at 2θ = 35.5°, 42.8°, 60.8° and 72.1°, they correspond to the crystallization peaks of β-SiC. This proves that SiC crystallization is formed in the high-temperature radar and infrared stealth SiBCN ceramic foam pyrolyzed at 1400 °C.

[0084] Test 3: Analyze the phase composition of the high-temperature radar and infrared stealth SiBCN ceramic foam in Example 4 by high-resolution transmission electron microscopy. The results are as Figure 5 shown.

[0085] From Figure 5 the high-resolution transmission electron microscopy image, a large number of lattice diffraction fringes can be observed, indicating that a large number of nanocrystals are formed inside the high-temperature radar and infrared stealth SiBCN ceramic foam under the pyrolysis conditions at 1400 °C, and the nanocrystals are irregularly distributed inside the high-temperature radar and infrared stealth SiBCN ceramic foam. Figure 5 Regions B and A in show two different widths of lattice fringes, 0.26 nm and 0.35 nm respectively, corresponding to the fringe spacings of SiC crystallization and graphite lattice. This is consistent withFigure 4 The conclusion obtained from the X-ray diffraction pattern is consistent. The nanocrystals are distributed inside the amorphous high-temperature radar and infrared stealth SiBCN ceramic foam, forming more heterogeneous interfaces. Under the action of an alternating electromagnetic field, more polarization sites can be generated, which helps to improve the loss ability of the high-temperature radar and infrared stealth SiBCN ceramic foam to electromagnetic waves.

[0086] Test 4: Use a scanning electron microscope to analyze the microstructure of the high-temperature radar and infrared stealth SiBCN ceramic foam of Example 6.

[0087] From Figure 6 the scanning electron microscope image, it is observed that the high-temperature radar and infrared stealth SiBCN ceramic foam of Example 6 is connected by dendritic ceramic veins, and the formed pores are all open-cell structures. The pore distribution is irregular and the shape is not fixed.

[0088] Test 5: Make a single piece of the high-temperature radar and infrared stealth SiBCN ceramic foam and grind it into a size of 22.86 mm × 10.16 mm, conduct dielectric property tests in the X-band, and calculate the emission coefficient. The test equipment uses a vector network analyzer.

[0089] Figure 7 is the curve of the reflection coefficient of the high-temperature radar and infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6 at room temperature changing with frequency at different thicknesses.

[0090] The reflection coefficient, whose English name is Reflection Coefficient, is abbreviated as RC. When the RC value is smaller, it means that more electromagnetic waves are attenuated. Specifically, when the RC value is below -10 dB in a certain frequency band, then this frequency band is defined as the effective absorption band, abbreviated as EAB, indicating that more than 90% of the electromagnetic waves can be absorbed in this frequency band. The lowest value of the reflection coefficient is denoted as RC min .

[0091] From Figure 7 it can be seen that the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 4 has the best wave absorption performance at room temperature. When the matching thickness is 3.8 mm, the effective absorption band can cover the X-band, and it has the lowest RC value among the high-temperature radar and infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6. At this time, the RC min = -22.4 dB. The 3D diagram of the reflection coefficient of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 4 with respect to thickness and frequency changes is as shown in Figure 8 and the 2D diagram is as shown in Figure 9 .

[0092] From Figure 7It can be seen that the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 1 does not have wave-absorbing performance. Compared with Example 1, the wave-absorbing performance of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 2 has been improved to a certain extent. When the matching thickness is 4.5 mm, the effective absorption band is 2.3 GHz, covering 9.1 GHz to 11.4 GHz. At this time, the RC min =-11.5 dB.

[0093] The high-temperature radar and infrared stealth SiBCN ceramic foams prepared in Example 5 and Example 6 both have certain wave-absorbing performance at room temperature. When the matching thickness of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 5 is 3.8 mm, the effective absorption band can cover the entire X-band; when the matching thickness is 3.5 mm, the effective absorption band of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 6 can cover the entire X-band. At this time, the RC min =-15.5 dB.

[0094] Test 6: Using a vector network analyzer, the RC curves of the high-temperature radar and infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6 were tested at a test temperature of 100 °C to 600 °C by the high-temperature waveguide method to evaluate the wave-absorbing performance of the high-temperature radar and infrared stealth SiBCN ceramic foams. The RC curves of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 4 at a test temperature of 100 °C to 600 °C are as Figure 10 shown.

[0095] As the temperature increases, the loss ability of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 1 to electromagnetic waves increases. At 100 °C, since the dielectric constant is not much different from that at room temperature, it does not have wave-absorbing performance at this time; when the test temperature exceeds 200 °C, it has certain wave-absorbing performance; when the test temperature is 300 °C, the effective absorption band at this time is 3.36 GHz; when the test temperature is 400 °C to 600 °C, the wave-absorbing performance is significantly enhanced, and the effective absorption band can cover the entire X-band. Among them, at 400 °C, it has the lowest RC value. At this time, the matching thickness is 3.9 mm, and the RC min is -29.8 dB.

[0096] As the test temperature increases, the wave-absorbing performance of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 2 first increases and then decreases. When the test temperature is 300 °C to 600 °C, the effective absorption band can cover the entire X-band. Among them, when the test temperature is 400 °C and the matching thickness is 3.7 mm, the RC min is -28.6 dB.

[0097] With the increase of the test temperature, the wave absorption performance of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 3 first increases and then decreases. Under the conditions of 200°C to 500°C, the effective absorption band can cover the entire X band.

[0098] The effective absorption band of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 5 can cover the entire X band at 100°C to 300°C. When the test temperature is 400°C, the wave absorption performance begins to decline.

[0099] The effective absorption band of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 6 can cover the entire X band at 100°C and 200°C. When the test temperature exceeds 300°C, the wave absorption performance begins to decline. This is because the relative dielectric constant at room temperature is relatively high, and the increase amplitude of the dielectric constant is relatively large during the process of increasing the test temperature, resulting in impedance mismatch. At this time, the electromagnetic wave reflection is enhanced, and the absorption ability of the ceramic foam to electromagnetic waves is weakened. When the test temperature is 500°C and 600°C, the ceramic foam no longer has wave absorption performance.

[0100] The high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 4 has a suitable dielectric constant and has wave absorption performance in the entire test temperature range, and can maintain relatively stable wave absorption performance. When the test temperature is 100°C to 400°C, the effective absorption band can cover the entire X band. When the test temperature is 100°C and the matching thickness is 3.8 mm, RC min is -18.7 dB. When the test temperature is 500°C and 600°C, the effective absorption bands are 3.7 GHz and 2.5 GHz.

[0101] Test 7: The thermal conductivity of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Examples 1-6 was tested to characterize its heat insulation performance. The test equipment was a Hot Disk TPS2200 thermal constant analyzer produced by AB Company of Sweden. The thermal conductivity is denoted as λ.

[0102] Figure 11The thermal conductivities of the high-temperature radar and infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6 are shown. It can be seen that the thermal conductivities of the six ceramic foams are all lower than 0.1 W / mK. Compared with the dense SiBCN ceramic with λ≈3.6 W / mK, there are a large number of pores inside the high-temperature radar and infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6. The air in the pores can significantly reduce the overall thermal conductivity to reach λ≈0.024 W / mK, effectively blocking the heat transferred to the outside and reducing the heat release. At the same time, the three-dimensional network structure prolongs the heat conduction path, reduces the solid-phase heat conduction efficiency, and the interface between the pores and the ceramic skeleton further scatters phonons, hindering heat transfer, thereby reducing the thermal radiation signal of the target in the infrared band and showing excellent heat insulation performance. Due to the vibration characteristics of the chemical bonds of the SiBCN ceramic and the enrichment of the carbon phase, it has a high emissivity. The high-temperature radar and infrared stealth SiBCN ceramic foam prepared in the embodiments of the present invention has excellent heat insulation performance, isolates heat through a low thermal conductivity, thereby reducing the surface temperature, and then offsetting the influence of the high emissivity to achieve infrared stealth.

[0103] Test 8: Use an infrared thermal imager to observe the surface temperature distribution of the high-temperature radar and infrared stealth SiBCN ceramic foam of Example 2, as Figure 12 shown, and visually evaluate the heat insulation effect. The test equipment is an infrared thermal imager of Uti 384H produced by China's UNI-T Company and a far-infrared graphite electric heating plate of DB-1GW produced by China's Lichen Company.

[0104] It can be seen from Figure 12 that at a background temperature of 440 °C, as time increases, the surface temperature of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 2 gradually increases and finally remains basically stable at about 2 min. Among them, its surface temperature is maintained at about 240 °C, reducing the background radiation temperature by about 200 °C. The Chinese name of the Stefan-Boltzmann law is the Stefan-Boltzmann law. According to the Stefan-Boltzmann law, the infrared radiation energy of a material is proportional to the fourth power of its surface temperature. When the surface temperature drops from 440 °C to 240 °C, the infrared radiation energy can be reduced to 26.8% of the original value, significantly reducing the probability of being recognized by an infrared detector, and fully verifying the potential of the high-temperature radar and infrared stealth SiBCN ceramic foam prepared in Example 2 as a high-temperature heat insulation and stealth integrated material. This performance can meet the dual requirements of high-efficiency heat insulation and infrared signal suppression in scenarios such as aerospace thermal protection and hypersonic vehicle skins.

[0105] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing high-temperature radar infrared stealth SiBCN ceramic foam, characterized in that: The following steps are involved: In a solvent system, borohalogen, vinyl halosilane, diphenyl halosilane and disilazane are polymerized to obtain vinyl-containing polyborosilazane; In a solvent system, vinyl-containing polyborosilazane and dithiol are subjected to a thiol-vinyl photocuring click reaction under the action of a photoinitiator to form a cross-linked polyborosilazane wet gel; The polyborosilazane wet gel is freeze-dried to be converted into polyborosilazane dry gel, which is then pyrolyzed under a protective atmosphere to obtain high-temperature radar infrared stealth SiBCN ceramic foam.

2. The method for preparing the high temperature radar infrared stealth SiBCN ceramic foam according to claim 1, characterized in that: The molar ratio of borohalide, vinyl halosilane, diphenyl halosilane and disilazane is 1:0.4:0.08-0.1:0.748-0.

77.

3. The method for preparing the high temperature radar infrared stealth SiBCN ceramic foam according to claim 1, characterized in that: The borohalogen is boron trichloride; the vinyl halosilane is at least one of vinyl trichlorosilane and dichloromethyl vinyl silane; the diphenyl halosilane is dichlorodiphenylsilane; and the disilazane is hexamethyldisilazane.

4. The method for preparing the high temperature radar infrared stealth SiBCN ceramic foam according to claim 1, characterized in that: The reaction temperature of the polymerization reaction is 170°C to 200°C, and the reaction time is 1h to 3h; the temperature of the pyrolysis is 1400°C.

5. The method for preparing the high temperature radar infrared stealth SiBCN ceramic foam according to claim 1, characterized in that: The mass ratio of vinyl-containing polyborosilazane to dithiol is 1.6 to 2:1; The mass percentage of the photoinitiator in the total solution of the mercapto-vinyl photocuring click reaction is 0.8% to 1%.

6. The method for preparing the high temperature radar infrared stealth SiBCN ceramic foam according to claim 1, characterized in that: The dithiol is any one of 1,5-pentanedithiol, 1,2-ethanedithiol and 1,6-hexanedithiol; and the photoinitiator is trimethylbenzoyl-diphenylphosphine oxide.

7. The method for preparing the high temperature radar infrared stealth SiBCN ceramic foam according to claim 1, characterized in that: The solvent used in the polymerization reaction is cyclohexane or n-hexane; The solvent used in the mercapto-vinyl photocuring click reaction is cyclohexane or n-hexane.

8. A high temperature radar infrared stealth SiBCN ceramic foam, characterized in that: The ceramic foam is prepared by the method for preparing the high-temperature radar infrared stealth SiBCN ceramic foam as described in any one of claims 1 to 7.

9. Use of the high-temperature radar infrared stealth SiBCN ceramic foam as claimed in claim 8 as a stealth material.

10. The use of the high temperature radar infrared stealth SiBCN ceramic foam as a stealth material according to claim 9, characterized in that: The stealth material is a wide temperature range absorbing material, and the temperature range of the wide temperature range absorbing material is 25° C. to 600° C.; the thermal conductivity of the stealth material is <0.1 W / mK.

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