High-temperature radar infrared stealth SiBCN ceramic foam and its preparation method and application

Abstract

The present invention relates to the technical field of polymer-converted ceramics and stealth functional materials, and specifically to high-temperature radar infrared stealth SiBCN ceramic foam, its preparation method and application. The specific preparation method comprises: subjecting a borohalide, a vinyl halosilane, a diphenyl halosilane and a disilazane to a polymerization reaction to obtain a vinyl-containing polyborosilazane; subjecting the vinyl-containing polyborosilazane and a dithiol to a mercapto-vinyl photocuring click reaction under the action of a photoinitiator to form a polyborosilazane wet gel; and subjecting the polyborosilazane to a freeze-drying treatment and a thermal decomposition under a protective atmosphere to obtain the gel. The method of the present invention can solve the problems of high production cost and safety risks in the preparation process of the existing SiBCN ceramic foam. The SiBCN ceramic foam of the present invention can maintain stable wave-absorbing performance within a wide temperature range and has the characteristics of low thermal conductivity, can effectively block heat, reduce the surface temperature of the hot end component, and thus effectively suppress infrared thermal radiation energy.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer-converted ceramics and radar / infrared compatible stealth materials, and in particular to high-temperature radar infrared stealth SiBCN ceramic foam, a preparation method and applications thereof. Background Art

[0002] The core contradiction in achieving radar / infrared-compatible stealth materials lies in the fact that radar stealth requires high absorption performance, such as low reflection from 2GHz to 18GHz, while infrared stealth requires low emissivity, such as high reflection from 3μm to 5μm and 8μm to 14μm. Furthermore, high temperatures of 400°C to 800°C exacerbate material oxidation and electromagnetic degradation, leading to impedance mismatch and a surge in infrared radiation. Based on the Stefan-Boltzmann law, which states that thermal radiation energy is proportional to the fourth power of temperature, actively lowering the material's surface temperature can significantly suppress infrared radiation. However, this requires simultaneous control of temperature-dependent electromagnetic parameters, such as the real and imaginary parts of the dielectric constant, to maintain impedance matching. This achieves radar-compatible infrared stealth in high-temperature environments, solving the multi-spectrum stealth compatibility challenge.

[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, the application of traditional oxide ceramics in the field of high-temperature stealth materials is limited by the shortcomings of poor dielectric controllability and complicated preparation process. Non-oxide ceramics can withstand extremely high temperatures and can usually maintain stable structure and performance at temperatures up to 1000°C or even higher. They also have high hardness and compressive strength. However, the absorption properties of non-oxide ceramics may change at high temperatures. The defects of narrow effective absorption band and poor dielectric adjustability 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 efficient stealth performance in high-temperature environments.

[0004] As a multiphase system composed of a matrix phase and a gas phase, foam materials have internal three-dimensional interconnected pores that can dissipate electromagnetic energy through multiple scattering of electromagnetic waves and the relaxation polarization effect induced by heterogeneous interfaces, significantly improving broadband radar stealth performance. At the same time, the multi-level pore topology within the material can construct a low-thermal conductivity barrier, effectively inhibiting the heat conduction path, thereby weakening the surface temperature rise of the hot end components and suppressing infrared radiation energy, showing the unique advantage of synergistic enhancement of electromagnetic absorption and thermal management. However, polymer foams and carbon foams are difficult to meet the application requirements of extreme environments such as high temperatures. Ceramic foams, due to their lightweight and porous nature and the high-temperature resistance of the ceramic matrix, have become an ideal candidate for integrated thermal protection and stealth materials for hypersonic aircraft. However, traditional preparation methods, such as template methods and foaming methods, have difficulty in achieving molecular-scale structural control, resulting in insufficient synergy between pore structure and electromagnetic / thermal insulation properties. Polymer-Derived Ceramics, also known as Polymer-Derived Ceramics (PDCs), have the characteristics of flexible dielectric controllability and diverse preparation processes. In particular, polymer-derived SiBCN ceramic materials have excellent high-temperature resistance and flexible dielectric controllability. Combined with porous foam structure, they provide new ideas for solving the problem of insufficient synergy between pore structure and electromagnetic / thermal insulation properties.

[0005] Currently, PDCs-SiBCN ceramic foams are primarily produced using polyborosilazane as a ceramic precursor, divinylbenzene as a crosslinker, and Karstedt catalysts through solvothermal reactions, drying, and high-temperature pyrolysis. Karstedt catalysts are also known as "Karstedt catalysts" in Chinese. The wet gel is obtained through a hydrosilylation reaction, which is expensive and resource-limited. The use of Karstedt catalysts significantly increases production costs during large-scale production, which is a significant factor limiting the large-scale application of SiBCN ceramic foams. Furthermore, solvothermal reactions typically require high temperatures and high pressures, making the process complex to control and posing safety risks. Furthermore, much of the research in the field of PDCs-SiBCN ceramic foams focuses on either single-aspect absorption or thermal insulation properties. Further exploration is urgently needed to integrate these two properties, particularly in the area of high-temperature radar-compatible infrared stealth, where related research is still in its infancy. Summary of the Invention

[0006] To address the above technical issues, the present invention provides a high-temperature radar infrared stealth SiBCN ceramic foam, as well as a preparation method and application. The preparation method of the present invention significantly shortens preparation time, improves production efficiency, and reduces production costs, resolving the high production costs and complex operation issues of existing SiBCN ceramic foam preparation processes. Furthermore, the high-temperature radar infrared stealth SiBCN ceramic foam prepared by the present invention overcomes the limitations of SiBCN ceramic foam's high intrinsic thermal conductivity, achieving lightweight insulation with low thermal conductivity, thereby breaking the functional compatibility bottleneck of high-temperature stealth materials in radar absorption and infrared radiation suppression.

[0007] To achieve the above objectives, the technical solutions of the present invention are as follows.

[0008] A first aspect of the present invention provides a method for preparing a high-temperature radar infrared stealth SiBCN ceramic foam, comprising the following steps:

[0009] In a solvent system, a borohalogen, vinyl halosilane, diphenyl halosilane and disilazane are polymerized to obtain vinyl-containing polyborosilazane; in 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 cross-linked polyborosilazane wet gel; the polyborosilazane wet gel is freeze-dried to convert it into a polyborosilazane dry gel, and then pyrolyzed under a protective atmosphere to obtain a high-temperature radar infrared stealth SiBCN ceramic foam.

[0010] The preparation method of the present invention utilizes a mercapto-vinyl photocuring click reaction, which rapidly crosslinks the polymer. Combined with freeze-drying technology, the method forms a well-structured, high-temperature, radar-infrared-stealthy SiBCN ceramic foam in a short period of time through thermal decomposition. The method is characterized by rapid reaction and ease of operation. Compared to existing preparation processes, it significantly shortens preparation time, improves production efficiency, reduces energy consumption, and lowers production costs. The low cost of raw materials required makes it suitable for large-scale production, addressing the high production costs and complex operating procedures associated with existing SiBCN ceramic foam preparation processes.

[0011] Preferably, the molar ratio of borohalide, vinylhalosilane, diphenylhalosilane 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.

[0012] The present invention uses vinyl-containing polyborosilazane as a ceramic precursor. By adjusting the content of diphenylhalosilane in the ceramic precursor and the ratio of dithiol to the ceramic precursor, the dielectric properties of SiBCN ceramic foam can be precisely controlled, thereby regulating the wave absorbing performance. It has good customization capabilities and can be optimized according to different needs.

[0013] Preferably, the borohalogen is boron trichloride; the vinyl halosilane is at least one of vinyltrichlorosilane and dichloromethylvinylsilane; the diphenyl halosilane is dichlorodiphenylsilane; and the disilazane is hexamethyldisilazane.

[0014] Preferably, the polymerization reaction temperature is 170° C. to 200° C., the reaction time is 1 hour to 3 hours, and the pyrolysis temperature is 1400° C. The present invention uses vinyl-containing polyborosilazane as a ceramic precursor, and the molecular weight and topological structure of the ceramic precursor are controlled by regulating the reaction temperature and reaction time.

[0015] 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 mercapto-vinyl photocuring click reaction is 0.8% to 1%.

[0016] The present invention achieves excellent radar absorption performance by adjusting the molar ratio of borohalane, vinyl halosilane, diphenyl halosilane, and disilazane, as well as the mass ratio of vinyl-containing polyborosilazane to dithiol, to produce a high-temperature radar infrared stealth SiBCN ceramic foam with suitable dielectric properties. In particular, adjusting the amount of diphenyl halosilane added can be used to adjust the dielectric constant of the prepared high-temperature radar infrared stealth SiBCN ceramic foam, thereby regulating its radar absorption performance. Preferably, the dithiol is any one of 1,5-pentanedithiol, 1,2-ethanedithiol, and 1,6-hexanedithiol; and the photoinitiator is trimethylbenzoyl-diphenylphosphine oxide.

[0017] Preferably, 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.

[0018] A second aspect of the present invention provides a high-temperature radar infrared stealth SiBCN ceramic foam, which is prepared by the preparation method of the high-temperature radar infrared stealth SiBCN ceramic foam described in the first aspect.

[0019] The third aspect of the present invention provides an application of the high-temperature radar infrared stealth SiBCN ceramic foam described in the second aspect as a stealth material.

[0020] Preferably, the stealth material is a wide-temperature-range absorbing material having a temperature range of 25°C to 600°C; and the thermal conductivity of the stealth material is less than 0.1 W / mK. Therefore, the stealth material of the present invention has a good thermal insulation effect.

[0021] Beneficial effects of the present invention:

[0022] 1. The preparation method of the present invention adopts a mercapto-vinyl photocuring click reaction, which can quickly realize a cross-linking reaction and form a high-temperature radar 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, reduce production costs, and require low raw material costs. It is suitable for large-scale production and solves the problems of high production cost and complex operation process in the existing SiBCN ceramic foam preparation process.

[0023] 2. The present invention designs the pore structure and components so that the prepared high-temperature radar infrared stealth SiBCN ceramic foam can maintain stable absorbing performance in the temperature range of 25°C to 600°C. Especially at high temperatures, the absorbing effect of the high-temperature radar infrared stealth SiBCN ceramic foam is still outstanding, which is significantly better than the existing high-temperature absorbing materials. Its wide temperature range applicability enables it to be widely used in the demand for high-temperature absorbing materials in aerospace, national defense and other fields.

[0024] 3. The high-temperature radar infrared stealth SiBCN ceramic foam prepared by the present invention has the characteristics of low thermal conductivity, can effectively block heat, reduce the surface temperature of hot end components, thereby effectively suppressing infrared thermal radiation energy, and is suitable for ultra-high temperature working conditions such as hypersonic aircraft thermal protection-stealth integrated skin and aerospace engine combustion chamber lining.

[0025] 4. The high-temperature radar infrared stealth SiBCN ceramic foam prepared by the present invention has a high porosity and a suitable pore size, which can significantly reduce the thermal conductivity. Its thermal conductivity is <0.1W / mK. The pores form a good insulation effect on heat conduction, thereby improving the thermal insulation effect. By controlling the surface temperature, the infrared radiation energy is effectively suppressed, thereby achieving the effect of infrared stealth. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the reaction equation for preparing vinyl-containing polyborosilazane in an embodiment of the present invention.

[0027] Figure 2 This is the H NMR spectrum of the vinyl-containing polyborosilazane prepared in Example 1.

[0028] Figure 3 This is the NMR boron spectrum of the vinyl-containing polyborosilazane prepared in Example 1.

[0029] Figure 4 These are X-ray diffraction curves of the high-temperature radar infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6.

[0030] Figure 5 This is a high-resolution transmission electron microscope image of the high-temperature radar infrared stealth SiBCN ceramic foam of Example 4.

[0031] Figure 6 This is a scanning electron microscope image of the high-temperature radar infrared stealth SiBCN ceramic foam of Example 6.

[0032] Figure 7 This is a curve showing how the reflection coefficient of the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Examples 1 to 6 at room temperature changes with frequency at different thicknesses.

[0033] Figure 8 This is a 3D graph showing the reflection coefficient of the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 4 versus thickness and frequency.

[0034] Figure 9 This is a 2D graph showing the reflection coefficient of the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 4 versus thickness and frequency.

[0035] Figure 10 This is an RC curve diagram of the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 4 at a test temperature of 100°C to 600°C.

[0036] Figure 11 This is a thermal conductivity diagram of the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Examples 1 to 6.

[0037] Figure 12 This is a graph showing the surface temperature of the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 2 detected at the set temperature of the hot plate over time. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0039] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0040] The present invention aims to reduce costs and improve reaction processes, and to improve the wave absorption performance and infrared stealth performance of the prepared high-temperature radar infrared stealth SiBCN ceramic foam in a wide temperature range.

[0041] This invention provides a method for preparing high-temperature radar infrared stealth SiBCN ceramic foam using a mercapto-vinyl photocuring click reaction. This method uses a rapid photocuring reaction to form a ceramic foam with a well-defined pore structure. Subsequent pyrolysis and sintering yield the SiBCN ceramic foam with excellent wave-absorbing properties. This high-temperature radar infrared stealth SiBCN ceramic foam exhibits stable wave-absorbing properties over a wide temperature range of 25°C to 600°C and offers excellent thermal insulation, making it particularly suitable for stealth applications in high-temperature and extreme environments.

[0042] The porous structure inside the high-temperature radar infrared stealth SiBCN ceramic foam prepared by the present invention is conducive to the attenuation of electromagnetic waves. The prepared high-temperature radar infrared stealth SiBCN ceramic foam shows good dielectric temperature stability. The six high-temperature radar infrared stealth SiBCN ceramic foams prepared in the following embodiments of the present invention all have certain high-temperature wave absorbing properties. Among them, the two prepared high-temperature radar infrared stealth SiBCN ceramic foams have wave absorbing properties at both room temperature and high temperature, at 300℃~600℃ and 25℃~400℃ respectively. The effective absorption bandwidth can cover the entire X-band, and the minimum reflection losses are -28.6dB and -18.7dB, respectively.

[0043] Infrared radiation energy is positively correlated to the fourth power of the material surface temperature. The high-temperature radar infrared stealth SiBCN ceramic foam prepared by the present invention significantly reduces the heat transfer from high-temperature components to the material surface through its low thermal conductivity of <0.1W / m·K, thereby lowering the surface temperature and fundamentally reducing the infrared radiation intensity.

[0044] Compared with bulk ceramics, under the condition of the same volume, the mass of the high-temperature radar 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%, which is conducive to reducing the weight of the high-temperature radar infrared stealth SiBCN ceramic foam and meeting the industry's demand for "light" absorbing materials.

[0045] The technical solution of the present invention is further described below through specific embodiments.

[0046] In the following examples, the methods described are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0047] In the following embodiments, polyborosilazane is referred to as PBSZ.

[0048] Contains vinyl polyborosilazane, English name Vinyl Polyborosilazane, abbreviated as Vi-PBSZ.

[0049] Polyborosilazane wet gel, English name Hydrogel-Polyborosilazane, abbreviated as HG-PBSZ.

[0050] Polyborosilazane dry gel, English name Xerogel-Polyborosilazane, abbreviated as X-PBSZ.

[0051] In the following examples, the temperature of the ice-water bath is 0°C ± 2°C, and the room temperature is 25°C ± 5°C.

[0052] In the following examples, the entire process of preparing the vinyl-containing polyborosilazane solution adopts a double-row pipe operation technique. The reaction equation is as follows: Figure 1 As shown. In the process of preparing the vinyl-containing polyborosilazane solution, the reaction temperature of the polymerization reaction is 170°C to 200°C, and the reaction time is 1h to 3h. The present invention uses vinyl-containing polyborosilazane as a ceramic precursor, and controls the molecular weight and topological structure of the ceramic precursor by regulating the reaction temperature and reaction time. The following is an example of a polymerization reaction temperature of 190°C and a reaction time of 2h, and explores the effects of different molar ratios of borohalides, vinyl halosilanes, diphenylhalosilanes and disilazolines on the performance of the prepared high-temperature radar infrared stealth SiBCN ceramic foam.

[0053] Example 1

[0054] A method for preparing high-temperature radar infrared stealth SiBCN ceramic foam comprises the following steps:

[0055] Step 1, preparing a vinyl-containing polyborosilazane solution:

[0056] A 500 mL reaction flask was subjected to three cycles of inert gas and then placed in an ice-water bath. To the reaction flask were added 100 mL of a 1.0 mol / L boron trichloride-n-hexane solution, 0.1 mol vinyltrichlorosilane, 0.3 mol dichloromethylvinylsilane, 0.08 mol dichlorodiphenylsilane, and 0.748 mol hexamethyldisilazane, in order to achieve a molar ratio of 1:0.4:0.08:0.748 for the mixture of boron trichloride, vinyltrichlorosilane, and dichloromethylvinylsilane, and dichlorodiphenylsilane to hexamethyldisilazane. The mixture was stirred and the reaction temperature was then raised to 190°C and maintained for 2 h. The heating device was then removed and the reaction flask was sealed to obtain a vinyl polyborosilazane solution, designated as Vi-PBSZ solution.

[0057] Step 2: Preparation of SiBCN wet gel by thiol-ene click reaction:

[0058] According to the mass ratio of Vi-PBSZ to 1,5-pentanedithiol of 2:1, 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%.

[0059] After thorough mixing, the mixture was quickly poured into a tetrafluoroethylene square mold and covered with a transparent lid. The square mold was placed in a UV curing box for curing to obtain a polyborosilazane wet gel, which was designated as HG-PBSZ.

[0060] Step 3: Preparation of high-temperature radar infrared stealth SiBCN ceramic foam:

[0061] The HG-PBSZ was placed in a freeze dryer for freeze drying, at which time the HG-PBSZ was converted into polyborosilazane xerogel, which was recorded as X-PBSZ.

[0062] 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 kept at 1400℃ for 4 hours, and the cooling rate was set to 2℃ / min. After cooling to 500℃, it was naturally cooled to room temperature to obtain high-temperature radar infrared stealth SiBCN ceramic foam.

[0063] Example 2

[0064] A method for preparing high-temperature radar infrared stealth SiBCN ceramic foam, which differs 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:

[0065] Step 1, preparing a vinyl-containing polyborosilazane solution: proceed according to the method of Example 1.

[0066] Step 2: Preparation of SiBCN wet gel by thiol-ene click reaction:

[0067] 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%.

[0068] After thorough mixing, the mixture was quickly poured into a tetrafluoroethylene square mold and covered with a transparent lid. The square mold was placed in a UV curing box for curing to obtain a polyborosilazane wet gel, which was designated as HG-PBSZ.

[0069] Step 3: Preparation of high-temperature radar infrared stealth SiBCN ceramic foam:

[0070] The HG-PBSZ was placed in a freeze dryer for freeze drying, at which time the HG-PBSZ was converted into polyborosilazane xerogel, which was recorded as X-PBSZ.

[0071] 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 kept at 1400℃ for 4 hours, and the cooling rate was set to 2℃ / min. After cooling to 500℃, it was naturally cooled to room temperature to obtain high-temperature radar infrared stealth SiBCN ceramic foam.

[0072] Example 3

[0073] A method for preparing a high-temperature radar infrared stealth SiBCN ceramic foam differs from Example 1 in that, in step 1, the molar ratio of boron trichloride, a mixture of vinyltrichlorosilane and dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.09:0.759. The specific preparation method includes the following steps:

[0074] Step 1, preparing a vinyl-containing polyborosilazane solution:

[0075] A 500 mL reaction flask was subjected to three cycles of inert gas and then placed in an ice-water bath. To the reaction flask were added 100 mL of a 1.0 mol / L boron trichloride-n-hexane solution, 0.1 mol vinyltrichlorosilane, 0.3 mol dichloromethylvinylsilane, 0.09 mol dichlorodiphenylsilane, and 0.759 mol hexamethyldisilazane, in that order, such that the molar ratio of boron trichloride, vinyltrichlorosilane, and dichloromethylvinylsilane to dichlorodiphenylsilane and hexamethyldisilazane was 1:0.4:0.09:0.759. The mixture was stirred and the reaction temperature was then raised to 190°C and maintained for 2 hours. The heating device was then removed and the reaction flask was sealed to obtain a vinyl polyborosilazane solution, designated as Vi-PBSZ solution.

[0076] 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, Vi-PBSZ solution and 1,5-pentanedithiol are placed in a brown glass bottle, and then trimethylbenzoyl-diphenylphosphine oxide and cyclohexane are added 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%.

[0077] After thorough mixing, the mixture was quickly poured into a tetrafluoroethylene square mold and covered with a transparent lid. The square mold was placed in a UV curing box for curing to obtain a polyborosilazane wet gel, which was designated as HG-PBSZ.

[0078] Step 3: Preparation of high-temperature radar infrared stealth SiBCN ceramic foam:

[0079] The HG-PBSZ was placed in a freeze dryer for freeze drying, at which time the HG-PBSZ was converted into polyborosilazane xerogel, which was recorded as X-PBSZ.

[0080] 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 kept at 1400℃ for 4 hours, and the cooling rate was set to 2℃ / min. After cooling to 500℃, it was naturally cooled to room temperature to obtain high-temperature radar infrared stealth SiBCN ceramic foam.

[0081] Example 4

[0082] A method for preparing high-temperature radar infrared stealth SiBCN ceramic foam differs from Example 1 in that, in step 1, the molar ratio of boron trichloride, a mixture of vinyltrichlorosilane and dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.09:0.759; and in step 2, the mass ratio of Vi-PBSZ to 1,5-pentanedithiol is 5:3. The specific preparation method includes the following steps:

[0083] Step 1, preparing a vinyl-containing polyborosilazane solution:

[0084] A 500 mL reaction flask was subjected to three cycles of inert gas and then placed in an ice-water bath. To the reaction flask were added 100 mL of a 1.0 mol / L boron trichloride-n-hexane solution, 0.1 mol vinyltrichlorosilane, 0.3 mol dichloromethylvinylsilane, 0.09 mol dichlorodiphenylsilane, and 0.759 mol hexamethyldisilazane, in that order, such that the molar ratio of boron trichloride, vinyltrichlorosilane, and dichloromethylvinylsilane to dichlorodiphenylsilane and hexamethyldisilazane was 1:0.4:0.09:0.759. The mixture was stirred and the reaction temperature was then raised to 190°C and maintained for 2 hours. The heating device was then removed and the reaction flask was sealed to obtain a vinyl polyborosilazane solution, designated as Vi-PBSZ solution.

[0085] Step 2: Preparation of SiBCN wet gel by thiol-ene click reaction:

[0086] 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%.

[0087] After thorough mixing, the mixture was quickly poured into a tetrafluoroethylene square mold and covered with a transparent lid. The square mold was placed in a UV curing box for curing to obtain a polyborosilazane wet gel, which was designated as HG-PBSZ.

[0088] Step 3: Preparation of high-temperature radar infrared stealth SiBCN ceramic foam:

[0089] The HG-PBSZ was placed in a freeze dryer for freeze drying, at which time the HG-PBSZ was converted into polyborosilazane xerogel, which was recorded as X-PBSZ.

[0090] 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 kept at 1400℃ for 4 hours, and the cooling rate was set to 2℃ / min. After cooling to 500℃, it was naturally cooled to room temperature to obtain high-temperature radar infrared stealth SiBCN ceramic foam.

[0091] Example 5

[0092] A method for preparing a high-temperature radar infrared stealth SiBCN ceramic foam differs from Example 1 in that, in step 1, the molar ratio of boron trichloride, a mixture of vinyltrichlorosilane and dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.1:0.77. The specific preparation method includes the following steps:

[0093] Step 1, preparing a vinyl-containing polyborosilazane solution:

[0094] A 500 mL reaction flask was subjected to three cycles of inert gas and then placed in an ice-water bath. To the flask were added 100 mL of a 1.0 mol / L boron trichloride-n-hexane solution, 0.1 mol vinyltrichlorosilane, 0.3 mol dichloromethylvinylsilane, 0.1 mol dichlorodiphenylsilane, and 0.77 mol hexamethyldisilazane, in that order, such that the molar ratio of boron trichloride, vinyltrichlorosilane, and dichloromethylvinylsilane to dichlorodiphenylsilane and hexamethyldisilazane was 1:0.4:0.1:0.77. The mixture was stirred and the reaction temperature was then raised to 190°C and maintained for 2 hours. The heating device was then removed and the flask was sealed to obtain a vinyl polyborosilazane solution, designated as Vi-PBSZ solution.

[0095] 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, Vi-PBSZ solution and 1,5-pentanedithiol are placed in a brown glass bottle, and then trimethylbenzoyl-diphenylphosphine oxide and cyclohexane are added 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%.

[0096] Step 3: Preparation of high-temperature radar infrared stealth SiBCN ceramic foam:

[0097] The HG-PBSZ was placed in a freeze dryer for freeze drying, at which time the HG-PBSZ was converted into polyborosilazane xerogel, which was recorded as X-PBSZ.

[0098] 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 kept at 1400℃ for 4 hours, and the cooling rate was set to 2℃ / min. After cooling to 500℃, it was naturally cooled to room temperature to obtain high-temperature radar infrared stealth SiBCN ceramic foam.

[0099] Example 6

[0100] A method for preparing high-temperature radar infrared stealth SiBCN ceramic foam differs from Example 1 in that, in step 1, the molar ratio of boron trichloride, a mixture of vinyltrichlorosilane and dichloromethylvinylsilane, dichlorodiphenylsilane, and hexamethyldisilazane is 1:0.4:0.1:0.77; and in step 2, the mass ratio of Vi-PBSZ to 1,5-pentanedithiol is 5:3. The specific preparation method includes the following steps:

[0101] Step 1, preparing a vinyl-containing polyborosilazane solution:

[0102] A 500 mL reaction flask was subjected to three cycles of inert gas and then placed in an ice-water bath. To the flask were added 100 mL of a 1.0 mol / L boron trichloride-n-hexane solution, 0.1 mol vinyltrichlorosilane, 0.3 mol dichloromethylvinylsilane, 0.1 mol dichlorodiphenylsilane, and 0.77 mol hexamethyldisilazane, in that order, such that the molar ratio of boron trichloride, vinyltrichlorosilane, and dichloromethylvinylsilane to dichlorodiphenylsilane and hexamethyldisilazane was 1:0.4:0.1:0.77. The mixture was stirred and the reaction temperature was then raised to 190°C and maintained for 2 hours. The heating device was then removed and the flask was sealed to obtain a vinyl polyborosilazane solution, designated as Vi-PBSZ solution.

[0103] 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 5:3, Vi-PBSZ solution and 1,5-pentanedithiol are placed in a brown glass bottle, and then trimethylbenzoyl-diphenylphosphine oxide and cyclohexane are added 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%.

[0104] After thorough mixing, the mixture was quickly poured into a tetrafluoroethylene square mold and covered with a transparent lid. The square mold was placed in a UV curing box for curing to obtain a polyborosilazane wet gel, which was designated as HG-PBSZ.

[0105] Step 3: Preparation of high-temperature radar infrared stealth SiBCN ceramic foam:

[0106] The HG-PBSZ was placed in a freeze dryer for freeze drying, at which time the HG-PBSZ was converted into polyborosilazane xerogel, which was recorded as X-PBSZ.

[0107] 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 kept at 1400℃ for 4 hours, and the cooling rate was set to 2℃ / min. After cooling to 500℃, it was naturally cooled to room temperature to obtain high-temperature radar infrared stealth SiBCN ceramic foam.

[0108] The performance of the high-temperature radar infrared stealth SiBCN ceramic foams prepared by the preparation methods of Examples 1 to 6 is tested below.

[0109] Test 1: Using Vi-PBSZ as a ceramic precursor, the ceramic precursor prepared in Example 1 was tested for H spectrum and B spectrum. The results are as follows: Figure 2 and Figure 3 shown.

[0110] The nuclear magnetic hydrogen spectrum and the nuclear magnetic boron spectrum of the ceramic precursor of Example 1 show that the target structure of the ceramic precursor prepared in Example 1 is consistent with the molecular formula, indicating that the vinyl-containing polyborosilazane is successfully prepared in Example 1 of the present invention.

[0111] Test 2: The crystallization behavior of the high temperature radar infrared stealth SiBCN ceramic foam prepared in Examples 1 to 6 was tested by X-ray diffraction. The results are as follows: Figure 4 shown.

[0112] pass Figure 4 It can be seen from the X-ray diffraction curves that the high-temperature radar infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6 all showed obvious broad peaks at 2θ=24°, corresponding to the graphite lattice plane (002); and at 2θ=35.5°, 42.8°, 60.8° and 72.1°, they correspond to the crystallization peaks of β-SiC, which proves that the high-temperature radar infrared stealth SiBCN ceramic foams obtained by pyrolysis at a temperature of 1400°C have SiC crystals generated.

[0113] Test 3: The phase composition of the high temperature radar infrared stealth SiBCN ceramic foam of Example 4 was analyzed by high resolution transmission electron microscopy. The results are as follows: Figure 5 shown.

[0114] pass Figure 5 From the high-resolution transmission electron microscope image, a large number of lattice diffraction fringes can be observed, which indicates that under the pyrolysis conditions of 1400℃, a large number of nanocrystals are generated inside the high-temperature radar infrared stealth SiBCN ceramic foam, and the nanocrystals are irregularly distributed inside the high-temperature radar infrared stealth SiBCN ceramic foam. Figure 5 Regions B and A show two different widths of lattice fringes, 0.26nm and 0.35nm respectively, corresponding to the lattice spacing of SiC crystal and graphite lattice. Figure 4 The conclusions drawn from the X-ray diffraction patterns of the high-temperature radar infrared stealth SiBCN ceramic foam are consistent. The nanocrystals are distributed within the amorphous high-temperature radar infrared stealth SiBCN ceramic foam, forming more heterogeneous interfaces. Under the action of the alternating electromagnetic field, they can generate more polarization sites, which helps to improve the electromagnetic wave loss capability of the high-temperature radar infrared stealth SiBCN ceramic foam.

[0115] Test 4: The microstructure of the high-temperature radar infrared stealth SiBCN ceramic foam of Example 6 was analyzed using a scanning electron microscope.

[0116] Depend on Figure 6It was observed from the scanning electron microscope image that the high-temperature radar infrared stealth SiBCN ceramic foam of Example 6 was connected by dendritic ceramic veins, and the holes formed were all open-pore structures with irregular distribution and non-fixed shape.

[0117] Test 5: A high-temperature radar infrared stealth SiBCN ceramic foam was formed into a single piece and polished to a size of 22.86mm x 10.16mm. The X-band dielectric properties were tested and the emissivity coefficient was calculated using a vector network analyzer.

[0118] Figure 7 This is a curve showing how the reflection coefficient of the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Examples 1 to 6 at room temperature changes with frequency at different thicknesses.

[0119] Reflection coefficient, English name is Reflection Coefficient, referred to as RC. The smaller the RC value, the more electromagnetic waves are attenuated. Specifically, when the RC value is lower than −10dB in a certain frequency band, then this band is defined as the effective absorption band, referred to as EAB, indicating that more than 90% of electromagnetic waves can be absorbed in this band. The lowest value of the reflection coefficient is recorded as RC. min .

[0120] from Figure 7 It can be seen that the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 4 has the best wave absorbing performance at room temperature. When the matching thickness is 3.8 mm, the effective absorption band can cover the X-band. It has the lowest RC value among the high-temperature radar infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6. At this time, the RC min =-22.4dB. The 3D graph of the reflection coefficient of the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 4 versus thickness and frequency is shown in FIG. Figure 8 As shown, the 2D diagram is Figure 9 shown.

[0121] from Figure 7 It can be seen that the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 1 does not have wave absorbing performance. Compared with Example 1, the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 2 has a certain improvement in wave absorbing performance. When the matching thickness is 4.5mm, the effective absorption band is 2.3GHz, covering 9.1GHz to 11.4GHz. At this time, RC min =-11.5dB.

[0122] The high-temperature radar infrared stealth SiBCN ceramic foams prepared in Examples 5 and 6 have certain wave absorbing properties under room temperature conditions. When the matching thickness of the high-temperature radar 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 infrared stealth SiBCN ceramic foam prepared in Example 6 can cover the entire X-band. At this time, the RC min =-15.5dB.

[0123] Test 6: Using a vector network analyzer, the RC curves of the high-temperature radar 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 infrared stealth SiBCN ceramic foams. The RC curves of the high-temperature radar infrared stealth SiBCN ceramic foams prepared in Example 4 were tested at a test temperature of 100°C to 600°C, as shown in FIG. Figure 10 shown.

[0124] As the temperature rises, the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 1 has an enhanced ability to lose electromagnetic waves. At 100°C, since the dielectric constant is slightly different from that at room temperature, it has no 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 3.36GHz; 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, it has the lowest RC value at 400°C, at which time the matching thickness is 3.9mm, and RC min It is -29.8dB.

[0125] As the test temperature increases, the absorption performance of the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 2 first increases and then decreases. When the test temperature is 300℃~600℃, the effective absorption band can cover the entire X-band. Among them, when the test temperature is 400℃ and the matching thickness is 3.7mm, RC min It is -28.6dB.

[0126] As the test temperature increases, the wave absorbing performance of the high-temperature radar 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.

[0127] The high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 5 has an effective absorption band of 100°C to 300°C that covers the entire X-band. When the test temperature reaches 400°C, the absorption performance begins to decline.

[0128] The high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 6 has an effective absorption band covering the entire X-band at 100°C and 200°C. However, its absorption performance begins to decline when the test temperature exceeds 300°C. This is because the dielectric constant is relatively high at room temperature, and the increase in dielectric constant as the test temperature increases is relatively large, resulting in an impedance mismatch. This enhances electromagnetic wave reflection and weakens the ceramic foam's ability to absorb electromagnetic waves. At test temperatures of 500°C and 600°C, the ceramic foam no longer has any absorption properties.

[0129] The high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 4 has a suitable dielectric constant and has wave absorbing properties in the entire temperature range of the test, and can maintain relatively stable wave absorbing properties. When the test temperature is 100℃~400℃, the effective absorption band can cover the entire X-band. When the test temperature is 100℃ and the matching thickness is 3.8mm, RC min At test temperatures of 500°C and 600°C, the effective absorption bands are 3.7 GHz and 2.5 GHz.

[0130] Test 7: The thermal insulation properties of the high-temperature radar infrared stealth SiBCN ceramic foams prepared in Examples 1-6 were characterized by thermal conductivity testing using a Hot Disk TPS2200 thermal constant analyzer manufactured by Swedish AB. Thermal conductivity is denoted as λ.

[0131] Figure 11 The thermal conductivity of the high-temperature radar infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6 is shown. It can be seen that the thermal conductivity of all six ceramic foams is less than 0.1 W / mK. Compared with the dense SiBCN ceramic with λ≈3.6 W / mK, the high-temperature radar infrared stealth SiBCN ceramic foams prepared in Examples 1 to 6 have a large number of pores inside. The air in the pores can significantly reduce the overall thermal conductivity to λ≈0.024 W / mK, effectively blocking the heat transferred to the outside world and reducing heat release. At the same time, the three-dimensional network structure extends the heat conduction path, reducing the solid-phase heat conduction efficiency. The interface between the pores and the ceramic skeleton further scatters phonons, hindering heat transfer, thereby reducing the target's thermal radiation signal in the infrared band and demonstrating excellent thermal insulation performance. Due to the vibration characteristics of the chemical bonds of SiBCN ceramics and the enrichment of the carbon phase, it has a high emissivity. The high-temperature radar infrared stealth SiBCN ceramic foam prepared in the embodiment of the present invention has excellent thermal insulation performance. It isolates heat through low thermal conductivity, thereby reducing the surface temperature, and then offsets the impact of high emissivity to achieve infrared stealth.

[0132] Test 8: Observe the surface temperature distribution of the high-temperature radar infrared stealth SiBCN ceramic foam of Example 2 using an infrared thermal imager. Figure 12 The test equipment used is a Uti 384H infrared thermal imager produced by China Uni-Tech Corporation and a DB-1GW far-infrared graphite heating plate produced by China Lichen Corporation.

[0133] Depend on Figure 12 It can be seen that at a background temperature of 440°C, as time goes by, the surface temperature of the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 2 gradually increases, and finally remains basically stable for about 2 minutes. Among them, its surface temperature is maintained at about 240°C, which reduces 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 infrared detectors, fully verifying the potential of the high-temperature radar infrared stealth SiBCN ceramic foam prepared in Example 2 as a high-temperature thermal insulation-stealth integrated material. This performance can meet the dual needs of efficient thermal insulation and infrared signal suppression in scenarios such as aerospace thermal protection and hypersonic aircraft skins.

[0134] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for 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 prepare vinyl-containing polyborosilazane; In a solvent system, vinyl-containing polyborosilazane and dithiol undergo a mercapto-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 convert it into polyborosilazane xerogel, which is then pyrolyzed under a protective atmosphere to generate a large amount of nanocrystals to produce high-temperature radar infrared stealth SiBCN ceramic foam. The molar ratio of borohalogen, vinyl halosilane, diphenyl halosilane and disilazane is 1:0.4:0.08-0.1:0.748-0.77; the mass ratio of vinyl-containing polyborosilazane to dithiol is 1.6-2:1; The reaction temperature of the polymerization reaction is 170° C. to 200° C., and the reaction time is 1 h to 3 h; the temperature of the pyrolysis is 1400° C.

2. 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 vinyltrichlorosilane and dichloromethylvinylsilane; the diphenyl halosilane is dichlorodiphenylsilane; and the disilazane is hexamethyldisilazane.

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

4. 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.

5. 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.

6. 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 according to any one of claims 1 to 5.

7. Use of the high-temperature radar infrared stealth SiBCN ceramic foam according to claim 6 as a stealth material.

8. The use of the high-temperature radar infrared stealth SiBCN ceramic foam as a stealth material according to claim 7, 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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