Method for preparing polyborosilazane precursor and application thereof

Abstract

The application belongs to the technical field of organic polymer compounds, and particularly relates to a preparation method and application of a polyborosilazane precursor. The preparation method of the polyborosilazane precursor comprises the following steps: dissolving a boron source and a silicon source in an organic solvent, and introducing an inorganic ammonia solution agent to perform inorganic ammonia solution; subsequently, introducing a capping agent to perform organic amine capping, and performing post-treatment and polycondensation to obtain the polyborosilazane precursor. The application comprises the following steps: pyrolyzing the borosilazane precursor in an inert atmosphere to obtain carbon-free SiBN ceramic. The polyborosilazane precursor is prepared by inorganic ammonia solution and organic amine capping, and thus the problem of carbon residue of the ceramic prepared from the precursor is avoided. The carbon-free SiBN ceramic prepared by the application has better wave-transmitting performance than the carbon-containing SiBCN ceramic, and also has good oxidation resistance.

Description

Technical Field

[0001] This invention belongs to the field of organic polymer compound technology, specifically relating to a method for preparing and applying a polyborosilicate precursor. Background Technology

[0002] Silicon boron nitride (SiBN) ceramics are high-temperature transparent ceramic materials with excellent dielectric properties and machinability, showing promising application prospects. Traditional processes, involving the blending, grinding, and sintering of Si, SiN, B, and BN powders, fail to produce highly uniform SiBN ceramics and require high sintering temperatures. Furthermore, the synthesis of SiBN ceramics from SiBCN polymer precursors often introduces carbon-containing components (such as methyl, phenyl, and carborane) during precursor synthesis, leading to the formation of nano-carbon clusters from residual carbon elements in the pyrolysis products. These carbon clusters readily combine with silicon atoms at high temperatures (>1400℃) to form β-SiC nuclei, leading to defects such as grain boundaries and anisotropy. As heterogeneous nucleation sites, carbon clusters disrupt the homogeneity of the SiBN amorphous network, forming SiN / SiC / BN multiphase interfaces, resulting in thermal stress concentration, mechanical property deterioration, and electromagnetic property deterioration. For example, the conductive pathways introduced by carbon elements significantly increase dielectric loss. Furthermore, during high-temperature oxidation, carbon elements preferentially participate in the reaction in the oxidizing environment, generating carbon dioxide gas, which increases the internal porosity of the material, forming a loose and porous mesophase, accelerating the degradation of the material structure, and thus reducing mechanical properties.

[0003] Although controlling the carbon content can improve the dielectric properties of SiBCN ceramics, the synthesis of carbon-free SiBN ceramics by pyrolysis of polyborosilicate precursors is very difficult. This is because, firstly, during the pyrolysis of SiBCN precursors to prepare SiBN ceramics, carbon can spontaneously separate to form a multiphase structure of SiN / SiC / BN. Furthermore, if SiBN ceramics are to be prepared using the same route as SiBCN ceramics, reactive gases such as ammonia need to be used in the ultra-high temperature environment of high-temperature sintering to remove carbon, which makes the preparation process more difficult, costly, and dangerous.

[0004] Chinese patent CN114133575A discloses a method for preparing a high-boron-content polysiloxane, the method comprising the following steps: S1, first purging an inert gas into carborane and a reaction solvent, and then adding n-butyllithium dropwise; S2, purging an inert gas into chlorosilane and a reaction solvent, and then adding the product from S1 dropwise; S3, adding a reaction solvent to the reaction product from step S2, or adding a reaction solvent and boron trichloride to the reaction product from step S2, followed by adding an amine compound dropwise, reacting at 20~110℃ for 1~15h, then raising the temperature to 150~300℃ for 5~15h to obtain the product.

[0005] The patent failed to effectively control the carbon content in SiBN ceramics because it introduced carbon atoms, which are difficult to remove during pyrolysis due to their distribution within the polysiloxane molecular chain. Furthermore, carbon atoms readily combine with silicon atoms at high temperatures to form β-SiC crystal nuclei, which affects the oxidation resistance, mechanical properties, dielectric properties, and ablation resistance of SiBN ceramics. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a polyborosilicate precursor, which ensures the formation of a complete chain structure by pre-organizing at the molecular level, thereby reducing the formation of other competing structures during the pyrolysis preparation of SiBN ceramics; this invention also provides the application of this precursor in the preparation of carbon-free silicon boron nitride ceramics.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The method for preparing the polyborosilicate precursor of the present invention involves dissolving a boron source and a silicon source in an organic solvent, introducing an inorganic ammonolysis agent for inorganic ammonolysis, then introducing an end-capping agent for organic amine end-capping, and finally performing post-treatment and polycondensation to obtain the polyborosilicate precursor.

[0008] The general molecular formula of polyborosilazane precursors is as follows: When the silicon source is dichlorosilane, the general molecular formula of the polyborosilicate precursor is: ; When the silicon source is trichlorosilane, the general molecular formula of the polyborosilicate precursor is: ; When the silicon source is tetrachlorosilane, the general molecular formula of the polyborosilicate precursor is: ; R1, R3, and R5 are one of methyl, ethyl, or trimethylsilyl groups. R2, R4, and R6 are one of hydrogen, methyl, ethyl, or trimethylsilyl groups. R1 and R2, R3 and R4, and R5 and R6 can be the same or different. The value of n ranges from 3 to 10.

[0009] in: The boron source is boron trichloride, the silicon source is one or more of dichlorosilane, trichlorosilane or tetrachlorosilane, the organic solvent is one of n-hexane, toluene, xylene or tetrahydrofuran, the inorganic ammonolysis agent is ammonia, and the end-capping agent is one of hexamethyldisilazane, dimethylamine or diethylamine.

[0010] The molar ratio of silicon atoms in the silicon source to boron atoms in the boron source is 1~3:1, and the total number of moles of chlorine atoms in the boron and silicon sources is nCl. The molar ratio of nitrogen atoms in the inorganic ammonolysis agent to nCl is 1.5~1.7:1; and the molar ratio of nitrogen atoms in the capping agent to nCl is 0.15~0.25:1.

[0011] The dissolution temperature is -10~0℃, the inorganic ammonolysis agent is introduced at a rate of 0.5~0.9 kg / h, and the inorganic ammonolysis temperature is -20~0℃.

[0012] The organic amine is capped at a temperature of -20 to 0°C for 1 to 3 hours.

[0013] The post-processing includes filtration at a temperature of 0~25℃.

[0014] The polycondensation temperature is 150~200℃, and the polycondensation time is 1~3h.

[0015] The polyborosilicate precursor has a number-average molecular weight of 794~2874 Da and a viscosity of 50~500 cP at 25°C.

[0016] The application of the polyborosilicate precursor described in this invention involves pyrolyzing the polyborosilicate precursor in an inert atmosphere to obtain carbon-free SiBN ceramics. The carbon-free SiBN ceramics have an oxygen content of 0.53~0.75wt%, a nitrogen content of 14.26~16.13wt%, a carbon content of 0.02~0.07wt%, a boron content of 0.48~0.72wt%, and a silicon content of 41.84~51.61wt%.

[0017] in: During the pyrolysis, the heating rate is 5~10℃ / min, the pyrolysis temperature is 800~1200℃, and the pyrolysis time is 2~4h.

[0018] The reaction equation for the preparation of the polyborosilazane precursor is as follows: When the silicon source is dichlorosilane, the reaction equation is: ; When the silicon source is trichlorosilane, the reaction equation is: ; When the silicon source is tetrachlorosilane, the reaction equation is: ; R1, R3, and R5 are one of methyl, ethyl, or trimethylsilyl groups. R2, R4, and R6 are one of hydrogen, methyl, ethyl, or trimethylsilyl groups. R1 and R2, R3 and R4, and R5 and R6 can be the same or different. The end-capping agent is one of hexamethyldisilazane, dimethylamine, or diethylamine.

[0019] The term "pre-organization" refers to the fact that this invention does not simply mix raw materials according to the ratio of boron, silicon, and nitrogen atoms. Instead, during the synthesis of the polyborosilicate precursor, through chemical design (i.e., selecting specific monomers and controlling reaction conditions and sequence), the Si, C, B, and N atoms are arranged to minimize the carbon content in the main chain. This ensures that carbon atoms are primarily distributed in the side chains, facilitating the subsequent pyrolysis to remove small hydrocarbon molecules from the side chains and thus produce carbon-free SiBN ceramics. Without pre-organization, excessive carbon atoms in the main chain would be difficult to remove through pyrolysis, adversely affecting the electrical properties of the ceramic. Furthermore, if boron, silicon, and nitrogen elements are not designed through pre-organization, they will easily form their own enrichment zones during pyrolysis, generating other byproducts and compromising the uniformity of the ceramic.

[0020] The beneficial effects of this invention are as follows: (1) This invention uses pre-organization to avoid introducing organic carbon sources into the main chain of the polyborosilicate precursor molecule by firstly using carbon-free boron sources (i.e., boron trichloride) and silicon sources (i.e., dichlorosilane / trichlorosilane / tetrachlorosilane); secondly, by inorganic ammonolysis and organic amine end capping (hexamethyldisilazane, dimethylamine or diethylamine), the side chains of the precursor molecule chain synthesized in the early stage contain a small amount of carbon. The carbon in the side chains and the carbon at the end can be removed by volatilization at high temperature during the pyrolysis process, thus eliminating the risk of carbon residue from the source.

[0021] (2) The structure of the precursor molecular chain is controlled by a two-step method of "inorganic ammonolysis + organic amine capping". The ammonolysis stage forms Si-NB, Si-N-Si and BNB backbones; the degree of ammonolysis of inorganic ammonolysis is controlled to perform organic amine capping, terminate the active groups, and control the generation of chain, cyclic or other amorphous structures formed by dynamic recombination of BN bonds during the high-temperature pyrolysis of polyborosilicate precursors: After inorganic ammonolysis, a large number of active groups (such as B-NH2, Si-NH2) remain on the surface of the precursor. These groups are prone to self-condensation at high temperatures. In this invention, one of hexamethyldisilazane, dimethylamine, or diethylamine is added for end-capping. In the early stage of pyrolysis, the end-capping groups decompose and are removed by heat, resulting in a stable BN chain structure and a small amount of BN six-membered ring network. In the later stage of pyrolysis, after the small amount of residual CH3 is completely removed, the pre-organized network has formed a stable structure, achieving the effect of interpenetration between the final linear structure (such as Si-NB, Si-N-Si, and BNB) and the network structure (B3N3). The pyrolysis products of hexamethyldisilazane, dimethylamine, or diethylamine (such as trimethylsilyl compounds, methyl, or ethyl compounds) can be completely volatilized above 600°C, avoiding the problem of residual carbon impurities. Attached Figure Description

[0022] Figure 1 The 1H NMR spectrum of the polyborosilicate precursor in Example 1; Figure 2 for Figure 1 A magnified view of the 1H NMR spectrum signal in the two regions with chemical shifts of -0.5 to 1 ppm and 4 to 5.5 ppm; Figure 3 The infrared spectrum of the polyborosilicate precursor in Example 1; Figure 4 This is a gel permeation chromatogram of the polyborosilicate precursor in Example 1; Figure 5 Thermogravimetric analysis (TGA) diagram of the polyborosilicate precursor in Example 1; Figure 6 The X-ray diffraction pattern of the carbon-free SiBN ceramic in Example 1 is shown below. Figure 7 The image shows the infrared spectrum of the carbon-free SiBN ceramic in Example 1. Detailed Implementation

[0023] The present invention will now be described and illustrated in detail with reference to the embodiments.

[0024] For simplicity, "n(Si)" refers to the number of moles of silicon atoms in the silicon source, "n(B)" refers to the number of moles of boron atoms in the boron source, "n(Cl)" refers to the total number of moles of chlorine atoms in the boron and silicon sources, "n1(N)" refers to the number of moles of nitrogen atoms in the inorganic ammonolysis agent, and "n2(N)" refers to the number of moles of nitrogen atoms in the capping agent.

[0025] Example 1 Preparation of polyborosilazane precursor The temperature was controlled at -5℃, and 29.8 kg of trichlorosilane and 11.7 kg of boron trichloride were dissolved in n-hexane at a ratio of n(Si):n(B) = 2.2:1 and stirred until homogeneous. The temperature was controlled at -10℃, and 26.11 kg of ammonia gas was introduced at a ratio of n1(N):n(Cl) = 1.6:1 for inorganic ammonolysis at a rate of 0.5 kg / h. After the ammonia gas was introduced, the mixture was stirred at -10℃ for 180 min. At the same temperature, 30.99 kg of hexamethyldisilazane was added dropwise at a ratio of n2(N):n(Cl) = 0.2:1. After the addition was completed, the mixture was stirred to seal the reaction for 3 h and then allowed to return to room temperature to obtain the crude product.

[0026] The crude product was filtered at 0°C to obtain a precipitate and a clear solution. The precipitate was washed twice with n-hexane to obtain a washing liquid. The precipitate was then discharged as an impurity. The washing liquid and the clear solution were combined and then distilled to remove the solvent, resulting in a pale milky white product. The pale milky white product was further heated at 150°C for 3 hours to further condense and remove low molecular weight molecules, finally yielding a viscous white liquid with a yield of approximately 61.37%.

[0027] The specific models of equipment used for polymer structure characterization are as follows: For infrared spectroscopy, Shimadzu (Japan) IRTracer-100 was used; for proton nuclear magnetic resonance (NMR) spectroscopy, Bruker (Germany) AVANCEIII HD-400 was used; for thermogravimetric analysis, Netzsch (Germany) STA 449 F5 was used; for gel permeation chromatography, Waters (USA) Waters-1515 was used; for oxygen and nitrogen content analysis, Leco (USA) ONH836 was used; for carbon content analysis, Leco (USA) CS844 was used; for silicon and boron content analysis, Hitachi (Japan) Z-2300 was used; and for X-ray diffraction, Bruker (Germany) D8 ADVANCE was used.

[0028] The number-average molecular weight of the polyborosilicate precursor was 986 Da, the viscosity at 25°C was 80 cP, and the solubility in most organic solvents was >50 wt%. In this example, organic solvents such as n-hexane, toluene, xylene, and tetrahydrofuran were used for the experiment.

[0029] Samples were taken for nuclear magnetic resonance (NMR) detection, and the proton NMR spectrum is shown below. Figure 1 , 2 As shown in the spectrum, the peaks at 4.0–5.5 ppm are the Si-H peaks in the structure, originating from trichlorosilane in the raw material; the peaks at -0.25–0.25 ppm are the hydrogens in the methyl group in the structure, originating from hexamethyldisilazane in the capping agent. The integral ratio of -SiH:-CH3 ≈ 1:14.7. The theoretical molecular structure is as follows: TMS is an abbreviation for trimethylsilyl.

[0030] Infrared spectrum of polyborosilazane precursor as shown in Figure Figure 3 As shown, 3382cm -1 and 1178cm -1 Characteristic peak of NH; 2954 cm⁻¹ -1 and 2896cm -1 Characteristic peak of -CH3; 2140 cm⁻¹ -1 Characteristic peak of Si-H; 1411 cm⁻¹ -1 and 604cm -1 Characteristic peak of BN; 1249 cm⁻¹ -1 836cm -1 766cm -1 and 451cm -1 Characteristic peak of Si-CH3; 928 cm⁻¹ -1 and 685cm -1 These peaks belong to the Si-NH-Si characteristic range. -CH3 and Si-CH3 are derived from the capping agent hexamethyldisilazane.

[0031] Thermogravimetric analysis (TGA) experiment: The polyborosilicate precursor was pyrolyzed in a tube furnace under an argon atmosphere, with the temperature increased from room temperature to 800℃ at a rate of 10℃ / min, yielding carbon-free SiBN ceramics. Characterization was performed using thermogravimetric analysis (e.g., ...). Figure 5 As shown in the figure, the yield of carbon-free SiBN ceramics was 32.66% based on polyborosilazane precursor.

[0032] Preparation of carbon-free SiBN ceramics The polyborosilicate precursor was pyrolyzed in a tube furnace under an argon atmosphere, and the temperature was raised from room temperature to 800℃ at a rate of 10℃ / min and held at 800℃ for 3 hours. The yield of carbon-free SiBN ceramics prepared from the polyborosilicate precursor was 31.79%, which is basically consistent with the results of thermogravimetric analysis.

[0033] The pyrolyzed SiBN ceramics were characterized by X-ray diffraction patterns (e.g.) Figure 6 As shown in the figure, this proves that the carbon-free SiBN ceramic is amorphous. The peak near 43° in the spectrum represents the α-Fe crystalline phase introduced during grinding in a stainless steel mortar.

[0034] The pyrolyzed SiBN ceramics were characterized by infrared spectroscopy (e.g. Figure 7 As shown), the main component of carbon-free SiBN ceramics is SiN ceramic (1000-1100 cm⁻¹). -1 and 500-600cm -1 BN ceramics (1300~1400cm) -1 and 800-850cm -1 about).

[0035] The pyrolyzed SiBN ceramic was analyzed by various elements, and the results were as follows: oxygen content 0.69 wt%, nitrogen content 14.26 wt%, carbon content 0.07%, boron content 0.48%, and silicon content 51.61%. This proves that carbon-free SiBN ceramic was obtained.

[0036] Example 2 Preparation of polyborosilazane precursor The temperature was controlled at 0℃, and 42.5 kg of tetrachlorosilane and 11.7 kg of boron trichloride were dissolved in toluene at a ratio of n(Si):n(B) = 2.5:1 and stirred until homogeneous. The temperature was controlled at -20℃, and 33.15 kg of ammonia gas was introduced at a ratio of n1(N):n(Cl) = 1.5:1 for inorganic ammonolysis at a rate of 0.75 kg / h. After the introduction was completed, the mixture was stirred at -20℃ for 180 min. At the same temperature, 23.77 kg of diethylamine was added dropwise at a ratio of n2(N):n(Cl) = 0.25:1. After the addition was completed, the mixture was stirred and the reaction was capped for 2 h to obtain the crude product.

[0037] The crude product was filtered at 10°C to obtain a precipitate and a clear solution. The precipitate was washed twice with n-hexane to obtain a washing liquid. The precipitate was then discharged as an impurity. The washing liquid and the clear solution were combined and then distilled to remove the solvent, yielding a milky white product. The milky white product was further heated at 200°C for 1 hour to further condense and remove low molecular weight molecules, finally yielding a viscous white liquid, namely the polyborosilicate precursor, with a yield of approximately 50.25%.

[0038] The number-average molecular weight of the polyborosilicate precursor was 2874 Da, the viscosity at 25°C was 500 cP, and the solubility in most organic solvents was >30 wt%. In this example, organic solvents such as n-hexane, toluene, xylene, and tetrahydrofuran were used for the experiment.

[0039] Preparation of carbon-free SiBN ceramics The polyborosilicate precursor was pyrolyzed in a tube furnace under an argon atmosphere, with the temperature increased from room temperature to 1000℃ at a rate of 5℃ / min and held for 4 hours to obtain carbon-free SiBN ceramics. Thermogravimetric analysis showed that the yield of carbon-free SiBN ceramics was 53.86% based on the polyborosilicate precursor.

[0040] Elemental analysis of the carbon-free SiBN ceramics revealed an oxygen content of 0.75 wt%, a nitrogen content of 14.37 wt%, a carbon content of 0.06%, a boron content of 0.68%, and a silicon content of 47.39%, confirming the presence of carbon-free SiBN ceramics.

[0041] Example 3 Preparation of polyborosilazane precursor The temperature was controlled at -10℃. 30.3 kg of dichlorosilane and 11.7 kg of boron trichloride were dissolved in tetrahydrofuran at a ratio of n(Si):n(B) = 3:1 and stirred until homogeneous. The temperature was controlled at 0℃. 26.01 kg of ammonia gas was introduced at a ratio of n1(N):n(Cl) = 1.7:1 for inorganic ammonolysis at a rate of 0.9 kg / h. After the introduction was completed, stirring was continued at 0℃ for 150 min. At the same temperature, 6.09 kg of gaseous dimethylamine was introduced at a ratio of n2(N):n(Cl) = 0.15:1. After the introduction was completed, the mixture was stirred and the reaction was capped for 1 h to obtain the crude product.

[0042] The crude product was filtered at 25°C to obtain a precipitate and a clear solution. The precipitate was washed twice with n-hexane to obtain a washing liquid. The precipitate was then discharged as an impurity. The washing liquid and the clear solution were combined and then distilled to remove the solvent, yielding a light white product. The light white product was further heated at 180°C for 2 hours to further condense and remove low molecular weight molecules, finally yielding a white liquid, namely the polyborosilazane precursor, with a yield of approximately 67.82%.

[0043] The number-average molecular weight of the polyborosilicate precursor was 794 Da, the viscosity at 25°C was 50 cP, and the solubility in most organic solvents was >60 wt%. In this example, organic solvents such as n-hexane, toluene, xylene, and tetrahydrofuran were used for the experiment.

[0044] Preparation of carbon-free SiBN ceramics The polyborosilicate precursor was pyrolyzed in a tube furnace under an argon atmosphere, with the temperature increased from room temperature to 1200℃ at a rate of 10℃ / min and held for 2 hours to obtain carbon-free SiBN ceramics. Thermogravimetric analysis showed that the yield of carbon-free SiBN ceramics was 48.66% based on the polyborosilicate precursor.

[0045] Elemental analysis of the carbon-free SiBN ceramic revealed an oxygen content of 0.53 wt%, a nitrogen content of 16.13 wt%, a carbon content of 0.02%, a boron content of 0.72%, and a silicon content of 41.84%, confirming the presence of carbon-free SiBN ceramic.

[0046] Comparative Example 1 Without adding organic amine end-capping agent, the organic amine end-capping agent is replaced with an equimolar amount of ammonia gas. The remaining steps and raw materials are the same as in Example 1, and a gel-like precursor is finally obtained. However, due to excessive cross-linking, the gel-like precursor has poor fluidity and is difficult to process. It cannot be used for coating preparation, melt spinning, or fiber-reinforced ceramic matrix composite prepreg preparation, and therefore cannot meet the requirements of industrial production.

[0047] Comparative Example 2 Adding ammonia and hexamethyldisilazane simultaneously disrupts the timing of organic amine end-capping. This causes end-capping of the polyborosilicate precursor during the early stages of molecular weight growth, resulting in excessively low molecular weight. This negatively impacts the yield of carbon-free SiBN ceramics prepared by pyrolysis and complicates subsequent material preparation processes. Furthermore, premature introduction of the organic amine end-capping agent leads to pyrolysis rearrangement of its structure during the intermediate temperature stage. Some carbon structures are introduced into the main chain, ultimately resulting in inability to remove them during pyrolysis and the formation of SiBN ceramics (leading to a carbon content greater than 5 wt%).

[0048] Test Example 1 Wave transmission performance comparison test: A vector network analyzer (VNA) and a resonant cavity were prepared. The carbon-free SiBN ceramics prepared in Examples 1-3 and commercially available carbon-containing SiBCN ceramics were processed into rectangular samples with smooth surfaces, uniform size, and slightly smaller than the width and height of the resonant cavity. The VNA was preheated and fully calibrated in a two-port configuration. Without the sample inserted, the cavity resonant frequency (f0) and unloaded quality factor (Q0) of the resonant cavity were scanned and found. The rectangular sample was then inserted, and a scan was performed to find the new resonant frequency (f1) and loaded quality factor (Q0) after the sample was inserted. L ).

[0049] ;where V c V is the effective volume of the resonant cavity. s For a rectangular sample volume, the dielectric constant (ε) can be obtained. r ).

[0050] ;where F d F is the field distribution factor. Since this is a comparative test, F can be considered as such in this invention. d The value is 1.

[0051] Antioxidant performance comparison test: One rectangular sample each from Examples 1-3 and commercially available carbon-containing SiBCN ceramics were selected. Three-point bending strength tests were performed according to the test method described in GB / T 6569-2006, and the average initial strength (σ0) and weight (W0) were recorded. Then, another rectangular sample was taken and placed in the homogenization zone of a high-temperature furnace, with flowing air introduced. It was held at 1500℃ for 50 hours, then slowly cooled to room temperature and weighed, with the weight (W1) recorded. Subsequently, three-point bending strength tests were performed according to the test method described in GB / T 6569-2006, and the average strength after the oxidation test (σ1) was recorded. The strength ratio (σ1 / σ0) and weight ratio (W1 / W0) were then calculated. Specific performance test data are shown in Table 1.

[0052] Table 1 Performance Test Results

[0053] As shown in Table 1, the carbon-free SiBN ceramic prepared by this invention exhibits superior wave transmission performance compared to carbon-containing SiBCN ceramics, while also possessing better oxidation resistance. This invention, through pre-organization design, ultimately aims to control the carbon content and produce carbon-free SiBN ceramics. This ceramic material has broad application prospects in radar / communication radomes and rectifiers, 5G communications, and other fields.

Claims

1. A method for preparing a polyborosilazane precursor, characterized in that, Boron and silicon sources are dissolved in an organic solvent, and an inorganic ammonolysis agent is introduced for inorganic ammonolysis. Subsequently, an end-capping agent is introduced for organic amine end-capping. After post-treatment and polycondensation, a polyborosilazane precursor is obtained. The boron source is boron trichloride, the silicon source is one or more of dichlorosilane, trichlorosilane, or tetrachlorosilane, the inorganic ammonolysis agent is ammonia, and the end-capping agent is one of hexamethyldisilazane, dimethylamine, or diethylamine. The molar ratio of silicon atoms in the silicon source to boron atoms in the boron source is 1~3:

1. Taking the total number of moles of chlorine atoms in the boron and silicon sources as nCl, the molar ratio of nitrogen atoms in the inorganic ammonolysis agent to nCl is 1.5~1.7:1; and the molar ratio of nitrogen atoms in the end-capping agent to nCl is 0.15~0.25:

1.

2. The method for preparing the polyborosilicate precursor according to claim 1, characterized in that, The organic solvent is one of n-hexane, toluene, xylene, or tetrahydrofuran.

3. The method for preparing the polyborosilazane precursor according to claim 1, characterized in that, The dissolution temperature is -10~0℃, the inorganic ammonolysis agent is introduced at a rate of 0.5~0.9 kg / h, and the inorganic ammonolysis temperature is -20~0℃.

4. The method for preparing the polyborosilazane precursor according to claim 1, characterized in that, The organic amine is capped at -20 to 0°C for 1 to 3 hours.

5. The method for preparing the polyborosilazane precursor according to claim 1, characterized in that, Post-treatment includes filtration at a temperature of 0~25℃.

6. The method for preparing the polyborosilazane precursor according to claim 1, characterized in that, The polycondensation temperature is 150~200℃, and the polycondensation time is 1~3h.

7. The method for preparing the polyborosilazane precursor according to claim 1, characterized in that, The polyborosilicate precursor has a number-average molecular weight of 794~2874 Da and a viscosity of 50~500 cP at 25°C.

8. The application of a polyborosilicate precursor prepared by the method of any one of claims 1 to 7, characterized in that, Carbon-free SiBN ceramics were prepared by pyrolysis of polyborosilicate precursors in an inert atmosphere. The carbon-free SiBN ceramics had an oxygen content of 0.53~0.75wt%, a nitrogen content of 14.26~16.13wt%, a carbon content of 0.02~0.07wt%, a boron content of 0.48~0.72wt%, and a silicon content of 41.84~51.61wt%.

9. The application of the polyborosilicate precursor according to claim 8, characterized in that, During pyrolysis, the heating rate is 5~10℃ / min, the pyrolysis temperature is 800~1200℃, and the pyrolysis time is 2~4h.

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