Preparation method and application of polyborosilazane precursor

Abstract

The invention belongs to the technical field of organic high-molecular 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 ammonolysis agent for inorganic ammonolysis; then introducing an end-capping reagent to carry out organic amine end capping, and carrying out post-treatment and polycondensation to obtain a polyborosilazane precursor; according to the application, a borosilazane precursor is subjected to pyrolysis in an inert atmosphere, and the carbon-free SiBN ceramic is prepared. The polyborosilazane precursor is prepared by designing inorganic ammonolysis and organic amine blocking, so that the problem of carbon residue of the ceramic when the precursor is used for preparing the ceramic is avoided, and the carbon-free SiBN ceramic prepared by the preparation method disclosed by the invention has the advantages that the wave-transparent property is superior to that of the carbon-containing SiBCN ceramic, and meanwhile, the carbon-free SiBN ceramic also has relatively good oxidation resistance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic polymer compounds, and particularly relates to a preparation method and application of a polysilaborazane precursor. BACKGROUND

[0002] Silicon boron nitride (SiBN) ceramic is a high-temperature wave-transparent ceramic material with good high-temperature resistance, excellent dielectric performance and excellent processability, and has good application prospects. In traditional processes, Si powder, SiN powder, B powder and BN powder are blended and ground in a certain ratio and then sintered, but it is difficult to obtain very uniform SiBN ceramic, and the sintering temperature is high. The synthesis of SiBCN polymer precursor for the preparation of SiBN ceramic will introduce carbon-containing components (such as methyl, phenyl, carborane, etc.) into the precursor, resulting in the formation of nanometer carbon clusters in the pyrolysis product. These carbon clusters are easy to combine with silicon atoms to form β-SiC crystal nuclei at high temperatures (> 1400℃), which can cause defects and anisotropy at the crystal boundary. The carbon clusters act as heterogeneous nucleation points, destroying the homogeneity of the SiBN amorphous network, forming a SiN / SiC / BN multi-phase interface, and causing thermal stress concentration, mechanical property degradation and electromagnetic property degradation. For example, the introduction of carbon elements significantly increases the dielectric loss, and in the high-temperature oxidation process, the carbon elements preferentially participate in the reaction in the oxidation environment, and the reaction generates carbon dioxide gas, causing the internal porosity of the material to rise, forming a loose porous intermediate phase, accelerating the degradation of the material structure, and thus reducing the mechanical properties.

[0003] Although controlling the carbon content can achieve better results in the dielectric performance of SiBCN ceramic, it is very difficult to synthesize carbon-free SiBN ceramic by pyrolysis of polysilaborazane precursor, because firstly, in the process of preparing SiBN ceramic by pyrolysis of SiBCN precursor, carbon can form a multi-phase structure of SiN / SiC / BN through spontaneous phase separation in the pyrolysis process, and if SiBN ceramic is prepared by the path of preparing SiBCN ceramic, a reactive gas such as ammonia gas needs to be used to remove carbon in the high-temperature sintering process, which makes the preparation process difficult to operate, increases the cost and increases the risk.

[0004] Chinese patent CN114133575A discloses a preparation method of a high-boron-content polysilaborazane, which comprises the following steps: S1, first filling inert gas into carborane and reaction solvent, and dropping n-butyl lithium for reaction; S2, filling inert gas into chlorosilane and reaction solvent, and dropping the product in S1 for reaction; S3, adding reaction solvent to the reaction product in S2, or adding reaction solvent and boron trichloride to the reaction product in S2, and then dropping amine compound, and then reacting at 20-110℃ for 1-15h, and then reacting at 150-300℃ for 5-15h to obtain the product.

[0005] The patent fails to effectively control the carbon content in SiBN ceramics because the patent introduces carbon atoms, which are difficult to remove during pyrolysis because they are distributed in the molecular chain of polysilazane, and because carbon atoms are easy to combine with silicon atoms to form beta-SiC crystal nuclei at high temperatures, which affects the oxidation resistance, mechanical properties, dielectric properties and ablation resistance of SiBN ceramics. SUMMARY

[0006] The present application aims to provide a preparation method of a polysilazane precursor, which ensures the formation of a complete chain structure by pre-organizing at the molecular level, so as to reduce the generation of other competitive structures during the pyrolysis of SiBN ceramics, and simultaneously provides the application of the precursor in the field of carbon-free silicon boron nitride ceramics.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is: The preparation method of the polysilazane precursor provided by the present application is to dissolve a boron source and a silicon source in an organic solvent, and then introduce an inorganic ammonolysis agent for inorganic ammonolysis; subsequently, an end-capping agent is introduced for organic amine end-capping, and the polysilazane precursor is obtained after post-treatment and polycondensation.

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

[0009] wherein: 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 gas, 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: ; Wherein R1, R3, R5 are one of methyl, ethyl or trimethylsilyl group. R2, R4, R6 are one of hydrogen, methyl, ethyl or trimethylsilyl group, R1 and R2, R3 and R4, R5 and R6 can be the same or different; the end-capping agent is one of hexamethyldisilazane, dimethylamine or diethylamine.

[0019] The "pre-organization" refers to that the present application is not simply mixed raw materials according to the proportion of boron, silicon and nitrogen atoms, but through chemical design (i.e. selecting specific monomers, controlling reaction conditions and sequence) when synthesizing polysilazane precursor, the arrangement of Si, C, B and N atoms is realized, the carbon content in the main chain is maximally reduced, the carbon atoms are basically distributed in the side chain, and the subsequent pyrolysis is facilitated to remove the side chain carbon and hydrogen small molecules and then obtain the carbon-free SiBN ceramic; if there is no pre-organization, too many carbon atoms in the main chain will be difficult to pyrolyze and remove, which will adversely affect the electrical properties of the ceramic; in addition, if the boron, silicon and nitrogen elements are not designed through pre-organization, they will easily form their own enrichment zones during pyrolysis, produce other by-products, and destroy the uniformity of the ceramic.

[0020] The beneficial effects of the present application are as follows: (1) The present application realizes pre-organization, which is to avoid introducing organic carbon source in the main chain of the polysilazane precursor molecule by using carbon-free boron source (i.e. boron trichloride) and silicon source (i.e. dichlorosilane / trichlorosilane / tetrachlorosilane); and by inorganic ammonolysis and organic amine capping (hexamethyldisilazane, dimethylamine or diethylamine), a small amount of carbon is contained in the side chain of the precursor molecule chain in the early stage, and the carbon in the side chain and the terminal carbon can be removed by volatilization at high temperature in the pyrolysis process, thereby eliminating the risk of carbon residue from the source.

[0021] (2) The structure of the precursor molecule chain is controlled by the two-step method of "inorganic ammonolysis + organic amine capping". The ammonolysis stage forms Si-N-B, Si-N-Si and B-N-B skeleton; the inorganic ammonolysis degree is controlled for organic amine capping to terminate active groups, and the formation of chain, ring or other amorphous structure by dynamic recombination of B-N bond during high-temperature pyrolysis of polysilazane precursor is controlled: After inorganic ammonia solution, a large number of active groups (such as B-NH2, Si-NH2) are left on the surface of the precursor, which are prone to self-condensation at high temperature. The present application selects one of hexamethyldisilazane, dimethylamine or diethylamine to cap. In the early stage of pyrolysis, the capped groups are decomposed and removed by heat, and then a stable B-N chain structure and a small amount of B-N six-membered ring network are generated. After the complete removal of the small amount of residual CH3 in the late stage of pyrolysis, the pre-organized network has formed a stable structure, achieving the effect of interpenetration of the final linear structure (such as Si-N-B, Si-N-Si and B-N-B) and the network structure (B3N3). The pyrolysis products of hexamethyldisilazane, dimethylamine or diethylamine (such as trimethylsilyl compounds, methyl or ethyl) can be completely volatilized above 600°C, avoiding the problem of residual carbon impurities. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 NMR spectrum of the polyborosilazane precursor in Example 1; Figure 2 NMR spectrum of the polyborosilazane precursor in Example 1; Figure 1 NMR spectrum of the polyborosilazane precursor in Example 1; Figure 3 NMR spectrum of the polyborosilazane precursor in Example 1; Figure 4 NMR spectrum of the polyborosilazane precursor in Example 1; Figure 5 NMR spectrum of the polyborosilazane precursor in Example 1; Figure 6 NMR spectrum of the polyborosilazane precursor in Example 1; Figure 7 NMR spectrum of the polyborosilazane precursor in Example 1. DETAILED DESCRIPTION

[0023] The present application will be described and explained in detail below in connection with the following examples.

[0024] For simplicity of expression, the following "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 source and the silicon source, "n1(N)" refers to the number of moles of nitrogen atoms in the inorganic ammonia solution 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°C, 29.8 kg of trichlorosilane and 11.7 kg of boron trichloride were dissolved in n-hexane in the proportion of n(Si):n(B)=2.2:1, and stirred uniformly; the temperature was controlled at -10°C, and inorganic ammonolysis was carried out by introducing ammonia gas 26.11 kg in the proportion of n1(N):n(Cl)=1.6:1, the introduction rate was 0.5 kg / h, after the introduction was completed, stirring was continued at -10°C for 180 min; at this temperature, hexamethyldisilazane 30.99 kg was dropped in the proportion of n2(N):n(Cl)=0.2:1, after the dropping was completed, the end-capping reaction was stirred for 3 h, and then the temperature was restored 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 with n-hexane twice to obtain a washing liquid, then the precipitate was discharged as impurities, and the washing liquid was combined with the clear solution, then the solvent was removed by distillation to obtain a light milky white product; the light milky white product was further heated at 150°C for 3 h, and low molecules were further removed by condensation to finally obtain a viscous white liquid, the yield was about 61.37%.

[0027] For polymer structure characterization, the specific models of the equipment used are as follows: for infrared spectroscopy characterization, a Japanese Shimadzu, model IRTracer-100, is selected; for nuclear magnetic hydrogen spectrum characterization, a German Bruker, model AVANCE III HD-400, is selected; for thermal gravimetric characterization, a German NETZSCH, model NETZSCH STA 449 F5, is selected; for gel chromatography characterization, a American Waters, model Waters-1515, is selected; for oxygen element and nitrogen element content analysis, a American LECO, model ONH836, is selected; for carbon element content analysis, a American LECO, model CS844, is selected; for silicon element and boron element content analysis, a Japanese Hitachi, model Z-2300, is selected; for X-ray diffraction characterization, a German Bruker, model D8 ADVANCE, is selected.

[0028] The number average molecular weight of the prepared polyborosilazane precursor is 986 Da, the viscosity at 25°C is 80 cP, and the solubility in most organic solvents is >50 wt%, and in this embodiment, n-hexane, toluene, xylene, tetrahydrofuran and other organic solvents are used for experiments.

[0029] The sample is taken for nuclear magnetic resonance detection, and the nuclear magnetic resonance hydrogen spectrum is as shown in Figure 1 、 2 The peak of 4.0-5.5 ppm in the spectrum is the Si-H peak in the structure, which is derived from trichlorosilane in the raw material, and the peak of -0.25-0.25 ppm is the hydrogen in the methyl structure, which is derived from hexamethyldisilazane in the end-capping agent, the integral ratio of the two is -SiH:-CH3≈1:14.7, and the theoretical structure of the molecular formula is: ; TMS is the abbreviation of 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 detected by elemental analysis, and the results were as follows: oxygen content 0.69wt%, nitrogen content 14.26wt%, carbon content 0.07%, boron content 0.48%, and silicon content 51.61%. It was proved that the carbon-free SiBN ceramic was obtained.

[0036] Example 2 Preparation of polyborosilazane precursor The temperature was controlled at 0°C, 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 uniformly; the temperature was controlled at -20°C, and 33.15 kg of ammonia was introduced for inorganic ammonolysis at a ratio of n1(N):n(Cl)=1.5:1, the introduction rate was 0.75 kg / h, after the introduction was completed, the stirring was continued at -20°C for 180 min; at the same temperature, 23.77 kg of diethylamine was dropped at a ratio of n2(N):n(Cl)=0.25:1, after the dropping was completed, the stirring was continued for 2 h for end-capping reaction, and the crude product was obtained.

[0037] The crude product was filtered at 10°C to obtain a precipitate and a clear solution, the precipitate was washed with n-hexane twice to obtain a washing liquid, and then the precipitate was discharged as impurities, the washing liquid was combined with the clear solution, and then the solvent was removed by distillation to obtain a milky white product; the milky white product was further heated at 200°C for 1 h, and low molecular was further condensed and removed, and finally a viscous white liquid, i.e. polyborosilazane precursor, was obtained, and the yield was about 50.25%.

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

[0039] Preparation of carbon-free SiBN ceramic The polyborosilazane precursor was pyrolyzed in a tube furnace under argon atmosphere, the temperature was increased from room temperature to 1000°C at a rate of 5°C / min, and the temperature was kept for 4 h, and carbon-free SiBN ceramic was obtained. The yield of carbon-free SiBN ceramic was 53.86% based on the polyborosilazane precursor by thermogravimetric characterization.

[0040] Elemental quantitative analysis was performed on the carbon-free SiBN ceramic, and the oxygen content was 0.75wt%, the nitrogen content was 14.37wt%, the carbon content was 0.06%, the boron content was 0.68%, and the silicon content was 47.39%, which proved that the carbon-free SiBN ceramic was obtained.

[0041] Example 3 Preparation of polyborosilazane precursor The temperature was controlled at -10°C, 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 uniformly; the temperature was controlled at 0°C, and 26.01 kg of ammonia was introduced at a ratio of n1(N):n(Cl)=1.7:1 for inorganic ammonolysis, the introduction rate was 0.9 kg / h, and after the introduction was completed, the stirring was continued at 0°C for 150 min; at this temperature, 6.09 kg of gaseous dimethylamine was introduced at a ratio of n2(N):n(Cl)=0.15:1, and after the introduction was completed, the stirring was continued for 1 h for end-capping reaction, and the crude product was obtained.

[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, and then the precipitate was discharged as impurities, the washing liquid was combined with the clear solution, and then the solvent was removed by distillation to obtain a light white product; the light white product was further heated at 180°C for 2 h, and low molecules were further removed by condensation to finally obtain a white liquid, i.e., a polysilazane precursor, and the yield was about 67.82%.

[0043] The number average molecular weight of the polysilazane precursor prepared in the embodiment was 794 Da, the viscosity at 25°C was 50 cP, and the solubility in most organic solvents was >60 wt%, and n-hexane, toluene, xylene, tetrahydrofuran and other organic solvents were used for experiments.

[0044] Preparation of carbon-free SiBN ceramic The polysilazane precursor was pyrolyzed in a tube furnace under an argon atmosphere, the temperature was increased from room temperature to 1200°C at a rate of 10°C / min, and the temperature was maintained for 2 h to obtain a carbon-free SiBN ceramic. The yield of the carbon-free SiBN ceramic was 48.66% based on the polysilazane precursor by thermogravimetric characterization.

[0045] Elemental quantitative analysis was performed on the carbon-free SiBN ceramic, and the oxygen content was 0.53 wt%, the nitrogen content was 16.13 wt%, the carbon content was 0.02%, the boron content was 0.72%, and the silicon content was 41.84%, which proved that the carbon-free SiBN ceramic was obtained.

[0046] Comparative Example 1 No organic amine capping agent was added, and the organic amine capping agent was replaced by an equal number of moles of ammonia, and the remaining steps and raw materials were the same as in Example 1, and finally a gel-like precursor was obtained. The gel-like precursor had poor flowability due to excessive crosslinking, and was difficult to process, and could not be used for coating preparation or melt spinning or fiber reinforced ceramic matrix composite prepreg preparation, and could not meet the requirements of industrial production.

[0047] Comparative Example 2 The simultaneous addition of ammonia and hexamethyldisilazane, i.e., the timing of the organic amine capping, will prematurely cap the polyborosilazane precursor before the initial stage of molecular weight growth, resulting in a too low molecular weight, which will affect the later pyrolysis to prepare carbon-free SiBN ceramic and will also complicate the later material preparation process. At the same time, the premature introduction of the organic amine capping agent will cause the structure to undergo thermal rearrangement at medium temperatures, and part of the carbon structure will be introduced into the main chain, ultimately resulting in the pyrolysis being unable to remove and forming SiBN ceramic (which will make the carbon content greater than 5wt%).

[0048] Test Example 1 Wave transmission performance comparison test: prepare a vector network analyzer (VNA) and a resonant cavity, and process the carbon-free SiBN ceramic prepared in Examples 1-3 and the commercially available carbon-containing SiBCN ceramic into rectangular samples with smooth surfaces, uniform sizes, and slightly smaller width and height than the resonant cavity. Turn on the VNA preheat, calibrate the VNA, and scan to find the cavity resonance frequency (f0) and unloaded quality factor (Q0) of the resonant cavity without the sample; put in the rectangular sample, perform scanning, and find the new resonance frequency (f1) and loaded quality factor (Q L ).

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

[0050] ; wherein F d is the field distribution factor, and since it is a comparison test, F d is considered to be 1 in the present application.

[0051] Oxidation resistance performance comparison test: select one rectangular sample each of the carbon-free SiBN ceramic prepared in Examples 1-3 and the commercially available carbon-containing SiBCN ceramic, and perform three-point bending strength test according to the test method described in GB / T 6569-2006, and record the average initial strength (σ0) and weight (W0); then take another rectangular sample each, and put them into the temperature uniform zone of a high-temperature furnace, and pass in flowing air, and heat at 1500℃ for 50h, slowly cool to room temperature with the furnace, and weigh, and record the weight (W1); then perform three-point bending strength test according to the test method described in GB / T 6569-2006, and record the average strength after oxidation resistance test (σ1), and then calculate the strength ratio (σ1 / σ0) and weight ratio (W1 / W0). The specific performance test data are shown in Table 1.

[0052] Table 1 Performance test results

[0053] As shown in Table 1, the SiBN ceramic without carbon prepared in the application has better wave permeability than the SiBCN ceramic with carbon and also has better oxidation resistance. Through pre-organization design, the final purpose is to control the carbon content, and the SiBN ceramic without carbon is prepared, and the ceramic material has wide application prospects in the fields of radar / communication antenna covers and fairings, 5G communication and the like.

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 organic amine is introduced for end-capping, and after post-treatment and polycondensation, a polyborosilicate precursor is obtained.

2. The method for preparing the polyborosilicate precursor according to claim 1, characterized in that, 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.

3. The method for preparing the polyborosilazane precursor according to claim 1, characterized in that, 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.

4. 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℃.

5. 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.

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

7. 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.

8. 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.

9. The application of a polyborosilicate precursor prepared by the method of any one of claims 1 to 8, 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%.

10. The application of the polyborosilicate precursor according to claim 9, 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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