A cross-linking strategy constructed polymer conversion wave-absorbing ceramic and a preparation method and application thereof

Abstract

The application discloses a kind of crosslinking strategy construction polymer conversion wave-absorbing ceramic and its preparation method and application, belong to ceramic technical field, solve the problem of uneven dispersion of material caused by the preparation method in the prior art.The method comprises the following steps: the hyperbranched polyborosilazane precursor containing silicon-hydrogen bond and poly(diacetylene) dimethylsilane containing alkyne group are uniformly dissolved in anhydrous tetrahydrofuran according to the mass ratio of 5-20:1, platinum (0) -1,3-divinyl-1,1,3,3-tetramethyldisiloxane is added, and the anhydrous tetrahydrofuran is removed after overnight reaction at 45-60℃ temperature condition, to obtain a polymer precursor;The polymer precursor is crosslinked at 400℃, ground into powder, pressed into embryo and pyrolyzed at 1400℃, to obtain a polymer conversion wave-absorbing ceramic.The preparation method provided by the application uniformly mixes and crosslinks two kinds of polysilane at the molecular level to obtain a new polymer precursor, and pyrolyzes at high temperature to prepare a wave-absorbing ceramic with uniform dispersion of structural components, achieving a more stable effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramics, and more particularly to a cross-linking strategy constructed polymer-derived wave-absorbing ceramic and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of wireless communication technology, radar, satellite communication and other fields, electromagnetic pollution has gradually become an important problem in daily life. Electromagnetic waves not only cause interference to electronic devices and communication systems, but also may pose a potential threat to human health. Especially in the field of stealth in aerospace, military and other fields, the performance of electromagnetic wave absorbing materials for equipment and systems in high temperature environment has put forward more stringent requirements. Therefore, the development of electromagnetic wave absorbing materials with good stability and high performance has become an urgent task to meet the needs of modern industry.

[0003] Polymer-derived ceramics (PDCs) are a class of ceramic materials prepared by high-temperature pyrolysis of polymer precursors. In high temperature environment, PDCs show excellent thermal stability and structural integrity, which is an important method for preparing ceramic-based wave-absorbing materials. In recent years, a series of research results on PDCs wave-absorbing materials have been achieved, including PDC-SiC, SiCN, SiCNO, SiOC and SiBCN, etc. Among them, PDC-SiBCN ceramic shows more superior high-temperature stability (up to 1600℃), excellent oxidation resistance and chemical stability due to its unique element composition, so the application prospect of PDCs-SiBCN wave-absorbing ceramic in military stealth technology is particularly outstanding.

[0004] At present, there are studies that directly introduce carbon nanotubes, graphene oxide, carbon nanowires and other materials into polymer precursors, or dope metals in the precursors, in order to improve the dielectric properties of ceramic materials and enhance their electromagnetic wave absorption capacity. However, using doping and blending methods to adjust the electromagnetic wave absorption performance of materials not only needs to spend a lot of time for material blending, but also faces the problem of difficult uniform dispersion of ceramic components. SUMMARY

[0005] The present application provides a cross-linking strategy constructed polymer-derived wave-absorbing ceramic and a preparation method and application thereof, to solve the problem of uneven material dispersion caused by the preparation method in the prior art.

[0006] In a first aspect, the present application provides a preparation method of a polymer converted wave-absorbing ceramic, comprising the following steps: uniformly dissolving hyperbranched polysilazane precursor containing silicon-hydrogen bond and poly(diacetylene)dimethylsilane containing alkyne group in anhydrous tetrahydrofuran according to a mass ratio of 5-20:1, adding catalyst platinum(0)-1,3-divinylene-1,1,3,3-tetramethyldisiloxane, removing anhydrous tetrahydrofuran after overnight reaction under temperature condition of 45-60℃, and obtaining polymer precursor; heat-crosslinking the polymer precursor at 400℃, grinding into powder, pressing into embryo and pyrolyzing at 1400℃ to obtain the polymer converted wave-absorbing ceramic.

[0007] As a possible implementation manner, the preparation of the hyperbranched polysilazane precursor containing silicon-hydrogen bond comprises the following steps: mixing borane dimethyl sulfide complex and methyl vinyl dichlorosilane under ice bath condition and adding into a reaction container, and then reacting at normal temperature to obtain tris(dichlorosilylethyl)borane monomer; adding dichloromethylsilane and hexamethyldisilazane into the tris(dichlorosilylethyl)borane monomer, and heating to 180℃ for 2-4h to obtain the hyperbranched polysilazane precursor containing silicon-hydrogen bond.

[0008] As a possible implementation manner, the mass ratio of the borane dimethyl sulfide complex, the methyl vinyl dichlorosilane, the dichloromethylsilane and the hexamethyldisilazane is 1:3:1:5.6; and / or, the reaction time at normal temperature is 48h.

[0009] As a possible implementation manner, the preparation of the poly(diacetylene)dimethylsilane containing alkyne group comprises the following steps: adding n-butyllithium and hexachloro-1,3-butadiene into anhydrous tetrahydrofuran under anaerobic condition at a temperature of-78℃, and stirring to react; slowly adding dichlorodimethylsilane and keeping the reaction; adding a capping agent, and performing purification treatment to obtain the poly(diacetylene)dimethylsilane containing alkyne group.

[0010] As a possible implementation manner, the purification treatment comprises the following steps: after removing excessive tetrahydrofuran in the reaction system by rotary evaporation, adding the reaction system dropwise into anhydrous methanol solution for precipitation, and performing suction filtration to obtain a crude product; after redissolving the crude product in tetrahydrofuran, adding anhydrous methanol for precipitation again, and performing suction filtration, repeating the step operation for 1-3 times, and vacuum drying to obtain the poly(diacetylene)dimethylsilane containing alkyne group.

[0011] As a possible implementation manner, the mass ratio of the n-butyllithium, the hexachloro-1,3-butadiene and the dichlorodimethylsilane is 4:1:1; and / or, the stirring reaction time is 6h; and / or, the keeping reaction time is 12h.

[0012] In a second aspect, the present application provides a polymer converted wave-absorbing ceramic prepared by the preparation method of any possible implementation manner of the first aspect.

[0013] In a third aspect, the present application provides an application of the polymer converted wave-absorbing ceramic of any possible implementation manner of the second aspect in the field of aerospace.

[0014] In view of the problems of the prior art, the present application takes PDCs-SiBCN as the research object, regulates the molecular structure of the precursor, adopts poly(diacetylene)dimethylsilane (PDSDA) containing acetylene groups to perform molecular crosslinking after complete dissolution of hyperbranched polyborosilazane (hb-PBSZ), constructs a new polymer precursor, and prepares a wave-absorbing ceramic through high-temperature pyrolysis. After the modification of hb-PBSZ by PDSDA, the carbon elements in the polymer converted SiBCN ceramic are converted into ordered carbon structures, and nanowires and silicon carbide nanocrystals are generated in situ, thereby endowing the material with excellent electromagnetic wave absorption performance. The technical scheme of the present application enables the components of the polymer converted ceramic to be uniformly dispersed by designing the structure at the molecular level, and achieves a more stable effect. Moreover, by adjusting the content of PDSDA, the dielectric constant and wave-absorbing performance of the material can be further adjusted.

[0015] The present application introduces PDSDA with an acetylene group structure in the main chain into hyperbranched polyborosilazane through molecular crosslinking, and prepares a wave-absorbing ceramic through high-temperature pyrolysis. It is shown that the addition of PDSDA helps to form structures such as ordered carbon, nanofibers, and silicon carbide nanocrystals in the ceramic wave-absorbing material. With the increase of the addition amount of PDSDA, the silicon carbide crystals of the ceramic gradually increase, and the proportion of ordered carbon increases. The hb-PBSZ@PDSDA ceramic as a new type of electromagnetic wave absorbing material has good electromagnetic wave absorption application potential. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0017] Figure 1 The Fourier transform infrared spectroscopy (FT-IR) diagrams of hb-PBSZ, hb-PBSZ@PDSDA-20:1 precursor, hb-PBSZ@PDSDA-10:1 precursor, hb-PBSZ@PDSDA-5:1 precursor, and PDSDA provided by the embodiments of the present application.

[0018] Figure 2A hydrogen element nuclear magnetic spectrum of PDSDA in a deuterated chloroform solvent provided by the embodiment of the present application.

[0019] Figure 3 A carbon element nuclear magnetic spectrum of PDSDA in a deuterated chloroform solvent provided by the embodiment of the present application.

[0020] Figure 4 Morphology characterization results of hb-PBSZ@PDSDA-10:1 provided by the embodiment of the present application, wherein A is a scanning electron microscope image, B is a transmission electron microscope image, and C is an element energy spectrum.

[0021] Figure 5 XRD analysis results of hb-PBSZ@PDSDA-1:0, hb-PBSZ@PDSDA-20:1, hb-PBSZ@PDSDA-10:1 and hb-PBSZ@PDSDA-5:1 provided by the embodiment of the present application.

[0022] Figure 6 Raman spectrum analysis results of hb-PBSZ@PDSDA-1:0, hb-PBSZ@PDSDA-20:1, hb-PBSZ@PDSDA-10:1 and hb-PBSZ@PDSDA-5:1 provided by the embodiment of the present application.

[0023] Figure 7 Reflection coefficient curve analysis results of hb-PBSZ@PDSDA-1:0, hb-PBSZ@PDSDA-20:1, hb-PBSZ@PDSDA-10:1 and hb-PBSZ@PDSDA-5:1 provided by the embodiment of the present application. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0025] To solve the problem of uneven dispersion of material components caused by the preparation method in the prior art, the present embodiment provides a preparation and characterization experiment of a cross-linking strategy constructed polymer converted wave-absorbing ceramic.

[0026] It can be seen from the characterization results that by regulating the molecular structure of the precursor, cross-linking of poly(diacetylene)dimethylsilane (PDSDA) containing acetylene groups and hyperbranched polyborosilazane (hb-PBSZ) is adopted, the conversion of carbon elements in the pyrolytic SiBCN ceramic to ordered carbon structure is promoted, and the in-situ generation of nanowires and silicon carbide nanocrystals is realized, thereby excellent electromagnetic wave absorption performance is given to the material; the internal structure of the molecule is designed to make the polymer conversion ceramic structure components disperse uniformly, and a more stable effect is achieved. Moreover, by adjusting the content of PDSDA, the dielectric constant and wave absorption performance of the material can be further adjusted.

[0027] The technical solutions of the present application will be further described below in combination with specific examples.

[0028] Example 1

[0029] The present embodiment provides a preparation experiment of a cross-linking strategy constructed polymer conversion wave absorbing ceramic.

[0030] The Schlenk glass bottle is treated with double-row tube technology without water and oxygen. In an argon atmosphere, 50 mL of anhydrous tetrahydrofuran is injected into a 250 mL reaction bottle, the reaction system is maintained at -78°C by a liquid nitrogen acetone bath, and n-butyllithium (0.1257 mol) and hexachloro-1,3-butadiene (0.0314 mol) are slowly added, and the reaction is stirred under magnetic stirring for 6 h. Subsequently, 0.0314 mol of dichlorodimethylsilane is slowly added at the same temperature and the reaction is maintained for 12 h. Finally, 2 mL of trimethylchlorosilane is added as a capping agent to cap the reaction system, and a dark brown liquid is obtained, and the experiment is completed. In the product purification process, first, the excess tetrahydrofuran is removed by rotary evaporation, then it is dropped into an excess of anhydrous methanol solution for precipitation, and the PDSDA crude product is obtained by suction filtration; after the crude product is dissolved in tetrahydrofuran, anhydrous ethanol is added for further precipitation, suction filtration, and vacuum drying after repeating three times to obtain the product PDSDA, whose chemical formula is shown as formula (1).

[0031]

[0032] The Schlenk bottle is treated without water and oxygen. First, 58 mmol of borane dimethyl sulfide complex and 174 mmol of methyl vinyl dichlorosilane are injected into a 250 mL Schlenk reaction bottle under ice bath conditions, and then the reaction is carried out at room temperature for 48 h to obtain tris(dichlorosilylethyl)borane monomer; then 58 mmol of dichloromethylsilane and 324.8 mmol of hexamethyldisilazane are added, and the reaction system is heated by oil bath, and a transparent viscous liquid is obtained after 2 hours at 180°C, which is a hyperbranched polyborosilazane precursor (hb-PBSZ) containing silicon-hydrogen bonds, and its chemical formula is shown as formula (2).

[0033]

[0034] The prepared hyperbranched polysilazaborazine precursor containing silicon-hydrogen bonds and the prepared PDSDA were completely dissolved in anhydrous tetrahydrofuran in proportions, wherein the mass ratio of the hyperbranched polysilazaborazine precursor to the PDSDA was 1:0, 20:1, 10:1, and 5:1, respectively. After stirring uniformly, a small amount of platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane was added as a catalyst, and the temperature was raised to 45°C in an oil bath overnight. After the reaction was completed, anhydrous THF was removed by a cold trap device to obtain a black viscous material, i.e., a PDSDA cross-linked hyperbranched polysilazaborazine precursor. The material was transferred to a ceramic boat, heat-crosslinked at 400°C, and then ground into powder with a planetary ball mill. Finally, the powder was pressed into a green body and pyrolyzed in a high-temperature tube furnace at 1400°C to obtain a ceramic product, which was named hb-PBSZ@PDSDA-1:0, hb-PBSZ@PDSDA-20:1, hb-PBSZ@PDSDA-10:1, and hb-PBSZ@PDSDA-5:1, respectively.

[0035] Example 2

[0036] This example provides characterization experiments of hb-PBSZ@PDSDA.

[0037] The PDSDA, hb-PBSZ, hb-PBSZ@PDSDA-20:1 precursor, hb-PBSZ@PDSDA-10:1 precursor, and hb-PBSZ@PDSDA-5:1 precursor in Example 1 were subjected to Fourier infrared spectroscopy, respectively, to obtain the results as shown in Figure 1 .

[0038] The hydrogen element nuclear magnetic resonance spectrum and the carbon element nuclear magnetic resonance spectrum of the PDSDA in Example 1 in deuterated chloroform solvent are shown in Figure 2 and Figure 3 , respectively.

[0039] The hb-PBSZ@PDSDA-10:1 prepared in Example 1 was subjected to scanning electron microscopy and transmission electron microscopy energy spectrum analysis, and the results are shown in Figure 4 .

[0040] The hb-PBSZ@PDSDA-1:0, hb-PBSZ@PDSDA-20:1, hb-PBSZ@PDSDA-10:1, and hb-PBSZ@PDSDA-5:1 prepared in Example 1 were subjected to XRD analysis, respectively, and the results are shown in Figure 5 .

[0041] Raman spectrum analysis was carried out on the hb-PBSZ@PDSDA-1:0, hb-PBSZ@PDSDA-20:1, hb-PBSZ@PDSDA-10:1 and hb-PBSZ@PDSDA-5:1 prepared in Example 1 respectively, and the results as shown in Figure 6 were obtained.

[0042] Reflection coefficient curve analysis was carried out on the hb-PBSZ@PDSDA-1:0, hb-PBSZ@PDSDA-20:1, hb-PBSZ@PDSDA-10:1 and hb-PBSZ@PDSDA-5:1 prepared in Example 1 respectively, and the results as shown in Figure 7 were obtained.

[0043] As can be seen from Figures 1-3 , the present application successfully prepared PDSDA, and with the increase of the content of PDSDA, the silicon hydrogen bond in the infrared spectrum gradually weakens, and the carbon-carbon triple bond gradually enhances, which indicates that hb-PBSZ and PDSDA successfully occur crosslinking reaction.

[0044] As can be seen from Figures 4-7 , the addition of PDSDA helps to form nanofibers and silicon carbide nanocrystals in the ceramic wave-absorbing material, and with the increase of the addition amount of PDSDA, the diffraction peak value of SiC also increases, and the ID / IG value decreases, indicating that PDSDA can improve the crystallinity of silicon carbide and the proportion of ordered carbon in the pyrolysis conversion ceramic. By adjusting the proportion of the two materials, when the mass ratio of hyperbranched polysilaborazane and PDSDA is 10:1, the SiBCN ceramic obtained by pyrolysis at 1400 DEG C exhibits excellent electromagnetic wave absorption performance in the X band, and the minimum reflection coefficient can reach-50.11 dB, and the effective absorption bandwidth reaches 2.21 GHz. In summary, the hb-PBSZ@PDSDA ceramic as a new type of electromagnetic wave absorbing material has good electromagnetic wave absorption application potential.

[0045] Although preferred embodiments of the application have been described, those skilled in the art will be able to make additional changes and modifications to these embodiments once they have the basic inventive concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0046] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A method for preparing polymer-converted microwave absorbing ceramics, characterized in that, Includes the following steps: A hyperbranched polyborosilazane precursor containing silane bonds and a poly(diacetylene)dimethylsilane containing alkynyl groups were uniformly dissolved in anhydrous tetrahydrofuran at a mass ratio of 5 to 20:

1. Platinum(O)-1,3-diethylene-1,1,3,3-tetramethyldisiloxane catalyst was added, and the mixture was reacted overnight at a temperature of 45 to 60 °C. After removing the anhydrous tetrahydrofuran, the polymer precursor was obtained. The polymer precursor was thermally crosslinked at 400 °C, ground into powder, pressed into a preform, and pyrolyzed at 1400 °C to obtain the polymer-converted microwave absorbing ceramic. The preparation of the hyperbranched polyborosilazane precursor containing silane-hydrogen bonds includes the following steps: Under ice bath conditions, the boran dimethyl sulfide complex and methyl vinyl dichlorosilane were mixed and added to the reaction vessel, and then reacted at room temperature to obtain tri(dichlorosilylethyl)borane monomer; Dichloromethylsilane and hexamethyldisilazane were added to the tri(dichlorosilylethyl)borane monomer, and the mixture was heated to 180°C and reacted for 2-4 h to obtain the hyperbranched polyborosilicate precursor containing silane-hydrogen bonds. The preparation of the alkyne-containing poly(diacetylene)dimethylsilane includes the following steps: n-Butyllithium and hexachloro-1,3-butadiene were added to anhydrous tetrahydrofuran at -78 °C under anaerobic conditions and stirred to react. Slowly add dichlorodimethylsilane while maintaining the reaction; An end-capping agent was added, and the mixture was purified to obtain the alkynyl-containing poly(diacetylene)dimethylsilane.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the boronane dimethyl sulfide complex, the methyl vinyl dichlorosilane, the dichloromethylsilane, and the hexamethyldisilazane is 1:3:1:5.

6. And / or, the reaction is carried out at room temperature for 48 hours.

3. The preparation method according to claim 1, characterized in that, The purification process includes the following steps: After removing excess tetrahydrofuran from the reaction system by rotary evaporation, the reaction system was added dropwise to anhydrous methanol solution for precipitation, and then filtered to obtain the crude product. After redissolving the crude product in tetrahydrofuran, anhydrous methanol was added for reprecipitation. The product was then filtered and this step was repeated 1 to 3 times before vacuum drying to obtain the alkynyl-containing poly(diacetylene)dimethylsilane.

4. The preparation method according to claim 1, characterized in that, The molar ratio of the n-butyllithium, the hexachloro-1,3-butadiene, and the dichlorodimethylsilane is 4:1:

1. And / or, the duration of the stirring reaction is 6 h; And / or, the duration of the holding reaction is 12 h.

5. The polymer conversion absorbing ceramic prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the polymer conversion absorbing ceramic according to claim 5 in the aerospace field.

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