A B / Bi2O3 / PVDF nanocomposite energetic thin film and its preparation method

Abstract

The application discloses a kind of B / Bi2O3 / PVDF nano-composite energetic film and preparation method thereof, belong to energetic material technical field.The nano-composite energetic film is composed of nano B, Bi2O3 and PVDF, and is prepared by the method that mechanical ball milling is combined with electrospinning.The method comprises the following steps: B and Bi2O3 are mechanically ball milled according to mass ratio 100:5 to 100:20, then the B / Bi2O3 compound after ball milling is mixed with PVDF solution, and nano-composite energetic fiber film is prepared by electrospinning method.The application realizes the effective removal of B2O3 passivation layer on the surface of B particles and the exposure of active B through the synergistic effect of Bi2O3 and PVDF, significantly reduces the initial oxidation temperature of B, improves the combustion temperature and energy release efficiency, and has important application value in the fields of micro ignition and initiation, multi-functional intelligent energetic device and the like.

Description

Technical Field

[0001] This invention relates to a B / Bi2O3 / PVDF nanocomposite energetic thin film and its preparation method, belonging to the field of energetic thin film technology. Background Technology

[0002] Energetic materials are substances capable of rapidly releasing large amounts of energy. Their systems typically contain fuel and oxidizer components and are widely used in explosives, propellants, pyrotechnics, and propellants. With the development of nanotechnology, nanocomposite energetic materials have become a new research hotspot, showing significant application potential in micro-ignition and detonation systems (MEMS) and multifunctional intelligent energetic devices. Boron (B) powder is considered a highly promising energetic material due to its excellent mass energy density (58.3 MJ / kg) and volumetric energy density, with energy characteristics significantly superior to traditional metallic fuels such as aluminum (31 MJ / kg) and magnesium (25 MJ / kg). However, in practical applications, B powder suffers from the problem of easily forming a natural B₂O₃ passivation layer (approximately 7-10 nm) on its surface, and melting into a high-viscosity barrier layer at approximately 450℃, hindering oxygen diffusion to the B nucleus, leading to ignition difficulties and insufficient energy release efficiency.

[0003] Existing studies have shown that the ignition and combustion performance of boron powder can be effectively improved by introducing active metals, metal oxides, and fluoropolymers. Among them, metal oxides such as Bi2O3 can promote the thermal oxidation reaction of boron powder, reduce the ignition temperature, and enhance the combustion propagation ability [MNOYAN A, CHROAY S, KIM M, et al. TiO2-Bi2O3 bimetallic oxide nanocomposite coatings for enhanced ignition and combustion of boron-based energetic materials[J]. Combustion and Flame, 2026, 283: 114598.]. In addition, fluoropolymers such as PVDF can generate fluorine-containing active species during pyrolysis, which react with the oxide layer on the surface of boron, thereby promoting the removal of B2O3 and improving the boron core reaction activity [VALLURI SK, SCHOENITZ M, DREIZIN EJD T. Fluorine-containing oxidizers for metal fuels in energetic formulations[J]. Defence Technology, 2019, 15(1): 1-22.]. Polyvinylidene fluoride (PVDF) not only possesses excellent thermochemical stability, hydrophobicity, and processing properties, but can also be used as a reactive binder in energetic nanocomposite systems. PVDF can improve the dispersibility of nano-metal particles and enhance the energy release efficiency of the system by forming a strong metal-fluorine reaction. For example, Ke et al. showed that Al / PVDF nanocomposite films can undergo a significant pre-ignition reaction during heating, thereby promoting the rupture of the oxide layer on the surface of Al particles and improving combustion performance [KE X, GUO S, ZHANG G, et al. Safe preparation,energetic performance and reaction mechanism of corrosion-resistant Al / PVDFnanocomposite films [J]. Journal of Materials Chemistry A, 2018, 6(36):17713-17723.].In addition, Zhang et al. prepared Si@PVDF nanostructured energetic films using electrospinning technology, which achieved uniform dispersion of nanoparticles in PVDF fibers and significantly improved the combustion stability and safety performance of the system [ZHANG C, MAO H, CUI R, et al. Electrospinning preparation, energetic characteristics and reaction mechanism of corrosion-resistant Si@PVDF nanostructured denergetic films[J]. 2022, 237: 111887].

[0004] Therefore, constructing a B / Bi2O3 / PVDF ternary nanocomposite energetic system and achieving comprehensive regulation of the ignition and energy release processes through a coupling mechanism of "fluorination-assisted depassivation-interface enhanced oxidation" is of great research significance and application value. Summary of the Invention

[0005] The purpose of this invention is to provide a B / Bi2O3 / PVDF nanocomposite energetic thin film and its preparation method, so as to solve the problems of high ignition temperature and low energy release efficiency of B powder due to the surface passivation layer in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a B / Bi2O3 / PVDF nanocomposite energetic thin film, comprising the following steps:

[0008] (1) B nanoparticles and Bi2O3 powder were loaded into a ball mill jar, and anhydrous ethanol was added as a dispersion medium. After ball milling, washing, vacuum drying and grinding, uniform B / Bi2O3 composite powder was obtained.

[0009] (2) Dissolve PVDF in a mixed solvent of N,N-dimethylformamide (DMF) and acetone, and prepare a PVDF solution with a mass fraction of 10% by ultrasonication and stirring. Add the above B / Bi2O3 composite powder to the PVDF solution at a mass ratio of (B / Bi2O3):PVDF = 30:70. Stir and mix for 10 minutes, then sonicate for 2 hours to ensure uniform dispersion, and finally continue stirring for 12 hours to obtain a uniform and stable spinning precursor solution.

[0010] (3) The precursor solution is loaded into a syringe, electrospinned, the electrospun film is collected and dried at room temperature to obtain the B / Bi2O3 / PVDF nanocomposite energetic film.

[0011] Furthermore, the mass ratio of B nanoparticles to Bi2O3 powder is 100:5 to 100:20, preferably 100:15.

[0012] Furthermore, the particle size of B nanoparticles is 100-200 nm; the particle size of Bi2O3 powder is 200-800 nm.

[0013] Furthermore, the process parameters for ball milling are as follows: ball-to-material ratio of 20:1, rotation speed of 300 rpm, and time of 2 h; vacuum drying temperature of 50 ℃ and time of not less than 4 h.

[0014] Furthermore, the molecular weight of PVDF is 250,000 to 500,000.

[0015] Furthermore, the volume ratio of N,N-dimethylformamide (DMF) to acetone is 1:1.

[0016] Furthermore, the electrospinning parameters are as follows: spinning rate 0.25 mm / min, positive voltage 8.5 kV, negative voltage -3 kV, collection distance 10 cm, temperature 25 ℃, and humidity 45%.

[0017] Secondly, the present invention provides a B / Bi2O3 / PVDF nanocomposite energetic thin film prepared by the method described in the first aspect.

[0018] Compared with the prior art, the significant advantages of this invention are:

[0019] 1. This invention pre-treats the B / Bi2O3 system by mechanical ball milling, so that Bi2O3 is uniformly and densely attached to the surface of B particles, which effectively increases the contact area of ​​the B-Bi2O3 interface and promotes the efficiency of subsequent reactions.

[0020] 2. This invention uses electrospinning technology to uniformly coat B / Bi2O3 into PVDF fibers, achieving uniform dispersion and interfacial coupling of B, Bi2O3 and PVDF at the nanoscale, thus constructing a continuous fiber network structure.

[0021] 3. In this invention, the HF generated by the pyrolysis of PVDF reacts with the B2O3 passivation layer on the B surface to fluorinate, effectively removing the passivation layer and exposing the active B core; Bi2O3 melts at high temperature, forming a continuous and flowable oxidant phase on the surface of B particles, continuously transporting active oxygen to the B interface, significantly accelerating the high-temperature oxidation of B.

[0022] 4. When the Bi2O3 content is 15%, the initial oxidation temperature of B can be reduced by about 174.19 ℃ (from 706.43 ℃ to 532.47 ℃), the combustion temperature can be increased from 1121-1133 ℃ to 1533 ℃, and the combustion duration can be shortened from 3.1 s to 2.2 s, resulting in the best overall thermal reaction and combustion performance. Attached Figure Description

[0023] Figure 1 SEM images of the B / Bi2O3 / PVDF samples are shown, where: (a, e) (100B / 5Bi2O3)30 / 70PVDF; (b, f) (100B / 10Bi2O3)30 / 70PVDF; (c, g) (100B / 15Bi2O3)30 / 70PVDF; (d, h) (100B / 20Bi2O3)30 / 70PVDF.

[0024] Figure 2 The XRD patterns are shown, where: (a) raw material B, raw material Bi2O3, raw material PVDF; (b) B / Bi2O3 / PVDF nanocomposite energetic thin film.

[0025] Figure 3 The images are FTIR spectra, where: (a) raw materials; (b) B / Bi2O3 / PVDF nanocomposite energetic thin films.

[0026] Figure 4 The static water contact angle (WCA) results for the B / Bi2O3 / PVDF samples are shown below: (a) (100B / 5Bi2O3)30 / 70PVDF; (b) (100B / 10Bi2O3)30 / 70PVDF; (c) (100B / 15Bi2O3)30 / 70PVDF; (d) (100B / 20Bi2O3)30 / 70PVDF.

[0027] Figure 5 The TG-DSC curves of the B / Bi2O3 / PVDF sample in air are shown, where: (a) TG; (b) DSC.

[0028] Figure 6 The TG-DSC curves of the B / Bi2O3 / PVDF sample in argon are shown, where: (a) TG; (b) DSC.

[0029] Figure 7The images show the combustion of B / Bi2O3 / PVDF films, where: (a) (100B / 5Bi2O3)30 / 70PVDF; (b) (100B / 10Bi2O3)30 / 70PVDF; (c) (100B / 15Bi2O3)30 / 70PVDF; (d) (100B / 20Bi2O3)30 / 70PVDF.

[0030] Figure 8 The following are the combustion temperature-time curves and infrared images of the samples, where: (a) (100B / 5Bi2O3)30 / 70PVDF; (b) (100B / 10Bi2O3)30 / 70PVDF; (c) (100B / 15Bi2O3)30 / 70PVDF; (d) (100B / 20Bi2O3)30 / 70PVDF; (e) temperature-time curves.

[0031] Figure 9 SEM images of the combustion products of the B / Bi2O3 / PVDF sample are shown, where: (a, e) (100B / 5Bi2O3)30 / 70PVDF; (b, f) (100B / 10Bi2O3)30 / 70PVDF; (c, g) (100B / 15Bi2O3)30 / 70PVDF; (d, h) (100B / 20Bi2O3)30 / 70PVDF.

[0032] Figure 10 The XRD pattern of the combustion products of B / Bi2O3 / PVDF. Detailed Implementation

[0033] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this disclosure and should not be regarded as specific limitations on this application.

[0034] The technical terms “first”, “second”, etc. in this application are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features.

[0035] The reference to "embodiment" in this application means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0036] The technical term "and / or" in this application is only a description of the relationship between related objects, indicating that there can be three kinds of relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist at the same time, and B exists alone.

[0037] In addition, the character " / " in this application generally indicates that the objects before and after it are in an "or" relationship.

[0038] In this application, "multiple" means two or more (including two), and "at least one" means one or more.

[0039] It should be noted that, unless otherwise specified in the examples, the conditions should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0040] The inventors conducted preliminary exploratory experiments to determine the optimal mass ratio of B and PVDF and the optimal PVDF concentration in the B / PVDF nanocomposite energetic thin film system. The experimental process is as follows:

[0041] The samples were based on three PVDF concentrations (8%, 10%, and 12%), each with four different B:PVDF mass ratios (10:90, 30:70, 50:50, and 70:30). First, a precise mass of PVDF was weighed and dissolved in a binary mixture of N,N-dimethylformamide (DMF) and acetone (volume ratio 1:1). This solution was sonicated for 1 h and magnetically stirred for 10 min to ensure complete polymer dissolution and the formation of a homogeneous solution. Next, an appropriate amount of B nanoparticles was added to the PVDF solution. The mixture was stirred for 10 min, then sonicated for 2 h to ensure uniform dispersion of the B nanoparticles, followed by continuous stirring for 12 h to obtain a uniform and stable precursor solution. Finally, the prepared precursor solution was loaded into a syringe and spun under the following conditions: spinning rate 0.25 mm / min, positive voltage 8.5 kV, negative voltage -3 kV, and collection distance 10 cm. Finally, the electrospun films were collected and dried at room temperature for 24 h to obtain B / PVDF nanocomposite energetic films. These energetic films were characterized and their performance was tested. When the PVDF concentration was 10% and the B:PVDF ratio was 30:70, the sample achieved a better balance between formability and combustion performance. Therefore, when using B / Bi₂O₃ composite powder to replace B nanoparticles, different B and Bi₂O₃ mass ratios in the B / Bi₂O₃ composite powder were studied using a PVDF concentration of 10% and a B / Bi₂O₃:PVDF ratio of 30:70 as process parameters.

[0042] Example 1

[0043] Preparation of (100B / 5Bi2O3)30 / 70PVDF nanocomposite energetic films and study of their thermal reaction and combustion properties:

[0044] (1) Preparation of B / Bi2O3 composite material: B nanoparticles and Bi2O3 were weighed separately at a mass ratio of 100:5 (i.e., 100B / 5Bi2O3), and loaded into a ball mill jar. Grinding balls were added at a ball-to-material ratio of 20:1. Anhydrous ethanol was added as a dispersion medium, and the mixture was mechanically ball-milled at 300 rpm for 2 h. Subsequently, the mixture was washed with anhydrous ethanol and dried in a vacuum oven at 50 ℃ for about 4 h. The resulting uniform B / Bi2O3 composite powder was obtained by grinding.

[0045] (2) Preparation of spinning precursor solution: PVDF was dissolved in a mixed solvent of DMF and acetone (volume ratio 1:1), ultrasonicated for 1 hour and then magnetically stirred for 10 minutes to prepare a PVDF solution with a mass fraction of 10%. The above B / Bi2O3 composite was added to the PVDF solution (the total mass ratio of B to Bi2O3 to PVDF was 30:70), stirred for 10 minutes, ultrasonicated for 2 hours, and finally stirred continuously for 12 hours to obtain a uniform and stable spinning precursor solution.

[0046] (3) Electrospinning preparation of thin films: The precursor solution was loaded into a syringe, and electrospinning was carried out under the conditions of spinning rate of 0.25 mm / min, positive voltage of 8.5 kV, negative voltage of -3 kV, and collection distance of 10 cm. The resulting film was dried at room temperature for 24 h to obtain (100B / 5Bi2O3)30 / 70PVDF nanocomposite energetic film.

[0047] Example 2

[0048] Preparation of (100B / 10Bi2O3)30 / 70PVDF nanocomposite energetic films and study of their thermal reaction and combustion properties:

[0049] (1) Preparation of B / Bi2O3 composite material: B nanoparticles and Bi2O3 were weighed separately at a mass ratio of 100:10 (i.e., 100B / 10Bi2O3), and loaded into a ball mill jar. Grinding balls were added at a ball-to-material ratio of 20:1. Anhydrous ethanol was added as a dispersion medium, and the mixture was mechanically ball-milled at 300 rpm for 2 h. Subsequently, the mixture was washed with anhydrous ethanol and dried in a vacuum oven at 50 ℃ for about 4 h. The resulting uniform B / Bi2O3 composite powder was obtained by grinding.

[0050] (2) Preparation of spinning precursor solution: PVDF was dissolved in a mixed solvent of DMF and acetone (volume ratio 1:1), sonicated for 1 hour and magnetically stirred for 10 minutes to prepare a PVDF solution with a mass fraction of 10%. The above B / Bi2O3 composite was added to the PVDF solution (the total mass ratio of B to Bi2O3 to PVDF was 30:70), stirred for 10 minutes, sonicated for 2 hours, and finally stirred continuously for 12 hours to obtain a uniform and stable spinning precursor solution.

[0051] (3) Electrospinning preparation of thin films: The precursor solution was loaded into a syringe, and electrospinning was carried out under the conditions of spinning rate of 0.25 mm / min, positive voltage of 8.5 kV, negative voltage of -3 kV, and collection distance of 10 cm. The resulting film was dried at room temperature for 24 h to obtain (100B / 10Bi2O3)30 / 70PVDF nanocomposite energetic film.

[0052] Example 3

[0053] Preparation of (100B / 15Bi2O3)30 / 70PVDF nanocomposite energetic films and study of their morphology, composition, thermal reaction and combustion properties:

[0054] (1) Preparation of B / Bi2O3 composite material: B nanoparticles and Bi2O3 were weighed separately at a mass ratio of 100:15 (i.e., 100B / 15Bi2O3), and loaded into a ball mill jar. Grinding balls were added at a ball-to-material ratio of 20:1. Anhydrous ethanol was added as a dispersion medium, and the mixture was mechanically ball-milled at 300 rpm for 2 h. Subsequently, the mixture was washed with anhydrous ethanol and dried in a vacuum oven at 50 ℃ for about 4 h. The resulting uniform B / Bi2O3 composite powder was obtained by grinding.

[0055] (2) Preparation of spinning precursor solution: PVDF was dissolved in a mixed solvent of DMF and acetone (volume ratio 1:1), sonicated for 1 hour and magnetically stirred for 10 minutes to prepare a PVDF solution with a mass fraction of 10%. The above B / Bi2O3 composite was added to the PVDF solution (the total mass ratio of B to Bi2O3 to PVDF was 30:70), stirred for 10 minutes, sonicated for 2 hours, and finally stirred continuously for 12 hours to obtain a uniform and stable spinning precursor solution.

[0056] (3) Electrospinning preparation of thin films: The precursor solution was loaded into a syringe, and electrospinning was carried out under the conditions of spinning rate of 0.25 mm / min, positive voltage of 8.5 kV, negative voltage of -3 kV, and collection distance of 10 cm. The resulting film was dried at room temperature for 24 h to obtain (100B / 15Bi2O3)30 / 70PVDF nanocomposite energetic film.

[0057] Example 4

[0058] Preparation of (100B / 20Bi2O3)30 / 70PVDF nanocomposite energetic thin films and study of their thermal reaction and combustion properties:

[0059] (1) Preparation of B / Bi2O3 composite material: B nanoparticles and Bi2O3 were weighed separately at a mass ratio of 100:20 (i.e., 100B / 20Bi2O3), and loaded into a ball mill jar. Grinding balls were added at a ball-to-material ratio of 20:1. Anhydrous ethanol was added as a dispersion medium, and the mixture was mechanically ball-milled at 300 rpm for 2 h. Subsequently, the mixture was washed with anhydrous ethanol and dried in a vacuum oven at 50 ℃ for about 4 h. The resulting uniform B / Bi2O3 composite powder was obtained by grinding.

[0060] (2) Preparation of spinning precursor solution: PVDF was dissolved in a mixed solvent of DMF and acetone (volume ratio 1:1), sonicated for 1 hour and magnetically stirred for 10 minutes to prepare a PVDF solution with a mass fraction of 10%. The above B / Bi2O3 composite was added to the PVDF solution (the total mass ratio of B to Bi2O3 to PVDF was 30:70), stirred for 10 minutes, sonicated for 2 hours, and finally stirred continuously for 12 hours to obtain a uniform and stable spinning precursor solution.

[0061] (3) Electrospinning preparation of thin films: The precursor solution was loaded into a syringe, and electrospinning was carried out under the conditions of spinning rate of 0.25 mm / min, positive voltage of 8.5 kV, negative voltage of -3 kV, and collection distance of 10 cm. The resulting film was dried at room temperature for 24 h to obtain (100B / 20Bi2O3)30 / 70PVDF nanocomposite energetic film.

[0062] Results analysis:

[0063] (1) Morphology analysis: The B / Bi2O3 / PVDF nanocomposite energetic films prepared in Examples 1-4 were characterized by scanning electron microscopy (SEM), and the results are as follows: Figure 1 As shown, all four groups of samples could form a three-dimensional network structure composed of continuous fibers, but the fiber density, surface particle adhesion, and continuity showed a regular change with increasing Bi2O3 content. Figure 1 As shown in (a, e), the film fibers obtained in Example 1 (B:Bi2O3 = 100:5) are the most dense, with a stable diameter distribution, smooth surface, and low particle adhesion. The B / Bi2O3 composite is uniformly dispersed in the PVDF matrix. Figure 1 As shown in (b, c, f, g), the film fibers obtained in Examples 2 and 3 (B:Bi2O3 = 100:10 and 100:15) maintain high overall continuity, with a significant increase in the number of particles that are uniformly distributed within and on the surface of the fibers, resulting in good network density; Figure 1 As shown in (d, h), the local network of the film obtained in Example 4 (B:Bi2O3 = 100:20) showed discontinuous and loose areas, the fiber diameter fluctuated more, the number of loaded particles decreased and the distribution was uneven, and the forming quality was significantly reduced.

[0064] It can be seen that as the Bi2O3 content gradually increases from 5% to 20%, the film morphology shows a gradual change from "high density, strong continuity, and smooth surface" to "medium density, uniform particle adhesion" and then to "loose structure and decreased continuity". Among them, Examples 2 and 3 (100:10~100:15) achieved a better balance between structure and activity.

[0065] (2) Structural analysis: X-ray diffraction (XRD) results are as follows Figure 2 As shown. Figure 2 As shown in (a), B nanoparticles exhibit two main diffraction peaks at 2θ ≈ 28° and 43°, corresponding to B₂O₃ and crystalline B, respectively, with the overall state predominantly amorphous. Bi₂O₃ shows diffraction peaks at 2θ = 27.9°, 32.687°, 46.215°, 54.265°, and 57.752°, consistent with the standard card PDF#65-1209. PVDF shows α-phase characteristic peaks at 18.3°, 19.9°, and 26.6°, and a weak β-phase peak near 38.3°. Figure 2 As shown in (b), in the composite films obtained in Examples 1-4, as the Bi2O3 content increased from 5% to 20%, the characteristic diffraction peaks of Bi2O3 gradually increased and became clearer, with no extra impurity peaks appearing. This indicates that B and Bi2O3 have been uniformly coated inside the PVDF fiber, and the electrospinning process did not change the crystal phase of the raw materials. The interaction between the components is mainly physical.

[0066] Fourier transform infrared (FTIR) results are as follows Figure 3 As shown. Figure 3 As shown in (a), pure PVDF at 1400, 1181 and 876 cm⁻¹ -1 Characteristic peaks of CH2 bending vibration, CF2 stretching vibration, and C–C skeletal vibration appear at this location. For example... Figure 3 As shown in (b), the composite films obtained in Examples 1 to 4 all retained the main vibration peaks of the pure PVDF. With the change of Bi2O3 content, the positions and intensities of the α-phase and β-phase related vibration peaks of PVDF remained basically stable, indicating that the chemical bonds of PVDF were intact after compositing and no new chemical bonds were generated in the system, further confirming that the components were mainly physically bonded.

[0067] (3) Hydrophobicity: The hydrophobicity of the raw materials and the prepared B / Bi2O3 / PVDF composite energetic film was evaluated by measuring the static water contact angle (WCA) using deionized water. Figure 4 As shown, the WCA of all samples exceeded 90°, indicating that the composite energetic film maintains good hydrophobic properties.

[0068] (4) Thermal performance analysis: The films obtained in Examples 1-4 were subjected to TG-DSC tests in an air atmosphere. The TG-DSC curves of the raw material PVDF and pure B are shown below. Figure 5 As shown, the TG-DSC curve of the composite thin film is as follows: Figure 5 As shown. Figure 5 As shown in (a), the thermal behavior of all samples can be divided into two weight loss stages (PVDF thermal decomposition and B fluorination reaction) and one high-temperature oxidation weight gain stage (B oxidation). Since the PVDF content is fixed, the initial weight loss behavior of each sample is basically the same. In the high-temperature oxidation weight gain stage, the initial oxidation temperatures of B in the films obtained in Examples 1-4 are 556.52 ℃, 544.88 ℃, 532.47 ℃ and 532.97 ℃, respectively, showing a pattern of first significantly decreasing and then stabilizing. Among them, the oxidation initiation temperature of Example 3 (B:Bi2O3=100:15) is the lowest, which is about 174.19 ℃ lower than that of pure B (initial oxidation temperature 706.43 ℃), and the total heat release is 5857.69 J / g; the change in Example 4 (100:20) has become gradual, and the system is close to catalytic saturation. The weight gain from oxidation was 23.12%, 21.18%, 18.00%, and 18.72%, respectively, and decreased overall with the increase of Bi2O3 content. This indicates that although Bi2O3 can promote the early oxidation of B, its increased content will correspondingly reduce the amount of effective B that can participate in oxidation.

[0069] like Figure 5 As shown in (b), the DSC curves exhibit three exothermic peaks, corresponding to PVDF decomposition, PIR (polymer-mediated reaction), and high-temperature oxidation of B, respectively. The PIR exothermic peak temperatures of Examples 1-4 are 499.77 °C, 487.38 °C, 483.41 °C, and 481.01 °C, respectively, which decrease monotonically with increasing Bi2O3 content, indicating that Bi2O3 can alter the thermal stability of the oxide layer on the B surface and promote interfacial reactions. The heat release during the weight loss stage was 3756.02, 4331.78, 4122.35 and 3952.06 J / g, respectively; the heat release during the weight gain stage was 1925.03, 1774.20, 1735.34 and 1589.19 J / g, respectively, decreasing with increasing Bi2O3 content; the total heat release was 5657.05, 6105.98, 5857.69 and 5541.25 J / g, respectively, showing a trend of first increasing and then decreasing, reaching the maximum value in Examples 2 and 3 (Bi2O3 content of 10%~15%).

[0070] The TG-DSC test results under an argon atmosphere are as follows: Figure 6 As shown. Since there is no high-temperature oxidation process of B, the exothermic peak mainly originates from the PIR reaction between the fluorine-containing free radicals generated by PVDF decomposition and B. The initial reaction temperature T of the films obtained in Examples 1-4... iThe temperatures were 414.68 ℃, 407.92 ℃, 413.97 ℃, and 415.40 ℃, respectively, showing a trend of first decreasing and then increasing; the peak temperature T of the exothermic peak was... p The temperatures were 448.60℃, 438.47℃, 428.59℃, and 443.95℃, respectively, with the lowest temperature recorded in Example 3. The total heat release Q was 372.59, 370.54, 391.27, and 390.54 J / g, respectively, showing a trend of first decreasing, then increasing, and finally stabilizing. Combining the test results under both air and argon atmospheres, a Bi₂O₃ content of 10%–15% can most effectively promote the earlier occurrence and extent of the PIR reaction without significantly increasing the initial energy barrier, with Example 3 (B:Bi₂O₃ = 100:15) exhibiting the best overall performance.

[0071] (4) Combustion performance analysis: The combustion process of the films obtained in Examples 1-4 was recorded using a high-speed camera and infrared thermal imaging (frame rate 2000 frames / s, single sample mass 20 mg). The combustion flame morphology is as follows: Figure 7 As shown. All samples were ignited and maintained self-sustaining combustion. The combustion durations of Examples 1-4 were 3.1 s, 2.7 s, 2.2 s, and 2.3 s, respectively, and generally decreased with increasing Bi2O3 content, indicating that the increased oxidant content facilitated rapid combustion propagation; at the same time, the flame morphology tended to be more uniform with increasing Bi2O3 content.

[0072] Combustion temperature-time curves and infrared thermal imaging results are as follows: Figure 8 As shown. The highest combustion temperatures of Examples 1-4 were 1121 ℃, 1133 ℃, 1533 ℃ and 1243 ℃, respectively. In Example 1 (5% Bi2O3), the reaction rate was low due to insufficient oxidant, and the flame area was localized; in Example 2 (10% Bi2O3), the heat release was slightly enhanced; in Example 3 (15%), the fuel / oxidant ratio was close to the optimal balance, and with the heat transfer and diffusion advantages of the PVDF fiber network, the flame spread evenly in the membrane, reaching the highest combustion temperature of 1533 ℃ and the most stable flame morphology; in Example 4 (20%), the excessive oxidant caused a heat sink effect and local accumulation, hindering heat diffusion, and hot spots and discontinuous flame areas appeared in the infrared image, and the combustion temperature dropped to 1243 ℃.

[0073] (5) Combustion product analysis: The SEM morphology of the combustion residue is as follows: Figure 9 As shown. The fiber network of all samples was destroyed during the combustion reaction, and the residue exhibited a porous agglomerate structure, composed of micron / submicron particles and their aggregates; as shown. Figure 9As shown in (eh), the residue surface is rough and has obvious pores and gaps; among them, the residue morphology of Examples 2 and 3 (Bi2O3 is 10%~15%) is more uniform and the particle distribution is more continuous, reflecting a more stable combustion process and a more complete interface reaction; while Example 4 (20%) shows more obvious blocky agglomeration.

[0074] XRD patterns of combustion products are as follows Figure 10 As shown, characteristic diffraction peaks of B, B2O3, Bi2O3, Bi, and B4C appeared in the spectra. With the increase of Bi2O3 content, the characteristic peak of B weakened and the characteristic peak of B2O3 strengthened, and the peak intensity of B2O3 reached its maximum value in Example 3 (15%), indicating that B combustion was most complete under this condition. The carbon produced by PVDF cracking reacted with B in a solid-state reaction at high temperature to generate B4C, whose diffraction peaks were clearly visible in the product. The Bi2O3 detected in the product originated from both unreacted oxidant and partly from the secondary oxidation of the combustion product Bi at high temperature. The byproduct BF3 was not detected in XRD due to its volatility.

[0075] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a B / Bi2O3 / PVDF nanocomposite energetic thin film, characterized in that, The steps include the following: (1) B nanoparticles and Bi2O3 powder were loaded into a ball mill jar, and anhydrous ethanol was added as a dispersion medium. After ball milling, washing, vacuum drying and grinding, uniform B / Bi2O3 composite powder was obtained. (2) Dissolve PVDF in a mixed solvent of DMF and acetone, and prepare a PVDF solution with a mass fraction of 10% by ultrasonication and stirring. Add the above B / Bi2O3 composite powder to the PVDF solution at a mass ratio of (B / Bi2O3):PVDF = 30:

70. Stir and mix for 10 minutes, then sonicate for 2 hours to ensure uniform dispersion, and finally continue stirring for 12 hours to obtain a uniform and stable spinning precursor solution. (3) The precursor solution is loaded into a syringe and electrospinned. The resulting electrospinned film is collected and dried at room temperature to obtain the B / Bi2O3 / PVDF nanocomposite energetic film.

2. The method as described in claim 1, characterized in that, The mass ratio of B nanoparticles to Bi2O3 powder is 100:5~100:20, preferably 100:

15.

3. The method as described in claim 1, characterized in that, The particle size of B nanoparticles is 100-200 nm; and / or, the particle size of Bi2O3 powder is 200-800 nm.

4. The method as described in claim 1, characterized in that, During ball milling, the following process parameters are used: ball-to-material ratio of 20:1; and / or rotation speed of 300 rpm; and / or time of 2 h.

5. The method as described in claim 1, characterized in that, In step 1, the vacuum drying temperature is 50 °C; and / or the time is not less than 4 h.

6. The method as described in claim 1, characterized in that, The molecular weight of PVDF is 250,000 to 500,000.

7. The method as described in claim 1, characterized in that, The volume ratio of DMF to acetone is 1:

1.

8. The method as described in claim 1, characterized in that, The electrospinning parameters were: spinning rate 0.25 mm / min, positive voltage 8.5 kV, negative voltage -3 kV, collection distance 10 cm, temperature 25 ℃, and humidity 45%.

9. A B / Bi2O3 / PVDF nanocomposite energetic thin film prepared by the method according to any one of claims 1-8.

Images