Hot press molding process of Mg / PVDF pyrotechnic composition

Abstract

The invention discloses a hot press molding process of Mg / PVDF pyrotechnic composition, and relates to the technical field of pyrotechnic composition material preparation. According to the process, magnesium powder and modified polyvinylidene fluoride are used as raw materials, an additional binder does not need to be added, and the modified polyvinylidene fluoride is prepared by compounding polyvinylidene fluoride and silane modified nano lanthanum fluoride. The pyrotechnic composition finished product is prepared through the steps of screening, wet mixing and grinding, die-filling oscillation, hot press molding, demolding and trimming and the like. Polyvinylidene fluoride is selected to replace traditional polytetrafluoroethylene as an oxidizing agent, has appropriate melting point and decomposition point characteristics, forms a stable hot working interval, is high in fluorine content, and can fully react with magnesium powder to release energy. The process improves the forming quality and combustion stability of the pyrotechnic composition.

Description

Technical Field

[0001] This application relates to the field of pyrotechnic material preparation technology, specifically to a hot pressing process for Mg / PVDF pyrotechnic materials. Background Technology

[0002] Pyrotechnics, as an important class of energetic materials, are widely used in military and civilian fields such as infrared decoys, ignition systems, and propellants. Their performance directly affects the effectiveness of the end product. Traditional molding processes for pyrotechnics mainly include two types: wet-mixing and granulation followed by cold pressing, and hot pressing with low-melting-point binders. The wet-mixing and granulation followed by cold pressing process requires a large amount of volatile organic solvents, posing safety hazards such as combustion, explosion, and the volatilization of toxic and harmful substances, as well as causing environmental pollution. Long-term exposure can cause irreversible damage to the health of operators. The low-melting-point binder hot pressing process requires the additional introduction of binders to ensure the mechanical strength of the product. However, the addition of binders dilutes the effective content of combustibles and oxidizers, significantly weakening the energy output and combustion performance of the pyrotechnics. Meanwhile, traditional pyrotechnic formulations often use polytetrafluoroethylene (PTFE) as an oxidant, but its high melting point (327-342℃) and narrow hot-working range require extremely high precision in temperature control of molding equipment. Furthermore, PTFE is almost insoluble in any solvent, leading to poor uniformity in raw material mixing, which in turn affects the stability and consistency of pyrotechnic combustion. Other fluorocarbons, such as hexachloroethane, have overlapping melting and sublimation temperatures, and polychlorotrifluoroethylene has a melting and decomposition temperature that are too close, both lacking suitable hot-pressing processing ranges and failing to meet the dual requirements of molding process and performance.

[0003] Therefore, developing a pyrotechnics preparation process that requires no organic solvents or additional binders, has a simple molding process, and produces products with excellent performance has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of existing pyrotechnic molding processes, such as safety and environmental hazards, weakened combustion performance, and high molding difficulty, and to provide a hot-pressing molding process for Mg / PVDF pyrotechnics. This process, through the rational selection of oxidants and optimization of the molding process, utilizes the dual functions of polyvinylidene fluoride as both an oxidant and a binder, eliminating the need for additional binders and avoiding the use of organic solvents. This effectively improves the molding quality, mechanical strength, combustion stability, and energy output efficiency of pyrotechnics, providing technical support for the large-scale production of high-performance pyrotechnics.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] This application provides a hot pressing process for Mg / PVDF pyrotechnic powder, including the following steps:

[0007] S1: Magnesium powder and modified polyvinylidene fluoride are selected as raw materials, and the magnesium powder is screened.

[0008] S2: The sieved magnesium powder is mixed with modified polyvinylidene fluoride, a dispersion medium is added and stirred to form a suspension, which is then ground and dried to obtain a mixed powder;

[0009] S3: Load the mixed powder into the mold, spread the powder using a scraper, and then mechanically vibrate the mold;

[0010] S4: Heat the mold containing the mixed powder to a preset temperature, then apply a preset pressure and hold the pressure for a preset time to hot press and form the product;

[0011] S5: After pressing, release the pressure and wait for the mold to cool to the ambient temperature before demolding. After trimming and cutting, the Mg / PVDF pyrotechnic powder product is obtained.

[0012] Among them, the modified polyvinylidene fluoride was prepared by polyvinylidene fluoride and silane-modified nano-lanthanum fluoride.

[0013] Furthermore, in S1, the screening process uses a 200-250 mesh screen and is continuously screened 2-4 times.

[0014] Furthermore, in S2, the preparation steps of the modified polyvinylidene fluoride include:

[0015] Take nano-lanthanum fluoride powder with a particle size of 50-100 nm, ultrasonically disperse it with anhydrous ethanol for 25-35 min, and then vacuum dry it at 75-85℃ for 1.5-2.5 h to obtain pretreated nano-lanthanum fluoride powder.

[0016] Add 5-8% of the silane coupling agent (by mass of nano-lanthanum fluoride) to anhydrous ethanol, stir until homogeneous, adjust the pH to 4-5 with dilute hydrochloric acid, then add the pretreated nano-lanthanum fluoride powder, stir at 55-65℃ for 1.5-2.5 h, centrifuge, wash 3-4 times with anhydrous ethanol, and vacuum dry at 65-75℃ for 2.5-3.5 h to obtain silane-modified nano-lanthanum fluoride.

[0017] Weigh 1%-3% of silane-modified nano-lanthanum fluoride by weight of polyvinylidene fluoride (PVDF), add it together with PVDF powder to a high-speed mixer, mix at 95-105℃ for 12-18 min, cool to room temperature, and then pulverize through a 180-200 mesh sieve to obtain modified PVDF powder.

[0018] Furthermore, silane coupling agents include γ-aminopropyltriethoxysilane or γ-aminopropyltrimethoxysilane.

[0019] Furthermore, in S2, the mass ratio of magnesium powder to modified polyvinylidene fluoride powder is (0.8-1.2):1; the ratio of the total mass of magnesium powder and polyvinylidene fluoride powder to the volume of the dispersion medium is 1g:(1-1.5)mL; and the dispersion medium is anhydrous ethanol.

[0020] Furthermore, in S2, the stirring time is 25-35 minutes and the stirring speed is 200-300 rpm;

[0021] The drying temperature is 55-65℃, and the drying time is 0.8-1.2h.

[0022] Furthermore, in S3, the amount of the mixed powder is 0.15-0.35g;

[0023] The mold measures 3cm in length and 0.5cm in width.

[0024] Furthermore, in S3, the speed of the mechanical vibration mold is 150-200 rpm, and the time is 5-10 min.

[0025] Furthermore, in S4, the preset temperature is 25-170℃, the preset pressure is 450-650Kg, and the preset pressure holding time is 2-4min.

[0026] Furthermore, in S4, the mold is heated by a heating table at a rate of 10-20℃ / min.

[0027] Furthermore, in S5, the depressurization rate is 50-100 kg / min.

[0028] This application discloses a hot-pressing process for Mg / PVDF pyrotechnic powder, using magnesium powder and modified polyvinylidene fluoride (PVDF) as core raw materials to prepare a Mg / PVDF pyrotechnic powder that requires no additional binder. In the selection of the oxidant, PVDF, which has a high melting point, is abandoned in traditional formulations. Instead, PVDF is selected and composite modified. By introducing a silane coupling agent to modify nano-lanthanum fluoride, the suitable melting and decomposition points of PVDF are utilized to form a stable hot-working range, meeting the requirements of hot-pressing, without premature reaction due to excessively low decomposition temperatures. Furthermore, this improves the decomposition efficiency and fluorine utilization rate of PVDF.

[0029] In modified polyvinylidene fluoride (PVDF), the ethoxy group at one end of the silane coupling agent molecule can hydrolyze to generate silanol (-Si-OH), which undergoes a condensation reaction with the hydroxyl groups on the surface of nano-LaF3. The amino group (-NH2) at the other end can form hydrogen bonds with fluorine atoms on the PVDF molecular chain, achieving a good interfacial bond between the modified particles and PVDF, preventing agglomeration and improving the material's processing stability. The lanthanum ions in nano-lanthanum fluoride have empty orbitals, which can coordinate with the CF bonds on the PVDF molecular chain. Through partial electron cloud transfer, the CF bond energy is weakened, lowering its breaking energy barrier, allowing PVDF to rapidly decompose in the early stages of pyrotechnic combustion, increasing the generation rate and release of fluorine-containing active substances. Simultaneously, nano-lanthanum fluoride itself can release fluoride ions at high temperatures, forming a dual fluorine source with the fluorine-containing active substances produced by PVDF decomposition, providing sufficient fluorine supply for the fluorination reaction of magnesium powder, improving fluorine utilization and magnesium fluoride formation rate, and enhancing the exothermic reaction. The aminosilane modification layer improves the dispersion of nano-lanthanum fluoride in polyvinylidene fluoride, ensuring uniform catalytic activity and avoiding uneven reaction caused by local agglomeration.

[0030] In the raw material pretreatment stage, sieving avoids magnesium powder agglomeration, wet mixing and grinding achieves microscopic uniform dispersion of modified polyvinylidene fluoride and magnesium powder, and low-temperature drying removes the dispersion medium. This ensures the uniformity of component mixing and avoids the safety and environmental risks associated with organic solvents in traditional wet mixing processes, providing a foundation for subsequent reaction sufficiency and molding. The scraper spreading and mechanical vibration during mold loading further ensure the uniformity of the mixed powder's filling density and height within the mold, avoiding localized pores or component enrichment, reducing molding defects. Simultaneously, the nanoscale size of the modified particles can further fill material gaps, improving the density of the pyrotechnic propellant.

[0031] In the hot-pressing stage, modified polyvinylidene fluoride (PVDF) is heated to a molten state, forming a viscous flow state, while the magnesium powder remains solid. Pressure is applied to drive the PVDF to flow fully, achieving complete wetting and tight coating of the magnesium powder particles, filling the tiny pores between the particles, and promoting system densification. The pressure-holding process strengthens the interfacial bonding between particles, preventing structural springback or pore regeneration after pressure release. Once the mold cools to ambient temperature, the PVDF solidifies to form a continuous binder phase, firmly locking the magnesium powder particles in place. This gives the product good mechanical strength, meeting the structural stability requirements during storage, transportation, and use, achieving the molding requirements without the need for additional binders.

[0032] Beneficial technical effects:

[0033] This application discloses a hot-pressing molding process for Mg / PVDF pyrotechnic powder. Using magnesium powder and modified polyvinylidene fluoride (PVDF) as core raw materials, a Mg / PVDF pyrotechnic powder requiring no additional binder is prepared through a hot-pressing process. PVDF possesses suitable melting and decomposition points, forming a stable hot-working range to meet molding requirements. Simultaneously, its high fluorine content makes it a highly efficient fluorine source, eliminating the need for additional binders. In the modified PVDF, aminosilane-modified nano-lanthanum fluoride weakens the CF bond energy through catalysis, lowering its fracture energy barrier. This allows PVDF to rapidly initiate decomposition in the early stages of pyrotechnic powder combustion, further improving the decomposition efficiency and fluorine utilization rate of PVDF. In the raw material pretreatment stage, modified polyvinylidene fluoride (PVDF) and magnesium powder are mixed and dispersed through sieving and wet grinding. Low-temperature drying removes the dispersion medium, avoiding the safety and environmental risks associated with organic solvents. During molding, scraper spreading and mechanical vibration ensure uniform powder filling and reduce molding defects. In the hot pressing stage, after the modified PVDF melts, it impregnates and coats the magnesium powder under pressure, filling the pores. After cooling, a continuous binder phase is formed, giving the pyrotechnic powder good mechanical strength. During combustion, the fluorine-containing active substances produced by the high-temperature decomposition of modified PVDF react fully with the magnesium powder, ensuring energy output. The dense and uniform molding structure avoids problems such as flame interruption and metal particle splashing, making combustion more stable. Ultimately, this achieves comprehensive optimization of the pyrotechnic powder molding quality, mechanical strength, combustion stability, and energy output. Attached Figure Description

[0034] Figure 1 This is a flow chart of a hot pressing process for a Mg / PVDF pyrotechnic powder according to this application;

[0035] Figure 2 This is a schematic diagram of the mold assembly for a hot pressing process of Mg / PVDF pyrotechnic powder according to this application;

[0036] Figure 3 This is a picture of the hot-pressed product of a Mg / PVDF pyrotechnic compound prepared in Example 3;

[0037] Figure 4 This is a picture of the product after combustion of a Mg / PVDF pyrotechnic compound prepared in Example 3;

[0038] Figure 5 This is an ignition delay diagram of a Mg / PVDF pyrotechnic propellant prepared in Example 1;

[0039] Figure 6 This is an ignition delay diagram of a Mg / PVDF pyrotechnic propellant prepared in Example 2;

[0040] Figure 7 This is an ignition delay diagram of a Mg / PVDF pyrotechnic propellant prepared in Example 3;

[0041] Figure 8 This is an ignition delay diagram of a Mg / PVDF pyrotechnic propellant prepared in Example 4;

[0042] Figure 9 The ignition delay diagram is for a Mg / PVDF pyrotechnic propellant prepared in Comparative Example 1. Detailed Implementation

[0043] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific implementation methods of this application will be described in detail below with reference to the embodiments.

[0044] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0045] Example 1

[0046] like Figure 1 As shown, this embodiment provides a hot pressing process for Mg / PVDF pyrotechnic powder, including the following steps:

[0047] S1: Magnesium powder and modified polyvinylidene fluoride powder were selected as raw materials. The magnesium powder was sieved twice using a 200-mesh sieve. The mass ratio of magnesium powder to modified polyvinylidene fluoride powder was 0.8:1. The preparation steps of the modified polyvinylidene fluoride powder included: taking 50nm nano-lanthanum fluoride powder, ultrasonically dispersing it with anhydrous ethanol for 25min, and then vacuum drying it at 75℃ for 1.5h to obtain pretreated nano-lanthanum fluoride powder; and adding the silane coupling agent γ-aminopropyltriethoxysilane according to the mass of the nano-lanthanum fluoride. 5% was added to anhydrous ethanol, stirred evenly, and the pH was adjusted to 4 with dilute hydrochloric acid. Then, pretreated nano-lanthanum fluoride powder was added, and the mixture was stirred at 55°C for 1.5 h. After centrifugation and washing three times with anhydrous ethanol, the mixture was vacuum dried at 65°C for 2.5 h to obtain silane-modified nano-lanthanum fluoride. 1% of the mass of polyvinylidene fluoride nano-lanthanum fluoride was weighed and added together with polyvinylidene fluoride powder to a high-speed mixer. The mixture was mixed at 95°C for 12 min, cooled to room temperature, and then pulverized through a 180-mesh sieve to obtain modified polyvinylidene fluoride powder.

[0048] S2: The sieved magnesium powder and modified polyvinylidene fluoride powder are mixed, and anhydrous ethanol is added as a dispersion medium to form a suspension. The ratio of the total mass of magnesium powder and modified polyvinylidene fluoride powder to the volume of anhydrous ethanol is 1g:1mL. The stirring time is 25min and the stirring speed is 200rpm. After grinding, the mixture is dried at 55℃ for 0.8h to obtain the mixed powder.

[0049] S3: Load the mixed powder into the mold (e.g., ... Figure 2 As shown), the amount of mixed powder is 0.15g, the mold size is 3cm long × 0.5cm wide, the powder is spread with a scraper, and then the mold is mechanically vibrated at 150rpm for 5min;

[0050] S4: Heat the mold containing the mixed powder to 25°C using a heating table at a heating rate of 10°C / min, then apply 450Kg pressure and hold for 2 minutes for hot pressing.

[0051] S5: After pressing, release the pressure at a rate of 50 kg / min. Once the mold has cooled to ambient temperature, demold. Trim and cut to obtain the Mg / PVDF pyrotechnic powder. The corresponding pyrotechnic powder ignition delay diagram is shown below. Figure 5 As shown.

[0052] Example 2

[0053] like Figure 1 As shown, this embodiment provides a hot pressing process for Mg / PVDF pyrotechnic powder, including the following steps:

[0054] S1: Magnesium powder and modified polyvinylidene fluoride powder were selected as raw materials. The magnesium powder was sieved four times using a 250-mesh sieve. The mass ratio of magnesium powder to modified polyvinylidene fluoride powder was 1.2:1. The preparation steps of the modified polyvinylidene fluoride powder included: taking 100nm nano-lanthanum fluoride powder, ultrasonically dispersing it with anhydrous ethanol for 35min, and then vacuum drying it at 85℃ for 2.5h to obtain pretreated nano-lanthanum fluoride powder; and adding the silane coupling agent γ-aminopropyltrimethoxysilane according to the mass of the nano-lanthanum fluoride. 8% was added to anhydrous ethanol, stirred evenly, and the pH was adjusted to 5 with dilute hydrochloric acid. Then, pretreated nano-lanthanum fluoride powder was added, and the mixture was stirred at 65°C for 2.5 h. After centrifugation and washing with anhydrous ethanol four times, the mixture was vacuum dried at 75°C for 3.5 h to obtain silane-modified nano-lanthanum fluoride. 3% of the mass of polyvinylidene fluoride nano-lanthanum fluoride was weighed and added together with polyvinylidene fluoride powder to a high-speed mixer. The mixture was mixed at 105°C for 18 min, cooled to room temperature, and then pulverized through a 200-mesh sieve to obtain modified polyvinylidene fluoride powder.

[0055] S2: The sieved magnesium powder and modified polyvinylidene fluoride powder were mixed, and anhydrous ethanol was added as a dispersion medium to form a suspension. The ratio of the total mass of magnesium powder and modified polyvinylidene fluoride powder to the volume of anhydrous ethanol was 1g:1.5mL. The stirring time was 35min and the stirring speed was 300rpm. After grinding, the mixture was dried at 65℃ for 1.2h to obtain the mixed powder.

[0056] S3: Load the mixed powder into the mold (e.g., ... Figure 2As shown), the amount of mixed powder is 0.35g, the mold size is 3cm long × 0.5cm wide, the powder is spread with a scraper, and then the mold is mechanically shaken at 200rpm for 10min;

[0057] S4: Heat the mold containing the mixed powder to 170°C using a heating table at a heating rate of 20°C / min, then apply 650Kg pressure and hold for 4min for hot pressing to form the mold.

[0058] S5: After pressing, depressurize at a rate of 100 kg / min. Once the mold has cooled to ambient temperature, demold. Trim and cut to obtain the Mg / PVDF pyrotechnic powder. The corresponding pyrotechnic powder ignition delay diagram is shown below. Figure 6 As shown.

[0059] Example 3

[0060] like Figure 1 As shown, this embodiment provides a hot pressing process for Mg / PVDF pyrotechnic powder, including the following steps:

[0061] S1: Magnesium powder and modified polyvinylidene fluoride powder were selected as raw materials. The magnesium powder was sieved three times using a 225-mesh sieve. The mass ratio of magnesium powder to modified polyvinylidene fluoride powder was 1:1. The preparation steps of the modified polyvinylidene fluoride powder included: taking 75nm nano-lanthanum fluoride powder, ultrasonically dispersing it with anhydrous ethanol for 30min, and then vacuum drying it at 80℃ for 2h to obtain pretreated nano-lanthanum fluoride powder; and adding the silane coupling agent γ-aminopropyltriethoxysilane at 6.5% of the mass of the nano-lanthanum fluoride. % was added to anhydrous ethanol, stirred evenly, and the pH was adjusted to 4.5 with dilute hydrochloric acid. Then, pretreated nano-lanthanum fluoride powder was added, and the mixture was stirred at 60℃ for 2 hours. After centrifugation and washing with anhydrous ethanol 4 times, the mixture was vacuum dried at 70℃ for 3 hours to obtain silane-modified nano-lanthanum fluoride. 2% of the mass of polyvinylidene fluoride nano-lanthanum fluoride was weighed and added together with polyvinylidene fluoride powder to a high-speed mixer. The mixture was mixed at 100℃ for 15 minutes, cooled to room temperature, and then pulverized through a 190-mesh sieve to obtain modified polyvinylidene fluoride powder.

[0062] S2: The sieved magnesium powder and modified polyvinylidene fluoride powder are mixed, and anhydrous ethanol is added as a dispersion medium to form a suspension. The ratio of the total mass of magnesium powder and modified polyvinylidene fluoride powder to the volume of anhydrous ethanol is 1g:1.25mL. The stirring time is 30min and the stirring speed is 250rpm. After grinding, the mixture is dried at 60℃ for 1h to obtain the mixed powder.

[0063] S3: Load the mixed powder into the mold (e.g., ... Figure 2As shown), the amount of mixed powder is 0.25g, the mold size is 3cm long × 0.5cm wide, the powder is spread with a scraper, and then the mold is mechanically vibrated at 175rpm for 7.5min;

[0064] S4: Heat the mold containing the mixed powder to 97.5°C using a heating table at a heating rate of 15°C / min, then apply a pressure of 550Kg and hold the pressure for 3 minutes for hot pressing.

[0065] S5: After pressing, release the pressure at a rate of 75 kg / min. Once the mold has cooled to ambient temperature, demold. Trim and cut to obtain Mg / PVDF pyrotechnic powder. (Product image shown). Figure 3 As shown, the product image after combustion of the obtained Mg / PVDF pyrotechnic powder is as follows. Figure 4 As shown, the corresponding pyrotechnic ignition delay diagram is as follows: Figure 7 As shown.

[0066] Example 4

[0067] like Figure 1 As shown, this embodiment provides a hot pressing process for Mg / PVDF pyrotechnic powder, including the following steps:

[0068] S1: Magnesium powder and modified polyvinylidene fluoride powder were selected as raw materials. The magnesium powder was sieved three times using a 230-mesh sieve. The mass ratio of magnesium powder to modified polyvinylidene fluoride powder was 0.9:1. The preparation steps of the modified polyvinylidene fluoride powder included: taking 80nm nano-lanthanum fluoride powder, ultrasonically dispersing it with anhydrous ethanol for 32min, and then vacuum drying it at 82℃ for 2.2h to obtain pretreated nano-lanthanum fluoride powder; and adding γ-aminopropyltrimethoxysilane as a silane coupling agent at 7% of the mass of nano-lanthanum fluoride. Add anhydrous ethanol, stir evenly, adjust the pH to 4.6 with dilute hydrochloric acid, then add pretreated nano-lanthanum fluoride powder, stir at 62℃ for 2.2h, centrifuge, wash 4 times with anhydrous ethanol, and vacuum dry at 72℃ for 3.2h to obtain silane-modified nano-lanthanum fluoride; weigh 2% of the mass of polyvinylidene fluoride nano-lanthanum fluoride, add it together with polyvinylidene fluoride powder to a high-speed mixer, mix at 100℃ for 16min, cool to room temperature, and pulverize through a 200-mesh sieve to obtain modified polyvinylidene fluoride powder.

[0069] S2: The sieved magnesium powder and modified polyvinylidene fluoride powder were mixed, and anhydrous ethanol was added as a dispersion medium to form a suspension. The ratio of the total mass of magnesium powder and modified polyvinylidene fluoride powder to the volume of anhydrous ethanol was 1 g: 1.3 mL. The stirring time was 28 min and the stirring speed was 260 rpm. After grinding, the mixture was dried at 58 °C for 1.1 h to obtain the mixed powder.

[0070] S3: Load the mixed powder into the mold (e.g., ... Figure 2 As shown), the amount of mixed powder is 0.2g, the mold size is 3cm long × 0.5cm wide, the powder is spread with a scraper, and then the mold is mechanically vibrated at 180rpm for 8min;

[0071] S4: Heat the mold containing the mixed powder to 120°C using a heating table at a heating rate of 12°C / min, then apply 500Kg pressure and hold for 2.5min for hot pressing.

[0072] S5: After pressing, release the pressure at a rate of 80 kg / min. Once the mold has cooled to ambient temperature, demold. Trim and cut to obtain the Mg / PVDF pyrotechnic powder. The corresponding pyrotechnic powder ignition delay diagram is shown below. Figure 8 As shown.

[0073] Comparative Example 1

[0074] This comparative example provides a hot-pressing process for Mg / PVDF pyrotechnic powder. The difference from Example 1 is that this comparative example does not prepare or use modified polyvinylidene fluoride powder. Other process parameters and operating steps are exactly the same as in Example 1. The corresponding pyrotechnic powder ignition delay diagram is shown below. Figure 9 As shown.

[0075] Comparative Example 2

[0076] This comparative example provides a hot pressing process for Mg / PVDF pyrotechnic powder. The difference from Example 1 is that this comparative example does not perform the S4 hot pressing step. Instead, the mixed powder is loaded into the mold and allowed to cool and demold naturally. Other process parameters and operating steps are exactly the same as in Example 1.

[0077] The performance of the Mg / PVDF pyrotechnics prepared in Examples 1-4 and Comparative Examples 1-2 was tested, and the results are shown in Table 1.

[0078] Table 1. Performance test results of Mg / PVDF pyrotechnics prepared in Examples 1-4 and Comparative Examples 1-2

[0079]

[0080] Examples 1-4 employ the Mg / PVDF pyrotechnic hot-pressing process described in this application. PVDF, acting as both an oxidizer and binder, achieves thorough coating and pore filling of magnesium powder through its molten flow during hot pressing, resulting in a dense and uniform microstructure. Test results show that the relative density of the products is consistently higher than 38.7%, with Example 2 reaching a maximum of 75.8%. The mechanical strength is sufficient to maintain structural integrity under a 2m free-fall impact, and the combustion process is stable and uninterrupted. The highest combustion temperature is concentrated between 2084-2333℃, and the MgF2 content in the combustion products ranges from 58.3% to 65.2%, fully demonstrating the synergistic optimization effect of the process on molding quality and combustion performance.

[0081] Examples 1-4 employ the Mg / PVDF pyrotechnic hot-pressing molding process of this application, utilizing modified polyvinylidene fluoride to function as an oxidant, binder, and catalyst, and silane-modified La in nano-lanthanum fluoride. 3+ LaF3 forms a weak coordination with the CF bond of polyvinylidene fluoride (PVDF), reducing the CF bond breaking energy and improving the release efficiency of fluorinated active substances. Simultaneously, LaF3 itself provides an additional fluorine source. Utilizing the melt flow of modified PVDF during hot pressing, it achieves full coating and pore filling of magnesium powder. Combined with the homogenizing effect of mold oscillation, this results in a denser and more uniform microstructure in the product. Test results show that the MgF2 content in the combustion products is 68.7%-76.3%, significantly higher than that of Comparative Example 1 (52.1%) without a catalyst. The relative density of the products is all above 48%, with Example 2 reaching 75.8%. The mechanical strength can withstand a 2m free-fall impact with structural integrity. The combustion duration is 1.56-2.32s, and the highest combustion temperature is concentrated in the range of 2184-2408℃. Excellent combustion stability demonstrates the optimization effect of the process on PVDF decomposition efficiency, molding quality, and combustion performance.

[0082] Comparative Example 1 lacked the S4 hot-pressing step, preventing the modified polyvinylidene fluoride (PVDF) from melting and forming a continuous binder phase. The resulting product had a relative density of only 48.3%, poor mechanical strength, and was completely brittle, unable to ignite stably, lacking a fixed combustion temperature, and containing only 52.1% MgF2. The core reason lies in the absence of a hot-pressing densification process. The modified PVDF failed to function as a binder, resulting in loosely dispersed magnesium powder and modified PVDF. Rapid component separation during combustion led to chaotic reactions, completely negating the comprehensive performance expected of pyrotechnics.

[0083] Comparative Example 2 used unmodified pure polyvinylidene fluoride powder. Although the process steps were complete, due to the lack of silane-modified nano-lanthanum fluoride catalysis and fluorine source replenishment, the decomposition efficiency of polyvinylidene fluoride was insufficient, the release of fluorine-containing active substances was limited, the relative density of the product was only 38.7%, and the proportion of MgF2 in the combustion products was 32.6%. All properties were significantly lower than those of Examples 1-4, which fully demonstrates the effect of polyvinylidene fluoride modification on improving the overall performance of pyrotechnics.

[0084] It should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application, and all such modifications and substitutions should be covered within the scope of the claims of this application.

Claims

1. A hot pressing process for Mg / PVDF pyrotechnic powder, characterized in that, Includes the following steps: S1: Magnesium powder and modified polyvinylidene fluoride are selected as raw materials, and the magnesium powder is screened. S2: The sieved magnesium powder is mixed with modified polyvinylidene fluoride, a dispersion medium is added and stirred to form a suspension, which is then ground and dried to obtain a mixed powder; S3: Load the mixed powder into the mold, spread the powder using a scraper, and then mechanically vibrate the mold; S4: Heat the mold containing the mixed powder to a preset temperature, then apply a preset pressure and hold the pressure for a preset time to hot press and form the product; S5: After pressing, release the pressure and wait for the mold to cool to the ambient temperature before demolding. After trimming and cutting, the Mg / PVDF pyrotechnic powder product is obtained. Among them, the modified polyvinylidene fluoride was prepared by polyvinylidene fluoride and silane-modified nano-lanthanum fluoride.

2. The hot pressing forming process for Mg / PVDF pyrotechnic powder according to claim 1, characterized in that, In S1, the screening process uses a 200-250 mesh screen and is continuously screened 2-4 times.

3. The hot pressing forming process for Mg / PVDF pyrotechnic powder according to claim 1, characterized in that, In S2, the preparation steps of the modified polyvinylidene fluoride include: Take nano-lanthanum fluoride powder with a particle size of 50-100 nm, ultrasonically disperse it with anhydrous ethanol for 25-35 min, and then vacuum dry it at 75-85℃ for 1.5-2.5 h to obtain pretreated nano-lanthanum fluoride powder. Add 5-8% of the silane coupling agent (by mass of nano-lanthanum fluoride) to anhydrous ethanol, stir until homogeneous, adjust the pH to 4-5 with dilute hydrochloric acid, then add the pretreated nano-lanthanum fluoride powder, stir at 55-65℃ for 1.5-2.5 h, centrifuge, wash 3-4 times with anhydrous ethanol, and vacuum dry at 65-75℃ for 2.5-3.5 h to obtain silane-modified nano-lanthanum fluoride. Weigh 1%-3% of silane-modified nano-lanthanum fluoride by weight of polyvinylidene fluoride (PVDF), add it together with PVDF powder to a high-speed mixer, mix at 95-105℃ for 12-18 min, cool to room temperature, and then pulverize through a 180-200 mesh sieve to obtain modified PVDF powder.

4. The hot pressing forming process for Mg / PVDF pyrotechnic powder according to claim 3, characterized in that, The silane coupling agent includes γ-aminopropyltriethoxysilane or γ-aminopropyltrimethoxysilane.

5. The hot pressing forming process for Mg / PVDF pyrotechnic powder according to claim 1, characterized in that, In S2, the mass ratio of magnesium powder to modified polyvinylidene fluoride powder is (0.8-1.2):1; The ratio of the total mass of the magnesium powder and the modified polyvinylidene fluoride powder to the volume of the dispersion medium is 1 g: (1-1.5) mL; the dispersion medium is anhydrous ethanol.

6. The hot pressing forming process for Mg / PVDF pyrotechnic powder according to claim 1, characterized in that, In S2, the stirring time is 25-35 min and the stirring speed is 200-300 rpm; The drying temperature is 55-65℃, and the drying time is 0.8-1.2h.

7. The hot pressing forming process for Mg / PVDF pyrotechnic powder according to claim 1, characterized in that, In S3, the amount of the mixed powder is 0.15-0.35g; The mold has a length of 3cm and a width of 0.5cm; The speed of the mechanical vibration mold is 150-200 rpm, and the time is 5-10 min.

8. The hot pressing forming process for Mg / PVDF pyrotechnic powder according to claim 1, characterized in that, In S4, the preset temperature is 25-170℃, the preset pressure is 450-650Kg, and the preset pressure holding time is 2-4min.

9. The hot pressing forming process for Mg / PVDF pyrotechnic powder according to claim 1, characterized in that, In S4, the mold is heated by a heating table at a rate of 10-20℃ / min.

10. The hot pressing forming process for Mg / PVDF pyrotechnic powder according to claim 1, characterized in that, In S5, the pressure relief rate is 50-100 kg / min.

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