Imidazolium metal tetrafluoroborate ionic liquid, its preparation method and application in coating aluminum powder

Abstract

This invention relates to a tetrafluoroborate imidazole-based metal ionic liquid, its preparation method, and its application in coating aluminum powder. The invention pertains to the preparation method of a tetrafluoroborate imidazole-based metal ionic liquid and its use in combination with aluminum powder to form a core-shell fuel (aluminum powder@metal ionic liquid). The aluminum powder@metal ionic liquid core-shell fuel uses aluminum as the core and a tetrafluoroborate imidazole-based metal ionic liquid as the shell material, prepared via solvent evaporation. This series of core-shell fuels exhibits excellent thermal properties and is primarily suitable for solid propellant fuel applications. Furthermore, the preparation method provided by this invention is simple, operates under mild conditions, and uses readily available raw materials.

Description

Technical Field

[0001] This invention relates to a tetrafluoroborate imidazole-based metal ionic liquid, its preparation method, and its application in coating aluminum powder, belonging to the field of aluminum powder coating technology in solid rocket propellants. Background Technology

[0002] Solid propellants are the power source of rockets, and their performance directly determines the rocket's launch scale and payload capacity. These propellants are energetic materials capable of stable combustion and releasing large amounts of high-temperature gas. They offer advantages such as easy storage and reliable transportation, and are widely used in solid rocket motors for missiles and spacecraft. Their performance directly affects the weapon's survivability and combat effectiveness. Fuel constitutes a significant portion of solid propellants, and its properties are closely related to the overall performance of the rocket. Aluminum powder is often used as a fuel component in propellants due to its high calorific value, high density, stable combustion products, wide availability, and low cost. However, the presence of an oxide layer on the surface of aluminum powder can lead to incomplete combustion, reduced combustion efficiency, and larger particle sizes of condensed phase products. To further improve the overall performance of propellants, aluminum powder usually needs to be modified; therefore, the development of novel aluminum-based fuels is of great significance.

[0003] Researchers both domestically and internationally have proposed optimization strategies such as modification of nano-aluminum powder, surface coating, and the introduction of fluorine-containing materials. Nano-aluminum powder particles can effectively improve combustion efficiency. At the nanoscale, the increased specific surface area leads to rapid oxidation and combustion reactions, resulting in the rapid release of stored energy. However, the application of nano-aluminum powder also faces some challenges. Nanoscale particles are highly reactive materials, which may lead to some safety issues. Surface coating can effectively reduce the surface energy of nano-aluminum powder, preventing further oxidation of active aluminum powder and exhibiting excellent air stability and unique water corrosion resistance. However, some coating materials, including metal oxides, are non-energized and do not release energy during combustion, which can affect overall energy performance.

[0004] Composite materials composed of fluorinated materials and aluminum powder have attracted increasing attention because the fluorinated materials can stimulate an exothermic surface reaction between aluminum powder (2O3) and fluorine on the aluminum powder surface, thereby enhancing ignition and combustion. In composite solid propellants, composite materials composed of aluminum powder and fluorinated materials hold promise as a replacement for ordinary aluminum powder. Fluoropolymers such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) have been shown to effectively reduce agglomeration. However, these particulate fluorinated materials cannot fully contact the aluminum powder surface, which reduces the bulk density of the solid fuel. Furthermore, these fluorinated materials are non-energized, affecting the overall energy performance of solid propellants based on modified aluminum powder. Therefore, developing novel energetic fluorinated materials to prepare modified aluminum powder is a significant undertaking. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose a tetrafluoroborate imidazole-based metal ionic liquid, its preparation method and its application in coated aluminum powder. The tetrafluoroborate imidazole-based metal ionic liquid forms a core-shell fuel with aluminum powder. This core-shell fuel has good combustion performance and can be used as a fuel component of solid propellants to improve the overall performance of propellants. Moreover, the preparation method is simple and the conditions are mild.

[0006] The technical solution of this invention is:

[0007] A tetrafluoroborate imidazole-based metal ionic liquid, the general structural formula of which is as follows:

[0008] Where m represents the number of substituted imidazole ligands, commonly 2, 4, 5, or 6; n represents the number of tetrafluoroborate ions, which is usually 2; The central metal atom M can be any one of Mn, Co, Ni, Cu, Fe, or Cd, and its valence state is one of the valence states of the corresponding metal ion. The imidazole substituent R is any one of alkane with 1-3 carbon atoms, alkene with 2-3 carbon atoms, or alkyne with 2-3 carbon atoms.

[0009] A method for preparing a tetrafluoroborate imidazole-based metal ionic liquid, the method comprising the following steps: The first step involves adding imidazole ligands to a metal salt solution and reacting them at a temperature of 10–90 °C for 0.2–8 h to obtain the reaction solution. In the second step, the tetrafluoroborate solution is added to the reaction solution obtained in the first step, and the reaction is carried out at a temperature of 10~90℃ for a time of 0.2~8 h. After the reaction is completed, the mixture is cooled to room temperature, filtered, and the precipitate is collected. The precipitate is washed with cold water, ethanol, etc., and then dried to obtain tetrafluoroborate imidazole metal ion liquid.

[0010] A method for preparing a tetrafluoroborate imidazole-based metal ionic liquid, the method comprising the following steps: The first step involves adding a tetrafluoroborate solution to a metal salt solution to initiate a reaction at a temperature of 10–90 °C for 0.2–8 h, thereby obtaining a reaction solution. In the second step, the imidazole ligand is added to the reaction solution obtained in the first step and the reaction is carried out at a temperature of 10~90℃ for a time of 0.2~8 h. After the reaction is completed, the mixture is cooled to room temperature, filtered and the precipitated product is collected. The precipitated product is washed with cold water, ethanol, etc. and then dried to obtain tetrafluoroborate imidazole metal ion liquid.

[0011] The molar ratio of imidazole ligands to metal salts is 1:1 to 8:1; The molar ratio of metal salt to tetrafluoroborate is 2:1 to 1:6; The concentration of the metal salt solution is 0.01~1M; The concentration of the tetrafluoroborate solution is 0.01~1M; The imidazole ligand is any one of N-alkane containing 1-3 carbon atoms, olefin containing 2-3 carbon atoms, and alkyne containing 2-3 carbon atoms; N-alkane is preferably N-methylimidazolium or N-ethylimidazolium, olefin is preferably N-allylimidazolium or N-vinylimidazolium, and alkyne is preferably N-propargylimidazolium. The metal salt is any one of the nitrates, hydrochlorides, or acetates of Mn, Co, Ni, Cu, Zn, and Cd.

[0012] An application of a tetrafluoroborate imidazole metal ionic liquid involves using the tetrafluoroborate imidazole metal ionic liquid as a shell material for aluminum powder, forming an aluminum powder@metal ionic liquid composition with the aluminum powder. The mass ratio of the shell material tetrafluoroborate imidazole metal ionic liquid to the aluminum core (i.e., aluminum powder) is 10:90 to 50:50. The preparation method of aluminum powder@metal ionic liquid includes the following steps: Step 1: Add tetrafluoroborate imidazole metal ionic liquid to anhydrous ethanol to obtain a solution; Step 2: Add aluminum powder to the obtained solution, stir magnetically, and perform ultrasonic treatment under water bath heating conditions to make the aluminum powder surface uniformly adsorb ionic liquid. During the water bath heating and ultrasonic process, anhydrous ethanol slowly evaporates. Step 3: After the anhydrous ethanol has completely evaporated, the resulting solid is transferred to a vacuum drying oven to dry, thus obtaining dry aluminum powder@metal ion liquid.

[0013] The mass ratio of the tetrafluoroborate imidazole metal ionic liquid to aluminum powder is 10:90 to 50:50.

[0014] The ultrasonic processing power is 100~800 W; The magnetic stirring speed is 200~1000 rpm; The ultrasonic treatment time is 5~30 min; The drying temperature is 50~80℃.

[0015] The present invention has the following beneficial effects: (1) The tetrafluoroborate imidazole-based metal ionic liquid of this invention has tetrafluoroborate ions that can interact with the oxide layer on the aluminum surface, destroying the oxide structure and thus enhancing the reactivity of aluminum. During combustion, this material can release a large amount of gas and heat, contributing additional energy; at the same time, the metal ions and fluorine radicals in the reaction process can further promote the oxidation process of aluminum and enhance combustion performance. Therefore, this material is a promising aluminum-based fuel for solid propellants.

[0016] (2) The tetrafluoroborate imidazole metal ion liquid and aluminum powder@metal ion liquid core-shell fuel of the present invention have low sensitivity and high safety.

[0017] (3) The raw materials for the preparation method of the tetrafluoroborate imidazole metal ion liquid and aluminum powder@metal ion liquid core-shell fuel of the present invention are readily available, the process is simple, the conditions are mild, and it is conducive to industrial production.

[0018] (4) This invention relates to tetrafluoroborate imidazole-based metal ionic liquids and their preparation method for core-shell fuels (aluminum powder@metal ionic liquid) composed of aluminum powder and aluminum powder. The aluminum powder@metal ionic liquid core-shell fuel is prepared by solvent evaporation, using aluminum as the core and tetrafluoroborate imidazole-based metal ionic liquid as the shell material. This series of core-shell fuels exhibits excellent thermal properties and is mainly suitable for the field of solid propellant fuels. Furthermore, the preparation method provided by this invention is simple, uses mild conditions, and uses readily available raw materials. Attached Figure Description

[0019] Figure 1 The molecular structure diagram of tetrafluoroborate vinylimidazolium copper is shown. Figure 2 The molecular structure diagram of nickel tetrafluoroborate vinylimidazolium; Figure 3 The molecular structure diagram of tetrafluoroborate allyl imidazolium copper; Figure 4 Infrared spectrum of aluminum powder@tetrafluoroborate vinylimidazolium copper core-shell fuel; Figure 5 DSC curves for aluminum powder@tetrafluoroborate vinylimidazolium copper core-shell fuel; Figure 6 The combustion process of aluminum powder@tetrafluoroborate vinylimidazolium copper and ammonium perchlorate mixture. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments.

[0021] Example 1: Preparation of copper tetrafluoroborate vinylimidazolium ether ether A tetrafluoroborate vinylimidazolium copper ionic liquid, the structural formula of which is as follows:

[0022] Where R is -CHCH2.

[0023] A method for preparing a tetrafluoroborate vinylimidazolium copper ionic liquid, the method comprising the following steps: First, 0.48 g (2 mmol) of copper nitrate trihydrate was dissolved in 20 mL of deionized water, and then 0.94 g (10 mmol) of 1-vinylimidazole was added. The mixture was magnetically stirred and reacted at 60 °C for 20 min to obtain the reaction solution. In the second step, 0.44 g (4 mmol) of tetrafluoroborate was added to 10 mL of deionized water to obtain a tetrafluoroborate solution. This solution was then added to the reaction mixture obtained in the first step, and the reaction was carried out at 60 °C for 1 h. After the reaction, the mixture was cooled to room temperature, and the precipitate was collected by filtration. The precipitate was washed three times alternately with cold water and ethanol, and then dried to obtain the tetrafluoroborate allyl imidazolium copper ionic liquid. The crystal structure was determined using X-ray single-crystal diffraction, and the results are as follows: Figure 1 As shown, by Figure 1 It can be known that the molecular formula is CuB2F8C 25 H 30 N 10 It belongs to the triclinic crystal system, space group P-1, with the following cell parameters: a=13.802(6) Å, b=17.6107(12) Å, c=12.998(2) Å, β=105.24(3)°, V=3048.3(14) Å. 3 The crystal density is 1.542 g / cm³. -3 This molecular structural unit contains a Cu 2+ It contains ions, 5 N-vinylimidazolium ions and 2 tetrafluoroborate ions.

[0024] An application of a tetrafluoroborate vinylimidazolium copper ionic liquid is described, in which the tetrafluoroborate vinylimidazolium copper ionic liquid is used as the shell material of aluminum powder to form an aluminum powder@metal ionic liquid. The mass ratio of the shell material tetrafluoroborate vinylimidazolium copper ionic liquid to the aluminum core (i.e., aluminum powder) is 15:85. The preparation method of aluminum powder@metal ionic liquid includes the following steps: Step 1: Add 1.5g of tetrafluoroborate vinylimidazolium copper ion liquid to anhydrous ethanol to obtain a solution; Step 2: Add 8.5g of aluminum powder to the obtained solution, stir magnetically at 300 rpm, and perform ultrasonic treatment under water bath heating (water bath temperature is 70 ℃) conditions. The ultrasonic treatment power is 500 W and the ultrasonic treatment time is 30 min, so that the aluminum powder surface can be uniformly adsorbed with ionic liquid. Step 3: After the anhydrous ethanol has completely evaporated, the resulting solid is transferred to a vacuum drying oven and dried at 60 ℃ to obtain dried aluminum powder@metal ion liquid. Infrared spectroscopy is then performed on the obtained aluminum powder@metal ion liquid, and the test results are as follows: Figure 4 As shown, by Figure 4 It can be seen that aluminum powder @ metal ionic liquid at 740 cm -1 and 3113 cm -1 A characteristic peak appears, corresponding to CH stretching motion. At 1385 cm⁻¹ -1 The characteristic peak that appears is due to the stretching motion of CN. Furthermore, at 838 cm⁻¹... -1 and 1098 cm -1 Characteristic peaks also appeared, corresponding to the symmetrical and asymmetrical stretching motions of PF, which all indicate the integrity of the chemical composition and structure of the metal ion liquid.

[0025] Differential scanning calorimetry (DSC) was performed on the obtained aluminum powder@metal ionic liquid. The thermal decomposition curve obtained by DSC is shown below. Figure 5 As shown, the thermal decomposition process of aluminum powder@metal ionic liquid can be divided into three stages: the first stage is the decomposition and exothermic reaction of the metal ionic liquid, and the second and third stages are the oxidation reaction of aluminum powder, with the third stage being the main oxidation process. In this stage, compared with pure aluminum powder, the decomposition temperature of aluminum powder@metal ionic liquid is advanced by 18.4℃. The obtained aluminum powder@metal ion liquid was mixed with ammonium perchlorate at a mass ratio of 1:3 and ground until homogeneous. The combustion process was recorded using high-speed photography. Figure 6 As shown in the figure. The results show that the mixture of pure aluminum powder and ammonium perchlorate cannot be ignited, while the mixture of aluminum powder@metal ion liquid and ammonium perchlorate can be ignited and achieve stable combustion.

[0026] Example 2: Preparation of nickel tetrafluoroborate vinylimidazolium hydroxide 0.58 g (2 mmol) of nickel nitrate hexahydrate was dissolved in 20 mL of deionized water and transferred to a beaker. 1.13 g (12 mmol) of 1-vinylimidazole was dissolved in 10 mL of deionized water and added to the above copper nitrate trihydrate aqueous solution. The mixture was placed in a 60 °C environment with magnetic stirring and reacted for 20 min to complete the reaction. 0.44 g (4 mmol) of tetrafluoroborate was dissolved in 10 mL of deionized water and added dropwise to the above reaction system. The mixture was stirred and reacted for another 60 min while maintaining thermodynamic conditions. The product was filtered, washed 2-3 times with cold water and ethanol, and the solid product was dried in a 60 °C oven for 6 h. After the filtrate slowly evaporated, a single crystal of the product was obtained. The crystal structure was determined by X-ray single-crystal diffraction. Figure 2 As shown, its molecular formula was determined to be NiB2F8C. 30 H 36 N 12 It belongs to the monoclinic crystal system, space group P21 / c, with the following cell parameters: a=18.4132(10) Å, b=13.4832(13) Å, c=17.163(2) Å, β=113.479(11)°, V=1785.7(3) Å. 3 The crystal density is 1.482 g / cm³. -3 This molecular structural unit contains one Ni. 2+ It contains 6 vinylimidazole ions and 2 tetrafluoroborate ions.

[0027] Example 3: Preparation of copper tetrafluoroborate allyl imidazolium ether Dissolve 0.48 g (2 mmol) of copper nitrate hexahydrate in 20 mL of deionized water and transfer to a beaker. Dissolve 0.87 g (10 mmol) of 1-allylimidazol in 10 mL of deionized water and add to the above copper nitrate trihydrate aqueous solution. With magnetic stirring, place the mixture at 60 °C and react for 20 min to complete the reaction. Weigh 0.44 g (4 mmol) of tetrafluoroborate, dissolve it thoroughly in 10 mL of deionized water, and add it dropwise to the above reaction system. Maintain thermodynamic conditions and continue stirring for 60 min. Filter, wash 2-3 times with cold water and ethanol, and dry the solid product in a 60 °C oven for 6 h. After slow evaporation of the filtrate, obtain a single crystal of the product. Determine the crystal structure by X-ray single-crystal diffraction. Figure 3 As shown.

[0028] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A tetrafluoroborate imidazole-based metal ionic liquid, characterized in that: The general structural formula of the tetrafluoroborate imidazole metal ionic liquid is as follows: Where m represents the number of substituted imidazole ligands, n represents the number of tetrafluoroborate ions, the central metal atom M is any one of Mn, Co, Ni, Cu, Fe, and Cd; the imidazole substituent R is any one of alkanes with 1-3 carbon atoms, alkenes with 2-3 carbon atoms, and alkynes with 2-3 carbon atoms.

2. The tetrafluoroborate imidazole-based metal ionic liquid according to claim 1, characterized in that: m can be 2, 4, 5, or 6.

3. The tetrafluoroborate imidazole-based metal ionic liquid according to claim 1, characterized in that: n is usually 2.

4. A method for preparing a tetrafluoroborate imidazole-based metal ionic liquid, characterized in that... The steps of this method include: The first step involves adding imidazole ligands to a metal salt solution and reacting them at a temperature of 10–90 °C for 0.2–8 h to obtain the reaction solution. In the second step, the tetrafluoroborate solution is added to the reaction solution obtained in the first step, and the reaction is carried out at a temperature of 10~90℃ for a time of 0.2~8 h. After the reaction is completed, the mixture is cooled to room temperature, filtered to collect the precipitate, washed and dried to obtain tetrafluoroborate imidazole metal ion liquid.

5. A method for preparing a tetrafluoroborate imidazole-based metal ionic liquid, characterized in that... The steps of this method include: The first step involves adding a tetrafluoroborate solution to a metal salt solution to initiate a reaction at a temperature of 10–90 °C for 0.2–8 h, thereby obtaining a reaction solution. In the second step, the imidazole ligand is added to the reaction solution obtained in the first step and the reaction is carried out at a temperature of 10~90℃ for a time of 0.2~8 h. After the reaction is completed, the mixture is cooled to room temperature, filtered and the precipitate is collected. The precipitate is washed and dried to obtain imidazole tetrafluoroborate metal ion liquid.

6. The method for preparing a tetrafluoroborate imidazole-based metal ionic liquid according to claim 4 or 5, characterized in that: The molar ratio of imidazole ligands to metal salts is 1:1 to 8:1; The molar ratio of metal salt to tetrafluoroborate is 2:1 to 1:6; The concentration of the metal salt solution is 0.01~1M; The concentration of the tetrafluoroborate solution is 0.01~1M.

7. The method for preparing a tetrafluoroborate imidazole-based metal ionic liquid according to claim 4 or 5, characterized in that: The imidazole ligand is any one of N-alkanes containing 1-3 carbon atoms, alkenes containing 2-3 carbon atoms, and alkynes containing 2-3 carbon atoms; The metal salt is any one of the nitrates, hydrochlorides, or acetates of Mn, Co, Ni, Cu, Zn, and Cd.

8. The method for preparing a tetrafluoroborate imidazole-based metal ionic liquid according to claim 7, characterized in that: N-Alkanes are N-methylimidazole or N-ethylimidazole, alkenes are N-allylimidazole or N-vinylimidazole, and alkynes are N-propylimidazole.

9. An application of a tetrafluoroborate imidazole-based metal ionic liquid, characterized in that: Tetrafluoroborate imidazole-based metal ionic liquid is used as the shell material of aluminum powder to form aluminum powder@metal ionic liquid, wherein the mass ratio of the shell material tetrafluoroborate imidazole-based metal ionic liquid to the aluminum core is 10:90~50:

50.

10. The application of a tetrafluoroborate imidazole-based metal ionic liquid according to claim 9, characterized in that: The preparation method of aluminum powder@metal ionic liquid includes the following steps: Step 1: Add tetrafluoroborate imidazole metal ionic liquid to anhydrous ethanol to obtain a solution; Step 2: Add aluminum powder to the obtained solution, stir magnetically, and perform ultrasonic treatment under water bath heating conditions to make the aluminum powder surface uniformly adsorb ionic liquid. During the water bath heating and ultrasonic process, anhydrous ethanol slowly evaporates. Step 3: After the anhydrous ethanol has completely evaporated, the resulting solid is transferred to a vacuum drying oven to dry, thus obtaining dry aluminum powder@metal ion liquid; The mass ratio of the tetrafluoroborate imidazole metal ionic liquid to aluminum powder is 10:90 to 50:

50. The ultrasonic processing power is 100~800 W; The magnetic stirring speed is 200~1000 rpm; The ultrasonic treatment time is 5~30 min; The drying temperature is 50~80℃.

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