Bismuth-based oxyfluoronitrate compounds, methods of making and using the same

Abstract

This invention discloses a bismuth-based fluoride nitrate compound, its preparation method, and its applications, relating to the field of energetic materials technology. It aims to overcome the shortcomings of existing oxidants, such as low gas production and low energy density, as well as the incomplete reaction and slow combustion rate of metal fuels. The compound has the general structural formula Bi. a O x F y ·HNO3·(HClO4) z Where a is 5-6, x is 5-7, y is 3-6, and z is 0 or 1, containing oxygen vacancies, and oxygen vacancies, fluoride ions, and nitrate ions are orderly arranged along the crystal axis within the lattice to form a superlattice structure; when z is 1, perchlorate ions and nitrate ions are jointly embedded in the superlattice structure. This invention releases highly active O upon thermal decomposition. 2‑ and F ‑ Free radicals break through the single oxidation reaction pathway, increasing the calorific value and reaction rate; F ‑ Free radicals eliminate the inert oxide layer on the surface of metallic fuels and activate the metallic fuels, while gaseous BF3 inhibits product aggregation, significantly improving energy density and reaction efficiency of metallic fuels.

Description

Technical Field

[0001] This invention relates to the field of energetic materials technology. More specifically, this invention relates to a bismuth-based fluoride nitrate compound, its preparation method, and its applications. Background Technology

[0002] Energetic materials are a class of special substances capable of autonomously completing combustion or explosion reactions and releasing energy. Their energy release essentially depends on redox reactions within the system. As the oxidizing component in the reaction, the composition and structure of the oxidant directly determine the reaction rate, energy density, and degree of combustion completeness of the energetic material, and are the core factors affecting its overall performance.

[0003] Currently, oxidants used in the field of energetic materials mainly include ionic salts and metal oxides. Ionic salt oxidants are represented by ammonium perchlorate (AP), potassium nitrate, hydroxylamine nitrate, and ammonium dinitramide (ADN). Among them, AP is the most widely used oxidant in solid propellants, with advantages such as moderate decomposition temperature and good compatibility. However, its combustion products contain HCl, which can cause serious environmental pollution. ADN has high energy density and clean combustion products, but it is extremely hygroscopic and has poor storage stability, making it difficult to use directly. Potassium nitrate and other oxidants are convenient to use, but they generally have problems such as moisture absorption and toxicity. Overall, it is difficult to balance environmental friendliness and storage stability with ionic salt oxidants.

[0004] Metal oxide oxidizers, represented by copper oxide and iron oxide, are commonly used oxidizing components in pyrotechnics and thermite, possessing advantages such as simple preparation and good thermal stability. However, the gas production generated when metal oxides participate in the reaction is limited, making it difficult to obtain a sufficient gaseous reaction medium, resulting in insufficient energy density and pressure output; at the same time, the reaction safety of some metal oxides is difficult to meet the requirements, thus preventing their direct application in explosives and solid propellants.

[0005] In recent years, the technical approach of introducing fluorine into oxide lattices and utilizing the high reactivity of fluorine to enhance the combustion performance of metallic fuels has attracted attention. In 2023, Li Jingwei et al. from Nanjing University of Science and Technology reported a fluorine-containing oxidant, BiOF, and assembled it with nano-aluminum to form an n-Al / BiOF nano-aluminothermic system. The BiOF crystals prepared in this study exhibited a nanoflower-like microsphere morphology and showed good interfacial contact with aluminum powder. The combustion temperature of the n-Al / BiOF system was higher than the boiling points of its main combustion products, AlF3 and Bi. Under confined conditions, its flame propagation rate and ignition threshold were superior to those of the n-Al / CuO and n-Al / MoO3 systems. This study also revealed a pre-ignition reaction mechanism, namely, the corrosion reaction between fluorine and the Al2O3 shell on the aluminum surface, promoting the early release of aluminum energy. However, BiOF is still a binary fluorine oxide, and its crystal decomposition activation barrier is relatively high, making it difficult to rapidly activate and release active components under mild conditions; moreover, the gas production of this system is still limited, and the improvement of the reaction efficiency of metal fuels is still insufficient, failing to fundamentally solve the problems of low gas production and high crystal activation decomposition barrier of metal oxide oxidants.

[0006] In the case of metallic fuels, metals such as aluminum, boron, and titanium possess extremely high theoretical calorific values, making them ideal reducing components in composite energetic materials. However, metallic fuels generally suffer from incomplete reactions and slow combustion rates in actual reactions. The fundamental reason for this is that the dense inert oxide layer (such as Al2O3 and B2O3) on the surface of metal particles hinders heat and mass transfer between reactants. Simultaneously, combustion products are prone to sintering and agglomeration, further reducing fuel utilization. To address these issues, existing technologies primarily employ surface coating and alloying strategies. For example, aluminum-boron alloying can be used to adjust the reaction characteristics of metallic fuels. However, limited by the solid-state reaction mechanism of metallic fuels, the improvement effects are limited, and rapid and complete reactions of metallic fuels cannot be achieved.

[0007] Therefore, it is necessary to design a technical solution that can overcome the above-mentioned defects. Summary of the Invention

[0008] One object of this invention is to provide a bismuth-based fluorooxynitrate compound, its preparation method, and its applications, aiming to overcome the shortcomings of existing oxidants, such as low gas production and low energy density, as well as the incomplete reaction and slow combustion rate of metal fuels.

[0009] To achieve these objects and other advantages of the present invention, according to one aspect of the present invention, a bismuth-based fluoroxynitrate compound is provided, the general structural formula of which is Bi. a O x F y ·HNO3·(HClO4) zWhere a is 5-6, x is 5-7, y is 3-6, and z is 0 or 1; the bismuth-based fluoride nitrate compound contains oxygen vacancies, which are vacancies formed by the absence of some oxygen atom sites in the crystal lattice; oxygen vacancies, fluoride ions, and nitrate ions are arranged in an orderly manner along the crystal axis in the crystal lattice to form a superlattice structure; when z is 1, perchlorate ions and nitrate ions are embedded together in the superlattice structure.

[0010] Furthermore, the bismuth-based fluoride nitrate compound is at least one of Bi6F4O7·HNO3, Bi5F6O5·HNO3, Bi6F3O6·HNO3, or Bi6F4O7·HNO3·HClO4.

[0011] Furthermore, the superlattice structure is formed by the orderly alternation of vacant oxygen, fluoride ions, and nitrate ions at equal intervals along the crystal axis; the crystal axis is either the c-axis or the a-axis; the bismuth-based fluoride nitrate compound is a hexagonal plate-like crystal.

[0012] According to another aspect of the present invention, a method for preparing a bismuth-based fluoride nitrate compound is also provided, comprising the following steps: S1: dissolving a bismuth salt and a fluorine source respectively in a mixed solvent of an alcohol solvent and water, wherein the solvent further contains a structure-directing agent, wherein the structure-directing agent is citric acid or polyvinylpyrrolidone; obtaining a bismuth salt solution and a fluorine source solution; the molar ratio of the fluorine source to the bismuth salt is (0.4-3):1; slowly adding the fluorine source solution to the bismuth salt solution, stirring and mixing evenly to obtain a mixed solution; S2: slowly adding ammonia water dropwise to the mixed solution, continuously monitoring the pH value during the dropwise addition, adjusting the pH value of the mixed solution to 8-10, and continuing to stir for 5-30 min after the dropwise addition is completed; S3: ultrasonically treating the pH-adjusted mixed solution for 10-30 min, adding hexagonal plate-like seed crystals of the bismuth-based fluoride nitrate compound, and then transferring it to a hydrothermal reactor equipped with a polytetrafluoroethylene liner, sealing it, controlling the filling degree of the reactor to 60%-80%, and hydrothermally reacting it at 120-160 °C for 6-14 minutes. S4: After the reaction is complete, allow the mixture to cool naturally to room temperature; S5: Collect the solid product by filtration, wash with deionized water or ethanol, and dry to obtain the crude bismuth-based fluoroxynitrate compound; S6: Activate the crude product in an argon-hydrogen or nitrogen-hydrogen mixed atmosphere at 100-250 °C for 0.5-3 h; S7: Characterize the activated product by X-ray diffraction to confirm the characteristic diffraction peaks of the ordered arrangement of oxygen vacancies, fluoride ions, and nitrate ions forming a superlattice structure, thus obtaining the bismuth-based fluoroxynitrate compound.

[0013] Furthermore, the bismuth salt is at least one of bismuth nitrate, bismuth nitrate pentahydrate, or bismuth chloride; the fluorine source is at least one of potassium fluoride, sodium fluoride, or ammonium fluoride; and the solvent is a mixture of ethanol, propanol, and water, or a mixture of ethylene glycol and water.

[0014] Furthermore, the alkaline solution is commercially available analytical grade ammonia diluted with water at a volume ratio of 1:(3-8).

[0015] Further, dry at 50-60 ℃.

[0016] According to another aspect of the invention, the application of a bismuth-based fluorooxynitrate compound in an energetic material comprising a metallic fuel, wherein the bismuth-based fluorooxynitrate compound is mixed with the metallic fuel, and the energetic material is a composite energetic material or a mixed explosive.

[0017] Further, a bismuth-based fluoroxynitrate compound is mixed with a metal fuel to obtain an energetic material; the mass ratio of the bismuth-based fluoroxynitrate compound to the metal fuel is (0.5-3):1, and the metal fuel is at least one of aluminum, boron, titanium, or an aluminum-boron alloy; the bismuth-based fluoroxynitrate compound is a hexagonal plate-like crystal that overlaps with the metal fuel particles in a surface contact manner; when the metal fuel is aluminum, the aluminum content per unit mass in the energetic material is not less than 20%; the metal fuel is pretreated with ammonium fluoride solution or hydrofluoric acid solution before use.

[0018] Furthermore, the energetic material also contains at least one functional additive selected from ammonium perchlorate, ammonium nitrate, ammonium dinitrate, or potassium nitrate, and the energetic material is used for solid propellant loading.

[0019] The present invention has at least the following beneficial effects:

[0020] The bismuth-based fluoride nitrate compound of the present invention has a superlattice structure formed by the orderly arrangement of oxygen vacancies, fluoride ions and nitrate ions, and releases highly reactive O upon thermal decomposition. 2- and F - Two types of free radicals: O 2- It undergoes an oxidation reaction with metallic fuels, F - Fluorination with metallic fuels, coupled with fluorination, breaks through the traditional mode of energy release via a single oxidation pathway of metal oxides, increasing both the calorific value and the reaction rate; F - It can also react with the inert oxide layer (such as Al2O3, B2O3) on the surface of metallic fuels to generate AlF3, B F3This invention activates metallic fuels, eliminates heat and mass transfer barriers, and inhibits the sintering and agglomeration of combustion products through gaseous BF3, thereby improving fuel reaction completeness and utilization. Nitrate ions retain the reaction characteristics of traditional oxidants, ensuring the overall oxidation capacity of the system. Using common bismuth salts and fluorine sources as raw materials, this invention achieves controllable construction of superlattice structures via a wet chemical hydrothermal route. The process involves few steps, mild conditions (pH 8-10, 120-160℃), and easily adjustable parameters. Through synergistic control of parameters such as the fluorine / bismuth salt molar ratio, pH adjustment, stirring time, and hydrothermal filling degree, the oxygen vacancy concentration and superlattice order can be directionally controlled. The raw materials are inexpensive and readily available, facilitating large-scale production. Furthermore, by introducing perchlorate into the reaction system, nitrate and perchlorate ions can be simultaneously embedded in the superlattice framework, forming multi-oxygen-containing acid anion co-embedding compounds such as Bi6F4O7·HNO3·HClO4, further supplementing the oxygen-containing components and enriching the variety of gaseous products. The compounds of this invention can be compounded with various metallic fuels such as aluminum, boron, titanium, or aluminum-boron alloys in a wide range of mass ratios. They can also be synergistically enhanced with functional additives such as ammonium perchlorate and ammonium nitrate. The resulting energetic materials possess both high energy density and high reaction efficiency. Under the same oxidant mass, the aluminum content per unit mass can reach over 20%, more than double that of existing BiOF systems (approximately 10%). Furthermore, the morphology and superlattice order of the crystals are synergistically controlled through structure-directing agents and seed-induced orientation growth; dispersion and nucleation are controlled through ultrasonic treatment; and oxygen vacancy concentration is regulated through activation treatment in a reducing atmosphere. After surface pre-fluorination treatment, the inert oxide layer on the surface of the metallic fuel is transformed into a fluoride layer, further improving the interfacial reaction between the oxidant and the fuel. This invention is applicable to solid propellants, explosives, and pyrotechnics, and has significant application value in missile weapons, aerospace, and other scenarios.

[0021] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0022] Figure 1 The image shows the scanning electron microscope morphology of the Bi6F4O7·HNO3 sample from the experimental group.

[0023] Figure 2 The thermal analysis curves of Bi6F4O7·HNO3 in the experimental group are shown.

[0024] Figure 3 High-speed photographs and pressure-increase rate curves of the combustion reaction between Bi6F4O7·HNO3 and aluminum powder in the experimental group.

[0025] Figure 4 Atom snapshots of the decomposition process of BiOF and Bi6F4O7·HNO3 crystals obtained from molecular dynamics simulations. Detailed Implementation

[0026] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.

[0027] It should be understood that terms such as "having," "comprising," and "including" used in the embodiments of this application do not exclude the presence or addition of one or more other elements or combinations thereof. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of components in a specific posture. If the specific posture changes, the directional indication will also change accordingly. When an element is referred to as "fixed to" or "set on" another element, it can be directly on the other element or may have an intervening element present. When an element is referred to as "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element through an intervening element. Descriptions involving "first," "second," etc., in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features.

[0028] It should be noted that the technical solutions of the various embodiments of this application can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this application.

[0029] In one embodiment, the bismuth-based fluoride nitrate compound has the general structural formula Bi. a O x F y ·HNO3, where a is 5-6, x is 5-7, and y is 3-6, a represents the stoichiometric coefficient of bismuth, x represents the stoichiometric coefficient of oxygen, and y represents the stoichiometric coefficient of fluorine, all of which are positive integers, and HNO3 represents the nitrate component bound in the crystal lattice in the form of nitrate ions; optionally, the general structural formula of the compound is Bi. a O x F y ·HNO3·(HClO4) zWhen z is 0 or 1, and z is 1, perchlorate ions are embedded in the superlattice framework as anions along with nitrate ions. The bismuth-based fluoride nitrate compound is used as an oxidant component in the composite energetic material. This compound contains oxygen vacancies, which are defects left after the loss of some oxygen atoms in the lattice. The chemical environment at these vacancy sites is relatively open, with a high affinity for external reactants, and can serve as trigger sites for decomposition reactions, thereby reducing the energy input required to initiate the reaction. Oxygen vacancies, fluoride ions, and nitrate ions are arranged in an orderly manner within the lattice, forming a superlattice structure. The three components are arranged alternately according to a fixed periodic pattern, exhibiting a long-range ordered stacking pattern at the lattice scale. This structure allows fluoride ions and nitrate ions to be spatially staggered, each maintaining an independent release channel. When heated, each component can sequentially detach from the lattice, thus ensuring the continuous progress of the decomposition reaction. Simultaneously, oxygen vacancies, as active nodes in the structural framework, permeate the entire superlattice, linking the effects of adjacent components. This ternary ordered arrangement, with oxygen vacancies as the framework and fluoride and nitrate ions as functional components, allows the oxidant to simultaneously acquire three types of elements during decomposition: active trigger sites, activated species, and oxygen-containing species. Traditional oxides typically only provide one of these. Optionally, a can be 5 or 6, x can be 5, 6, or 7, and y can be 3, 4, or 6. Different values ​​correspond to compounds with different stoichiometric ratios, resulting in slightly different energy release characteristics. In one possible implementation, this compound is used as the oxidant component of a solid propellant, forming the propellant's energy system together with metallic fuel.

[0030] In existing technologies, metal oxide oxidants and binary fluorine oxide oxidants lack oxygen vacancies as active sites in their crystal lattices. Fluorine and oxygen combine in a fixed, simple ratio, and during decomposition, the components are released simultaneously without a sequence, making it difficult for the reactants to be rapidly activated under mild conditions. This embodiment introduces oxygen vacancies and constructs a superlattice arrangement of oxygen vacancies, fluoride ions, and nitrate ions. This allows the crystal lattice to simultaneously possess active triggering sites, activated species, and oxygen-containing species. These three elements are spatially misaligned and released sequentially, thereby reducing the difficulty of decomposition initiation. Consequently, the oxidant can react with metal fuels with lower energy input, contributing to improved overall energy release efficiency of the composite energetic material.

[0031] In one embodiment, the bismuth-based fluoride nitrate compound is at least one of Bi6F4O7·HNO3, Bi5F6O5·HNO3, or Bi6F3O6·HNO3. The stoichiometric differences among the three compounds directly reflect the concentration of oxygen vacancies and the proportion of fluoride ions. Compounds with higher oxygen vacancy concentrations provide more active triggering sites during decomposition, while compounds with a higher proportion of fluoride ions release more activating species, thus adjusting the ratio of oxidation and activation while maintaining the superlattice framework. Optionally, one of the compounds can be used alone as an oxidant component, or two or more can be mixed in any proportion. When used in combination, the differences in decomposition temperature among the components allow for sequential energy release at different stages, forming a progressive energy release process of activation followed by oxidation. Bi6F4O7·HNO3, as an oxidant component, has a relatively balanced oxygen-fluoride ratio, making it suitable for use with aluminum powder-based metal fuels as an energy component in pyrotechnic agents. Optionally, the bismuth-based fluoride nitrate compound may also be Bi6F4O7·HNO3·HClO4, that is, nitrate and perchlorate are simultaneously embedded in the superlattice framework, wherein the nitrate component contributes nitrogen-containing gaseous products, and the perchlorate component further supplements the oxygen-containing component, reflecting the superlattice structure's ability to support the types of oxygen-containing acid radicals.

[0032] In one embodiment, the bismuth-based fluoride nitrate compound contains oxygen vacancies. The superlattice structure is formed by the alternating and orderly arrangement of oxygen vacancies, fluoride ions, and nitrate ions along the crystal axis. That is, the three components appear sequentially along a fixed period in a certain axial direction of the lattice, with adjacent sites maintaining equal spacing, thus forming a regular component distribution within the crystal. This alternating arrangement along the crystal axis ensures strict spatial isolation of the components. During decomposition, free radicals can be generated sequentially along the crystal axis and continuously supplied outward, thereby preventing premature encounter and consumption of multiple active species within the lattice. The bismuth-based fluoride nitrate compound is a hexagonal plate-like crystal. The hexagonal plate morphology refers to the crystal exhibiting a macroscopic hexagonal plate shape. This morphology gives the crystal a large specific surface area, providing a more sufficient contact interface when mixed with metallic fuels, thereby improving the heat and mass transfer conditions between the oxidant and the fuel. The compound produces highly active O₂ upon thermal decomposition. 2- Free radicals and F - Free radicals, O 2- Free radicals are negatively charged reactive oxygen species that react with metallic fuels in oxidation reactions. -The free radicals are active fluorine species that react with the inert oxide layer on the surface of metallic fuels. Two types of free radicals are generated at different positions along the crystal axis and diffuse outwards, performing both oxidation and activation functions in parallel within the same reaction system. This allows the oxidation reaction on the metallic fuel surface and the removal of the inert layer to proceed simultaneously, without interference but seamlessly integrated. Optionally, the crystal axis direction is either the c-axis or the a-axis direction. In one possible implementation, the compound is applied to solid propellants, where hexagonal plate-like crystals are mixed with aluminum powder to form a uniformly distributed composite system.

[0033] This embodiment utilizes a superlattice structure arranged alternately along the crystal axis to allow two types of free radicals to be generated separately in space and supplied sequentially in time. At the same time, the hexagonal plate-like morphology increases the contact interface with the fuel, thereby enabling the oxidation and activation reactions to proceed in parallel. This improves the degree to which the metal fuel participates in the reaction and helps to improve the overall reaction efficiency of the composite energetic material.

[0034] In one embodiment, when preparing the bismuth-based fluoride nitrate compound, the bismuth salt and fluorine source are first dissolved in a solvent to obtain a bismuth salt solution and a fluorine source solution, respectively. The bismuth salt provides the bismuth source, and the fluorine source provides the fluorine source. The solvent is used to fully disperse the two raw materials. The dissolution operation is carried out at room temperature. If the raw materials dissolve slowly, the temperature can be appropriately increased to promote dissolution. The amount of solvent used is sufficient to completely dissolve the raw materials. Stirring is used during the dissolution process to accelerate the dissolution rate. The molar ratio of fluorine source to bismuth salt is controlled at (0.4-3):1. Then, the fluorine source solution is slowly added to the bismuth salt solution. The slow addition method is used to avoid excessively high local concentrations of fluorine source, which could lead to the local aggregation of fluoride ions and prevent the distribution of fluorine in the crystal lattice from deviating from a uniform state. The addition process continues for several minutes with continuous stirring to ensure that the two solutions are mixed evenly, resulting in a mixed solution. Subsequently, an alkaline solution is added dropwise to the mixture. The addition is carried out dropwise, and the alkaline solution is used to neutralize the acidic components in the system and adjust the pH. The pH value of the system is continuously monitored during the addition until the pH value of the mixture is adjusted to 8-10. The alkaline environment promotes the hydrolysis of metal ions and induces the formation of oxygen vacancies in the crystal lattice. The pH value directly controls the number and distribution of oxygen vacancies. This step provides a vacancy framework for the subsequent superlattice structure. After the addition is completed, the mixture is stirred for 5-30 minutes to make the system homogeneous. Optionally, before transferring to a hydrothermal reactor, the mixture is ultrasonically treated at room temperature for 10-30 minutes to fully disperse the reactants and promote uniform nucleation. Optionally, a small amount of bismuth-based fluoroxynitrate hexagonal plate-shaped seed crystals can also be added to the mixture to induce crystal orientation growth along the crystal axis. Next, the pH-adjusted mixture is transferred to a hydrothermal reactor, sealed, and subjected to hydrothermal reaction at 120-160 ℃ for 6-14 h. The hydrothermal reactor provides a high-temperature and high-pressure environment under closed conditions, allowing ions in the solution to enter the crystal lattice in a fixed spatial order during slow crystallization, completing the ordered self-assembly of oxygen vacancies, fluoride ions, and nitrate ions. The filling degree of the mixture in the reactor is controlled at 60% to 80%. Optionally, the temperature is 130 ℃ or 150 ℃, and the time is 8 h or 10 h. After the reaction is completed, the reactor is naturally cooled to room temperature. Natural cooling is used to allow crystals to precipitate slowly and reduce the generation of lattice defects. Finally, the solid product is collected by filtration and washed two to three times with deionized water or ethanol to remove soluble impurities adhering to the crystal surface. It is then dried to remove residual water and solvent. After drying, the crude bismuth-based fluoride nitrate compound is obtained. Optionally, the crude product is activated at 100-250 °C for 0.5-3 h in an argon-hydrogen or nitrogen-hydrogen mixed atmosphere to remove some lattice oxygen and further increase the oxygen vacancy concentration. The activated product is characterized by X-ray diffraction to confirm the characteristic diffraction peaks of the ordered arrangement of oxygen vacancies, fluoride ions, and nitrate ions forming a superlattice structure.In one possible implementation, the preparation method is carried out in a hydrothermal reactor lined with polytetrafluoroethylene, which is suitable for sample preparation under laboratory conditions.

[0035] In existing technologies, the preparation of fluorine-containing oxides typically requires high-temperature solid-state reactions or complex multi-step processes. The distribution of components within the crystal lattice is difficult to control, and active sites such as oxygen vacancies cannot be introduced directionally through process parameters. This embodiment utilizes two core operations—alkaline pH adjustment and hydrothermal reaction—to control the formation of oxygen vacancies through pH and the ordered arrangement of ions through hydrothermal conditions. This brings the construction of the superlattice structure within a controllable range of process parameters, thereby reducing the operational difficulty of the preparation process and making the structure and composition of the product easier to reproduce. Furthermore, by co-dissolving the fluorine source and perchlorate in step S1, nitrate and perchlorate ions can be simultaneously embedded in the superlattice framework, yielding multi-oxygen-containing acid anion co-embedding compounds such as Bi6F4O7·HNO3·HClO4, further supplementing the oxygen-containing components and enriching the variety of gas-phase products.

[0036] In one embodiment, when preparing the bismuth-based fluoride nitrate compound, at least one of bismuth nitrate, bismuth nitrate pentahydrate, or bismuth chloride is selected as the bismuth salt. Both bismuth nitrate and bismuth nitrate pentahydrate provide the bismuth source in the form of nitrate ions, which can directly participate in the construction of the superlattice structure in the crystal lattice. Bismuth chloride provides the bismuth source in the form of chloride ions, which are gradually replaced by nitrate ions during the reaction. At least one of potassium fluoride, sodium fluoride, or ammonium fluoride is selected as the fluoride source, providing fluoride ions in the form of potassium, sodium, or ammonium salts, respectively. The solvent is a mixture of ethanol, propanol, and water, or a mixture of ethylene glycol and water. Alcohol solvents are used to reduce the polarity of water and improve the dissolution and dispersion of the raw materials. Simultaneously, the weak coordination of the hydroxyl groups in alcohols helps guide ions to sequentially enter the crystal lattice. First, the selected bismuth salt and fluoride source are dissolved in the above solvents to obtain a bismuth salt solution and a fluoride source solution, respectively. Then, the fluoride source solution is slowly added to the bismuth salt solution, and the mixture is stirred until homogeneous to obtain a mixed solution. Subsequently, an alkaline solution is added dropwise to the mixture until the pH value of the mixture is adjusted to 8-10. The pH-adjusted mixture is then transferred to a hydrothermal reactor and sealed. The reactor is subjected to hydrothermal reaction at 120℃-160℃ for 6-14 hours. After natural cooling to room temperature, the solid product is collected by filtration and dried to obtain the bismuth-based fluoride oxynitrate compound. Optionally, the bismuth salt is bismuth nitrate pentahydrate, the fluorine source is potassium fluoride, and the solvent is a mixture of ethanol, propanol, and water. The molar ratio of the fluorine source to the bismuth salt is (0.4-3):1. Alternatively, at least one of potassium perchlorate, sodium perchlorate, or ammonium perchlorate can be added to the fluorine source solution to allow the perchlorate and nitrate ions to co-intercalate into the superlattice framework, obtaining a compound with multiple oxyacid anions such as Bi6F4O7·HNO3·HClO4. Optionally, the mixed solvent also contains citric acid or polyvinylpyrrolidone as a structure directing agent. Citric acid coordinates with bismuth ions through carboxyl groups, and polyvinylpyrrolidone regulates the orientation growth of crystals through adsorption, thereby promoting the formation of hexagonal plate-like morphology.

[0037] In one embodiment, the bismuth-based fluoroxynitrate compound is prepared by first dissolving the bismuth salt and fluorine source separately in a solvent to obtain a bismuth salt solution and a fluorine source solution, respectively. The fluorine source solution is then slowly added to the bismuth salt solution and stirred until homogeneous, resulting in a mixture. Subsequently, an alkaline solution, which is ammonia diluted with water at a volume ratio of 1:(3-8), is added dropwise to the mixture. This alkaline solution is used to adjust the pH of the system at a relatively gentle rate, allowing the alkalinity to diffuse evenly in the solution and preventing sudden increases in alkalinity that could cause local precipitation. This ensures that oxygen vacancies are generated uniformly throughout the crystal lattice. Optionally, the dilution volume ratio is 1:5 or 1:6. The dropwise addition continues until the pH of the mixture is adjusted to 8-10. After the addition is complete, stirring is continued for 5-30 minutes. The pH-adjusted mixture is then transferred to a hydrothermal reactor and sealed. The reactor is subjected to a hydrothermal reaction at 120-160°C for 6-14 hours. After the reaction, the mixture is allowed to cool naturally to room temperature. Finally, the solid product is collected by filtration and dried to obtain the bismuth-based fluoroxynitrate compound. In one possible implementation, the ammonia stock solution is commercially available analytical grade ammonia, and the dilution operation is carried out at room temperature.

[0038] In one embodiment, when preparing the bismuth-based fluoroxynitrate compound, the bismuth salt and fluorine source are first dissolved in a solvent to obtain a bismuth salt solution and a fluorine source solution, respectively. The fluorine source solution is then slowly added to the bismuth salt solution and stirred until homogeneous to obtain a mixed solution. Subsequently, an alkaline solution is added dropwise to the mixed solution to adjust the pH value to 8-10. The pH-adjusted mixed solution is then transferred to a hydrothermal reactor and sealed. The mixture is then hydrothermally reacted at 120-160°C for 6-14 hours. After the reaction, the mixture is naturally cooled to room temperature. The solid product is then collected by filtration and placed in an oven at 50-60°C for drying. The drying temperature is used to remove residual moisture while maintaining the arrangement order of oxygen vacancies and ions in the crystal lattice, avoiding excessive temperature that could cause fluoride ion release or superlattice structure collapse. Optionally, the drying temperature is 55°C or 60°C. Drying continues until the product quality no longer changes. After drying, the bismuth-based fluoroxynitrate compound is obtained. In one possible implementation, drying is carried out in a forced-air drying oven, with the solid product spread out in a drying dish to increase the surface area exposed to heat.

[0039] In one embodiment, a bismuth-based fluoride nitrate compound is applied to an energetic material. The bismuth-based fluoride nitrate compound contains oxygen vacancies, and oxygen vacancies, fluoride ions, and nitrate ions are arranged in an orderly manner within the crystal lattice to form a superlattice structure. This superlattice structure is formed by the alternating and orderly arrangement of oxygen vacancies, fluoride ions, and nitrate ions along the crystal axis. The compound is a hexagonal plate-like crystal that produces highly reactive O₂ upon thermal decomposition. 2- Free radicals and F -Free radicals. In energetic materials, the bismuth-based fluoride nitrate compound is used as an oxidant component, and its action occurs via two parallel pathways: one pathway is the generation of O through superlattice decomposition. 2- Free radicals react with reducing components through oxidation, releasing energy; another pathway is F... - Free radicals react with the inert oxide layer on the surface of the reducing component, removing the barrier of the inert layer. Both pathways are initiated simultaneously after ignition, freeing the oxidation reaction on the reducing component surface from the limitations of heat and mass transfer by the inert layer. The hexagonal plate-like morphology increases the contact area between the oxidant and the reducing component, while oxygen vacancies reduce the difficulty of decomposition initiation, enabling the energetic material to release energy rapidly and continuously after ignition. Optionally, the energetic material is a composite energetic material or a mixed explosive. In one possible implementation, the compound is used in a solid propellant as an oxidant component of the propellant formulation.

[0040] In one embodiment, a bismuth-based fluoroxynitrate compound is mixed with a metallic fuel to obtain an energetic material. The bismuth-based fluoroxynitrate compound contains oxygen vacancies, and the oxygen vacancies, fluoride ions, and nitrate ions are arranged in an ordered manner within the crystal lattice to form a superlattice structure. Upon thermal decomposition, it generates highly reactive free radicals. The metallic fuel is at least one of aluminum, boron, titanium, or an aluminum-boron alloy. The metallic fuel provides a reducing component, reacting with the active species generated by the decomposition of the oxidant to release energy. During the mixing process, the mass ratio of the bismuth-based fluoroxynitrate compound to the metallic fuel is (0.5-3):1, meaning that each part by mass of metallic fuel corresponds to 0.5 to 3 parts by mass of the bismuth-based fluoroxynitrate compound. This ratio range ensures that the free radicals generated by the superlattice decomposition simultaneously cover the oxidation requirements of the metallic fuel and the inert layer removal requirements, keeping the supply of the two types of active species synchronized with the consumption of the metallic fuel. Optionally, the mass ratio is 1:1 or 2:1. The mixing process employs mechanical stirring or grinding to uniformly disperse the two powders, allowing the hexagonal oxidizer crystals to overlap with the metal fuel particles, thus forming a uniformly distributed composite system. Optionally, the metal fuel undergoes surface pretreatment with a 1%-10% (w / w) ammonium fluoride aqueous solution or hydrofluoric acid solution before use, converting the inert oxide layer on the surface of the metal fuel into a fluoride layer. In one possible implementation, the aforementioned energetic material is filled into the shell of a pyrotechnic agent, releasing energy upon ignition.

[0041] In one embodiment, the bismuth-based fluoride nitrate compound is mixed with a metallic fuel, and at least one functional additive selected from ammonium perchlorate, ammonium nitrate, ammonium dinitramide, or potassium nitrate is added to the energetic material. The functional additive is used to regulate the combustion process and energy release rhythm of the energetic material. Ammonium perchlorate, ammonium nitrate, ammonium dinitramide, and potassium nitrate are all oxyacid salts that provide additional oxidizing power, and their addition amount is selected according to a certain proportion of the total mass of the energetic material. The bismuth-based fluoride nitrate compound contains oxygen vacancies. Oxygen vacancies, fluoride ions, and nitrate ions are arranged in an ordered manner within the crystal lattice to form a superlattice structure. Its mass ratio with the metallic fuel is (0.5-3):1. The metallic fuel is at least one selected from aluminum, boron, titanium, or an aluminum-boron alloy. The functional additive is uniformly dispersed together with the oxidant and metallic fuel during the mixing process. At the start of combustion, the superlattice structure decomposes to generate highly reactive free radicals, F... - Free radicals first remove the inert oxide layer on the surface of the metallic fuel, opening a pathway for subsequent reactions. 2- The free radicals then undergo an oxidation reaction with the exposed metallic fuel, while the functional additive replenishes the oxidizing components in the subsequent stage, maintaining the concentration of active species in the later stages of the reaction. This forms a segmented, relay-style energy release process of activation, oxidation, and then afterburning. Optionally, the functional additive may be ammonium perchlorate or potassium nitrate. In one possible implementation, the aforementioned energetic material is used in solid propellant loading, and the functional additive is used to adjust the combustion stability of the propellant.

[0042] The following is a description of a specific embodiment.

[0043] I. Experimental Group and Control Group

[0044] Experimental group 1, the product is Bi6F4O7·HNO3. In preparation, 0.10 g of potassium fluoride powder and 0.05 g of citric acid were dissolved in a mixture of ethanol, propanol, and water. 2.00 g of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) was dissolved in a solution of ethanol and propanol (the molar ratio of fluoride source to bismuth salt was approximately 0.42:1). The potassium fluoride solution was slowly poured into the bismuth nitrate solution and stirred until homogeneous. Then, ammonia water diluted 1:7 was added dropwise to the mixture to adjust the pH to 8.00. After the addition was complete, stirring was continued for 10 min. The mixture was ultrasonically treated for 20 min, and a small amount of hexagonal plate-like Bi6F4O7·HNO3 seed crystals were added. The mixture was then poured into a 200 mL polytetrafluoroethylene-lined reactor and sealed. The reactor was hydrothermally reacted at 160℃ for 6-9 h. After the reaction, the mixture was allowed to cool naturally, and the solid particles were collected by filtration. The particles were dried in an oven at 50-60℃ for 3-6 h, and then activated at 150℃ in an argon-hydrogen mixed atmosphere. h, Bi6F4O7·HNO3 was obtained, and X-ray diffraction characterization confirmed that it has a superlattice structure formed by the orderly arrangement of oxygen vacancies, fluoride ions and nitrate ions. 1.0 g of aluminum powder was soaked in a 5% ammonium fluoride aqueous solution for 2 h, filtered and dried, and then mixed evenly with 3.0 g of the obtained oxidant to form a composite energetic material.

[0045] Experimental group 2, the product was Bi5F6O5·HNO3. In preparation, 0.30 g of sodium fluoride powder and 0.05 g of citric acid were dissolved in a mixture of ethanol, propanol, and water. 1.20 g of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) was dissolved in a solution of ethanol and propanol (the molar ratio of fluoride source to bismuth salt was approximately 2.9:1). The sodium fluoride solution was slowly poured into the bismuth nitrate solution and stirred until homogeneous. Then, ammonia water diluted 1:3 was added dropwise to the mixture to adjust the pH to 9.00. After the addition was complete, stirring was continued for 10 min. The mixture was ultrasonically treated for 20 min, and a small amount of hexagonal plate-like Bi5F6O5·HNO3 seed crystals were added. The mixture was then poured into a 200 mL polytetrafluoroethylene-lined reactor and sealed. The reactor was hydrothermally reacted at 130℃ for 8-10 h. After the reaction, the mixture was allowed to cool naturally, and the solid particles were collected by filtration. The particles were dried in an oven at 50-60℃ for 3-6 h, and then activated at 150℃ in an argon-hydrogen mixed atmosphere. The process yielded Bi5F6O5·HNO3, which was confirmed by X-ray diffraction to possess a superlattice structure formed by the orderly arrangement of oxygen vacancies, fluoride ions, and nitrate ions. 3.0 g of aluminum powder was immersed in a 5% (w / w) ammonium fluoride aqueous solution for 2 h, filtered, dried, and then mixed uniformly with 2.0 g of the obtained oxidant to form a composite energetic material.

[0046] Experimental group 3 produced Bi6F3O6·HNO3. During preparation, 0.30 g of potassium fluoride powder and 0.05 g of citric acid were dissolved in a mixture of ethylene glycol and water. 2.30 g of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) was dissolved in an ethylene glycol solution (the molar ratio of fluorine source to bismuth salt was approximately 1.1:1). The potassium fluoride solution was slowly poured into the bismuth nitrate solution and stirred until homogeneous. Then, ammonia water diluted 1:6 was added dropwise to the mixture, adjusting the pH to 9. After the addition was complete, stirring was continued for 10 min. The mixture was ultrasonically treated for 20 min, and a small amount of hexagonal plate-like Bi6F3O6·HNO3 seed crystals were added. The mixture was then poured into a 100 mL polytetrafluoroethylene-lined reactor and sealed. The reaction was carried out hydrothermally at 130℃ for 10-12 h. After the reaction, the mixture was allowed to cool naturally, and the solid particles were collected by filtration and dried in an oven at 50-60℃ for 3-6 hours. The material was then activated at 150°C for 1 hour in an argon-hydrogen mixed atmosphere to obtain Bi6F3O6·HNO3. X-ray diffraction characterization confirmed that it possessed a superlattice structure formed by the orderly arrangement of oxygen vacancies, fluoride ions, and nitrate ions. 2.0 g of boron powder was soaked in a 5% (w / w) ammonium fluoride aqueous solution for 2 hours, filtered, dried, and then mixed uniformly with 1.0 g of the obtained oxidant to form an energetic material.

[0047] Experimental group 4, the product is Bi6F4O7·HNO3·HClO4. In preparation, 1.0 g of sodium fluoride powder, 0.2 g of ammonium perchlorate, and 0.08 g of citric acid were dissolved in a mixture of ethylene glycol and water. 5.80 g of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) was dissolved in an ethylene glycol solution (the molar ratio of fluoride source to bismuth salt was approximately 2.0:1). The sodium fluoride solution was slowly poured into the bismuth nitrate solution and stirred until homogeneous. Then, ammonia water diluted 1:7 was added dropwise to the mixture to adjust the pH to 9.00. After the addition was complete, stirring was continued for 10 min. The mixture was ultrasonically treated for 20 min, and a small amount of hexagonal plate-like Bi6F4O7·HNO3·HClO4 seed crystals were added. The mixture was then poured into a 100 mL polytetrafluoroethylene-lined reactor and sealed. The mixture was hydrothermally reacted at 150℃ for 9-10 h. After the reaction, the mixture was allowed to cool naturally, and the solid particles were collected by filtration and dried in an oven at 50-60℃ for 3-6 hours. After activation treatment at 150℃ for 1 h in an argon-hydrogen mixed atmosphere, Bi6F4O7·HNO3·HClO4 was obtained. X-ray diffraction characterization confirmed that it possessed a superlattice structure with co-intercalation of oxygen vacancies, fluoride ions, nitrate ions, and perchlorate ions. 1.2 g of boron powder was soaked in a 5% ammonium fluoride aqueous solution for 2 h, filtered and dried, and then mixed uniformly with 2.0 g of the obtained oxidant to form a composite energetic material. This experimental group simultaneously intercalated nitrate ions and perchlorate ions in a bismuth-based fluoride-oxygen superlattice framework. The nitrate component contributed to the nitrogen-containing gaseous products, while the perchlorate ions further supplemented the oxygen-containing components, demonstrating the superlattice structure's ability to support various types of oxyacid ions.

[0048] Control group 1: Existing BiOF technology, prepared according to the literature method, see Li J, Liu X, et al. Chemical Engineering Journal, 2023, 468: 143591, formed an n-Al / BiOF system with aluminum powder, with an Al content of 10% per unit mass.

[0049] Control group 2: Bismuth oxynitrate (BiONO3) was prepared according to the literature method and formed an n-Al / BiONO3 system with aluminum powder, with an Al content of 10% per unit mass.

[0050] Control group 3: BiOF and potassium nitrate were mechanically mixed at a mass ratio of 1:1 to obtain a BiOF / KNO3 mixture in which the fluorine and nitrate components were not ordered in the crystal lattice. This mixture was then combined with aluminum powder to form an n-Al / BiOF / KNO3 system with an Al content of 10% per unit mass.

[0051] Both the experimental group and the control group were tested using laser ignition to measure the flame propagation speed and calorific value of the combustion reaction. The test conditions were the same, and the data obtained were comparable.

[0052] II. Comparative Explanation

[0053] Figure 1 The images show the scanning electron microscope (SEM) morphology of the Bi6F4O7·HNO3 sample from the experimental group. The figures show that the product from the experimental group consists of regular hexagonal plate-like crystals. At high magnification, the hexagonal plate morphology is clearly visible, while at low magnification, the crystals are uniformly dispersed with regular morphology and good dispersibility. BiOF crystals are described in the literature as having a "nanoflower" microsphere morphology. This morphological difference leads to different interfacial contact mechanisms. During mixing, the hexagonal plate-like crystals overlap with the metal fuel particles through surface contact, resulting in a larger and more thorough contact area. In contrast, the microsphere particles primarily interact with the fuel through point contact. Therefore, the plate-like morphology of the experimental group is beneficial for improving the heat and mass transfer conditions between the oxidant and the metal fuel.

[0054] Figure 2 The thermal analysis curves of the experimental group Bi6F4O7·HNO3 are shown. The DSC curves reveal a significant exothermic peak in the approximately 500-900℃ range, with an integrated exothermic value of -325 J / g, indicating a high energy release capacity. The TG curves show that the experimental group exhibits staged weight loss, with values ​​of -0.85%, -1.64%, and -2.48% respectively, with the main weight loss occurring after 700℃. This staged weight loss corresponds to the sequential release of fluoride ions, nitrate ions, and other components from the superlattice structure. The decomposition of nitrate ions contributes to the nitrogen-containing gaseous products, a weight loss pattern consistent with the stepwise decomposition mechanism of the superlattice structure. Control group 1 (BiOF) is an oxyfluorine binary compound, with decomposition products mainly consisting of bismuth-containing fluoride oxides and fluorine radicals, lacking the nitrogen-containing decomposition stage corresponding to nitrate ions, and exhibiting a relatively simple decomposition pathway. The stepwise decomposition characteristics of the experimental group result in a sequential release of its active species, which is beneficial for the sequential connection of reactions with metallic fuels.

[0055] Figure 3 High-speed photography and pressure-boost rate curves of the combustion reaction between Bi6F4O7·HNO3 and aluminum powder in the experimental group are shown. The high-speed photography reveals a strong flame propagation and rapid reaction after laser ignition. Pressure testing shows that the peak pressure of the experimental composite system reaches 160.5 kPa, and the boost rate reaches 7804.2 kPa / s, indicating a vigorous combustion reaction and concentrated energy output. A more direct comparison is made in fuel carrying capacity. The mixture of Bi6F4O7·HNO3 and aluminum powder in the experimental group has an Al content of 20.55% per unit mass, while the mixture of control group 1 (BiOF) and aluminum powder has an Al content of only 10% per unit mass. That is, under the same oxidant mass, the experimental group can carry approximately twice the amount of metallic fuel as the control group, indicating that the effective oxygen and fluorine components of the oxidant in the experimental group are utilized more efficiently, and the overall energy density of the composite system is significantly higher than that of the control group.

[0056] Figure 4 These are atomic snapshots of the decomposition processes of BiOF and Bi6F4O7·HNO3 crystals obtained from molecular dynamics simulations. In the control group (BiOF), the decomposition process from 0 to 10 ps resulted in intermediate products such as BiF2O, Bi2O, and F radicals, indicating a relatively simple decomposition pathway. In the experimental group (Bi6F4O7·HNO3), a rich variety of intermediate products appeared sequentially within the same timescale, including Bi-O, F, O / O2 / O3 / HO, O / NO / NO2, O2, and HO, ultimately producing BiFO and HF. The comparison shows that the experimental group exhibited significantly more decomposition intermediate products, a lower decomposition energy barrier, and a more diverse decomposition pathway than the control group. Notably, reactive oxygen species such as O2 / O3 / HO and nitrogen-containing gaseous products such as NO / NO2 were not present in the control group (BiOF). These species contribute to oxidation and gas production, respectively, supporting the higher reactivity and energy release capacity of the experimental group at the microscopic level.

[0057] To eliminate the contribution of nitrate or fluorine components when they are present alone, control group 2 (BiONO3) and control group 3 (a mechanical mixture of BiOF and potassium nitrate) were further set up for comparative testing.

[0058] Control group 2 contains only nitrate and no fluorine, thus it cannot provide F- radicals to remove the inert oxide layer on the surface of the metal fuel and lacks activation effect on the metal fuel. In control group 3, the fluorine and nitrate components are spatially separated, there is no ordered arrangement in the crystal lattice, and there are no oxygen vacancy active trigger sites. During decomposition, the two types of active species lack a sequential release order and are prone to premature encounter and consumption. The comparative test results are as follows: Decomposition onset temperature: experimental group approximately 500℃, control group 2 approximately 380℃, control group 3 approximately 460℃; DSC heat release: experimental group approximately -325 J / g, control group 2 approximately -260 J / g, control group 3 approximately -290 J / g; Pressure rise rate: experimental group 7804.2 kPa / s, control group 2 approximately 1250 kPa / s, control group 3 approximately 3200 kPa / s; Al content per unit mass: experimental group 20.55%, control groups 2 and 3 both 10%. The above comparison shows that the performance advantage of the experimental group comes from the overall synergistic effect of the orderly arrangement of oxygen vacancies, fluoride ions, and nitrate ions in the crystal lattice to form a superlattice, rather than the simple superposition of nitrate or fluoride components.

[0059] III. Conclusion

[0060] The structural differences between experimental groups 1-3 (Bi6F4O7·HNO3, Bi5F6O5·HNO3, Bi6F3O6·HNO3) and control group 1 (BiOF) are reflected in four aspects: composition, arrangement, vacancies, and morphology. Chemically, the experimental groups consist of bismuth, oxygen, fluorine, and nitrate, while control group 1 consists only of bismuth, oxygen, and fluorine. The additional nitrate component in the experimental groups can contribute nitrogen-containing gaseous products during decomposition. In terms of lattice arrangement, oxygen vacancies, fluorine ions, and nitrate ions in the experimental groups are arranged alternately and orderly along the crystal axis to form a superlattice structure. In control group 1, fluorine and oxygen are combined in a simple ratio, and there is no ordered multi-component arrangement within the lattice. Regarding vacancy design, the experimental group lattice contains oxygen vacancies, which penetrate the lattice and act as active triggering sites. This type of vacancy is absent in the control group lattice. In terms of crystal morphology, the experimental groups are hexagonal plate-like crystals that overlap with the metal fuel through surface contact, while control group 1 consists of nanoflower microspheres that primarily contact the fuel through point contact.

[0061] Regarding thermal decomposition data, the experimental group exhibited a DSC exothermic response of -325 J / g, with weight loss occurring in three stages: -0.85%, -1.64%, and -2.48%, corresponding to the stepwise decomposition of the superlattice structure. Control group 1, being an oxyfluorine binary composition, did not include the nitrogen-containing decomposition stage corresponding to nitrate, indicating a single decomposition process. In terms of combustion pressure data, the experimental group achieved a peak pressure of 160.5 kPa and a pressure rise rate of 7804.2 kPa / s. While the literature did not provide pressure data for control group 1 under the same conditions, its fuel loading capacity was significantly lower than that of the experimental group. Regarding fuel loading data, under the same oxidant mass, the experimental group could support a unit mass Al content of 20.55%, while control group 1 could only support 10%, a difference of more than double. In terms of decomposition pathway data, the intermediate products of the experimental group include multiple species such as Bi-O, F, O / O2 / O3 / HO, O / NO / NO2, O2, and HO, while the control group 1 only includes three species: BiF2O, Bi2O, and F. The additional active oxygen species and nitrogen-containing gaseous products in the experimental group all come from its nitrate component and superlattice structure.

[0062] The experimental group, containing nitrate components, produces nitrogen-containing gaseous products such as NO and NO2 during decomposition, thus enhancing its gas production capacity, corresponding to the staged weight loss in thermal analysis and pressure output during combustion. The presence of oxygen vacancies and their superlattice-ordered arrangement in the experimental group lowers the decomposition energy barrier, resulting in richer intermediate products and more complete release of active species. Furthermore, the hexagonal plate-like morphology of the experimental group, in contact with the metallic fuel surface, improves interfacial heat and mass transfer conditions. These structural differences ultimately manifest in fuel carrying capacity data, with the Al content per unit mass increasing from 10% in control group 1 to 20.55% in the experimental group. Under the same oxidant mass, the amount of metallic fuel that can be carried nearly doubles, leading to a corresponding increase in the energy density of the composite system. As can be seen from the above comparison, the bismuth-based fluoride oxynitrate compound of this invention differs fundamentally from BiOF, BiONO3, and BiOF / nitrate mechanical mixtures in four aspects: chemical composition, lattice arrangement, oxygen vacancy design, and crystal morphology. Consequently, it exhibits significantly superior performance compared to control groups 1, 2, and 3 in terms of decomposition pathway, gas production capacity, fuel carrying capacity, and energy density. Furthermore, compared with control group 2 (BiONO3) and control group 3 (BiOF / nitrate mechanical mixture), the experimental group also showed significant advantages in fuel carrying capacity and combustion performance, indicating that the overall synergistic effect of the superlattice structure, rather than the simple superposition of components, is the key to achieving performance improvement.

[0063] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A bismuth-based fluorooxynitrate compound, characterized in that, The general structural formula of bismuth-based fluoride nitrate compounds is Bi. a O x F y ·HNO3·(HClO4) z Where a is 5-6, x is 5-7, y is 3-6, and z is 0 or 1; the bismuth-based fluoride nitrate compound contains oxygen vacancies, which are vacancies formed by the absence of some oxygen atom sites in the crystal lattice; oxygen vacancies, fluoride ions, and nitrate ions are arranged in an orderly manner along the crystal axis in the crystal lattice to form a superlattice structure; when z is 1, perchlorate ions and nitrate ions are embedded together in the superlattice structure.

2. The bismuth-based fluorooxynitrate compound as described in claim 1, characterized in that, The bismuth-based fluoride nitrate compound is at least one of Bi6F4O7·HNO3, Bi5F6O5·HNO3, Bi6F3O6·HNO3, or Bi6F4O7·HNO3·HClO4.

3. The bismuth-based fluorooxynitrate compound according to any one of claims 1-2, characterized in that, The superlattice structure is formed by the orderly arrangement of vacant oxygen, fluoride ions and nitrate ions in a periodic alternation at equal intervals along the crystal axis; the crystal axis is either the c-axis or the a-axis; the bismuth-based fluoride nitrate compound is a hexagonal plate-like crystal.

4. A method for preparing the bismuth-based fluorooxynitrate compound according to any one of claims 1-3, characterized in that, Includes the following steps: S1: Dissolve the bismuth salt and fluorine source separately in a mixed solvent of alcohol and water. The solvent also contains a structure directing agent, which is citric acid or polyvinylpyrrolidone. This yields a bismuth salt solution and a fluorine source solution. The molar ratio of fluorine source to bismuth salt is (0.4-3):

1. The fluorine source solution is slowly added to the bismuth salt solution and stirred until homogeneous to obtain a mixed solution. S2: Slowly add ammonia water dropwise to the mixture, continuously monitor the pH value during the dropwise addition, adjust the pH value of the mixture to 8-10, and continue stirring for 5-30 minutes after the dropwise addition is completed; S3: After adjusting the pH value, sonicate the mixture for 10-30 min, add hexagonal plate-shaped seed crystals of bismuth-based fluoride nitrate compound, then transfer it to a hydrothermal reactor with a polytetrafluoroethylene liner, seal it, control the filling degree of the reactor to 60%-80%, and hydrothermally react at 120-160 ℃ for 6-14 h. After the reaction is completed, allow it to cool naturally to room temperature. S4: Collect the solid product by vacuum filtration, wash with deionized water or ethanol, and dry to obtain crude bismuth-based fluoride nitrate compound. S5: Activate the crude product at 100-250 °C for 0.5-3 h in an argon-hydrogen or nitrogen-hydrogen mixed atmosphere; S6: X-ray diffraction characterization of the activated product confirmed the characteristic diffraction peaks of the ordered arrangement of oxygen vacancies, fluoride ions and nitrate ions to form a superlattice structure, thus obtaining the bismuth-based fluoride oxynitrate compound.

5. The preparation method according to claim 4, characterized in that, The bismuth salt is at least one of bismuth nitrate, bismuth nitrate pentahydrate, or bismuth chloride; the fluorine source is at least one of potassium fluoride, sodium fluoride, or ammonium fluoride; the molar ratio of the fluorine source to the bismuth salt is (0.4-3):1; the solvent is a mixture of ethanol, propanol, and water, or a mixture of ethylene glycol and water.

6. The preparation method according to claim 4, characterized in that, The alkaline solution is commercially available analytical grade ammonia diluted with water at a volume ratio of 1:(3-8).

7. The preparation method according to claim 4, characterized in that, Dry at 50-60 ℃.

8. The use of the bismuth-based fluoroxynitrate compound according to any one of claims 1-3 in energetic materials, characterized in that, Energetic materials include metallic fuels, bismuth-based fluoride nitrate compounds mixed with metallic fuels, and are either composite energetic materials or mixed explosives.

9. The application as described in claim 8, characterized in that, A bismuth-based fluoroxynitrate compound is mixed with a metallic fuel to obtain an energetic material; the mass ratio of the bismuth-based fluoroxynitrate compound to the metallic fuel is (0.5-3):1, and the metallic fuel is at least one of aluminum, boron, titanium, or an aluminum-boron alloy; the bismuth-based fluoroxynitrate compound is a hexagonal plate-shaped crystal that overlaps with the metallic fuel particles in a surface contact manner; when the metallic fuel is aluminum, the aluminum content per unit mass in the energetic material is not less than 20%; the metallic fuel is pretreated with ammonium fluoride solution or hydrofluoric acid solution before use.

10. The application as described in claim 9, characterized in that, Energetic materials also contain at least one functional additive selected from ammonium perchlorate, ammonium nitrate, ammonium dinitrate, or potassium nitrate. Energetic materials are used in solid propellant loading.

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