In-situ fluorination activity protection process and application of aluminum-lithium alloy fuel

Abstract

The invention belongs to the field of metal fuels, and discloses an in-situ fluorination activity protection process and application of an aluminum-lithium alloy fuel, a fluorination method comprises the following steps: putting aluminum-lithium alloy fuel particles to be fluorinated into a fluidized bed filled with a protective gas, and forming a fluidized state; and then mixed gas of protective gas and fluorine gas is introduced into the fluidized bed, fluoridation reaction is carried out on the aluminum-lithium alloy fuel particles based on a fluidized bed-chemical vapor deposition process, and the aluminum-lithium fluoride alloy fuel particles with fluoride protective layers on the surfaces can be obtained. A fluidized bed-chemical vapor deposition process is used for carrying out fluorination reaction on aluminum-lithium alloy fuel particles, so that the metal fuel with a fluorinated protective layer, good compatibility and good oxidation resistance is obtained; the problems that aluminum-lithium alloy powder in existing alloy fuel is difficult to be compatible with other components in a solid propellant, easy to oxidize and difficult to store for a long time are solved.

Description

Technical Field

[0001] The present invention belongs to the field of metal fuels, and more specifically, relates to an in-situ fluorination active protection process and application of an aluminum-lithium alloy fuel. Background Art

[0002] As the core part of a missile weapon engine, the performance of a solid propellant has a significant impact on the combat effectiveness of the missile. And the main energy source of the solid propellant is the metal fuel. Therefore, to improve the energy density of the solid propellant, it is necessary to improve the performance of the metal fuel.

[0003] Elemental aluminum powder is widely used as a metal fuel in the fields of solid propellants and explosives due to its high energy density and low price. However, there are still some defects in its combustion process: the dense aluminum oxide film on the surface of the aluminum powder leads to a long combustion time and a slow combustion rate. In addition, the aluminum powder is prone to caking during combustion, resulting in incomplete combustion and insufficient energy release. To overcome this problem, in the prior art, elemental lithium has been added as an additive to the elemental aluminum fuel to form an Al-Li metal fuel.

[0004] The theoretical mass combustion enthalpy (H t = 43100 J·g -1 ) of elemental lithium is 1.39 times that of aluminum. Adding lithium as an additive to the elemental aluminum fuel can effectively improve its energy performance. However, due to the low melting point of lithium, the aluminum-lithium intermetallic compound phase exists on the particle surface during the solidification process. In addition, due to the high activity of lithium and its extremely easy oxidation, the aluminum-lithium alloy powder presents problems such as being difficult to be compatible with other components (such as crosslinking agents, etc.) in the solid propellant, being prone to oxidation, and being difficult to store for a long time.

[0005] Therefore, if a suitable protective layer can be found to protect the aluminum-lithium alloy powder, improving the compatibility and antioxidant performance of the metal fuel will undoubtedly greatly promote the application of the Al-Li metal fuel. Summary of the Invention

[0006] Aiming at the above defects or improvement requirements of the prior art, the purpose of the present invention is to provide an in-situ fluorination active protection process and application of an aluminum-lithium alloy fuel. The fluidized bed-chemical vapor deposition process is used to carry out a fluorination reaction on the aluminum-lithium alloy fuel particles to obtain a metal fuel with a fluorinated protective layer, good compatibility, and good antioxidant characteristics, solving the problems that the aluminum-lithium alloy powder in the existing alloy fuel is difficult to be compatible with other components (such as crosslinking agents, etc.) in the solid propellant, is prone to oxidation, and is difficult to store for a long time. The obtained fluorinated aluminum-lithium alloy fuel particles can be especially used in the fields of aerospace and military industry for combustion energy release, such as being used as a rocket propellant, etc.

[0007] To achieve the above object, according to one aspect of the present invention, there is provided a method for fluorinating an aluminum-lithium alloy fuel, characterized in that the aluminum-lithium alloy fuel particles to be fluorinated are placed into a fluidized bed filled with a protective gas to form a fluidized state; then, under the condition that the particles maintain the fluidized state, a mixed gas of the protective gas and fluorine gas is introduced into the fluidized bed, and a fluorination reaction is carried out on the aluminum-lithium alloy fuel particles based on the fluidized bed-chemical vapor deposition process, and thus fluorinated aluminum-lithium alloy fuel particles with a fluoride protective layer on the surface can be obtained.

[0008] As a further preference of the present invention, at the start of the fluorination reaction, the temperature in the fluidized bed is 20°C - 50°C, and the air pressure is 0.1 MPa - 0.2 MPa;

[0009] Preferably, at the start of the fluorination reaction, the temperature in the fluidized bed is room temperature, and the air pressure is normal pressure.

[0010] As a further preference of the present invention, the volume concentration of fluorine gas in the mixed gas is 1% - 50%;

[0011] The reaction duration of the fluorination reaction is 0.1 - 30 hours.

[0012] As a further preference of the present invention, the gas flow rate in the fluidized bed is 5 L / min - 25 L / min.

[0013] As a further preference of the present invention, in the aluminum-lithium alloy fuel particles to be fluorinated, the mass of lithium accounts for 0.5% - 20% of the total mass of the alloy fuel, preferably 0.5% - 10% of the total mass of the alloy fuel.

[0014] As a further preference of the present invention, the aluminum-lithium alloy fuel particles to be fluorinated are spherical granular powders; the aluminum-lithium alloy fuel particles to be fluorinated are prepared by melting aluminum and lithium into an alloy base material by vacuum arc melting, and then the alloy base material is prepared into spherical granular powders;

[0015] Preferably, the preparation of the alloy base material into spherical granular powders is specifically: melting the alloy base material by tight-coupling gas atomization powder making method and then atomizing and condensing to prepare spherical granular powders;

[0016] More preferably, the average particle size D of the aluminum-lithium alloy fuel particles to be fluorinated 50 does not exceed 50 μm.

[0017] As a further preference of the present invention, the fluoride protective layer is LiF.

[0018] According to another aspect of the present invention, the present invention provides fluorinated aluminum-lithium alloy fuel particles prepared by the above fluorination method.

[0019] As a further preference of the present invention, the mass combustion enthalpy is not less than 28 kJ / g.

[0020] In another aspect of the present invention, the present invention provides the application of the above lithium aluminum fluoride alloy fuel particles, characterized in that it is used as a solid propellant.

[0021] Through the above technical solutions conceived by the present invention, compared with the prior art, the present invention uses fluorine as a surface modifier for the aluminum lithium alloy fuel, and performs surface treatment on the surface of the aluminum lithium alloy particles through a fluidized bed-chemical vapor deposition process to introduce a fluoride protective layer, and can obtain a metal fuel with good antioxidant properties and excellent energy performance. The surface modifier fluorine element can effectively protect the additive lithium element, reduce the content of active lithium elements on the surface of the metal fuel powder, prevent the active lithium elements from contacting other components in the propellant, greatly improve its compatibility, prevent the active lithium elements from contacting air, reduce its oxidation rate, and improve the storage stability of the metal fuel, solving the problems of low combustion efficiency, insufficient energy release, difficulty in compatibility with other components in the propellant, and difficulty in long-term storage of existing fuels.

[0022] The method of the present invention uses a fluidized bed-chemical vapor deposition process for fluorination treatment, which can realize the large-scale preparation of fluorinated alloy fuel powder. This method can be carried out especially at normal temperature and normal pressure (that is, no additional heating and pressurization are required to meet the reaction conditions), which is beneficial to reducing costs and improving efficiency. The method of the present invention can preferably control the gas flow rate in the fluidized bed to be 5 L / min - 25 L / min, and the powder dispersion degree is good.

[0023] In the metal fuel obtained by the present invention, the fluorine element and the lithium element form a fluoride protective layer, which can effectively protect the active lithium element inside the alloy powder particles, and improve the compatibility, antioxidant property and storage stability of the metal fuel. The fluorinated lithium aluminum alloy fuel obtained by the method of the present invention, in terms of elemental composition, includes aluminum, lithium and fluorine (including single-phase Al, AlLi intermetallic compound phase and LiF phase). Among them, aluminum is used as the matrix, the mass of lithium accounts for 0.5% - 20% of the total mass of the entire metal fuel, fluorine combines with the lithium on the particle surface, and is coated on the surface of the alloy fuel powder particles in the form of a LiF protective layer, and the inside of the particles is still the combination of lithium and aluminum (lithium exists in the single-phase Al matrix in the form of AlLi intermetallic compound, that is to say, the fluorination process of the present invention will not affect the inside of the aluminum lithium alloy fuel particles).

[0024] It is known in the prior art that aluminum-lithium alloy fuel uses aluminum as a matrix, and lithium is combined with aluminum to exist in the form of AlLi intermetallic compounds in a single Al matrix. The addition of lithium elements can improve the overall energy level of the metal fuel (the additive lithium has the characteristic of high energy content, and the theoretical mass combustion enthalpy of single lithium is as high as 43100 J / g, which is much higher than other metals, and can greatly improve the energy level of the metal fuel); at the same time, there are mature methods for preparing aluminum-lithium alloy fuel particles. For example, vacuum arc melting combined with tightly coupled gas atomization powder making technology can obtain regular spherical granular powder. In the tightly coupled gas atomization powder making method, the moving atomizing gas is used to impact the molten metal or alloy liquid to form fine droplets, and the fine droplets are condensed to form solid powder to maintain the sphericity (especially the average particle size D 50 When the particle size does not exceed 50 μm, such a particle size has the advantage of a high specific surface area to ensure the contact area between the metal fuel powder particles and the oxidant, thereby achieving full combustion and improving energy release efficiency).

[0025] The aluminum-lithium fluoride alloy fuel obtained by the method of the present invention not only inherits the above-mentioned characteristics known in conventional aluminum-lithium alloy fuels, but also overcomes the defects of conventional aluminum-lithium alloy fuels that the aluminum has a low melting point and is easily oxidized, and the aluminum-lithium metal compound phase exists on the particle surface during the solidification process, resulting in the aluminum-lithium alloy powder being easily oxidized and difficult to store for a long time. The present invention obtains a metal fuel with lithium cohesion and good antioxidant properties and excellent energy performance through fluorination treatment, which can effectively convert the active lithium on the surface of the particles into lithium fluoride that does not react with water, perform active protection, reduce the active lithium element content on the surface of the metal powder particles, and prevent the active lithium element from directly contacting other components in the propellant and air, thereby improving the compatibility and storage stability of the alloy fuel.

[0026] The fluorination process of the present invention can improve the compatibility of aluminum-lithium alloy fuel powder, protect the activity of aluminum-lithium alloy fuel powder particles, and improve storage stability. The present invention can preferably control the mass percentage of the additive lithium in the aluminum-lithium alloy particles to 0.5-10% of the total mass of the aluminum-lithium alloy metal fuel, and the volume concentration of fluorine gas in the mixed gas used for fluorination treatment is preferably controlled to 1%-50%, and the obtained aluminum-lithium fluoride alloy fuel has good antioxidant properties and excellent energy performance. As illustrated in the embodiments below, when the mass percentage of lithium is 5% of the total mass of the aluminum-lithium alloy metal fuel and the volume concentration of fluorine gas is 20%, the corresponding measured mass combustion enthalpy of the aluminum-lithium fluoride alloy fuel is not less than 28kJ / g, and can meet the requirements of large-scale powder production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 1 is a schematic diagram of the fluorination process flow of the fluorinated Al-5Li alloy fuel powder used in the embodiment of the present invention and a physical diagram of the equipment; wherein: Figure 1(a) in it corresponds to the schematic diagram of the fluorination process flow, Figure 1 (b) in it corresponds to the physical picture of the equipment.

[0028] Figure 2 It is the scanning electron microscope image of the samples of Al-5Li after fluorination for different times at different fluorine concentrations provided in Examples 4-6 of the present invention; among them, Figure 2 (a)-(e) in it correspond to the fluorinated samples obtained in Example 4; Figure 2 (f)-(j) in it correspond to the fluorinated samples obtained in Example 5; Figure 2 (k)-(o) in it correspond to the fluorinated samples obtained in Example 6.

[0029] Figure 3 It is the secondary ion mass spectrometry image of the Al-5Li metal fuel powder particles before and after fluorination provided in Example 3 of the present invention; among them, Figure 3 (a)-(f) in it correspond to the Al-5Li metal fuel powder particles before fluorination; Figure 3 (g)-(l) in it correspond to the A5F metal fuel powder particles obtained after fluorination of Al-5Li.

[0030] Figure 4 The physical picture and scanning electron microscope image of the compatibility test of the Al-5Li metal fuel powder before and after fluorination provided in Example 3 of the present invention with a blank epoxy resin inlay; among them, Figure 4 (a), (d), (g) in it correspond to the blank epoxy resin inlay; Figure 4 (b), (e), (h) in it correspond to the Al-5Li-epoxy resin inlay constructed by the Al-5Li metal fuel powder particles before fluorination; Figure 4 (c), (f), (i) in it correspond to the A5F-epoxy resin inlay constructed by the A5F metal fuel powder particles obtained after fluorination of Al-5Li.

[0031] Figure 5 It is the physical picture of the reaction of the Al-5Li and the fluorinated Al-5Li alloy fuel powder provided in Example 3 of the present invention with deionized water respectively; among them, Figure 5 (a), (b) in it correspond to the Al-5Li metal fuel powder particles before fluorination; Figure 5 (c), (d) in it correspond to the A5F metal fuel powder particles obtained after fluorination of Al-5Li.

[0032] Figure 6 It is the SEM image of the Al-5Li alloy fuel powder before and after fluorination provided in Example 3 of the present invention after being aged in air for different days; among them, Figure 6 (a)-(e) in it correspond to the Al-5Li metal fuel powder particles before fluorination; Figure 6(f)-(j) therein correspond to the A5F metal fuel powder particles obtained after the fluorination of Al-5Li.

[0033] Figure 7 It is a broken line graph of the measured mass combustion enthalpy of the Al-5Li alloy fuel powder before and after fluorination provided in Example 3 of the present invention after being aged in air for different days. Detailed implementation manners

[0034] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] The fluorination process adopted in the subsequent embodiments is to use a fluidized bed-chemical vapor deposition device, as Figure 1 shown in (b) therein; different from the traditional fluidized bed-chemical vapor deposition device, the device used in this embodiment has been improved as follows: ① Remove the stirring paddle to avoid jamming the stirring paddle with powder; ② Disconnect the middle of the fluidized bed body and install a flange to facilitate cleaning the inside of the bed body; ③ Install a discharge static tank to avoid the sample directly contacting the air.

[0036] As Figure 1 shown in (a) therein, the fluidization process is as follows: ① Introduce argon gas; ② Put the alloy fuel powder to be fluorinated into the feed tank; ③ Adjust the total gas flow rate (such as 15.6 L / min used in the subsequent embodiments), and first use argon gas to disperse the alloy fuel powder to be fluorinated (such as, Al-5Li alloy fuel powder particles) through the fluidized bed-vapor deposition method to make it in a fluidized state; ④ Adjust the temperature inside the fluidized bed (to be at room temperature 20°C or slightly higher than room temperature, such as 20°C - 50°C) and the air pressure (the air pressure can be either normal pressure, that is, 1 standard atmosphere 0.1 MPa, or slightly higher than normal pressure, such as 0.1 MPa - 0.2 MPa); ⑤ Under the condition of continuous introduction of argon gas, then introduce a certain concentration of fluorine gas into the fluidized bed to form a fluorine-argon mixed gas atmosphere inside the fluidized bed; The fluorine gas contacts the fluidized alloy fuel powder particles to be fluorinated, and the reaction generates a fluorinated layer to perform single-particle coating on the Al-Li alloy fuel powder particles; ⑥ After a certain time, stop introducing fluorine gas, keep introducing argon gas, and after there is no fluorine gas residue in the reaction chamber and return to normal temperature and pressure, take out the sample.

[0037] The Al-Li alloy particles used in the following examples were prepared with reference to the prior art. Specifically, vacuum arc melting was used to melt aluminum and lithium to prepare an alloy base material (with aluminum as the matrix, and the mass of lithium can account for 0.5% - 20% of the total mass of the alloy fuel, and the specific mass ratio can be adjusted according to actual needs), and then the close-coupled gas atomization powder preparation technology was used to melt and atomize the alloy base material and then condense it to prepare spherical particles. Among them, the vacuum arc melting method specifically refers to using arc heat to prepare a low-segregation and high-purity alloy base material in a vacuum environment. The close-coupled gas atomization powder preparation technology refers to using a rapidly moving atomizing gas to impact the molten metal or alloy liquid to form a mist-like fragmented fine droplet, and the small droplet forms a solid powder through the condensation process to meet the requirement of preparing an alloy powder with a relatively high sphericity.

[0038] Specifically, first, an appropriate amount of lithium particles (with a purity preferably of 99.99 wt.%, and a particle size preferably less than 1 mm) and aluminum ingots (with a purity preferably of 99.95 wt.%) were melted and prepared into a uniformly distributed Al-Li alloy base material by using an ultra-close-coupled vacuum suspension melting method, and then the close-coupled gas atomization powder preparation method was used to appropriately adjust parameters such as the spray gas pressure and heating temperature to prepare the alloy base material into Al-Li metal fuel powder with uniform composition and high sphericity. Specifically, when using the close-coupled gas atomization powder preparation method to prepare spherical powder, the spray gas pressure can be 5 MPa, and the heating temperature can be 1600 °C.

[0039] The prepared Al-Li alloy particles are similar to the common Al-Li alloy particle metal fuels in the prior art, and lithium exists in the form of AlLi intermetallic compounds.

[0040] The following are specific examples:

[0041] Example 1

[0042] The composition of the lithium hexafluoroaluminate alloy fuel prepared in this example includes aluminum and lithium. Among them, aluminum is used as the matrix, and the mass of lithium accounts for 0.5% - 10% of the total mass of the entire metal fuel, and the fluorine gas concentration in the fluorine-argon mixed gas is 1% - 50% (the fluorine gas concentration refers to the volume percentage, the same below). In this example, the mass of lithium accounts for 0.5% of the total mass of the entire metal fuel, the fluorine gas concentration is 1%, the fluorination time is 0.1 hour, the temperature is room temperature (20 °C), the pressure is normal pressure (0.1 MPa), and the gas flow rate is 5 L / min.

[0043] The preparation method of this example includes the following steps:

[0044] S1: Preparation of Al-Li alloy particles

[0045] Using an ultra-tight coupling vacuum suspension melting method, an appropriate amount of lithium grains (preferably with a purity of 99.99 wt.%, and a particle size preferably less than 1 mm) and aluminum ingots (preferably with a purity of 99.95 wt.%) are melted to prepare an Al-Li alloy base material with a uniform composition distribution.

[0046] Using the tight coupling gas atomization powder preparation method, appropriately adjust parameters such as the spray gas pressure and heating temperature, and prepare the alloy base material into Al-Li metal fuel powder with a uniform composition and high sphericity. Specifically, when preparing spherical powder by the tight coupling gas atomization powder preparation method, the spray gas pressure is 8 MPa, the heating temperature is 1600 °C, and it is cooled with the furnace to obtain Al-Li metal fuel powder with a relatively high sphericity, whose particle size is 22 - 48 μm, and the average particle size D 50 is 31 μm. It does not exceed 50 μm.

[0047] S2: Feed the prepared Al-Li metal fuel powder into a storage tank protected by an inert atmosphere, and feed it into a fluidized bed - chemical vapor deposition device from the top, and perform fluorination treatment according to the fluorination process of this embodiment.

[0048] For the product obtained after fluorination, in terms of the phase, the alloy fuel includes elemental Al phase and AlLi intermetallic compound phase. Lithium combines with aluminum and exists in the metal fuel in the form of AlLi intermetallic compound. Fluorine combines with lithium and performs single-particle coating on the AlLi alloy fuel in the form of LiF.

[0049] The product obtained in step S1 of this embodiment (before fluorination) is metal fuel powder Al-0.5Li (the code "Al-xLi" in the present invention, where x corresponds to the mass percentage of Li, and x% is the mass percentage of Li; Al-0.5Li represents an Al-Li alloy with a Li content of 0.5 wt%). The product obtained in step S2 (after fluorination) is metal fuel powder A0.5F (the code "AxF" in the present invention, where x corresponds to the mass percentage of Li, and x% is the mass percentage of Li; F represents after fluorination; A0.5F represents the fluorinated Al-0.5Li alloy fuel).

[0050] During the combustion process of the A0.5F metal fuel obtained after fluorination in this embodiment, the measured mass combustion enthalpy of the metal fuel is 28.9 kJ / g.

[0051] Example 2

[0052] In this embodiment, the composition of the lithium aluminum fluoride alloy fuel includes aluminum and lithium. Among them, aluminum is used as the matrix, and the mass of lithium accounts for 0.5% - 10% of the total mass of the entire metal fuel. The concentration of fluorine gas in the fluorine-argon mixed gas is 1% - 50%. In this embodiment, the mass of lithium accounts for 20% of the total mass of the entire metal fuel, the fluorine gas concentration is 50%, the fluorination duration is 30 hours, the temperature is 50°C, the pressure is 0.2 MPa, and the gas flow rate is 25 L / min.

[0053] The preparation method of this embodiment includes the following steps:

[0054] S1: Preparation of Al-Li alloy particles

[0055] Using the ultra-tight coupling vacuum suspension melting method, an appropriate amount of lithium grains (preferably with a purity of 99.99 wt.%, and a particle size preferably less than 1 mm) and aluminum ingots (preferably with a purity of 99.95 wt.%) are melted to prepare an Al-Li alloy base material with a uniform composition distribution.

[0056] Using the tight coupling gas atomization powder making method to appropriately adjust parameters such as the spray gas pressure and heating temperature, and prepare the alloy base material into Al-Li metal fuel powder with a uniform composition and high sphericity. Specifically, when using the tight coupling gas atomization powder making method to prepare spherical powder, the spray gas pressure is 8 MPa, the heating temperature is 1600°C, and it is cooled with the furnace to obtain Al-Li metal fuel powder with a relatively high sphericity, whose particle size is 22 - 48 μm, and the average particle size D 50 is 31 μm. It does not exceed 50 μm.

[0057] S2: Feed the prepared Al-Li metal fuel powder into a storage tank protected by an inert atmosphere, and feed it into a fluidized bed - chemical vapor deposition device from the top, and carry out fluorination treatment according to the fluorination process of this embodiment. After the fluorination is completed, stop the introduction of fluorine gas, keep the introduction of argon gas, and wait until there is no fluorine gas residue in the reaction chamber and it returns to normal temperature and pressure, then take out the sample.

[0058] For the product obtained after fluorination, in terms of phase, the alloy fuel includes elemental Al phase and AlLi intermetallic compound phase. Lithium combines with aluminum and exists in the metal fuel in the form of AlLi intermetallic compound. Fluorine combines with lithium and coats the AlLi alloy fuel in the form of LiF on a single particle basis.

[0059] During the combustion process of the A20F metal fuel obtained after fluorination in this embodiment, the measured mass combustion enthalpy of the metal fuel is 28.4 kJ / g.

[0060] Example 3

[0061] In this embodiment, the composition of the lithium aluminum fluoride alloy fuel includes aluminum and lithium. Among them, aluminum serves as the matrix, and the mass of lithium accounts for 0.5% - 10% of the total mass of the entire metal fuel. The concentration of fluorine gas in the fluorine-argon mixed gas is 1% - 50%. In this embodiment, the mass of lithium accounts for 5% of the total mass of the entire metal fuel, the fluorine gas concentration is 20%, the fluorination duration is 4 hours, the temperature is room temperature, the pressure is normal pressure, and the gas flow rate is 15.6 L / min.

[0062] The preparation method of this embodiment includes the following steps:

[0063] S1: Preparation of Al-Li alloy particles

[0064] The preparation method of this embodiment is as follows: Using the ultra-tight coupling vacuum suspension melting method, an appropriate amount of lithium particles (preferably with a purity of 99.99 wt.%, and a particle size preferably less than 1 mm) and aluminum ingots (preferably with a purity of 99.95 wt.%) are melted to prepare an Al-Li alloy base material with a uniform composition distribution.

[0065] Using the tight coupling gas atomization powder preparation method, appropriately adjust parameters such as the spray gas pressure and heating temperature to prepare the alloy base material into Al-Li metal fuel powder with a uniform composition and high sphericity. Specifically, when using the tight coupling gas atomization powder preparation method to prepare spherical powder, the spray gas pressure is 8 MPa, the heating temperature is 1600 °C, and it is cooled with the furnace to obtain Al-Li metal fuel powder with a relatively high sphericity, with a particle size of 22 - 48 μm and an average particle size D 50 is 31 μm. Not exceeding 50 μm.

[0066] S2: Feed the prepared Al-Li metal fuel powder into a storage tank protected by an inert atmosphere, and feed it into a fluidized bed-chemical vapor deposition device from the top, and perform fluorination treatment according to the fluorination process of this embodiment.

[0067] For the product obtained after fluorination, in terms of phase, the alloy fuel includes elemental Al phase and AlLi intermetallic compound phase. Lithium combines with aluminum and exists in the metal fuel in the form of AlLi intermetallic compound. Fluorine combines with lithium and coats the AlLi alloy fuel in the form of LiF on a single particle basis.

[0068] During the combustion process of the A5F metal fuel obtained after fluorination in this embodiment, the measured mass combustion enthalpy of the metal fuel is 29.3 kJ / g.

[0069] Example 4

[0070] In this embodiment, the composition of the lithium aluminum fluoride alloy fuel includes aluminum and lithium. Among them, aluminum is used as the matrix, and the mass of lithium accounts for 0.5% - 10% of the total mass of the entire metal fuel. The concentration of fluorine gas in the fluorine-argon mixed gas is 1% - 50%. This embodiment discusses the influence of different fluorination times on the metal fuel under the same fluorine gas concentration. In this embodiment, the mass of lithium accounts for 5% of the total mass of the entire metal fuel, the fluorine gas concentration is 10%, the fluorination durations are 2, 4, 6, 8, and 10 hours respectively, the temperature is room temperature, the pressure is normal pressure, and the gas flow rate is 15.6 L / min.

[0071] The preparation method of this embodiment includes the following steps:

[0072] S1: Preparation of Al-Li alloy particles

[0073] The preparation method of this embodiment is as follows: Using the ultra-tight coupling vacuum suspension melting method, appropriate lithium grains (preferably with a purity of 99.99 wt.%, and a particle size preferably less than 1 mm) and aluminum ingots (preferably with a purity of 99.95 wt.%) are melted to prepare an Al-Li alloy base material with a uniform composition distribution.

[0074] Using the tight coupling gas atomization powder preparation method, appropriately adjusting parameters such as the spray gas pressure and heating temperature, the alloy base material is prepared into Al-Li metal fuel powder with a uniform composition and high sphericity. Specifically, when using the tight coupling gas atomization powder preparation method to prepare spherical powder, the spray gas pressure is 8 MPa, the heating temperature is 1600 °C, and it is cooled with the furnace to obtain Al-Li metal fuel powder with a relatively high sphericity, with a particle size of 22 - 48 μm and an average particle size D 50 of 31 μm. Not exceeding 50 μm.

[0075] S2: The prepared Al-Li metal fuel powder is sent into a storage tank protected by an inert atmosphere and fed into a fluidized bed-chemical vapor deposition device from the top. According to the fluorination process settings of this embodiment, fluorination treatments are carried out respectively to obtain metal fuel particles after fluorination treatment with different fluorination times.

[0076] For the product A5F obtained after fluorination with different fluorination times, in terms of phase, it is as follows: The alloy fuel includes a single Al phase and an AlLi intermetallic compound phase. Lithium combines with aluminum and exists in the metal fuel in the form of an AlLi intermetallic compound. Fluorine combines with lithium and coats the AlLi alloy fuel in the form of LiF on a single particle basis.

[0077] For the metal fuel particles obtained after fluorination with different fluorination times in this embodiment, during the combustion process of the fuel, the measured mass combustion enthalpy of the metal fuel is between 28.2 kJ / g and 29.8 kJ / g, as shown in Table 1 below. Table 1: Measured mass combustion enthalpy of A5F metal fuel particles obtained by fluorinating Al-5Li at a fluorine gas concentration of 10% for different times in Example 4

[0078]

[0079] Example 5

[0080] The composition of the lithium aluminum fluoride alloy fuel prepared in this embodiment includes aluminum and lithium. Among them, aluminum is used as the matrix, and the mass of lithium accounts for 0.5% - 10% of the total mass of the entire metal fuel. The fluorine gas concentration in the fluorine-argon mixed gas is 1% - 50%. This embodiment discusses the influence of different fluorination times on the metal fuel under the same fluorine gas concentration. In this embodiment, the mass of lithium accounts for 5% of the total mass of the entire metal fuel, the fluorine gas concentration is 20%, the fluorination durations are 2, 4, 6, 8, and 10 hours respectively, the temperature is room temperature, the pressure is normal pressure, and the gas flow rate is 15.6 L / min.

[0081] The preparation method of this embodiment includes the following steps:

[0082] S1: Preparation of Al-Li alloy particles

[0083] Appropriately sized lithium grains (preferably with a purity of 99.99 wt.% and a particle size preferably less than 1 mm) and aluminum ingots (preferably with a purity of 99.95 wt.%) are melted by an ultra-tight coupling vacuum suspension melting method to prepare a homogeneous Al-Li alloy base material.

[0084] Using a tight coupling gas atomization powder making method, appropriately adjust parameters such as the spray gas pressure and heating temperature to prepare the alloy base material into Al-Li metal fuel powder with uniform composition and high sphericity. Specifically, when preparing spherical powder by the tight coupling gas atomization powder making method, the spray gas pressure is 8 MPa, the heating temperature is 1600 °C, and it is cooled with the furnace to obtain Al-Li metal fuel powder with a relatively high sphericity, whose particle size is 22 - 48 μm, and the average particle size D 50 is 31 μm. It does not exceed 50 μm.

[0085] S2: Feed the prepared Al-Li metal fuel powder into a storage tank protected by an inert atmosphere, and feed it into a fluidized bed - chemical vapor deposition device from the top. According to the fluorination process settings of this embodiment, perform fluorination treatment respectively to obtain metal fuel particles after fluorination treatment with different fluorination times.

[0086] The product A5F obtained after fluorination with different fluorination times is, in terms of phase, an alloy fuel including elemental Al phase and AlLi intermetallic compound phase. Lithium combines with aluminum and exists in the metal fuel in the form of AlLi intermetallic compound. Fluorine combines with lithium and coats the AlLi alloy fuel in the form of LiF on a single-particle basis.

[0087] For the metal fuel particles obtained after fluorination with different fluorination times in this example, during the combustion process of the fuel, the measured mass combustion enthalpy of the metal fuel is between 27.2 kJ / g and 29.5 kJ / g, as shown in Table 2 below. Table 2: Measured mass combustion enthalpy of A5F metal fuel particles obtained by fluorinating Al-5Li at a fluorine gas concentration of 20% for different times in Example 5

[0088]

[0089] Example 6

[0090] The composition of the lithium-aluminum fluoride alloy fuel prepared in this example includes aluminum and lithium. Among them, aluminum is used as the matrix, and the mass of lithium accounts for 0.5% - 10% of the total mass of the entire metal fuel. The fluorine gas concentration in the fluorine-argon mixed gas is 1% - 50%. This example discusses the influence of different fluorination times on the metal fuel under the same fluorine gas concentration. In this example, the mass of lithium accounts for 5% of the total mass of the entire metal fuel, the fluorine gas concentration is 30%, the fluorination durations are 2, 4, 6, 8, and 10 hours respectively, the temperature is room temperature, the pressure is normal pressure, and the gas flow rate is 15.6 L / min.

[0091] The preparation method of this example includes the following steps:

[0092] S1: Preparation of Al-Li alloy particles

[0093] The preparation method of this example is as follows: Appropriate lithium grains (preferably with a purity of 99.99 wt.% and a particle size preferably less than 1 mm) and aluminum ingots (preferably with a purity of 99.95 wt.%) are melted by the ultra-tight coupling vacuum suspension melting method to prepare a homogeneous Al-Li alloy base material.

[0094] Using the tight coupling gas atomization powder preparation method, appropriately adjust parameters such as spray gas pressure and heating temperature to prepare the alloy base material into Al-Li metal fuel powder with uniform composition and high sphericity. Specifically, when preparing spherical powder by the tight coupling gas atomization powder preparation method, the spray gas pressure is 8 MPa, the heating temperature is 1600 °C, and it is cooled with the furnace to obtain Al-Li metal fuel powder with a relatively high sphericity, with a particle size of 22 - 48 μm and an average particle size D 50 of 31 μm. Not exceeding 50 μm.

[0095] S2: Feed the prepared Al-Li metal fuel powder into a storage tank protected by an inert atmosphere, and then feed it into a fluidized bed-chemical vapor deposition device from the top. Set according to the fluorination process of this embodiment and perform fluorination treatment respectively to obtain metal fuel particles after fluorination treatment for different fluorination times.

[0096] For the product A5F obtained after fluorination for different fluorination times, in terms of phase, it is as follows: The alloy fuel includes elemental Al phase and AlLi intermetallic compound phase. Lithium combines with aluminum and exists in the metal fuel in the form of AlLi intermetallic compound. Fluorine combines with lithium and coats the AlLi alloy fuel in the form of LiF on a single particle basis.

[0097] For the metal fuel particles obtained after fluorination for different fluorination times in this embodiment, during the combustion process of the fuel, the measured mass combustion enthalpy of the metal fuel is between 24.2 kJ / g and 28.9 kJ / g, as shown in Table 3 below. Table 3: Measured mass combustion enthalpy of A5F metal fuel particles obtained by fluorinating Al-5Li for different times at a fluorine gas concentration of 30% in Example 6

[0098]

[0099] Microscopic morphology characterization:

[0100] Figure 2 are scanning electron microscope images of samples after fluorinating Al-5Li using different parameters (such as fluorine gas concentration, fluorination time, etc.) during the fluorination process provided in Examples 4-6 of the present invention. It can be seen from the figure that when the fluorination time is the same, as the fluorine gas concentration decreases, the particle size of the fluoride particles formed on the surface of the alloy fuel powder becomes finer, as shown in Figure 2 (a), (f), (k) in. When the fluorine gas concentration is 30%, the fluorides on the surface of the alloy fuel powder are dispersed on the powder surface in the form of particulate matter, and as the fluorination time prolongs, the fluoride particles gradually become denser. When the fluorine gas concentration is 20%, the fluorides on the surface of the alloy fuel powder are all in a film shape as a whole, and as the fluorination time increases, the fluorination layer gradually forms a complete protective shell. When the fluorine gas concentration drops to 10%, there are fewer fluorides on the surface of the alloy fuel powder, and as time goes by, it can also be observed that the film formed by the fluorides gradually thickens. It can be seen from Figure 2 that the optimal condition for fluorine gas treatment is to fluorinate for 4 h in an atmosphere environment with a fluorine gas concentration of 20%. At this time, the film formed on the surface of the product is the most uniform, covers the most completely, and has no cracks.

[0101] Figure 3 are secondary particle mass spectrometry images of Al-5Li metal fuel powder particles before and after fluorination provided in Example 3 of the present invention. It can be seen from the figure that Figure 3Among them, (a) and (g) are the scanning electron microscope images of the Al-5Li alloy fuel powder particles before and after fluorination respectively. Since the EDS spectrometer equipped with a conventional scanning electron microscope cannot detect the signal of Li element, in order to deeply study the element distribution state, in the present invention, the sample particles are cut by a focused ion beam (FIB), and a SIMS mass spectrometer is used to observe the obtained single-particle profile, and the element signal distribution images obtained are respectively as shown in Figure 3 (c)-(f) and (i)-(l) in. The brighter the part in the image, the higher the content of the element. It can be seen that after the fluorination treatment, as shown in Figure 3 (k) in, the F element forms an obvious aperture, indicating that a thin and uniform fluoride protective layer is formed on the surface of the Al-5Li alloy fuel sample particles after fluorination.

[0102] Compatibility test:

[0103] Considering that the epoxy resin and the cross-linking agent used in the propellant also contain active hydrogen, the present invention uses epoxy resin for the compatibility test:

[0104] Sample a: Take 10 grams of epoxy resin glue and 10 grams of curing agent, mix them and let them stand, and directly cure to obtain a blank epoxy resin inlay, as shown in Figure 4 (a) in;

[0105] Sample b: Take 5 grams of the Al-5Li alloy fuel powder before fluorination in Example 3, 10 grams of epoxy resin glue, and 10 grams of curing agent, mix them and let them stand and cure to obtain an Al-5Li-epoxy resin inlay, as shown in Figure 4 (b) in;

[0106] Sample c: Take 5 grams of the A5F alloy fuel powder after fluorination in Example 3, 10 grams of epoxy resin glue, and 10 grams of curing agent, mix them and let them stand and cure to obtain an A5F-epoxy resin inlay, as shown in Figure 4 (c) in;

[0107] After 12 hours, first observe the overall expansion and the number of bubbles of samples a, b, and c. Subsequently, cut samples a, b, and c and observe the compactness of their cross-sections and the number of bubbles. The results are as shown in Figure 4 It can be clearly seen from this that the cross-section of the inlay of the Al-5Li alloy fuel powder without fluorination treatment is honeycombed, full of pores, and has poor compatibility. Although there are also a small number of slight depressions distributed on the cross-section of the inlay of the Al-5Li alloy fuel powder after fluorination, the overall flatness is the same as that of the blank inlay cross-section shown in Figure 4 (g). There are no bubbles and the compatibility is good, indicating that the surface stability of the Al-5Li sample after fluorination has been greatly improved.

[0108] Reaction of alloy fuel powder with deionized water:

[0109] The pre-fluorination Al-5Li alloy fuel powder and the post-fluorination A5F alloy fuel powder in Example 3 were respectively reacted with deionized water, and the results are as Figure 5 shown. It is not difficult to see that for the Al-5Li alloy fuel powder, violent and obvious bubbles were immediately generated after the powder contacted the water surface, and the powder floated on the water surface. For the A5F alloy fuel powder, the powder slowly sank in the deionized water, and no obvious bubbles were observed.

[0110] Meanwhile, 0.1 g of each product obtained by fluorination for different times in Example 5 was respectively added to 50 mL of deionized water. After observing that the gas generation stopped, the liquid level reading of the water column was read to obtain the amount of hydrogen released. The experiment was repeated 5 times, and the results are shown in Table 4. As the fluorination time extended, the hydrogen release amount first decreased and then increased. The reason for the initial decrease in the hydrogen release amount is that the film formed by the fluoride that does not react with water prevents moisture from contacting the active lithium inside the alloy fuel powder. As the fluorination time further extended, the hydrogen release amount was not zero. This is very likely because in the case of cracks in the fluoride film, moisture entered the particle interior again, resulting in hydrogen generation. It shows that a dense lithium fluoride layer was formed on the surface of the 20%-A5F-4 alloy fuel powder after 4 hours of fluorination (in the present invention, the code "a%-AxF-b", where a represents the fluorine gas concentration, b represents the fluorination duration in hours, x corresponds to the mass percentage of Li, and x% is the mass percentage of Li; here, 20%-A5F-4 represents the Al-5Li alloy fuel powder fluorinated in 20% volume concentration of fluorine gas for 4 hours), which can block the deionized water outside, greatly improving the surface compatibility of the alloy fuel powder.

[0111] Table 4: Amount of hydrogen released by reacting 0.1 g of samples fluorinated for different times with deionized water

[0112]

[0113]

[0114] Note: The 20%-A5F-0 sample is the pre-fluorination Al-5Li alloy fuel powder.

[0115] Aging experiment:

[0116] The pre- and post-fluorination Al-5Li alloy fuel powders in Example 3 were respectively placed in the air for aging for different days, and their SEM images are as Figure 6As shown in the figure, it can be seen from the figure that the surface of the fresh Al-5Li alloy fuel powder without fluorination treatment is clean and smooth; after being exposed to air for 10 days, irregular oxides grow rapidly on the surface; after 20 days, the oxides are strip-shaped and gradually connect into a network; after 30 days, the oxides have formed a shell structure, and an incomplete oxide layer can be observed attached to the surface of the powder particles from Figure 6 as shown in (d) of

[0117] ; after 40 days, multiple layers of irregular oxides have formed on the particle surface.

[0118] However, after the fluorinated 20%-A5F-4 alloy fuel powder is placed in air for 30 days, dispersed dot-shaped oxide particles can be observed on the powder surface, indicating that its oxidation rate is significantly slower than that of the non-fluorinated Al-5Li alloy fuel powder. That is, fluorination can effectively improve the storage stability of Al-5Li alloy fuel powder by slowing down its oxidation rate. Figure 7 In addition, the Al-5Li alloy fuel powder before and after fluorination in Example 3 is respectively placed in air for different aging days, and the measured mass combustion enthalpy is measured. The results are as

[0119] shown in Table 5. It can be seen from the chart that after being placed in air for 40 days, the measured mass combustion enthalpy of the Al-5Li alloy fuel powder decreases from 30378 J / g to 21835 J / g, and the energy loss rate reaches 28.12%; while the measured mass combustion enthalpy of the 20%-A5F-4 alloy fuel powder only changes from 29831 J / g to 28712 J / g, and the energy loss rate is only 3.75%. This shows that the lithium fluoride layer on the surface of the fluorinated A5F alloy fuel powder can effectively block the erosion of air, thereby improving the storage stability of the Al-5Li alloy fuel powder. That is to say, the fluorination layer can significantly improve the oxidation resistance of metal fuels and improve their storage stability.

[0120]

[0121]

[0122] Note: H t is the theoretical mass combustion enthalpy of Al-5Li; "H g for 0 day" is the measured mass combustion enthalpy measured immediately after preparation.

[0123] It is easy for those skilled in the art to understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for fluorination of aluminum-lithium alloy fuel, characterized in that: The aluminum-lithium alloy fuel particles to be fluorinated are placed in a fluidized bed through which a protective gas is passed, and a fluidized state is formed; then, while the particles are kept in a fluidized state, a mixed gas of a protective gas and a fluorine gas is passed into the fluidized bed, and the aluminum-lithium alloy fuel particles are subjected to a fluorination reaction based on a fluidized bed-chemical vapor deposition process, thereby obtaining fluorinated aluminum-lithium alloy fuel particles having a fluoride protective layer on the surface.

2. The method for fluorination of aluminum-lithium alloy fuel according to claim 1, characterized in that: When the fluorination reaction starts, the temperature in the fluidized bed is 20°C-50°C and the gas pressure is 0.1MPa-0.2MPa; Preferably, when the fluorination reaction starts, the temperature in the fluidized bed is room temperature and the gas pressure is normal pressure.

3. The method for fluorination of aluminum-lithium alloy fuel according to claim 1, characterized in that: The volume concentration of fluorine gas in the mixed gas is 1%-50%; The reaction time of the fluorination reaction is 0.1-30 hours.

4. The method for fluorination of aluminum-lithium alloy fuel according to claim 1, characterized in that: The gas flow rate in the fluidized bed is 5L / min-25L / min.

5. The method for fluorination of aluminum-lithium alloy fuel according to claim 1, characterized in that: In the aluminum-lithium alloy fuel particles to be fluorinated, the mass of lithium accounts for 0.5% to 20% of the total mass of the alloy fuel, preferably 0.5% to 10% of the total mass of the alloy fuel.

6. The method for fluorination of aluminum-lithium alloy fuel according to claim 1, characterized in that: The aluminum-lithium alloy fuel particles to be fluorinated are spherical granular powders; the aluminum-lithium alloy fuel particles to be fluorinated are prepared by melting aluminum and lithium into an alloy matrix by vacuum arc melting, and then preparing the alloy matrix into spherical granular powders; Preferably, the alloy parent material is prepared into spherical particle powder, specifically: the alloy parent material is melted and then atomized by a close-coupled gas atomization powder making method, and then condensed to prepare the spherical particle powder; More preferably, the average particle size D of the aluminum-lithium alloy fuel particles to be fluorinated is 50 Not more than 50μm.

7. The method for fluorination of aluminum-lithium alloy fuel according to claim 1, characterized in that: The fluoride protective layer is LiF.

8. Aluminum-lithium fluoride alloy fuel particles prepared by the fluorination method as claimed in claims 1 to 7.

9. The lithium aluminum fluoride alloy fuel particle according to claim 8, characterized in that: The mass combustion enthalpy is not less than 28kJ / g.

10. The use of the lithium aluminum fluoride alloy fuel particles as claimed in claim 8 or 9, characterized in that: It is used as a solid propellant.

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