A continuous in-situ coating method after aluminum powder etching

Abstract

The application provides a continuous in-situ coating method for aluminum powder after etching, comprising the following steps: in step one, a first reaction precursor and a second reaction precursor are alternately introduced into a reaction cavity by using a gas phase etching method, a surface chemical reaction occurs on the surface of aluminum powder particles, a self-oxidation layer on the surface of the aluminum powder is peeled off layer by layer, and high-activity aluminum powder is obtained; in step two, a third reaction precursor and a fourth reaction precursor are alternately introduced into the reaction cavity, a surface chemical reaction occurs on the surface of the high-activity aluminum powder in-situ, the high-activity aluminum powder is in-situ deposited and coated, and etched and continuously in-situ coated aluminum powder is obtained. The method can prevent the re-oxidation of the aluminum powder without a self-oxidation layer after the etching process. The in-situ coating of the environmental barrier layer is carried out in a vacuum inert atmosphere on the same equipment as the etching process, the peeling and coating modification are realized in a true sense, and the reaction activity, thermal stability and energy density of the aluminum powder can be flexibly controlled.

Description

Technical Field

[0001] This invention belongs to the field of propellant technology, and relates to aluminum powder, specifically to a method for continuous in-situ coating of aluminum powder after etching. Background Technology

[0002] Aluminum powder possesses excellent properties such as high density, high calorific value, wide availability, and low cost, making it a commonly used energy additive in energetic material systems and widely applied in aerospace, military, and other fields. Highly active nano-aluminum powder, characterized by its large specific surface area and numerous active sites, exists in a highly activated state, significantly enhancing its energy, combustion, and ignition performance, which is of great significance for improving the energy and energy release rate of energetic material systems. However, the practical application of nano-aluminum powder still faces certain challenges. Due to its unique nano-surface effect and instability, nano-aluminum particles exposed to air are highly sensitive to the environment, readily reacting with oxygen and moisture to form a dense, inert alumina layer. The mass fraction of this oxide layer increases with decreasing particle size, occupying a significant percentage of the aluminum powder's mass, leading to a loss of active aluminum content and energy density. Simultaneously, the formed dense alumina layer hinders the contact between the oxidant and active aluminum, increasing the apparent activation energy of the redox reaction and directly affecting the energy release process of the nano-aluminum powder. The main challenge in aluminum powder applications is how to improve its energy output performance without affecting its energy density by addressing the issues of easy oxidation and poor stability.

[0003] Surface modification techniques, specifically altering the chemical composition and structure of aluminum powder surfaces, are the primary means of addressing this problem. In 2011, Israeli scientists Rosenband et al. disclosed an activation method for micron-sized (25 μm) aluminum powder containing an inert alumina oxide layer. This method involved pitting corrosion of the aluminum powder using a magnesium chloride solution (MgCl2 to Al ratio of 5%). Mass spectrometry revealed that Mg and Cl atoms gradually penetrated into the aluminum substrate, and the metallic aluminum sites reacted with the corrosion solution, forming pits on the particle surface. This introduced defects into the inert oxide layer, effectively disrupting the Al2O3 shell. However, this method's disruption of the surface inert Al2O3 layer relies on reducing the active aluminum content and lacks controllability.

[0004] Geisler et al. reported a method for directly treating spherical aluminum powder with gaseous HF at 25°C, removing the alumina layer on the surface of the spherical aluminum powder by fluorination, significantly improving the combustion rate of the spherical aluminum powder as a solid rocket propellant. A series of experiments verified that, due to their extremely small atomic radius, fluorine atoms can pass through the Al2O3 layer on the aluminum powder surface and react with the aluminum nuclei to form an AlF3 layer with a lower melting point, thereby causing the surface inert oxide layer to crack. This study successfully destroyed the oxide layer on the aluminum powder surface, but it was unable to completely etch the Al2O3 inert layer, and it was difficult to determine the amount of etchant used, resulting in extremely poor reproducibility.

[0005] Chinese invention patent application CN116655441A discloses a layer-by-layer self-assembled energetic aluminum powder, its preparation method, and its application. The method involves adding a solvent and hydrofluoric acid aqueous solution to a reactor, stirring and mixing them evenly, then introducing an inert gas before adding micron-sized aluminum powder. After even dispersion, an aluminum suspension is obtained. Various alcohols, ethers, and other reagents are then added sequentially to obtain self-assembled energetic aluminum powder. This method successfully destroys the aluminum oxide layer on the surface of the micron-sized aluminum powder by etching it with hydrofluoric acid, forming a strong Al-F electron interaction layer on the powder surface. This effectively improves the energy and stability of the aluminum powder. However, it does not completely etch the Al2O3 inert layer, and it is difficult to determine the amount of etchant used. The process is complex and has poor repeatability. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a continuous in-situ coating method for aluminum powder etching, thereby solving the technical problems of incomplete removal of the Al2O3 inert layer and easy re-oxidation after removal in existing technologies.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for continuous in-situ coating of aluminum powder after etching, the method comprising the following steps:

[0009] Step 1: The first reaction precursor and the second reaction precursor are alternately introduced into the reaction chamber using vapor phase etching to carry out a surface chemical reaction on the surface of aluminum powder particles, thereby achieving the layer-by-layer removal of the spontaneous oxide layer on the surface of aluminum powder and obtaining highly active aluminum powder.

[0010] Step 2: For the highly active aluminum powder, the third and fourth reaction precursors are alternately introduced into the reaction chamber to carry out a surface chemical reaction in situ on the surface of the highly active aluminum powder, thereby achieving in-situ deposition and coating of the highly active aluminum powder and obtaining aluminum powder with continuous in-situ coating after etching.

[0011] The vapor phase etching temperature of the aforementioned vapor phase etching method is 250–300℃; the deposition temperature of the aforementioned in-situ deposition coating is 100–250℃.

[0012] The first reaction precursor is hydrogen fluoride.

[0013] The second of the two reaction precursors is trimethylaluminum (Al(CH3)3) or tin acetylacetonate (Sn(acac)2).

[0014] The third reaction precursor is trimethylaluminum (Al(CH3)3), molybdenum hexafluoride (MoF6), or tungsten hexafluoride (WF6).

[0015] The fourth reaction precursor is hydrogen fluoride (HF) or silane (Si2H6).

[0016] The present invention also has the following technical features:

[0017] Preferably, the thickness of the alumina shell layer on the surface of the highly active aluminum powder is in the range of 0 to 6 nm; in the aluminum powder with continuous in-situ coating after etching, the thickness of the coating layer is controlled within the range of less than or equal to 5 nm, and the content of the coating layer is controlled within the range of 1 to 10 wt%; the material of the coating layer is aluminum fluoride, molybdenum or tungsten.

[0018] Specifically, step two is performed as follows:

[0019] Step 201: After the temperature in the reaction chamber reaches and stabilizes at the deposition temperature of 100–250°C, a coating layer is deposited and grown in situ on the surface of the highly active aluminum powder.

[0020] A single cycle of the in-situ deposition and growth of the coating layer includes the following four stages:

[0021] First, a third reaction precursor, trimethylaluminum (Al(CH3)3), molybdenum hexafluoride (MoF6), or tungsten hexafluoride (WF6), is injected into the reaction chamber to allow it to undergo a saturated surface chemical reaction with the highly active aluminum powder.

[0022] Secondly, an inert carrier gas is introduced to purge the unreacted third reaction precursor.

[0023] Then, a fourth reaction precursor, hydrogen fluoride (HF) or silane (Si2H6), is injected into the reaction chamber to react with the third reaction precursor adsorbed on the surface of the aluminum powder.

[0024] Finally, an inert carrier gas is introduced to purge the unreacted fourth reaction precursor.

[0025] Step 202: Repeat step 201 for multiple cycles to perform in-situ deposition coating, and obtain aluminum powder continuously coated in-situ after etching.

[0026] Preferably, in step 201, the pulse sequence of the four stages of a single cycle of the in-situ deposition growth coating layer is represented by t5-t6-t7-t8, where: t5 is the injection time of the third reaction precursor, t7 is the injection time of the fourth reaction precursor, t6 and t8 are both inert carrier gas purging times; t1 = 20s, t2 = 20s, t3 = 20s, t4 = 60s.

[0027] Preferably, in step 202, step 201 is repeated for 1 to 10 cycles.

[0028] Specifically, step one is to follow these steps:

[0029] Step 101: Place aluminum powder particles in the vapor phase etching reaction chamber, seal the reaction chamber, evacuate the chamber and introduce inert carrier gas into the reaction chamber, and adjust the pressure in the reaction chamber to the range of 10 Pa to 500 Pa.

[0030] Step 102: After the vapor phase etching temperature in the vapor phase etching reaction chamber reaches 250-300℃ and stabilizes, vapor phase etching of the oxide layer on the surface of the aluminum powder begins.

[0031] The single cycle of vapor phase layer-by-layer etching includes the following four steps:

[0032] First, an excess of the first reaction precursor, hydrogen fluoride, is injected into the reaction chamber, where it is saturated and adsorbed onto the surface of the aluminum powder to undergo a fluorination reaction.

[0033] Secondly, stop the flow of the first reaction precursor and introduce an inert carrier gas to purge and remove the reaction product water and excess first reaction precursor.

[0034] Then, an excess of the second reaction precursor, trimethylaluminum or tin acetylacetone, is injected into the reaction chamber to induce a ligand exchange reaction.

[0035] Finally, an inert carrier gas is introduced to remove excess of the second precursor, completing the etching of a single-atom-layer alumina.

[0036] Step 103: Repeat step 102 for multiple cycles to perform layer-by-layer etching on the aluminum powder particles to obtain highly active aluminum powder containing aluminum oxide shells of different thicknesses.

[0037] Preferably, in step 102, the pulse sequence of the four stages of the single cycle of the vapor phase layer-by-layer etching is represented by t1-t2-t3-t4, where: t1 is the injection time of the first reaction precursor, t3 is the injection time of the second reaction precursor, and t2 and t4 are both inert carrier gas purging times; t1 = 20s, t2 = 60s, t3 = 20s, t4 = 20s.

[0038] Preferably, in step 103, step 102 is repeated for 1 to 200 cycles.

[0039] More preferably, in step 103, step 102 is repeated for 100 to 200 cycles.

[0040] Preferably, the inert carrier gas is nitrogen or helium.

[0041] Preferably, the aluminum powder has a particle size of nanometer or micrometer.

[0042] Compared with the prior art, the present invention has the following technical effects:

[0043] (I) The method of the present invention can prevent the re-oxidation of nano-aluminum powder without spontaneous oxide layer after the etching process. The present invention will carry out in-situ coating of environmental barrier layer in the same equipment of the etching process under vacuum inert atmosphere, so as to achieve true stripping and coating modification, and flexibly control the reactivity, thermal stability and energy density of aluminum powder.

[0044] (II) This invention utilizes vapor-phase layer-by-layer etching technology to achieve complete and uniform layer-by-layer removal of the oxide shell on the surface of aluminum powder without touching or damaging the active aluminum. By controlling the number of etching cycles, highly selective and precise removal of the spontaneous oxide layer of aluminum powder is achieved. To further avoid secondary oxidation of aluminum powder in contact with an oxidizing atmosphere, an in-situ deposited coating layer with precisely controllable thickness is formed, significantly improving the proportion of active aluminum mass, energy density, and energy release efficiency, thus promoting the application of aluminum powder in equipment in the fields of national defense and aerospace.

[0045] (III) The method of the present invention has the advantages of high automation, strong repeatability of preparation process, high quality reliability and high operational safety, and is easy to implement and promote in industry.

[0046] (IV) The method of the present invention alternately introduces two reaction precursors into the reaction chamber, and a self-limiting surface chemical reaction occurs on the particle surface, achieving complete and uniform in-situ coating, and the thickness of the modified layer is precisely adjustable in the nanoscale range.

[0047] (V) The method of the present invention is applicable to the surface treatment of micron or nano-sized aluminum powder particles. After the spontaneous oxide layer on the surface is removed by vapor phase layer-by-layer etching technology, functional materials are deposited in situ on the surface of the aluminum powder to form a gas barrier layer, which improves the air stability of the aluminum powder, establishes the correlation between the composition of the surface shell of the aluminum powder and its physicochemical properties and energy release process, realizes the flexible control of aluminum powder reactivity, energy density and stability optimization, and obtains nano-aluminum powder with excellent comprehensive performance. Attached Figure Description

[0048] Figure 1 This is a transmission electron microscope (TEM) image of raw 100 nm aluminum powder without surface modification.

[0049] Figure 2This is a transmission electron microscope (TEM) image of nano-aluminum powder after 100 cycles of vapor phase etching.

[0050] Figure 3 This is a transmission electron microscope (TEM) image of nano-aluminum powder after 150 cycles of vapor phase etching.

[0051] Figure 4 This is a transmission electron microscope (TEM) image of nano-aluminum powder after 200 cycles of vapor phase etching.

[0052] Figure 5 This is an EDX mapping image of nano-aluminum powder after 100 cycles of vapor phase etching.

[0053] Figure 6 This is an EDX mapping image of nano-aluminum powder after 150 cycles of vapor phase etching.

[0054] Figure 7 The images show the Al 2p XPS curves of the original 100nm aluminum powder and the nano-aluminum powder after 100 cycles of vapor phase etching.

[0055] Figure 8 The O1s XPS curves are of the original 100nm aluminum powder and the nano-aluminum powder after 100 cycles of vapor phase etching.

[0056] Figure 9 The image shows the DSC curves of nano-aluminum powder under air atmosphere after 100 cycles of vapor phase etching.

[0057] Figure 10 The TG curve of nano-aluminum powder in air atmosphere after 100 cycles of vapor phase etching.

[0058] Figure 11 XPS full spectrum curves of aluminum fluoride nanoparticles after 100 cycles of vapor phase etching and 10 cycles of in-situ coating.

[0059] Figure 12 XPS depth profile atomic ratio of aluminum fluoride nanoparticles after 100 cycles of vapor phase etching and 10 cycles of in-situ coating.

[0060] Figure 13 The DSC curves of aluminum fluoride nanoparticles under air atmosphere are obtained by 100 cycles of vapor phase etching followed by 10 cycles of in-situ coating.

[0061] Figure 14 The TG curves of aluminum fluoride nanoparticles under air atmosphere are obtained by 100 cycles of vapor phase etching followed by 10 cycles of in-situ coating.

[0062] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0063] It should be noted that, unless otherwise specified, all materials and devices used in this invention are those known in the art.

[0064] This invention uses field emission transmission electron microscopy (FEI Tecnai G2 F20S-TWIN) to determine the thickness of the oxide layer on the surface of aluminum powder after etching, X-ray photoelectron spectroscopy (Thermo Scientific K-Alpha XPS) to analyze the surface structure composition of aluminum powder, thermogravimetric analysis (TA 2950TGA) and microcomputer-controlled fully automatic calorimeter (ZDHW-HN7000A) to characterize the energy release performance of aluminum powder, and laser ignition equipment to test the ignition and combustion performance of aluminum powder.

[0065] The aluminum powder used in the following examples has an average particle size of 130 nm and a nano-aluminum active aluminum content of 70%.

[0066] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0067] Example 1:

[0068] This embodiment provides a vapor phase layer-by-layer etching method for spontaneous aluminum powder oxide layers, which is performed according to the following steps:

[0069] Step 101: Place aluminum powder particles (average particle size 130 nm) in the vapor phase etching reaction chamber, seal the reaction chamber, evacuate and introduce nitrogen into the reaction chamber at a flow rate of 200 ml / min, adjust the pressure inside the chamber to 160 Pa; and stabilize the sample temperature at 275 °C by heating.

[0070] Step 102: Begin the vapor-phase layer-by-layer etching of the aluminum powder surface oxide layer. A single etching cycle includes the following four steps: First, using a "quasi-static" injection method, nitrogen gas at a bypass rate of 200 ml / min is discharged, the pressure inside the reaction chamber is 3 Pa, and hydrogen fluoride gas at 150 Pa is injected into the reaction chamber for 20 s. The hydrogen fluoride gas is saturated and adsorbed onto the aluminum powder surface, undergoing an alumina fluorination reaction. Second, the hydrogen fluoride gas is stopped, and nitrogen gas at a rate of 200 ml / min is introduced for 60 s purging. The pressure inside the reactor is restored to the baseline pressure of 160 Pa, removing the reaction product water and excess hydrogen fluoride. Then, trimethylaluminum at 10 Pa is injected into the reaction chamber for 20 s, resulting in a ligand exchange reaction and the formation of the volatile byproduct dimethylaluminum fluoride (Al(CH3)2F). Finally, nitrogen carrier gas is introduced for 20 s purging, completing the etching of a single atomic layer of alumina. In this embodiment, the pulse sequence used is 20 s-60 s-20 s-20 s.

[0071] Step 103: Repeat step 102 for 100, 150, and 200 cycles to perform vapor phase etching on the surface of nano-aluminum powder to obtain highly active nano-aluminum (L-nmAl) with oxide shells of different thicknesses, where L represents the alumina thickness on the surface of aluminum powder in nm, the total mass of the sample decreases by η%, and the etching rate per cycle is R (nm / cycle).

[0072] The structure and composition of the aluminum powder after vapor phase etching were characterized. The surface morphology of the nano-aluminum powder and the thickness of the oxide layer on the metallic aluminum surface were analyzed by transmission electron microscopy (TEM). The results are as follows: Figures 1 to 4 The images shown are, in order, TEM images of the original unmodified aluminum nanoparticles, the aluminum nanoparticles after 100 cycles of vapor phase etching, the aluminum nanoparticles after 150 cycles of vapor phase etching, and the aluminum nanoparticles after 200 cycles of vapor phase etching. The original aluminum nanoparticles are regular spheres with a diameter of approximately 150 nm. After layer-by-layer etching of the surface alumina, the original spherical morphology remains unchanged. With the increase of the number of etching cycles, the surface oxide layer is uniformly removed layer by layer.

[0073] The results of 100 and 150 cycles of etching aluminum powder EDX mapping characterization are as follows: Figure 5 and Figure 6 As shown in the figure, the red and green colors represent aluminum and oxygen elements, respectively. After 150 etching cycles, the oxygen content of the nano aluminum powder was significantly reduced compared to the sample treated for 100 cycles. Through mass normalization, it can be seen that the oxygen content percentage decreased from 8.13% to 6.70%.

[0074] Figure 7 and Figure 8 The images show the XPS spectra of the nano-aluminum powder after 100 cycles of alumina etching. Comparison with the fine scan spectra of the original nano-aluminum powder's Al 2p and O1s values ​​reveals a characteristic peak at 74.23 eV (Al 2p and O1s). 3+ The intensity of the oxygen characteristic peak was significantly reduced.

[0075] In summary, vapor-phase layer-by-layer etching achieved quantitative removal and modification of the spontaneous oxide layer on the surface of nano-aluminum powder, as shown in Table 1. The etching rate was [missing data]. / cycle.

[0076] Table 1. Oxide layer thickness and etching rate data for different samples

[0077]

[0078] Example 2:

[0079] This embodiment provides a method for vapor phase layer-by-layer etching of spontaneous oxide layer of aluminum powder. Based on the method in Example 1, this embodiment uses thermogravimetric and differential calorimetry (TG-DSC) to test the energy release characteristics of nano-aluminum powder modified by 100 cycles of vapor phase etching in an air atmosphere. The heating rate is 10℃ / min, and the test temperature range is 30~1000℃.

[0080] Figure 9 and Figure 10 These are DSC and thermogravimetric curves obtained under air atmosphere. There is an exothermic peak before and after the melting point of the nano-aluminum powder. The first exothermic process mainly occurs in the heat and mass transfer between the gas and the particle surface. When the aluminum powder core reaches the melting temperature, the molten aluminum expands outward through the cracked oxide layer and undergoes a combustion reaction. After etching modification, the oxide layer on the surface of the aluminum powder is thinned, and the exothermic heat in this part increases significantly, and the reaction is more complete.

[0081] Example 3:

[0082] This embodiment provides a method for vapor phase layer-by-layer etching of spontaneous oxide layer of aluminum powder. Based on the method in Embodiment 1, this embodiment uses a laser ignition device and a microcomputer-controlled fully automatic calorimeter to test the ignition and heat release performance of aluminum powder after 100 cycles of etching modification.

[0083] Meanwhile, raw 100nm aluminum powder was used as a control sample. Approximately 30mg of sample was used in each test, and each sample was tested three times, with the ignition delay time recorded. The ignition delay time of the raw 100nm aluminum powder was 49.3ms. The experiment showed that the ignition delay time of the nano-aluminum powder modified by 100 cycles of vapor phase etching was shortened to 40ms.

[0084] Meanwhile, raw 100nm aluminum powder was used as a control sample. Approximately 160mg of sample was used in each test, and each sample was tested three times, with the calorific value recorded. The calorific value of the raw 100nm aluminum powder was 20340.9 J / g, while the calorific value of the nano-aluminum powder modified by 100 cycles of vapor phase etching increased to 23626.5 J / g. The thinning of the oxide shell on the surface of the nano-aluminum powder promoted the oxide shell rupture rate, accelerated the contact between molten active aluminum and the oxidizing atmosphere, enhanced the combustion process, and increased the heat release.

[0085] Based on the schemes and experimental data of Examples 1 to 3, the following conclusions can be drawn:

[0086] First, the schemes in Examples 1 to 3 employ vapor phase layer-by-layer etching technology to achieve single-atom-layer etching in an inert environment. By controlling the number of etching cycles, the spontaneously oxidized alumina shell on the surface of the nano-aluminum powder is precisely and controllably removed, thus preparing highly active nano-aluminum powder with or without a small amount of alumina shell. The reactivity and energy density of the modified aluminum powder are significantly improved.

[0087] Secondly, the schemes in Examples 1 to 3 utilize vapor phase etching technology to achieve complete and uniform layer-by-layer removal of the oxide shell on the surface of aluminum powder without touching or damaging the active aluminum. By controlling the number of etching cycles, highly selective and precise removal of the spontaneous oxide layer of aluminum powder is achieved. Aluminum powder with a dense surface oxide layer removed exhibits significantly improved active aluminum mass ratio, energy density, and energy release efficiency, promoting the application of aluminum powder in equipment used in defense, aerospace, and other fields.

[0088] Third, the aluminum powder modified using the methods described in Examples 1 to 3 showed significantly improved energy density and reactivity in thermal analysis and laser ignition tests compared to the unetched powder. This method has advantages such as high automation, strong repeatability of the preparation process, high quality reliability, and high operational safety, making it easy to implement and promote in industry.

[0089] Fourth, the schemes in Examples 1 to 3 use vapor phase etching to alternately introduce two reaction precursors into the reaction chamber, causing a self-limiting surface chemical reaction on the surface of aluminum powder particles, thereby achieving the layer-by-layer conformal removal of the spontaneous oxide layer (alumina) on the surface of aluminum powder, with the removal thickness precisely adjustable within the nanoscale range.

[0090] Fifth, the schemes in Examples 1 to 3 are applicable to surface treatment of micron or nano-sized aluminum powder particles, which selectively and directionally remove the surface inert oxide layer without damaging the active aluminum substrate, thus preparing highly active aluminum powder with little or no alumina shell.

[0091] Example 4:

[0092] This embodiment provides a method for continuous in-situ coating after aluminum powder etching, which includes the following steps:

[0093] Step 1: The first reaction precursor and the second reaction precursor are alternately introduced into the reaction chamber using vapor phase etching to carry out a surface chemical reaction on the surface of aluminum powder particles, thereby achieving the layer-by-layer removal of the spontaneous oxide layer on the surface of aluminum powder and obtaining highly active aluminum powder.

[0094] The specific process of step one adopts the specific process of the aluminum powder spontaneous oxide layer vapor phase etching method given in Example 1.

[0095] Step 2: For the highly active aluminum powder, the third and fourth reaction precursors are alternately introduced into the reaction chamber to carry out a surface chemical reaction in situ on the surface of the highly active aluminum powder, thereby achieving in-situ deposition and coating of the highly active aluminum powder and obtaining aluminum powder with continuous in-situ coating after etching.

[0096] The specific process of step two is as follows:

[0097] Step 201: Reset the reaction temperature. After the reaction chamber temperature reaches 170°C and stabilizes, deposit aluminum fluoride in situ on the surface of aluminum powder that has been etched for 100 cycles of alumina. The deposition of aluminum fluoride in one cycle includes the following four steps: (1) Injecting trimethylaluminum into the reaction chamber for 20 seconds to undergo saturated chemical adsorption with the aluminum powder; (2) Introducing nitrogen gas for 20 seconds to clean the unreacted trimethylaluminum and methane byproducts; (3) Injecting hydrogen fluoride into the reaction chamber for 20 seconds to react with Al(CH3)2* adsorbed on the surface of the aluminum powder to generate aluminum fluoride; (4) Introducing nitrogen gas for 60 seconds to clean the unreacted hydrogen fluoride and methane byproducts.

[0098] Step 202: Repeat step 201 for 10 cycles to complete 10 cycles of aluminum fluoride deposition.

[0099] XPS structure and XPS depth profile composition characterization were performed on aluminum powder with surface alumina etched layer by layer in the vapor phase and in-situ coated with aluminum fluoride. The characterization results are as follows: Figure 11 and Figure 12 As shown, the characteristic peak of F1s (Al-F) indicates the formation of the AlF3 coating layer on the aluminum powder, while the signal peak of O1s indicates that the oxide layer on the surface of the aluminum powder was not completely removed. Since the morphologies of inorganic aluminum fluoride and aluminum oxide are difficult to distinguish under transmission electron microscopy, we used XPS depth profiling technology. Adjusting the voltage to 14795.4V, the current to 0.0108A, and the thinning rate to approximately 0.02nm / sec, semi-quantitative atomic ratio analysis revealed that the F content decreased and the oxygen content increased at approximately 3nm. Therefore, the thickness of the aluminum fluoride coating layer is approximately 3nm, and the deposition rate of the coating layer is approximately 0.3nm / cycle.

[0100] Example 5:

[0101] This embodiment provides a method for continuous in-situ coating of aluminum powder after etching. Based on the method given in Example 4, this embodiment uses thermogravimetric and differential calorimetry (TG-DSC) to test the energy release characteristics of nano-aluminum powder (100c ALE Al2O3-10c AlF3-nmAl) after 100 cycles of vapor phase etching modification and in-situ deposition of 10 cycles of aluminum fluoride coating. The heating rate is 10℃ / min, and the test temperature range is 30-1000℃.

[0102] Figure 13 and Figure 14These are DSC and thermogravimetric curves obtained under air atmosphere. The nano-aluminum powder exhibits an exothermic peak before and after its melting point. The first exothermic process mainly occurs through heat and mass transfer between the gas and the particle surface. When the aluminum powder core reaches its melting temperature, the molten aluminum expands outward through the cracks in the oxide layer, undergoing a combustion reaction. The graph clearly shows an increased exothermic peak area near the melting point. The aluminum fluoride coating has a lower melting point than alumina. The thinner oxide layer and the more easily cracked aluminum fluoride coating effectively promote the first-stage exothermic oxidation reaction of the aluminum powder, increasing its energy density.

[0103] Example 6:

[0104] This embodiment provides a method for continuous in-situ coating of aluminum powder after etching. Based on the method given in Embodiment 4, this embodiment uses a laser ignition device and a microcomputer-controlled fully automatic calorimeter to test the ignition and heat release performance of aluminum powder modified by 100 cycles of etching.

[0105] Meanwhile, raw 100nm aluminum powder was used as a control sample. Approximately 30mg of sample was used in each test, and each sample was tested three times, with the ignition delay time recorded. The ignition delay time of the raw 100nm aluminum powder was 49.3ms. The experiment showed that the ignition delay time of 100c Al2O3-10c AlF3-nmAl was shortened to 46ms.

[0106] Meanwhile, raw 100nm aluminum powder was used as a control sample, with approximately 160mg of sample used in each test. Each sample was tested three times, and the calorific value was recorded. The calorific value of the raw 100nm aluminum powder was 20340.9J / g, while that of 100c Al2O3-10cAlF3-nmAl increased to 23139.3J / g. The thinning of the oxide shell on the surface of the nano-aluminum powder promoted the fracture rate of the oxide shell, accelerated the contact between the molten active aluminum and the oxidizing atmosphere, enhanced the combustion process, and increased the heat release. At the same time, the aluminum fluoride coating effectively inhibited the secondary oxidation of the aluminum powder surface after the oxide layer was removed, without hindering the outward diffusion and reaction process of the core aluminum element.

Claims

1. A method for continuous in-situ coating after aluminum powder etching, characterized in that, This method includes the following procedures: Step 1: Using vapor phase etching, the first reaction precursor and the second reaction precursor are alternately introduced into the reaction chamber to cause a surface chemical reaction on the surface of the aluminum powder particles, thereby achieving the layer-by-layer removal of the spontaneous oxide layer on the surface of the aluminum powder and obtaining highly active aluminum powder; the first reaction precursor is hydrogen fluoride; the second reaction precursor is trimethylaluminum or tin acetylacetonate. Step one is to follow these steps: Step 101: Place aluminum powder particles in the vapor phase etching reaction chamber, seal the reaction chamber, evacuate and introduce inert carrier gas into the reaction chamber, and adjust the pressure in the reaction chamber to the range of 10 Pa to 500 Pa. Step 102: After the vapor phase etching temperature in the vapor phase etching reaction chamber reaches 250-300℃ and stabilizes, vapor phase etching of the oxide layer on the surface of aluminum powder begins. The single cycle of vapor phase layer-by-layer etching includes the following four steps: First, an excess of the first type of reaction precursor is injected into the reaction chamber, which is saturated and adsorbed onto the surface of aluminum powder to undergo a fluorination reaction. Secondly, stop the flow of the first reaction precursor and introduce inert carrier gas to purge and remove the reaction product water and excess first reaction precursor; Then, an excess of the second type of reaction precursor is injected into the reaction chamber to induce a ligand exchange reaction; Finally, an inert carrier gas is introduced to remove excess of the second precursor, completing the etching of a single-atom-layer alumina. Step 103: Repeat step 102 for multiple cycles to perform layer-by-layer etching on the aluminum powder particles to obtain highly active aluminum powder containing aluminum oxide shells of different thicknesses. Step two: For the highly active aluminum powder, the third and fourth reaction precursors are alternately introduced into the reaction chamber to conduct an in-situ surface chemical reaction on the surface of the highly active aluminum powder, thereby achieving in-situ deposition and coating of the highly active aluminum powder and obtaining aluminum powder with continuous in-situ coating after etching; the third reaction precursor is molybdenum hexafluoride or tungsten hexafluoride; the fourth reaction precursor is hydrogen fluoride or silane.

2. The continuous in-situ coating method after aluminum powder etching as described in claim 1, characterized in that, The thickness of the alumina shell layer on the surface of the highly active aluminum powder is less than 6 nm; in the aluminum powder with continuous in-situ coating after etching, the thickness of the coating layer is controlled within the range of less than or equal to 5 nm, and the content of the coating layer is controlled within the range of 1 to 10 wt%; the material of the coating layer is aluminum fluoride, molybdenum or tungsten.

3. The continuous in-situ coating method after aluminum powder etching as described in claim 1, characterized in that, Step two is to be performed as follows: Step 201: After the temperature in the reaction chamber reaches and stabilizes at the deposition temperature of 100–250°C, a coating layer is deposited and grown in situ on the surface of the highly active aluminum powder. A single cycle of the in-situ deposition and growth of the coating layer includes the following four stages: First, a third type of reaction precursor is injected into the reaction chamber to allow it to undergo a saturated surface chemical reaction with the highly active aluminum powder. Secondly, an inert carrier gas is introduced to purge the unreacted third reaction precursor; Then, a fourth type of reaction precursor is injected into the reaction chamber to react with the third type of reaction precursor adsorbed on the surface of the aluminum powder. Finally, an inert carrier gas is introduced to purge the unreacted fourth reaction precursor. Step 202: Repeat step 201 for multiple cycles to perform in-situ deposition coating, and obtain aluminum powder continuously coated in-situ after etching.

4. The continuous in-situ coating method after aluminum powder etching as described in claim 3, characterized in that, In step 201, the pulse sequence of the four stages of a single cycle of in-situ deposition and growth of the coating layer is represented by t5-t6-t7-t8, where: t5 is the injection time of the third reaction precursor, t7 is the injection time of the fourth reaction precursor, t6 and t8 are both inert carrier gas purging times; t1=20s, t2=20s, t3=20s, t4=60s.

5. The continuous in-situ coating method after aluminum powder etching as described in claim 3, characterized in that, In step 202, step 201 is repeated for 1 to 10 cycles.

6. The method for continuous in-situ coating of aluminum powder after etching as described in claim 1, characterized in that, In step 102, the pulse sequence of the four stages of the single cycle of vapor phase layer-by-layer etching is represented by t1-t2-t3-t4, where: t1 is the injection time of the first reaction precursor, t3 is the injection time of the second reaction precursor, and t2 and t4 are both inert carrier gas purging times; t1=20s, t2=60s, t3=20s, t4=20s.

7. The method for continuous in-situ coating of aluminum powder after etching as described in claim 6, characterized in that, In step 103, step 102 is repeated for 1 to 200 cycles.

8. The continuous in-situ coating method after aluminum powder etching as described in claim 1 or 3, characterized in that, The inert carrier gas is nitrogen or helium.

9. The method for continuous in-situ coating after aluminum powder etching as described in claim 1, characterized in that, The aluminum powder has a particle size of nanometer or micrometer.

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