Al@M@Al composite aluminum powder and preparation method thereof

Abstract

The present invention discloses an Al@M@Al composite aluminum powder and its preparation method. The Al@M@Al composite aluminum powder is an "aluminum-dimetal-aluminum" sandwich structure composite aluminum powder, with an aluminum core, a 5-20nm copper, iron, or nickel coating, and an outer shell of a 1-2μm aluminum thin film. The aluminum powder is first coated with a layer of copper, iron, or nickel by chemical reduction, and then a layer of aluminum thin film is deposited by magnetron sputtering. The Al@M@Al composite aluminum powder of the present invention has a particle size only 1-2μm larger than that of the original aluminum powder, significantly improving the reaction completion rate of the aluminum powder, and its combustion calorific value is significantly higher than that of the core-shell structure M@Al powder.

Description

Technical Field

[0001] The invention belongs to the field of energetic materials and relates to an Al@M@Al composite aluminum powder and a preparation method thereof. Background Art

[0002] Aluminum powder is the most commonly used metal fuel in the explosives industry. It can significantly increase the explosive heat and workability of explosives, enhancing the detonation efficiency of ammunition. With the advancement of nanotechnology, nano-aluminum powder has demonstrated superior performance compared to traditional aluminum powder. For example, its application in mixed explosives can improve multiple properties, such as detonation velocity, detonation heat, and peak shock wave overpressure. Its use in propellants can significantly increase the propellant's heat of combustion, improving the specific impulse of rocket engines. However, aluminum, as a reactive metal, readily reacts with oxygen and water in air, leading to the formation of a 0.5-4 nm thick passivation layer composed of components such as aluminum oxide on the aluminum surface. The presence of this passivation layer inhibits further oxidation of aluminum particles, but the high melting point of this passivation layer (primarily aluminum oxide) can increase the ignition temperature of the aluminum powder and reduce its burning rate. The primary advantage of micron-sized aluminum powder lies in its high reactive aluminum content. However, the presence of a thick passivation layer on its surface can exacerbate the agglomeration of aluminum nuclei during combustion, reducing the burning rate or even leading to incomplete combustion. While nano-aluminum powders have a fast combustion rate and a low ignition temperature, the presence of a nanometer-thick passivation layer significantly reduces the active aluminum content and energy density of the material. Furthermore, the extremely high surface area of ​​nanoparticles leads to easy agglomeration of the particles, which is exacerbated by the formation and growth of the passivation layer on the particle surface. This, in turn, hinders the effective dispersion of the aluminum powder and affects its rapid energy release.

[0003] There are two common methods to inhibit the formation and growth of the passivation layer on the surface of aluminum particles: one is to protect the particles with vacuum or protective gas to prevent the metal aluminum from coming into contact with oxidants, thereby preventing oxidation. This requires that the aluminum powder be in an external environmental protection state during production, transportation, and finished product processing, which greatly increases the cost of use. In addition, when used as an energetic material, aluminum powder may be mixed with solid oxidants, and aluminum powder, especially nano-aluminum powder, will react with solid oxidants at higher temperatures. Therefore, this method of protecting energetic aluminum powder is difficult to achieve the desired effect. The second is to use surface modification technology to treat and modify the particle surface, improve the chemical and physical properties of the micro-nano particle surface, and thus inhibit the oxidation reaction on the particle surface. This is currently a common method for treating the surface of active metals.

[0004] In recent years, a large number of studies have been conducted domestically and internationally on energetic aluminum powders with core-shell structures, aiming to improve their ignition, combustion, and storage properties. Chinese patent CN 112250530B discloses a double-layer core-shell thermite and its preparation method. The double-layer core-shell thermite comprises a core of micron-sized aluminum particles, a PVDF layer, and a metal oxide layer, wherein the PVDF layer is coated on the surface of the aluminum particles, and the metal oxide layer is coated on the surface of the PVDF layer. The improved thermite has a combustion calorific value of 19,000 to 24,500 J / g. Chinese patent CN 114853554 A discloses a catalytic aluminum-copper core-shell metal fuel. The fuel comprises a core-shell structure comprising a micron-sized aluminum powder and a copper coating, the core and the shell being tightly bonded. The above methods all improve the performance of aluminum powder by preparing a core-shell structure. However, the outermost layer of the core-shell structure is made of non-aluminum materials (metal oxides or copper). Different types of non-aluminum materials will be accompanied by compatibility issues in application, thus affecting the actual application of aluminum powder. Summary of the Invention

[0005] The object of the present invention is to provide an Al@M@Al composite aluminum powder and a preparation method thereof.

[0006] The technical solution for achieving the purpose of the present invention is:

[0007] An Al@M@Al composite aluminum powder is an "aluminum-two metals-aluminum" sandwich structure composite aluminum powder, the core of which is aluminum powder, the sandwich layer is a two-metal coating layer, and the outer shell is an aluminum single-element film. The two metals are copper, iron or nickel, wherein the sandwich layer has a thickness of 5 to 20 nm and the outer shell has a thickness of 1 to 2 μm.

[0008] Furthermore, the aluminum powder is a micron-sized aluminum powder conventionally used in the field of energetic materials, and its shape is spherical, and preferably has a medium particle size (D 50 ) is a micron-sized aluminum powder of 10 to 60 μm.

[0009] Furthermore, the second metal coating layer is coated on the surface of the aluminum powder by a chemical reduction method.

[0010] Furthermore, an aluminum thin film is deposited on the surface of the two metal coating layers by magnetron sputtering.

[0011] The preparation method of the Al@M@Al composite aluminum powder comprises the following steps:

[0012] (1) A second metal coating layer is coated on the surface of aluminum powder by chemical reduction to obtain M@Al powder with a core-shell structure;

[0013] (2) A layer of aluminum thin film was deposited on the surface of the core-shell structured M@Al powder by magnetron sputtering to obtain Al@M@Al composite aluminum powder.

[0014] Furthermore, the specific method of step (1) is: dissolving a dimetallic salt, sodium hypophosphite, sodium borate and ethylenediaminetetraacetic acid in water, adjusting and stabilizing the pH of the mixed solution to 8.5-9.5, adding aluminum powder, reacting at 40-60° C. for 5-120 minutes, filtering, washing with water, washing with ethanol, and drying to obtain M@Al powder with a core-shell structure.

[0015] The dimetallic salts in the present invention are copper salts, iron salts, and nickel salts. In a specific embodiment, copper sulfate, nickel chloride, and ferric chloride are taken as examples.

[0016] Preferably, in the mixed solution, the concentration of the dimetallic salt is 6-10 g / L, the concentration of sodium hypophosphite is 23-28 g / L, the concentration of sodium borate is 30-40 g / L, the concentration of EDTA is 2-5 g / L, and the pH is adjusted using sodium hydroxide or sulfuric acid solution.

[0017] Furthermore, the specific method of step (2) is: using magnetron sputtering technology, using aluminum plate as target material, evacuating the sputtering chamber to a background vacuum of 8.0×10 -4 After Pa, argon gas was introduced to deposit a layer of aluminum thin film on the surface of the core-shell structured M@Al powder to obtain Al@M@Al composite aluminum powder.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The present invention first coats the surface of Al powder with copper, iron, or nickel, which catalyzes the combustion of aluminum powder. Then, a thin film of aluminum is coated on the outer layer, thereby preventing the "sandwich layer" of copper, iron, or nickel from affecting the original formulation. At the same time, by controlling the coating thickness of the sandwich layer and the outer shell, the prepared Al@M@Al composite aluminum powder with a sandwich structure has a particle size only 1-2 μm larger than the original aluminum powder, resulting in a high reaction completion rate and combustion calorific value. Testing has shown that the reaction completion rate of the Al@Cu@Al composite aluminum powder is 10-20% higher than that of aluminum powder, while the combustion calorific value is 2-4 kJ / g higher than that of Cu@Al. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 These are SEM images of the aluminum powder, Cu@Al powder, and Al@Cu@Al composite aluminum powder in Example 1. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific examples and accompanying drawings. The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are purchased from commercial channels unless otherwise specified.

[0022] Example 1

[0023] (1) 6 g of copper sulfate pentahydrate, 30 g of sodium borate, 23 g of sodium hypophosphite, and 2 g of ethylenediaminetetraacetic acid were weighed separately and prepared into solutions. The mixture was then added with water to make 1 L of the mixed solution. The pH was adjusted to 8.5. 30 g of 30 μm aluminum powder was then added to stabilize the pH at 8.5. The solution was heated to 60°C for 5 min and reduced. After the reaction, the solution was filtered, washed with water, washed with ethanol, and dried to obtain the Cu@Al powder sample.

[0024] (2) Using the magnetron sputtering method, the sample Cu@Al powder was placed in the coating powder preparation box, installed on the carrier disc, and then the aluminum target sputtering source was installed. The magnetron sputtering chamber was closed and the vacuum pumping system was turned on for vacuum extraction. When the vacuum extraction reached the background vacuum of 8.0×10 -4 After Pa, the argon valve is opened to introduce argon, and then the target sputtering power is turned on to pre-sputter the target to remove impurities attached to the target surface; then the ultrasonic vibration motor is started to coat a layer of Al single-element film on the surface of the Cu@Al powder. After the powder coating on the conveyor belt is completed, the target sputtering source power is turned off, the ultrasonic vibration motor is turned off, and the powder is transported to the powder collection box to obtain Al@Cu@Al composite aluminum powder.

[0025] The median particle size of the Al@Cu@Al composite aluminum powder prepared in this example is 31 μm. Figure 1 The SEM images of the aluminum powder, Cu@Al powder, and Al@Cu@Al composite aluminum powder used in this example show that the Al@Cu@Al composite aluminum powder has a particle size only 1 μm larger than the original aluminum powder. Tests conducted within the formulation showed a reaction completion rate of 74% for the Al@Cu@Al composite aluminum powder, a 15% increase compared to 59% for aluminum powder. Automatic calorimetry testing, in compliance with GB / T 213-2008, revealed a calorific value of 25.0 kJ / g, a 2.8 kJ / g increase compared to 22.2 kJ / g for Cu@Al.

[0026] Example 2

[0027] (1) 10 g of nickel chloride hexahydrate, 40 g of sodium borate, 28 g of sodium hypophosphite, and 5 g of ethylenediaminetetraacetic acid were weighed separately and prepared into solutions. The mixture was then added with water to make 1 L of the mixed solution. The pH was adjusted to 9.5. 30 g of 10 μm aluminum powder was added to stabilize the pH at 9.5. The solution was heated to 60°C for 60 min and reduced. After the reaction, the solution was filtered, washed with water, washed with ethanol, and dried to obtain the Ni@Al sample.

[0028] (2) Using the magnetron sputtering method, the Ni@Al powder sample was placed in the coating powder preparation box, mounted on the carrier disc, and then the aluminum target sputtering source was installed. The magnetron sputtering chamber was closed and the vacuum pumping system was turned on for vacuum extraction. When the vacuum extraction reached the background vacuum of 8.0×10-4 After Pa, the argon valve is opened to introduce argon, and then the target sputtering power is turned on to pre-sputter the target to remove impurities attached to the target surface; then the ultrasonic vibration motor is started to coat a layer of Al single-element film on the surface of the Ni@Al powder. After the powder coating on the conveyor belt is completed, the target sputtering source power is turned off, the ultrasonic vibration motor is turned off, and the powder is transported to the powder collection box to obtain Al@Ni@Al composite aluminum powder.

[0029] The Al@Ni@Al composite aluminum powder prepared in this example had a median particle size of 11 μm. Testing showed a reaction completion rate of 72% for the Al@Ni@Al composite aluminum powder, a 12% improvement over aluminum powder (60%). Automatic calorimetry testing, in compliance with GB / T213-2008, showed a calorific value of 24.6 kJ / g, a 2.5 kJ / g improvement over Ni@Al (22.1 kJ / g).

[0030] Example 3

[0031] (1) 6 g of ferric chloride hexahydrate, 30 g of sodium borate, 23 g of sodium hypophosphite, and 5 g of ethylenediaminetetraacetic acid were weighed separately and prepared into solutions. The mixture was then added with water to make 1 L of the mixed solution. The pH was adjusted to 9.5. 30 g of 60 μm aluminum powder was added to stabilize the pH at 9.5. The solution was heated to 60°C and reduced for 120 min. After the reaction, the solution was filtered, washed with water, washed with ethanol, and dried to obtain the Fe@Al sample.

[0032] (2) Using the magnetron sputtering method, the Fe@Al powder sample was placed in the coating powder preparation box and installed on the carrier disc. Then, the aluminum target sputtering source was installed, the magnetron sputtering chamber was closed, and the vacuum pumping system was turned on for vacuum extraction. When the vacuum extraction reached the background vacuum of 8.0×10 -4 After Pa, the argon valve is opened to introduce argon, and then the target sputtering power is turned on to pre-sputter the target to remove impurities attached to the target surface; then the ultrasonic vibration motor is started to coat a layer of Al thin film on the surface of the Fe@Al powder. After the powder coating on the conveyor belt is completed, the target sputtering source power is turned off, the ultrasonic vibration motor is turned off, and the powder is transported to the powder collection box to obtain Al@Fe@Al composite aluminum powder.

[0033] The Al@Fe@Al composite aluminum powder prepared in this example had a median particle size of 62 μm. The reaction completion rate of the Al@Fe@Al composite aluminum powder was 70%, an 11% increase compared to aluminum powder (59%). Automatic calorimetry testing, in compliance with GB / T213-2008, showed a calorific value of 25.1 kJ / g, a 3 kJ / g increase compared to Fe@Al (22.1 kJ / g).

Claims

1. An Al@M@Al composite aluminum powder, characterized in that: It is an "aluminum-two metals-aluminum" sandwich structure composite aluminum powder, with an aluminum core, a two-metal coating layer, and an outer shell of an aluminum thin film. The two metals are copper, iron, or nickel. The thickness of the sandwich layer is 5-20nm, and the thickness of the outer shell is 1-2μm. The two-metal coating layer is coated on the surface of the aluminum powder by chemical reduction, and the aluminum thin film is deposited on the surface of the two-metal coating layer by magnetron sputtering.

2. The Al@M@Al composite aluminum powder according to claim 1, characterized in that The aluminum powder is micron-sized aluminum powder with a medium particle size of 10 to 60 μm and a spherical shape.

3. The method for preparing Al@M@Al composite aluminum powder according to claim 1, characterized in that: The following steps are involved: (1) A second metal coating layer was coated on the surface of aluminum powder by chemical reduction method to obtain M@Al powder with core-shell structure; (2) A layer of aluminum thin film was deposited on the surface of the core-shell structured M@Al powder by magnetron sputtering to obtain Al@M@Al composite aluminum powder.

4. The preparation method according to claim 3, characterized in that The specific method of step (1) is as follows: dissolving a dimetallic salt, sodium hypophosphite, sodium borate and ethylenediaminetetraacetic acid in water, adjusting and stabilizing the pH of the mixed solution to 8.5-9.5, adding aluminum powder, reacting at 40-60° C. for 5-120 min, filtering, washing with water, washing with ethanol, and drying to obtain a core-shell structured M@Al powder.

5. The preparation method according to claim 4, characterized in that The dimetallic salts are copper salts, iron salts, and nickel salts.

6. The preparation method according to claim 5, characterized in that The dimetallic salt is copper sulfate, nickel chloride or ferric chloride.

7. The preparation method according to claim 4, characterized in that In the mixed solution, the concentration of the dimetallic salt is 6-10 g / L, the concentration of sodium hypophosphite is 23-28 g / L, the concentration of sodium borate is 30-40 g / L, and the concentration of ethylenediaminetetraacetic acid is 2-5 g / L. Sodium hydroxide or sulfuric acid solution is used to adjust the pH.

8. The preparation method according to claim 3, characterized in that The specific method of step (2) is: using magnetron sputtering technology, using aluminum plate as target material, evacuating the sputtering chamber to a background vacuum of 8.0×10 -4 After Pa, argon gas was introduced to deposit a layer of aluminum thin film on the surface of the core-shell structured M@Al powder to obtain Al@M@Al composite aluminum powder.

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