High-activity concentrated heat-releasing Al-In-Sn alloy fuel and preparation method thereof

Abstract

This invention discloses a highly active, concentrated exothermic Al-In-Sn alloy fuel and its preparation method. By controlling the alloy's melting temperature, casting temperature, and composition, this invention prepares a liquid-phase two-phase separated alloy in which the minority phase is uniformly distributed on the surface of the majority phase, forming a core-shell structure where the minority phase encapsulates the majority phase. The aluminum alloy fuel described in this invention has a combustion temperature of 930℃~980℃, an exothermic heat of 2485μvs / mg~4388μvs / mg, and a combustion efficiency of up to 0.76. Compared with pure Al powder fuel, the alloy fuel provided by this invention can reduce the combustion temperature by up to 107℃ and increase the exothermic heat by up to 11.48 times. It effectively achieves the goals of high energy density, high combustion efficiency, and low combustion temperature, showing great application potential in the fields of solid propellants and explosives.

Description

Technical Field

[0001] This invention belongs to the field of metal fuel preparation technology, specifically relating to a highly active, concentrated exothermic aluminum alloy fuel and its preparation method. Background Technology

[0002] Currently, solid propellants are widely used in strategic and tactical weapons. To enhance the propellant's power, high-energy metallic fuels are typically added. Due to their high energy density and combustion enthalpy, metallic fuels can significantly improve the performance of both propellants and explosives. Metallic fuels in solid propellants generally serve as high-energy additives and combustion catalysts, increasing engine specific impulse, propellant density, and heat of explosion. However, with the rapid development of science and technology, various new weapons and space exploration equipment are becoming increasingly sophisticated. Future warfare and space exploration place ever higher demands on propulsion technology, and existing propellant fuels are increasingly unable to meet these requirements. Therefore, the development of high-performance metallic fuels has become increasingly important. Consequently, researchers have continuously studied metallic fuels for use in explosives, constantly researching new fuels to meet the energy needs of modern aerospace and weaponry.

[0003] Common metallic fuels include aluminum powder, boron powder, magnesium powder, and alloy powders. Aluminum powder is relatively inexpensive, abundant in raw materials, safe to use, and possesses a relatively high volumetric enthalpy of combustion and a large energy density. Therefore, it is often used as a metallic fuel additive and is widely applied in solid propellants, explosives, and pyrotechnics. However, in practical applications, several problems remain to be solved when using aluminum powder as a metallic fuel. For example, aluminum powder has disadvantages such as high ignition temperature, long ignition delay time, easy agglomeration on the surface forming large aluminum droplets, slow combustion speed, and incomplete combustion. These defects limit the further application of aluminum powder. Among these, the most difficult to solve is the problem of long ignition delay and high ignition temperature caused by the oxide film on the surface of aluminum powder.

[0004] To address the aforementioned problems with aluminum powder used as a metallic fuel, domestic and international research has begun exploring modifications to aluminum powder by disrupting or altering its surface shell composition. Some researchers have used a non-thermal plasma process to modify the aluminum powder surface, reducing the thickness of the oxide layer or changing its composition, thereby increasing the content of active aluminum and hindering the accumulation of the oxide layer during storage. Due to the stable liquid-phase two-phase separation system present in Al-based cyclohexene alloys, other studies have utilized the theory of liquid-phase two-phase separation in Al-based cyclohexene alloys and gas atomization powdering technology to prepare Al-Bi-Sn and Al-Bi-Zn ternary alloy composite powders. These composite powders all form a core-shell structure with a discontinuous Bi-rich phase or (Bi,Sn)-rich phase encapsulating an Al-rich phase, exhibiting excellent oxidation resistance and metallic activity. However, while Al-Bi-Sn and Al-Bi-Zn ternary alloy composite powders obtained through gas atomization powder preparation exhibit excellent sphericity and uniform particle size distribution, the rapid cooling rate during gas atomization causes some (Bi,Sn) phases to cool down before reaching the powder surface, resulting in a low content of (Bi,Sn)-rich phases on the composite powder surface. These phases mainly appear as meshes and spots on the aluminum powder surface. As the doping amount of Bi and Sn increases, the area of ​​the spot-like (Bi,Sn) phases increases. If the Bi and Sn content continues to increase, the (Bi,Sn) phases will eventually coat the entire powder. However, excessive Bi and Sn content reduces the content of metallic Al, ultimately decreasing the performance of the Al alloy composite powder.

[0005] This invention obtains an alloy fuel with an irregular core-shell structure, consisting of an Al matrix and an In-Sn phase continuously encapsulating an Al-rich phase, through high-temperature melting, high-temperature mold cooling, and high-power crushing. This alloy exhibits excellent oxidation resistance and high metallic activity. Utilizing the stable liquid-phase two-phase separation system present in Al-In-Sn eccentric alloys, this invention achieves uniform distribution of the In-Sn phase on the Al phase surface by controlling the alloy formulation and preparation process. This not only lowers the combustion exothermic temperature of the alloy fuel but also significantly increases its combustion exothermic capacity, resulting in a highly active concentrated exothermic phenomenon at high temperatures. Summary of the Invention

[0006] This invention aims to solve the problems of difficult ignition, incomplete combustion, and low heat release in aluminum powder fuel, and proposes a method for preparing a highly active, concentrated heat-releasing alloy fuel. The preparation method of this invention differs from conventional one-step pulverization methods such as gas atomization, ball milling, and high-temperature sintering. This invention's method consists of two steps: first, melting all metal components in a high-temperature environment and cooling them in a high-temperature mold to form an alloy with uniform component distribution; then, pulverizing the alloy using a high-power crusher. The high-temperature environment allows the Al-In-Sn eccentric alloy melt to generate a large temperature gradient during cooling, thereby increasing the interfacial energy of the system. Based on the principle of minimum energy, the second-phase droplets tend to move from the low-temperature surface region to the high-temperature center region to reduce the interfacial energy and stabilize the system. Simultaneously, the high-temperature mold reduces the cooling rate of the alloy, jointly promoting the formation of the Al-In-Sn eccentric alloy core-shell structure. The alloy powder prepared by the crusher achieves a more compact particle packing, thereby improving the stability of the alloy powder's core-shell structure and protecting the excellent performance of the alloy fuel.

[0007] The preparation method of the alloy fuel is as follows:

[0008] Step 1: Weigh a piece of metal Al and place it in a high-alumina crucible. Then weigh a certain mass of In and Sn and add them to the high-alumina crucible containing the Al block. The mass ratio of In to Sn is 0.25 to 4, and the ratio of the total mass of In and Sn to the mass of the Al-In-Sn alloy is in the range of 0.05 to 0.25 g.

[0009] Step 2: Place the crucible containing the raw materials into a box-type atmosphere-protected stirring furnace, evacuate the furnace and introduce nitrogen gas. Under nitrogen atmosphere protection, heat the furnace at a rate of 10-20℃ / min from room temperature to 800-900℃, hold at this temperature for 1-2 hours, and stir at a uniform rate for 10-15 minutes.

[0010] Step 3: Open the furnace door of the box-type atmosphere-protected stirring furnace, and pour the molten liquid alloy into a preheated mold at 300-600℃. After natural cooling, remove it from the mold, wrap it with sealing film, and store it in a vacuum-sealed bag.

[0011] Step 4: Use a high-power crusher to crush the alloy cast in Step 3 into powder, and then pass it through a 300-460 mesh molecular sieve to collect the sieved alloy powder into a sealed bag.

[0012] Another object of the present invention is to provide the application of the above-mentioned highly active, concentrated exothermic aluminum alloy fuel in the field of solid propellants and explosives.

[0013] The beneficial effects of this invention are as follows:

[0014] (1) This invention provides a highly active, concentrated exothermic alloy fuel and its preparation method. The aluminum alloy fuel described herein has a combustion temperature of 930℃~980℃, an exothermic heat of 2485μvs / mg~4388μvs / mg, and a combustion efficiency of up to 0.76. Compared with pure Al powder fuel, the alloy fuel provided by this invention can reduce the combustion temperature by up to 107℃ and increase the exothermic heat by up to 11.48 times. It effectively achieves the goal of satisfying both high energy density, high combustion efficiency, and low combustion temperature.

[0015] (2) Compared with the previous aluminum-based cycloid alloys that could only form alloy composite powders with discontinuous core-shell morphology, the Al-In-Sn cycloid alloy powder designed in this invention can form alloy fuels with metallic Al as the matrix and In-Sn phase continuously encapsulating Al-rich phase with irregular core-shell structure.

[0016] (3) The aluminum alloy fuel preparation method provided by the present invention is simple, easy to operate and easy to industrialize.

[0017] In summary, this invention provides a highly active, concentrated exothermic alloy fuel with a simple preparation process and excellent combustion performance. By forming a core-shell structure with a low-melting-point phase, aluminum oxidation is effectively reduced. Furthermore, replacing alumina with an outer protective shell made of aluminum powder, whose coefficient of thermal expansion is much smaller than that of alumina, further improves the performance of the alloy fuel. This research provides a feasible method for improving the performance of metallic fuels using liquid-phase two-phase separation alloys and has significant guiding implications. Attached Figure Description

[0018] Figure 1 The XRD curves of aluminum alloy powder and aluminum powder in different proportions are shown in the embodiments of the present invention.

[0019] Figure 2 The figures show the DTA curves of aluminum alloy powder and aluminum powder in different proportions in the embodiments of the present invention.

[0020] Figure 3 The DTA curves are for aluminum alloy powders with different indium-tin ratios in the embodiments of the present invention.

[0021] Figure 4 DTA curves of aluminum alloy powder cooled at different mold temperatures in embodiments of the present invention.

[0022] Figure 5 The X-ray diffraction patterns of aluminum alloy powder and aluminum powder oxidation products in the embodiments of the present invention are shown.

[0023] Figure 6 These are SEM images of aluminum alloy powder and aluminum powder at different temperatures in embodiments of the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and examples, but the scope of the present invention is not limited to the examples below.

[0025] Implementation Case 1: Weigh 18.27g of aluminum, 1.015g of indium, and 1.015g of tin into a high-alumina crucible. Then, place the crucible in a box-type atmosphere-protected stirring furnace, evacuate the furnace, and introduce nitrogen gas. Under nitrogen atmosphere protection, heat the furnace at a rate of 10℃ / min from room temperature to 900℃ and hold for 1 hour. Then, turn on the stirring control switch and stir at a uniform speed for 10 minutes. Pour the molten alloy into a preheated mold at 500℃ and allow it to cool naturally. Finally, use a high-power crusher to crush the cooled aluminum alloy into powder, and then screen the powder with a 460-mesh molecular sieve to obtain small-particle-size alloy powder.

[0026] Implementation Case 2: Weigh 16.405g of aluminum, 1.4475g of indium, and 1.4475g of tin into a high-alumina crucible. Place the crucible in a box-type atmosphere-protected stirring furnace, evacuate, and purge with nitrogen. Under nitrogen atmosphere protection, heat the furnace from room temperature to 900℃ at a rate of 10℃ / min, hold for 1 hour, then turn on the stirring control switch and stir at a uniform speed for 10 minutes. Pour the molten alloy into a preheated mold at 500℃ and allow it to cool naturally. Finally, use a high-power crusher to crush the cooled aluminum alloy into powder, and then sieve through a 460-mesh molecular sieve to obtain small-particle alloy powder.

[0027] Implementation Case 3: Weigh 17.45g of aluminum, 2.1813g of indium, and 2.1813g of tin into a high-alumina crucible. Then, place the crucible into a box-type atmosphere-protected stirring furnace, evacuate the furnace, and introduce nitrogen gas. Under nitrogen atmosphere protection, heat the furnace at a rate of 10℃ / min from room temperature to 900℃ and hold for 1 hour. Then, turn on the stirring control switch and stir at a uniform speed for 10 minutes. Pour the molten alloy into a preheated mold at 500℃ and allow it to cool naturally. Finally, use a high-power crusher to crush the cooled aluminum alloy into powder, and then screen the small-particle alloy powder through a 460-mesh molecular sieve.

[0028] Implementation Case 4: Weigh 19.69g of aluminum, 3.2812g of indium, and 3.2812g of tin into a high-alumina crucible. Place the crucible in a box-type atmosphere-protected stirring furnace, evacuate, and purge with nitrogen. Under nitrogen atmosphere protection, heat the furnace from room temperature to 900℃ at a rate of 10℃ / min, hold for 1 hour, then turn on the stirring control switch and stir at a uniform speed for 10 minutes. Pour the molten alloy into a preheated mold at 500℃ and allow it to cool naturally. Finally, use a high-power crusher to crush the cooled aluminum alloy into powder, and then sieve through a 460-mesh molecular sieve to obtain small-particle alloy powder.

[0029] Implementation Case 5: Weigh 18.36g of aluminum, 0.918g of indium, and 3.672g of tin into a high-alumina crucible. Place the crucible in a box-type atmosphere-protected stirring furnace, evacuate, and purge with nitrogen. Under nitrogen atmosphere protection, heat the furnace from room temperature to 900℃ at a uniform rate of 10℃ / min, hold for 1 hour, then turn on the stirring control switch and stir uniformly for 10 minutes. Pour the molten alloy into a preheated mold at 500℃ and allow it to cool naturally. Finally, use a high-power crusher to crush the cooled aluminum alloy into powder, and then sieve through a 460-mesh molecular sieve to obtain small-particle alloy powder.

[0030] Implementation Case 6: Weigh 20.31g of aluminum, 4.062g of indium, and 1.0155g of tin into a high-alumina crucible. Place the crucible in a box-type atmosphere-protected stirring furnace, evacuate, and purge with nitrogen. Under nitrogen atmosphere protection, heat the furnace from room temperature to 900℃ at a uniform rate of 10℃ / min, hold for 1 hour, then turn on the stirring control switch and stir uniformly for 10 minutes. Pour the molten alloy into a preheated mold at 500℃ and allow it to cool naturally. Finally, use a high-power crusher to crush the cooled aluminum alloy into powder, and then sieve through a 460-mesh molecular sieve to obtain small-particle alloy powder.

[0031] In Implementation Case 7, 19.326g of aluminum, 2.4158g of indium, and 2.4158g of tin were weighed and placed in a high-alumina crucible. The crucible was then placed in a box-type atmosphere-protected stirring furnace, evacuated, and purged with nitrogen. Under nitrogen atmosphere protection, the temperature was uniformly increased from room temperature to 300℃ at a rate of 10℃ / min and held for 1 hour. Then, the stirring control switch was turned on, and the mixture was stirred uniformly for 10 minutes. The molten liquid alloy was then poured into a preheated mold at 500℃ and allowed to cool naturally. Finally, the cooled aluminum alloy was crushed into powder using a high-power crusher, and the small-particle alloy powder was then screened through a 460-mesh molecular sieve.

[0032] In Implementation Case 8, 20.31g of aluminum, 2.3575g of indium, and 2.3575g of tin were weighed and placed in a high-alumina crucible. The crucible was then placed in a box-type atmosphere-protected stirring furnace, evacuated, and purged with nitrogen. Under nitrogen atmosphere protection, the temperature was uniformly increased from room temperature to 900℃ at a rate of 10℃ / min and held for 1 hour. Then, the stirring control switch was turned on, and the mixture was stirred uniformly for 10 minutes. The molten alloy was then poured into a preheated mold at 600℃ and allowed to cool naturally. Finally, the cooled aluminum alloy was crushed into powder using a high-power crusher, and the small-particle alloy powder was then screened through a 460-mesh molecular sieve.

[0033] Comparative example: Aluminum powder with a particle size of 6-20μm and a purity of 99.99% was selected as the comparative example.

[0034] Implementation Case 9: To evaluate the combustion performance of aluminum alloy fuel, DTA testing was used to study the aluminum powders of Examples 1-8 and the comparative example. The heating rate was 20℃ / min, the atmosphere was high-purity O2, and the sample mass was 2mg. Among them, the highly reactive aluminum alloy fuel prepared according to Example 3 began to react at around 945℃, and the combustion temperature was advanced by 92℃ compared with pure aluminum powder, with an exothermic effect of approximately 11.5 times that of pure aluminum powder. To investigate the oxidation process of aluminum alloy powder and aluminum powder, the aluminum alloy powder and aluminum powder prepared in Example 3 were heated to 1200℃ at a heating rate of 20℃ / min under an O2 atmosphere. After annealing, oxidation products were obtained. The obtained oxidation products and the unoxidized samples were characterized by XRD and SEM, respectively. Compared with aluminum powder at room temperature (25℃), the XRD of the aluminum powder oxidation products annealed at 1200℃ showed a very weak Al2O3 peak intensity, while the aluminum peak intensity remained very strong. This indicates that when aluminum powder is sintered to 1200℃, very little Al powder undergoes an exothermic oxidation reaction, and a large amount of elemental Al is still present in the combustion products. In contrast, the aluminum alloy powder sample annealed at 1200℃ (i.e., after a vigorous oxidation reaction at 945℃) produced only oxides, namely Al2O3, In2O3, and SnO2. The presence of these oxides indicates that the single exothermic oxidation reaction that occurred at 945℃ was essentially complete. SEM data further confirmed the conclusions drawn from XRD data. Compared with the surface morphology of aluminum powder at room temperature (25℃), the surface morphology of the aluminum powder oxidation products after annealing at 1200℃ showed very little change. The vast majority of product particles maintained a relatively complete spherical shape with a layered lamellar structure on the spherical surface. This indicates that the oxidation reaction of pure aluminum powder only occurred on the surface, with minimal oxidation inside the particles, which is consistent with the conclusions drawn from the XRD data of aluminum powder and its oxidation products. Conversely, the surface morphology of aluminum alloy powder annealed at 1200℃ (i.e., after a severe oxidation reaction at 945℃) showed significant damage compared to the surface morphology of aluminum alloy powder at room temperature (25℃). This cracking manifested as numerous defects, pores, and fragments on the oxide layer, forming irregular fracture surfaces. This indicates a high degree of oxidation in the aluminum alloy powder particles. The defects and pores on the particle surface show that the aluminum alloy powder was in full contact with the surrounding oxygen, leading to continued oxidation and deep oxidation.

Claims

1. A high activity concentrated exothermic Al-In-Sn alloy fuel, characterized by: The alloy fuel formulation contains an In to Sn mass ratio of 1:1, with the total mass of In and Sn accounting for 5%-25% of the alloy fuel. The alloy fuel has an irregular core-shell structure with metallic Al as the matrix and (In,Sn)-rich phase continuously encapsulating Al-rich phase. The surface (In,Sn)-rich phase ensures that the internal Al-rich phase is not oxidized, thereby reducing the ignition temperature of the aluminum alloy fuel, increasing the heat release during alloy combustion, and improving the alloy combustion efficiency. The preparation method of the highly active, concentratedly exothermic Al-In-Sn alloy fuel includes the following steps: (1) According to the mass percentage: the mass ratio of indium and tin is 1:1, and the mass percentage of indium and tin in the alloy is 5-25%. Place the three elemental metals of aluminum, indium and tin in a crucible, and then place the crucible containing the above metals into a box-type resistance furnace. Turn on the vacuum pump to evacuate the resistance furnace to a vacuum, and then introduce nitrogen into the furnace. The nitrogen flow rate is 3-4 L / min. (2) Heat the resistance furnace to 800-900℃ and keep it at that temperature for 1 hour. Then stir the molten alloy liquid for 10 minutes and pour it into an iron mold that has been preheated to 500-600℃. (3) The alloy column obtained in step 2 is crushed into powder in a high-power crusher and then passed through a 460-mesh sieve. The alloy powder collected below the sieve is the alloy fuel with uniform particles and special microstructure.

2. The high activity concentrated exothermic Al-In-Sn alloy fuel according to claim 1, characterized by, The (In,Sn)-rich phase on the surface of the alloy fuel not only reduces the loss of active Al before the fuel combustion releases heat, but also, because the expansion coefficient of the (In,Sn)-rich phase is much smaller than that of Al, at high temperatures, the thermal stress generated by the melting and expansion of aluminum inside the alloy fuel makes it easier for the outer layer to crack compared to aluminum powder fuel, allowing more aluminum vapor to be released outwards, thus improving the combustion performance of the alloy fuel. Compared to aluminum powder fuel, the combustion temperature of the alloy fuel is reduced by 92°C, and the heat release is increased by 11.48 times, exhibiting good concentrated heat release performance at high temperatures.

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