Nano Al Powder has the characteristics of small particle size, large specific surface area and high surface energy, and is currently widely used in the formulation of thermite, propellant and pyrotechnic powder. With the development of nanotechnology, nano-aluminum powder exhibits better performance than traditional aluminum powder, and has become a more active research hotspot.
Why is Nano Al Powder surface coated?
In the process of powder storage, transportation and processing, Nano Al Powder is often expected to show low activity and be less affected by external environmental factors (temperature, humidity, etc.), so that the product has stable performance for a long time, but aluminum as a kind of Active metal materials can easily react with oxygen and water in the air, forming a layer of aluminum oxide film covering the surface of Nano Al Powder, which affects the energy release effect of Nano Al Powder. Dispersion and homogenization in the system, so scholars at home and abroad have adopted the method of coating and modifying the surface of nano-aluminum powder to try to improve these deficiencies, in order to achieve satisfactory results in the field of energetic materials.
Analysis of Nano Al Powder Surface Coating Technology
At present, the surface coating of Nano Al Powder mainly adopts the methods of surface passivation and in-situ coating.
1. Surface passivation and coating of Nano Al Powder
1.1 Passivation mechanism: Unpassivated charged particles remain in the dispersion medium (Ar) due to the strong induced dipole/dipole interaction. The uncharged particles interact with Ar by diffusion, and electrons are transported from the metal surface through the oxide layer to the oxidant, while the oxidant (proton H+) itself is transported through the metal-oxide interface. Positively charged particles accumulate into an electrostatic field sufficient to stop the redox process. Before the negative charge is fully compensated, the redox process is strengthened. In order to stabilize the electric field, the additional metal will be oxidized, so that the effect of the energy barrier will stabilize the nano-aluminum powder and enhance the anti-oxidation performance of the nano-aluminum powder.
1.2 Significance of passivation: The passivation treatment of nano-aluminum powder improves the oxidation resistance of nano-aluminum powder, but this shell layer has no contribution to the energy release of nano-aluminum powder. It is necessary to comprehensively consider the preparation method of nano-aluminum powder, and the particle size The type, structure, thickness, etc. of the surface coating shell layer, and it is meaningful to solve the activity control and anti-oxidation performance on this basis.
2. In-situ coating of Nano Al Powder
2.1 Electric explosion method
The electric explosion method refers to applying a pulse current with an energy density of 1.0×(106~109)A/cm2 on the aluminum wire, so that the aluminum wire is heated and melted instantly, vaporized in the form of an explosion, and the product is dispersed in an inert atmosphere and cooled to form Nano-aluminum particles. The in-situ coating by electric explosion method mainly considers the following three aspects: (1) to ensure that the active aluminum content of the nano-aluminum powder reaches the micron level of activity (95% to 98%); (2) the high content of nano-aluminum powder will significantly improve the propellant. (3) After coating modification, while preventing the oxidation inactivation of nano-aluminum powder, it has a good effect on the combustion performance of the propellant. should have a certain promotion effect. Table 1 is a summary of commonly used coating materials for surface modification of nano-aluminum powder.
2.2 Wet chemical method
The wet chemical method uses tertiary amine aluminum hydride to decompose under the action of titanium isopropoxide catalyst to form nano-aluminum powder. After the catalyst is added, the solution is dark brown. In the process of turning black, adding a coating can prevent nano-aluminum powder from agglomerating in the process. The surface of the container wall finally forms nano-aluminum powder composite particles coated on the surface.
This method has the inherent safety of processing active aluminum powder in liquid. Meanwhile, the decomposition rate of tertiary amine aluminum hydride and the introduction time of organic coating have a very important influence on the formation of aluminum powder and the morphology of composite particles. of organic matter can also have different effects. In summary, in addition to forming a coating on the surface of nano-aluminum powder, the shell coating also plays a very important role in the entire chemical reaction process, and different organic coatings have different effects. The mechanism of action is the focus of future research.
Luoyang Trunnano Tech Co., Ltd (TRUNNANO) is a professional
Nano Al Powder supplier with over 12 years experience in chemical products research and development. We accept payment via Credit Card, T/T, West Union and Paypal. Trunnano will ship the goods to customers overseas through FedEx, DHL, by air, or by sea.
