Nano Al Powder Usually Requires Surface Coating

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The characteristics of nano-al powder include a small particle size, high specific surface area, and high surface energy. This powder is used widely in the formulations of thermite as well as propellant and pyrotechnic. The development of nanotechnology has made nano-aluminum a more active research area. It is now capable of producing better results than traditional aluminum powder.
Why are Nano Al Powder surfaces coated?

Nano Al Powder’s activity is expected to be low and less affected by environmental factors, such as temperature and humidity. The product should be stable for a long period of time. However, aluminum as an active metal can react with oxygen and other gases in the air to form a layer of aluminum oxide that covers the Nano Al Powder. This reduces the energy-release effect of Nano Al Powder. In order to avoid dispersion or homogenization in this system, researchers at home and overseas have used the technique of coating and modifying the surface of Nano-Aluminum Powder to improve their results in the area of energetic materials.

Analysis on Nano Al Powder Surface Coating Technology

Nano Al Powder currently surfaces using a mixture of in-situ or surface passivation.

1. Nano Al Powder surface passivation and coating

1.1 Passivation mechanism. The strong induced diper/dipole interaction means that unpassivated, charged particles remain in dispersion medium (Ar). The diffusion of uncharged particles with Ar results in electrons being transported from the metal surface to the oxidant. However, the oxidant (proton HC+) itself is transported through a metal-oxide interface. Electrostatic fields are created when positive-charged particles accumulate and stop the redox reaction. The redox reaction is strengthened before the negative charge is fully offset. The additional metal will be oxidized in order to stabilize and increase the electric field.
1.2 Significance and significance of passivation. Although passivation improves nano-aluminum’s oxidation resistance, this shell layer does not contribute to the energy release from nano-aluminum. It is essential to fully consider the preparation of nano-aluminum dust, as well as the particle size, type, structure, thickness and so on. The shell layer of the surface coating is essential for determining the activity control performance and anti-oxidation performance.

2. Nano Al Powder in-situ coating

2.1 Electric explosion method
The electric explosion technique involves using a pulse current having an energy density of 1.0x (106109)A/cm2 upon the aluminum wire. The aluminum wire is heated up and melted immediately, then vaporized under the form of an explosion. Finally, the product is dispersed within an inert atmosphere, where it is cooled to make Nano-aluminum particle. In-situ coating with electric explosion is primarily concerned with the following three aspects. (1) The active aluminum content of the Nano-aluminum Powder must reach the micron level (95 to 98%); (2) The propellant’s performance will be significantly improved by the high nano-aluminum content. (3) The propellant’s combustion performance is improved by coating modification. It prevents the oxidation-inactivation of nanoaluminum powder. should have a promotion effect. Table 1 lists the most common coating materials used for the surface modification nano-aluminum particles.
2.2 The wet chemical method
The wet chemical procedure uses tertiary aluminum hydride to undergo decomposition under the control of titanium isopropoxide to create nano-aluminum. The solution will turn dark brown once the catalyst has been added. A coating can be applied to prevent nano-aluminum particles from agglomerating during the process of turning black. The container wall eventually forms nano-aluminum mixture composite particles.
This method allows for the safe processing of active aluminum powder in liquid. Decomposition rates of tertiary aluminum aluminum hydride and time for organic coating play a major role in the formation of aluminum powder as well as the morphology and size of the composite particles. Other effects of organic matter may also be possible. The shell coating is responsible for forming a protective coating on nano-aluminum powder’s surface. It also plays an important part in chemical reactions. Different organic coatings may have different effects. Future research should focus on the mechanism of operation.

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