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 combination of in-situ coating and surface passivation.
1. Nano Al Powder surface passivation and coating
1.1 Passivation mechanism. The strong induced dipole/dipole interaction means that unpassivated, charged particles remain in dispersion media (Ar). The diffusion of uncharged particles with Ar results in electrons being transported from the metal surface to the oxidant. However, the oxidant (protonH+), is transported through the interface metal-oxide. Electrostatic fields are created when positive-charged particles build up to a sufficient level to stop the redox reaction. The redox reaction is strengthened before the negative charge is fully balanced. 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 energy release. 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
Method for 2.1 Electric Explosion
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. The three main aspects of in-situ electroexplosion coating are (1) to ensure that the active aluminium content of the nanoaluminum particles reaches the micron level (95 to 98%); (2) to improve the propellant’s performance. (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 surface modification on 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 added to stop 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 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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