Enhancing the combustion of nAl with AlF coating: gas-solid reaction mechanism for reducing combustion agglomeration of Al powder.

The combustion agglomeration of nano-aluminum (nAl) powder leads to incomplete combustion, which seriously hinders its application as metal fuel. In this work, nAl@AlF composites were produced by coating nAl with AlF a facile chemical deposition method. TEM and SEM analyses indicated that the AlF layer was evenly coated on the surface of nAl with a thickness of 4.6-9.1 nm, thereby varying the quantity of AlF applied. Experimental results from combustion indicated that the prepared nAl@AlF composites exhibit superior combustion efficiency, a higher combustion rate, and reduced combustion agglomeration as compared to raw nAl. Contrary to the widely accepted explanation that volatilization of AlF hinders Al combustion agglomeration, we proved that the gas-solid reaction between nAl and AlF plays an important role in inhibiting the sintering of nAl particles produced. The gaseous intermediate (, AlOF and HF) released from the hydrolysis of AlF could reduce the diffusion barrier of AlO to facilitate the reaction of Al core, which enhances the combustion reaction kinetics. More importantly, these gaseous products actively participate in the reaction cycle to continuously exert their catalytic effects.