Enhancing the combustion of nAl with AlF 3 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 3 composites were produced by coating nAl with AlF 3 via a facile chemical deposition method. TEM and SEM analyses indicated that the AlF 3 layer was evenly coated on the surface of nAl with a thickness of 4.6-9.1 nm, thereby varying the quantity of AlF 3 applied. Experimental results from combustion indicated that the prepared nAl@AlF 3 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 3 hinders Al combustion agglomeration, we proved that the gas-solid reaction between nAl and AlF 3 plays an important role in inhibiting the sintering of nAl particles produced. The gaseous intermediate ( i.e. , AlOF and HF) released from the hydrolysis of AlF 3 could reduce the diffusion barrier of Al 2 O 3 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.