Combustion behavior of surface functionalized aluminum nanoparticle dispersions in Kerosene

Combustion analysis of aluminum (Al) nano-particles with and without surface functionalization combined with kerosene was performed. Three mixtures of 0.5wt % Al nanoparticles with kerosene containing different surfactants (oleic acid and perfluorohexadecanoic acid, PFHD) were tested to compare the effect of surfactants on regression rates. The Al particles were functionalized with a PFHD self-assembled monolayer around the alumina shell (Al₂O₃) encapsulating the Al core. The PFHD acts as a surfactant and allows a homogeneous dispersion of functionalized Al nano-particles throughout the kerosene. Mixtures with functionalized Al nano-particles had a two stage regression rate with second stage burn rate constant increased by about 51% and average regression rate increase by about 11% compared to pure kerosene. The functionalized Al nano-particles provide nucleation sites that promote boiling in the second stage which significantly increases regression rate. Further thermogravimetric (TG) and laser flash (LF) analyses, (mass loss and thermal diffusivity respectively) showed that Al-PFHD particles exhibit multiple stages of decomposition and had the lowest thermal diffusivity such that the PFHD aided regression via enhanced energy transport by convection (gas generation). The PFDH coating may have also promoted exothermic reactions on the Al particle surface between fluorine and alumina adding to the exothermicity of the overall reaction. These results provide new insight on how to optimize nanoparticle dispersion and to enhance regression rate.