As the landscape of nanoenergetic materials expands, silicon nanostructures have emerged as promising fuels. Porous silicon in particular has demonstrated unmatched combustion velocity in part due to the high surface availability of surface terminated hydrogen. Amorphous silicon nanoparticles resemble the surface chemistry of porous silicon, yet their energetic characteristics are rarely studied. In this work, a non-thermal plasma was used to prepare uniform sub-10 nm Si particles with varying degrees of crystallinity by tuning the level of power coupled into plasma discharge. Temperature-programmed desorption spectroscopy determines quantitatively that as-prepared amorphous Si nanoparticles (a-nSi) incorporate more hydrogen than crystalline Si nanoparticles (c-nSi). Further, hydrogen is incorporated in the material in the form of higher silicon hydrides with a lower desorption temperature. Combustion cell measurements show that when formulated with KClO4, a-nSi outperforms its crystalline counterpart with respect to pressure output. The pressurization rate of a-nSi/KClO4 composite increases by a factor of six compared with nanoaluminum to 0.66 MPa μs-1. Temperature-jump time-of-flight mass spectrometry (T-Jump TOFMS) of a-nSi/KClO4 suggests that hydrogen release occurs prior to ignition. The dual role of hydrogen in improving the energetic performance is proposed: 1) The facile release of hydrogen from a-nSi leaves behind highly reactive Si dangling bonds. The ignition occurs instantly when Si dangling bonds are in contact with oxygen. 2) The desorbed H2 reacts with O2 explosively, leading to the rapid pressure rise. The enhanced energetic performance of hydrogenated a-nSi suggests that incorporation of hydrogen could be a promising strategy for improving the performance of nanoenergetics.

Enhanced energetic characteristics of amorphous silicon via in situ hydrogen release

ACS Fall 2021

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