Quantification of Oxidizer Systems for Porous Silicon Combustion
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Quantification of Oxidizer Systems for Porous Silicon Combustion Ani Abraham,1,2 Nicholas W. Piekiel,1 Cory R. Knick,1 Christopher J. Morris1, Edward Dreizin2 1
U.S. Army Research Laboratory, Adelphi, Maryland, 20783, USA
2
New Jersey Institute of Technology (NJIT), University Heights, Newark, NJ 07102, USA
ABSTRACT We present the first quantitative assessment of combustion dynamics of on-chip porous silicon (PS) energetic material using sulfur and nitrate-based oxidizers with potential for improved moisture stability and/or minimized environmental impact compared to sodium perchlorate (NaClO4). Material properties of the PS films were characterized using gas adsorption porosimetry, and profilometry to calculate specific surface area, porosity and etch depth. The PS/sulfur energetic composite was formed using three pore loading techniques, where the combustion speeds ranged from 2.9 – 290 m/s. The nitrate-based oxidizers were solution-deposited using different compatible solvents, and depending on the metal-nitrate yielded combustion speeds of 3.1 – 21 m/s. Additionally, the combustion enthalpies from bomb calorimetry experiments are reported for the alternative PS/oxidizer systems in both nitrogen and oxygen environments. INTRODUCTION Nanostructured porous silicon prepared using galvanic etching in hydrofluoric acid has been the subject of recent investigations for use in on-chip energetic combustion applications.1-3 Previous efforts by us and other energetic porous silicon researchers have primarily focused on nanostructured pores impregnated with concentrated sodium perchlorate oxidizer in a methanol solution. The combustion performance is highly tunable through changes in material properties such as porosity and specific surface area, exhibits high energy density, and in some cases results in extremely rapid burn rates.1, 2 However, sodium perchlorate is known to be moisture sensitive (hygroscopic), and therefore can demonstrate inconsistent combustion performance for some aged materials. Furthermore, perchlorates may present detrimental environmental and health impacts due to the long-term stability of the chlorate ion and its tendency to mimic iodide ions in biological processes.4, 5 Therefore, in this study, porous silicon combustion using alternative oxidizers with improved moisture stability and/or perchlorate-free formulations are explored. Although some qualitative studies have shown sulfur and nitrate based oxidizers as potential alternatives, quantitative reports of combustion output are not currently available.6 Therefore, we present the first quantitative combustion study of porous silicon (PS) energetic composite prepared with sulfur and nitrate-based oxidizers. In the case of sulfur, we have successfully impregnated the pores using three different pore loading techniques. The nitrate-based oxidizers were solutiondeposited using different compatible solvents, depending on the metal-nitrate. We quantified reaction characteristics using high speed videography and bomb calorimetry, ultimately provid
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