Nanoporous Silicon Combusion: Observation of Shockwave and Flame Synthesis of Nanoparticle Silicon Oxide
John G. Gillen, Collin Becker, Conrad Stoldt, Matthew E. Staymates
The persistent hydrogen termination present in nanoporous silicon (nPS) is unique compared to other forms of nanoscale silicon (Si) which typically readily form a silicon dioxide passivation layer. The hydrogen terminated surface combined with the extremely high surface area of nPS yields a material capable of powerful exothermic reactions when combined with strong oxidizers. Here a galvanic etching mechanism is used to produce nPS both in bulk Si wafers as well as in patterned regions of Si wafers with microfabricated ignition wires. An explosive composite is generated by filling the pores with sodium perchlorate (NaClO4). Using high speed video including Schlieren photography, a shock wave is observed to propagate through air at 1127 +/- 116 ms-1. Additionally, a fireball is observed above the region of nPS combustion which persists for nearly 3x as long when reacted in air compared to N2, indicating highly reactive species are generated that can further combust with excess oxygen. 2 Additionally, reaction products captured in a pressure bomb are analyzed from either nPS ignited using only high pressure O2 (400 psig) gas as an oxidizer or as a composite of nPS and NaClO4 oxidizer. In both cases, the products are verified by transmission electron microscopy (TEM) to include nano- to micrometer scale SiOx particles. This work highlights the complex oxidation mechanism of nPS composites and demonstrates the ability to use a solid state reaction to create a secondary gas phase
, Becker, C.
, Stoldt, C.
and Staymates, M.
Nanoporous Silicon Combusion: Observation of Shockwave and Flame Synthesis of Nanoparticle Silicon Oxide, ACS Applied Materials and Interfaces, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=919537
(Accessed July 6, 2022)