Enhancement of on-chip combustion via nanoporous silicon microchannels

Abstract

Due to its high energy density and MEMS compatible fabrication methods, on-chip porous silicon shows considerable promise as an energetic material. Rapid combustion events have been demonstrated with flame propagation speeds eclipsing 3km/s, but much is still unknown about the controlling parameters of porous silicon combustion. Recent studies show that implementation of microstructure within a nanoporous silicon film greatly increases reaction rate of a relatively slow burning system. The present work utilizes porous silicon microchannels to enhance an already rapidly-reacting system. Reactions in channeled porous silicon regions of this system propagated at speeds up to 1.2km/s faster than similar neat porous silicon films. The fastest propagation speed was 3660m/s, the highest reported flame speed for comparable nanoenergetic systems to date. We provide evidence that the enhancement of flame propagation rates by channeled porous silicon is mechanistically different from the convectively controlled burning of neat porous silicon. This evidence suggests the presence of acoustically aided reactions for porous silicon channel combustion where the channels more readily ignite compared to neat porous silicon. We predict this allows for propagation of the reaction by intense sound waves within the porous medium.