Thermal-induced hydrosilylation to endow nanoporous silicon energetic films with long-term chemical stability

Abstract

The huge energy release and highly adjustable combustion characteristics of nanoporous silicon (nPS) make it one of the most attractive inorganic energetic materials. However, nPS will be oxidized slowly from its surface when it is left in ambient air to be aged. Explanations vary as to the aging mechanism, and the corresponding anti-ageing strategy remains to be fully investigated. The present study provides an efficient strategy of a thermal-induced hydrosilylation to improve the long-term chemical stability of H-terminated nPS. The nPS of 75 μm in depth was etched with a pore diameter of 52.5 nm and a gravimetry-determined porosity of 79.6%. The DSC and FTIR data confirm that oxygen is able to infiltrate the H-terminated layer and preferentially attack the weak Si-Si over Si-H bonds. The prime oxidizer is not sodium perchlorate but oxygen from the air to cause a backbond oxidation. After a modification, the heat of reaction is determined to be 1436 J·g−1. Interestingly, this value is of almost no detectable change to be 1402 J·g−1 and 1387 J·g−1 when aged for 24 or 48 h, respectively. All the evidences suggest that the alkyl-terminated nPS exhibits an excellent anti-oxidation ability to ambient air, which is well consistent with a high-speed video analysis from the combustion behavior of nPS impregnated with NaClO4·H2O. This work suggests that only one step may be away from a practical application of nPS energetic materials.