Fabrication and reaction mechanism study of Co(OH)F@Al nanowire arrays: A functional fluorine-containing metastable intermolecular composite

Abstract

Metastable intermolecular composites (MICs) comprising solid fuels and oxidizers at nano-scale exhibit high energy densities and fast reaction speeds. As most metal and metalloid fuels are passivated by the natural oxide layer on the surface which acts as a reaction barrier, fluorine-containing oxidizers are of particular interest to promote the reactivity through interfacial fluoridation. In this work, cobalt hydroxy fluoride (Co(OH)F) was introduced as a functional fluorine-containing oxidizer, and core-shell structured Co(OH)F@Al nanoarray was fabricated onto a glass substrate. The thermal behavior and reaction mechanism of pure Co(OH)F and Co(OH)F@Al composites were thoroughly investigated, and Co(OH)F@Al was compared with CoO@Al and Co3O4@Al with identical morphology. In the Co(OH)F@Al composite, a pre-ignition reaction was observed which was attributed to the etching of Al2O3 shell by HF and the fluoridation of Al core by HF and CoF2. With the assistance of pre-ignition reaction, Co(OH)F@Al can complete main exothermal reaction before Al melting in a solid-state mechanism, and its peak temperature is around 200 ℃ lower than those of MICs employing CoO and Co3O4 as oxidizers.