Preparation of nanocomposite materials containing WS₂, δ-WN, Fe₃O₄, or Fe₉S₁₀ in a silica aerogel host

Abstract

Nanocomposite materials based on silica aerogel hosts have been produced using chemical vapour infiltration/decomposition methods and characterized by X-ray diffraction and electron microscopy. Amorphous tungsten in SiO₂ aerogel was formed by the decomposition of W(CO)₆ at 250 °C. Alternatively, reaction of this material with sulphur at 700 °C produced needle-shaped WS₂ crystals with lengths ranging from 25–230 nm. Reaction of the W/SiO₂ composite with anhydrous NH₃ formed crystals of δ-WN with diameters of 1–5 nm. Fe(CO)₅ is readily absorbed into the silica aerogel, forming an amorphous iron oxide/SiO₂ composite after slow oxidation in air. Treatment of this material with additional Fe(CO)₅ produced an Fe₃O₄/SiO₂ aerogel composite. Fe₃O₄ particle sizes were 20–55 nm. After additional heat treatment, this composite exhibited soft ferromagnetic behaviour with a coercivity of ∼170 Oe. Fe₉S₁₀ crystals with diameters of 30–90 nm were formed by the reaction of the amorphous iron oxide/SiO₂ composite with H₂S at 900 °C.