The sol-gel method was used to prepare iron oxide-silica nanocomposite mate
rials. Different drying conditions were used in order to obtain aerogel and
xerogel materials. The samples were characterized by thermal analysis, X-r
ay diffraction (XRD), N-2-physisorption and transmission electron microscop
y (TEM) techniques. Aerogel samples have a much higher surface area than th
e xerogel samples; moreover, different supercritical drying conditions give
rise to a different porous structure. The stabilization of the maghemite p
hase in the xerogel nanocomposites depends on the iron content and it is mo
re difficult in the aerogel samples. The early sol-gel preparation stages a
lso play an important role. (C) 2001 Elsevier Science B.V. All rights reser
ved.