Studio microstrutturale e magnetico di nanocomposti innovativi a matrice silicea mesoporosa

This study deals with the characterization of innovative nanostructured composite materials made out of nanocrystals based on transition metals dispersed on an highly porous amorphous silica matrix. In particular, the research has been focused on the morphological, structural, compositional, and magnetic investigation of two series of nanocomposites: mesoporous ordered silica SBA16 containing iron-cobalt alloy nanocrystals, and silica aerogel embedding zinc ferrite nanocrystals. The materials have been investigated both by conventional (bright field and dark field imaging, electron diffraction) and advanced (high resolution transmission electron microscopy, and high resolution scanning electron microscopy in high annular angle dark field mode) electron microscopy techniques. Scanning transmission measurements have been combined with simultaneous X-ray energy dispersion spectroscopy measurements. The results obtained from the microscopy investigation have been compared with the information obtained by the Xray diffraction study of the same materials. The magnetic behavior has been investigated by ZFC-FC static and dynamic magnetization measurements, by thermoremnant magnetization, by isothermal hysteresis cycles, and by Mössbauer spectroscopy. The ZFC-FC experimental magnetization curves have been fitted though a simplified model by a FORTRAN code which has been defined, optimized, and implemented with a user-friendly graphic interface. The aim of this study it to highlight the key role of advanced characterization in determining and interpreting the chemico-physical properties of nanocomposite innovative materials. The two series of materials investigated in this work have been selected mainly in view of the peculiar morphological features of the porous matrix (silica aerogel and mesoporous silica with cubic symmetry) as well as in view of the functional catalytic and magnetic) properties of the resulting nanocomposite. The results enabled to define the features of the nanocomposites responsible for their functional properties, such as: composition, crystallinity, shape, size and size distribution of the nanophase, and its dispersion within the porous matrix. Particular attention has been given to the correlation between chemico-physical features of the nanocomposites and interpretation interpretation and prediction of the magnetic behavior.