In order to investigate the effects of nanosized metallic palladium loading and calcination on the characteristics of composite silica, the silica was prepared by sol-gel technique, leading to an amorphous solid with mesoporosity, and the pore size distribution is narrow, centered at 35nm. The composite silica was formed by impregnating palladium precursor into the porous network with sequel calcination in hydrogen. The results show that the nanosized palladium as guest phase in the composite silica is subjected to the mesoporous structure and calcination, resulting in the changes of optical adsorption that red-shifted to higher wavelength with the palladium loading and the heating temperature. The tailoring of the optical properties can be ascribed to the effect of the nanosized metal particles and interactions occurred between palladium and silica.

Nanosized palladium particles were incorporated into mesoporous silica matrix to obtain nanocomposites using the sol-gel technique. Effects of the finely dispersed metallic palladium on the microstructure and properties of the nanocomposites were investigated. By means of X-ray diffraction and optical absorption, it was found that palladium particles were 5～9nm in diameter and their uniform dispersion in the mesoporous silica depended on both the content of the palladium and the structural features of the silica matrix. The results showed that the mixing method of preparation led to wider size distribution of the nanosized particles as compared to the immersion method, but dispersed degree was reduced. Although the incorporation of nanosized palladium particles could not substantially induce significant structural changes of the matrix, the apparent red-shifted optical absorptions for the nanocomposites were observed as compared to the parent monolithic silica, particularly with increase in palladium loading and calcination temperature.

The interfacial defects of hard magnetic Pr-Fe14B phase from amorphous to nanostructures have been investigated by positron lifetime spectroscopy. The nanostructure was produced by melt-spinning and nanocrystallization route. The two main components can be ascribed to vacancy-like defects in the intergranular layers or the interfaces, and microvoids or large free volumes with size compared to several missing atoms at the interactions of the atomic aggregates or the crystallites. The remarkable changes in the positron lifetimes from the amorphous structure to the nanocrystructure with varied sizes can be interpreted, indicating that the structural transformation and the grain growth induce the defect changes occurring at the interfaces with different shapes and sizes.

The preparation and optical characterization of nanocomposites comprised of palladium into mesoporous silica are presented in this paper. Introduction of palladium was conducted through two different routes involving the sol-gel technique. In the first route, monolithic porous silica produced by hydrolysis of alkoxides in advance was then impregnated into the concentrated solution containing palladium precursor, and the nanocomposite was manufactured after a sequent thermal treatment. In the another route, a mixture made with the alkoxides and palladium precursor added in water was stoichiometrically prepared with the hydrolysis and condensation reactions, resulting in a formation of the composite silica gel. The introduced palladium particle was subjected to the matrix, varied with the composition and found to be 5-10nm in scale. The optical absorption measurements show that the edges were red-shifted to a certain extent with an increase in the composition and heated temperature. The changes can be responsible for the interactions between the matrix and the introduced phase. IR characterization for the monolithic silica and the nanocomposites was also performed for the further explanation.