Structural characterization and porosity analysis in self-supported porous alumina-silica thin films

In this study, alumina, silica and alumina-silica binary (36% mol silica) thin films are synthesized using the sol-gel technique. These form the basis for future gas separation membranes. The characterization of the synthesized oxides was performed using nitrogen physisorption, X-ray diffraction (XRD), Doppler-broadening measurements on the 511 keV annihilation photon peak, together with 3γ/2γ analysis, and Fourier transform infrared spectroscopy (FTIR) of adsorbed CO. It is found that silica is microporous, γ-alumina is mesoporous, and the binary material shows fingerprints of both the meso- and microporous nature of its constituents as well as of the respective crystal structures. These results open the possibility to also investigate thin supported porous films (a few microns thick), and especially the setting and drying aspects on porous supports for membrane production, using the positron annihilation technique.