Effect of Aluminum Doping on the Performance and Microstructure of Methyl-Modified SiO2 Sol

Abstract

With methyltriethoxysilane as hydrophobic precursors and aluminum isopropoxide as the aluminum source, the Al₂O₃/SiO₂ sols and their gel materials were prepared. The effects of aluminum content (n_Al) on the viscosity (η), density (ρ), reaction rate constant (k), Gibbs energies of activation for viscous flow (ΔG*), particle size of Al₂O₃/SiO₂ sols were studied. And the high temperature calcined materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The results show that, with the increase of n_Al, the η, n and ΔG* values of the Al₂O₃/SiO₂ sols decrease while the k and ρ values and average particle sizes increase. There is strong intermolecular interaction between the Al₂O₃ and SiO₂ sol molecules. The Al-O-Si bond exists in the Al₂O₃/SiO₂ materials before and after calcination at 350?°C. Calcination at 350?°C in N₂ atmosphere can change the phase structure of Al₂O₃/SiO₂ sample greatly, which can make the γ-AlOOH in the Al₂O₃/SiO₂ gel material convert to γ-Al₂O₃ through dehydration.