Acid-catalysed Al2O3 sol and its gel material: influence of HNO3 content and stability

Abstract

A series of Al2O3 sols were prepared by HNO3 catalysis of aluminum isopropoxide (AIP), using different molar ratios of HNO3/AIP (nH). The changes in sol densities, viscosities, refractive indices, stability and particle sizes were reported. Derived properties such as Gibbs energies (ΔG*) and the reaction rate constant (k) have been calculated from the experimental density and viscosity data. The phase-chemical structures of Al2O3 materials were characterized using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) measurement. The results show that, when the molar ratio of HNO3/AIP is 0.25, the prepared Al2O3 sol was transparent, uniform and stable, and the sol average particle size gets the minimum. The chemical structure of the non-calcined Al2O3 gel material is dominated by Al–O–H and Al–O bonds. After calcination at 350 °C, the Al–O–H bond will break and is transformed into Al–O bonds, and the phase structure is changed from γ-AlOOH to γ-Al2O3.