Effect of fluoride and sodium ions on structural and thermal properties of γ-Al2O3

Authors:

• Zenon Sarbak

Abstract

The structural properties of alumina as well as its fluoride and sodium modifications were characterized by X-ray diffraction, infrared spectroscopy and differential thermal analysis. We have shown, that fluoride ions interact with hydroxyls type Ia of γ-Al₂O₃ forming Al-F species, which then react at 400°C forming β-Al₂O₃. Morever, F/Al₂O₃ sample heated up to 400°C contain two acidic hydroxyls type IIa and III, which are also represented on a differential thermal curve as endoeffect with minima at 470 and 500°C. For Na/Al₂O₃ sample the same types of hydroxyls interact with Na⁺ ions leading to substitution of their protons. After heating at 400°C this sample contains also hydroxyls type IIa and III, which are represented by two endothermal effects with minima at 450 and 520°C. Differential thermal analysis shown to be a powerful and simple technique to characterize surface hydroxyl types of Na and F samples supported on γ-alumina.