Structure of oxide gels and glasses by infrared and Raman scattering

Optically clear monolithic gels and fine gel powders have been synthesized using various alkoxide hydrolysis reactions. The gels have been characterized using various methods to determine their structures. (X-ray diffraction, DTA, TGA, DSC, IR and Raman spectroscopies). The spectra and the nature of gels depend on the solvent and the hydrolysis conditions (rate, pH, etc.). The use of acetone as solvent allows reduction of the hydrolysis time, from weeks to hours. If the hydrolysis of aluminium sec-butoxide is too rapid, at high pH, crystalline bayerite Al(OH)₃ is formed. Regular hydrolysis leads to amorphous optically clear gel with sometimes boehmite (or diaspore) traces. Formation of the (porous) glass (300 to 600°C) and also of the γ-alumina does not modify the Raman spectra strongly whereas large modifications are observed on IR spectra with the evolution of protonic species. The structure of alumina gel and glass is of the spinel type. The α-alumina phase grows above 1200 to 1250°C (above 1050°C if boehmite traces are present).