Effect of Sol Concentration on Properties of Alumina Aerogels

Alumina aerogels have been prepared from aluminum chloride hexahydrate using propylene oxide as a gelation agent followed by supercritical drying in CO2. Lyogels have been obtained using sols with concentration from 0.063 to 0.567 mol/L. When sol concentration decreased, gelation time increased from 2 to 25 min while specific surface area of aerogels remained almost constant within 335 to 406 m2/g. Samples obtained from sols with higher concentration contained larger number of macropores. The microstructure of samples has been studied by scanning electron microscopy, it was independent of sol concentration. All samples were amorphous when studied by X-ray fluorescent analysis. Concentration limit of gelation was 0.251 mol/L.