2.4 Thermal analysis
The thermal transformations of the gel were followed by differential thermoanalysis (DTA) and
thermogravimetric analysis (TGA) using a thermobalance and alumina as reference. A few
milligrams of dried gel placed in side a microbalance were pyrolyzed under nitrogen from ambient
temperature to 800°C with a constant heating rate of 10°C/min.
2.5 Adsorption-desorption isotherms
Measurements are performed using a Micrometrics equipment ASAP 2020. We use N2 at the
temperature of 77K. Before adsorption, all samples were degassed in vacuum at 250°C during 15
hours. This technique of gas adsorption gives access to the specific surface SBET (m2
.g-1).
Determination of specific area was carried out taking 16.2 Å2
as cross sectional area of N2.
2.6 Scanning electronic microscopy
The images of SEM were obtained with a Hitachi S-2600N apparatus, using a detector of secondary
electrons.