Mechanism of cordierite formation obtained by the sol–gel technique

The mechanism of cordierite formation obtained by sol–gel method was studied using DTA and XRD techniques to follow the reactions occurring during gel calcination up to full cordierite conversion (1300 °C). Aluminum acetate gel, tetraethylorthosilicate (TEOS), magnesium acetate solution, ethanol and phenol–formaldehyde resin were used as starting materials to obtain the gel. Spinel and magnesium–aluminum silicate (XRD card: 35-0310) are formed at the beginning of calcination, followed by the formation of quartz, sapphirine and cristobalite. At 1203 °C, crystallization of cristobalite is observed as an exothermic reaction; then, at 1246 °C, other exothermic reactions between spinel and the remaining amorphous silica, and lastly between cristobalite, sapphirine and magnesium–aluminum silicate produce cordierite.When the calcination was performed in a strongly reducing atmosphere followed by a second calcination at 1000 °C in air, a porous cordierite material with a sharp pore size distribution was obtained.