Thermally activated sintering–coarsening–coalescence-polymerization of amorphous silica nanoparticles

Abstract An onset sintering–coarsening–coalescence-polymerization (SCCP) event of amorphous SiO 2 nanoparticles (ca. 40–100 nm in size) by isothermal firing in the 1150–1300 °C range in air was characterized by an N 2 adsorption–desorption hysteresis isotherm coupled with X-ray diffraction and vibrational spectroscopy. The apparent activation energy of such a rapid SCCP process was estimated as 177±32 kJ/mol, based on 30% reduction of a specific surface area with an accompanied change of medium range orders, i.e. forming Si 2 O 5 while retaining the Si–2ndO yet losing the Si–2ndSi without appreciable crystallization. The minimum temperature of the SCCP process, as of concern to industrial silica applications and sedimentary/metamorphosed sandstone formation, is 1120 °C based on the extrapolation of steady specific surface area reduction rates to null.