EFFECT OF MECHANICALLY MIXED ZNO ON THE EVOLUTION OF PORE STRUCTURE OF SIO2 UPON THERMAL-TREATMENT

N-2 adsorption at 77 K was used to follow the change in the pore struc ture of silica (mesoporous) produced on heating at 300 and 600 degrees C in the presence of different contents of mechanically mixed ZnO (15 -85 mol%). Heating of pure silica at 300 degrees C caused pore narrowi ng. This proceeded differently in the presence of ZnO, the pore system being split into two ranges of limited sizes. The pore widening effec t upon heating silica at 600 degrees C was greatly reduced upon the ad dition of ZnO, to the extent of the evolution of some micropores at lo w levels of ZnO. At both heating temperatures, the composition 30% ZnO represented a transient state through the flux of pore system change. The IR spectra indicated that at this composition the silica particle s are more oblate. The pore structure variations due to heating at the examined temperatures correlated with the solid-state reactions that take place at 1000 degrees C, where the spinel Zn2SiO4 is detected.