With Si(OC2H5)4 as raw material

ultrafine SiO2 powder was prepared by the alkoxide-hydrolysis method under ultrasonic irradiation.XRD

SEM

FT-IR and DTA were used to characterize the phase

micro-morphology

functional group structure and thermal stability of SiO2 powder.The results indicated that the regular mono-disperse ultrafine spherical SiO2 particles were amorphous with uniform size and narrow size distribution.There existed much hydroxyl in SiO2 powder

which could be eliminated by calcining.The crystal form began to transform to cristobalite at 1150℃

and transformation was completed at 1200℃.The growth mechanism of SiO2 particle was also discussed by observing the morphologies of samples at different stages of the preparation process.