4. Conclusions In this study, ultrasonication method has been developed suc- cessfully to synthesize colloidal nanosilica using silica fume as a suitable source material of silica. It was found that proper utiliza tion of ultrasound waves not only reduces the processing time, but also can significantly reduce production expenses. The obtained results confirm that application of ultrasonic waves with the power and frequency of 30 w and 20 kHz, respectively, for only 15 s easily break down the silica gel microstructure into a col can solution with 80.7% of particles demonstrating loidal sizes less than 50 nm. The results also confirm that continued son- ication results in significantly lower size reduction rates with evi- dences for some particle agglomeration.