Add to ORKGAmorphous monodispersed silica spheres with particle size smaller than 0.8 μm were synthesized from the system Si(OC_2H_5)_4-NH_3 (or amine derivative)-H_2O-C_2H_5OH (or n-C_3H_7OH) in the temperature range 1.5-20°C. Silica particles grew larger at lower reaction temperatures. A linear correlation was observed between concentration of ammonia in the range of 0.5-4.0mol/l and average particle size of the silica. Plots of particle size against the concentration of water showed a maximum at about 8mol/l. Under a constant concentration of amine derivative, the growth rate of silica particles increased in the following order; (C_2H_5)_3N<(CH_3)_3N<(C_2H_5)_2NH<(CH_3)_2NH<CH_3NH_2. The diameter of silica spheres decreased to 3/4 of its initial di...