Monodisperse colloidal silica particles were obtained in the ethanol medium in the presence of TEOS as silicon source and ammonia as catalyst.Transmission electron microscope and laser scattering particle analyzer were used to determine the average particle size.The effects of the amount of ammonia and water,the concentration of TEOS and the type of solvents on particle sizes were investigated.The formation mechanisms of the SiO_2 particles under these conditions were also studied and discussed.The results ...