-The experimental conditions were optimized for the synthesis of amorphous SiO 2 particles by the reaction of neutralization of sodium silicate solution with H 2 SO 4 solution. Amorphous SiO 2 particles were characterized by XRD, FT-IR, FE-SEM, EDS and microelectrophoresis. The amorphous peak was located at 2θ = 21.8 o in the XRD pattern. Primary SiO 2 particles were ~ 15 to ~ 30 nm in size and they aggregated into bigger particles. Amorphous SiO 2 particles showed a specific surface area up to 130 m 2 g -1, dependent on the parameters of the precipitation process. The EDS spectrum of amorphous SiO 2 particles did not show contamination with sulfate or other ions, which cannot be excluded in traces. pH zpc =1.7 was obtained by microelectrophoresis.

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