Surface modification of ultrafine precipitated silica with 3-methacryloxypropyltrimethoxysilane in carbonization process

Ultrafine precipitated silica was obtained from Na2SiO3 solutions and simulative lime kiln gas by carbonization process. The surface modification of ultrafine precipitated silica using 3-methacryloxypropyltrmethoxysilane (KH570) at the rear stage of carbonization process was investigated. The optimum synthesis condition of precipitated silica was obtained from the orthogonal tests: reaction temperature of 80 °C, limekiln gas flow rate of 1.2 L/min, sodium silicate concentration of 40 g/L and polyethylene glycol 6000 (PEG6000) concentration of 4 g/L. The modification degree and basic physicochemical properties of precipitated silica were analyzed by Fourier transformation infrared spectroscopy (FT-IR), thermogravimetry (TG) and X-ray diffraction (XRD). The result demonstrates that KH570 is mainly grafted to the silica surface by chemical bond rather than physical adsorption. Average activation index of precipitated silica is nearly 90% for KH570 dosage of 1%. After modification, the BET (Brunauer–Emmett–Teller) specific surface area and DBP (dimethyl terephthalate) absorption value of precipitated silica become smaller, while the average pore diameter becomes larger.