Surface Modification Of Nano-silica

The surface modification of nano-silica was studied in the fixed bed and vibro-fluidized bed by using nano-silica as raw material, methanol and water as modification assistant agent, hexamethyldisiloxane and dimethyldichlorosilane as modification agent, dry method as preparing process in this paper. The effect of some factors such as sorts of modification agent, amount of modification agent, preprocessing temperature, preprocessing time, reaction temperature, reaction time, blowing time, sorts of modification assistant agent, amount of modification assistant agent, amplitude and frequency on hydroxyl number on surface of nano-silica was investigated. Hydroxyl number on surface of nano-silica was measured by the titrimetric method.The results through investigating surface modification of nano-silica in the fixed bed were showed that nano-silica could be modified by hexamethyldisiloxane, dimethyldichlorosilane, memyltrimethoxysilane and octanol. The hydroxyl number on surface of nano-silica is reduced prominently by hexamethyldisiloxane and dimethyldichlorosilane. The better modifying conditions were obtained. These process conditions are amount of modification agent 55%, reaction temperature 300℃, reaction time 15 minutes, preprocessing temperature 300℃, preprocessing time 15 minutes, blowing time 7.5 minutes. A small quantity of methanol obviously accelerated the surface modification reaction of nano-silica by using hexamethyldisiloxane or dimethyldichlorosilane as modifying agent. A small quantity of water also obviously accelerated the surface modification reaction of nano-silica by using hexamethyldisiloxane as modifying agent, but not by using dimethyldichlorosilane as modifying agent.The results through investigating surface modification of nano-silica in the vibro-fluidized bed indicated that the hydroxyl number on surface of nano-silica could be reduced obviously by hexamethyldisiloxane. but small by dimetliyldichlorosilane. The better modifying conditions are amplitude 0.5mm, frequency 18Hz, amount of modification agent 55%. reaction temperature 300℃. reaction time 15min, flux of N₂ 1.5m³/h, preprocessing temperature 300℃, preprocessing time 15min, blowing time 7.5min. A quantity of water obviously accelerated the surface modification reaction of nano-silica when hexamethyldisiloxane was used as modification agent. But methanol has a small effect on the surface modification reaction of nano-silica by hexamethyldisiloxane as modification agent.It was showed through measuring sedimentation of nano-silica with different hydroxyl number in ethanol and water, water contents of storage as well as influence on viscosity of paraffin that the less hydroxyl number of nano-silica, the better the solubility in organic solvent, the less the water content. It was proved by the infrared spectra that some of hydroxyls on nano-silica surface are substituted by methyl group of modification agent. It indicated through SEM and TEM that the less hydroxyl number of nano-silica, the better its dispersibility, the less size of agglomeration.