Coating of Inorganic Oxides on Monodisperse Particles by Seed Growth Method

Monodisperse silica seed particles were coated with silica, titania and iron oxide by a seed growth method that employs the hydrolysis and condensation of the metal alkoxides (tetraethoxysilan (TEOS), titanium tetraisopropoxide (TTIP) and iron tri-n-butoxide (TNBI)). The resultant composite particles kept the characteristics of monodisperse particles. Electroconductive particles were prepared by nitriding the titania-coated particles. The nitriding of the composite particles were carried out with ammonia gas in a tube furnace at various temperatures. The surface of titania-coated particles changed to titanium nitride at a temperature higher than 700°C, and the electroconductivity of the composite particles was high enough for the practical usage. Magnetic particles were also prepared by reducing the iron oxide coated silica particles with hydrogen gas at 500°C. The particles could be used as the model particles such as an EMR fluid although the magnetic property was relatively poor.