Effect of Tween 20 Concentration on Macropore Formation in Spherical Diopside Particles

We previously succeeded in fabrication of spherical diopside particles having a uniformly and continuously macroporous structure by heat treatment of silica gel particles impregnated with an aqueous mixed solution of Ca(NO3)2 and MgCl2 above 900°C [Y. Nakamura, et al., J. Ceram. Soc. Jpn., 112, 133 (2004).]. In preparing the mother silica gel particle, the nonionic surfactant, Tween 20, was employed as an emulsifier for maintaining an O/W emulsion of tetraethyl orthosilicate. In this study, we investigate influence of Tween 20 concentrations on macropore formation of spherical diopside particles. When silica gel particles prepared at Tween 20 concentration ranged from 0.75 to 15 wt% is impregnated with the Ca(NO3)2 and MgCl2 aqueous mixed solution and is heat-treated at 950°C, spherical diopside particles having macroporous structure can be fabricated. However, silica gel particles produced at 0 and 25 wt% of Tween 20 are largely unable to condense Si-OH groups and cannot crystallize to form diopside by the heat treatment, forming no macroporous structure. The nonformation of the macroporous structure in the case of the silica gel particle produced at 0 and 25 wt% of Tween 20 may be attributable to the fact that the silica gel particle is difficult for the silica gel particle to be impregnated with the Ca(NO3)2 and MgCl2 aqueous mixed solution.