Porous diopside microspheres, CaO·MgO·2SiO2, were prepared by heat treatment, at various temperatures, of spherical silica gel particles impregnated with Ca(NO3)2 and MgCl2. Spherical silica gel particles were prepared by the sol-gel method in an O/W emulsion using tetraethyl orthosilicate. When the silica gel particles containing Ca(NO3)2 and MgCl2 were heated at temperatures above 900°C, the results of X-ray powder diffractionmetry (XRD) and Fourier transform infrared spectroscopy (FT-IR) showed that the silica gels were crystallized into diopside, and scanning electron microscopy (SEM) observation revealed that a uniform porous structure was formed in the particles. The porosity in the diopside is believed to be caused by the mutual adhesion of smaller pores in the silica gel particles during the viscous sintering process.
