Novel nano‐composite particles: titania‐coated silica cores

The purpose of this paper is to develop methods to produce white composite pigments consisting of a silica core with a titania shell.

Silica cores were coated with titanium dioxide (TiO₂) via forced hydrolysis of a solution prepared from titanium tetrachloride (TiCl₄). The morphology, surface charge and particle size of obtained composite particles were studied.

Dispersions of well‐dispersed composite particles, having silica cores of uniform size in the range from 300 to 500 nm with a homogeneous titania coating are obtained. The coating thickness corresponded to 150‐400 per cent by weight of titania based on the core. Modification of the silica core by incorporation of 1.5 aluminosilicate sites per square nanometre of core surface proves to be favourable in achieving a homogeneous coating on the silica core. Deposition of such titania coating is also favoured by agitating the dispersion well, keeping electrolyte content low, maintaining pH at 2.0 and the temperature at 75°C during the coating process.

Only TiCl₄ is used as titania source. In addition, only silica cores obtained by Stöber synthesis are used while commercially available silica solutions made from sodium silicate are not used.

The process offers a method of producing a white composite pigment with a narrow particle size distribution in order to maximise light scattering as well as using a core with lower density than the shell. This kind of particle would be of interest for coating applications and white inorganic inks.

The developed method provides a straightforward process to produce well‐defined composite particles.