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Hollow microspheres of titanium dioxide have been prepared by spray-drying a colloidal suspension of an exfoliated titanate followed by heating above 400 °C. The individual hollow sphere with a diameter of tens of micrometers is characterized by its extremely thin crust, tens of nanometers thick. Because 99% of the particle volume is empty, the powder is very light with an apparent density of ∼0.02 g cm-3. These microspheres can be converted into thin flaky particulates of TiO2 by gentle milling.
Iida et al. (1998) studied this question.