Electron Microscopic Observation of Coatings on Titanium Dioxide Pigments

Abstract

IT is common practice in the final stages of the manufacture of titanium dioxide pigments to apply coatings to the crystal surfaces, in order to reduce their photochemical activity and improve their dispersibility in various media. These coatings often take the form of 1–3 per cent of oxides or hydrated oxides precipitated in an aqueous dispersion of the pigment. It is important to know whether the products are truly coated pigments, merely mixtures of the pigment and coating material, or something between the two extremes. For a uniform coating, the thickness to be expected is about 50 Å, or one-fiftieth of the crystal diameter.