Particle surface treatment

A method of treating particulate titanium dioxide, the method comprising:

• i) providing the particulate titanium dioxide comprising a crystal structure, wherein the particulate titanium dioxide comprises aluminum oxide within the crystal structure in a molar excess of an amount required to compensate any Nb2O5 in the crystal structure;
• and then
• ii) treating the particulate titanium dioxide by adding a coating agent that is an alkylphosphonic acid or an ester thereof, the alkylphosphonic acid comprising a C6-C22 alkyl group, and steam micronizing the particulate titanium dioxide with a steam micronizer so that a vapor exit temperature from the steam micronizer is 150° C. or higher, so as to obtain a micronized particulate titanium dioxide that is provided with the coating agent at an outer surface,
• wherein,
• the molar excess of the aluminum oxide in the crystal structure of the particulate titanium dioxide to be treated is from 0.2% to 2% on a molar basis.