A method of treating particulate titanium dioxide, the method comprising: i) providing particulate titanium dioxide, wherein the particulate titanium dioxide is coated with aluminium oxide, and/or includes within its crystal structure aluminium oxide in molar excess of the amount required to compensate any Nb 2 O 5 in said crystal structure; and then ii) treating the particulate titanium dioxide with a coating agent that is an alkylphosphonic acid or ester thereof, wherein the alkylphosphonic acid has a C6-C22 alkyl group, and steam micronizing the particulate titanium dioxide, wherein the vapour exit temperature from the steam micronizer is 150°C or higher, so as to obtain a micronized particulate titanium dioxide that is provided with coating agent at its outer surface; wherein the coating agent is represented by the formula: wherein: R is an alkyl group or a cycloalkyl group containing from 6 to 22 carbon atoms, R 1 and R 2 are each independently selected from hydrogen, an alkyl group, a cycloalkyl group, an aryl group and an aralkyl group, and the R 1 and R 2 groups each independently contain up to 16 carbon atoms; and wherein the amount of the coating agent added, when measured as an amount of phosphorus by weight with respect to TiO 2 , is from 0.1% to 0.2%. i) providing particulate titanium dioxide, wherein the particulate titanium dioxide is coated with aluminium oxide, and/or includes within its crystal structure aluminium oxide in molar excess of the amount required to compensate any Nb 2 O 5 in said crystal structure; and then ii) treating the particulate titanium dioxide with a coating agent that is an alkylphosphonic acid or ester thereof, wherein the alkylphosphonic acid has a C6-C22 alkyl group, and steam micronizing the particulate titanium dioxide, wherein the vapour exit temperature from the steam micronizer is 150°C or higher, so as to obtain a micronized particulate titanium dioxide that is provided with coating agent at its outer surface; wherein the coating agent is represented by the formula: wherein: R is an alkyl group or a cycloalkyl group containing from 6 to 22 carbon atoms, R 1 and R 2 are each independently selected from hydrogen, an alkyl group, a cycloalkyl group, an aryl group and an aralkyl group, and the R 1 and R 2 groups each independently contain up to 16 carbon atoms; and wherein the amount of the coating agent added, when measured as an amount of phosphorus by weight with respect to TiO 2 , is from 0.1% to 0.2%. wherein the coating agent is represented by the formula: wherein: R is an alkyl group or a cycloalkyl group containing from 6 to 22 carbon atoms, R 1 and R 2 are each independently selected from hydrogen, an alkyl group, a cycloalkyl group, an aryl group and an aralkyl group, and the R 1 and R 2 groups each independently contain up to 16 carbon atoms; R is an alkyl group or a cycloalkyl group containing from 6 to 22 carbon atoms, R 1 and R 2 are each independently selected from hydrogen, an alkyl group, a cycloalkyl group, an aryl group and an aralkyl group, and the R 1 and R 2 groups each independently contain up to 16 carbon atoms; and wherein the amount of the coating agent added, when measured as an amount of phosphorus by weight with respect to TiO 2 , is from 0.1% to 0.2%. <EOS>