IR SURFACE CHARACTERIZATION OF SOME TIO2-BASED PIGMENTS .1. PREPARATION OF PIGMENTARY MATERIALS

Several preparations of TiO2 (anatase) containing different additives, bound to play different roles either temporarily during the sintering process or permanently, in the final pigment, have been studied by in situ FTIR spectroscopy. The samples were examined by checking the changes of the background spectra as well as the room-temperature adsorptive properties toward pyridine (py) on varying the oven firing temperature, from the starting gel phase (300 K) to the final pigmentary product stage (1185 K). Up to a firing temperature of almost-equal-to 1047 K, no appreciable differences can be noted in the behavior of the various preparations, and the gradual spectral changes observed mainly involve the degree of surface hydration and the surface coverage/decomposition of sulfate groups deriving from the preparative process. These two parameters affect the relative importance of the Lewis and Bronsted surface acidity. For firing at T > 1073 K, the various preparations start differing appreciably: the elements added to the TiO2 matrix in the gel precipitation stage tend to segregate (to a variable extent) at the surface of the solid and modify the surface acidic behavior of the sintering pigmentary material.