Nanosize silica, titania and alumina metal oxide particles are common xerographic toner additives for control of flow, charge, development and transfer. While silica is the most common and most studied oxide, titania and alumina have a more complex surface, comprised of surface acidic, basic and neutral sites. Further, superacid sites can be created by treatment with sulphuric, phosphoric or boric acids. These treated oxides show increased negative charge and admix when used as toner surface additives. For titania the charge increases with the acidity of the acid, in the order: boric acid < phosphoric acid < sulphuric acid.Infrared spectroscopy shows that calcining results in surface attachment of these acidic sites to the TiO2 surface. Further, these acidic sites, which involve about 5% of the total hydroxyl sites, can form ionic salts with triethylamine, a result of proton transfer from the acid to the amine. This results in a further increase in charge, and improvement in toner admix rates and RH sensitivity.
Richard P. N. Veregin, Carl P. Tripp, Maria N. V. McDougall, "Chemical Surface Modification of Alumina and Titania Surface Additives for Charge Control of Xerographic Toners" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP15), 1999, pp 561 - 564, https://doi.org/10.2352/ISSN.2169-4451.1999.15.1.art00046_2