Crystal structure and size evolution of nanoparticles during heating of ceramic inks by synchrotron x-ray diffraction

Ceramic inks based on titania or spinel nanoparticles are gaining more and more industrial interest in different fields (e.g. photocatalysis and ink-jet printing decoration). The ink performance and behaviour depend widely on crystal structure and size of as synthesized nanoparticles and on the evolution of these features during heating as well. A direct determination of the crystal structure of nanoparticles (10-30 nm observed under TEM) both dried as powders and dispersed in the ink was performed by temperature-resolved synchrotron X-ray powder diffraction (ESRF Grenoble, GILDA line). Phase transformations and the evolution of unit-cell parameters and crystallite size were monitored during heating up to 900 °C of TiO2 (pure and co-doped with Cr+Sb and V+Sb). Titania inks phase composition and crystallite size depend upon type of dopants and synthesis method. More in details, when the synthesis was carried out in glycol, crystallite size ranges between 5 and 10 nm up to 240°C and the only phase detected is anatase up to 700°C when rutile begins to appear. Whenever the synthesis is carried out in water, crystallite size ranges between 5 to 6 nm up to 100°C and the samples is biphasic (anatase plus brookite) while rutile begins to appear at 430°C. In vanadium doped samples, anatase completely transformed in rutile in less than 50°C, starting from 690°C, while in Cr-doped samples the only phase detected up to 950°C was anatase.