Au-Ag nanoparticles as red pigment in ceramic inks for digital decoration

Novel pigments, consisting of Au-Ag mixed nanoparticles, were developed for digital decoration by ink-jet printing of ceramic wares. Special attention was paid to set up a microwave assisted synthesis route, with a low environmental impact, easily transferable to large-scale production. Several suspensions, based on Au, Ag and Au-Ag mixed nanoparticles were prepared, trying to get a core-shell assemblage, and the synthesis parameters like metal concentration, Ag/Au ratio, time, temperature and chelating agent amount were optimized. The suspensions are stable over many months and a total reaction yield, assessed by ICP-AES analysis, was achieved. Particle size, shape, composition and optical properties were measured by DLS, TEM-EDS, XRD and UV-VIS spectroscopy. The so-prepared inks were applied on ceramic tiles simulating the ceramic process and the colour performance, assessed by colourimetry, were expressed in the CIELab parameters.