Synthesis and Characterization of ceramic pigments based on Co- MgTi2O5 pseudobrookites and effect of Zn co-doping

Abstract

Different titanate-based structures are being investigated in the last years as a new or emergent family of ceramic pigments. For this reason, this investigation is based on Co- MgTi2O5 pseudobrookites. The first objective is the synthesis and characterization of these pigments and the second objective is analyzing the effect of zinc co-doping, observing its influence on their stability against decomposition, the possible modification of their optical properties and also their pigmenting performance within ceramic glazes. Solid solutions of Mg1-xCoxTi2O5 (x=0.05, 0.1, 0.2, 0.4) and Mg1-x-y Cox ZnyTi2O5 (x=0.05, 0.1, 0.2 and y=0.2) pseudobrookite (karrooite) were prepared by traditional ceramic route using fast firing conditions (1200 ºC/3h). Fired powders were characterized by X-ray diffraction (XRD), enameling of the samples with different glazes, ultraviolet visible spectroscopy (UV-Vis) and colorimetry CIE-L*a*b*. XRD results confirmed the effective formation of solid solutions of (Co,Zn,Mg)Ti2O5 and the presence of seconday phase ilmenite. More intense and darker green colorations were obtained with increasing Co-doped. This colour is associated with electronic transitions of Co+2 in octahedral environments. The colouring potential of the pigments was tested by applying them in different industrial double-firing transparent glazes. Green colour was obtained using a high temperature glaze (1050 °C, CaO- and ZnO-enriched glazes) being less stable pigments in low temperature glazes which had blue colour. This colour is associated with Co+2 in tetrahedral environments. Selected compositions were also prepared using an unconventional method, metalorganic decomposition route (MOD), and rapid firing conditions (1000-1200 °C). The objective was to analyze the advantages in reactivity, chemical stability and colorimetric properties. XRD confirms an improvement of reactivity but colour only presents a slightly change.