Synthesis and optical properties of Ilmenite pigments containing Mg, Zn and Co(Mg0.8- xZnxCo0.2TiO3)(x=0;0.2;0.4;0.6;0.8)

Abstract

The present work studies the synthesis, stability and optical properties of new Mg ilmenite (MgTiO3) pigments doped with Co and Zn (Mg0.8-xZnxCo0.2TiO3) which have been prepared by means of the MOD-citrate route (metal-organic decomposition of citrates). The pigments obtained have been submitted to different calcination temperatures (600, 800, 900, 1000 and 1200 C), characterized by X-ray diffraction (XRD) and the reactivity, formation and stability of the ilmenite solid phase have been studied for the different temperatures, analyzing the effect of increasing amounts of Zn2+. Morevoer, the UV-vis-NIR electronic absorption spectra have been examined (300-2500 nm) correlating the color based on the incorporation of the chromophore (Co+2) in the octahedral (Oh) and tetrahedral (Td) sites present phases (Ilmenite, Spinel, pseudo-Brookite). Their stability and yield as a pigment in a conventional double cooked ceramic glaze (1050°C) has been analyzed. It has been noted that the Zn+2 ions can be incorporated into Mg ilmenite (geikielite) structure doped with 20 mol% Co (Mg0.8-xZnxCo0.2TiO3) forming a solid solution up to a molar amount compressed between 40 (x = 0.4) and 60% (x = 0.6). For compositions with a larger amount of Zn (x = 0.6 and 0.8) a mixture of Mg-Ti phases coexists (M2TiO4 spinel, MTi2O5 pseudobrookite and MTiO3 ilmenite), in which ilmenite is still the predominant phase at low (600 C) and intermediate temperatures (800-1000 C), while the spinel phase appears at 800 C and becomes the predominant phase at high firing temperatures (1000 and 1200 C) and high Zn doping (x= 0.8). The prepared compositions were finally tested as potential ceramic pigments for the coloration of a conventional ceramic glaze. However, all the fired pigments were not stable enough to withstand the glazing process (firing at 1050 ºC as it was demonstrated by in the glazing process the pigments were used a temperatures 600, 800, 900, and 1200°. As a result, they did not survive the glazing process as demonstrated by the blue-violet coloration of the glaze, which is characteristic of the tetrahedral transitions of Co+2 when incorporated to the vitreous phase.