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Development of Zn-Al-Cr-O spinel ceramic color pigment nanopowders by pechini method

The objective of this study was to investigate the Pechni processing as a synthesis method for producing spinel-type color pigments commercially employed in ceramic glazes for decoration purposes. The synthesis was carried out through polymeric precursors assisted in the gelation and combustion processes. Calcination temperatures were varied in order to probe phase formation of the spinel phase. Calcining at higher than 500°C was required for proper removal of unwanted residues. Thermal decomposition and behavior could be further reflected by infrared spectroscopy. Raman spectroscopy pointed to the possible cationic substitution, resulting in formation of solid solution in the complex spinel oxide. Successful substitution of Cr in the Zn lattices has been further confirmed by XRD from which only a single phase was observed as also confirmed by lattice refinement which revealed an increase in lattice parameter. The oxidation of chromium chromophore was found to be 3+ from XPS. Well-faceted particles with an octahedron shape could be observed in the Cr-doped composition, indicating a high degree of crystallization in the F3dm system. Incorporation of Cr into the octahedrally coordinated Al lattice induced strong absorbance at 410 nm. From the crystal field theory, a change from the ground state to the excited state in this system involved absorbance in the 550 nm range (yellowish green), yielding a pink tone in these pigments. The stability of the synthesized color pigments in low-fire glaze has been examined by several techniques instead of simply just probing changes in the CIELab parameters by colorimetric method.