Synthesis and characterization of colourful aluminates based on nickel and zinc

Gradual changes in the chemical composition of spinel cause variations in the distribution of cations in sites, which affects their properties and colouration. Thus, pigments with nickel-zinc spinel structures (NixZn1-xAl2O4) were synthesized by combustion and characterized by varying the chromophore ion content (x = 0; 0.1; 0.2; 0.4 and 1) and calcination temperature (600 degrees, 800 degrees and 1000 degrees C). Characterization of aluminates through thermal analysis (TGA) showed a less than 10% mass loss until approximately 500 degrees C in not-calcined samples, indicating the combustion reaction could be classified as adequate. The spinel phase was confirmed in all samples by X-ray diffraction (XRD) with segregated phases: ZnO in samples with x = 0 and NiO in samples with x = 0.4 and 1. The post-synthesis thermal treatment at high temperature led to higher crystallinity of the material and the incorporation of secondary phases into the spinel structure. The crystallite size varied between 22.9 and 43.2 nm. Scanning Electron Microscopy (SEM) analysis indicated that the pore size increased with the increasing calcination temperature, and infrared spectroscopy indicated the displacement of the A106 band (665 cm(-1)) to A104 (730 cm(-1)) after the addition of Ni2+ ions, revealing the inversion of the crystalline structure. Colorimetric analysis by the CIELab method showed the colour of the zinc-nickel pigments ranged between white (x = 0) and cyan tones (0 < x <= 1). Furthermore, the significant influence of the chromophore ion content and calcination temperature on the colouration of the synthesized pigments was verified by the Tukey test at 5% in terms of the luminosity (L*) and chromaticity (a* and b*). The difference between dry powder and that dispersed in varnish was considered evident. The colorimetric data were used to develop a mathematical model to satisfactorily describe the values of L*, a* and b* as functions of the calcination temperature and nickel load. (C) 2019 Elsevier B.V. All rights reserved.