Synthesis and Fabrication of Co1−xNixCr2O4 Chromate Nanoparticles and the Effect of Ni Concentration on Their Bandgap, Structure, and Optical Properties

In the present work, cobalt-chromite-based pigment Co1-xNixCr2O4 chromate powder and nanoparticles with various transition metal concentrations (x = 0.2, 0.4, 0.6, and 0.8) were manufactured by applying aqueous synthesis approaches and sol–gel synthesis routes. XRD analysis of the powder shows that all samples formulated by the sol–gel method were crystalline with a spinel structure. Chromites show green color with a higher nickel concentration, while Co-substituent shows blackish pigments. Samples were annealed at distinct temperatures ranging from 600 °C to 750 °C. The nanoparticles obtained were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (RS), photoluminescence (PL), and energy-dispersive X-ray spectroscopy (EDS). The particle size of the parent compound (CoCr2O4) ranges from 100 nm to 500 nm, as measured by SEM. The tendency of particles to form aggregates with increasing annealing temperature was observed. These compounds may be successfully used as an effective doped nickel-cobalt ceramic pigment.

Synthesis and characterization of nano-ceramic pigment Co0.5Zn0.5Al2O4 via polyacrylamide gel method

Purpose The purpose of this paper is to synthesize and characterize nano-ceramic blue pigment Co0.5Zn0.5Al2O4 via polyacrylamide gel method. Generally, the high cost and the environmental toxicity of cobalt aluminate pigments lead them to become less common and cause problems in production process. To significantly reduce this problem, it is required to reduce the cobalt in the pigment and replace the cobalt with some amounts of zinc in the structure. Design/methodology/approach In this paper, calcination temperature and its effects on phase specification and color properties of final product were investigated. The powders were studied by using XRD, FESEM, TG/DTA, FTIR, UV-Vis and colorimetric in CIELab space, in which the calcination temperatures were set to 600°C, 800°C and 1,000 °C, and the inert atmosphere was air. Findings According to the XRD patterns, single-phase spinel structure with a good crystallinity was formed even in the low temperature. The infrared spectra displayed vibrations at about 500, 560 and 680 cm−1, which were ascribed to the spinel structure. FESEM images showed nanoscale particles with an average size of 32 nm. Regarding the Co2+ spin transitions in tetrahedral sites, the UV-Vis spectra presented three bands at 552, 598 and 628 nm. Practical implications The colorimetric data indicated the formation of blue pigments corresponding to negative values of b*. The color of pigments was affected by calcination temperature. Originality/value The characterization analysis shows that a blue pigment has been obtained in this research. Different degrees of blue color were obtained at different calcination temperatures.