Effect of calcination atmosphere and Fe3+ content on NiFexAl2-xO4 nano pigments synthesized via a polyacrylamide gel method

In this research, NiFexAl2-xO4 pigments (x=0, 0.3, 0.7, and 1.5) were synthesized using a polyacrylamide gel method, and the effects of calcination atmosphere and the dopant amount on the formed phases and optical properties were investigated. The obtained pigments' physical, optical, and microstructural properties were clarified using the XRD, UV-Vis spectroscopy, and FESEM techniques. The phase analysis showed that the nickel carbide was formed in the reducing atmosphere instead of the spinel phase. So, the rest of the samples were prepared in an oxidizing atmosphere. The pigments that were obtained had a spherical morphology and a narrow particle size distribution due to the growth inhibitor role of the polyacrylamide network. The iron ions entered both tetrahedral and octahedral sites of the nickel aluminate structure, acted as the main chromophore, and turned the color from cyan to brown. Further addition of iron led to the darkening of the brown color.