Structural investigation and optical properties of cobalt aluminate pigments derived from thermal decomposition of mixed-metal nitrate co-crystals

Color stability of blue aluminates obtained from recycling and applied as pigments

“…29 The homogeneous coloration observed in the samples is associated with the formation of monophase aluminates since there is no presence of possible interferents such as Al 2 O 3 . 15 The aluminates obtention samples caused a decrease in crystallinity (Table 1) compared to the Al 2 O 3 sample due to the difference in the ionic radius of these metals that can cause deformations in the crystal lattice. 30…”

“…4b and c) refer to Al-O vibrations, indicating greater organization in normal spinel-like structures. 15 In the NiAl 2 O 4 sample, the signal extending from ∼470 to 650 was associated with the normal cubic spinel Fd3m of NiAl 2 O 4 . 34 The low-intensity band centered at 780 cm −1 can be associated with metal-Ni-oxygen bonds.…”

“…This was due to the structural arrangement of aluminates in the spinel form, which is stable even in harsh environments. 15,48 Fig. 13 shows the graph DE vs. exposure time of the samples in both environments studied, and it is possible to see that the least stable coloration in both environments was the one obtained with the NiAl 2 O 4 sample, indicating lower stability compared to cobalt aluminate.…”

“…This phase presents a cubic arrangement, 28 where the divalent cations (Co 2+ ) occupy 1/8 of the tetrahedral sites of this structure. 15 Whereas in the XRD of the NiAl 2 O 4 sample (Fig. 3d), only the crystallographic phase of nickel aluminate [96-900-1433] was observed.…”

“…Aluminates have been widely used as dyes and pigments due to their structural arrangement in the spinel form (A 2+ B 2 3+ O 4 2− ) that allows the insertion of chromophore ions, which guarantee intense color and high thermal stability, in addition to resistance to chemically aggressive environments. 15,16 The synthetic routes most used to obtain aluminates are coprecipitation, 17 mixed oxide calcination, 18 solid-state reactions, 19 and the sol–gel method. 20 In addition, there is the possibility of recycling aluminum to be used as a pigment precursor, 17 providing a more sustainable synthesis compatible with the circular economy concept, which is based on reducing, repairing, recycling, remanufacturing, and redirecting the materials life cycle, 21,22 contributing to the production of more sustainable materials.…”