Thermal synthesis of NiMn₂O₄ spinel employing Mn oxide ores as starting material

Abstract

It is described for the first time the synthesis and characterization of NiMn₂O₄ employing the Mn ores from the Amazon Region as starting material, instead of using commercial reagents as normally occurs in its synthesis process. Initially, an Mn ore was transformed into a single product, the octahedral layer (OL) manganese oxide with Ni²⁺ ions interlayer (Ni-OL-2), which was used as a matrix to obtain NiMn₂O₄ by thermal decomposition. The following techniques were used for characterization: X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), infrared spectroscopy (FTIR), thermal analysis (TG-DTA), scanning (SEM) and transmission (TEM) electron microscopies. The results revealed that Mn oxide ore composed of nsutite mineral transformed into a well-ordered crystalline Ni-OL-2 phase, after the hydrothermal and cation exchange process. The thermal decomposition of Ni-OL-2 produced the nickel manganite phase at 850 °C with spherical ball morphology and crystal sizes in the range of 200-300 nm.

Keywords:
Amazon region; Mn oxide ore; synthesis; characterization; NiMn₂O₄