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Published in Zbigniew Galazka, Transparent Semiconducting Oxides, 2020
In2O3 crystallizes in a body-centered cubic structure (space group Ia3 ), which is named after the mineral bixbyite (Fe,Mn)2O3. The structure can be derived from the fluorite (CaF2 = ½Ca2F4) structure by removing one-quarter of the anions and a subsequent shift in the remaining ions [99]. As a consequence of this shift, the cations are surrounded by distorted octahedra. Three-fourths of the cations are on the Wyckoff position d (site symmetry 2) and one-fourth on the Wyckoff position b (site symmetry з̄); these positions are marked in Fig. 5.1 by blue or red circles, respectively. It results in two inequivalent In sites In1 (¼, ¼, ¼), and In2 (u, O, ½) and one O site. Both In1 and In2 are six-fold coordinated, surrounded by O atoms, while all O atoms are four-fold coordinated to In atoms. The local structure of In1 is highly symmetric, while the local structure of In2 is less symmetric. The local structure of O forms a distorted tetrahedron with all four In–O bonds inequivalent [100]. Indeed, the refined crystal structure given by Marezio [101] revealed equal In1–O bond lengths of 2.18 Å, and different In2–O bond lengths of 2.13, 2.19, and 2.23 Å. The measured lattice parameter of a single crystal is 10.117 ± 0.001 Å. The In2O3structure contains 80 atoms in a unit cell.
Investigation of transformations of low-grade manganese ore during the roasting process
Published in Mineral Processing and Extractive Metallurgy, 2023
Heba Ali, Mohamed El-Sadek, Hesham Ahmed
The isothermal roasting of Umm-Bogma low-grade manganese ore in air atmosphere has been studied at temperatures up to 1200°C. The findings can be summarised as follows. The composition of the manganese ore was effectively controlled by the roasting temperature. It was observed that at 500°C MnO2 transformed to Mn5O8, and then the Mn5O8 decomposed to bixbyite (Mn2O3) at 600°C, while at 800°C bixbyite (Mn2O3) decomposed to hausmannite (Mn3O4). Hematite remained unchanged over the same temperature range. Above 900°C, the formed hausmannite combined with hematite to form manganese ferrite (MnFe2O4), which increased by increasing the roasting temperature up to 1200°C. Moreover, a metastable braunite Mn7SiO12 was formed at 1000°C and decomposed when the roasting temperature increased to 1200°C to rhodonite, MnSiO3.As a result of the transformation of MnO2, the magnetic susceptibility was increased from 0.119 × 10−3 at room temperature to 80 × 10−3 at 1200°C. This increase resulted from the formation of a ferromagnetic jacobsite.The roasting of low-grade manganese ore in the air is effective in converting nonmagnetic manganese oxide into magnetic forms without the reduction of hematite. According to this approach, magnetic separation can be applied based on the magnetic properties of the formed lower manganese oxides. Magnetic separation could be effective for samples roasted at temperatures up to 800°C. Above 800°C, formed lower manganese oxide (hausmannite) reacts with hematite and forms a magnetic solid solution of manganese ferrite.