Enhancing magnetism of ferrite via regulation of Ca out of sit a from spinel-type structure by adjusting the CaO/SiO2 mass ratio: Clean and value-added utilization of minerals

AbstractThe reactivity of the H2-activated Ni(II)- and Co(II)-bearing ferrites with different levels of metal substitution have been studied for CO2 → C decomposition in comparison with that of the H2-activated magnetite. Ni 2+ and Co2+ have been substituted for Fe2+ or Fe3+ in magnetite with the spinel-type structure up to 14 % and 26 % of the mole ratio of Ni2+ and Co2 + to the total Fe content respectively. The reactivity of the Ni(II)- and Co(II)-bearing ferrite increased with the level of metal substitution. Especially, the Ni(II) substitution significantly facilitated the CO2 → C decomposition in a batch system. The rates of H2-activation (reduction) and CO2-decomposition (oxidation) for N(II)-bearing ferrite were studied by a thermogravimeteric analysis. The rates of both H2-activation and CO2-decomposition were much improved in the Ni(II)-bearing ferrite with the Ni(II)/Fetoul mole ratio of 14%. It is considered that the reduced Ni(II) ions which were formed on the surface of the ferrite is very active to facilitate both dissociation reactions of 1) H2 → 2 Hads and 2) CO2→ Cads + 2Oads,. From the change in the lattice constant of the Ni(II)-bearing ferrite during the H2-activation and CO2-decomposition, the oxygens in CO2 were considered to be incorporated into the oxygen deficient spinel lattice of the oxygen deficient Ni(II)-bearing ferrite which had been formed by the H2-activation.

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Effect of Mn Doping on the Electronic Structure of ZnGa2O4with Spinel-Type Structure

Chemistry Letters ◽

10.1246/cl.2001.664 ◽

2001 ◽

Vol 30 (7) ◽

pp. 664-665 ◽

Cited By ~ 2

Author(s):

Moriyasu Nonaka ◽

Takumi Tanizaki ◽

Shigenori Matsushima ◽

Masataka Mizuno ◽

Chao-Nan Xu

Keyword(s):

Electronic Structure ◽

Type Structure ◽

Spinel Type ◽

Mn Doping

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Determination of the tegengrenite superstructure: another case of tetrahedral Mn3+ in spinel-type minerals?

Mineralogical Magazine ◽

10.1180/minmag.2015.079.2.19 ◽

2015 ◽

Vol 79 (2) ◽

pp. 425-436

Author(s):

Paola Bonazzi ◽

Luca Bindi

Keyword(s):

Unit Cell Volume ◽

Structure Refinement ◽

Close Packing ◽

Type Structure ◽

Cation Ordering ◽

Spinel Type ◽

Octahedral Sites ◽

Tetrahedral Sites ◽

Scattering Factor

AbstractThe crystal structure of the spinel-related, Sb mineral tegengrenite from the Filipstad district, Värmland, Sweden, has been solved in the space group R3 [a = 16.0285(9), c = 14.8144(8) Å, V = 3296.1(3) Å3, Z = 42] and refined up to R = 0.0484 for 3589 reflections with Fo > 4σ(Fo). Tegengrenite exhibits a rhombohedrally distorted spinel-type structure with cations occupying 1/8 of the tetrahedral (T) and 1/2 of the octahedral (M) interstices of a nearly regular cubic close-packing of oxygen atoms. Due to the cation ordering, which leads to a complex superstructure with a unit-cell volume of 21/4 that of a common spinel, the M and T sites of the spinel-type structure split into ten and six independent sites, respectively. Chemical composition determined by electron microprobe led to the empirical formula Mg1.26Mn0.852+Zn0.04Mn0.193+Al0.01Si0.12Ti0.03Sb0.505+O4, on the assumption that no vacancies occur in the mineral (Σcat = 3.00 and Σcharge = 8.00 per formula unit). Crystal-chemical considerations indicate that octahedra are occupied mainly by Mg, Mn3+ and Sb5+ (+Al, + Ti), whereas tetrahedra are filled mainly by Mn2+ and Mg (+Zn) with Si ordered in a specific site. However, the structure refinement shows a low site-scattering factor for one octahedral site, implying substantial vacancies and a larger overall mean Mn valence than stated above. Long mean distances also suggest some Mn2+ on octahedral sites. Together, these observations necessitate the presence of substantial Mn3+ on tetrahedral sites.

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