scholarly journals Factors Controlling the Gallium Preference in High-Al Chromitites

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 623 ◽  
Author(s):  
Eliopoulos ◽  
Eliopoulos
Keyword(s):  
Electronic Configuration ◽  
Parent Magma ◽  
Geochemical Data ◽  
Key Factors ◽  
Abrupt Increase ◽  
Critical Metals ◽  
Strong Negative Correlation ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Disorder Degree

Gallium (Ga) belongs to the group of critical metals and is of noticeable research interest. Although Ga3+ is highly compatible in high-Al spinels a convincing explanation of the positive Ga3+–Al3+ correlation has not yet been proposed. In the present study, spinel-chemistry and geochemical data of high-Al and high-Cr chromitites from Greece, Bulgaria and the Kempirsai Massif (Urals) reveals a strong negative correlation (R ranges from −0.95 to −0.98) between Cr/(Cr + Al) ratio and Ga in large chromite deposits, suggesting that Ga hasn’t been affected by re-equilibration processes. In contrast, chromite occurrences of Pindos and Rhodope massifs show depletion in Ga and Al and elevated Mn, Co, Zn and Fe contents, resulting in changes (sub-solidus reactions), during the evolution of ophiolites. Application of literature experimental data shows an abrupt increase of the inversion parameter (x) of spinels at high temperature, in which the highest values correspond to low-Cr3+ samples. Therefore, key factors controlling the preference of Ga3+ in high-Al chromitites may be the composition of the parent magma, temperature, redox conditions, the disorder degree of spinels and the ability of Al3+ to occupy both octahedral and tetrahedral sites. In contrast, the competing Cr3+ can occupy only octahedral sites (due to its electronic configuration) and the Ga3+ shows a strong preference on tetrahedral sites.

A Magnetically Ordered Non-Stoichiometric Zinc Ferrite for the Oxidative Dehydrogenation Reactions.

2001 ◽  
Vol 676 ◽  
Author(s):  
J. A. Toledo ◽  
N. Nava ◽  
X. C. Sun ◽  
X. Bokhimi
Keyword(s):  
Catalytic Activity ◽  
Oxidative Dehydrogenation ◽  
Spinel Structure ◽  
Zinc Ferrite ◽  
Room Temperature ◽  
Annealing Temperature ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Dehydrogenation Reactions ◽  
Hydrothermal Reduction

ABSTRACTZnFe2O4 nanoparticles were prepared by hydrothermal reduction approach. A considerable amount of α-Fe2O3 was segregated in the as-synthesized sample, which diffused into the tetrahedral and octahedral sites of the ZnFe2O4 spinel structure with increasing the annealing temperature. The introduction of Fe3+ into the tetrahedral positions was observed by Mössbauer spectra. Magnetization measurements showed an unusual ferrimagnetic behavior of the ZnFe2O4 phase, even at room temperature, confirming the introduction of Fe3+ into the tetrahedral sites of the spinel structure. Catalytic activity measured in the oxidative dehydrogenation of 1-butene reaction increased with increasing annealing temperature, indicating that those interactions of Fe3+ in tetrahedral and octahedral positions also promotes the activity and selectivity to butadiene formation.

Impact of lithium excess on the structural and electrochemical properties of the LiNi0.5Mn1.5O4high-voltage cathode material

2015 ◽  
Vol 3 (40) ◽  
pp. 20103-20107 ◽  
Author(s):  
Yu-Feng Deng ◽  
Shi-Xi Zhao ◽  
Peng-Yuan Zhai ◽  
Guozhong Cao ◽  
Ce-Wen Nan
Keyword(s):  
Transition Metal ◽  
Cathode Material ◽  
Metal Ions ◽  
Phase Change ◽  
Electrochemical Properties ◽  
Transition Metal Ions ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
One Step ◽  
Co Precipitation

Li1+xNi0.5−xMn1.5O4, madeviaa novel one-step co-precipitation route, undergoes a disordered-to-ordered phase change. Transition metal ions in tetrahedral sites could influence the performance more than the cationic ordering in octahedral sites does.

Zn-rich staurolite from the Uvete area, central Kenya

1985 ◽  
Vol 49 (353) ◽  
pp. 573-578 ◽  
Author(s):  
Akira Miyake
Keyword(s):  
Optical Properties ◽  
Absorption Spectra ◽  
Optical Dispersion ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Cell Dimensions ◽  
Infra Red ◽  
Central Kenya

AbstractZn-rich staurolite occurs in a pelitic gneiss from the Uvete area, central Kenya. The rock was metamorphosed to staurolite-kyanite grade during the Mozambique metamorphism. Microprobe analyses of the staurolite gave the following values (in wt. %): SiO2 26.2–27.3, Al2O3 52.4–53.5, FeO 8.3–9.2, MgO 2.2–2.6, and ZnO 6.0–7.5. Cell dimensions are a = 7.874(± 0.003), b = 16.620(±0.006), c = 5.656(±0.002) Å and β = 90.00 (± 0.002)°. Optical properties are 2Vz = 82–85°, α = 1.742 (±0.002), β = 1.747(±0.002) and γ = 1.753(±0.002). The optical dispersion is moderate and r > v. Density is 3.83(±0.01) g/cm3. Infra-red absorption spectra were also recorded. The cation correlation suggests that the principal substitutions in the staurolite are Zn ⇆ Fe in the tetrahedral sites in the hydroxide sheet and Al ⇆ Mg in the octahedral sites.

ISING MODEL FOR INTERSTITIAL ALLOYS AND SUPERCONDUCTING OXIDES

1989 ◽  
Vol 03 (09) ◽  
pp. 1425-1433 ◽  
Author(s):  
J. HAUCK ◽  
D. HENKEL ◽  
K. MIKA
Keyword(s):  
Ising Model ◽  
Nearest Neighbor ◽  
Cluster Formation ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Repulsive Interactions ◽  
Superconducting Oxides ◽  
Maximum Separation

The interstitial alloys MZx with Z= H, C, N, O etc. at octahedral or tetrahedral sites of the fcc or bcc M lattice are analysed for nearest and next-nearest neighbor Z-Z interactions. Many compounds have repulsive interactions close to the borderline of maximum separation, which is characterized by Pauling’s electrovalence rule. There are also borderlines for attractive interactions, e.g. cluster formation or segregation. The new superconducting oxides Ba 2 YCu 3 O x, La 2 CuO 4, Bi 2 Sr 2 Ca n−1 Cu n O 2n+4 can be viewed as bcc M= Ba, Cu, Bi etc. lattice with Z= O atoms at octahedral sites. The low T c compounds Nbo , NbC x, TiO x, TiN x, PdH x, etc. have Z= C, N, O, H atoms at octahedral sites of the fcc M= Nb, Ti, Pd lattice.

CALCULATIONS OF HYDROGEN DIFFUSION IN THE Ti(0001)–(1 × 1) SURFACE BY FIRST PRINCIPLES

2009 ◽  
Vol 16 (06) ◽  
pp. 905-908 ◽  
Author(s):  
J. X. GUO ◽  
L. GUAN ◽  
B. GENG ◽  
Q. LI ◽  
Q. X. ZHAO ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Outer Layer ◽  
Density Functional ◽  
Hydrogen Diffusion ◽  
Generalized Gradient ◽  
Energy Barriers ◽  
Functional Theory ◽  
Atom Diffusion ◽  
Octahedral Sites ◽  
Tetrahedral Sites

Diffusion of H atom in the Ti (0001) outer-layer and inter-layer surface is studied using density functional theory based on generalized gradient approximation (GGA). The energy barriers for the hydrogen atom diffusion in different interstitial sites at the same layers or between adjacent layers are calculated. It is found that the energy barriers of H atom diffusion in the adjacent interstitial layers are bigger than that in the same interstitial layers. For the diffusion of H atom between adjacent interstitial layers, the diffusion between tetrahedral sites is easier than that between octahedral sites. While for diffusion of H atom between the same interstitial layers, the diffusion between tetrahedral sites is easier than that between tetrahedral and octahedral sites. Moreover, it is found that the most possible inside diffusion from hcp site of a hydrogen atom in the Ti (0001) outer-layer goes through tetrahedral sites.

scholarly journals Key Factors Controlling Microbial Distribution on a DNAPL Source Area

2021 ◽  
Author(s):  
Jofre Herrero ◽  
Diana Puigserver ◽  
Ivonne Nijenhuis ◽  
Kevin Kuntze ◽  
José M. Carmona
Keyword(s):  
Microbial Community ◽  
Chlorinated Solvents ◽  
Source Area ◽  
Vital Role ◽  
Environmental Data ◽  
Geochemical Data ◽  
Key Factors ◽  
High Concentration ◽  
Terminal Electron Acceptor ◽  
Microbial Distribution

Abstract The chlorinated solvents are among the common groundwater contaminants that show high complexity in their distribution in the subsoil. Microorganisms play a vital role in the natural attenuation of chlorinated solvents. Up to now, how the in situ soil microbial community responds to chlorinated solvents contamination remains unclear. In this study, the microbial community distribution within two boreholes located in the source area of perchloroethene (PCE) were investigated via terminal restriction fragment length polymorphism (T-RFLP) and clone library analysis. Microbial data were related to the lithological and geochemical data and the concentration and isotopic composition of chloroethenes to stablish the key factors controlling the distribution of the microbial communities. The results indicated that Proteobacteria, Actinobacteria and Firmicutes were the most abundant phylums in the sediment. The statistical correlation with the environmental data proved that fine granulometry, oxygen tolerance, terminal electron acceptor processes and toxicity control microbial structure. This study improves our understanding of how the microbial community in the subsoil responds to high concentration of chlorinated solvents.

Zaisho—a pallasite containing pyroxene and phosphoran olivine

1984 ◽  
Vol 48 (347) ◽  
pp. 229-235 ◽  
Author(s):  
Peter R. Buseck ◽  
Jim Clark
Keyword(s):  
Small Group ◽  
Cooling Rate ◽  
Charge Balance ◽  
Octahedral Sites ◽  
Olivine Composition ◽  
Tetrahedral Sites

AbstractThe Zaisho meteorite, one of only four known pallasite falls, contains pyroxene, which is rare in pallasites, and it is only the fourth meteorite known to contain phosphoran olivine. Except for a recent report by Goodrich (1984) such olivine appears to be restricted to pallasites, and to those containing the rare Mg phosphate, farringtonite. It is unique among olivines in having P in tetrahedral sites and having vacancies, for charge balance, in octahedral sites. Zaisho also contains stanfieldite and a phosphate having a composition between that of stanfieldite and farringtonite. Its metallographic cooling rate is similar to that of many other pallasites, but its average olivine composition, Fa18.3, places it in a small group with more Fe-rich olivines than most pallasites.

Disentangling site occupancy, cation regulation, and oxidation state regulation of the broadband near infrared emission in a chromium-doped SrGa4O7 phosphor

2020 ◽  
Vol 7 (12) ◽  
pp. 2313-2321 ◽  
Author(s):  
Jun'an Lai ◽  
Jianbei Qiu ◽  
Qi Wang ◽  
Dacheng Zhou ◽  
Zhangwen Long ◽  
...  
Keyword(s):  
Oxidation State ◽  
Near Infrared ◽  
Site Occupancy ◽  
Infrared Emission ◽  
State Regulation ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Near Infrared Emission

The Cr3+ ions in octahedral sites and the Cr4+ ions in tetrahedral sites generate unique broadband near infrared emission.

Controls on tetrahedral Fe(III) abundance in 2:1 phyllosilicates

2019 ◽  
Vol 104 (11) ◽  
pp. 1608-1619
Author(s):  
Javier Cuadros ◽  
Joseph R. Michalski ◽  
M. Darby Dyar ◽  
Vesselin Dekov
Keyword(s):  
Additional Data ◽  
Similar Proportion ◽  
Crystal Chemical ◽  
Biological Processes ◽  
Data Set ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Wide Range ◽  
Chemical Factors ◽  
First Time

Abstract Fe(II) only occupies octahedral sites in phyllosilicates, whereas Fe(III) can occupy both octahedral and tetrahedral sites. The controls on Fe(III) distribution between tetrahedral and octahedral sites have been a matter of great interest to understand the interplay between formation environment (Fe abundance, redox conditions) and crystal-chemical factors (stability of the crystal lattice) during crystallization of Fe-phyllosilicates. Here, for the first time, we present a model of Fe(III) distribution in 2:1 phyllosilicates. We investigated 21 samples of 2:1 phyllosilicates of submarine hydrothermal origin using XRD, chemical analysis, and Mössbauer spectroscopy (and other supporting techniques not presented here). An additional data set of 49 analyses of 2:1 phyllosilicates from the literature was also used. Overall, the data cover a wide range of dioctahedral and trioctahedral phyllosilicates, including end-member minerals and interstratified phases. Dioctahedral phyllosilicates have a steric control whereby tetrahedral Fe(III) is only allowed if at least five out of six octahedral atoms are larger than Al (typically Fe[III], Fe[II], Mg) that produces an expanded structure where tetrahedral sites can accommodate Fe(III). After this threshold, further Fe(III) atoms occupy tetrahedral sites preferentially (~73% of further Fe[III] atoms) over octahedral sites. In trioctahedral 2:1 phyllosilicates there is no steric hindrance to tetrahedral Fe(III) because the crystal dimensions are such that tetrahedral sites can accommodate Fe(III). On average, Fe(III) enters tetrahedral and octahedral sites in similar proportion, and the only apparent control on tetrahedral Fe(III) abundance is Fe(III) availability during crystallization. This model allows to predict Fe(III) distribution between structural sites, provides an avenue for further exploration of the thermodynamic stability of phyllosilicates using cationic size, and provides a tool to better describe stability/reactivity of Fe-rich phyllosilicates, the most reactive of phyllosilicates and very relevant in geochemical and biological processes.

MAGNETIC STRUCTURE OF ZINC-FERRITE APPROACHING NANOMETER SIZES

2001 ◽  
Vol 15 (24n25) ◽  
pp. 3312-3316 ◽  
Author(s):  
A. H. MORRISH ◽  
Z. W. LI ◽  
J. Z. JIANG
Keyword(s):  
Magnetic Structure ◽  
Zinc Ferrite ◽  
Bulk Material ◽  
Spinel Ferrite ◽  
Average Particle Size ◽  
Average Particle ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Zn Ferrite ◽  
Nanometer Particles

A unit cell of a spinel ferrite is just under 1 nm, actually about 0.8 nm. Particles approaching this size can be expected to possess properties that differ from the bulk material. Bulk polycrystalline Zn-ferrite ( ZnFe2O4 ) has been ball milled; after 50 h the average particle size is about 13 nm. The 57 Fe Mössbauer spectra at T = 4.2 K with and without a large (52 kOe) magnetic field applied longitudinally establish that the antiferromagnetic structure of the bulk has become ferrimagnetic in the ten nanometer particles via the transfer of some Zn cations from the A (tetrahedral) sites to the B (octahedral) sites. In addition, there is a large non-collinearity in the magnetic structure.

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