Computer modelling techniques based on the density functional theory were employed to calculate the geometries and surface free energies of a number of surfaces at different compositions, including the stoichiometric plane, and those with a deficiency or excess of oxygen atoms, finding the most stable surfaces are the (001) and (111). The renewed interest …
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Magnetite (Fe3O4) nanoparticles (NPs) are attractive nanomaterials in the field of material science, chemistry, and physics because of their valuable properties, such as soft ferromagnetism, half ...
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This value is lower than the saturation magnetization of bulk magnetite (85-90 emu/g [36,37]) but it is in line with the surface effect described for magnetite nanoparticles, wherein a higher ...
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1. Introduction. Hematite (α-Fe 2 O 3) is the major iron rock-forming mineral and, along with magnetite (Fe 3 O 4), it is one of two archetypical naturally-occurring magnetic materials.Like magnetite, hematite has played a significant part in developing key concepts in localized magnetism such as antiferromagnetic spin-reorientation transitions, the …
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hematite is shown in Fig. 1, together with the rhombohedral primitive cell used in our calculation. All iron atoms have an equivalent octahedral environment. Therefore, electronic and magnetic …
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A spherical model of magnetite nanoparticle was simulated with varied diameter size from 40 nm to 100 nm. It is observed that the domain structure transition from single domain to multi-domain occurred between 68 nm and 69 nm. The changing of domain structure is followed by changing the magnetization energy.
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Dive into the research topics of 'Bulk and key surface structures of hematite, magnetite, and goethite: A density functional theory study'. Together they form a unique fingerprint.
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The use of magnetite-based iron ore fines by means of fluidized bed technology has become a promising route to produce direct reduced iron. The significant influence of a prior oxidation treatment, which occurs in the preheating stage, on the subsequent fluidization and reduction behavior was observed in our previous study. As a result, it is important to …
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The crystal structures of magnetite and hematite both can be described in terms of close-packed oxygen layers with Fe ions in the interstices. ... The permeability enables efficient mass transport between the reaction front and the bulk solution and maintains the interfacial fluid in a state of undersaturation with respect to the parent phase ...
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Structure and Unit Cell of Magnetite 2 BULK PROPERTIES This section will explore the bulk properties (physical, ... slightly lighter than reddish-brown hematite (α-Fe2O3; 5.26 ... and Schwertmann, 1996) Effective surface areas of magnetite vary according to synthesis method as certain procedures generate coarser/finer particles; however ...
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Three key interfaces deserve attention: hematite–substrate (usually FTO), hematite–catalysts, and hematite grain boundaries. ... The migration of holes from the bulk to the surface of hematite often results in significant recombination. 126 In the case of semiconductors, two important effects should be considered: the potential drop across ...
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The iron oxides hematite, magnetite, and goethite were studied with density functional theory to establish a consistent set of structures for both the bulk mineral and key …
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Magnetite also demonstrated significant photoactivity; however, when surface area is taken into account, hematite actually outperformed both magnetite and goethite. The surface-specific rate is a more intrinsic measure of a material's catalytic capacity, as surface area is closely connected to the number of viable active sites.
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The three main iron oxides found in nature are magnetite (Fe₃O₄), maghemite (γ-Fe₂O₃), and hematite (α-Fe₂O₃). Magnetite is the oldest and most magnetic, while maghemite is a metastable ferromagnetic oxide [5].Hematite, a n-type semiconductor with a narrow bandgap (2.0–2.2 eV), crystallizes in a corundum structure (space group R3c) and is about 70 % iron by weight [6].
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Hematite (α-Fe2O3) films were prepared by cathodic polarization in an aqueous solution containing iron (II) sulfate hydrate, potassium hydroxide, dimethylamine-borane (DMAB), and …
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Therefore, this lack of transformation into magnetite in the presence of strongly bonded ligand point out the key role of Fe II surface sorbed and electron injection within the oxide particle. In addition, the difference in reactivity of ferric oxides against Fe II may result from the molecular interaction characteristics of ferrous ion with ...
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Hematite (α-Fe 2 O 3) surfaces represent one of the most common redox-active interfaces in the environment, playing an important role in the biogeochemical cycling of metal elements in the subsurface.Fe(II)-catalyzed recrystallization of iron (hydr)oxides is a fundamental process of iron cycling in earth's surface environments, but the proposed Fe(II) aq-Fe(III) …
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The α-Fe2O3(11̅02) surface (also known as the hematite r-cut or (012) surface) was studied using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling microscopy (STM), noncontact atomic force microscopy (nc-AFM), and ab initio density functional theory (DFT)+U …
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Beta-Hematite: Less common than alpha-hematite, beta-hematite has a more complex crystal structure and exhibits stronger magnetic properties. This form of hematite can be more significantly magnetic, though it is still less magnetic than magnetite.
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Download scientific diagram | Crystal structure and crystallographic data of the hematite, magnetite and maghemite (the black ball is Fe 2+, the green ball is Fe 3+ and the red ball is O 2 − ).
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Magnetite (Fe 3 O 4) is a transition metal oxide with vast applications in heterogeneous catalysis during Fischer–Tropsch synthesis and water–gas shift reaction [1–3].Exhibiting a complex defect chemistry, the stoichiometry of iron oxides can have a smooth transition from wüstite (Fe 1−x O) through magnetite to hematite (α-Fe 2 O 3) depending on …
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The iron oxides hematite, magnetite, and goethite were studied with density functional theory to establish a consistent set of structures for both the bulk mineral and key surfaces, characterize surface relaxation, and predict and test calculated scanning tunneling microscopy (STM) images. Spinpolarized, plane-wave pseudopotential calculations were …
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structure nearly to that of magnetite [25, 27]. Figure 1: Crystal structure of the Hematite, Magnetite, and Maghemite (the black ball is Fe2+, the green ball is Fe3+ and the red ball is O2−) [25]. 3. Properties of Magnetite (Fe 3 O 4) Nanoparticles The magnetic characteristics of Fe 3 O 4 NPs are controlled via the size of the particle.
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Surface roughness and porosity, at macroscopic and molecular scales, constitute key properties that influence most sorption phenomena. In first approximation, the direct determination of the surface area of a molecular/crystallographic model is the nominal area, A, which can be calculated by using the cell parameters (a and b in Fig. 2 ...
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The size-dependent magnetic behavior of ferrihydrite (Fh), magnetite (Fe3O4), and maghemite (γ-Fe2O3) has been studied in relation to the surface structure. The selected minerals have in common ...
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To understand why hematite of different genesis behave diversely in flotation systems, this study assesses the flotation response at pH 5 of bulk (morphology, texture, Crystal Preferential Orientation (CPO)) plus interfacial (surface area, zeta potential, immersion enthalpy, contact angle, induction time) characteristics of species formed under distinct metamorphic …
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The iron oxides hematite, magnetite, and goethite were studied with density functional theory to establish a consistent set of structures for both the bulk mineral and key surfaces, characterize surface relaxation, and predict and test calculated scanning tunneling …
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Abstract The iron oxides hematite, magnetite, and goethite were studied with density functional theory to establish a consistent set of structures for both the bulk mineral and key …
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Magnetite has an inverse spinel structure with Fe (III) ions distributed randomly between octahedral and tetrahedral sites, and Fe (II) ions in octahedral sites [4]. Maghemite has a spinel...
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The replacement of magnetite by hematite is commonly observed in various geologic systems, especially in banded iron formations (BIF), iron oxide copper-gold deposits, and iron skarn deposits (Angerer et al., 2012; Franchini et al., 2000; Ehrig et al., 2021).The transformation of magnetite to hematite was attributed to an oxidizing reaction, generally …
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Also the Boettger relation does not converge very well for this surface, because the bulk energy is calculated from two slabs of similar ... [17] Martin G J, Cutting R S, Vaughan D J and Warren M C 2009 Bulk and key surface structures of hematite, magnetite, and goethite: a density functional theory study Am. Mineral. 94 1341. Go to reference ...
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A key feature of most of the magnetite particles analyzed is the presence of an amorphous layer near their surface (e.g., compare Fig. 4 C, 1 with C, 2 and Fig. 4 I, 3 with I, 4). EDXA of this 1–4 nm thick amorphous surface layer shows no evidence of elements other than Fe, O, C, or Cu (the latter two associated with the support film and TEM ...
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