Fe Atomic Ratio Research Articles

Peculiar Mg–Ca–Si metasomatism along a shear zone within the mantle wedge: inference from fine-grained xenoliths from Avacha volcano, Kamchatka

We found extremely high-Mg# (=Mg/(Mg + total Fe) atomic ratio) ultramafic rocks in Avacha peridotite suite. All the high-Mg# rocks have higher modal amounts of clinopyroxene than ordinary Avacha peridotite xenoliths, and their lithology is characteristically heterogeneous, varying from clinopyroxenite through olivine websterite to pyroxene-bearing dunite. The Mg# of minerals is up to 0.99, 0.98 and 0.97 in clinopyroxene, orthopyroxene and olivine, respectively, decreasing progressively toward contact with dunitic part, if any. The petrographical feature of pyroxenes in the high-Mg# pyroxenite indicates their metasomatic origin, and high LREE/HREE ratio of the metasomatic clinopyroxene implies that the pyroxenites are the products of reaction between dunitic peridotites and high-Ca, silicate-rich fluids. The lithological variation of the Avacha high-Mg# pyroxenites from clinopyroxenite to olivine websterite resulted from various degrees of fluid-rock reaction coupled with fractional crystallization of the high-Ca fluids, which started by precipitation of high-Mg# clinopyroxene. Such fluids were possibly generated originally at a highly reduced serpentinized peridotite layer above the subducting slab. The fluids can reach the uppermost mantle along a shear zone as a conduit composed of fine-grained peridotite that developed after continent-ward asthenospheric retreats from the mantle wedge beneath the volcanic front. The fluids are incorporated in mantle partial melts when the magmatism is activated by expansion of asthenosphere to mantle wedge beneath the volcanic front.

XMCD study of Fe–Cr–Co alloy under electron irradiation

The effect of electron irradiation on the electronic structure of Fe–Cr–Co alloy was investigated by soft X-ray magnetic circular dichroism (XMCD) technique. The magnetic moments of Fe and Co atoms in the alloy were calculated by sum rules, and the change of local environment of magnetic atoms after electron irradiation were discussed. It was shown that the larger spin–orbit interaction exists in the 3d orbitals of Fe and Co atoms, and the electron irradiation significantly affected the spin–orbit coupling interaction of magnetic atoms, resulting in the decrease of orbital-to-spin moment ratio of Fe and Co atoms after electronic irradiation. This was found to be primarily due to the effect of irradiation on the electron structure and crystal-field. The variation of absorption spectrum at L edge indicates that a charge transfer occurred between Fe and Co atoms during electron irradiation.

Superparamagnetic mesoporous Mg–Fe bi-metal oxides as efficient magnetic solid-base catalysts for Knoevenagel condensations

Superparamagnetic mesoporous Mg-Fe bi-metal oxides with varied Mg-Fe atomic ratios have been successfully synthesized as solid base catalysts. The M2F-400 catalyst with Mg/Fe atomic ratio = 2 showed extraordinarily high activities for Knoevenagel reactions even at room temperature. It could be magnetically separated, recycled, and reused for at least five cycles.

Effects of PO2 at Flux State on the Fluorine Dissolution from Synthetic Steelmaking Slag in Aqueous Solution

This paper studies effect of oxygen partial pressure at molten flux state on the fluorine dissolution from synthetic steelmaking slag solidified from the flux. The PO2's were set as 6.6×10−8, 8.1×10−5, 2.9×10−3, 1.5×10−2, 1.1×10−1, or 6.6×103 Pa, by changing the CO/CO2 ratio of environmental flowing gas. The Ca : Al : Fe atomic ratio of major cations of the slag (oxide) is 23 : 9 : 13, and minor constituents are Mg (~3 at%) and F (~0.3 at%). The phases and their distribution is characterized using SEM, EDS (point and mapping), Rietveld refinement of XRD. Increase of PO2 reduces fluorine dissolution, and the amounts of dissolution are higher than 1 mg/L when processed at PO2<10−2 Pa, but are about or less than 0.5 mg/L when processed at PO2>10−2 Pa. These results indicate that the low PO2 processed slag has large fraction of low density Mayenite (Ca12Al14O33) with most of fluorine in its sparse crystal structure, and liberates large amount of fluorine. On the contrary, the high PO2 processed slag is mainly composed of high density Brownmillerite (Ca2AlxFe2−xO5), and the fluorine exists as CaF2 particles not to liberate fluorine easily. It is concluded that the fluorine dissolution is strongly governed by the amount of phases, the density and empty space of each crystal structure to accommodate fluorine, and their distribution.

Alteration Mechanisms of Chromian‐Spinel during Serpentinization at Wadi Sifein Area, Eastern Desert, Egypt

AbstractWadi Sifein podiform chromite deposits, Central Eastern Desert of Egypt, are hosted by fully serpentinized peridotite that is a part of the dismembered Pan‐African ophiolite complexes. Relics of primary minerals and the chemical characters indicate that the ophiolitic rocks were derived from depleted mantle peridotite of harzburgite and subordinate dunite compositions. The mantle rocks were initially formed at a mid‐oceanic ridge and subsequently thrust at a supra‐subduction zone. The chromite mineralization at Wadi Sifein area displays either pod‐shaped bodies with massive and lumpy chromitite appearance or dissemination of chromian‐spinel in serpentinite matrix. The podiform chromitite exhibits a very limited compositional range in terms of Cr# [Cr/(Cr + Al) atomic ratio] and Mg# [Mg/(Mg + Fe) atomic ratio]. The chromian‐spinel, however, frequently displays optical and geochemical zoning. Four zones can be identified from core to edge: inner core representing the original composition of the chromian‐spinel; narrow Cr‐rich ferritchromit zone; wide ferritchromit zone; and outer Cr‐magnetite/magnetite zone. The zonation of chromian‐spinel is interpreted to be a result of serpentinization rather than magmatic or metamorphic processes. The geochemical data obtained from the chromitite and chromian‐spinel was statistically processed using discriminant and R‐mode factor analyses. Two trends, minor and major, were achieved considering the formation of ferritchromit. The minor trend is controlled by the redistribution of trivalent cations, where Cr2O3 increased on the expense mainly of Al2O3 and to less extent Fe2O3 to form zone II during the peak of serpentinization. The major trend of alteration, however, is explained by the exchange between Mg‐Fe2+ rather than Cr, Al, and Fe3+ to form zone III. Kammererite formation was accompanied the formation of zones III and IV at a 314°C temperature of formation.

Subarc magmatic and hydration processes inferred from a hornblende peridotite xenolith in spessartite from Kyoto, Japan

Hornblende peridotite xenolith in the spessartite dike in the Tamba belt, northern Kyoto city, is mainly composed of olivine with high Fo and NiO contents (Fo87−94 and 0.22-0.51 wt%). The olivine encloses chromian spinels with a high Cr/(Cr + Al) atomic ratio, 0.66-0.80, partly replaced and digested by hornblendes with a low Mg/(Mg + total Fe) atomic ratio, 0.68-0.81. Microscopic and geochemical features of the hornblende peridotite xenolith indicate a reaction between a dunitic cumulate from a high-Mg and -Cr melt and an evolved hydrous high-Mg melt to form hornblendes. Olivines are lower in Fo when in contact with hornblendes. Rare earth element (REE) patterns of the hornblendes, common to the xenolith and host spessartite, indicate that all the involved melts are similar but different in the degree of differentiation. The strong hydration of olivine in the xenolith suggests a wide distribution of hornblende-rich rocks, such as hornblendites, formed by the hydration of olivine-rich rocks, such as dunites, around the Moho beneath the arc. This may give rise to a layer with a Vp intermediate between typical lower crustal and mantle values.

B-type olivine fabrics developed in the fore-arc side of the mantle wedge along a subducting slab

B-type olivine fabrics are pervasive within highly depleted dunites of the small-sized Imono peridotite body located within the subduction-type Sanbagawa metamorphic belt of the southwest Japan arc. The dunites contain various microstructures, ranging from porphyroclastic to fine-grained intensely sheared textures. The Mg/(Mg + Fe) atomic ratios (Fo number) of olivine within these dunites are consistently around 0.9, as are the Cr/(Cr + Al) atomic ratios (Cr number) of chromian spinel, suggesting their evolution from a highly depleted magma (boninite). These data provide strong thermal constraints on the formation of the highly depleted dunites, as their formation requires hot, hydrous, shallow mantle (> 1250 °C at < 30 km depth) in the mantle wedge. Because the Sanbagawa metamorphic belt finally entrained these peridotites during progressive retrogression, B-type olivine fabrics probably developed in the fore-arc side of the subduction zone, above or along the subducting slab, possibly in association with dehydration fluids derived from the slab. The previously documented small magnitude of S-wave splitting can be explained by the seismic properties of B-type peridotites within an anisotropic layer of approximately several kilometers in thickness, oriented by flow parallel to the subducting slab, under maximum temperatures of 880–1030 °C depending on the flow stress. These findings indicate that such a B-type layer could constitute a dominant source of seismic S- and P-wave anisotropy in mantle wedge regions.

Two-carrier transport and ferromagnetism in FeSe thin films

α - and β-FeSe thin films were grown by metal organic chemical vapor deposition. Compared to the other parameters, the growth temperature shows decisive influence on the phase transition of the FeSe samples. In temperature-dependent electrical measurements, n-type to p-type reversion was observed for both the α- or and β-FeSe samples. Furthermore, the p-type character of the films becomes more and more obvious with increasing the Se∕Fe atomic ratio in the samples. Ferromagnetism was observed in the α-FeSe films although which is not supported by calculation on density of states. The ferromagnetic character shows significant dependence on Se∕Fe atomic ratio in the films and was attributed to the Fe vacancies or Fe clusters in the α-FeSe thin films. The magnetic domain and hysteresis loop of the β-FeSe thin films are also studied.

Laboratory simulations of sulfur depletion at Eros

The X-ray spectrometer of the Near-Earth Asteroid Rendezvous (NEAR) mission discovered a low abundance of sulfur on the surface of asteroid Eros, which is seemingly inconsistent with the match of the overall surface composition to that of ordinary chondrites. Since troilite, FeS, is the primary sulfur-bearing mineral in ordinary chondrites, we investigated the hypothesis that sulfur loss from surface FeS could result from ‘space weathering’ by impact of solar wind ions and micrometeorites. We performed laboratory studies on the chemical alteration of FeS by 4 keV ions simulating exposure to the solar wind and by nanosecond laser pulses simulating pulsed heating by micrometeorite impact. We found that the combination of laser irradiation followed by ion impact lowers the S:Fe atomic ratio on the surface by a factor of up to 2.5, which is consistent with the value of at least 1.5 deduced from the NEAR measurements. Thus, our results support the hypothesis that the low abundance of sulfur at the surface of Eros is caused by space weathering.

Electro-codeposition synthesis and room temperature ferromagnetic anisotropy of high concentration Fe-doped ZnO nanowire arrays

Fe-doped ZnO dilute magnetic semiconductor (DMS) nanowire arrays were fabricated in anodic aluminum oxide (AAO) membranes using electro-codeposition followed by long-time anneal process. The morphology, chemical composition and crystal structure were characterized by field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscope (HRTEM) equipped with an energy dispersive x-ray spectrometer, and X-ray diffraction (XRD) spectroscopy. The results prove that the Fe has been successfully doped in the lattice of ZnO nanowire arrays and the estimated Fe atomic ratio is around 22%. Micro-superconducting quantum interference device (SQUID) shows that the nanowire arrays exhibit room temperature (300 K) ferromagnetic and anisotropic ferromagnetic behavior which may be a consequence of the easy magnetization direction along the wire axes and magnetostatic interaction.

Calcic amphiboles in peridotite xenoliths from Avacha volcano, Kamchatka, and their implications for metasomatic conditions in the mantle wedge

Abstract Highly metasomatized parts of peridotite xenoliths from Avacha volcano, Kamchatka, Russia, characteristically contain calcic amphiboles, especially tremolites. They are rich in metasomatic pyroxenes with high Mg-number (= Mg/(Mg+Fe) atomic ratio), up to 0.94–0.98, and contain Cr-poor aluminous spinels. They have the spinel lherzolite mineral assemblage and equilibrium temperatures of 900–1000 °C or higher, beyond the stability field of tremolite. The tremolite was therefore retrogressively formed after the peak of high-temperature metasomatism. The high-Mg-number, low-alkali environment facilitates the formation of tremolite instead of Al-rich calcic amphiboles. A sulphur-bearing silicic melt derived from a slab is a probable agent involved in the metasomatism. High f O 2 recorded in the highly metasomatized peridotites is consistent with this process. This type of metasomatism can produce high-Mg-number peridotites and pyroxenites with low-Cr-number spinel within the mantle wedge where the Mg-number of silicates is positively correlated with the Cr-number of spinel in ambient peridotites.

Synthesis of linear alkylbenzene sulphonate intercalated iron(II) iron(III) hydroxide sulphate (green rust) and adsorption of carbon tetrachloride

AbstractGreen rusts, GRs, can act as both sorbents and reductants towards selected pollutants. Organo-GRs are expected to combine these properties with a high affinity for hydrophobic substances. A novel organo-GR, GRLAS, was synthesized by incorporating a mixture of linear alkylbenzenesulphonates (LAS) into the interlayer space of synthetic sulphate green rust, GRSO4 . Mössbauer analysis of GRLAS indicates that the structure of the organo-GR is very similar to that of the initial GRSO4 with regard to the FeII/FeIII ratio and local coordination of Fe atoms. X-ray diffraction demonstrates that the GRLAS formed was well ordered, although a mixture of surfactant was used for intercalation. The basal spacings of the GRLAS and the kinetics of the ion-exchange process were dependent on the initial surfactant loading; basal spacings of ~2.85 nm were obtained at LAS solution concentrations &gt;10 mM. The ratio LASadsorbed/SO42–desorbed significantly exceeded the stoichiometric ratio of 2 during the initial part of the ion-exchange process (t = 5 h). However, this ratio was reached progressively with time. GRSO4 preferentially sorbed LAS homologues with long alkyl chains over short ones. Carbon tetrachloride was successfully adsorbed into GRLAS. The adsorption isotherm was linear with a distribution coefficient, Kd, of 505±19 litre kg–1.

Generation of Palaeocene Adakitic Andesites by Magma Mixing; Yanji Area, NE China

Palaeocene (c. 55^58Ma) adakitic andesites from the Yanji area, NE China, are typically clinopyroxene-bearing sodic andesites containing 60 9^62 2% SiO2 and 4 02^4 36% MgO, with high Mg-number [100Mg/(Mgþ Fe) atomic ratio] from 65 5 to 70 1. Whole-rock geochemical features include high Cr (128^161ppm) and Ni (86^117 ppm) concentrations, extremely high Sr (2013^2282 ppm), low Y (10^11ppm) and heavy rare earth elements (HREE; e.g. Yb1⁄4 0 79^1 01ppm), and mid-ocean ridge basalt (MORB)-like Sr^Nd^Pb isotopic compositions [e.g. Sr/ Sr(i)1⁄4 0 70298^0 70316, eNd(t)1⁄4þ3 8 to þ6 3 and Pb/ Pb1⁄417 98 ^ 18 06], analogous to high-Mg adakites occurring in modern subduction zones. However, mineralogical evidence from clinopyroxene phenocrysts and microcrystalline plagioclase clearly points to magma mixing during magma evolution. Iron-rich clinopyroxene (augite) cores with low Sr, high Y and heavy REE contents, slightly fractionated REE patterns and large negative Eu anomalies probably crystallized along with low-Ca plagioclase from a lower crustal felsic magma. In contrast, high Mg-number clinopyroxene (diopside and endiopside) mantles and rims have higher Sr and lower HREE and Yconcentrations, highly fractionated REE patterns (high La/Yb) and negligible Eu anomalies, similar to those found in adakites from subduction zones.The Yanji adakitic andesites can be interpreted as a mixture between a crust-derived magma having low Mg-number and Sr, and high Y and HREE, and a mantle-derived high Mg-number adakite having high Sr and low Y and HREE concentrations. During storage and/or ascent, the mixed magma experienced further crustal contamination to capture zircons, of a range of ages, from the wall rocks.The absence of coeval arc magmatism and an extensional tectonic regime in the Yanji area and surrounding regions suggest that these Palaeocene adakitic andesites were formed during post-subduction extension that followed the late Cretaceous Izanagi^Farallon ridge subduction. Generation of these adakitic andesites does not require contemporaneous subduction of a young, hot oceanic ridge or delamination of eclogitic lower crust as suggested by previous models.

A new type of orthopyroxenite xenolith from Takashima, Southwest Japan: silica enrichment of the mantle by evolved alkali basalt

We found fine-grained Fe-rich orthopyrox- ene-rich xenoliths (mainly orthopyroxenite) containing partially digested dunite fragments of Group I from Takashima, Southwest Japan. Orthopyroxenite vein- lets, some of which contain plagioclase at the center, also replace olivine in dunite and wehrlite xenoliths of Group I. This shows high reactivity with respect to olivine of the melt involved in orthopyroxenite for- mation, indicating its high SiO2 activity. The secondary orthopyroxene of this type is characterized by low Mg# (= Mg/(Mg + total Fe) atomic ratio) (down to 0.73) and high Al2O3 contents (5-6 wt%). It is differ- ent in chemistry from other secondary orthopyroxenes found in peridotite xenoliths derived from the mantle wedge. Clinopyroxenes in the Fe-rich orthopyroxenite show a convex-upward REE pattern with a crest around Sm. This pattern is strikingly similar to that of clinopyroxenes of Group II pyroxenite xenoliths and of phenocrystal and xenocrystal clinopyroxenes, indicat- ing involvement of similar alkali basaltic melts. The Fe- rich orthopyroxenite xenoliths from Takashima formed by reaction between evolved alkali basalt melt and mantle olivine; alkali basalt initially slightly undersat- urated in silica might have evolved to silica-oversatu- rated compositions by fractional crystallization at high- pressure conditions. The Fe-rich orthopyroxenites oc- cur as dikes within the uppermost mantle composed of dunite and wehrlite overlying pockets of Group II pyroxenites. The orthopyroxene-rich pyroxenites of this type are possibly common in the uppermost mantle beneath continental rift zones where alkali basalt magmas have been prevalent.

Effects of iron oxide (Fe 2O 3, Fe 3O 4) on hydrogen storage properties of Mg-based composites

When magnesium powder containing small additions of certain multiple valence transition metal oxides (TMOs) is ball milled in hydrogen, the hydrogenated Mg-based product can show remarkable improvements in hydrogen absorption/desorption properties. Using a magnetically controlled Uni-Ball-Mill, small amounts of the iron oxides, Fe 2O 3 and Fe 3O 4, were ball milled with Mg powder in a hydrogen atmosphere (Mg to Fe atomic ratio; 20:1). Milling products as well as samples used in hydrogen absorption/desorption experiments were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. TG analysis combined with DSC revealed a higher hydrogen storage capacity for the Mg + Fe 2O 3 + H 2-milled product (6 wt% H) compared with 5 wt% H for Mg + Fe 3O 4 + H 2. XRD revealed that during heating, both iron oxides were reduced to pure Fe, a result not previously reported for similar materials milled using different milling devices. For both samples, there was little difference found in the decomposition temperature of the as-prepared MgH 2 and rehydrogenated composites. However, storage capacity degradations were observed for the rehydrogenated composites (4 wt% H storage capacity for MgH 2 + Fe 2O 3 and 4.4 wt% H for MgH 2 + Fe 3O 4). The higher capacity degradation of rehydrogenated MgH 2 + Fe 2O 3 composite is also believed to be a result of the reduction reaction, during which more magnesium was consumed than was consumed by the same amount of Fe 3O 4. The results also were related to the particular ball-milling equipment and low-energy shearing milling mode employed, which promoted the development of a nanostructural hydride product which subsequently changed structure significantly during the first desorption cycle.

초음파분무법을 이용한 산화철이 혼합된 ZnO막의 제조

In this Paper, ZnO films mixed with iron oxide were prepared by an ultrasonic spray pyrolysis method. The chemical composition and structural properties as a function of the Fe atomic ratio in the deposition solution were studied. Zinc acetate and ferrous chloride were used as precursors of Zn and Fe, respectively. Fe atomic ratio to Zn varied from 0.15 to 10.0. Substrate temperature was fixed at . The crystallographic properties and surface morphologies of the films were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Electron probe X-ray microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS) were carried out to analyse the chemical composition and state of Zn and Fe atoms.

The influence of the oxidative dehydrogenation of butene-1 on the phase composition of the nickel ferrite/γ-Al2O3 catalyst

The influence of the oxidative dehydrogenation of butene-1 on the phase composition of a ferrite-containing catalyst on γ-Al2O3 with a Ni: Fe atomic ratio of 1: 4 was studied. It was found by X-ray diffraction, EPR, IR absorption spectroscopy, and derivatography that the reduction of Fe3+ to Fe2+ with the formation of The Fe3O4 magnetite phase occurred under various conditions of olefin (reaction mixture)-catalyst surface contact. The treatment of the catalyst with the reaction mixture and its oxidation decrease the degree of spinel phase imperfection.

Chemical synthesis and magnetic properties of well-coupled FePt/Fe compositenanotubes

A simple two-step hydrogen reduction method was used to synthesize FePt/Fe composite nanotubes. As thefirst step, L10 FePt nanotubes were prepared by heating a porous alumina template loaded with analcohol solution of a Fe chloride and Pt chloride mixture in flowing hydrogen at670 °C. Then, FePt/Fe composite nanotubes were obtained by reducing the alcohol solution of theFe chloride within the formed FePt nanotubes at a lower temperature, namely470 °C.Through changing the concentrations of initial alcohol solutions, the FePt:Fe atomic ratios of thecomposite nanotubes were easily adjusted and the magnetic properties were tuned accordingly. For(FePt)100−x/Fex compositenanotubes with x ranging between 0 and 26 at.%, the hard and soft phases were well coupled andthe coercivity was tunable over a large range (1.27–2.73 T). Furthermore, themarked interdiffusion between Fe and FePt, which usually exists in FePt-basedcomposites fabricated by using conventional methods, was not observed in the formedcomposite nanotubes. This indicates the two-step hydrogen reduction method to be apromising route for synthesizing nanocomposites which are difficult to fabricate byusing conventional methods due to the interdiffusion between different phases.

Effect of Ce(IV) doping on formation of goethite and its transformation to hematite

Cerium-doped goethite (α-FeOOH) samples were prepared by aqueous precipitation route. During doping Ce(IV)/Fe(III) atomic ratio was varied in the range of ∼0.014 to ∼0.07. The characterization by XRD showed that irrespective of the amount of cerium doping, all the sample were well crystallized showing only goethite as the crystalline phase. The cell parameter a of goethite marginally decreased while b and c marginally increased as the Ce(IV)/Fe(III) atomic ratio increased till 0.035:1 and further increase in this ratio showed much more increase in b and c cell parameters. The lattice image of a typical sample with Ce(IV)/Fe(III) = 0.035:1, indicated (1 1 0) plane of goethite lattice and no plane growth corresponding to any phase of cerium. On heating the samples to 673 K, it was observed that goethite is completely transformed to nano-sized α-Fe 2O 3 while the formation of cerium oxide was only partial. Further calcination to 1073 K showed the formation of two distinct phases of CeO 2 and α-Fe 2O 3. Lattice image of the same sample revealed that crystal growth of CeO 2 occurs along (1 1 1) plane. CeO 2 crystallites did not separate from α-Fe 2O 3. Nano-structures of CeO 2–α-Fe 2O 3 were retained even after calcination at 1073 K.

Conduction type and defect levels of β-FeSi 2 films grown by MBE with different Si/Fe ratios

[1 0 0]-oriented β-FeSi 2 films were grown on Si(0 0 1) substrates by molecular beam epitaxy (MBE) with a deposited Si to Fe atomic ratio (Si/Fe ratio) varied from 1.6 to 2.8. It was found that the conduction type of the β-FeSi 2 films changed from p- to n-type between the deposited Si/Fe=2.4 and 2.8. Rutherford Back Scattering (RBS) measurements revealed that the real Si/Fe ratio of β-FeSi 2 is 2.0–2.1 for all the samples after 900°C annealing for 14 h, showing that stoichiometry of the grown films is almost satisfied even though the deposited Si/Fe ratio was away from stoichiometry.