Fe-Mn Phases Research Articles

Selective leaching studies of sediments from a seamount flank in the Central Indian Basin: Resolving hydrothermal, volcanogenic and terrigenous sources using major, trace and rare-earth elements

We have investigated the sediments from a site where a newly discovered submarine hydrothermal alteration of recent origin is located to identify the source components and estimate their relative contribution. The site is situated on the flank of a seamount in the Central Indian Basin along the 76° 30′ E fracture zone which traces the movement of the Rodriguez triple junction. Detailed analyses of major, trace and rare earth elements (REE) on the bulk, leach, residue and clay fraction, and infra red spectroscopy studies of the clay fraction helped characterize the hydrothermal nature of the sediments. Selective dissolution carried out using HCl has allowed the discrimination between a leach phase (leachable Fe–Mn oxide) and a residue phase (refractory). The sediments are iron-rich, majority of Fe, Mn is in leachable fraction and are compositionally comparable to ridge-crest metalliferous sediments. Elemental ratios and geochemical discrimination plots of major element data reveal that the sediments are a mixture of Fe-rich mineral phases on one hand apparently from hydrothermal sources and aluminosilicates such as illite, zeolites, micaceous clays and smectites contributed from the Bengal fan, weathering of basinal basalts and authigenic processes. Ternary mixing calculations of bulk sediment major element data show that 35–45% metalliferous sediments could reproduce Fe and Mn values of our sediments. The shale normalized REE patterns of the bulk sediments are remarkably similar to those of the HCl soluble leach fraction, implying that the REEs in the HCl soluble leach fraction dominate the bulk fraction. HCl leacheates exhibit characteristics of vent fluids as well as seawater with pronounced Eu anomaly with HREE enrichment and negative Ce anomaly. The residue on the other hand has a high concentration of Fe, V, Zn, and Pb indicating a sulfidic input to the sediments. Ternary mixing calculations of REEs carried out on the residual fraction indicate that the sulfide-like material dominates (64–72%) over terrigenous (10–20%) and MORB derived (16–18%) components. This study helped us identify and quantify two types of hydrothermal material in the sediments, dominated by Fe–Mn phases (ferruginous oxides and silicates; Mn-oxides) in leachable fraction and sulfide-like material in residual phases. The clay fraction is mainly composed of dioctahedral smectites and has a composition similar to Alvin nontronite. The geochemical and mineralogical characteristics collectively suggest that these sediment-hosted precipitates formed at relatively low temperatures ranging between 50 and 100 °C from a mixture of seawater and hydrothermal fluids. The presence of hydrothermal sediments in the vicinity of a fracture zone suggests the occurrence of localized hydrothermal activity associated with intra plate volcanism. This is probably induced by reactivation of tectonic forces along the fracture zones.

Correlation between crystal structure and exchange bias of FePt/FeMn multilayers in parallel and perpendicular directions

AbstractA systematic study of parallel and perpendicular exchange biases and blocking temperatures in correlation with the crystal structure of FePt/FeMn multilayers fabricated onto MgO(001) substrates by ion beam sputter‐deposition system was conducted. It was evident that the exchange bias and blocking temperature have a close relation with the formation of the fcc FeMn phase. Besides, the blocking temperature of parallel exchange bias was found to be higher than that of the perpendicular one. The discrepancy was interpreted as due to the spin canting out of plane at the interface. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Study of the effect of Mn and Cu in Fe–Mn–Al–C–Cu alloys by ICEMS and XRD

Experimental analysis of magnetic and structural properties of Fe–Mn–Al–C–Cu alloys with compositions Fe x Mn0.915 − x Al0.075C0.01 (series A) and Fe x Mn0.912 − x Al0.075C0.01Cu0.003 (series B), 0.500 ≤ x ≤ 0.800, in steps of 0.050 is presented and discussed. The analysis was performed by integral conversion electrons Mossbauer spectrometry and X-ray diffraction at room temperature. The results suggest, for both series of alloys, that for the highest Mn content, samples exhibit an antiferromagnetic behavior, typical of the FCC or austenite FeMn phase rich in Mn; for those of low Mn content, the coexistence of paramagnetic austenite, typical of the FeMn alloy poor in Mn, a ferromagnetic BCC or ferrite phases can be observed, while for the lowest Mn content, only ferromagnetic (FM) phase tends to prevail. The FM phase is associated to the BCC FeMnAl as was corroborated by X-ray diffraction. The samples with the highest Mn content, the influence of Cu addition is to reduce the mean hyperfine field and to stabilize the antiferromagnetic behavior.

Fate of Heavy Metal Contaminants in Road Dusts and Gully Sediments in Guangzhou, SE China: A Chemical and Mineralogical Assessment

ABSTRACT The urban environment of Guangzhou, the largest industrialized center in SE China, has elevated levels of heavy metals. In places, Cu, Pb, and Zn contents exceed 490, 920, and 1,820 mg/kg, respectively. The accumulation of these contaminants is likely to accelerate as a consequence of rapid economic and industrial growth in the region. Understanding of the possible fate of the contaminants is therefore imperative in order to assess their potential long-term ecological impacts. This article documents the results of a sequential extraction procedure involving five operationally defined fractions to determine the chemical partitioning of Cu, Pb, and Zn in the urban deposits represented by road dusts and corresponding gully sediments. Special emphasis was given to the mineralogical characteristics of the urban deposits. Road dusts were mainly composed of quartz, K-Feldspar, plagioclase, and calcite, and contained minor amounts of mica and clay minerals. The corresponding gully sediments, however, typically contained minor amounts of calcite, mica, and clay minerals, and were dominated by quartz and K-feldspar. The road dusts and gully sediments exhibited comparable chemical partitioning patterns of Cu, Pb, and Zn, despite significant differences in the relative abundances of minerals, especially of calcite. Lead and Zn occurred mainly in the operationally defined carbonate/ specifically adsorbed (Pb: 48%; Zn: 50%) and Fe-Mn (Pb: 36%; Zn: 27%) phases, whereas Cu was largely associated with the organic (70%) and residual (15%) phases. In general, the residual phases of the heavy metal contaminants were equal or less than 15%, suggesting their dominantly anthropogenic origin. The relative mobility and bioavailability of the heavy metals in the urban deposits of Guangzhou was: Pb ∼ Zn > Cu. The ever-increasing accumulations of heavy metals may pose a threat in the region both to the environment and to human health.

Laser ablated Fe 100− xPd x and Fe 100− xMn x thin films ( x=20 and 50)

Thin films (50 nm) of Fe 100− x Pd x and Fe 100− x Mn x ( x=20 and 50) were deposited by laser ablation on a Si wafer and studied by X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS). In all cases, the XRD patterns of the target surface before and after ablation show a congruent transfer of ablated material. For the Fe 80Pd 20 thin film, XRD spectra show the formation of FePd, iron, Pd oxide and traces of hematite in the ablated film. Complementary information obtained by CEMS indicates the presence of an upper 50-nm thick surface layer of hematite in the deposited film. Fe 50Pd 50 phase was observed by CEMS and a Pd oxide component was identified by XRD, along with traces of hematite. In the case of Fe 80Mn 20, the CEMS spectrum is consistent with the occurrence of the antiferromagnetic FeMn phase and the XRD pattern also shows the presence of Fe in the structure. For the system Fe 50Mn 50, we obtain by CEMS an antiferromagnetic phase of FeMn and by XRD we trace the presence of nanohematite and in-depth iron. For x=20 in both iron-rich systems investigated, we observe the segregation of iron with subsequent conversion to hematite. The study shows that the stoichiometry of the compounds plays a decisive role in determining their structural and magnetic properties.

Reevaluation of the Fe-Mn phase diagram

New results for the enthalpy of mixing of liquid Fe-Mn alloys, the enthalpy of formation of γ-Fe-Mn solid solutions and the heat capacity of α-Fe-Mn and γ-Fe-Mn alloys obtained by isoperibolic calorimetry and differential thermal analysis (DTA) measurements have been used for the reassessment of the molar Gibbs energy of the various phases of the Fe-Mn system. Experimental information about martensitic transformation temperatures in Fe-Mn alloys published recently was incorporated in the updating of the occurring metastable equilibria. The present reevaluation results in a good fit with all available experimental data and is compared with the results of previous assessments.

Fe-Mn-Zn (Iron-Manganese-Zinc)

The Fe-Mn phase diagram [1993Oka] contains no intermediate phases. It depicts a wide range of mutual solid solubility between fcc Fe and Mn. At 450 °C, the stable solid solutions are: bcc Fe based has a range of 0-3 at.% Mn, the fcc solid solution has a range of 25.5-52 at.% Mn, and ( Mn) is stable between 69.5-100 at.% Mn. The Fe-Zn phase diagram (Fig. 1 under the Fe-Zn system on page 544) exhibits a loop, extensive solubility of Zn in bcc Fe ( ), and four intermediate phases: , 1, , and . For crystal structure data of the Fe-Zn compounds, see Table 1 under Fe-Zn. The Mn-Zn phase diagram [1990Oka] depicts a number of intermediate phases. Due to disagreements between various reports and the lack of confirmatory work, many parts of the diagram are tentative and qualitative [1990Oka]. At the temperature of interest here (450 °C), the stable phases are ( Mn), ( Mn), the three modifications of the hexagonal phase ( , 1, and 2), the hexagonal MnZn9 phase (denoted by [1990Oka]), and the liquid. The low temperature modification of MnZn9 (denoted 1 by [1990Oka]) is isostructural with (FeZn10) [1995Reu] and forms peritectoidally at 424 °C [1990Oka]. The monoclinic MnZn13 phase, which is isostructural with (FeZn13), forms peritectically at 428 °C [1990Oka].

Statistical study of trace elements in the soluble organic and amorphous Fe-Mn phases of surficial sediments, Sudbury Basin. 1. Multivariate and spatial analysis

Samples of humus and B-and C-horizon till collected from the north and east margins of the Sudbury Basin were analyzed for about 30 trace elements. The data consist of two sets of analyses, one being a conventional “near total” analysis following an aqua regia digestion, the other being a “partia” analysis from a selective leach designed to extract the metals bound to the soluble organic fraction of humus and to the amorphous Fe and Mn oxides of B- and C-horizon till. Statistical processing, using both standard approaches and some newly developed methods of spatial analysis, were applied to evaluate spatial geochemical patterns and their relationship to geological factors such as proximity to known mineral occurrences. In particular, the information content of the partial analyses was evaluated to determine whether the partial analyses reveal interpretable patterns not detected in the “near total” analyses. From a visual appraisal of dotplots of Ni and Cu in till, it is difficult to determine whether the partial data add anything not already seen in the “total” data. However, when residuals obtained by removing that part of the partial variation explained by the “total” variation are mapped, distinctive patterns are produced. These patterns are enhanced by applying an adaptive filtering technique using a spatial U-statistic. Multielement groups (“total” data, 30 elements in till) determined by principal components analysis show that the first two components are due to Ni-Co-Cr-Cu-Zn and Pd-Au-Pt-Sb associations. A multifractal area-concentration model fitted to component scores allows multielement anomalies to be mapped. The first component is shown to be spatially associated with Ni-Cu deposits, the second with Au and Ni-Cu-Au deposits. Analysis of variance, with “total”, partial and residual data taken in turn as the dependent (“response”) variable, shows that both Ni and Cu in till are significantly “explained” by geological factors (underlying rock type, proximity to contacts and to mineralization). Neither the “total” nor the partial analyses on their own show significant associations with these geological factors for either element in C-horizon till. This demonstrates the value of selective leach analyses, where they are carried out in addition to the “total” analyses, for this dataset. A multivariate analysis of variance shows that if all three surfical media (humus, B- and C-horizon till) are used, the selective extraction data are not so advantageous, although still adding some predictive capability, because additional “explanatory” information comes from multimedia rather than multiphase sources.

Effect of interface on exchange coupling in NiFe/FeMn system

The influence of the interface between NiFe and FeMn layers on the exchange coupling in the NiFe/FeMn system was investigated experimentally. The state of the interface between NiFe and FeMn thin films depends on the sequence of the NiFe and FeMn layers, deposition conditions and underlayer. The exchange coupling was exhibited only for samples with the FeMn film crystallized into the /spl gamma/-phase. The value of an exchange bias field barely depends on the amount of the /spl gamma/-FeMn phase. Even a small amount of the /spl gamma/-FeMn phase localized at the interface can provide a strong enough exchange coupling in the NiFe/FeMn system. The samples deposited on the Ta underlayer at room temperature exhibited the lowest roughness, smallest crystallite size and highest exchange coupling. At these conditions the interface between the NiFe and FeMn layers is smooth and sharp and results in a homogeneous and strong enough exchange bias field and low coercivity. The annealing changes the exchange coupling in the NiFe/FeMn system due to modification of the interface between the layers.

Imaging of the grain-to-grain epitaxy in NiFe/FeMn thin-film couples

It is known that a metastable crystalline thin-film structure can often be stabilized by choosing a suitable substrate. For single-crystal thin films, this pseudomorphic growth has been attributed to the stabilization of the metastable phase by epitaxial growth. However, in the polycrystalline structure, the mechanism is less clear. In this study, we have observed through plane-view and cross-section transmission electron microscopy (TEM) that the metastable fcc FeMn phase was stabilized by the underlaying NiFe layer. The continuous moiré fringes across the FeMn/NiFe interface as revealed by the cross-section TEM image indicate the existence of the epitaxial relationship between FeMn and NiFe. The epitaxial strain involved has also been found to be confined locally within each grain and was accommodated by the coherent strain across the interface. Consistent with the epitaxial strain observation, it is also found that this metastable fcc FeMn phase exists at the interface of NiFe and FeMn, and away from this interface, the stable A12 cubic FeMn phase is formed. Microdiffraction study showed that the epitaxially grown FeMn lattice was rotated through a small angle relative to the NiFe lattice. This rotation suggests that, in addition to the conventional lattice-dilation strain-epitaxy mechanism observed in single crystals with small misfit, there may be a rotation-epitaxy mechanism in the polycrystalline thin-film epitaxial structure.

An X-ray microanalysis study of the partition of manganese in 6 and 9% Mn cryogenic steels and its influence on the stability of austenite dispersed in a tempered martensitic matrix

X-ray microanalysis associated with scanning transmission electron microscopy has been used to study the partition of Mn between reverted austenite and tempered martensite laths in 6 and 9% Mn cryogenic steels tempered in the intercritical range. This partition is much smaller than that dictated by the equilibrium Fe-Mn phase diagram, which shows that austenite and ϵ-martensite can be stabilised in dispersed form even though their Mn content is much smaller than required by Schumann's diagram for martensitic transformation of bulk austenites. It is suggested that the very small size of these austenite islands has a stabilizing influence with respect to the γ → α′ transformation.