Fe-rich Ones Research Articles

(Invited) Electrochemical Deposition of Fe-Pt Magnetic Alloy Films with Large Magnetic Anisotropy

Electrodeposited films of Fe-Pt with a compact morphology, small grain size and low oxygen content have been obtained from a slightly alkaline solution containing Pt2+ diamino-dinitrite and Fe3+ complexed by citrate/glycine. As-deposited films exhibit a FCC structure for Pt-rich compositions, while Fe-rich ones are BCC; all these alloys are magnetically soft. Upon thermal annealing of equiatomic films in forming gas, phase transformation to the ordered tetragonal L10 structure occurs in parallel with magnetic hardening; the temperature for the onset of transformation is lower for thicker films. In particular, for ~100nm thick films, hardening starts at 350¢ªC, and coercivity saturates already at 450¢ªC, yielding values up to 13 kOe. Bilayers comprised of 15nm equiatomic Fe-Pt on top of Fe 75at. % films (5nm to 50nm) facilitate the hardening process in thin films, yielding about 50% increase in coercivity with respect to a single Fe-Pt layer of similar thickness when annealing at 550¢ª-650¢ªC.

Thermal stability of Fe–Mn binary olivine cathodes for Li rechargeable batteries

The phase stability of binary Fe and Mn olivine materials is extensively studied with temperature-controlled in situ X-ray diffraction (XRD) for various Fe/Mn ratios and state of charges (SOCs). We identify that the thermal behavior of partially charged olivine materials is sensitively affected by the Fe/Mn ratio in the crystal. While Fe-rich binary olivine materials readily formed a solid solution phase of Li1−yFe1−xMnxPO4 near room temperature or with only slight heating, the Mn-rich binary olivine retained its two-phase characteristic up to ca. 250 °C before decomposition into non-olivine phases. The thermal stability and decomposition mechanism of fully delithiated olivine materials are more sensitively affected by the Fe/Mn ratio in the crystal. The decomposition temperature varies from 200 °C to 500 °C among the different Fe/Mn ratios. It is generally observed that the Mn-rich binary olivine materials are inferior to the Fe-rich ones with respect to the thermal stability in the delithiated state.

Growth Behavior of Surface Oxide Layer on SUS316L Stainless Steel at the Early Stage of Exposure to 288°C Water

Surface oxide layer on SUS316L stainless steels exposed to 288°C pure water with 2 ppm dissolved oxygen (DO) for 1–100 h were analyzed using Focused Ion Beam (FIB) and Scanning Transmission Electron Microscope (STEM) technique to understand the early stage of surface oxide layer formation. In order to analyze the multi layered surface oxide, the interfaces between the outer and the inner oxide layers and that between the inner oxide layer and SUS316L substrate were determined from Energy Dispersive X-ray Spectroscopy (EDX) line profiles. At 1 h exposure, double oxide layer which is composed of compact inner oxide layer and outer oxide layer with Fe-rich and Ni-rich oxide particles was formed. At the outermost region of the SUS316L substrate, Ni and Cr were enriched. At 100 h exposure, growth of the inner oxide layer was suppressed and the Ni and Cr enriched region at the alloy substrate was preserved underneath the Ni-rich outer oxide particles. At 1 h exposure, most of the outer oxide particles were composed of Fe-rich ones, at 10 h exposure, another Ni-rich outer oxide particles were nucleated and grew faster than Fe-rich ones. Consequently, a part of pre-formed Fe-rich outer oxide particles were covered with Ni-rich ones.

Fe–Pt magnetic multilayers by electrochemical deposition

A series of magnetically soft/hard bilayers (BL) and multilayers with various sublayer thickness and configurations were prepared by electrodeposition from an alkaline solution using potential modulated waveforms and successive thermal annealing. In the as-deposited conditions the equiatomic layers grow with a face centered cubic FCC structure, and the Fe-rich ones with a body-centered cubic BCC structure. Annealing induces partial transformations of both structures to a L1 0 FCT phase. The coercivity of bilayers after annealing at or above 450 °C shows a maximum when the Fe-rich layer thickness is 10 nm; this configuration yields up to 45% increase in coercivity compared with single layers of 15 nm equiatomic Fe–Pt. Multilayer structures with fixed 5 or 10 nm Fe-rich layers show a coercivity enhancement similar to that of bilayers, suggesting that a bilayer structure is sufficient to facilitate magnetic hardening while minimizing the overall structure thickness. Either BLs or multilayers with 5 nm thick Fe-rich layers show a single phase magnetization behavior, behaving like a rigid magnet; those with 10 nm thick Fe-rich layers show instead a two stage magnetization switching, implying partial exchange decoupling.

The Fe-rich clay microsystems in basalt-komatiite lavas: importance of Fe-smectites for pre-biotic molecule catalysis during the Hadean eon.

During the Hadean to early Archean period (4.5-3.5 Ga), the surface of the Earth's crust was predominantly composed of basalt and komatiite lavas. The conditions imposed by the chemical composition of these rocks favoured the crystallization of Fe-Mg clays rather than that of Al-rich ones (montmorillonite). Fe-Mg clays were formed inside chemical microsystems through sea weathering or hydrothermal alteration, and for the most part, through post-magmatic processes. Indeed, at the end of the cooling stage, Fe-Mg clays precipitated directly from the residual liquid which concentrated in the voids remaining in the crystal framework of the mafic-ultramafic lavas. Nontronite-celadonite and chlorite-saponite covered all the solid surfaces (crystals, glass) and are associated with tiny pyroxene and apatite crystals forming the so-called "mesostasis". The mesostasis was scattered in the lava body as micro-settings tens of micrometres wide. Thus, every square metre of basalt or komatiite rocks was punctuated by myriads of clay-rich patches, each of them potentially behaving as a single chemical reactor which could concentrate the organics diluted in the ocean water. Considering the high catalytic potentiality of clays, and particularly those of the Fe-rich ones (electron exchangers), it is probable that large parts of the surface of the young Earth participated in the synthesis of prebiotic molecules during the Hadean to early Archean period through innumerable clay-rich micro-settings in the massive parts and the altered surfaces of komatiite and basaltic lavas. This leads us to suggest that Fe,Mg-clays should be preferred to Al-rich ones (montmorillonite) to conduct experiments for the synthesis and the polymerisation of prebiotic molecules.

Compositions of heavy minerals in Northeastern China sandlands and provenance analysis

Sand samples deposited since the Last Glacial Maximum (LGM) from the Hulun Buir, Horqin and Otindag sandlands were measured for their assemblages of heavy minerals and chemical compositions of detrital garnets and tourmalines. Heavy mineral assemblages of these three sandlands consist mainly of garnet, ilmenite, epidote and minor amphibole and magnetite. Garnets consist mainly of high Mg type-A ones (58% on average), and minor type-B ones. Toumalines are mainly composed of Mg-rich and minor Fe-rich ones. Compared with those of central-southern Mongolia and central Tarim, these three sandlands are derived from the Phanerozoic rocks of the Central Asian Orogenic Belt and the Archean and Paleoprotorozoic basement rocks of the North China Craton. Our results provide direct evidence that the present-day sands may be reworked from LGM ones. Differences of heavy mineral compositions occur between the samples of the three sandlands and Taklimakan Desert, indicating that the material of the western arid regions contributes little to the eastern sandlands.

An experimental study of the Fe-Mn exchange between garnet and ilmenite

The exchange equilibrium was studied by reversal experiments as a function of temperature (650 ≤ T ≤ 1000 °C), pressure (10 ≤ P ≤ 20 kbar), and chemical composition. Experiments were performed in a piston-cylinder apparatus using starting mixtures consisting of 95% garnet and 5% ilmenite. At the lower temperatures, 3–5% PbO flux was added to the reactants. The PbO was reduced to metallic lead by the graphite of the capsules. The EMP analysis shows that ilmenite is essentially a solid solution of FeTiO3 and MnTiO3 with up to 4.5 mol% Fe2O3 (for Fe-rich compositions). Garnet is compositionally close to (Fe,Mn)3 Al2Si3O12 but apparently contains up to 1.0 wt% TiO2. As garnet was usually analyzed within 5–15 μm distance from ilmenite grains, the Ti measured in garnet appears to be largely an analytical artifact (due to secondary fluorescence). This was confirmed by analyzing profiles across a couple constructed from ilmenite and Ti-free garnet. The more than 100 exchange runs indicate that the distribution coefficient KD [=(X Mn gnt·X Fe ilm)/(X Fe gnt·X Mn ilm)] is essentially independent of P and decreases with T. With a few exceptions at Mn-rich compositions, the present results are consistent with previous studies on the Fe-Mn partitioning between garnet and ilmenite. Contrary to previous studies, however, the narrow experimental brackets obtained during the present calibration constrain that, at constant T, KD is larger for Mn-rich compositions than for Fe-rich ones. This compositional dependence of KD will complicate garnet-ilmenite geothermometry. Mutually consistent activity models for Fe-Mn garnet and ilmenite, based on a thermodynamic analysis of the present results and other phase equilibria studies in the system Fe-MnO-Al2O3-TiO2-SiO2-O2, will be presented in a following contribution (M. Engi and A. Feenstra, in preparation).

Mineralogy, chemical composition and structure of the MIR Mound, TAG Hydrothermal Field

The study of samples collected from the surface of the MIR mound (TAG Hydrothermal Field) by video‐controlled hydraulic grab allowed identification of a number of mineralogical types. These include pyrite‐chalcopyrite (Py‐Cp), bornite‐chalcopyrite‐opaline (Bn‐Cp‐Op) and sphalerite‐opaline (Sp‐Op) sulfide chimneys, massive sulfides composed of pyrite (Py), chalcopyrite‐pyrite (Cp‐Py), marcasite‐pyrite‐opaline (Mc‐Py‐Op), sphalerite‐pyrite‐opaline (Sp‐Py‐Op) and sphalerite‐chalcopyrite‐pyrite‐opaline (Sp‐Cp‐Py‐Op), as well as siliceous and Fe‐Mn oxide hydrothermal deposits. Most of the minor elements (Ag, Au, Cd, Ga, Hg, Sb and Pb) are associated with Zn‐rich massive sulfides, Co Bi, Pb, and As with Ferich ones, while Cu‐rich sulfides are depleted of trace metals. Cu‐enriched assemblages are concentrated in the northern part, Zn‐enriched in the center, and siliceous rocks in the south of the MIR mound. According to paragenetic relations, the development of the mound started with the formation of quartz (originally opaline) rocks and dendritic assemblages of melnikovite‐pyrite, followed by deposition of chalcopyrite and recrystallization of primary pyrite, subsequent generation of sphalerite‐rich assemblages and final deposition of opaline rocks. The late renewal of hydrothermal activity led to local formation of Cu‐rich chimneys enriched in Au, Ag, Hg and Pb probably due to their remobilization from inner parts of the deposit.

Magnetic, Chemical, and Microscopical Characterization of Urban Soiling on Historical Monuments

The paper reports a study on the magnetic fraction in soiling crusts on urban building stones which, due to their high porosity and surface roughness, act as preferential depositional sites for airborne particles including Fe-rich ones. A new analytical procedure involving magnetic measurements of bulk samples followed by magnetic separation of the particulate fraction in the crusts for scanning electron microscopy (SEM) combined with quantitative energy dispersive spectroscopy (EDS) has been tested to assess its efficiency in differentiating between sources of magnetic airborne particles deposited at the surface of historical buildings in the U.K.

A transitional structural state and anomalous Fe-Mg order-disorder in Mg-rich orthopyroxene (Mg (sub 0.75) Fe (sub 0.25) )2Si2O6

ABSTRACf From in-situ structure and site occupancy refinements of a synthetic orthopyroxene, (Mm and (2) the In KD values (where KD = FeM1MgM2/ FeM2MgM1) vary linearly with liT (K) between 1000 and 1200 K, but nonlinearly between 1200 and 1300 K. The drastic straightening of the silicate chains at 1300 K is accompanied by the attainment of very similar configurations of the SiO. tetrahedra, SiA and SiB, in shapes, sizes, and out-of-plane tiltings. The rigid-body thermal vibration analysis suggests that the librational motion of the SiA tetrahedron (8.1°2) is slightly larger than that of SiB (5.2°2) at 296 K but becomes considerably smaller (48.0°2) than that of SiB (77.3°2) at 1300 K. The M I octahedron remains nearly regular from 296 to 1300 K, whereas the M2 coordination changes from sixfold (296 K) to sevenfold (1200 K) and to sixfold (1300 K) because of the bridging 03B moving out and 03B' moving into the coordination sphere (r ~ 3.0 A) at elevated temperatures. At 1300 K, the highly distorted M2 octahedron shares two edges with SiA and SiB, rather than one with SiA at 296 K, and the structure has all features of the high-temperature orthopyroxene phase predicted by Pannhorst (1979), which, in fact, is a transitional structural state between orthopyroxene and the so-called protoenstatite. On the basis of the configurations of the silicate chains in Mg- and Fe-rich orthopyroxenes at high temperature, an explanation is given as to why Mg-rich orthopyroxenes tend to transform to the protoenstatite structure with increasing temperature, whereas Fe-rich ones tend to transform to a clinopyroxene with space group C2/c. The anomalous behavior of the Fe-Mg order-disorder above 1200 K is attributed to the existence of the transitional state, particularly the changing charge distribution around the M2 site.

Thermal expansion, Debye temperature and Gr�neisen parameter of synthetic (Fe, Mg)SiO3 orthopyroxenes

Thermal expansion properties of synthetic orthopyroxenes (Fe0.20Mg0.80)SiO3, (Fe0.40Mg0.60)SiO3, (Fe0.50Mg0.50)SiO3, (Fe0.75Mg0.25)SiO3 and (Fe0.83Mg0.17)SiO3 were systematically studied by means of single-crystal x-ray diffraction in the temperature range from 296 to 1300 K. The measurements of unit cell dimensions as a function of temperature reveal that the a and c dimensions and the unit cell volume V increase nonlinearly with a positive curvature with rising temperature, whereas the b dimension behaves differently, depending on the total Fe content. For Mg-rich orthopyroxenes (Fe/(Fe+Mg) 30%. Together with the high temperature neutron diffraction data on enstatite (MgSiO3) (McMullan, Haga and Ghose, unpublished) and x-ray diffraction data on ferrosilite (FeSiO3) (Sueno et al. 1976), the measured unit cell dimensions were analyzed in terms of the Gruneisen theory of thermal expansion. The linear thermal expansion coefficients α a and α c both increase as temperature is elevated, with α c increasing faster, while α b changes gradually from increasing for Mg-rich orthopyroxenes to decreasing for Fe-rich orthopyroxenes. The relative magnitudes of linear thermal expansion coefficients are always in the order α b >α c >α a between 300 and 500 K, but at higher temperatures, the order changes to α c >α b >α a for Mg-rich orthopyroxenes and α c >α a >α b for Fe-rich ones. The linear thermal expansion behavior is interpreted on the basis of the structural mechanical model of Weidner and Vaughan (1982). The anomalous behavior of α b is mainly attributed to the changes in the Fe2+ population at the M2 site and the relative stiffness of the M2(Fe2+)-O bonds compared to the M2(Mg2+)-O bonds. The volume thermal expansion coefficients are nonlinear functions of temperature and lie between 23 and 49×10−6/K. The previously reported results of mean volume thermal expansion coefficients appear to represent the α V values characteristic of higher temperatures compared to our results. The thermal Debye temperatures are composition-dependent, decreasing linearly from 812 (MgSiO3) to 561 K (FeSiO3), and are systematically higher than the corresponding acoustic Debye temperatures. The Gruneisen parameters range from 0.85 to 0.89 and do not seem to vary with composition. The linear compressibilities derived from thermal expansion and elastic moduli data agree very well. The pressure derivatives of the isothermal bulk modulus (dK0/dP) are also composition-dependent and decrease from 11.2 (MgSiO3) to 8.77 (FeSiO3). Such large values indicate possible anomalous elastic behavior of orthopyroxenes at high pressures in the Earth's upper mantle.

Authigenesis of Impact Spheroids in the K/T Boundary Clay from Italy: New Constraints for High-Resolution Stratigraphy of Terminal Cretaceous Events

ABSTRACT Detailed chemical and mineralogical analyses of authigenically altered impact spheroids contained in the Cretaceous/Tertiary (K/T) boundary clay of the northeastern Apennines provide information about the chemical conditions on the sea floor of a deep pelagic basin immediately after the impact of a large extraterrestrial object against the Earth's surface. The temporal alteration of global meterologic conditions resulting from this catastrophic event caused the death of most planktonic and nektonic biomass of the oceans. Dead organisms settled on the seafloor creating low-pH, low-Eh conditions at the water-sediment interface. Reducing and slightly acidic waters percolated in the top sediment, causing reduction and leaching of iron and dissolution of the top surface of the calcareous o ze. The suppression of biogenic calcium carbonate production in the upper water column, and the reducing conditions in the seafloor, lasted for a period not longer than 50 Ka. During this time, only detrital silt and clay were deposited in the basin, along with the fallout material derived from the impact cloud. The fallout included spherules of sub-millimeter size which condensed from vaporized and/or molten terrestrial target rock admixed with the vaporized impactor. The heterogeneous chemical composition of the spherules, and the wide range of shapes of relict crystals preserved in them, suggest that they were originally made of a suite of high-temperature quenched minerals ranging in composition from silica-rich/iron-poor ones (plagioclase), to iron-rich/silica-poor ones (spinel-beat ng clinopyroxene and olivine). The slightly reducing conditions of the seafloor favored the authigenic growth of K-feldspar in Si-rich spherules, and of glaucony in the Fe-rich ones. In some parts of the paleobasin, characterized by stronger reducing conditions, K-feldspar authigenesis did not occur, and spheroids were preferentially altered to pyrite and glaucony. The resumption of carbonate deposition resulting from the post-K/T plankton bloom coincided with the restoration of normal oxidizing conditions in most parts of the paleobasin. Such conditions caused the arrest of glauconitic growth and the alteration of the most Fe-rich spherules to goethite. Bioturbation activity also resumed in the top sediment, causing slight vertical mixing in the K/T boundary clay layer. In addition to the mineralogical and chemical description and the interpretation of the authigenic phases contained in the Italian K/T boundary clay, this paper includes a high-resolution stratigraphic analysis of the boundary clay in the Petriccio section which is the best preserved among the several K/T sections studied in the northeastern Apennines. The most relevant discovery from this study is that the impact spherules are concentrated in the central part of the clay layer along with the peak of an iridium anomaly, whereas grains of quartz with multisets of parallel lamellae, which are considered a product of impact shock-metamorphism, are mostly concentrated in the bottom part of the layer. This clear decoupling may represent several thousands of years of delay in deposition of ridium and spheroids with respect to shocked quartz and suggests two impact events closely spaced in time. However, further high-resolution analyses in other sections in the northeastern Apennines and elsewhere around the world is advised for more definitive confirmation for a terminal Cretaceous multiple-impact hypothesis.

Calcium-poor garnet in relation to metamorphism

1. (1) The writer has carried out a systematic study of pyralspites (calcium-poor garnets) in pelitic metamorphic rocks of the Gosaisyo-Takanuki district. With the increase in metamorphic grade of their host-rocks, the MnO content of the pyralspites decreases, while the FeO content increases. Accompanying the variations in composition, the edge length of the unit cell of the minerals shortens and the refractive index becomes generally higher. The associated biotite also varies in composition and proportion with advancing metamorphism. 2. (2) The MnO content of pyralspites in ordinary politic metamorphic rocks generally decreases with the increase in metamorphic grade. When we use main mineral facies as a scale of metamorphic grade, however, the MnO contents of pyralspites in ordinary politic metamorphic rocks of the same mineral facies differ in different districts, owing to the difference in character of metamorphism in different districts. Thus, the MnO contents of pyralspites in ordinary pelitic metamorphic rocks are a useful indicator of the character of metamorphism (Fig. 5). 3. (3) When we treat pyralspites not only from ordinary pelitic metamorphic rooks, but also from rocks of a much wider range of composition, the minerals show a progressive enlargement of their composition field from Mn-rich compositions to Fe-rich ones, and further to Mg-rich ones, with advancing metamorphism, instead of the above-mentioned gradual decrease in MnO content (Fig. 7). 4. (4) The progressive enlargement of the composition field in pyralspite with advancing metamorphism can be explained in terms of crystal chemistry. Mn +2 ions are the most appropriate in size to enter the crystal structure of pyralspite, and so only pyralspite rich in Mn +2 can be formed at very low temperatures. With the increase in the temperature of its formation, ions whose ionic radii are less appropriate to the crystal, such as Fe +2 and further Mg +2, become increasingly free to enter the crystal, and so the composition field of pyralspite becomes progressively larger with advancing metamorphism of the host-rocks. Such cryatallo-chemical properties of pyralspite reveal themselves also in the distribution of Mn +2, Fe +2, and Mg +2 in pyralspites and associated ferromagnesian minerals.