Showing papers on "Hematite published in 2001"
TL;DR: In this article, the authors argue that these hematite deposits have formed by a process involving chemical precipitation from aqueous fluids, under either ambient or hydrothermal conditions, and provide evidence that liquid water has been stable at or near the surface for millions of years by analogy with terrestrial iron formations, in specific locations on early Mars.
Abstract: Near-global (60°S to 60°N) thermal infrared mapping by the Thermal Emission Spectrometer (TES) on Mars Global Surveyor has revealed unique deposits of crystalline gray hematite (α-Fe2O3) exposed at the Martian surface in Sinus Meridiani, Aram Chaos, and in numerous scattered locations throughout Valles Marineris. The Sinus Meridiani material is an in-place, rock stratigraphic sedimentary unit characterized by smooth, friable layers composed primarily of basaltic sediments with ∼10–15% crystalline gray hematite. This unit has outliers to the north that appear to have formed by stripping and removal. The hematite within Aram Chaos occurs in a sedimentary layer within a closed basin that was likely formed during the basin infilling and predates the formation of nearby chaos and outflow terrains. This unit appears to be exposed by erosion and may be more extensive beneath the surface. The Valles Marineris occurrences are closely associated with the interior layered deposits and may be in place within the layers or eroded sediments. Overall, crystalline gray hematite is extremely uncommon at the surface, yet in all observed locations it is closely associated with layered, sedimentary units. Here we argue that these hematite deposits have formed by a process involving chemical precipitation from aqueous fluids, under either ambient or hydrothermal conditions. Thus the TES mineralogic data provide evidence that liquid water has been stable at or near the surface, probably for millions of years by analogy with terrestrial iron formations, in specific locations on early Mars.
345 citations
TL;DR: The aim of this study was to examine the catalyzed decomposition of hydrogen peroxide and 2-chlorophenol in the presence of iron oxides and granular ferrihydrite, goethite, and hematite were selected as catalysts.
259 citations
TL;DR: In the presence of sulfate-reducing bacteria ( Desulfovibrio desulfuricans ) hematite (α-Fe 2 O 3 ) dissolution is affected potentially by a combination of enzymatic (hydrogenase) reduction and hydrogen sulfide oxidation as mentioned in this paper.
195 citations
TL;DR: In this paper, a model for the growth of epitaxially grown iron oxides and for redox processes involving the oxides was suggested for the formation of several equilibrium surface phases.
Abstract: Thermodynamic stability ranges of different iron oxides were calculated as a function of the ambient oxygen or water gas phase pressure (p⩽1 bar) and temperature by use of the computer program EquiTherm. The phase diagram for Fe–H2O is almost completely determined by the O2 pressure due to the H2O dissociation equilibrium. The formation of epitaxially grown iron oxide films on platinum and ruthenium substrates agrees very well with the calculated phase diagrams. Thin films exhibit the advantage over single crystals that bulk diffusion has only limited influence on the establishment of equilibrium phases. Near the phase boundary Fe3O4–Fe2O3, surface structures are observed consisting of biphase ordered domains of FeO(111) on
both oxides. They are formed due to kinetic effects in the course of the oxidation to hematite or reduction to magnetite, respectively. Annealing a Fe3O4(111) film in 5 × 10−5
mbar oxygen at 920–1000 K results in a new γ-Fe2O3(111)-like
intermediate surface phase during the oxidation to α-Fe2O3(0001). A model is suggested for the growth
of iron oxides and for redox processes involving iron oxides. The formation of several equilibrium surface phases is discussed.
188 citations
TL;DR: Band component analysis data of FTIR spectra support the fact that the hydroxyl units mainly affect the a plane in goethite and the equivalent c plane in hematite.
152 citations
TL;DR: In this article, a plausible dehydration mechanism, which is compatible with our DTA/DSC results, is deduced from TEM investigations, and transformation enthalpies and activation energies for the dehydration process are given.
Abstract: Synthetic pigments of goethite (BayferroxR) of different particle size were investigated by DTA, IR, DSC, TG and X-ray diffraction measurements. It follows that a so-called ‘hydrohematite’ described in the literature does not exist as a discrete intermediate during the dehydration course from goethite to hematite. Instead we observed a dependence of the dehydration mechanism on the particle size. Transformation enthalpies and activation energies for the dehydration process will be given. A plausible dehydration mechanism, which is compatible with our DTA/DSC results, is deduced from TEM investigations.
147 citations
TL;DR: In this paper, the influence of surface-bound fulvic acid on the sorption of colloidal hematite particles was studied experimentally and the results were compared with model calculations based on the linear additivity assumption.
143 citations
TL;DR: Transmission electron microscopy observations of cells prepared by whole-mount, conventional embedding, and freeze-substitution methods confirmed the close association between cells and minerals and suggested that in some instances, the mineral crystals had even penetrated the outer membrane and peptidoglycan layers.
Abstract: Shewanella putrefaciens, a gram-negative, facultative anaerobe, is active in the cycling of iron through its interaction with Fe (hydr)oxides in natural environments. Fine-grained Fe precipitates that are attached to the outer membranes of many gram-negative bacteria have most often been attributed to precipitation and growth of the mineral at the cell surface. Our study of the sorption of nonbiogenic Fe (hydr)oxides revealed, however, that large quantities of nanometer-scale ferrihydrite (hydrous ferric oxide), goethite (alpha-FeOOH), and hematite (alpha-Fe(2)O(3)) adhered to the cell surface. Attempts to separate suspensions of cells and minerals with an 80% glycerin cushion proved that the sorbed minerals were tightly attached to the bacteria. The interaction between minerals and cells resulted in the formation of mineral-cell aggregates, which increased biomass density and provided better sedimentation of mineral Fe compared to suspensions of minerals alone. Transmission electron microscopy observations of cells prepared by whole-mount, conventional embedding, and freeze-substitution methods confirmed the close association between cells and minerals and suggested that in some instances, the mineral crystals had even penetrated the outer membrane and peptidoglycan layers. Given the abundance of these mineral types in natural environments, the data suggest that not all naturally occurring cell surface-associated minerals are necessarily formed de novo on the cell wall.
143 citations
TL;DR: In this paper, the top 135 m of the Luochuan section on the Chinese Loess Plateau was examined with a diffuse reflectance spectrophotometer from the near ultraviolet, through the visible, and into the near infrared.
133 citations
TL;DR: The oxide-scale structure developed on commercial hot-rolled steel strip at the mid-coil position was examined in this article, where various final scale structures developed after coiling, depending on the coiling temperature, oxygen availability, and cooling rate.
Abstract: The oxide-scale structure developed on commercial hot-rolled steel strip at the mid-coil position was examined. The initial oxide scale after rolling and cooling on the run-out table had a three-layer (hematite, magnetite, and wustite) structure; the thickness was found to be a function of the finishing temperature. From this initial structure, various final scale structures developed after coiling, depending on the coiling temperature, oxygen availability, and cooling rate. For relatively low coiling temperatures (e.g., at 520°C), the final scale structure comprised an inner magnetite/iron mixture layer, an outer magnetite layer, and, at regions away from the center, a very thin outermost hematite layer. For higher coiling temperatures (e.g., in the range of 610 to 720°C), a two-layer hematite/magnetite structure was observed at the edge regions, whereas at the center regions, these two layers were absent and the entire scale layer comprised a mixture of the wustite-transformation products, i.e., a mixture of proeutectoid magnetite, magnetite+iron eutectoid, and a certain amount of retained wustite. At regions between the edges and the center, the oxide structures were similar to those developed at low coiling temperatures (<570°C), i.e., an inner layer comprising a mixture of the wustite-transformation products, an intermediate magnetite layer and at regions near the edges, an outermost hematite layer. In addition, two distinct structures were observed on strips with a coiling temperature of 720°C. One structure comprised a very thick hematite layer (3–5 μm) formed near the edges (within 10–20 mm from the edges), while the other structure comprised a substantial amount of retained wustite formed at the center regions. The formation mechanisms of various oxide scale structures are discussed.
125 citations
TL;DR: The results provide the first strong evidence for direct use (i.e., without prior dissolution) of colloidal iron by mixotrophic phytoplankton by flagellates and document a new pathway of iron acquisition that may be important for their survival in low-iron waters of the sea.
Abstract: Three species of photosynthetic flagellates capable of phagotrophy (mixotrophic species) were tested for their abilities to use inorganic iron colloids for growth. Ochromonas sp., Chrysochromulina ericina (a coastal strain), and C. ericina (an oceanic strain) were grown in iron-free seawater supplemented with 1 mM Fe-ferrihydrite (amorphous hydrous ferric oxide), magnetite (Fe3O4)/maghemite (g-Fe2O3), hematite (a-Fe2O3), or goethite (a-FeOOH). Desferrioxamine B, an iron-binding siderophore, was used to reduce the concentration of dissolved iron in the colloid-amended media, and none of the flagellates were able to use its iron complex as an iron source under the conditions of the experiments. Both strains of Chrysochromulina grew at 35%‐70% of their maximum rates with goethite, hematite, and magnetite/maghemite but were unable to use ferrihydrite. Ochromonas grew well with ferrihydrite but could not use any of the other forms. Thalassiosira oceanica (clone 1003) and Thalassiosira pseudonana (clone 3H), diatoms that could only take up dissolved forms of iron, were unable to use any of the colloids tested. The mechanism of iron acquisition by the flagellates appeared to involve ingestion of the iron colloids, because bacteria resident in the cultures were too iron poor to be a significant source of iron and were unable to use the iron contained in the colloids themselves. Variations in the sizes of the colloids were hypothesized to account for differences in their availability, independent of colloid chemical stability. The results provide the first strong evidence for direct use (i.e., without prior dissolution) of colloidal iron by mixotrophic phytoplankton and document a new pathway of iron acquisition that may be important for their survival in low-iron waters of the sea.
TL;DR: In this article, the preparation of nanocrystalline β-FeO(OH) by precipitation from an aqueous solution of the chloride salt and the investigation of relative surface properties of the iron oxyhydroxide gel were the aims of the study.
TL;DR: In this article, the adsorption of Fe(II) onto hematite was measured as a function of pH, surface area, and time, and the effects of anions (chloride, sulfate, or nitrate) and of Zn(II), were also determined.
TL;DR: In this paper, the spectral properties of phyllosilicate-poor palagonitic tephra from the upper slopes of Mauna Kea Volcano (Hawaii) were studied by X-ray diffraction (XRD), XRF, visible and near-IR reflectance spectroscopy, and transmission electron microscopy (TEM).
Abstract: The mineralogical and elemental composition of dust size fractions (<2 and <5 μm) of eight samples of phyllosilicate-poor palagonitic tephra from the upper slopes of Mauna Kea Volcano (Hawaii) were studied by X-ray diffraction (XRD), X-ray fluorescence (XRF), visible and near-IR reflectance spectroscopy, Mossbauer spectroscopy, magnetic properties methods, and transmission electron microscopy (TEM). The palagonitic dust samples are spectral analogues of Martian bright regions at visible and near-IR wavelengths. The crystalline phases in the palagonitic dust are, in variable proportions, plagioclase feldspar, Ti-containing magnetite, minor pyroxene, and trace hematite. No basal reflections resulting from crystalline phyllosilicates were detected in XRD data. Weak, broad XRD peaks corresponding to X-ray amorphous phases (allophane, nanophase ferric oxide (possibly ferrihydrite), and, for two samples, hisingerite) were detected as oxidative alteration products of the glass; residual unaltered glass was also present. Mossbauer spectroscopy showed that the iron-bearing phases are nanophase ferric oxide, magnetite/titanomagnetite, hematite, and minor glass and ferrous silicates. Direct observation by TEM showed that the crystalline and X-ray amorphous phases observed by XRD and Mossbauer are normally present together in composite particles and not normally present as discrete single-phase particles. Ti-bearing magnetite occurs predominantly as 5–150 nm particles embedded in noncrystalline matrix material and most likely formed by crystallization from silicate liquids under conditions of rapid cooling during eruption and deposition of glassy tephra and prior to palagonitization of glass. Rare spheroidal halloysite was observed in the two samples that also had XRD evidence for hisingerite. The saturation magnetization Js and low-field magnetic susceptibility for bulk dust range from 0.19 to 0.68 Am2/kg and 3.4×10−6 to 15.5×10−6 m3/kg at 293 K, respectively. Simulation of the Mars Pathfinder Magnet Array (MA) experiment was performed on Mauna Kea Volcano in areas with phyllosilicate-poor palagonitic dust and with copies of the Pathfinder MA. On the basis of the magnetic properties of dust collected by all five MA magnets and the observation that the Pathfinder MAs collected dust on the four strongest magnets, the value for the saturation magnetization of Martian dust collected in the MA experiments is revised downward from 4±2 Am2/kg to 2.5±1.5 Am2/kg. The revised value corresponds to 2.7±1.6 wt % magnetite if the magnetic mineral is magnetite (using Js = 92 Am2/kg for pure magnetite, Fe3O4) or to 5.0±3.0 to 3.4±2.0 wt % maghemite if the magnetic mineral is pure maghemite (using Js = 50 to 74 Am2/kg for pure maghemite, γ-Fe2O3). Comparison of the magnetic properties of bulk Mauna Kea palagonitic dust to those for dust collected by MA magnets shows that the MA magnets extracted (culled) a subset (25–34 wt %) of composite magnetic particles from bulk dust. The extent of culling of Martian dust is not well constrained. Because the Mauna Kea palagonitic dust satisfies the essential constraints of the Pathfinder magnetic properties experiment (composite and magnetic particles capable of being collected by five MA magnets), a working hypothesis for the strongly magnetic mineral present in Martian dust and soil is magnetite (possibly Ti-bearing) formed by rapid crystallization from silicate liquids having volcanic and/or impact origins. Subsequent palagonitization of the glass produces the nanophase ferric oxide phases that dominate the spectral properties of Martian bright regions at visible and near-IR wavelengths. Magnetic and phyllosilicate-poor palagonitic dust from Mauna Kea Volcano is thus a spectral and magnetic analogue for magnetic Martian dust.
TL;DR: It is found that the by-product--Bayer sodalite--has the high exchange capacity for Na+ that might contribute to the long-term environmental problems.
TL;DR: A framework doping method was proposed to dope transition-metal iron ions into the framework instead of the tunnels of 2 × 2 tunnel structure manganese octahedral molecular sieve cryptomelane as mentioned in this paper.
Abstract: A framework doping method was proposed to dope transition-metal iron ions into the framework instead of the tunnels of 2 × 2 tunnel structure manganese octahedral molecular sieve cryptomelane. Iron was first doped into the MnO6 octahedra layers of layered structure birnessite, which served as a synthetic precursor for tunnel structure cryptomelane. Iron-doped cryptomelane was obtained by the thermal transformation of iron-doped birnessite. The effects of temperature and the amount of iron doping on the thermal transformation from birnessite to cryptomelane were also studied. Iron was evenly doped into the framework without producing other phases if iron doping was less than 10% of the total manganese. Hematite phases appeared if iron doping reached 16% of the total manganese. A doping limit of iron was observed for tunnel structure cryptomelane. X-ray photoelectron spectroscopy and electron paramagnetic resonance were used to analyze the local chemical environment of manganese and iron in cryptomelane, su...
TL;DR: In this article, a planetary ball mill was used to transform hematite α-Fe 2 O 3 powder with a dispersing liquid (ethanol) for different times using a steel vial, and both high resolution transmission electron microscopy (HRTEM), X-ray diffraction and zero and in-field Mossbauer spectrometry measurements reveal that the nanostructured powders contain maghemite.
TL;DR: Aeromagnetic maps of the Egersund mid-proterozoic igneous province show a spectacular range of positive and negative magnetic anomalies with a contrast up to 15 600 nT.
Abstract: Aeromagnetic maps of the Egersund Mid-Proterozoic igneous province show a spectacular range of positive and negative magnetic anomalies with a contrast up to 15 600 nT. The positive magnetic anomalies are over magnetite norites and overlying mangerites and quartz mangerites of the Bjerkreim-Sokndal layered intrusion. These rocks are dominated by multi-domain (MD) magnetite. The negative magnetic anomalies are over ilmenite-rich norites of the Bjerkreim-Sokndal layered intrusion, the Tellnes ilmenite norite ore deposit, and massif anorthosites. These rocks are dominated by hemo-ilmenite and/or by silicates containing fine-grained oxide exsolution lamellae. Electron microprobe analyzes of coexisting Fe-Ti oxides in the layered intrusion confirm earlier observations that oxides in early magmatic rocks are dominated by hemo-ilmenite with minor end-member magnetite, followed by more reduced oxides dominated by titanomagnetite with minor near end-member ilmenite. What is not fully understood is the property of ilmenite with hematite exsolution lamellae, or, even more striking, hematite with ilmenite lamellae, to produce strong remanent magnetization of high coercivity and with a Neel temperature equal to or above the Curie temperature of magnetite. This property makes the rhombohedral oxides an important candidate to explain some high-amplitude deep-crustal anomalies on earth, or strong remanent magnetization on other planets. A remarkable feature in the Egersund province is that primitive magmas produced rocks rich in hemo-ilmenite causing negative magnetic anomalies related to magnetic remanence, and more evolved magmas produced rocks rich in magnetite related to positive induced magnetic anomalies, all in the course of crystallization-differentiation.
TL;DR: In this article, the authors used optical microscopy, electron microprobe (EMP), transmission electron microscopy (TEM), and rock-magnetic measurements to identify antiferromagnetically ordered (AF) hematite and ilmenite.
Abstract: Mid-Proterozoic granulites in SW Sweden, having opaque minerals hematiteilmenite with minor magnetite, and occurring in an area with negative aeromagnetic anomalies, have strong and stable reversed natural remanent magnetization ∼9.2 A/m, with 100% remaining after demagnetization to 100 mT. Samples were characterized by optical microscopy, electron microprobe (EMP), transmission electron microscopy (TEM), and rock-magnetic measurements. Earliest oxide equilibrium was between grains of titanohematite and ferri-ilmenite at 650°–600°C. Initial contacts were modified by many exsolution cycles. Hematite and ilmenite (Ilm) hosts and lamellae by EMP are Ilm 24–25, ILm 88–93, like titanohematite, and ilmenite above 520°C on Burton's diagram [1991]. Finer hosts and lamellae by TEM are Ilm16 ±3 and Ilm 88±4, like coexisting antiferromagnetically ordered (AF) hematite and ilmenite below 520°C on Burton's diagram. This may be the first example of analytical identification, in one sample, of former hematite, now finely exsolved, and AF hematite. TEM microstructures consist of gently curving semicoherent ilmenite lamellae within hematite, flanked by precipitate-free zones and abundant ilmenite disks down to unit cell scale (1–2 nm). Strain contrast of disks suggests full coherence with the host, and probable formation at the reaction titanohematite ---> AF hematite + ilmenite at 520°C. Magnetic properties are a consequence of chemical and magnetic evolution of hematite and ilmenite with bulk compositions ilmenite-richer than Ilm 28, that apparently exsolved without becoming magnetized, down to 520°C where hematite broke down to AF hematite plus ilmenite, producing abundant AF hematite below its Neel temperature. Intensity of magnetization is greater than possible with hematite alone, and TEM work suggests that ultrafine ilmenite disks in AF hematite are associated with a ferrimagnetic moment due to local imbalance of up and down spins at coherent interfaces.
TL;DR: In this article, Orange II was adsorbed on hematite and the products of the catalytic oxidation in air atmosphere were analyzed and the Ea for the desorption of CO2 and other PAHs from the hematitic surface was determined at 9.9 Kcal/mol.
Abstract: The low temperature adsorption and subsequent catalytic combustion of the azo-dye Orange II on hematite suggests a novel use of iron oxide as an inexpensive catalytic ecomaterial. Orange II was adsorbed on hematite and the products of the catalytic oxidation in air atmosphere were analyzed. The Ea for the desorption of CO2 and other PAHs from the hematite surface was determined at 9.9 Kcal/mol. By temperature programmed GC-MS analysis, the gaseous products of Orange II adsorbed on hematite were observed to be different and with a simpler structure than when the dye was combusted in the absence of hematite at the same temperatures. The catalytic oxidation of the dye on hematite was able to be sustained in a cyclic repetitive fashion. XPS analysis of the hematite surface did not vary practically during dye oxidation revealing the stable nature of the iron oxide during this process. Electron microscopy gives evidence for a low degree of particle aggregation at the working temperature. A higher degree of hematite crystallization was observed with increasing temperature. This observation was confirmed by X-ray analysis. The modeling of the Orange II species in solution and the surface hematite surface were carried according to the two-layer diffuse model (Diffuse/GTL) fitting the experimental data within 5%. The considerations used during this calculation allowed to calculate the electrostatic interaction of the oxide and the dye as function of the solution pH.
TL;DR: In this paper, the authors examined the interaction between Paenibacillus polymyxa, with different minerals such as hematite, corundum and quartz, and showed that the maximum adsorption of cells on hematites and corundums occurs at a pH below the isoelectric point.
TL;DR: In this paper, the two most common low-temperature iron(III) oxides on Earth are goethite (α-FeOOH) and hematite (β-Fe2O3) and the plots of δD against δ18O for continental goethites are approximately parallel to the meteoric water line of Craig.
Abstract: ▪ Abstract The two most common low-temperature iron(III) oxides on Earth are goethite (α-FeOOH) and hematite (α-Fe2O3). The δ18O values of natural goethites range from −15.5‰ to +3.3‰, whereas δ18O values of low-temperature hematites range from −16.7‰ to +4.7‰. Plots of δD against δ18O for continental goethites are approximately parallel to the meteoric water line of Craig (H Craig. 1961. Science 133:1702–3). This suggests that goethite-water fractionation factors are systematic over a wide range of surficial environments and may indicate that isotopic equilibrium is commonly attained or closely approached. Several experimental or calculated mineral-water, oxygen isotope fractionation curves have been determined for both goethite and hematite. Although there is not yet a consensus on which of these curves best approximates isotopic fractionation in natural samples, oxygen isotope measurements of both goethite and hematite have provided evidence of significant continental climate change on time scales that...
TL;DR: In this paper, Paenibacillus polymyxa and iron ore minerals such as hematite, corundum, calcite, quartz and kaolinite brought about significant surface chemical changes on all the minerals.
TL;DR: In this paper, it was shown that the self-demagnetizing field H d opposing large domain wall displacements is proportional to the spontaneous magnetization M s in hematite.
Abstract: Thermoremanent magnetization (TRM) in hematite is larger than TRM in magnetite for grain sizes ≥ 10 μm. We show that hematite's weak spontaneous magnetization M s causes its strong TRM, since the self-demagnetizing field H d opposing large domain wall displacements is proportional to M s . In hematite, H d is comparable to the Earth's magnetic field but in magnetite, H d is 1000 times larger. As a result, Earth's field TRM of MD hematite (0.3 Am 2 /kg) outweighs TRM and induced magnetization of MD magnetite ( 0.01-0.02 Am 2 /kg) and rivals TRM of single-domain and PSD magnetite as a source of magnetic anomalies on Earth and perhaps on Mars.
TL;DR: In this paper, aqueous ammonium sulfate particles containing hematite and corundum inclusions were investigated in an aerosol flow tube at 298 K. The strong size dependence can be rationalized by an active site model.
Abstract: Mineral dusts inside aqueous atmospheric particles provide surfaces that induce crystallization during episodes of decreasing relative humidity (RH). Submicron aqueous ammonium sulfate particles containing hematite (α-Fe 2 O 3 ) and corundum (α-Al 2 O 3 ) inclusions are investigated in an aerosol flow tube at 298 K. As compared to 35% RH where homogeneous nucleation is rapid, the heterogeneous nuclei regulate the RH from 35% up to 60% RH as the inclusion size varies from 50 to 450 nm. The strong size dependence can be rationalized by an active site model. Model optimization yields 10 10.4 sites cm -2 and m < 0 for α-Al 2 O 3 and 10 9 sites cm -2 and m = 0.04 for α-Fe 2 O 3 particles.
TL;DR: In this article, the composition and structure of the plant-iron biominerals, constituting the inorganic cores of phytoferritin, have remained unknown.
Abstract: Plants, like animals, use and store iron in their cells. Yet, the composition and structure of the plant-iron biominerals, constituting the inorganic cores of phytoferritin, have remained unknown. Transmission electron microscopy (TEM) and diffraction studies of subcellular phytoferritin, extracted from disrupted plant cells, indicate that phytoferritin occurs as crystalline magnetite (Fe 3 O 4 ) ϵ-Fe 2 O 3 , and hematite (α-Fe 2 O 3 ), with typical sizes of single crystallites in the 1 — 50 nm range and agglomerate grain sizes up to 4 μm. The three-dimensional agglomerates are built with different biomineral nanocrystals in three distinct modes of biological self-assembly: 1) ordered magnetite; 2) semi-ordered mixture of magnetite and ϵFe 2 O 3 ; and 3) random hematite. These self-assemblies correspond to prior TEM reports of crystalline, paracrystalline and amorphous phytoferritin arrangements in sectioned cell samples. A fourth plant-iron biomineral, tentatively assigned as calcium ferrate hexahydrate, has a morphology and diffraction patterns distinct from the phytoferritin aggregates. We do not attribute the plant iron observed in this study to be the results of atmospheric pollution.
TL;DR: In this paper, the authors demonstrated the conversion of methane to methanol over zeolitic cr-oxygen sites using Fe-ZSM-5 and showed that shape-selective formation of nano-clusters of iron oxides with various sizes is realized inside the pore-sizes varying from 10.0 to 8.0 and 6.3 to 4.3 Angstrom of the CFI, MOR, MFI, and CHA zeolites.
Abstract: The conversion of methane to methanol over zeolitic cr-oxygen sites has been demonstrated using Fe-ZSM-5. To discriminate between mono- and poly-nuclear active sites, we prepared the [Fe]-ZEO with iron in the ZEOlite lattice via direct synthesis and Fe, -ZEO, by dispersion of x wt.% iron on the ZEOlite. Shape-selective formation of nano-clusters of iron oxides with various sizes is realized inside the pore-sizes varying from 10.0 to 8.0 and 6.3 to 4.3 Angstrom of the CFI, MOR, MFI, and CHA zeolites. The Fe-K edge X-ray absorption data were obtained for the Fe-CIT-5, Fe-ZSM-5, Fe-MOR and Fe-CHA zeolites containing iron clusters. In Mossbauer spectroscopy the absence and presence of a hyperfine magnetic field (HMF) for [Fe]-CIT-5 and Fe-CIT-5 are seen. The quantum mechanics calculations analyze the different environments of iron, e,g, the tetrahedral lattice occluded species, the di-nuclear sites attached to the zeolite, the nano-phase hematite sites. The molecular mechanics calculations involve a new molecular mechanics force field, the universal force field (UFF). alpha -Oxygen can be formed on di-nuclear iron rites in zeolites by N2O decomposition at elevated temperatures and is dependent on the zeolite structure utilized. Fe-chabazite (CHA), Fe-mordenite (MOR) and Fe-CIT-5 (CFI) were found to be less active than Fe-ZSM-5. A range of preparative and activation conditions were studied preceding methane conversion. Proper activation is essential to maximize catalyst actvity, e.g. pretreatment under vacuum at 800-900 degreesC, activation with N2O at 250 degreesC and reaction with methane at 20 degreesC, Extraction of methanol from the catalyst is performed with H2O Structure-activity effects are discussed. (C) 2001 Elsevier Science B.V, All rights reserved.
TL;DR: In this article, the influence of colloidal iron oxide slime on particle flotation was investigated and a combination of physical and chemical methods was most effective at removing the slime from the particles.
TL;DR: The results of a Mossbauer study of the Morin transition behavior in three series of hematite and Al-hematite samples are reviewed and discussed in this paper, where a model involving intermediate states is suggested.
Abstract: The results of a Mossbauer study of the Morin transition behaviour in three series of hematite and Al-hematite samples are reviewed and discussed. The first two series comprise small-particle hematites and Al-hematites prepared from decomposition of lepidocrocite, whereas in the third series Al-hematites up to the µm range are obtained from co-precipitated oxinates. It is demonstrated that the Morin transition temperature follows quite well the overall properties of the samples such as particle size and Al substitution, while the transition region is rather determined by all kind of distributive effects. A model involving intermediate states is suggested for the Morin transition behaviour in non-ideal hematite.
TL;DR: The potential for long-term preservation of microfossils by iron oxide mineralization in specimens of the approximately 2,100-Ma banded iron deposit of the Gunflint Formation, Canada is reported and interpreted as microbial cells permineralized by an iron oxide, presumably hematite.
Abstract: Defining locations where conditions may have been favorable for life is a key objective for the exploration of Mars. Of prime importance are sites where conditions may have been favorable for the preservation of evidence of prebiotic or biotic processes. Areas displaying significant concentrations of the mineral hematite (alpha-Fe2O3), recently identified by thermal emission spectrometry, may have significance in the search for evidence of extraterrestrial life. Since iron oxides can form as aqueous mineral precipitates, the potential exists to preserve microscopic evidence of life in iron oxide-depositing ecosystems. Terrestrial hematite deposits proposed as possible analogs for hematite deposits on Mars include massive (banded) iron formations, iron oxide hydrothermal deposits, iron-rich laterites and ferricrete soils, and rock varnish. We report the potential for long-term preservation of microfossils by iron oxide mineralization in specimens of the approximately 2,100-Ma banded iron deposit of the Gunflint Formation, Canada. Scanning and analytical electron microscopy reveals micrometer-scale rods, spheres, and filaments consisting predominantly of iron and oxygen with minor carbon. We interpret these objects as microbial cells permineralized by an iron oxide, presumably hematite. The confirmation of ancient martian microbial life in hematite deposits will require the return of samples to terrestrial laboratories. A hematite-rich deposit composed of aqueous iron oxide precipitates may thus prove to be a prime site for future sample return.