Surface Fe Content Research Articles

Ligand-Induced Atomically Segregation-Tunable Alloy Nanoprobes for Enhanced Magnetic Resonance Imaging.

Bimetallic iron-noble metal alloy nanoparticles have emerged as promising contrast agents for magnetic resonance imaging (MRI) due to their biocompatibility and facile control over the element distribution. However, the inherent surface energy discrepancy between iron and noble metal often leads to Fe atom segregation within the nanoparticle, resulting in limited iron-water molecule interactions and, consequently, diminished relaxometric performance. In this study, we present the development of a class of ligand-induced atomically segregation-tunable alloy nanoprobes (STAN) composed of bimetallic iron-gold nanoparticles. By manipulating the oxidation state of Fe on the particle surface through varying molar ratios of oleic acid and oleylamine ligands, we successfully achieve surface Fe enrichment. Under the application of a 9 T MRI system, the optimized STAN formulation, characterized by a surface Fe content of 60.1 at %, exhibits an impressive r1 value of 2.28 mM-1·s-1, along with a low r2/r1 ratio of 6.2. This exceptional performance allows for the clear visualization of hepatic tumors as small as 0.7 mm in diameter in vivo, highlighting the immense potential of STAN as a next-generation contrast agent for highly sensitive MR imaging.

Toward a comprehensive hypothesis of oxygen-evolution reaction in the presence of iron and gold

This study investigates the effects of Fe on the oxygen-evolution reaction (OER) in the presence of Au. Two distinct areas of OER were identified: the first associated with Fe sites at low overpotential (∼330 mV), and the second with Au sites at high overpotential (∼870 mV). Various factors such as surface Fe concentration, electrochemical method, scan rate, potential range, concentration, method of adding K2FeO4, nature of Fe, and temperature were varied to observe diverse behaviors during OER for FeOxHy/Au. Trace amounts of Fe ions had a significant impact on OER, reaching a saturation point where the activity did not increase further. Strong electronic interaction between Fe and Au ions was indicated by X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) analyses. In situ visible spectroscopy confirmed the formation of FeO42− during OER. In situ Mössbauer and surface-enhancedRamanspectroscopy (SERS) analyses suggest the involvement of Fe-based species as intermediates during the rate-determining step of OER. A lattice OER mechanism based on FeOxHy was proposed for operation at low overpotentials. Density functional theory (DFT) calculations revealed that Fe oxide, Fe-oxide clusters, and Fe doping on the Au foil exhibited different activities and stabilities during OER. The study provides insights into the interplay between Fe and Au in OER, advancing the understanding of OER mechanisms and offering implications for the design of efficient electrocatalytic systems.

Electronic structure exquisite modulation of NiSe2 interface via rationally controlling Fe doping for boosting electrochemical oxygen evolution activity

Rationally developing electrocatalysts toward oxygen evolution reaction (OER) is of fundamental concern for enhancing water electrolysis efficiency. Nickel based selenides are deemed as promising OER catalysts thanks to their good electrical conductivity and easy regulation. In this work, different amount of Fe was incorporated into NiSe2 nanoparticles through a facile one-pot solvothermal approach, the impact of which was investigated detailedly and deeply. Modifying NiSe2 with a small content of Fe can enlarge electrochemical active surface area and regulate electronic structure and valence state of active center. Moreover, density functional theory (DFT) calculations manifest Fe incorporation can increase Bader charge of Ni site, improve electron delocalization and electronic conductivity, and tune the interaction between catalyst and OH*, therefore significantly enhancing OER activity. The increase of surface Fe content within a definite scope can cause gradual decrease of band gap, and increase of OH– adsorption strength. The intrinsic activity follows the order of NiSe2 < Fe0.17Ni0.83Se2 < Fe0.33Ni0.67Se2 ≈ Fe0.5Ni0.5Se2. Accordingly, the as-prepared Fe-NiSe2-25 with surface Ni/Fe ratio of 2:1 delivers markedly boosted OER activity and remarkable stability, demanding a low overpotential of 250 mV to drive 10 mA cm−2. Moreover, rechargeable liquid and solid Zn-air batteries and water electrolysis tests manifest the potential real application of Fe-NiSe2-25 in energy conversion devices. This work can provide a profound and revealing insight into the impact of iron incorporation on electrochemical properties, and inspire more research to explore other types of Fe-doped transition metal-based compounds by engineering the band gap and electronic structure.

Structural Evolution and Durability of Ultrafine NiFe Phosphide Nanoparticle/Carbon Composite Films in Water Oxidation at High Current Densities

NiFe phosphide (NiFe-P) is a highly active precatalyst for the oxygen evolution reaction (OER), but its compositional and structural changes during sustained electrolysis have not been thoroughly understood. Moreover, the size control of NiFe-P particles remains challenging yet desirable without multistep synthesis or surface capping agents. To realize this, flame aerosol synthesis (FAS) is a promising method due to its short particle residence time, tunable redox environment, and good scalability. Herein, the one-step FAS of NiFe-P is reported for the first time. With the controlled coformation of carbon, interlaced NiFe-P nanoplates and <5 nm NiFe-P nanoparticles are selectively synthesized on nickel foam in 10 min. At the anodic potential of OER, NiFe-P transforms into highly active (oxy)hydroxides in situ by surface oxidation and dephosphorylation. The overpotential of the optimal film at 500 mA cm–2 increases at only 0.28 mV h–1 over 100 h, making it among the most durable NiFe-based catalysts reported. Post-OER cyclic voltammetry, double-layer capacitance, and inductively coupled plasma mass spectrometry (ICP-MS) measurements indicate performance degradation to be mainly caused by the selective leaching of Fe from the (oxy)hydroxides. Counterintuitively, slight structural instability of the films induced by the electrochemical removal of carbon enhances durability by keeping a relatively stable surface Fe content through a self-refreshing mechanism.

Structural features, thermal stability and catalytic implication of Fe–Ni nanoparticles

We have carried out Monte Carlo and molecular dynamics simulations on FexNi1-x nanoparticles (NPs), and systematically studied their structural features and thermal stability. The required potential adopted the angular-dependent potential, which was newly obtained by us. It is found that when x ​< ​0.375, the surface of FexNi1-x NPs is completely occupied by Ni atoms. When x ​> ​0.375, the surface Fe concentration gradually increases with the increase of x. Inside the NPs, Fe atoms occupy the subsurface preferentially, and the Fe atom layer and Ni atom layer are arranged alternately. With the increase of x, the melting temperature of FexNi1-x nanoparticle first ascends, then descends near x ​= ​0.375, and then rises again near x ​= ​0.875. In addition, the catalytic performance of FexNi1-x NPs in methane dry reforming was discussed. Considering the catalytic activity, carbon deposition resistance and sintering resistance, Fe0.375Ni0.625 NPs are the best choice.

Isotopic fingerprinting of biogeochemical processes and iron sources in the iron-limited surface Southern Ocean

Iron (Fe) is an essential micronutrient that limits primary productivity throughout the surface of the Southern Ocean. Here, we present the first high-resolution depth profiles for dissolved Fe and Fe isotope ratios (δ56Fe) from all major zones of the Southern Ocean, collected during the Antarctic Circumnavigation Expedition in austral summer 2017. Open-ocean surface waters are characterized by remarkably high δ56Fe values (up to +1.6‰) and very low Fe concentrations (<0.05 nmolkg−1). We attribute the elevated δ56Fe values above the ferricline to the effect of continuous shallow cycling processes (uptake, recycling, and binding of Fe to organic ligands), with only a very limited resupply of Fe from below. Below the ferricline, δ56Fe values approach ∼0‰ and remain constant down to our deepest samples at 1000 m, with no obvious isotope signal from regeneration. This overall pattern in δ56Fe is modified near islands, continental shelves and hydrothermal vents, where distinct δ56Fe signatures are associated with different Fe sources. Near the volcanic Balleny Islands, elevated surface Fe concentrations associated with low δ56Fe are indicative of reductive release of isotopically light Fe from sediments. Elevated δ56Fe values at depth near the Balleny seamount chain and near the East Scotia Arc may reflect distal hydrothermal influences, caused by fractionation associated with precipitation or the loss of specific phases of Fe during long-range transport. Sedimentary sources of isotopically light Fe on the Antarctic Peninsula are important for shelf waters. Long-distance transport of this sediment-derived Fe and its influence on surface waters are strongly dependent on the regional circulation, and may ultimately be the source of light Fe previously observed within Antarctic Intermediate Water in the Atlantic sector of the Southern Ocean.

Photocatalysis of naphthalene by Fe3O4/Oxone/UV: Simultaneous radical and non-radical pathways

Naphthalene (Nap) degradation by photocatalysis of Fe3O4/Oxone/UV was studied. The system eliminated Nap in 30 min and the kinetics is described by a novel mixed order model with adsorption and decay dominant rate constants, representing non-radical and radical pathways respectively. The reaction is dominated by catalysis in acidic pHs as Oxone anions are adsorbed onto the protonated Fe3O4 surface for activation; In alkaline solution, the adsorption of Nap to the deprotonated Fe3O4 surface is the main removal pathway. The catalyst was reused for 5 cycles and the performance was enhanced after reuse. XPS study confirmed that the surface Fe content of Fe3O4 remained stable after reusing due to the effective UV-assisted ≡FeII—≡FeIII catalytic cycle. An additional C‒O bond on Fe3O4 surface was detected after reuse, which is proposed to be an OH bond on catalyst as an extra adsorption site and for radical generation.

Comparative study of the effect of rice husk-based powders used as physical conditioners on sludge dewatering

The effects of rice husk flour (RHF), rice husk biochar (RHB), and rice husk-sludge cake biochar (RH-SCB, expresses sludge cake biochar deriving from a sludge that has been previously conditioned with rice husk) used as physical conditioners on sludge dewaterability were compared. The effects of characteristics of physical conditioners on sludge compressibility and zeta potential were analyzed. The optimal rice husk-based powder was RH-SCB, which presented the highest net sludge solid yield (YN, expresses the dry mass flow by filtration) at 20.39 kg/(m2 h) for 70% dry sludge (DS). Characterization analysis indicates that the hardness and surface Fe content of powders which could influence the compressibility coefficient of sludge cake and sludge zeta potential were the major factors influencing sludge dewaterability. The comparison of feasibility and economic analysis showed that adding RH-SCB improves the quality of the sludge filtrate and reduces the pollution potential of conditioned sludge (the ratio of secondary and primary (RSP) of Cu, Zn, Cd reduces from 43.05, 144.00, 7.25 to 7.89, 14.63, 4.27, respectively), and the costs of using RH-SCB were the lowest (at 88.4% lower than that of the raw sludge). Therefore, it is feasible to use RH-SCB to improve sludge dewaterability.

Unprecedented Fe delivery from the Congo River margin to the South Atlantic Gyre

Rivers are a major supplier of particulate and dissolved material to the ocean, but their role as sources of bio-essential dissolved iron (dFe) is thought to be limited due to rapid, efficient Fe removal during estuarine mixing. Here, we use trace element and radium isotope data to show that the influence of the Congo River margin on surface Fe concentrations is evident over 1000 km from the Congo outflow. Due to an unusual combination of high Fe input into the Congo-shelf-zone and rapid lateral transport, the Congo plume constitutes an exceptionally large offshore dFe flux of 6.8 ± 2.3 × 108 mol year−1. This corresponds to 40 ± 15% of atmospheric dFe input into the South Atlantic Ocean and makes a higher contribution to offshore Fe availability than any other river globally. The Congo River therefore contributes significantly to relieving Fe limitation of phytoplankton growth across much of the South Atlantic.

Structural and elemental influence from various MOFs on the performance of Fe@C catalysts for Fischer-Tropsch synthesis.

The structure and elementary composition of various commercial Fe-based MOFs used as precursors for Fischer-Tropsch synthesis (FTS) catalysts have a large influence on the high-temperature FTS activity and selectivity of the resulting Fe on carbon composites. The selected Fe-MOF topologies (MIL-68, MIL-88A, MIL-100, MIL-101, MIL-127, and Fe-BTC) differ from each other in terms of porosity, surface area, Fe and heteroatom content, crystal density and thermal stability. They are re-engineered towards FTS catalysts by means of simple pyrolysis at 500 °C under a N2 atmosphere and afterwards characterized in terms of porosity, crystallite phase, bulk and surface Fe content, Fe nanoparticle size and oxidation state. We discovered that the Fe loading (36-46 wt%) and nanoparticle size (3.6-6.8 nm) of the obtained catalysts are directly related to the elementary composition and porosity of the initial MOFs. Furthermore, the carbonization leads to similar surface areas for the C matrix (SBET between 570 and 670 m2 g-1), whereas the pore width distribution is completely different for the various MOFs. The high catalytic performance (FTY in the range of 1.9-4.6 × 10-4 molCO gFe-1 s-1) of the resulting materials could be correlated to the Fe particle size and corresponding surface area, and only minor deactivation was found for the N-containing catalysts. Elemental analysis of the catalysts containing deliberately added promoters and inherent impurities from the commercial MOFs revealed the subtle interplay between Fe particle size and complex catalyst composition in order to obtain high activity and stability next to a low CH4 selectivity.

Effect of surface composition of Fe catalyst on the activity for the production of high-calorie synthetic natural gas (SNG)

An Fe2O3 catalyst was applied to the production of high-calorie synthetic natural gas (SNG). With this catalyst, the product distribution changed as the surface composition of the Fe2O3 catalyst changed. The effect of these changes on the catalytic activity was investigated. The active phases of the Fe2O3 catalyst were a mixture of low-carbon FeCx and Fe3C, which was maintained for 10 h, accompanied by the regeneration of Fe3O4. The surface Fe concentration increased after 10 h reaction, and this increased the CO conversion. In addition, the amounts of adsorbed C2H4 and C3H6 increased, which resulted in an increase in carbon chain growth. The surface concentration of oxygen also increased due to the regeneration of Fe3O4, thus reducing the C3H6 adsorption strength; in contrast, C2H4 adsorption increased, resulting in an enhanced paraffin-to-olefin (p/o) ratio for C2 hydrocarbons and reduced p/o ratio for C3 hydrocarbons.

Carbonaceous thin film coating with Fe–N4 site for enhancement of dioxovanadium ion reduction

It has been found that carbonaceous materials containing a transition metal coordinated by 4 nitrogens in the square-planar configuration (metal–N4 site) on the surface possessed a catalytic activity for various electrochemical reactions related to energy conversion and storage; i.e., oxygen reduction, hydrogen evolution, and quite recently, the electrode reactions in vanadium redox flow batteries (VRFB). The catalyst for the VRFB positive electrode discharge reaction, i.e., the dioxovanadium ion reduction, was formed by coating the surface of cup-stack carbon nanotubes with a carbonaceous thin film with the Fe–N4 site generated by the sublimation, deposition, and pyrolysis of iron phthalocyanine. In this study, the influence of the physical properties of the catalyst on the electrochemical reactions was investigated to optimize the coating. With an increase in the coating, the specific surface area increased, whereas the pore size decreased. The surface Fe concentration was increased in spite of the Fe aggregation inside the carbon matrix. The catalytic activity enhancement was achieved due to the increase in the specific surface area and the surface Fe concentration, but was lowered due to the decrease in the pore size, which was disadvantageous for the penetration of the electrolyte and the mass transfer.

Heat Treatment of Carbonized Hemoglobin with Ammonia for Enhancement of Pore Development and Oxygen Reduction Activity

A highly porous carbonaceous material was formed from hemoglobin, which is a natural compound that could be abundantly and inexpensively obtained. Porous carbonized hemoglobin was formed using MgO nanoparticles as a template; in addition, heat treatment of the carbonized hemoglobin with ammonia was performed. Two series of ammonia treatments were examined: long-time heat treatments at various temperatures and high-temperature heat treatments for various times. The specific surface area and, in particular, the pore volume were increased by the ammonia treatment most efficiently at a high temperature for a short period of time. X-ray photoelectron spectroscopy showed a significant decrease in the surface nitrogen concentration and a slight decrease in the surface Fe concentration by the ammonia treatment. The extended X-ray absorption fine structure at the Fe K-edge indicated that Fe was coordinated with four nitrogen atoms (Fe–N4 moiety) in the ammonia-treated carbonized hemoglobin. The oxygen reduction activity was evaluated using rotating disk electrodes. The enhancement was observed in accordance with the pore development. A polymer electrolyte fuel cell formed using the ammonia-treated carbonized hemoglobin in the cathode showed an improved performance compared to that formed using the carbonized hemoglobin before the treatment.

Coastal iron and nitrate distributions during the spring and summer upwelling season in the central California Current upwelling regime

Distributions of iron and nitrate in the central California Current System upwelling regime (cCCS) from 34 to 41°N were determined during cruises in May 2010 and August 2011. High spatial and temporal resolution data for dissolved Fe and NO3− (nitrate+nitrite) in the cCCS from this study greatly expands upon previous studies that were narrower in scope (e.g., focused on just the Monterey Bay region). Shelf sediments from mid-shelf mud belts in this region provide the dominant source of Fe, and there are areas in the cCCS where insufficient Fe is upwelled to accompany elevated levels of other macronutrients (nitrate, phosphate, silicate) to fuel extensive diatom blooms. Surface dissolved Fe concentrations were related to continental shelf width and upwelling strength, and surface Fe concentrations tended to be lower in the late summer than early spring. We present extensive benthic boundary layer (BBL) dissolved and leachable particulate Fe data from both seasons in the mid-shelf region along the central California coast. Leachable particulate Fe concentrations were strongly related to the width of the mid-shelf mud belts (i.e., the continental shelf between the 50 and 90m isobaths). Dissolved Fe concentrations in the BBL over the mid-shelf were generally highest in wide mud belt areas as well as in areas with very low dissolved oxygen concentrations but did not show a clear seasonal trend. Evidence for probable Fe limitation in upwelled waters was found by using surface dissolved Fe:NO3− ratios and the estimated specific growth rate of coastal diatoms based on either Fe or NO3− concentrations. Several coastal upwelling regions with only moderate to narrow continental shelves (Pt. Arena to Cape Mendocino and the Big Sur Coast) exhibited evidence for Fe limitation in both the spring and summer upwelling seasons.

Synthesis and characterization of iron-impregnated porous carbon spheres prepared by ultrasonic spray pyrolysis

Porous carbon microspheres impregnated with iron-based nanoparticles are prepared in a single step, continuous process using ultrasonic spray pyrolysis (USP). Precursor solutions containing a carbon source, an inorganic salt, and an iron salt are ultrasonically aerosolized and pyrolyzed. Solutions containing nitrate or chloride salts are examined. During pyrolysis, sucrose is dehydrated to carbon, and the metal salt is converted to crystalline or non-crystalline iron species, depending on processing conditions. The product’s porosity is generated from: (1) aromatization of carbon around an in situ template, (2) in situ gasification of isolated carbon, or (3) in situ chemical activation of the carbon precursor. Porous carbon spheres (0.5–3 μm diameter) containing well-dispersed iron oxide nanoparticles (4–90 nm diameter), referred to here as Fe–C, are prepared. Iron loadings between 1 and 35 wt.% are achieved while maintaining well-dispersed Fe nanoparticles with as-produced surface areas up to 800 m 2/g. Post-pyrolysis heat and hydrogen treatments increase the surface area of the materials while reducing iron species. USP Fe–C materials may have useful catalytic applications due to their potential for high-loading of well-dispersed metal nanoparticles. Despite negligible surface Fe content, chromium reduction tests indicate that internal Fe sites are catalytically active.

Use of purine and pyrimidine bases as nitrogen sources of active site in oxygen reduction catalyst

Abstract There are increasing expectations and demands for sufficiently active noble-metal-free catalysts for the electrode reactions in polymer electrolyte fuel cells. One of the most promising candidates for the cathode catalyst is a carbon material with Fe–N x moiety embedded on the surface as the active site. We previously found that this carbon-based catalyst was formed by heat treatment of a mixture of Fe lactate, glucose, and amino acids as the nitrogen sources of the active site. In this study, various purine and pyrimidine bases were used as the nitrogen sources for the active site generation in order to obtain fundamental information on the activity enhancement of the carbon-based noble-metal-free cathode catalyst. The specific surface area and the surface Fe concentration of the carbon material formed by heat treatment of the Fe lactate–glucose–base mixture were dependent on the molecular structure and the number of nitrogen atoms contained in the molecule of the base, which then affected the catalytic activity for oxygen reduction and the number of electrons involved in the per oxygen molecule. Especially, the activity increased with an increase in the number of nitrogen atoms contained in the molecule. Efficient generation of the active site was also observed.

A kinetic model for bacterial Fe(III) oxide reduction in batch cultures

A model has been developed describing the microbial reduction of solid‐phase electron acceptors (Fe(III) oxides) as well as dissolved electron acceptors (chelated Fe(III) or organic electron shuttles) in Shewanella alga BrY. The model utilized a multiple‐substrate, Monod kinetics formulation. The Monod description of solid Fe(III) reduction requires a normalization of surface Fe concentration to biomass concentration in order to describe the “bioavailable” Fe(III) concentration. The model also contains provisions for irreversible sorption of Fe(II) to Fe(III) oxide surfaces and for the precipitation of Fe(III) carbonates. The loss of bioavailable Fe(III) due to sorption of Fe(II) was found to be minor, even for highly sorptive amorphous Fe(III) oxyhydroxides. However, the final extent of microbial reduction is very sensitive to the rate of siderite precipitation, assuming that siderite precipitation could partially occlude Fe(III) surface sites. The use of a multisubstrate Monod kinetics model enabled an evaluation of the effects of electron shuttles on solid Fe(III) reduction. Because the electron shuttle is recycled, very small additions can greatly increase the overall rate of solid Fe(III) reduction.

Dissolution of well and poorly ordered kaolinites by an aerobic bacterium

Previous research by our group (e.g., [Chem. Geol. 132 (1996) 25; Geochim. Cosmochim. Acta 64 (2000) 1363]) has shown that an aerobic Pseudomonas mendocina bacterium enhances Fe(hydr)oxide dissolution in order to obtain Fe under Fe-limited conditions. The P. mendocina is incapable of utilizing Fe as a terminal electron acceptor and requires several orders of magnitude lower Fe concentrations than do dissimilatory Fe reducing bacteria. The research reported here compared the effects of the P. mendocina on dissolution of well and poorly ordered Clay Minerals Society Source Clay kaolinites KGa-1b and KGa-2, respectively, under Fe-limited conditions. KGa-1b and KGa-2 contain 0.04 and 0.94 bulk wt.% Fe, respectively, and their surface Fe/Si atomic ratios=0.008 and 0.012. Following strong cleaning of the kaolinites in 5.8 M HCl at 85 °C, the surface Fe/Si atomic ratios decreased to 0.004 and 0.008, respectively. Both kaolinites also developed a Si-enriched surface precipitate upon strong cleaning. Because the P. mendocina take up Fe, we could not measure Fe release from the kaolinite directly, but rather had to monitor it indirectly by comparing microbial populations sizes under Fe-limited growth conditions. We found that microbial growth on uncleaned, weakly cleaned, and strongly cleaned kaolinites increased with the amount of Fe readily available to organic ligands as estimated by dissolution in 0.001 M oxalate (pH 3). This suggests that it is the amount of readily accessible Fe that controls Fe acquisition and hence microbial growth. The trend is based on only a relatively small range of kaolinite Fe contents, and the research thus needs to be expanded to include kaolinites with a broader range of bulk and surface Fe concentrations. Significant enhancement of Al release was observed in the presence of the bacteria, along with generally some enhancement of Si release. This enhancement of kaolinite dissolution could be related to an observed pH increase from ∼7–8 to ∼9 in the presence of the bacteria and/or to production of Al chelating agents. The P. mendocina produce a variety of organic exudates, including siderophores [Chem. Geol. 132 (1996) 25; Geomicrobiology (2001b)], and further studies into the effects of the siderophores on Al complexation and on kaolinite dissolution are ongoing.

Effect of SC-1 Process Parameters on Particle Removal and Surface Metallic Contamination

ABSTRACTThe effect of bath temperature, megasonic power, and NH4-OH:H2O ratio are studied for particle removal efficiency, surface roughness, and surface Fe concentration in SC-1 cleaning solutions. Experimental results are presented which show removal efficiencies better than 97% on bare silicon wafers for optimized process conditions. These results are related to the etch rate of thermal oxides and a model is developed for reducing surface roughness and minimizing Fe contamination levels while maximizing particle removal efficiency.

Fundamental properties of intrinsic gettering of iron in a silicon wafer

Properties of intrinsic gettering of Fe were studied by measuring Fe-B complex concentration and interstitial Fe concentration in a denuded zone after isochronal or isothermal annealing followed by quenching using deep level transient spectroscopy. We calculated the Fe concentration as the Fe-B complex concentration plus the interstitial Fe concentration. Silicon wafers were contaminated with a surface Fe concentration of 4.2×1011 to 3.2×1013 cm−2 to show the relation between Fe concentration in the wafer and the temperature at which gettering occurs. Supersaturation of Fe impurities was found necessary for intrinsic gettering of Fe in the contamination range of 4.0×1012 to 3.5×1014 cm−3. Therefore, the gettering temperature is lower for low-level Fe contamination than for high-level contamination. The reduction of Fe concentration saturated with annealing time, which shows that the oxygen precipitates in the bulk defect region do not work as an infinite gettering sink. We found that the saturated Fe concentration follows a simple Arrhenius relationship, so that gettering stops at the thermal equilibrium concentration. We think that in intrinsic gettering, Fe precipitates preferentially in the bulk defect region when the Fe impurities supersaturate with decreasing temperature.