Fe-rich Layer Research Articles

Reduced formation of peroxide and radical species stabilises iron-based hybrid catalysts in polymer electrolyte membrane fuel cells

The incorporation of Pt into an iron-nitrogen-carbon (FeNC) catalyst for the oxygen reduction reaction (ORR) was recently shown to enhance catalyst stability without Pt directly contributing to the ORR activity. However, the mechanistic origin of this stabilisation remained obscure. It is established herein with rotating ring disc experiments that the side product, H2O2, which is known to damage FeNC catalysts, is suppressed by the presence of Pt. The formation of reactive oxygen species is additionally inhibited, independent of intrinsic H2O2 formation, as determined by electron paramagnetic resonance. Transmission electron microscopy identifies an oxidised Fe-rich layer covering the Pt particles, thus explaining the inactivity of the latter towards the ORR. These insights develop understanding of FeNC degradation mechanisms during ORR catalysis, and crucially establish the required properties of a precious metal free protective catalyst to improve FeNC stability in acidic media.

Investigation on the mechanism of deteriorated oxidation resistance of Ti(C0.7,N0.3)-304ss cermet doped with Y during the early oxidation stage

The high-temperature oxidation resistance of the Ti(C0.7,N0.3)-304ss cermets during the early oxidation stage was deteriorated by adding Y. The outward diffusion of Fe atoms was improved with Y addition, and a Fe-rich outer oxide layer was generated on the surface. Impurities at phase boundary act as barriers to suppress the diffusion of Fe and O atoms; while they were purified by Y atoms, and the barriers were destroyed. As a result, the oxidation resistance deteriorated. The apparent activation energy of the cermets declined from 207.18 KJ/mol to 149.97 KJ/mol by doping with Y.

Thermodynamic investigations of fuel-cladding chemical interaction in U-5Fs and U-10Zr metallic fuels with the TAF-ID

Fuel-Cladding Chemical Interaction (FCCI) in metallic nuclear fuels is a key phenomenon that limits the maximum burn-up and operating power as it can cause premature failure of the fuel cladding. Therefore, being able to accurately predict the interactions of the fuel-cladding system by means of thermodynamic calculations contributes to our understanding of how to mitigate this failure mechanism. In order to test the capabilities of the Thermodynamic of Advanced Fuels – International Database (TAF-ID) to predict these interactions, calculations have been performed on two irradiated metallic fuels: U-5Fs in SS316 cladding and U-10Zr in HT9 cladding, for which experimental observations are available in the literature. TAF-ID calculations have allowed the confirmation of some of the phases that were observed during experimental characterizations and the identification of unknown ones: Particularly for the U-5Fs fuel, two primary Fe-rich phases have been predicted: (i) FeU6, that extends up to 120 μm into the fuel, and (ii) UFe2 with >30 wt.% Fe, likely to be the Fe-rich layer observed experimentally adjacent to the cladding on the fuel side. Also, minor phases that have been experimentally observed, such as U-Mo, U-Ru, and lanthanoid-noble metals (Nd,Ce-Pd), have been predicted to be stable. As for the U-10Zr fuel, calculations predicted several U-Fe-Zr phases (e.g., FeU6, UFe2, and χ-FeUZr), Fe-(Ce,Nd) phases (e.g., Fe17Ln2), and a FCC phase consisting of Ce, Nd, La, Y, and Sr. These predicted phases are in excellent agreement with experimental observations.

High temperature oxidation behavior and mechanism of FeXCr0.5Ti ferritic stainless steels

In order to investigate the oxidation mechanism of ferritic stainless steel during long-term oxidation at high temperature. The oxidation behavior of Fe-Cr-Ti ferritic stainless steels with 10.38 wt% Cr and 17.41 wt% Cr at 800 °C and 900 °C for 100 h was studied by a constant temperature weight gain method. The morphology and composition of the oxide film were characterized by SEM, EDS and XRD. The experimental results indicate that the oxygen element mainly diffuses inward at 800 °C for two stainless steels, and the oxide film is composed of (Cr1.3Fe0.7)O3 + MnCr2O4. When the temperature rises to 900 °C, metal element mainly diffuses outward, and Fe2O3 outer oxide layer and Fe rich Fe-Cr inner oxide layer are formed in Fe11Cr0.5Ti stainless steel; Cr2O3 + Cr rich M3O4 spinel oxide film is formed in Fe18Cr0.5Ti stainless steel, while the inner layer is composed of SiO2. The main reason for the significant decrease of oxidation resistance of Fe11Cr0.5Ti stainless steel is that the low content of Cr cannot form a Cr rich oxide layer to inhibit the outward diffusion of Fe element, and the stability of oxide film is poor to protect the matrix.

Facile modified polyol synthesis of FeCo nanoparticles with oxyhydroxide surface layer as efficient oxygen evolution reaction electrocatalysts

The oxygen evolution reaction (OER) at anode requires high overpotential and is still challenging. The metallic core-oxyhydroxide layer structure is an efficient method to lower an overpotential. We synthesized Fe rich FeCo core-Co rich FeCo oxyhydroxide layer with a different particle size of 173 nm, 225 nm, and 387 nm (FeCo 173, 225, 387) through a difference in the reduction rate of Fe/Co precursors using facile modified polyol synthesis. To investigate the effect of conductivity, CoFe2O4 nanoparticles of 80–130 nm were synthesized. Among samples, FeCo 173 showed remarkable catalytic performance of 316 mV at a current density of 10 mA/cm2 in 0.1 M KOH compared to RuO2 (408 mV), FeCo 225 (323 mV), FeCo 387 (334 mV), CoFe2O4 (382 mV). Moreover, FeCo 173 showed good stability for 60,000 s while RuO2 showed a gradual increase in overpotential to maintain 10 mA/cm2 after 15,000 s in chronopotentiometry. The excellent performance was attributed to Fe-rich metallic core, a small amount of Fe doping into CoOOH, and the synergic effect between the active site of Co rich FeCoOOH and conductive Fe rich metallic core. Following this result, it shows that the use of such FeCo electrodes has advantages in the production of hydrogen via electrochemical water oxidation.

Corrosion Behavior of Ferritic-Martensitic Steel in H2O Containing CO2 and O2 at 50°C to 245°C and 8 MPa

To understand the corrosion mechanisms of structural materials in low-temperature components of direct supercritical CO2 power cycles, immersion experiments were performed in aqueous environments expected at these conditions. A ferritic-martensitic steel (UNS K91560) was selected as the candidate material. Steel specimens were fully submerged in H2O pressurized with 99% CO2 and 1% O2 to 8 MPa, and heated up to temperature (50°C, 100°C, 150°C, or 245°C), with a test duration of 500 h. Corrosion rates were calculated based on mass loss. Scanning electron microscope, x-ray diffraction, x-ray photoelectron spectroscopy, and Raman spectroscopy were used to characterize microstructure, phases, crystallinity, and composition of the corrosion product layer. Experimental results show that specimens exposed at 100°C had the highest corrosion rate, followed by the specimens exposed at 50°C. The specimens exposed at the highest temperature exhibited the lowest corrosion rate. An outer noncontinuous, nonprotective Fe-rich oxide layer and a well-adhered inner oxide layer containing both Fe and Cr formed on the specimen surfaces. The inner oxide layer changed from amorphous to crystalline as the temperature increased.

Effect of high flow velocity on corrosion behavior of Ni based and Ni-Fe based alloys in supercritical water oxidation environment

In this study, the corrosion behavior of Ni-based alloy 625, 825, and Ni-Fe based alloy 800 was investigated in SCW containing salts and oxygen at 400 °C. The flow velocity of the corrosion medium near the sample surface was around 2 m/s. The surface and cross-section morphologies were observed, and the oxide phase was analyzed. After 100 h exposure, a bi-layer structure was formed on the alloy surface. The Ni and Fe rich outer layer was loose and porous, and the Cr rich inner layer was compact. Weight loss and oxide spallation were observed in the samples after exposure. The flow pattern near the test alloys was turbulent flow, but the outer oxide layer was immersed in the viscous sublayer. Once the Ni and Fe cations reached the alloy surface, some of them were carried away by the fast flowing fluid. Force analysis was done on an oxide particle from the outer oxide layer. The combining effect of the lifting force in the vertical direction and the shear force in the horizontal direction is the major reason for the porous structure of the outer layer and the oxide layer spallation.

Tribochemical changes of alloy 800HT under sliding contact at elevated temperature in impure helium environment

This study investigates the chemical changes of the surface of Alloy 800HT during sliding contact under helium atmosphere in the presence of impurities at 750 °C, which is of interest for the nuclear industry. The alloy samples are exposed to helium (He) atmosphere at high temperature for long duration of 500 h to identify the chemical and topographical changes of the alloy surface. The oxidation rate constant is reported based on the weight change data. For the tribo-experimental samples, the surfaces inside and outside the wear track are studied thoroughly using techniques such as secondary electron microscopy, energy dispersive spectroscopy, x-ray diffraction, Raman spectroscopy and secondary ion mass spectroscopy. The formation and evolution of surface oxides are discussed in He atmosphere, compared with air. The presence of Fe-rich thin layer of oxide on top of a thicker Cr-rich oxide and a mixed spinel-based inner layer on the bulk is found. The persistent presence of thicker Fe3O4in the wear track in high temperature air proved to be the reason of lower friction property. Pre-oxidation of the samples in air or He does not improve but worsen the tribological behavior in He atmosphere.

Thermomechanical characterisation of W-Eurofer 97 brazed joints

The preliminary conceptual design of both the blanket and the divertor of the future DEMO reactor envisages tungsten as plasma-facing material joined to Eurofer 97 steel as the structural element. Therefore, the development of new joining technologies to constitute these first wall components has become an essential task in the fusion community. In this regard, there is a lack of knowledge on the thermal stability and mechanical behaviour of these W-Eurofer 97 joints under the expected service temperatures, which will be situated around 400–600 °C. In this paper, successful diffusion brazing of Eurofer 97 steel with tungsten was achieved by using a copper interlayer. Its microstructure, hardness and flexural strength were investigated for different configurations and thermal histories in its predicted operating temperature range.Investigations on as-brazed specimens showed defect-free interfaces and a continuous metallic bond between W and Eurofer 97 was successfully accomplished; although the hardening of steel base material was detected after joining. Microstructure alterations were observed just at the W-Eurofer 97 interface, with the diffusion of Cu braze into the iron grain boundaries and the formation of a Fe-rich hard intermetallic layer, which was, in fact, the weakest part of the joint during thermo-mechanical testing.The flexural strength of the brazed specimens at room temperature was relatively low, with a strong dependence on the anisotropy of the W base material and little influence of the stress-relieving thermal treatment. However, testing at temperatures up to 600 °C showed high strength of the bonded specimens, with values as high as 470 MPa, comparable to those of the Eurofer 97 steel.

U-Pb zircon geochronology and geochemistry of metavolcanics and associated iron ores of the magnetite-rich BIF deposits in the Western Kunlun orogenic belt: Constraints on the depositional age, origin and tectonic setting

Large amounts of magnetite-rich banded iron formation (BIF) deposits, located in the Western Kunlun orogenic belt (WKOB), are hosted within the greenschist- to amphibolite-facies metamorphosed Bulunkuole complex. The iron (Fe) orebodies of these BIF deposits are interlayered with biotite-quartz schist and amphibolite, indicating that they are temporally closely associated. Analyses of the contents and ratios of major and trace elements indicate that the protoliths of the amphibolite should be basalt and andesite. LA-ICP-MS U-Pb dating of zircons from three representative amphibolite samples suggests that the studied BIF deposits were formed in the Early Cambrian (516–520 Ma). Based on regional geology and geochemistry of the amphibolite, we propose that these BIF deposits were formed in a back-arc basin setting. A wide range of Ce and Eu anomalies for Fe ores indicate that the studied BIF deposits were formed in both oxygenated surface seawater and deeper suboxic to anoxic seawater. Linking the tectonic setting with geochemical characteristics of bulk-rock Fe ores, we propose Fe and Si are predominantly seafloor-derived, with pulsed contribution of high- to low-T hydrothermal fluids that were closely associated with the extension of back-arc basin. In addition, we postulate that periodically upwelled metalliferous hydrothermal fluids were subsequently oxidized by surface seawater and mixed with detrital components, which ultimately led to the rhythmic precipitation of the Fe-rich and Si-rich layers.

The Late Pleistocene-Holocene sedimentary evolution of the Sines Contourite Drift (SW Portuguese Margin): A multiproxy approach

The Sines Contourite Drift (SCD), located in the Alentejo margin, southwest Iberian continental margin, has been through many depositional phases in result of climatic variations and bottom current oscillations, which determined a variable depositional pattern and an irregular sedimentary evolution since the Late Pleistocene. The SCD, being in the main path of the Mediterranean Outflow Water (MOW), which greatly constrains the sedimentary building of this drift, constitutes the distal part of the Gulf of Cadiz Contourite Depositional System and its sedimentary evolution therefore reflects the history of MOW variations.In order to investigate this, we report on a multiproxy analysis of grain-size, carbon content and physical, geochemical, and environmental-magnetic properties on the AMS 14C dated 350-cm long gravity core CO14-GC-07, retrieved in the SCD, at 1425 meters water depth (mwd). The main objective is to reconstruct the evolution of the sedimentary package of the SCD from >43 cal kyr BP to Present and bring new insights about the impact of bottom currents' activity on the morphosedimentary evolution of the margin. Results show the existence of four distinct depositional phases in response to climate variations and bottom current oscillations during the Late Pleistocene-Holocene. Phase 1 (350–322 cm: >42.9 cal kyr BP) occurred in Marine Isotope Stage (MIS) 3 and presents silty-muddy sediments with presence of shell fragments and moderate bioturbation. Phase 2 (322–176 cm: >42.9–~30.5 cal kyr BP), which lasted from middle MIS 3 to the onset of MIS 2, reveals sediment coarsening towards the top limit, suggesting climate cooling and strong bottom current winnowing. Phase 3 (176–144 cm: ~30.5–17.1 cal kyr BP) covers most of MIS 2 prior to the last deglaciation and shows the sharpest variations on all sediment properties and the coarsest sediment facies, with Fe-rich layers associated with the increase of terrigenous input and sea-level regression that coincide with the enhancement of MOW. Phase 4 (144–0 cm: <17.1 cal kyr BP) is associated with the deglacial sea-level rise and represents a calmer depositional environment with finer sediments and increasing contributions of biogenic material. The MOW is the most prominent bottom current and the most active seabed shaping agent in the study area, whose vertical shifting during glacial (~800–2200 mwd) and interglacial (600–1500 mwd) periods is coincident with the most active morphosedimentary sector of the area, contributing to the development of landslide scars and sediment waves.

Oxidation behavior of 316L austenitic stainless steel in high temperature air with long-term exposure

The oxidation behavior of 316L stainless steel exposed at 400, 600 and 800 °C air for 100, 500 and 1000 h was investigated using different characterization techniques. Weight gain obeys a parabolic law, but the degree of deviation of n index is increasingly larger with the increase of temperature. A double oxide film, including Cr2O3 and Fe2O3 oxide particles in outer and FeCr2O4 oxides in inner, is observed at 400 °C. As regards to samples at 600 °C, a critical exposure period around 100 h exists in the oxidation process, at which a compact oxide film decorated with oxide particles transforms to a loose oxide layer with a pore-structure. In addition, an oxide film containing Fe-rich outer oxide layer and Cr-rich inner oxide layer is observed at 600 °C for 500 and 1000 h. Spallation of oxide scale is observed for all samples at 800 °C regardless of exposure periods, resulting in different oxidation morphologies, and the degree of spallation behavior is getting worse. A double oxide film with the same chemical composition as 600 °C is observed, and the thickness increases over exposure periods.

Oxidation performance and degradation mechanism of the slurry aluminide coating deposited on Super304H in steam at 600–650 °C

A triple-layered slurry aluminide coating was prepared on Super304H, composed of Al-rich FeAl layer, Fe-rich FeAl layer and α-Fe(Cr, Al, Ni) interdiffusion layer dispersed with (Ni, Fe)Al particles from outer to inner. Oxidation and degradation process of the coating has been investigated at 600 °C~650 °C in steam, by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Results showed an extremely thin α-Al2O3 scale was formed on the coating. The microstructural degradation of the aluminide coating occurred due to phase transformation from FeAl to α-Fe and (Ni, Fe)Al particles near the interface between the FeAl layer and the interdiffusion zone. Related mechanisms were discussed.

Presence of biogenic magnetite in ferromanganese nodules.

Transmission electron microscopy (TEM) and rock magnetic study of ferromanganese nodule sample JC120-104B collected from Clarion-Clipperton zone (CCZ) in the eastern Pacific Ocean indicate the presence of biogenic magnetite (magnetofossils). First-order reversal curves (FORCs) and decomposition of isothermal remanent magnetization (IRM) curves were used as the main tool for the characterization of magnetic properties of the bulk magnetic minerals present in the sample. TEM was performed for the direct identification of biogenic magnetic minerals (magnetofossils). The nodule sample has distinctive alternating Mn and Fe-rich layers per micro-X-ray fluorescence data. While diagenetic precipitation of Mn is known for the less oxygenated environment, the presence of biogenic magnetite is also common in the environments where the supply of oxygen is limited. Moreover, the increase in magnetic properties is consistent with the increase in Mn-content, which is related to favourable conditions for Mn precipitation as well as magnetite biomineralization in oxic-suboxic transition zone. Investigations on magnetofossil fingerprints lead to a better understanding of paleoenvironmental conditions involved in the formation and growth of deep-sea ferromanganese nodules.

Characterization and origin of two Fe-rich bentonites from Westerwald (Germany)

The Westerwald region is one of the major ceramic clay mining areas of Germany. The mined clays were deposited on the weathered Rhenish massif during Eocene and Oligocene and were protected from erosion by a large alkaline basalt cover. Two Fe-rich bentonite layers exposed in quarries of the Eastern part of the Westerwald were investigated with X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, optical microscopy, scanning electron microscopy, chemical analyses and cation exchange capacity (CEC). In both bentonite layers, the main mineral is a high-charge Fe-rich beidellite containing exchangeable Ca and Mg. Even if they both derive from mafic volcanic rocks, the difference in accessory minerals and trace element content leads to the conclusion that they have a different precursor. The lower bentonite layer also contains talc, saponite, halloysite, goethite and anatase. It is part of the Paleozoic bedrock and results from the weathering of a Lower Carboniferous metabasalt. The upper bentonite layer has Upper Oligocene age and has been derived from the alteration of tuffite with a composition ranging from alkali basalt to trachyte. This bentonite is linked to the first eruptions of the intraplate Cenozoic volcanic activity of the Westerwald.

Effects of dissolved oxygen on the oxide scales formed on ferritic-martensitic steel T12 exposed to supercritical water

Abstract The oxidation behavior of T12 after exposure to 560 °C/25 MPa supercritical water with different dissolved oxygen contents was investigated. The weight gain increases while the resistance of the oxide scale decreases with the increasing dissolved oxygen content. The oxide scale is a typical multi-layered structure including a Fe-rich outer layer and a Cr-rich inner layer. The Cr-rich hematite layer oxide was observed on specimen tested at high dissolved oxygen. The possible oxidation mechanism was proposed and the effects of oxygen on the oxidation of alloys in supercritical water were discussed.

High temperature oxidation of alloy 617, 740, HR6W and Sanicro 25 in supercritical water at 650°C

ABSTRACTIn this study, the oxidation behaviour of alloy 617, alloy 740, alloy HR6W and Sanicro 25 was investigated in SCW and vapour environment at 650°C for 320 h. The weight gain and the thickness of the oxide films of samples after exposure in SCW are higher than that in vapour. Inner oxidation phenomena were observed on alloy HR6W and Sanicro 25, which have higher content of Fe. The structure of the oxide films formed on alloy 617, alloy 740, alloy HR6W and Sanicro 25 after exposure in SCW at 650°C for 320 h is composed by a Fe-rich (mainly hematite) outer layer and a Cr-rich inner layer. The thickness of the outer Fe-rich layer is related with the Fe content in alloy matrix. Oxide films spallation phenomena were found on alloy HR6W after exposure in SCW.

Small-scale heterogeneity of trace metals including rare earth elements and yttrium in deep-sea sediments and porewaters of the Peru Basin, southeastern equatorial Pacific

Abstract. Due to its remoteness, the deep-sea floor remains an understudied ecosystem of our planet. The patchiness of existing data sets makes it difficult to draw conclusions about processes that apply to a wider area. In our study we show how different settings and processes determine sediment heterogeneity on small spatial scales. We sampled solid phase and porewater from the upper 10 m of an approximately 7.4×13 km2 area in the Peru Basin, in the southeastern equatorial Pacific Ocean, at 4100 m water depth. Samples were analyzed for trace metals, including rare earth elements and yttrium (REY), as well as for particulate organic carbon (POC), CaCO3, and nitrate. The analyses revealed the surprisingly high spatial small-scale heterogeneity of the deep-sea sediment composition. While some cores have the typical green layer from Fe(II) in the clay minerals, this layer is missing in other cores, i.e., showing a tan color associated with more Fe(III) in the clay minerals. This is due to varying organic carbon contents: nitrate is depleted at 2–3 m depth in cores with higher total organic carbon contents but is present throughout cores with lower POC contents, thus inhibiting the Fe(III)-to-Fe(II) reduction pathway in organic matter degradation. REY show shale-normalized (SN) patterns similar to seawater, with a relative enrichment of heavy REY over light REY, positive LaSN anomaly, negative CeSN anomaly, and positive YSN anomaly and correlate with the Fe-rich clay layer and, in some cores, also correlate with P. We therefore propose that Fe-rich clay minerals, such as nontronite, as well as phosphates, are the REY-controlling phases in these sediments. Variability is also seen in dissolved Mn and Co concentrations between sites and within cores, which might be due to dissolving nodules in the suboxic sediment, as well as in concentration peaks of U, Mo, As, V, and Cu in two cores, which might be related to deposition of different material at lower-lying areas or precipitation due to shifting redox boundaries.

Thermal stability of the passive film formed on 316L stainless steel surface studied by ToF-SIMS

The modifications of the passive film formed on 316 L stainless steel surface during stepwise heating in ultra-high vacuum up to 300 °C have been studied in situ by ToF-SIMS. The pre-formed passive film (in 0.05 M H2SO4) has a bilayer structure, comprising Fe-rich, Mo-rich (outer) and Cr-rich (inner) layers. Below 100 °C, the passive film is stable. At 100 °C–250 °C, dehydroxylation and dehydration is observed. Above 250 °C, the main modification in the film is formation of chromium oxide at the expense of oxidized iron. At higher temperature, thicker Cr-rich inner layer with sharper inner/outer oxide interface is formed.

Effect of Hot Stamping Heat Treatment Temperature on Resistance Spot Weldability of Al-10% Si Coated 30MnB5 Steel

Hot stamping is the most efficient manufacturing process to produce high strength automotive parts with reduced springback. Recently, 30MnB5 steel has been developed for hot stamping steel which can provide above 1700 MPa. However, resistance spot weldability of this steel is insufficient due to the need for a large amount of carbon addition. In this study, the effect of the hot stamping heat treatment temperature on resistance spot weldability of Al-10% Si coated 30MnB5 was evaluated to improve the resistance spot weldability of 30MnB5. In terms of nugget diameter, weldable current range, tensile shear strength and cross tension strength, the specimen heat treated at 850 oC achieved better performance than the specimen heat treated at 950 oC. There was a coating microstructure difference between the specimens heat treated at 850 oC and 950 oC whereas both specimens had similar microstructure and mechanical properties of their substrates. The Fe-rich layer of the specimen heat treated at 950 oC was twice as thick as the specimen heat treated at 850 oC because the diffusion rate was much higher at 950 oC. The thick Fe-rich layer deteriorated the resistance spot weldability due to high electrical resistivity during resistance spot welding. Key words: hot stamping, Al-10%Si coating, 30MnB5, resistance spot welding, dynamic resistance