Diffusion Of Iron Research Articles

Microscale chemical imaging to characterize and quantify corrosion processes at the metal-electrolyte interface

We introduce an experimental setup to chemically image corrosion processes at metal-electrolyte interfaces under stagnant, confined conditions—relevant in a wide range of situations. The setup is based on a glass capillary, in which precipitation of corrosion products in the interfacial aqueous phase can be monitored over time with optical microscopy, and chemically and structurally characterized with microscopic synchrotron-based techniques (X-ray fluorescence, X-ray diffraction, and X-ray absorption spectroscopy). Moreover, quantification of precipitates through X-ray transmission measurements provides in-situ corrosion rates. We illustrate this setup for iron corrosion in a pH 8 electrolyte, revealing the critical role of O2 and iron diffusion in governing the precipitation of ferrihydrite and its transformation to goethite. Corrosion and coupled reactive transport processes can thus be monitored and fundamentally investigated at the metal-electrolyte interface, with micrometer-scale resolution. This capillary setup has potential applications for in-situ corrosion studies of various metals and environments.

In situ observation of the structural transformations behind the emergence and disappearance of exchange bias in polycrystalline Ni-Mn/Fe20Ni80 films

The antiferromagnetic L10θ-NiMn compound has a Néel temperature of up to 800 ºC and is capable of providing the exchange bias effect in multilayered structures with adjacent ferromagnetic layers, such as Fe20Ni80, up to 350 ºC. The value of the exchange bias field can be non-decreasing up to 150 ºC, making Ni-Mn a compelling choice for applied devices based on the exchange bias effect. In this work we study the structural transformations occurring in magnetron-sputtered Ni-Mn/Fe20Ni80 films that first lead to the emergence of exchange bias in these structures, and then to its disappearance. Employing in situ X-ray diffractometry and vibrating-sample magnetometry we observe how under annealing the phases of Ni-Mn follow Ostwald’s rule of stages on their way to form the equilibrium θ-NiMn. Our findings suggest that at temperatures of around 350 ºC diffusion of iron from the ferromagnetic layer causes decomposition of θ-NiMn, ultimately resulting in the irreversible disappearance of exchange bias. Our results reveal the role of adjacent Fe20Ni80 layers in the transformations, and how crystal texture in the Ni-Mn layer affects exchange bias. The results of our work not only clarify the fundamental mechanisms but also provide valuable insights for engineering and utilizing of applied devices with Ni-Mn, making it of interest to material scientists and engineers of different specializations.

Preliminary Characterisation of Thermal Upgrading of Nickel from Saprolite via Selective Reduction

The mineralogical properties and distribution of information established in saprolite from Indonesia were investigated using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy energy dispersion spectroscopy (SEM–EDS) and differential thermal analysis (DTA) measurements. The findings suggest that laterite ore has a complex inner core. The percentages of nickel, iron, magnesium, aluminium and silicon in saprolite are 1.82 wt%, 30.47 wt%, 10–20 wt%, 4.86 wt% and 8.1 wt%. Saprolite has 53.1 wt% iron oxide/oxyhydroxide, 38.3 wt% lizardite and 8.7 wt% silicate. According to DTA, saprolite undergoes a phase shift from goethite to haematite at low temperatures (200–300°C). This is a suitable phase to optimise nickel diffusion in iron. Furthermore, the thermal upgrading approach was utilised for this saprolite.

Diffusion of iron in zinc selenide during hot isostatic pressing

The diffusion of iron impurities in zinc selenide (ZnSe) during hot isostatic pressing (HIP) in the temperature range T = 1000–1300 °C and pressures P = 100–190 MPa has been investigated. The iron concentration and its distribution over the sample volume with a step from 20 to 50 μm was determined by IR spectroscopy in combination with an IR microscope. The diffusion coefficients of Fe in ZnSe at various temperatures and pressures were determined. The diffusion coefficients of Fe in ZnSe at P = 100 MPa and T = 1000 °C were (5.3 ± 0.6)x10−10 cm2/s, T = 1300 °C were (9.4 ± 0.9)x10−9 cm2/s. It is shown that the temperature dependences are described by the Arrhenius equation, and the isostatic pressure does not affect the value of the diffusion coefficients.

Effect of the Saccharin Concentration on Electrodeposition of the Fe-Ni Alloy

The FMM (Fine Metal Mask) used in the OLED display manufacturing process is a metal sheet with holes formed to allow the deposition of diode material only in the sub-pixel area. To prevent deformation and misalignment of the FMM (Fine Metal Mask) caused by heat during the RGB organic deposition process, an Invar plate with a thermal expansion coefficient (CTE) close to 0 is used. The Invar sheet applied to the current FMM is manufactured through a metallurgical process, and its final thickness after rolling is 20 micron. However, due to limitations in reducing thickness with the rolling process, for manufacturing FMM with a thickness of under 10 micron for next-generation high-resolution (UHD-level) displays, the bottom-up electroplating process is suitable. However, to maintain the shape of the electroplated Invar sheet while ensuring commercial-grade low CTE, heat treatment at temperatures exceeding 600℃ for an extended period is required, utilizing thermo-mechanical processing methods. If uniformity in the microstructure composed of nano-grains is ensured in the electroplated Invar alloy in the As-deposited, it is possible to increase the efficiency of the process by reducing the heat-treatment processing cost.Therefore, in this study, we investigated the microstructural evolution in the Invar alloy by controlling the surface stress of the electroplated layer during pre-plating. We controlled the key additive, saccharin, in the Fe-Ni alloy electrolyte to assist the diffusion of iron and nickel ions. By examining the relation between microstructural uniformity, determined by the plated layer, and CTE, we propose optimized process conditions for the pre-plated Invar sheet.

Atomically Resolved Transition Pathways of Iron Redox.

The redox transition between iron and its oxides is of the utmost importance in heterogeneous catalysis, biological metabolism, and geological evolution. The structural characteristics of this reaction may vary based on surrounding environmental conditions, giving rise to diverse physical scenarios. In this study, we explore the atomic-scale transformation of nanosized Fe3O4 under ambient-pressure H2 gas using in-situ environmental transmission electron microscopy. Our results reveal that the internal solid-state reactions dominated by iron diffusion are coupled with the surface reactions involving gaseous O or H species. During reduction, we observe two competitive reduction pathways, namely Fe3O4 → FeO → Fe and Fe3O4 → Fe. An intermediate phase with vacancy ordering is observed during the disproportionation reaction of Fe2+ → Fe0 + Fe3+, which potentially alleviates stress and facilitates ion migration. As the temperature decreases, an oxidation process occurs in the presence of environmental H2O and trace amounts of O2. A direct oxidation of Fe to Fe3O4 occurs in the absence of the FeO phase, likely corresponding to a change in the water vapor content in the atmosphere. This work elucidates a full dynamical scenario of iron redox under realistic conditions, which is critical for unraveling the intricate mechanisms governing the solid-solid and solid-gas reactions.

Effects of Mn addition on oxidation behaviour of heat-resistant steel in a high-temperature steam environment

A comparative study of high chromium (Super304H) and high manganese low chromium heat-resistant steel (HT630) was carried out at 650 °C in steam. Results indicate that the high manganese content in HT630 significantly improved its oxidation resistance. It is ascribed to the formation of a dense protective MnCr2O4 oxide layer during oxidation. MnCr2O4 layer effectively inhibits the diffusion of iron, suppresses the growth of iron-rich oxides, promotes the formation of an iron-rich protective interface with the matrix, and improves the overall oxidation resistance.

Effects of heat treatment on microstructure and mechanical properties of 17-4PH/IN625 bimetallic parts fabricated through extrusion-based sintering-assisted additive manufacturing

The mechanical properties of bimetallic composites are significantly influenced by their interfacial morphologies. This study delves into the impact of various heat treatment conditions on the microstructure and mechanical attributes of steel/nickel bimetallic (17-4PH/IN625) components produced through extrusion-based sintering-assisted additive manufacturing (ES-AM). The bimetallic composites were annealed at 1150°C for 1, 4, and 8 h, followed by an aging treatment at 482°C for samples annealed for 8 h. After annealing, microstructural heterogeneities, including variations in grain size and elemental distribution within the transition zone close to the interface, were observed. It was found that in the diffusion transition zone between the two alloy layers, the diffusion of iron (Fe) and nickel (Ni) elements increased with longer holding times, as corroborated by microhardness tests and quantified through theoretical parabolic diffusion law. The transition zone exhibited two distinct areas: an Fe-predominant zone and a Ni-predominant zone, with the latter containing oxides and molybdenum (Mo)- and niobium (Nb)-rich precipitates. No new phases emerged post-heat treatment; however, shifts in peak due to stress relaxation and the emergence of precipitates were identified through X-ray diffraction (XRD) observations. Microhardness within the transition zone increased following heat treatment, peaking at 186 HV1.0 after a 4-h annealing. The optimal heat treatment condition was identified as 1150°C for 4 h, which facilitated the development of uniform microstructures and improved bonding strength. This study demonstrates an enhanced interfacial bonding strength in 17-4PH and IN625 bimetallic parts manufactured through ES-AM, suggesting their wide-ranging potential applications in industry.

Microstructure and properties of 316 L lattice/Al composites by additive manufacturing and infiltration with different temperature

Interface between lattice reinforcement and matrix played a key factor on properties of the lattice reinforced aluminum matrix composites. However, the effect of interface composed of intermetallic compounds on the properties of 316 L lattice/Al composites was still unclear. In this study, 316 L lattice reinforced aluminum composite with continuous interface were prepared by combining laser powder bed fusion (LPBF) and vacuum infiltration, and effect of infiltration temperature on interface evolution and properties of the composite was investigated. Results indicated that a continuous dual-phase interfacial layer consisting of hard intermetallic compounds η-Fe2Al5 and θ-FeAl3 was formed between the reinforcement and matrix due to diffusion and reaction of iron and aluminum atoms, and the size of needle-type FeAl3 phase in the interfacial zone increased when infiltration temperature was up from 800 °C to 900 °C. It also confirmed that reinforced by 316 L lattice and hard intermetallic compounds layer, the composite showed excellent mechanical and wear resistant properties, with compressive strength of 657 ± 32 MPa and specific wear rate of 0.20 × 10−3 (mm3/N·m) for the sample prepared at 800 °C, which were over 10 times and one fifth of that of the aluminum matrix individually. This study provides a new strategy for developing 316 L lattice/Al composites with excellent properties.

Shot peening of AZ31 magnesium alloy: role of surface microstructure and iron diffusion on corrosion behaviour

ABSTRACT In the present work, surface grain refined AZ31 magnesium (Mg) alloy was produced by shot peening (SP). X-ray diffraction analysis demonstrated iron diffusion into the surface of AZ31 Mg alloy during SP. Higher hardness, increased surface energy and decreased corrosion resistance were observed for the shot-peened surface due to nanostructured grains resulted from SP. From the immersion studies in a simulated physiological solution carried out for 3 days, higher level of biomineralization was observed for the shot peened AZ31 compared with the base alloy that dominated the adverse effect of iron diffusion in resisting the biocorrosion. The results suggest that the nano-structuring of AZ31 Mg alloy surface helps to enhance the biomineralization to control the degradation. However, the selection of processing medium is crucial to eliminate the effect of chemical composition change during the process in tailoring the corrosion behaviour of AZ31 Mg alloy for biomedical implant applications.

Intermixing of iron and cobalt with oxygen-rich magnesium oxide in CoFeB/MgO/CoFeB magnetic tunneling junctions

Atomic-scale spectroscopic imaging of sputtered magnetic tunnel junction structures with a thick oxygen-rich MgO barrier reveals the diffusion of iron and cobalt into the MgO barrier from CoFeB electrodes. First principles calculations are performed to (1) confirm that Fe diffusion through Mg vacancies is energetically favorable, (2) quantify the reduction of interfacial perpendicular magnetic anisotropy due to Fe diffusion into MgO, and (3) predict that the presence of Fe impurities in MgO causes an increased leakage and a tunneling magnetoresistance decrease. Through the chemical shift of the Fe L3 edge and the peak ratio Fe L3/Fe L2 measured by electron energy loss spectroscopy, we suggest that, within MgO, iron with mixed oxidation state Fe2+ and Fe3+ or higher is found in the as-grown structure, which is reduced by annealing to Fe2+. These results indicate that the stoichiometry of as-deposited MgO barrier layers plays an important role in controlling the microstructure and optimizing the performance of magnetic tunnel junctions.

Corrosion Behaviour of Ni-based Alloys 230, 617 and 601 in CO2 Gas at 750 and 850 °C

This paper investigated the corrosion behavior of three nickel-based alloys (230, 617 and 601) at 750 °C and 850 °C in a carbon dioxide environment for up to 500 h. All three alloys showed good oxidation resistance by forming mainly a protective chromia layer with low weight gains. Internal Al2O3 was precipitated beneath a thin chromia layer in all cases. For 230 and 617 alloys, NiO and Cr-rich spinel outer layers were formed, but for 601 less iron and nickel outward diffusion was observed at both temperatures. Furthermore, some minor alloy elements (Mn, Ti, and Co) were also observed in the chromia layers. Very limited carburization due to the CO2 reaction was revealed in the matrix underneath the oxide scale. Wagner’s theory was applied to examine the critical chromium concentration for forming a protective chromia scale. This prediction indicated that alloy concentrations were marginal for chromia formation at both temperatures and the critical chromium concentration decreased with increasing the oxidation temperature. The presence of other alloying elements, e.g. Al, Mn, Ti, Si etc could increase corrosion resistance of these alloys by forming either additional protective oxide barriers or integrating with chromium oxide to enhance its protection.

Kinetics of hydrogen and vacancy diffusion in iron: A kinetic activation relaxation technique (k-ART) study

Kinetics of hydrogen and vacancy diffusion in iron: A kinetic activation relaxation technique (k-ART) study

Corrosion Behaviour of Ni-Based Alloys 230, 617 and 601 in CO2 Gas at 750 and 850°C

As a newly developed technology, oxyfuel combustion makes CO2 capture and sequestration feasible but raises a corrosion problem because of high concentrations of CO2 in flue gases at high temperatures. Conventional ferritic/martensitic heat resisting steels are sufficient to resist corrosion in oxygen or air but cannot survive in CO2-rich gases. To increase the process efficiency, higher temperatures will be used for energy production. As a result, austenitic steels and/or nickel-base alloys are required because of their superior corrosion resistance and mechanical properties at high temperature. This paper investigated the corrosion behavior of three nickel-based chromia-forming commercial alloys (230, 617 and 601) at 750°C and 850°C in a carbon dioxide environment for up to 500 h.Samples were cut to form 10mm x 8mm x (0.8-3) mm rectangular shaped coupons. After cutting, all surfaces of samples were ground up to 1200-grit finish, and further polished down to 3μm. Electro-polishing in 15% concentrated hydrochloric acid was used to remove the subsurface deformation zone. The grain sizes of 617 are larger (100-200μm) than those of 230 (20-80μm) alloy, and the 601 (10-30μm) alloy has the smallest grain size. All samples were ultrasonically cleaned with ethanol before being reacted in Ar-20%CO2 at 750℃ and 850°C, for up to 500 h. After reaction, samples were analysed by surface X-ray diffraction, metallographic cross-section analysis by optical microscopy, and scanning electron microscopy together with energy dispersive X-ray analysis.All three alloys showed good oxidation resistance by forming mainly a protective chromia layer with low weight changes. Internal Al2O3 was precipitated beneath a thin protective chromia layer for all cases. For 230 and 617 alloys, NiO and Cr-rich spinel outer layers were formed, but for 601 less iron and nickel outward diffusion was observed at both temperatures. Furthermore, some minor alloy elements (Mn, Ti, and Co) were also observed to diffuse into the chromia layers.Wagner’s Theory was applied to examine the critical chromium concentration for forming a protective chromia. This prediction indicated alloy concentrations were marginal for chromia formation at both temperatures for the test alloys. The observation of protective chromia formation can be attributed to the effect of other alloying elements, e.g. Al, Mn, Ti, Si etc. Because of the temperature effect on diffusion, the predicted result from Wagner’s Theory showed that the critical chromium concentration needed to form and maintain a protective chromia layer decreased with increasing the oxidation temperature, which is consistent with the experimental observation.The Al and Si oxides formed an additional protective barrier between the matrix and the chromia layer, preventing the diffusion of iron and nickel outwards and therefore increasing the oxidation resistance. Manganese effectively prevented carburization by combining with chromium oxide to form the outermost spinel oxide layer, increasing oxidation/carburisation resistance. Titanium diffused through the chromia layer, accelerating chromium diffusion and leading to higher kinetic rates. Tungsten reduced oxidation resistance by increasing the metal vacancies and therefore outward diffusion of Ni, Fe and Mn through the chromia scale.In general, no significant carbide formation was found in any of the Ni-base alloys in these reaction conditions. At 750℃, carburization due to CO2 reaction was found for 230 alloy but not for 617 and 601 alloys after 500h reaction. However, at 850°C, internal carbides from the reaction were observed for all three alloys. The variation in carburization extent among the different alloys can be attributed to the formation of oxides of aluminum, manganese and silicon, which can impede the inward diffusion of carbon, resulting in the reduction of carburizing kinetics.

Formation Mechanism of the “Green Above, Brown Below” Phenomenon in Yaozhou Kiln Celadon

Yaozhou Kiln is a famous ancient center for celadon production in China, located in present-day Shaanxi Province. While analyzing its olive-green celadon produced during the Song Dynasty, a common occurrence of brownish base (foot and bottom) was observed. This phenomenon can also be found in porcelain produced at other kilns in China and Vietnam. However, previous research has not systematically explored the coloration mechanism behind it. Through different analytical methods, coupled with reproduction firing experiments, this paper concludes that the brownish base is attributed to the diffusion of iron from the body and sand cushion into the thinly applied glaze on the base, as well as the crystallization formed by the combination of the sand cushion and the surface glaze. Factors influencing the depth of the brownish color include: (1) the iron content of the body; (2) the thickness of the base glaze; and (3) the sand cushion material.

Thermal Conductivity and Thermal Diffusivity of Iron in the Temperature Range of 300–1700 K

Abstract—Using the laser flash method, the thermal diffusivity (a) of carbonyl iron is measured in the temperature range of 300–1700 K with a detailed study of the critical region 980–1170 K. The initial experimental data in the field of magnetic phase transformation are processed by the scaling power law. The values of the critical indexes for thermal diffusivity (\(\gamma {\kern 1pt} ',\) γ) are obtained below and above the Curie temperature TС = 1048 ± 5 K: \(\gamma {\kern 1pt} '\) = 0.51 and γ = 0.35, which in absolute value significantly exceed the value of the characteristic critical index for the heat capacity (γ ≈ –0.1). The thermal conductivity (λ) is calculated from measured data of the thermal diffusivity. The results are compared with the known literature data, special attention is paid to the behavior of the curves a(T), λ(T) in the region of the magnetic phase transformation. A table of recommended temperature dependences for a and λ along with estimated errors has been developed.

Thermal Conductivity and Thermal Diffusivity of Iron in the Temperature Range of 300–1700 K

Thermal Conductivity and Thermal Diffusivity of Iron in the Temperature Range of 300–1700 K

Corrosion Behaviour of Ni-Based Alloys 230, 617 and 601 in CO2 Gas at 750 and 850°C

This paper investigated corrosion behaviors of three nickel-based chromia-forming commercial alloys (230, 617 and 601) at 750°C and 850°C in a CO2 environment for up to 500 h. All three alloys showed good oxidation resistance by forming mainly a protective chromia layer with low weight changes. Internal Al2O3 was precipitated beneath a thin protective chromia layer for all cases. For 230 and 617 alloys, NiO and Cr-rich spinel outer layers were formed, but for 601 less iron and nickel outward diffusion was observed at both temperatures. Furthermore, some minor alloy elements (Mn, Ti, and Co) were observed to diffuse into the chromia layers.Wagner’s theory predicted that alloy concentrations were marginal for chromia formation at both temperatures for the test alloys. The observation of protective chromia formation can be attributed to the effect of other alloying elements, e.g. Al, Mn, Ti, Si etc. Wagner’s theory also predicted that this critical chromium concentration decreased with increasing the oxidation temperature, which is consistent with the experimental observation.The Al and Si oxides formed an additional protective barrier between the matrix and the chromia layer, preventing the diffusion of iron and nickel outwards and therefore increasing oxidation resistance. Manganese effectively prevented carburization by combining with chromia to form the outermost spinel oxide layer, increasing oxidation/carburisation resistance. Titanium diffused through the chromia layer, accelerating chromium diffusion and leading to higher kinetic rates. Tungsten reduced oxidation resistance by increasing the metal vacancies and therefore outward diffusion of Ni, Fe and Mn through the chromia scale.

Influence of the iron additive on the microstructural behavior of an aluminum-copper foundry alloy B206

Although used and studied since the beginning of the century, the mechanical properties of aluminum-based structural hardening alloys still conceal some secrets that metallurgists are trying to uncover. In this work we are interested in aluminum alloys and more particularly in an Al-Cu alloy. The main objective of this work was to study the influence of structural hardening heat treatments on the evolution of the mechanical and structural properties of B206 alloys. For that, we used several experimental methods adapted to this kind of scientific work. We quote essentially: the thermal treatments of setting in hardening, as well as measurements of the hardness. The analysis of the experimental results obtained by these methods allowed us to explain and to affirm that Al-Cu alloys do not give appreciable structural hardening; because of the difficulty of diffusion of iron and silicon which influences the treatment and brought in a general way to the precipitation of the phase β; plays an important role in the evolution of the mechanical characteristics of Al-Cu alloys.

Effect of Mo on the high-temperature oxidation behavior of Cr-Ni-Mo hot-work die steels

To investigate the effect of molybdenum (Mo) on the high-temperature oxidation behavior of low-carbon hot-work die steels in a Cr-Ni-Mo system, five 3Cr3MoxNiW steels were prepared. The addition of Mo resulted in a decrease in the grain size of the 3Cr3MoxNiW steel, as well as an improvement in its oxidation resistance. The addition of Mo to 3Cr3MoxNiW steel reduces the inward diffusion of oxygen and the outward diffusion of iron, which accelerates the formation of chromium oxide. The oxide of Mo can then also participate in the process of protective oxide film formation, thus improving its oxidation resistance.