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Cobalt-iron alloys containing from 7.0 to 9.3 percent iron prepared from ultrapure cobalt and iron have the highest Curie point of all known magnetically soft materials. Their high permeability, low hysteresis loss, good saturation induction, and square loop characteristics recommend them for use in power transformers and rotating machinery.
The exchange coupling between a hard magnetic layer MnBi and a soft magnetic layer Co-Fe has been found to significantly improve the maximum energy product. In this work, the spin structure of exchange coupled MnBi:Co-Fe bilayers is experimentally investigated by X-ray magnetic circular dichroism (XMCD) and polarized neutron reflectometry (PNR). We find that the out-of-plane magnetization reversal process of the MnBi:Co-Fe bilayer structure involves formation of a curling-type twisting of the magnetization in the film plane at low or intermediate reversal fields. Additionally, micromagnetic simulations are further performed to provide a detailed view of the spins at the curling center. Reminiscent of chiral spin structures known as spin bobbers, this curling in the exchange-coupled hard-soft magnetic bilayers is a new type of skyrmionic spin structure and worth further investigation.
Abstract Iron alloying of oxidic cobaltate catalysts results in catalytic activity for oxygen evolution on par with Ni-Fe oxides in base but at much higher alloying compositions. Zero-field 57 Fe Mössbauer spectroscopy and X-ray absorption spectroscopy (XAS) are able to clearly identify Fe 4+ in mixed-metal Co-Fe oxides. The highest Fe 4+ population is obtained in the 40–60% Fe alloying range, and XAS identifies the ion residing in an octahedral oxide ligand field. The oxygen evolution reaction (OER) activity, as reflected in Tafel analysis of CoFeO x films in 1 M KOH, tracks the absolute concentration of Fe 4+ . The results reported herein suggest an important role for the formation of the Fe 4+ redox state in activating cobaltate OER catalysts at high iron loadings.
Corrosion is a major concern for many industries, as corrosive environments can induce structural and morphological changes that lead to material dissolution and accelerate material failure. The progression of corrosion depends on nanoscale morphology, stress, and defects present. Experimentally monitoring this complex interplay is challenging. Here we implement in situ Bragg coherent X-ray diffraction imaging (BCDI) to probe the dissolution of a Co-Fe alloy microcrystal exposed to hydrochloric acid (HCl). By measuring five Bragg reflections from a single isolated microcrystal at ambient conditions, we compare the full three-dimensional (3D) strain state before corrosion and the strain along the [111] direction throughout the corrosion process. We find that the strained surface layer of the crystal dissolves to leave a progressively less strained surface. Interestingly, the average strain closer to the centre of the crystal increases during the corrosion process. We determine the localised corrosion rate from BCDI data, revealing the preferential dissolution of facets more exposed to the acid stream, highlighting an experimental geometry effect. These results bring new perspectives to understanding the interplay between crystal strain, morphology, and corrosion; a prerequisite for the design of more corrosion-resistant materials.
Current U.S. policies aim to establish domestic supply chains of critical minerals for the energy transition. The Iron Creek deposit in the Idaho cobalt belt (ICB) is one of the most promising cobalt (Co) targets. Our case study illustrates the importance of mineralogy in strategic evaluations of critical mineral potential. Most of the Co at Iron Creek occurs as Fe substitution in pyrite, with lattice-bound and inclusion-hosted Ag, As, Bi, Ni, Pb, Se, Te ± trace Au and Sb. Cobalt also occurs in minor cattierite-vaesite. The Co minerals are intergrown with Co-poor chalcopyrite hosting Cu ± minor In and Zn. Worldwide, most Co is recovered from deposits mineralogically distinct from the ICB, and the United States currently lacks infrastructure to recover this Co and its associated metals. ICB ore minerals could be processed by autoclave, roaster, smelter, bioleach, or heap leach. Recovery of the Ag, As, Au, Bi, In, Pb, Se, Te, and Zn would be costly by autoclave, and construction of a custom smelter for ICB ores is likely uneconomic, so these elements would become waste irrespective of criticality. The Co-Fe and Co-As sulfide minerals are most suitable for Co and Ni recovery by a hydrometallurgical autoclave process, with potential pretreatment of cobaltiferous pyrite/arsenopyrite in an inert-atmosphere roaster, in new domestic or anticipated international facilities. The ICB is the second largest known Co resource in the United States. Consideration of ore mineralogy in the ICB is essential in strategies for domestic production.
The primary goals of this project were to understand the formation mechanisms and reactivity of mix-metal sulfide nanophases (Cu-Fe, Ni-Fe, Co-Fe sulfides) produced via biological and abiotic pathways that are relevant to low-temperature aqueous environments. These mix-metal sulfide nanophases have been identified in a range of natural and anthropogenic systems and are considered to play key roles in the biogeochemical cycling of elements, biomineralization, environmental remediation, resource recovery, eco-toxicity, and the origin and evolution of life. Using a comparative approach, we aimed to elucidate: (i) if these mix-metal sulfides tend to form nanoscale phases regardless of their formation pathways; (ii) what mechanisms are involved in the biological and abiotic crystallization processes; (iii) what phases form that have been otherwise expected; and (iv) if we can combine the experimental results with what we see and surmise from field studies to facilitate a more comprehensive understanding regarding the origin and biogeochemical roles of these mix-metal sulfides. Along a related pathway of electron transfer in nano-systems, in this case dealing with Fe-oxides instead of Fe-sulfides, we have continued to explore the reactions and solid products of heterogeneous catalytic oxidation of aqueous Mn(II) by dissolved oxygen in the presence of iron oxides (hematite) nanoparticles. The nano-Mn-oxides produced are known to be efficient sorbents of transition metal elements, including Cu, Ni, and Co studied in our sulfide work.
Cobalt is an essential element for life and plays a crucial role in supporting the drive to clean energy, due to its importance in rechargeable batteries. Co is often associated with Fe in the environment, but the fate of Co in Fe-rich biogeochemically-active environments is poorly understood. To address this, synchrotron-based scanning X-ray microscopy (SXM) was used investigate the behaviour of cobalt at the nanoscale in Co-Fe(III)-oxyhydroxides undergoing microbial reduction. SXM can assess spatial changes in metal speciation and organic compounds helping to elucidate the electron transfer processes occurring at the cell-mineral interface and inform on the fate of cobalt in redox horizons. G. sulfurreducens was used to reduce synthetic Co-ferrihydrite as an analogue of natural cobalt-iron-oxides. Magnetite [Fe(II)/Fe(III) 3 O 4 ] production was confirmed by powder X-ray diffraction (XRD), SXM and X-ray magnetic circular dichroism (XMCD) data, where best fits of the latter suggested Co-bearing magnetite. Macro-scale XAS techniques suggested Co(III) reduction occurred and complementary SXM at the nanoscale, coupled with imaging, found localised biogenic Co(III) reduction at the cell-mineral interface via direct contact with outer membrane cytochromes. No discernible localised changes in Fe speciation were detected in the reordered cobalt-iron-oxides that were formed and at the end point of the experiment only 11% Co and 1.5% Fe had been solubilised. The solid phase retention, alongside the highly localised and preferential cobalt bioreduction observed at the nanoscale is consistent with retention of Co in redox zones. This work improves our fundamental molecular-scale understanding of the fate of Co in complex environmental systems and supports the development of biogenic Co-doped magnetite for industrial applications from drug delivery systems to magnetic recording media.
The sulfur poisoning and performance recovery of the state-of-the-art SOFC cathodes (La 0 . 80 Sr 0 . 20 ) 0 . 95 MnO 3 ± δ (LSM) and (La 0 . 60 Sr 0 . 40 ) 0 . 95 Co 0 . 20 Fe 0 . 80 O 3 – δ (LSCF), have been studied. Electrochemical impedance spectroscopy measurements of LSCF|GDC and LSM|YSZ half-cells are carried out in alternating atmospheres of air and SO 2 –air at 700°C for hundreds of hours. In the presence of SO 2 , the electrochemical performance of both the cells decays with ohmic and non-ohmic losses, owing to the absorption and chemical interaction of SO 2 with the electrodes. In LSCF, the SrO segregated on the surface tends to absorb and react with SO 2 , forming SrSO 4 followed by the exsolution of Co-Fe. As for LSM, SO 2 is absorbed onto the Sr-rich areas of LSM, including the active reaction sites near the TPBs, leading to Sr exsolution and SrSO 4 formation, leaving a Sr-deficient LSM. During the subsequent exposure to air, the performance of the sulfur-contaminated LSM is almost restored. The LSM particles, exposed to alternating atmospheres of air and SO 2 -air during the electrochemical tests, show a relatively clean surface with sparsely distributed SrSO 4 particles, indicating a high stability against sulfur poisoning. It is suggested that the loosely adsorbed SO 2 at the TPBs is readily swept away by the SO 2 -free air flow, recovering its ORR activity, whereas the Sr-deficient LSM due to Sr-exsolution stays modified, contributing to the incomplete performance restoration. Unlike the case of LSM, the performance of the sulfur-poisoned LSCF partially recovers during the subsequent exposure to air. Correspondingly, the LSCF particles have a modified morphology covered with numerous nanoparticles, mostly SrSO 4 , showing the irreversible aspect of the sulfur poisoning. The morphology modification is not concentrated near the electrode/electrolyte interface but over the entire cathode, indicating that the degree of recovery from sulfur poisoning is closely related to the presence of SrO and chemical activity of Sr in the electrodes at the solid-gas interface. These results also show the potential application of LSM for a sulfur sensor available in high-temperature harsh conditions.
Fe15Co is Tungsten-derived structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. there are four inequivalent Fe sites. In the first Fe site, Fe is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. All Fe–Fe bond lengths are 2.47 Å. In the second Fe site, Fe is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. All Fe–Fe bond lengths are 2.47 Å. In the third Fe site, Fe is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. All Fe–Fe bond lengths are 2.46 Å. In the fourth Fe site, Fe is bonded in a distorted body-centered cubic geometry to seven Fe and one Co atom. The Fe–Co bond length is 2.46 Å. Co is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms.
FeCo is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Fe is bonded in a body-centered cubic geometry to eight equivalent Co atoms. All Fe–Co bond lengths are 2.46 Å. Co is bonded in a body-centered cubic geometry to eight equivalent Fe atoms.
Fe3Co is Tungsten-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are two inequivalent Fe sites. In the first Fe site, Fe is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. All Fe–Fe bond lengths are 2.47 Å. In the second Fe site, Fe is bonded in a distorted body-centered cubic geometry to four equivalent Fe and four equivalent Co atoms. All Fe–Co bond lengths are 2.47 Å. Co is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms.
Fe9Co7 is Tungsten-derived structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. there are two inequivalent Fe sites. In the first Fe site, Fe is bonded in a distorted body-centered cubic geometry to one Fe and seven Co atoms. The Fe–Fe bond length is 2.47 Å. All Fe–Co bond lengths are 2.47 Å. In the second Fe site, Fe is bonded in a distorted body-centered cubic geometry to eight equivalent Fe and six equivalent Co atoms. All Fe–Co bond lengths are 2.85 Å. There are three inequivalent Co sites. In the first Co site, Co is bonded in a body-centered cubic geometry to eight equivalent Fe atoms. In the second Co site, Co is bonded in a distorted body-centered cubic geometry to ten Fe atoms. In the third Co site, Co is bonded in a body-centered cubic geometry to eight equivalent Fe atoms.
Fe11Co5 is Tungsten-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are four inequivalent Fe sites. In the first Fe site, Fe is bonded in a distorted body-centered cubic geometry to three Fe and five Co atoms. All Fe–Fe bond lengths are 2.47 Å. All Fe–Co bond lengths are 2.47 Å. In the second Fe site, Fe is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. In the third Fe site, Fe is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. In the fourth Fe site, Fe is bonded in a distorted body-centered cubic geometry to eight equivalent Fe and six Co atoms. There are two shorter (2.85 Å) and four longer (2.86 Å) Fe–Co bond lengths. There are three inequivalent Co sites. In the first Co site, Co is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. In the second Co site, Co is bonded in a distorted body-centered cubic geometry to ten Fe atoms. In the third Co site, Co is bonded in a distorted body-centered cubic geometry to ten Fe atoms.
Fe13Co3 is Tungsten-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are four inequivalent Fe sites. In the first Fe site, Fe is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. All Fe–Fe bond lengths are 2.47 Å. In the second Fe site, Fe is bonded in a distorted body-centered cubic geometry to five Fe and three Co atoms. There are two shorter (2.47 Å) and one longer (2.48 Å) Fe–Fe bond lengths. All Fe–Co bond lengths are 2.47 Å. In the third Fe site, Fe is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. In the fourth Fe site, Fe is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. There are three inequivalent Co sites. In the first Co site, Co is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. In the second Co site, Co is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms. In the third Co site, Co is bonded in a distorted body-centered cubic geometry to eight equivalent Fe atoms.
FeCo3 is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Fe is bonded to twelve equivalent Co atoms to form FeCo12 cuboctahedra that share corners with twelve equivalent FeCo12 cuboctahedra, edges with twenty-four equivalent CoFe4Co8 cuboctahedra, faces with six equivalent FeCo12 cuboctahedra, and faces with twelve equivalent CoFe4Co8 cuboctahedra. All Fe–Co bond lengths are 2.50 Å. Co is bonded to four equivalent Fe and eight equivalent Co atoms to form CoFe4Co8 cuboctahedra that share corners with twelve equivalent CoFe4Co8 cuboctahedra, edges with eight equivalent FeCo12 cuboctahedra, edges with sixteen equivalent CoFe4Co8 cuboctahedra, faces with four equivalent FeCo12 cuboctahedra, and faces with fourteen equivalent CoFe4Co8 cuboctahedra. All Co–Co bond lengths are 2.50 Å.