Evolution of lamellar architecture and microstructure during redox cycling of Fe-Co and Fe-Cu foams

Pennell, Samuel  M.; Mack, Jacob B.; Dunand, David C.

doi:10.1016/j.jallcom.2022.165606

Cited by 8 publications

(5 citation statements)

References 40 publications

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“…Such a process significantly increases the solid solubility of Fe in Cu, reduces the residual Fe content in the Cu matrix, and mitigates chemical microsegregation. Subsequent aging treatment promotes the separation of Fe from the solid solution and enhances the dispersion of α-Fe phases, leading to substantial improvements in tensile strength, wear resistance, and corrosion resistance while maintaining the good electrical conductivity of the alloy [8][9][10]. Chen et al [11] prepared Cu-Fe alloys via the rapid cooling process and found that with the increase in the cooling rate, the number of Fe-rich spheres in the microstructure increased.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Research on Fe Precipitation Behavior of Cu95Fe5 Alloys during Rapid Cooling

Wang,

Gao,

Lai

et al. 2024

Metals

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To investigate structural changes, the Cu95Fe5 alloy system was subjected to cooling rates of 1 × 1013 K/s, 2 × 1012 K/s, 2 × 1011 K/s, and 2 × 1010 K/s using the molecular dynamics simulation method. The results revealed that decreasing the cooling rate caused an increase in the phase transition temperature. Further, the structure of the alloy system exhibited a tendency towards increased stability following cooling at lower cooling rates. The Fe precipitation behavior of the Cu95Fe5 alloys during cooling at the rate of 2 × 1010 K/s was further explored, with the results suggesting that the formation and growth of the Fe cluster is a continuous process governed by the nucleation and growth mechanism. The size and number of Fe clusters formed at different stages were found to be affected by three factors, namely, the interaction force between the Fe atoms, the diffusion ability of the Fe atoms, and the interfacial energy between the Fe cluster and Cu matrix. When the alloy temperature exceeded 1400 K, the accumulation of the Fe atoms was facilitated by their strong interaction. However, the high temperatures and the large diffusion coefficient of the Fe atoms acted as inhibitors to the growth of Fe clusters, despite the intense thermal activities. As the temperature was reduced from 1400 K to 1050 K, the Fe atoms moved with a reduced intensity in a narrower area, and both the number of Fe atoms in the largest cluster and the number of clusters increased due to the action of the interaction force between the Fe atoms. Upon lowering the temperature from 1050 K to 887 K, the size of the largest Fe cluster increased rapidly, while the number of clusters decreased gradually. The growth of the largest Fe cluster could be partly attributed to the diffusion of single Fe atoms into the cluster under the action of the interaction force between the Fe atoms, in addition to the gathering and combination of multiple clusters. When the temperature was lowered from 967 K to 887 K, the diffusion coefficient of the Fe atoms approached 0, indicating that the non-diffusive local structure rearrangements of atoms dominated in the system structure change process. The interface energy governed the combination of the Fe clusters in this stage. At a temperature below 887 K, the alloy crystallized, the activities of the Fe atoms were reduced due to a low temperature, and the movement range of the Fe atoms was small at a fast cooling rate. As such, both the size and number of Fe clusters showed no obvious changes.

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Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Research on Fe Precipitation Behavior of Cu95Fe5 Alloys during Rapid Cooling

Wang,

Gao,

Lai

et al. 2024

Metals

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show abstract

Section: Introductionmentioning

confidence: 99%

“…[25] The reduction reaction is known to be accelerated by the presence of transition metals (including Ni), such that the reduction reaction begins at the interface between the oxide and the transition metal and proceed along the moving interface (i.e., inside out). [26][27][28] High-temperature H 2 reduction of MoO 2 (and Fe 2 Mo 3 O 8 ) proceeds via a different mechanism. As mentioned above, the gaseous MoO 2 (OH) 2 forms at high temperatures in the presence of steam.…”

Section: Introductionmentioning

confidence: 99%

“…These lamellar Fe structures, with high porosity and low tortuosity ideal for solid-gas reactions, [33] were shown to extend the useful redox lifetime of the Fe-based material, particularly with alloying additions to Fe. [27,34] Nevertheless, these freeze-cast structures degrade during cycling due to the collapse of the lamellar structure due to buckling, contact, and sintering between neighboring lamellae, as well as flaring of lamellar tips resulting in the formation of a dense shell encapsulating the structure, as also seen in packed powder beds. [35,36] The above strategies can be combined to increase degradation resistance of porous Fe structures.…”

Section: Introductionmentioning

confidence: 99%

“…Freeze-cast lamellar structures alloyed with Fe-soluble, redox-inactive metals such as Ni or Co can accelerate the reduction reaction and provide a ductile backbone to provide additional mechanical stability to the lamellae. [26,27,34,37] Alloying with Mo was found to be particularly effective due to the sintering inhibition effect provided by Mo. [32] Based on our understanding of the degradation mechanisms in freeze-cast lamellar structures, it is useful to now consider other porous geometries.…”

Section: Introductionmentioning

confidence: 99%

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Hierarchically Porous Iron Alloys with High Sintering Resistance During Cyclic Steam Oxidation and Hydrogen Reduction

Pennell,

Chappuis,

Carpenter

et al. 2023

Adv Funct Materials

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Hydrogen release/storage materials for iron/air batteries are fabricated as Fe‐16Mo and Fe‐24Ni (at.%) lattices via 3D‐extrusion printing of foamed inks containing oxide microparticles, followed by H2 reduction and sintering. A hierarchical open porosity is designed: (i) channels between walls created during printing, (ii) mesopores within walls, created during ink foaming, and (iii) micropores within ligaments between mesopores, created from partial sintering metal particles and gas escape during cycling. When subjected to H2/H2O redox cycling at 800 °C, the lattices of both compositions gradually undergo sintering. The Fe‐16Mo lattice remains fully redox‐active after 50 cycles unlike the Fe‐24Ni lattice, which loses 90% of its redox capacity after 30 cycles. The increased lifetime of the Fe‐16Mo lattice is attributed to the sintering inhibition of Mo, the formation of a mixture of oxide phases in the oxidized state, and the cyclic formation of submicron Fe2Mo by reduction of MoO2 and Fe2Mo3O8. The microstructure of the foamed walls is examined throughout cycling to track changes in morphology and composition. These are correlated to volume and porosity changes in the lattice. A comparison is made to previously‐studied Fe‐Mo and Fe‐Ni freeze‐cast lamellar foams, and variations in performance are discussed in the context of the different architectures.

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Tungsten's Role in Enhancing Sintering Resistance of Fe‐W Hierarchical Foams during Redox Cycling

Chen,

Pennell,

Dunand

2024

Adv Funct Materials

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Directional freeze‐cast Fe‐W lamellar foams with 10–33 at.% W show distinct microstructural evolutions during steam/hydrogen redox cycling between oxidized and reduced states at 800 ⁰C, depending on W concentration. The Fe‐18 W and Fe‐25 W foams exhibit a sufficient volume fraction of W‐rich phases – λ‐Fe2W to inhibit sintering for α‐Fe in the reduced state and FeWO4 to inhibit sintering for Fe3O4 in the oxidized state – thus forming ligaments comprising two phases (Fe/λ‐Fe2W and Fe3O4/FeWO4, respectively). In contrast, a Fe‐10 W foam with a lower volume fraction of W‐containing phases (λ‐Fe2W and FeWO4) shows lamellae densification as well as core‐shell structure formation, due to Fe outward diffusion during oxidation. While higher W concentration enhances the stability of lamellar structure in Fe‐W foams, degradation still occurs, via buckling of lamellae and swelling of foams after extensive cycling. In situ XRD characterization shows that W addition has a minor effect on the oxidation process but slows reduction due to the sluggish kinetics of FeWO4 reduction. This influence is mitigated by the formation of nanocrystalline W‐rich phases due to the chemical vapor transport (CVT) mechanism during the reduction of FeWO4 to boost the reaction kinetics during redox cycling.

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Evolution of lamellar architecture and microstructure during redox cycling of Fe-Co and Fe-Cu foams

Cited by 8 publications

References 40 publications

Molecular Dynamics Research on Fe Precipitation Behavior of Cu95Fe5 Alloys during Rapid Cooling

Molecular Dynamics Research on Fe Precipitation Behavior of Cu95Fe5 Alloys during Rapid Cooling

Hierarchically Porous Iron Alloys with High Sintering Resistance During Cyclic Steam Oxidation and Hydrogen Reduction

Tungsten's Role in Enhancing Sintering Resistance of Fe‐W Hierarchical Foams during Redox Cycling

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