Microstructural evolution of lamellar Fe-25Ni foams during steam-hydrogen redox cycling

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

doi:10.1016/j.actamat.2022.118148

Microstructural evolution of lamellar Fe-25Ni foams during steam-hydrogen redox cycling

Jacob B. Mack^*, Samuel M. Pennell, David C. Dunand

^*Corresponding author for this work

Materials Science and Engineering

Research output: Contribution to journal › Article › peer-review

9 Scopus citations

Abstract

Cyclical steam oxidation and hydrogen reduction, relevant to iron-air batteries, is performed on freeze-cast Fe-25Ni (at.%) foams consisting of colonies of parallel lamellae separated by channels, both ∼20 µm thick and millimeters in length. This structure is designed to accommodate volumetric changes associated with the cyclical oxidation and reduction of Fe. Metallographic imaging performed at various redox stages, together with time-resolved in situ X-ray diffraction during redox cycling, detail the reaction kinetics and phase evolution of the foam, the evolution of its lamellar microstructure, and the eventual degradation of its internal architecture. As Fe preferentially oxidizes over Ni, each lamella develops an outer Fe-oxide scale, with metallic Ni rejected to the cores of the lamellae which develops an interconnected network of Fe-oxide veins. The Ni-rich metallic core limits the accumulation of Kirkendall pores and provides adhesion to the Fe-oxide scale, thus preventing lamellar fracture observed in unalloyed Fe foams. While the oxidation rate is slowed by the presence of Ni, the reduction rate is accelerated, as Ni acts as a catalyst and as the network of oxidized veins reduces quickly and become open microchannels, thereby providing rapid hydrogen access (driving reduction) and steam egress to the lamellar interior. After complete reduction, the Fe-rich shell and the Ni-rich core interdiffuse and homogenize, which helps eliminate both Kirkendall pores and microchannels from the lamellae. Furthermore, the ductile Ni-rich core limits lamellar buckling (another densification mechanism active in Fe foams). Architectural changes also affect resistance to internal damage, with smaller lamellar colonies exhibiting better resistance to buckling. These combined effects provided by Ni alloying allow the Fe-25Ni foams to maintain a high channel porosity (>40% porous), and thus high active surface area, after 10 redox cycles, as compared to a near complete loss of open channel porosity reported in unalloyed Fe foams.

Original language	English (US)
Article number	118148
Journal	Acta Materialia
Volume	237
DOIs	https://doi.org/10.1016/j.actamat.2022.118148
State	Published - Sep 15 2022

Funding

The research was funded by the US National Science Foundation under grant CMMI-2015641 . The authors acknowledge Dr. Christos Malliakas (NU) for assistance with XRD experiments, Dr. Christoph Kenel (NU) for help with XRD analysis, and Dr. Stephen Wilke (Materials Development Inc.) for insightful discussions. Experiments and characterization made use of the Materials Characterization and Imaging Facility , the NUANCE Center (supported by SHyNE under NSF ECCS-1542205 , MRSEC under NSF DMR-1720139 , the International Institute for Nanotechnology, the Keck Foundation, and the State of Illinois), and the IMSERC X-Ray facility (supported by SHyNE under NSF ECCS-2025633 ) at Northwestern University (NU). The research was funded by the US National Science Foundation under grant CMMI-2015641. The authors acknowledge Dr. Christos Malliakas (NU) for assistance with XRD experiments, Dr. Christoph Kenel (NU) for help with XRD analysis, and Dr. Stephen Wilke (Materials Development Inc.) for insightful discussions. Experiments and characterization made use of the Materials Characterization and Imaging Facility, the NUANCE Center (supported by SHyNE under NSF ECCS-1542205, MRSEC under NSF DMR-1720139, the International Institute for Nanotechnology, the Keck Foundation, and the State of Illinois), and the IMSERC X-Ray facility (supported by SHyNE under NSF ECCS-2025633) at Northwestern University (NU).

Keywords

Alloys
Metal-foam
Microstructure
Oxidation
X-ray diffraction

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
Ceramics and Composites
Polymers and Plastics
Metals and Alloys

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10.1016/j.actamat.2022.118148

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title = "Microstructural evolution of lamellar Fe-25Ni foams during steam-hydrogen redox cycling",

abstract = "Cyclical steam oxidation and hydrogen reduction, relevant to iron-air batteries, is performed on freeze-cast Fe-25Ni (at.%) foams consisting of colonies of parallel lamellae separated by channels, both ∼20 µm thick and millimeters in length. This structure is designed to accommodate volumetric changes associated with the cyclical oxidation and reduction of Fe. Metallographic imaging performed at various redox stages, together with time-resolved in situ X-ray diffraction during redox cycling, detail the reaction kinetics and phase evolution of the foam, the evolution of its lamellar microstructure, and the eventual degradation of its internal architecture. As Fe preferentially oxidizes over Ni, each lamella develops an outer Fe-oxide scale, with metallic Ni rejected to the cores of the lamellae which develops an interconnected network of Fe-oxide veins. The Ni-rich metallic core limits the accumulation of Kirkendall pores and provides adhesion to the Fe-oxide scale, thus preventing lamellar fracture observed in unalloyed Fe foams. While the oxidation rate is slowed by the presence of Ni, the reduction rate is accelerated, as Ni acts as a catalyst and as the network of oxidized veins reduces quickly and become open microchannels, thereby providing rapid hydrogen access (driving reduction) and steam egress to the lamellar interior. After complete reduction, the Fe-rich shell and the Ni-rich core interdiffuse and homogenize, which helps eliminate both Kirkendall pores and microchannels from the lamellae. Furthermore, the ductile Ni-rich core limits lamellar buckling (another densification mechanism active in Fe foams). Architectural changes also affect resistance to internal damage, with smaller lamellar colonies exhibiting better resistance to buckling. These combined effects provided by Ni alloying allow the Fe-25Ni foams to maintain a high channel porosity (>40% porous), and thus high active surface area, after 10 redox cycles, as compared to a near complete loss of open channel porosity reported in unalloyed Fe foams.",

keywords = "Alloys, Metal-foam, Microstructure, Oxidation, X-ray diffraction",

author = "Mack, {Jacob B.} and Pennell, {Samuel M.} and Dunand, {David C.}",

note = "Publisher Copyright: {\textcopyright} 2022 Acta Materialia Inc.",

year = "2022",

month = sep,

day = "15",

doi = "10.1016/j.actamat.2022.118148",

language = "English (US)",

volume = "237",

journal = "Acta Materialia",

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TY - JOUR

T1 - Microstructural evolution of lamellar Fe-25Ni foams during steam-hydrogen redox cycling

AU - Mack, Jacob B.

AU - Pennell, Samuel M.

AU - Dunand, David C.

PY - 2022/9/15

Y1 - 2022/9/15

N2 - Cyclical steam oxidation and hydrogen reduction, relevant to iron-air batteries, is performed on freeze-cast Fe-25Ni (at.%) foams consisting of colonies of parallel lamellae separated by channels, both ∼20 µm thick and millimeters in length. This structure is designed to accommodate volumetric changes associated with the cyclical oxidation and reduction of Fe. Metallographic imaging performed at various redox stages, together with time-resolved in situ X-ray diffraction during redox cycling, detail the reaction kinetics and phase evolution of the foam, the evolution of its lamellar microstructure, and the eventual degradation of its internal architecture. As Fe preferentially oxidizes over Ni, each lamella develops an outer Fe-oxide scale, with metallic Ni rejected to the cores of the lamellae which develops an interconnected network of Fe-oxide veins. The Ni-rich metallic core limits the accumulation of Kirkendall pores and provides adhesion to the Fe-oxide scale, thus preventing lamellar fracture observed in unalloyed Fe foams. While the oxidation rate is slowed by the presence of Ni, the reduction rate is accelerated, as Ni acts as a catalyst and as the network of oxidized veins reduces quickly and become open microchannels, thereby providing rapid hydrogen access (driving reduction) and steam egress to the lamellar interior. After complete reduction, the Fe-rich shell and the Ni-rich core interdiffuse and homogenize, which helps eliminate both Kirkendall pores and microchannels from the lamellae. Furthermore, the ductile Ni-rich core limits lamellar buckling (another densification mechanism active in Fe foams). Architectural changes also affect resistance to internal damage, with smaller lamellar colonies exhibiting better resistance to buckling. These combined effects provided by Ni alloying allow the Fe-25Ni foams to maintain a high channel porosity (>40% porous), and thus high active surface area, after 10 redox cycles, as compared to a near complete loss of open channel porosity reported in unalloyed Fe foams.

AB - Cyclical steam oxidation and hydrogen reduction, relevant to iron-air batteries, is performed on freeze-cast Fe-25Ni (at.%) foams consisting of colonies of parallel lamellae separated by channels, both ∼20 µm thick and millimeters in length. This structure is designed to accommodate volumetric changes associated with the cyclical oxidation and reduction of Fe. Metallographic imaging performed at various redox stages, together with time-resolved in situ X-ray diffraction during redox cycling, detail the reaction kinetics and phase evolution of the foam, the evolution of its lamellar microstructure, and the eventual degradation of its internal architecture. As Fe preferentially oxidizes over Ni, each lamella develops an outer Fe-oxide scale, with metallic Ni rejected to the cores of the lamellae which develops an interconnected network of Fe-oxide veins. The Ni-rich metallic core limits the accumulation of Kirkendall pores and provides adhesion to the Fe-oxide scale, thus preventing lamellar fracture observed in unalloyed Fe foams. While the oxidation rate is slowed by the presence of Ni, the reduction rate is accelerated, as Ni acts as a catalyst and as the network of oxidized veins reduces quickly and become open microchannels, thereby providing rapid hydrogen access (driving reduction) and steam egress to the lamellar interior. After complete reduction, the Fe-rich shell and the Ni-rich core interdiffuse and homogenize, which helps eliminate both Kirkendall pores and microchannels from the lamellae. Furthermore, the ductile Ni-rich core limits lamellar buckling (another densification mechanism active in Fe foams). Architectural changes also affect resistance to internal damage, with smaller lamellar colonies exhibiting better resistance to buckling. These combined effects provided by Ni alloying allow the Fe-25Ni foams to maintain a high channel porosity (>40% porous), and thus high active surface area, after 10 redox cycles, as compared to a near complete loss of open channel porosity reported in unalloyed Fe foams.

KW - Alloys

KW - Metal-foam

KW - Microstructure

KW - Oxidation

KW - X-ray diffraction

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Microstructural evolution of lamellar Fe-25Ni foams during steam-hydrogen redox cycling

Abstract

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Keywords

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