부산대학교 도서관

국외단행본

High Temperature Redox Cycling of Iron Alloy Foams [electronic resource].

Northwestern University. Materials Science and Engineering.

[S.l.] : Northwestern University. 2024 Ann Arbor : ProQuest Dissertations & Theses , 2024

1 online resource(184 p.)

Source: Dissertations Abstracts International, Volume: 85-11, Section: B.
Includes supplementary digital materials.
Advisor: Dunand, David C.

Thesis (Ph.D.)--Northwestern University, 2024.

Effective implementation of clean energy technology requires technological development of novel energy storage systems to buffer the intermittent generation of wind and solar sources. The use of iron as an energy storage material is desirable due to the low cost, abundance, and non-toxicity of iron and iron oxides. The high temperature oxidation and reduction of iron has been implemented in several systems relevant to energy storage and generation, as well as carbon capture, notably the rechargeable oxide battery (ROB), chemical looping combustion reactor (CLC), and carbon dioxide utilization reactor. However, the development and practical use of these technologies has been stunted by the poor cycling lifetime of unmodified iron at high temperatures. The cyclical expansion and contraction of Fe during redox cycling paired with relatively fast sintering in both the reduced and oxidized states lead to extreme densification of the material in just a few cycles. This greatly reduces gas access to the material, effectively reducing the capacity due to the increasingly long times needed for a full reaction to take place. Herein I examine novel Fe foam compositions and architectures subjected to high temperature redox cycling, characterize their phase and microstructural evolution with a focus on how the changing phases and microstructures affect redox cycling kinetics, and draw comparisons between different strategies that can be used to resist or prevent the degradation of Fe materials during high temperature redox cycling.The elements available to modify Fe for redox cycling fall into three categories: (i) redox inactive metals, (ii) redox inactive oxides, and (iii) redox active metals. Redox inactive metals include those elements which can be readily reduced by H2 but will not be oxidized by H2O at the operating temperature of 800 °C or below. Redox inactive oxides include the reverse: elements that will be oxidized by H2O but will not be reduced by H2. Redox active elements are those that, like iron itself, can be both oxidized by H2O and reduced by H2. In this work I examine the behavior of Fe-X directionally freeze cast foams for three redox inactive metals: Fe-Ni, Fe-Co, and Fe-Cu, and two redox active metals: Fe-Mo and Fe-W. The ternary Fe-Ni-W system is also explored. The behavior of Fe-W foams when using CO2 rather than H2O as the oxidizing gas is characterized as well, opening the door for further research into chemical looping applications. Redox inactive Co and Ni help prevent degradation by limiting the formation of Kirkendall pores, but buckling, contact, and sintering still limit their efficacy. Redox inactive Cu actively degrades the structure by rapidly segregating. All three redox inactive metals show an acceleration of the reduction reacting, and Cu also shows an acceleration of the oxidation reacting in the first cycle, before Cu has segregated out.Redox active Mo and W show improved degradation resistance due to the formation of hierarchical porosity within the foam. The efficacy of Mo is somewhat lower than that of W due to the gradual segregation of Mo during cycling. W shows excellent stability, and a regenerative microstructure due to the chemical vapor transport reduction of the mixed oxide FeWO4.Architecture can also be used to alter degradation during redox cycling, as highly porous architectures can maintain open gas channels to limit degradation. While directionally freeze-cast foams are the main architecture studied, the behavior of freeze cast foams strengthened with bridging fibers, 3-D ink-printed lattices, and simple tapped powder beds are also compared to better understand the interplay between macroscale architectural design and microstructural evolution. Bridging fibers showed the desired effect, with buckling limited for fibers long enough to bridge the freeze cast channels, but degradation still occurred due to rapid engulfment of the bridging fibers leading to sintering and densification. Printed foams showed similar microstructure to freeze cast foams, but a much more consistent shrinkage and densification. Tapped powder beds of Fe-25W showed identical microstructures to freeze cast foams of the same composition, indicating that the freeze cast channels are not needed to obtain the microstructural resistance to degradation.

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