Freeze-casting is a versatile, inexpensive, and scalable manufacturing technique, making it attractive for creating functional materials such as those used in batteries or other redox processes, since these materials traditionally require expensive nanofabrication techniques that do not easily scale beyond the laboratory. In our recent NSF-sponsored research, we demonstrated directional freeze-casting to manufacture Fe-based foams for high-temperature batteries and redox cycling applications (2Fe + 3H2O = Fe2O3 + 3H2). One of the greatest barriers to commercialization of Fe-based redox applications is the materials’ mechanical degradation: the repeated oxidations and reductions cause large volume expansions and contractions, leading to mechanical stresses that plastically deform the Fe phase and fracture the brittle Fe2O3. Combined with sintering at the high operating temperatures, these effects result in densification of the Fe-foams and choking of the gas flow. Our proposed manufacturing method addresses these challenges by incorporating Ni to the freeze-casting process, based on our recent demonstration that alloyed Fe-Ni foams show superior porosity retention during redox degradation as compared to conventional Fe-powder beds. We hypothesize that this lifetime enhancement arises from two mechanisms: (i) Ni helps mitigate Kirkendall microporosity formation, and (ii) when the foam is oxidized, a ductile, Ni-rich scaffold prevents oxide spallation. To provide the necessary validation of this manufacturing technique, we propose a fundamental study of freeze-cast Fe-based foams alloyed with either Ni, Co, or Cu. These alloys will shed light on the hypothesized mechanisms affect redox stability for FCC (Fe-Ni), BCC (Fe-Co), and FCC+BCC mixture (Fe-Cu) systems. In-situ synchrotron X-ray diffraction and nano-tomography will reveal the phase and microstructural evolution of alloys of various compositions during reduction from fabrication and subsequent redox cycling. These in-situ studies will be complemented by thermogravimetry, ex-situ redox cycling, and metallography. Lastly, CALPHAD, phase-field, and finite-element models will be developed to help guide alloy and composition selection, with validation provided by the experimental results.
|Effective start/end date||9/1/20 → 8/31/23|
- National Science Foundation (CMMI-2015641-001)
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