Freeze-Cast Manufacturing of Stable Iron-Alloy Foams for Energy Conversion and Storage

冷冻铸造是一种制造多孔材料或泡沫的低成本制造技术。该奖项研究冷冻铸造作为一种制造铁-镍、铁-钴和铁-铜泡沫的方法，这些泡沫有助于为电网中储存能量的电池提供动力，或改进化学循环技术以捕获发电厂的二氧化碳排放。通过推进用于这些应用的材料制造，该项目有助于国家能源安全、气候行动目标以及美国在先进能源材料领域的竞争力。在冷冻铸造多孔材料方面开发的知识也使其他工业部门受益，如通过多孔骨替代植入物的医疗保健，以及通过轻质结构的汽车和航空航天。目前使用冷冻铸造能量材料的一个限制是它们在使用过程中会降解。为了解决这个问题，本研究探索了一些方法，如添加合金元素，以稳定冻铸铁泡沫并提高其使用寿命。制造参数与材料性能之间的关系为这种冷冻铸造合金的优化和商业化奠定了基础。该项目积极促进妇女和代表不足的少数群体参与研究，并继续建立跨学科和国际合作。在能源应用中，如高温固体氧化物电池或化学循环燃烧，铁基氧化还原材料由于氧化/还原反应引起的摩尔体积反复变化而迅速降解。冷冻铸造的片状泡沫的孔隙结构非常适合解决这个问题，因为它为每个片层提供了自由膨胀和收缩的空间，而不受相邻片层的限制。然而，由于扩散通量不平衡和氧化相的断裂/剥落而形成的Kirkendall微孔，仍然发生了机械降解。将泡沫铁与镍、钴或铜合金化，作为抑制上述降解过程的一种策略，通过在片层中创建富镍、钴或铜的延性核心，并通过使扩散通量更加平衡来进行研究。利用原位同步X射线衍射仪和纳米层析技术研究了这些合金在氧化还原循环过程中的相结构和微观结构的变化。这些现场研究与热重分析、非原位氧化还原循环和金相研究相辅相成。最后，开发了CALPHAD、相场和有限元模型来帮助指导合金和成分的选择，并由实验提供了验证。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Freeze casting is a low-cost manufacturing technique for creating porous materials or foams. This award investigates freeze casting as a means to make iron-nickel, iron-cobalt, and iron-copper foams that help power batteries for storing energy on the electricity grid, or improve chemical looping technologies for capturing carbon dioxide emissions from power plants. By advancing the materials manufacturing for these applications, this project contributes to national energy security, climate action goals, and U.S. competitiveness in the advanced energy materials sector. The knowledge developed in freeze casting of porous materials also benefits other industrial sectors such as healthcare, via porous bone-replacement implants, and automotive and aerospace, via lightweight structures. One current limitation to using freeze-cast energy materials is that they degrade during use. To address this problem, this research investigates methods, such as adding an alloying element, to stabilize freeze-cast iron foams and increase their usable lifetime. The relationships between manufacturing parameters and materials performance lay the groundwork for optimization and commercialization of such freeze-cast alloys. This project actively promotes participation of women and underrepresented minorities in research and continues building interdisciplinary and international collaborations.In energy applications, such as high-temperature solid-oxide batteries or chemical looping combustion, iron-based redox materials rapidly degrade due to the repeated molar volume changes associated with oxidation/reduction reactions. The pore architecture of freeze-cast, lamellar foams is ideally suited to address this issue, as it provides space for each lamella to expand and contract freely, without constraints from neighboring lamellae. Nevertheless, mechanical degradation still occurs due to Kirkendall micropore formation from imbalanced diffusion fluxes and fracture/spallation of the oxide phase. Alloying iron foams with nickel, cobalt, or copper is investigated as a strategy to suppress the above degradation processes, by creating Ni-, Co- or Cu-rich ductile cores within the lamellae, and by making diffusional fluxes more balanced. In-situ synchrotron X-ray diffraction and nano-tomography are used to reveal the phase and microstructural evolution in these alloys during redox cycling. These in-situ studies are complemented by thermogravimetry, ex-situ redox cycling, and metallography studies. Lastly, CALPHAD, phase-field, and finite-element models are developed to help guide alloy and composition selection, with validation provided by experiment.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.