Processing, Microstructure, and Oxidation Behavior of Iron Foams
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INTRODUCTION
IRON (Fe)-based materials are one of the most friendly and common materials in both our daily lives and major industrial areas, because they have been widely used as the most important structural material for items such as weapons, machine tools, vehicles, and building components over hundreds of years, owing to their low cost and superior mechanical properties.[1] Recently, use of Fe-based materials has been extended to functional materials as well, in applications such as catalysts,[2] environmental protection,[3] sensors,[4] lithium-ion batteries,[5] and biomaterials.[6,7] Furthermore, Fe-based materials are likely to become even more popular with the discovery that they can also be made porous, i.e. in the form of three-dimensional (3-D) Fe-based foam, which is expected to offer particular advantages as an advanced structural and functional material owing to its 3-D structure, low cost, low weight, large specific surface area, and high impact absorbability, along with high mechanical strength and high stiffness-to-weight ratio.[8–10] Only during recent years, several studies have been reported on the processing and properties of Fe foam
HYEJI PARK, Ph.D. Student, HYELIM CHOI, Research Professor, KICHEOL HONG, Graduate Student, and HEEMAN CHOE, Associate Professor, are with the School of Advanced Materials Engineering, Kookmin University, 77 Jeongneung-ro, Seongbuk-gu, Seoul, 136-702, Republic of Korea. Contact e-mail: heeman@kook min.ac.kr YOONSOOK NOH, Product Engineer, formerly with the School of Advanced Materials Engineering, Kookmin University, is now with the iMOSS Company, Seoul, Republic of Korea. KYUNGJUNG KWON, Associate Professor, is with the Department of Energy & Mineral Resources Engineering, Sejong University, Seoul, 05006, Republic of Korea Manuscript submitted September 15, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
manufactured by a variety of processes, such as powder metallurgy,[6,11] gas foaming,[12] slag foaming,[13] hollow spheres,[14] and lotus-type[15,16] most likely for structural applications. Therefore, there still exists considerable demand for developing Fe foams with controlled porosity, pore size, and strut width to be potentially applied as a ‘platform’ material for various functional fields described above. In this study, Fe foam was synthesized through a freeze-casting or ice-templating method, followed by the formation of Fe oxide on the surface. We are particularly interested in this method, because the freeze-casting method is known for producing micrometer-scale porous structures with facile, low-cost processing steps. This method consists of freezing a slurry in a mold with a cold surface, sublimating the frozen slurry under reduced pressure and low temperatures, and subsequent sintering, in order to produce a 3-D directional porous structure with uniformly distributed pores a few tens of micrometers in diameter.[17–23] This paper discusses the morphological influences of various parameters (i.e., mold bottom temperature, powder content, and sintering tim
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