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One-dimensional nanostructures are typically single-crystalline, yet the mechanisms by which crystallographic orientation governs their thermal morphological evolution, a process that critically dictates their structural integrity and functional performance in high-temperature applications, remain poorly understood. Here, by observing the shape evolution of single-crystalline α-Fe nanopillars near 0.48 of the melting temperature, we show that increasing axial index results in stronger spheroidization and faster shortening. This behavior originates from a coupled thermodynamic-kinetic effect. On low-index axial pillars, strong effective surface-energy anisotropy stabilizes {100} and {110} facets, while limited adatom generation on these facets slows surface diffusion and shortening. In contrast, geometric constraints on high-index axial pillars promote the exposure of high-index facets, reducing effective surface-energy anisotropy and facilitating adatom formation, thereby accelerating spheroidization and shortening. These results identify axial orientation as a key parameter governing the thermal evolution pathway of one-dimensional nanostructures and provide design principles for engineering thermally robust nanoscale systems.
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One-dimensional nanostructures are typically single-crystalline, yet the mechanisms by which crystallographic orientation governs their thermal morphological evolution, a process that critically dictates their structural integrity and functional performance in high-temperature applications, remain poorly understood. Here, by observing the shape evolution of single-crystalline α-Fe nanopillars near 0.48 of the melting temperature, we show that increasing axial index results in stronger spheroidization and faster shortening. This behavior originates from a coupled thermodynamic-kinetic effect. On low-index axial pillars, strong effective surface-energy anisotropy stabilizes {100} and {110} facets, while limited adatom generation on these facets slows surface diffusion and shortening. In contrast, geometric constraints on high-index axial pillars promote the exposure of high-index facets, reducing effective surface-energy anisotropy and facilitating adatom formation, thereby accelerating spheroidization and shortening. These results identify axial orientation as a key parameter governing the thermal evolution pathway of one-dimensional nanostructures and provide design principles for engineering thermally robust nanoscale systems.
Journal article(2022)
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Yan Ma, Isnaldi R. Souza Filho, Dirk Ponge, Stefan Zaefferer, Baptiste Gault, Jaber R. Mianroodi, Dierk Raabe, Yang Bai, Johannes Schenk, Fabrice Patisson, Arik Beck, Jeroen A. van Bokhoven, Marc G. Willinger, Kejiang Li, Degang Xie
Fossil-free ironmaking is indispensable for reducing massive anthropogenic CO
2 emissions in the steel industry. Hydrogen-based direct reduction (HyDR) is among the most attractive solutions for green ironmaking, with high technology readiness. The underlying mechanisms governing this process are characterized by a complex interaction of several chemical (phase transformations), physical (transport), and mechanical (stresses) phenomena. Their interplay leads to rich microstructures, characterized by a hierarchy of defects ranging across several orders of magnitude in length, including vacancies, dislocations, internal interfaces, and free surfaces in the form of cracks and pores. These defects can all act as reaction, nucleation, and diffusion sites, shaping the overall reduction kinetics. A clear understanding of the roles and interactions of these dynamically-evolving nano-/microstructure features is missing. Gaining better insights into these effects could enable improved access to the microstructure-based design of more efficient HyDR methods, with potentially high impact on the urgently needed decarbonization in the steel industry.
...
Fossil-free ironmaking is indispensable for reducing massive anthropogenic CO
2 emissions in the steel industry. Hydrogen-based direct reduction (HyDR) is among the most attractive solutions for green ironmaking, with high technology readiness. The underlying mechanisms governing this process are characterized by a complex interaction of several chemical (phase transformations), physical (transport), and mechanical (stresses) phenomena. Their interplay leads to rich microstructures, characterized by a hierarchy of defects ranging across several orders of magnitude in length, including vacancies, dislocations, internal interfaces, and free surfaces in the form of cracks and pores. These defects can all act as reaction, nucleation, and diffusion sites, shaping the overall reduction kinetics. A clear understanding of the roles and interactions of these dynamically-evolving nano-/microstructure features is missing. Gaining better insights into these effects could enable improved access to the microstructure-based design of more efficient HyDR methods, with potentially high impact on the urgently needed decarbonization in the steel industry.
