Journal
ACS NANO
Volume 14, Issue 11, Pages 15131-15143Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.0c05250
Keywords
high-entropy alloys; nanoparticles; in situ transmission electron microscopy; oxidation; phase segregation; Kirkendall
Categories
Funding
- National Science Foundation [DMR-1809439, DMR-1809085]
- Pittsburgh Quantum Institute
- University of Pittsburgh Center for Research Computing [DE-AC02-06CH11357]
- U.S. Department of Energy Office of Science User Facility
- U.S. Department of Energy, Office of Science [DE-AC02-06CH11357]
- MRI-R2 grant from the National Science Foundation [DMR-0959470]
- Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF) [ECCS-1542205]
- MRSEC program [NSF DMR1720139]
- International Institute for Nanotechnology (IIN)
- Keck Foundation
- State of Illinois, through the IIN
- ONR MURI
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Although high-entropy alloys (HEAs) have shown tremendous potential for elevated temperature, anticorrosion, and catalysis applications, little is known on how HEA materials behave under complex service environments. Herein, we studied the high-temperature oxidation behavior of Fe(0.28)Co(0.21)Ni(0.20)Cu(0.08)Pt(0.23)HEA nanoparticles (NPs) in an atmospheric pressure dry air environment by in situ gas-cell transmission electron microscopy. It is found that the oxidation of HEA NPs is governed by Kirkendall effects with logarithmic oxidation rates rather than parabolic as predicted by Wagner's theory. Further, the HEA NPs are found to oxidize at a significantly slower rate compared to monometallic NPs. The outward diffusion of transition metals and formation of disordered oxide layer are observed in real time and confirmed through analytical energy dispersive spectroscopy, and electron energy loss spectroscopy characterizations. Localized ordered lattices are identified in the oxide, suggesting the formation of Fe2O3, CoO, NiO, and CuO crystallites in an overall disordered matrix. Hybrid Monte Carlo and molecular dynamics simulations based on first-principles energies and forces support these findings and show that the oxidation drives surface segregation of Fe, Co, Ni, and Cu, while Pt stays in the core region. The present work offers key insights into how HEA NPs behave under high-temperature oxidizing environment and sheds light on future design of highly stable alloys under complex service conditions.
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