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Title: NiAl Oxidation Reaction Processes Studied In Situ Using MEMS-Based Closed-Cell Gas Reaction Transmission Electron Microscopy

The nanoscale oxidation mechanisms and kinetics of a model β-NiAl system were investigated using in situ closed-cell gas reaction scanning transmission electron microscopy (STEM). Here, we directly visualize the dynamic structural and chemical changes that occur during high-temperature oxidation at a high spatial resolution of 50.3Ni–49.7Al (at.%) nanoparticles under static air conditions at 730 Torr with heating up to 750 °C at 5 °C/s. A MEMS-based gas cell system, with microfabricated heater devices and a gas delivery system, was used to reveal site-specific oxidation initiation sites. Through time-resolved annular dark-field STEM imaging, we tracked the nanoscale oxidation kinetics of Al 2O 3. After oxidation at 750 °C, nucleation of voids at the Ni/Al 2O 3 interface was observed along a NiAl grain boundary, followed by the formation of faceted NiO crystals. Small faceted cubic crystals of NiO were formed at the initial stage of oxidation at high PO 2 due to the outward self-diffusion of Ni 2+ ions, followed by the formation of a mixture of metastable and stable α-Al 2O 3 at the oxide/metal interface that is attributed to a PO 2 decrease with oxidation time, which agreed with thermodynamic modeling calculations. Furthermore, the results from these in situmore » oxidation experiments in the β-NiAl system are in agreement with the established oxidation mechanisms; however, with in situ closed-cell gas microscopy it is now feasible to investigate nanoscale oxidation mechanisms and kinetics in real time and at high spatial resolution and can be broadly applied to understand the basic high-temperature oxidation mechanisms for a wide range of alloy compositions.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Center for Nanophase Materials Sciences Div., Oak Ridge, TN (United States)
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Oxidation of Metals
Additional Journal Information:
Journal Volume: 88; Journal Issue: 3-4; Journal ID: ISSN 0030-770X
Publisher:
Springer
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Fossil Energy (FE)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; NiAl; Oxidation; In situ TEM; MEMS-based closed-cell gas
OSTI Identifier:
1394581

Unocic, Kinga A., Shin, Dongwon, Unocic, Raymond R., and Allard, Jr., Lawrence Frederick. NiAl Oxidation Reaction Processes Studied In Situ Using MEMS-Based Closed-Cell Gas Reaction Transmission Electron Microscopy. United States: N. p., Web. doi:10.1007/s11085-016-9676-2.
Unocic, Kinga A., Shin, Dongwon, Unocic, Raymond R., & Allard, Jr., Lawrence Frederick. NiAl Oxidation Reaction Processes Studied In Situ Using MEMS-Based Closed-Cell Gas Reaction Transmission Electron Microscopy. United States. doi:10.1007/s11085-016-9676-2.
Unocic, Kinga A., Shin, Dongwon, Unocic, Raymond R., and Allard, Jr., Lawrence Frederick. 2017. "NiAl Oxidation Reaction Processes Studied In Situ Using MEMS-Based Closed-Cell Gas Reaction Transmission Electron Microscopy". United States. doi:10.1007/s11085-016-9676-2. https://www.osti.gov/servlets/purl/1394581.
@article{osti_1394581,
title = {NiAl Oxidation Reaction Processes Studied In Situ Using MEMS-Based Closed-Cell Gas Reaction Transmission Electron Microscopy},
author = {Unocic, Kinga A. and Shin, Dongwon and Unocic, Raymond R. and Allard, Jr., Lawrence Frederick},
abstractNote = {The nanoscale oxidation mechanisms and kinetics of a model β-NiAl system were investigated using in situ closed-cell gas reaction scanning transmission electron microscopy (STEM). Here, we directly visualize the dynamic structural and chemical changes that occur during high-temperature oxidation at a high spatial resolution of 50.3Ni–49.7Al (at.%) nanoparticles under static air conditions at 730 Torr with heating up to 750 °C at 5 °C/s. A MEMS-based gas cell system, with microfabricated heater devices and a gas delivery system, was used to reveal site-specific oxidation initiation sites. Through time-resolved annular dark-field STEM imaging, we tracked the nanoscale oxidation kinetics of Al2O3. After oxidation at 750 °C, nucleation of voids at the Ni/Al2O3 interface was observed along a NiAl grain boundary, followed by the formation of faceted NiO crystals. Small faceted cubic crystals of NiO were formed at the initial stage of oxidation at high PO2 due to the outward self-diffusion of Ni2+ ions, followed by the formation of a mixture of metastable and stable α-Al2O3 at the oxide/metal interface that is attributed to a PO2 decrease with oxidation time, which agreed with thermodynamic modeling calculations. Furthermore, the results from these in situ oxidation experiments in the β-NiAl system are in agreement with the established oxidation mechanisms; however, with in situ closed-cell gas microscopy it is now feasible to investigate nanoscale oxidation mechanisms and kinetics in real time and at high spatial resolution and can be broadly applied to understand the basic high-temperature oxidation mechanisms for a wide range of alloy compositions.},
doi = {10.1007/s11085-016-9676-2},
journal = {Oxidation of Metals},
number = 3-4,
volume = 88,
place = {United States},
year = {2017},
month = {2}
}