The Effect of CO2 Pressure on Chromia Scale Microstructure at 750°C

B. A. Pint; K. A. Unocic

doi:10.1007/s11837-018-2963-4

The Effect of CO₂ Pressure on Chromia Scale Microstructure at 750°C

B. A. Pint, K. A. Unocic

Research output: Contribution to journal › Article › peer-review

27 Scopus citations

Abstract

To understand and model performance in supercritical CO₂ (sCO₂) for high-efficiency, concentrating solar power (CSP) and fossil energy power cycles, reaction rates are compared at 750°C in 0.1 MPa CO₂ and 30 MPa sCO₂ as well as laboratory air as a baseline on structural materials such as Ni-based alloy 625. Due to the thin reaction products formed even after 5000 h, scanning transmission electron microscopy was used to study the Cr-rich surface oxide scale. The scales formed in CO₂ and sCO₂ had a much finer grain size with more voids observed in CO₂. However, the observations on alloy 625 were complicated by Mo and Nb-rich precipitates in the adjacent substrate and Al internal oxidation. To simplify the system, a binary Ni-22Cr alloy was exposed for 1000 h in similar environments. After exposure in sCO₂, there was an indication of carbon segregation detected on the Cr₂O₃ grain boundaries. After exposure in air, metallic Ni precipitates were observed in the scale that were not observed in the scale formed on alloy 625. The scale formed in air on a second Ni-22Cr model alloy with Mn and Si additions did not contain Ni precipitates, suggesting caution when drawing conclusions from model alloys.

Original language	English
Pages (from-to)	1511-1519
Number of pages	9
Journal	JOM
Volume	70
Issue number	8
DOIs	https://doi.org/10.1007/s11837-018-2963-4
State	Published - Aug 1 2018

Bibliographical note

Publisher Copyright:
© 2018, The Minerals, Metals & Materials Society.

Funding

The author would like to thank M. Howell, M. Stephens, G. Garner, T. Lowe, T. Jordan, D. Coffey and C. Parrish at ORNL for assistance with the experimental work and S. Dryepondt and L. Allard for comments on the manuscript. The authors appreciate the donation of alloy 625 from Haynes International. This research was funded by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy, Solar Energy Technology Office: SuNLaMP award number DE-EE0001556 and by the Office of Fossil Energy (Grant No. FEAA123), Crosscutting Technology Program. The STEM work was supported by the Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science User Facilities.

Funders	Funder number
Crosscutting Technology Program
Haynes International
U.S. Department of Energy
Office of Fossil Energy	FEAA123
Office of Energy Efficiency and Renewable Energy
Oak Ridge National Laboratory
Solar Energy Technologies Office	DE-EE0001556

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This output contributes to the following UN Sustainable Development Goals (SDGs)

Access to Document

10.1007/s11837-018-2963-4

Cite this

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