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Title: The Effect of CO 2 Pressure on Chromia Scale Microstructure at 750°C

Abstract

To understand and model performance in supercritical CO 2 (sCO 2) for high-efficiency, concentrating solar power (CSP) and fossil energy power cycles, reaction rates are compared at 750°C in 0.1 MPa CO 2 and 30 MPa sCO 2 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 CO 2 and sCO 2 had a much finer grain size with more voids observed in CO 2. 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 sCO 2, there was an indication of carbon segregation detected on the Cr 2O 3 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 Nimore » precipitates, suggesting caution when drawing conclusions from model alloys.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE Office of Fossil Energy (FE)
OSTI Identifier:
1471923
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
JOM. Journal of the Minerals, Metals & Materials Society
Additional Journal Information:
Journal Volume: 70; Journal Issue: 8; Journal ID: ISSN 1047-4838
Publisher:
Springer
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Pint, B. A., and Unocic, K. A. The Effect of CO2 Pressure on Chromia Scale Microstructure at 750°C. United States: N. p., 2018. Web. doi:10.1007/s11837-018-2963-4.
Pint, B. A., & Unocic, K. A. The Effect of CO2 Pressure on Chromia Scale Microstructure at 750°C. United States. doi:10.1007/s11837-018-2963-4.
Pint, B. A., and Unocic, K. A. Mon . "The Effect of CO2 Pressure on Chromia Scale Microstructure at 750°C". United States. doi:10.1007/s11837-018-2963-4. https://www.osti.gov/servlets/purl/1471923.
@article{osti_1471923,
title = {The Effect of CO2 Pressure on Chromia Scale Microstructure at 750°C},
author = {Pint, B. A. and Unocic, K. A.},
abstractNote = {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.},
doi = {10.1007/s11837-018-2963-4},
journal = {JOM. Journal of the Minerals, Metals & Materials Society},
number = 8,
volume = 70,
place = {United States},
year = {2018},
month = {6}
}

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