Research Papers

Impact of Corrosion Test Container Material in Molten Fluorides

[+] Author and Article Information
Luke C. Olson

Savannah River National Laboratory,
Aiken SC, 29808
e-mail: luke.olson@srnl.doe.gov

Roderick E. Fuentes, Michael J. Martinez-Rodriguez, Brenda L. Garcia-Diaz, Joshua Gray

Savannah River National Laboratory,
Aiken SC, 29808

James W. Ambrosek

Woodward Inc.,
1000 East Drake Road,
Fort Collins, CO 80525

Kumar Sridharan, Mark H. Anderson, Todd R. Allen

Department of Engineering Physics,
University of Wisconsin-Madison,
1500 Engineering Drive,
Madison WI, 53711

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received October 8, 2014; final manuscript received September 1, 2015; published online October 15, 2015. Assoc. Editor: Prof. Nathan Siegel.The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Sol. Energy Eng 137(6), 061007 (Oct 15, 2015) (8 pages) Paper No: SOL-14-1286; doi: 10.1115/1.4031682 History: Received October 08, 2014; Revised September 01, 2015

The effects of crucible material choice on alloy corrosion rates in immersion tests in molten LiF–NaF–KF (46.5–11.5-42 mol. %) salt held at 850 °C for 500 hrs are described. Four crucible materials were studied. Molten salt exposures of Incoloy-800H in graphite, Ni, Incoloy-800H, and pyrolytic boron nitride (PyBN) crucibles all led to weight-loss in the Incoloy-800H coupons. Alloy weight loss was ∼30 times higher in the graphite and Ni crucibles in comparison to the Incoloy-800H and PyBN crucibles. It is hypothesized galvanic coupling between the alloy coupons and crucible materials contributed to the higher corrosion rates. Alloy salt immersion in graphite and Ni crucibles had similar weight-loss hypothesized to occur due to the rate limiting out diffusion of Cr in the alloys to the surface where it reacts with and dissolves into the molten salt, followed by the reduction of Cr from solution at the molten salt and graphite/Ni interfaces. Both the graphite and the Ni crucibles provided sinks for the Cr, in the formation of a Ni–Cr alloy in the case of the Ni crucible, and Cr carbide in the case of the graphite crucible.

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Fig. 1

Gibbs free energy of fluoride formation per F2 molecule of metals present in the salt and materials at 850 °C. The more negative the Gibb’s free energy of formation an alloy constituent is in comparison to the salt constituents, the less stable it will likely be in the molten salt.

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Fig. 2

Gibbs free energy of carbide formation per C atom for elements present in the alloys at 850 °C. Favorable reactions have more negative Gibb’s free energy of formations.

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Fig. 3

Schematic illustration of one corrosion capsule apparatus used in the present study for testing corrosion performance of alloys in molten FLiNaK salt at 850 °C for 500 hrs. Dimensions are in centimeters. This design utilized graphite or Incoloy-800H for the crucible material.

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Fig. 4

Sketch of corrosion cells used in research

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Fig. 5

SEM of Cr-rich film on graphite fixturing rod from Incoloy-800H containing crucible tests

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Fig. 6

SEM on graphite central fixturing rod from (a) Incoloy-800H corrosion experiments with a ∼15 μm thick carbide layer. EDS X-ray mapping of elemental (b) Cr and (c) Fe, show the elements are concentrated on the surface and do not penetrate into the graphite.

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Fig. 7

XRD data showing identifying peaks for graphite and Cr7C3 from the Cr film present on the graphite fixturing rod from the Incoloy-800H containing crucible

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Fig. 8

XPS data from the Cr rich film found on the graphite rod that was used to fixture the Incoloy-800H coupons. The sample was progressively sputtered with Ar, followed by sampling of the electron binding energy, leading to a decreasing peak from C contamination and increasing peaks from the graphite rod and carbide.

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Fig. 9

RBS data from the graphite crucible’s bottom and side that held Hastelloy-X coupons during the FLiNaK exposure test

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Fig. 10

EDS line scan taken from the Ni crucible containing a single Incoloy-800H coupon. The mounting material identified in the SEM image is located on the salt exposed side of the Ni crucible wall.

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Fig. 11

Schematic of nonelectric transfer described by Ozeryanaya, as applied to the Fe–Ni–Cr/graphite/FLiNaK system




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