Breakdown mechanisms of Al/sub 2/O/sub 3/, Cr/sub 2/O/sub 3/ and SiO/sub 2/ scales in H/sub 2//H/sub 2/O/H/sub 2/S environments: Final report, Volume 1

Technical Report · Tue Jan 31 00:00:00 EST 1989

DOI:https://doi.org/10.2172/5976591· OSTI ID:5976591

Kim, G. M.; Meier, G. H.

The breakdown mechanisms of preformed oxide scales, Cr/sub 2/O/sub 3/, Al/sub 2/O/sub 3/ and SiO/sub 2/, have been studied at low oxygen and high sulfur potentials in the temperature range 550 to 950/degree/C. For Cr/sub 2/O/sub 3/ on Ni-30Cr, sulfur penetration occurs through thin areas in the Cr/sub 2/O/sub 3/ scale. The first sulfides to form on Fe-25Cr and Co-30Cr were observed at the scale/gas interface as the result of Fe or Co transport through the Cr/sub 2/O/sub 3/ scale. Alumina scales on Fe-18Cr-6Al-1Hf were broken down by crack formation. Addition of Hf to the alloy improved scale adherence and extended the time to breakdown. Additions of Ti to Fe-18Cr-6Al provided improved scale adherence without introducing continuous paths through the oxide scales. These scales were even more resistant than those on the Hf-containing alloys when exposed in high sulfur potential atmospheres. These results also extended to long term cyclic sulfidation/oxidation experiments and simulated syngas exposures. Pure alumina scales were never formed on Ni-18Cr-6Al and Co-18Cr-6Al alloys and the NiCrAl alloy underwent catastrophic corrosion in most sulfidation/oxidation exposures. For SiO/sub 2/ on Ni-20Si, although porosity can form at the scale/gas interface due to the high vapor pressures of SiS and SiO, the formation of a thin layer of vitreous silica and good scale adherence provide better resistance to sulfur penetration than do Cr/sub 2/O/sub 3/ and Al/sub 2/O/sub 3/. The SiO/sub 2/ scales formed on Fe-20Si and Co-20Si were not as protective as those formed on Ni-20Si. 33 refs., 42 figs.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Pittsburgh Univ., PA (USA). Dept. of Materials Science and Engineering
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5976591
• Report Number(s): ORNL/Sub-83-43346/02; ON: DE89014789
• Resource Relation: Other Information: Portions of this document are illegible in microfiche products
• Country of Publication: United States
• Language: English

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ALUMINIUM OXIDES
DECOMPOSITION
CHROMIUM ALLOYS
CHROMIUM OXIDES
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SULFIDATION
ALLOYS
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CHALCOGENIDES
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CHROMIUM COMPOUNDS
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CRYSTAL STRUCTURE
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ELEMENTS
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HYDROGEN COMPOUNDS
MINERALS
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OXIDES
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