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 · Mon Jan 30 23:00:00 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., TN (USA); 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
• Country of Publication: United States
• Language: English

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ALLOYS
ALUMINIUM ALLOYS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
CHROMIUM ALLOYS
CHROMIUM COMPOUNDS
CHROMIUM OXIDES
COAL GASIFICATION
COATINGS
CORROSION PRODUCTS
CORROSIVE EFFECTS
CRYSTAL STRUCTURE
DECOMPOSITION
DIFFUSION
DOCUMENT TYPES
ELEMENTS
EQUIPMENT
GASIFICATION
HAFNIUM ALLOYS
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN SULFIDES
IRON ALLOYS
MICROSTRUCTURE
MINERALS
NICKEL ALLOYS
NONMETALS
OXIDATION
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PROGRESS REPORT
PROTECTIVE COATINGS
SCALING
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SULFIDATION
SULFIDES
SULFUR COMPOUNDS
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPOUNDS
WATER