Corrosion of SiC and oxide-composite ceramics by a simulated steam-reformer atmosphere
To achieve higher process efficiency by using pressurized reactants and/or heat transfer fluids, the US DOE is promoting development of high-pressure heat exchanger systems under cost-sharing agreements with industrial contractors. The steam reformer would contain more than 600 tubes. Because the combination of high temperature and pressure differential of 12.7 kg/cm{sup 2} (180 psig) across the tube wall is too severe for metallic tubes, ceramic materials are being considered for reformer tubes. Their use is expected to increase the efficiency of steam reformers by about 19%. At ORNL, four SiC ceramics, a SiC-TiB{sub 2} composite, a Si{sub 3}N{sub 4}-bonded SiC ceramic, and two alumina-matrix composites were selected as candidate materials for heat exchanger/steam-reformer tubes. These commercially available materials were exposed to a simulated steam-reformer atmosphere for up to 2000 h at 1260{degrees}C to assess their corrosion behavior and the effect of the exposure on their flexure strength (in air) at 20 and 1260{degrees}C. The approximate partial pressures of the constituents of the gas mixture at 1 atm total pressure were 0.54 H{sub 2}, 0.13 CO, 0.03 CO{sub 2}m 0.004 CH{sub 4}, and 0.30 H{sub 2}O. All but one material had net weight gains during the exposure test. The flexure strengths of the SiC and Si{sub 3}N{sub 4} ceramics and the SiC-TiB{sub 2} composite at 20 and 1260{degrees}C were not changed significantly by corrosion. The strengths of the alumina-matrix composites were decreased by corrosion; however, the strength of one of these (reinforced with SiC whiskers) was still higher than that of any other material after 500 h. The other alumina composite (containing SiC particles) exhibited the largest strength decrease of any material. The strength retention of the SiC ceramics and the SiC-TiB{sub 2} composite and the strength loss of the composites were associated with surface layers caused by corrosion. 12 refs., 12 figs., 4 tabs.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 5128601
- Report Number(s):
- ORNL/TM-11828; ON: DE92002391
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
CERAMICS
FLEXURAL STRENGTH
HEAT EXCHANGERS
EFFICIENCY
ALUMINIUM OXIDES
COMPOSITE MATERIALS
CORROSION
CORROSION RESISTANCE
PRESSURE EFFECTS
SILICON CARBIDES
SILICON NITRIDES
SIMULATION
TESTING
TITANIUM BROMIDES
WHISKERS
WORKING FLUIDS
ALUMINIUM COMPOUNDS
BROMIDES
BROMINE COMPOUNDS
CARBIDES
CARBON COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
CRYSTALS
FLUIDS
HALIDES
HALOGEN COMPOUNDS
MATERIALS
MECHANICAL PROPERTIES
MONOCRYSTALS
NITRIDES
NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PNICTIDES
SILICON COMPOUNDS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
320303* - Energy Conservation
Consumption
& Utilization- Industrial & Agricultural Processes- Equipment & Processes
360203 - Ceramics
Cermets
& Refractories- Mechanical Properties