Corrosion behavior of continuous-filament-wound ceramic composite tubes

Technical Report · Wed May 01 00:00:00 EDT 1991

OSTI ID:5619356

Federer, J I

Ceramic composites are being developed for heat exchanger tubes in industrial furnaces. Because industrial furnace atmospheres often contain alkali compounds, the corrosion behavior of ceramic composites was investigated in an oxidizing atmosphere containing Na{sub 2}CO{sub 3} vapor. The composites, the form of tubes, consisted of Al{sub 2}O{sub 3}-20 wt % ZrO{sub 2} continuous-filament-wound bodies impregnated with Al{sub 2}O{sub 3} or ZrO{sub 2} matrices. The matrices contained 20 to 30% porosity. The tubes were thermally cycled three or four times between 20 and 1150{degree}C with cumulative holding times at 1150{degree}C, of 300 or 500 h. One set of specimens was thermally cycled in air for comparison with a similar set thermally cycled in the Na{sub 2}Co{sub 3}-containing atmosphere. Specimens heat-treated in air had almost no visual evidence of degradation, but specimens exposed to the corrosive atmosphere exhibited bending, nonuniform expansion, cracking, and spalling. Dimensional changes in specimens heat-treated in air were < {plus minus} 0.5% compared to values up to + 6% in specimens exposed to the corrosive atmosphere. In specimens with ZrO{sub 2} matrices, Na was found to be concentrated at the interfaces between matrix and filaments, indicating that the matrix porosity allowed access of the atmosphere to the filaments. In the specimen with an Al{sub 2}O{sub 3} matrix, Na was concentrated on the outer surface, indicating high reactivity between Na and Al{sub 2}O{sub 3}. X-ray diffraction analysis showed that several sodium aluminates had formed by reaction of Na{sub 2}CO{sub 3} with the Al{sub 2}O{sub 3} matrix and high Al{sub 2}O{sub 3} filaments, but no sodium zirconates were detected. The degradation of the specimens was attributed to the volume increases associated with formation of sodium aluminates. 10 refs., 25 figs., 4 tabs.

• Research Organization: Oak Ridge National Lab., TN (United States)
• Sponsoring Organization: USDOE; USDOE, Washington, DC (United States)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5619356
• Report Number(s): ORNL/TM-11691; ON: DE91014959
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
CORROSION
TUBES
ZIRCONIUM OXIDES
HEAT EXCHANGERS
OPTICAL MICROSCOPY
SODIUM CARBONATES
X-RAY DIFFRACTION
ALKALI METAL COMPOUNDS
ALUMINIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATES
CHALCOGENIDES
CHEMICAL REACTIONS
COHERENT SCATTERING
DIFFRACTION
MICROSCOPY
OXIDES
OXYGEN COMPOUNDS
SCATTERING
SODIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
ZIRCONIUM COMPOUNDS
360205* - Ceramics
Cermets
&amp; Refractories- Corrosion &amp; Erosion