IMPROVED CORROSION RESISTANCE FOR ALUMINA REFRACTORY
In order to increase the efficiency of advanced coal-fired power systems, higher working fluid temperatures must be reached. Some system surfaces will have to be protected by covering them with corrosion-resistant refractories. Corrosion is the degradation of the material surfaces or grain boundaries by chemical reactions with melts, liquids, or gases causing loss of material and, consequently, a decrease in the strength of the structure. In order to develop methods of reducing corrosion, the microstructure that is attacked must be identified along with the mechanism and rates of attack. Earlier tests with several commercially available high-temperature castable refractories showed that the fused-alumina aggregate grains within the materials had the highest corrosion resistance of any of the castable materials. However, the cement holding the grains was easily attacked. Therefore, to improve the corrosion resistance and thermomechanical properties of alumina-based refractories, we attempted to change the cement to a more corrosion- and erosion-resistant bonding material through the addition of rare-earth oxides (REO). Phase diagrams were used to identify stable high-melting-temperature materials within the lanthanide-alumina series that could modify the bonding phase of the alumina-based refractory. Two mechanisms of reducing corrosion were investigated. One was the formation of corrosion-resistant layers within the refractory. The other was increased sintering to increase strength and seal continuous pores that would reduce slag penetration. Garnets (Re{sub 3}Al{sub 5}O{sub 12}) and perovskites (ReAl{sub 2}O{sub 3}), where Re is the REO, are two of the stable high-melting-temperature materials identified that were believed could be formed in the refractory matrix to help reduce corrosion rates. For the base refractory, Plicast 99 made by Plibrico was chosen. It is a 99% alumina castable composed of fused alumina aggregate and a cement made primarily from Alphabond 100, produced by Alcoa. The initial work involved designing a test matrix to study the effects of selected REOs on the corrosion resistance of the refractory. Three different processing methods were employed for fabricating the test samples. These included bulk mixing, impregnation, and surface coatings. Two different corrosion test methods were used to test the mixtures. The first was the static cup test that was used to screen the samples for the second corrosion test which used flowing slag. In addition to the corrosion tests, three-point modulus-of-rupture (MOR) tests were performed using the standard American Society for Testing and Materials (ASTM) C133 procedure to determine if the addition of an REO improved the strength of the refractory. A strength increase would show that the refractory was more resistant to erosion and also that sintering had occurred, which would imply a reduction in porosity.
- Research Organization:
- Federal Energy Technology Center Morgantown (FETC-MGN), Morgantown, WV (United States); Federal Energy Technology Center Pittsburgh (FETC-PGH), Pittsburgh, PA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- FC26-98FT40320
- OSTI ID:
- 778409
- Report Number(s):
- FC26-98FT40320-01; TRN: US200301%%404
- Resource Relation:
- Other Information: PBD: 30 Apr 1999
- Country of Publication:
- United States
- Language:
- English
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Task 6.7.2 - Improved Corrosion Resistance of Alumina Refractories
Improved corrosion resistance of alumina refractories. Semi-annual report, January 1--June 30, 1997