Preparation and testing of corrosion and spallation-resistant coatings
This Energy & Environmental Research Center (EERC) project is designed to determine if plating APMT, a specific highly oxidation-resistant oxide dispersion-strengthened FeCrAl alloy made by Kanthal, onto nickel-based superalloy turbine parts is a viable method for substantially improving the lifetimes and maximum use temperatures of the parts. The method for joining the APMT plate to the superalloys is called evaporative metal bonding. It involves placing a thin foil of zinc (Zn) between the plate and the superalloy, clamping them together, and heating in an atmosphere-controlled furnace. Upon heating, the Zn melts and dissolves the oxide skins of the alloys at the bond line, allowing the two alloys to diffuse into each other. The Zn then diffuses through the alloys and evaporates from their surfaces. Laboratory testing has shown that the diffusion rate of Zn through the FeCrAl alloy is much faster than through the nickel superalloys. This means that the FeCrAl will serve as a sink for the Zn bonding alloy during the evaporative metal bonding process. Also, the testing has shown that the Zn diffusion mechanism is bulk diffusion, and not intergranular. This is a surprise. However, it means that quantification of the Zn diffusivities in these samples will be significantly simpler than would have been the case if grain boundary diffusion dominated. In addition to the laboratory testing, gas impinger and particulate samples are being collected from a combustor firing syngas and natural gas to determine what types of microcontaminants may reach a turbine firing syngas. The syngas is created in one of two different pilot-scale pressurized coal gasifiers. The initial analysis of the impinger solutions was for standard U.S. Environmental Protection Agency (EPA) Method 29 determination of hazardous metals and did not include major element analysis. When syngas is fired, the amount of Mn in the combustor gas increases substantially. Halogens (Br2 and Cl2) and hydrogen halides (HF, HCl, and HBr) are present in amounts close to or below 1 ppm. In the near future, the solutions will be reanalyzed for major elements. SEM analysis showed that the particulate matter is primarily nonstoichiometric iron sulfate. Most of the particles were 3 μm in diameter or less. Elements such as O, Fe, S, Cr, and Si make up the majority of the compositions of 3089 particles analyzed on the filter surface. The concentrations of O and S are high in almost all particles. The concentrations of S and Fe tend to be higher in the larger particles than in the smaller. In contrast the concentrations of O showed the reverse trend. We currently believe that the high values of Fe and Cr come from a reaction of the syngas with the stainless steel pipes used to transport the syngas, most likely by forming a vapor-phase carbonyl. During combustion, the carbonyls form nonstoichiometric sulfate particles. The excess Si is most likely coming from the coal ash, possibly through the formation of a silicon monoxide fume.
- Research Organization:
- Univ. of North Dakota, Grand Forks, ND (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FE0007325
- OSTI ID:
- 1222702
- Country of Publication:
- United States
- Language:
- English
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Preparation and Testing of Corrosion-and Spallation-Resistant Coatings
Preparation and testing of corrosion and spallation-resistant coatings