Enhanced High Temperature Corrosion Resistance in Advanced Fossil Energy Systems by Nano-Passive Layer Formation

Marder, Arnold R.

Lehigh University

关键词: Corrosion;    Aluminium;    Alloys;    Corrosion Protection;    X-Ray Photoelectron Spectroscopy;   

DOI  :  10.2172/923024
RP-ID  :  None
RP-ID  :  FG26-04NT42169
RP-ID  :  923024

美国|英语

来源: UNT Digital Library

【 摘 要 】

Due to their excellent corrosion resistance, iron aluminum alloys are currently being considered for use as weld claddings in fossil fuel fired power plants. The susceptibility to hydrogen cracking of these alloys at higher aluminum concentrations has highlighted the need for research into the effect of chromium additions on the corrosion resistance of lower aluminum alloys. In the present work, three iron aluminum alloys were exposed to simulated coal combustion environments at 500 C and 700 C for both short (100 hours) and long (5,000 hours) isothermal durations. Scanning electron microscopy was used to analyze the corrosion products. All alloys exhibited excellent corrosion resistance in the short term tests. For longer exposures, increasing the aluminum concentration was beneficial to the corrosion resistance. The addition of chromium to the binary iron aluminum alloy prevented the formation iron sulfide and resulted in lower corrosion kinetics. A classification of the corrosion products that developed on these alloys is presented. Scanning transmission electron microscopy (STEM) of the as-corroded coupons revealed that chromium was able to form chromium sulfides only on the higher aluminum alloy, thereby preventing the formation of deleterious iron sulfides. When the aluminum concentration was too low to permit selective oxidation of only aluminum (upon initial exposure to the corrosion environment), the formation of chromium oxide alongside the aluminum oxide led to depletion of chromium beneath the oxide layer. Upon penetration of sulfur through the oxide into this depletion layer, iron sulfides (rather than chromium sulfides) were found to form on the low aluminum alloy. Thus, it was found in this work that the role of chromium on alloy corrosion resistance was strongly effected by the aluminum concentration of the alloy. STEM analysis also revealed the encapsulation of external iron sulfide products with a thin layer of aluminum oxide, which may provide a secondary layer of a corrosion protection in these regions. In a separate set of experiments, in-situ oxidation performed in x-ray photoelectron spectroscopy (XPS) equipment showed that the formation of aluminum oxide in a pure oxygen environment at 500 C was slowed by the addition of chromium.