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The ageing of Fe-Cr model alloys in 0.5 % SO2 and 99.5 % Ar atmosphere was investigated to aim in a fundamental and systematic analysis of the combined oxidation and sulfidation mechanism. The crystallization and reaction paths for oxide and sulfide formation were followed in-situ by energy dispersive X-ray diffraction (EDXRD) in an early stage of corrosion (30 s – 24 h). For this technique, high energetic white synchrotron X-ray radiation (10-100 keV) was used as radiation source. Diffraction pattern were collected continuously in an early stage of corrosion up to 24 h during the complete ageing experiment.
The crystalline phases, growing on top of the coupons, were identified directly via their specific dhkl values. The evolution of the extracted integral intensities of specific reflections of the corrosion products as a function of time access direct information about the kinetics of the nucleation and growth. The results presented here show for iron with 2 wt% Cr wuestite formation first. Wuestite vanishes after 10 min of reaction only and magnetite and hematite appear. Magnetite formation proceeds simultaneously with sulfide formation. Sulfides growth proceeds after an incubation time, which differs for low alloyed (2 wt% Cr) and high alloyed (9 wt% Cr) material.
The ageing of Fe-Cr model alloys in 0.5 % SO2 and 99.5 % Ar atmosphere was investigated to aim in a fundamental and systematic analysis of the combined oxidation and sulfidation mechanism. The crystallization and reaction paths for oxide and sulfide formation were followed in-situ by energy dispersive X-ray diffraction (EDXRD) in an early stage of corrosion (30 s – 24 h). For this technique, high energetic white synchrotron X-ray radiation (10-100 keV) was used as radiation source. Diffraction pattern were collected continuously in an early stage of corrosion up to 24 h during the complete ageing experiment.
The crystalline phases, growing on top of the coupons, were identified directly via their specific dhkl values. The evolution of the extracted integral intensities of specific reflections of the corrosion products as a function of time access direct information about the kinetics of the nucleation and growth. The results presented here show for iron with 2 wt% Cr wuestite formation first. Wuestite vanishes after 10 min of reaction only and magnetite and hematite appear. Magnetite formation proceeds simultaneously with sulfide formation. Sulfides growth proceeds after an incubation time, which differs for low alloyed (2 wt% Cr) and high alloyed (9 wt% Cr) material.
Ferritic-martensitic high temperature alloys are widely used as boiler tube and heat exchanger materials in combustion based power plants. All technologies have in common that the applied materials are exposed to different temperatures, process pressures and reactive atmospheres which lead to a change of the material properties and a further degradation of the material.
To date corrosion analytics mainly proceeds via the use of various microscopic techniques and the analysis of the corrosion products after the reaction is completed. Comprehensive efforts have been made to study high temperature corrosion by the use of environmental SEM’s or in-situ TEM technologies. The here presented work will show a different approach to study high temperature gas corrosion in a multiple gas atmosphere by energy dispersive X-ray diffraction (EDXRD). For this technique high energetic white X-ray radiation (10-100 keV) was used as radiation source instead of conventional monochromatic radiation. It enables us to study crystallization procedures on short and medium time scales (1 min < t < 24 h) and the collection of Bragg-Signals of the phases of interest as a function of process time. Their occurrence can directly be correlated with thermodynamic and kinetic parameters. A special designed corrosion reactor was used to combine high temperature gas corrosion experiments with the collection of diffraction patter. The crystallization and reaction paths for oxide and sulfide formation was followed in-situ on Fe-Cr and Fe-Cr-Mn model alloys in a hot SO2 containing (T=650 °C) atmosphere.