Investigations on high-temperature corrosion of commercial materials and model alloys in simulated waste and biomass combustion environments
- Untersuchungen zur Hochtemperaturkorrosion von kommerziellen Werkstoffen und Modelllegierungen unter simulierten Müll- und Biomasse-Verbrennungsbedingungen
Schmitt, Markus; Spiegel, Michael (Thesis advisor)
Aachen : Publikationsserver der RWTH Aachen University (2013)
Dissertation / PhD Thesis
Aachen, Techn. Hochsch., Diss., 2013
The motivation of this work was to find cost-effective and corrosion resistant alloys as alternatives to commercial materials, which meet the requirements in waste incineration and biomass combustion power plants. As commercial materials low- and high-alloyed steels and a Nickel-based alloy were investigated. The model alloys were 9%Cr-alloys modified with nickel, aluminium and silicon, and binary iron-aluminides with max. 40 at.% Al. In the exposure experiments, the materials were covered with synthetic deposits of chlorides and sulfates and corroded in N2-8%O2-15%H2O-0.2%HCl-0.02%SO2- and N2-5%O2-22%H2O-13%CO2-0.02%HCl-atmospheres, respectively, in a temperature range of 320°C to 600°C. The corrosion behaviour of the materials was determined concerning their mass loss, kinetics, and scale analysis. The degradation was discussed regarding the influence of the alloy composition, and the thermodynamic driving force in terms of activities and gradients in the governing corrosion mechanisms. The two main high-temperature corrosion mechanisms were the chlorinecatalysed ’Active Oxidation’ and in the presence of molten salt the ’Hot Corrosion’, i.e. acidic and basic fluxing. Under these conditions, the commercial materials with a high chromium or Cr/Ni-content showed most of the time a very low material loss. In comparison with commercial 9%Cr-steels, modified 9%Cr-alloys with additions of 5 wt.-% Ni, 2.5 wt.% Al and 2.5 wt.% Si, respectively, showed a predominantly improved corrosion resistance. Also, Fe-Al materials with an aluminium content of at least 26 at.-% showed a considerably increased corrosion resistance. With regard to high-temperature corrosion in waste incineration and biomass combustion atmospheres, respectively, and salt deposits it was demonstrated that under most experimental conditions the model alloys have shown an economical alternative to high-alloyed austenitic steels and nickel-based alloys with respect to their corrosion resistance.