Abstract
Corrosion problems in many industrial environments, such as waste incinerators or other advanced combustion power generation systems, are usually rather severe due to ash deposits of heavy and/or alkali metal chlorides and sulfate salts, especially those of Zn, K, Pb etc. In the present study, the individual effect of Zn$Cl_2$ and KCI on the corrosion behavior of pure metals such as Fe, Ni, Cr and AI, several Ni- and Fe-based alloys as well as Fe-AI intermetallics, was examined at 450$^{\circ}C$ in oxidizing atmosphere. On the other hand, the corrosion tests of one carbon steel and 310SS with and without aluminide coatings were also conducted beneath thin KCI salt films at 650$^{\circ}C$, to study whether aluminide coating is a suitable protective means against such corrosives. As a conclusion, most of the materials suffered from accelerated corrosion beneath KCl, Zn$Cl_2$, and Zn$Cl_2$-KCI mixture deposits, characterized by rapid formation of porous, multi-layered and protective-less oxide scales as well as localized corrosion induced by chlorine. The oxide scales formed on pure Fe and pure Ni were rather thick and porous, while the most serious spallation of the corrosion products occurred on pure Cr. Ni-based alloys exhibited comparatively lower corrosion rates than Fe-based alloys, and AI either as bulk alloying element or as overlay coatings could remarkably enhance corrosion resistance of the alloys due to formation of a protective external alumina-rich scale. Finally, continuous mass loss was observed for Fe-based alloys during immersion test in Zn$Cl_2$-KCI molten salts, and the corrosion was depressed with increasing Cr or Ni content, which was quite different from the results obtained in the case with salt deposits, as a direct consequence of the insufficient oxygen supply in the molten salts.