Laboratory experiments were carried out to study the corrosion behaviour of steels and nickel-based alloys beneath heavy-metal-rich chloride and sulfate melts. Exposure tests on low- and high alloy steels in (Ca, K, Na, Pb, Zn)-sulfate mixtures in N2-5 vol.% O2 at 600°“C have shown accelerated corrosion after addition of PbSO4 and ZnSO4. The corrosion products were identified as (Fe, Ni)-oxide precipitates in contact with the gas phase and chromium-rich corrosion products close to the metal.
Thermogravimetric investigations in He-5 vol.% O2 with the 2.25Cr-lMo steel and also Alloy 625 have shown that severe corrosion oecured in the presence of a 50 wt.% ZnCl2-50wt.% KClsalt mixture in the
temperature range from 300 to 500°C. The corrosion products on 2.25Cr-lMo were found to be Zn-rich iron-oxide precipitates in contact with the gas phase and a Fe2O3 layer underneath. In contact with the metal, a mixture of iron-chlorides and Fe2O3 was detected, together with variable amounts of K and Zn. A thick scale has formed on Alloy 625, consisting of nickel- and chromium-oxides with some dissolved Mo.
Keywords: waste incineration, fly ash deposits, chloride and sulfate melts, heavy metal compounds, fluxing, oxide precipitates