Corrosion of metals and alloys in sulfate melts at 750°C |
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Authors: | Ajay K Misra |
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Affiliation: | (1) Department of Metallurgy and Materials, Case Western Reserve University, Cleveland, Ohio;(2) Present address: NASA Lewis Research Center, Cleveland, Ohio |
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Abstract: | The corrosion of Ni, Co, Ni-10Cr, Co-21Cr, and IN738 was studied at 750°C in the presence of molten sulfate mixtures (Na2SO4-Li2SO4 and Na2SO4-CoSO4) and in an atmosphere consisting of O2+0.12% SO2-SO3. The corrosion was observed to be similar for both Na2SO4-Li2SO4 and Na2SO4-CoSO4 melts. The corrosion of Ni and Co tookplace by the formation of a mixed oxide plus sulfide scale, very similar to the corrosion in SO2 or SO3 alone. The initial stage for the corrosion of Ni-10Cr involved the formation of a thick NiO+Ni3S2 duplex scale, and Cr sulfide was formed during the later stages. A pitting type of morphology was observed for both Co-21 Cr and IN738. The pit was Cr sulfide at the beginning, and subsequently the sulfides oxidized to Cr2O3. A base-metal oxide layer was present above the pit, and this was observed to be formed very early in the corrosion process. A mechanism is proposed to explain this. In general, the formation of sulfides appears to be the primary mode of degradation in mixed sulfate melts. |
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Keywords: | nickel cobalt alloys hot corrosion sulfates sulfides |
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