HIGH-TEMPERATURE CORROSION OF NI-20CR AND NI-15CR-8FE ALLOYS IN SULFUR-DIOXIDE

Two nickel-base alloys, Ni-20Cr and Ni-15Cr-8Fe, in the form of wire s pecimens, have been exposed to 100 mbar of sulfur dioxide between 550 and 850-degrees-C For Ni-20Cr, an outer Cr2O3 layer formed only at the beginning of the reaction, but very quickly Ni3S2 grew preferentially at the exterior by outward diffusion of nickel. The reaction rate is regulated by an external interfacial process. A barrier effect was not ed near 645-degrees-C associated with the formation of NiCr2O4; a new acceleration takes place above 680-degrees-C The external growth of Ni 3S2 is attributed to the low radius of curvature of the samples. For N i-15Cr-8Fe, the reaction mechanism is rather similar, except that no b arrier effect occurred A protective Cr2O3 layer formed above 800-degre es-C in both cases.