Abstract:The corrosion behaviors of a Co-Ce alloy containing approximately 15%Ce, pure Co and pure Ce have been studied at 700℃in H₂-H₂S mixtures providing a sulfur pressure of 10^-3Pa. It is shown that the alloy corroded more slowly than pure cobalt, but more rapidly than pure cerium. The corrosion of the alloy produced duplex scales, containing an outermost layer of pure cobalt sulfide and an inner layer of a cerium sulfide mixed with cobalt sulfide and an innermost layer where cerium sulfide was mixed with cobalt metal. The cobalt sulfide formed a continuous CoS layer on the surface of the alloy, even though at rates reduced with respect to pure cobalt. Thus, a cerium content of 15% was not sufficient to prevent the sulfidation of the base metal. These results were interpreted by taking into account the limited solubility of cerium in the base metal and the presence in the alloy of intermetallic compound rich in cerium.

Key words: Co-Ce alloy　sulfidation　corrosion