Oxidation behavior of Fe-20Cr-5Al rare earth alloys in air and synthetic exhaust gas

Abstract

Fe-20Cr-5Al alloy foils are used in automotive catalytic converters. This work examines oxidation behavior of four production-processed alloy foils in both air and synthetic exhaust gas environments. Oxidation tests were performed between 750° C and 1150° C for times to 96 hrs. Weight gain results in both atmospheres were similar, an indication that the same mechanism controls oxidation in both environments. At high temperatures (>-950° C) both atmospheres produce weight gains consistent with α-alumina growth. Activation energies of 323 kJ/gmole and 271 kJ/gmole were calculated for oxidation in air and synthetic exhaust gas, respectively. At lower temperatures (<-850° C), accelerated weight gains can occur from growth of transition alumina. Despite similar weight gain results, the two atmospheres produce different oxide morphologies: at 950° C and above, air produces a rounded, porous oxide while synthetic exhaust produces a more compact, angular oxide. Unexpectedly, oxide spalling occurred on foils oxidized in synthetic exhaust at 1050° C and above.