THE SULFIDATION BEHAVIOR OF AN FE-10 ATOMIC PERCENT AL-ALLOY IN AR-S2 AND H2-H2S ATMOSPHERES AT 1023-K

The sulfidation behavior of Fe-10 atom percent (a/o) Al has been studied at 1023 K in static Ar-S//2 gas for exposures up to 72h and, for a shorter reaction time of 6h, in flowing H//2-H//2S atmospheres. The sulfur pressure in the gas varied between 10** minus **3 and 10**4 Pa. Development of a triplex scale occurred, comprising an outer columnar-grained FeS layer, an intermediate Al//2S//3 layer, and an inner FeS-Al//2S//2 zone. Studies employing radioactive sulfur demonstrated that growth of the inner FeS-Al//2S//3 layer proceeded primarily by the ingress of ambient gas along fissures in the outer FeS and Al//2S layers. In the Ar-S//2 atmosphere, slow parabolic growth, at a rate approximately one-twentieth of that for unalloyed iron, was observed for reaction up to 40h, following which mechanical failure in the scale led to an increased rate of reaction.