SULFIDATION OF THE FE-40 AT-PERCENT AL-ALLOY IN H-2 H2S MIXTURES AT HIGH-TEMPERATURES/

Sulphidation of an ordered bcc alloy having the nominal composition Fe -40 at.% Al was studied at temperatures of 1073-1273 K in hydrogen/hyd rogen sulphide mixtures at sulphur pressures of 10(-5)-10(-2) Pa. The sulphidation runs were followed thermogravimetrically. Phase and chemi cal composition of the sulphide scales and the scale morphologies were determined by means of XRD, EDX, EPMA and SEM. The sulphidation runs showed a relatively fast uptake of sulphur at the beginning followed b y a gradual slowdown. The estimated parabolic rate constants for the s econd stage of the reaction were of the order of 10(-12)-10(-11) kg(2) /m(4)s, i.e. comparable to the oxidation rates of alumina formers in t he same temperature range. The initial faster growth of the sulphide s cale was attributed to the formation of iron-aluminum sulphospinel whe reas the second stage to the development of aluminum sulphide at the a lloy/scale interface.