TEMPERATURE OXIDATION OF THIN FOIL OF FeCrAl STEEL IN SO_2+O_2 MIXTURE

摘要

In the present paper the results of high temperature oxidation of thin foil of FeCrAl steel are shown. The oxidation processes of FeCrAl steel were studied in air, SO_2 and SO_2/O_2 gas mixtures under atmospheric pressure. The reaction kinetics have been studied at temperature range 1073-1123 K in pure SO_2, at 1093 K in SO_2/O_2 gas mixture and at 1123 K in air. The kinetics of studied steel for all experimental conditions obeys parabolic rate law. Phase composition and morphology of the scales have been studied by X-ray diffraction, SEM and EDX techniques. It was found that in all case of oxidation forms alumina oxide. Using Gibbs free energy (ΔG~0_T), phase diagram was constructed for Fe-S-O, Cr-S-O and Al-S-O systems at 1093K. In order to check whether some sulfides forms during the initial stage of the reaction the radioisotope investigations were performed using sulfur dioxide labeled with radioactive sulfur. The oxidation was carried out for a short duration (15 min.) at 1093 K. The location of ~(35)S in the scale was established by means of autoradiography of the sample surface. Such autoradiograph shows that any layer containing sulfide was formed during the initial stage. In some places of the autoradiograph a small number of grains containing sulfur is visible. It was found, that the thin Al_2O_3 passive layer was formed at the beginning of the process. This effect can be induced by high oxygen potential.