Papers by Author: Jolanta Gilewicz-Wolter

Abstract: As the result of oxidation of Cr-Mn steels in SO2 the three layer scale is formed. The intermediate layer of this scale is composed mainly of MnCr2O4 spinel whereas FeCr2O4 spinel is present in small amount. MnO dominates in the outer layer. The inner, very thin scale layer contains oxides/sulfides mixture. The aim of this study was to examine self-diffusion processes in both spinels by multitracer method of diffusion measurements to know which of the transport processes during oxidation is the smallest one and deciding on the corrosion rate. In diffusion experiments the radioisotopes 54Mn, 51Cr and 59Fe were used. The serial sectioning method was applied to simultaneous evaluation of diffusion rates of chromium, manganese and iron in both spinels at 1073 K and 1173 K under the pressure of 105 Pa in SO2 containing 10 Pa O2. These spinels were obtained by modified sol-gel method from nitrates. Structures of the spinels were examined by X-ray spectrometry. It was found, that the diffusion rates of metals are higher in MnCr2O4 spinel. Moreover the dominant mechanism of manganese transport (the highest one) in studied samples is the volume diffusion while chromium and iron are transported mainly through the high diffusivity paths.

Abstract: The paper presents the application of multitracer method of diffusion measurement in Cr-Mn steels. Two austenitic steels were investigated: Cr13Mn18SiCa and Cr17Mn17 as well as austenitic-ferritic one: Cr15Mn19. The serial sectioning technique was used for simultaneous evaluation of diffusion coefficients of radioisotopes of chromium 51Cr, manganese 54Mn and iron 59Fe at 1073K and 1173 K. Diffusion coefficients of radiotracers at 1173 K were calculated on the basis of both: activity of removed layer (differential method) and residual activity of the sample (integral method). The evaluated diffusion coefficients of metals in austenitic steels are higher than those in austenitic-ferritic one; their values are about 10-12 ÷ 10-11 cm2s-1. Moreover it was found that at 1173 K the diffusion rate of manganese is higher than that for iron and chromium while at 1073 K diffusion rates of chromium and manganese are comparable and higher than that for iron. Furthermore the experimental results point out that at 1173 K the volume diffusion is the dominant mechanism of metals’ transport while at 1073 K the high diffusivity paths diffusion prevails.

Abstract: The results of the study of the scale growth mechanism on the 50 µm thick foil of Fe18Cr5Al are reported. The experiments were carried out at 1093 K using a two-stage-oxidation approach. In the first stage, the samples were exposed to the SO2 + 1 vol. % O2 mixture for 1.5 h and 24 h in order to produce the primary scale. Subsequently, the samples were cooled down to the room temperature and moved to the furnace where they were exposed to the atmosphere rich in 18O2. The duration of the second stage was 0.5 h and 4.5 h for samples previously oxidized for 1.5 h, 8 h and 72 h, for the samples oxidized previously for 24 h. The elemental distributions were determined using high resolution SIMS, while the scale morphology was observed by means of SEM. In addition the radioisotopic studies using 35SO2 were carried out in order to assess whether sulfide phases developed at the initial stage of oxidation. All the results were interpreted in terms of the transport processes in the oxide scale.