Papers by Author: Zbigniew Żurek

Abstract: The presented paper discusses a possibility of developing and modifying surface of nickel substrate by applying of Ni, Pt, Pt/Ni porous metallic layers by zol-gel method using EDTA as a complexing agent. Then gel containing Pt or Ni or Ni/Pt was decomposed during pyrolysis process and then transformed into the porous metal during oxidation/reduction process at 600°C respectively in air or H₂ atmosphere. The thermal decomposition of gels were studied by TG/DTA method. Compositions of oxidized as well as metallic layers were determined by EDX and XRD method. The morphology of Pt, Ni and Pt/Ni layers were studied by SEM method.

Abstract: Influence of a platinum layer on the nickel powder sintered electrode on electrochemical processes of hydrogen generation is presented and discussed in this paper. The sinters of metallic nickel with developed area were obtained by subsequent oxidation/reduction of Ni powder. The process of platinum layer deposition on surface of nickel sinters was carried out with the PVD method. The morphology characteristics of Ni and Ni-Pt layered sinters were carried out with the application of SEM/EDS method. The electrochemical properties of above mentioned sinters were examined by potentiostatic method at 40°C in 1M KOH vs. Hg|HgO, using a rotating disc electrode. It was found that the platinum layer on the surface of nickel grains was well adherent and stable. The presence of platinum on nickel sintered electrodes results in an increase of observed current density in the process of hydrogen evolution.

Abstract: Surface treatment of TiAl alloys by the small amounts of halogens leads to the formation of the protective alumina scale. The halogens can be applied by ion techniques as well as by spraying or dipping with halogen-containing compounds. In this work the results of the oxidation in air of a Ti-47Al-6Nb alloy dipped in a fluorine-containing resin were presented. The thermal cycling runs were carried out in the temperature 900°C.

Abstract: The work presents analyses of Crofer 22APU steel oxidation in hydrogen atmosphere containing 300 ppm H₂S and in hydrogen atmosphere containing 300 ppm and 1% H₂O. The oxidation process was conducted on two kinds of samples: pre-oxidized (pre-oxidation process was carried out in the air at a temperature of 800°C during 100 h), and not pre-oxidized at a temperature of 600 and 800°C using periodic method during 500 h. It was established that oxidation rate may be described by means of parabolic law. Determined parabolic rate constants indicate that not pre-oxidized samples undergo sulphurization in H₂/300ppm H₂S atmosphere, while in H₂/300ppm H₂S + 1%H₂O atmosphere they undergo oxidation 3-4 orders of magnitude slower.

Abstract: The authors present studies of behavior of Crofer steel in H2 polluted by H2S. The high temperature corrosion behavior of Crofer 22APU steel pre-oxidized samples and not pre-oxidized ones were studied in the temperature range of 600 – 900°C in H2/H2S atmospheres in sulphur vapor pressures in the range of 10-7-10-1 Pa. Kinetics depend on the temperature and sulphur pressure, however the process of sulfurization for pre-oxidized samples was slower.

Abstract: There are several ways to improve the oxidation resistance of TiAl alloys. One of them is alloying with elements such as Nb, Ta, W, Si, Ag, Zr or Hf. However, bulk alloying influences the mechanical properties. Surface treatment of TiAl alloys by the small amounts of halogens leads to the formation of the protective alumina scale (“halogen effect”). The halogens can be applied by ion techniques (ion implantation, plasma immersion implantation) but also by spraying or dipping with halogen-containing inorganic and organic compounds. Deposition of the fluorine-containing resin on the surface of TiAl alloys is the easiest way to achieve the best results. SO2 impurity in air significantly influences oxidation behavior of TiAl alloys. In this work the results of the oxidation of a Ti-48Al-2Cr alloy coated with a fluorine-containing resin in the synthetic air and air containing 1% SO2 were presented. The oxidation runs were carried out in the temperature range 800-1000°C.

Abstract: The oxidation mechanism of FeCrAl (+RE), RE: reactive elements: Y and Hf) thin foils was studied at temperatures ranging from 1093 K to 1173 K in SO2+1%O2 atmosphere. Materials were subjected to isothermal and thermal cycling exposures as well as to the so-called two-stage-oxidation. In the latter, an oxygen isotope 18O2 was used as a tracer. Starting materials and scales were characterized using Grazing Angle X-Ray Diffraction (GA-XRD), EDX, SEM, XPS and High Spatial Resolution Secondary Ion Mass Spectrometry (HSR-SIMS). The obtained results showed within the studied range of exposure conditions the scales on all the studied alloys grow via outward mechanism typical for transient oxides and not for the -Al2O3 which is consistent with phase composition results and scale morphology and/or microstructure. It was also found that ‘as received’ foils are not bare metals but complex oxide-on-metal systems resulting from their manufacturing procedure. The obtained results are discussed in terms of the diffusion-related transport properties of the scale and of the scale phase composition.

Abstract: The high temperature corrosion behavior of Fe20Cr6Al-Y,Hf steel was studied in the range of temperature 800-1000oC in H2/H2S atmospheres at pS2=10-2 ,10-3 and 10-4 Pa sulphur vapor pressures. Kinetics depend on the temperature and sulphur vapor pressure. After 24 hours the whole specimen was practically consumed because the samples were 0,06 cm thick. Morphology of the scales have been performed by SEM techniques. Phase and chemical composition have been studied by EDX and XRD techniques. It was found that scale formed on Fe20Cr6Al-Y,Hf alloy was built with porosity sulphides layer. EDX analysis of the scale surface show that the any aluminum, hafnium and yttrium sulfides were found in the formed scale layer, however small amounts of Al2S3 was detected in scale/steel interface. Also internal sulphidation was observed. A phase analysis of the formed scale revealed that it is composed mainly of an FeS, Fe7S8 phases and CrS, Cr5S6. Result were compared with data obtained on the pure Fe and Cr samples.

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.