Papers by Author: Kazimierz Przybylski

Abstract: The present paper is a review on the oxidation kinetics, electrical properties, chromium vaporization rate and microstructure investigations of oxide products formed on an uncoated Crofer 22 APU alloy and 1.4762 steel and coated by means of pulsed laser deposition and screen-printing methods with films of (La,Sr)CoO₃, (La,Ca)CrO₃, (La,Sr)CrO₃, (La,Sr)(Co,Fe)O₃ and MnCo₂O₄ in air and Ar-H₂-H₂O and Ar-CH₄-H₂O gas mixtures at 1023-1173 K for up to 1200 hrs. Microstructure investigations using SEM-EDS showed the influence of the reaction products formed in different atmospheres at the steel/coating interface on the electrical properties and Cr vaporization rate of these composite materials, which are used for construction of SOFC interconnects.

Abstract: Isothermal oxidation of two g-TiAl-based intermetallic alloys: Ti48Al and Ti46Al8Nb alloys was studied in synthetic air at 1073-1223 K for up to 240 hrs. Mass change per unit area for the oxidized samples followed approximately the parabolic rate law. The k_p values for the studied temperature interval were in the range from 7.2×10^-13 to 1.8×10^-11 g²cm^-4s^-1. The activation energy for oxidation of Ti48Al alloy in air at 1073-1223 K was E_a = 165±12 kJ/mol. Niobium addition to Ti48Al alloy in the amount of 8% increased its oxidation resistance. Structure and chemical composition of the oxidation products, and morphology of the oxidized samples were investigated using XRD, SEM-EDS, and TEM. The oxide scales formed on Ti48Al and Ti46Al8Nb alloys were well adherent to the metallic substrates and exhibited a multilayer structure. Depending on the oxidation temperature and the alloy composition, the scale consisted of variable amounts of TiO₂ and Al₂O₃. Additionally TiN, and niobium rich particles were also identified in the appropriate oxide scale. To understand the growth mechanism of oxide scale formed on Ti46Al8Nb alloy, two stage oxidation experiment was performed using ¹⁶O₂/¹⁸O₂, followed by SNMS and TEM-EDS. Particular attention was paid to the use of TEM in order to precisely characterize the reaction products on the Ti46Al8Nb alloy.

Abstract: The paper describes an examination of the effect of the addition of zirconium as a third element on the heat-resisting properties and explains the high temperature oxidation mechanism of Fe3Al intermetallic compounds. The Fe3Al and Fe3Al-0,05Zr specimens have been isothermally oxidized in the temperature range of 1173-1473 K in synthetic air for 100 hrs. The formed oxide layer, about 1,5-2 μm thick, was Al2O3. An examination of the cross-sectioned scales by SEM-EDS showed that the alumina layer consisted of a small inner columnar layer and an outer equiaxed grain layer. Additionally, very fine (50-150 nm) oxide grains rich in Zr, further identified as ZrO2, were found across the alumina scales. To understand the role of Zr on the growth mechanism of α–Al2O3 oxide scale on Fe3Al materials, two-stage oxidation experiments were performed (16O2/18O2), followed by SIMS and TEM-SAD observations. Particular attention was paid to the use of TEM in order to precisely characterize the products on samples prepared using the FIB (Focused Ion Beam) method. A combination of analytical techniques revealed that ZrO2 particles, most of which were formed along alumina grain boundaries, enhanced oxygen diffusion along grain boundaries due to oxygen-deficient composition of zirconium oxide (ZrO2-y).

Abstract: The oxidation kinetics, electrical properties, microstructure and chromium vaporization effects of the oxide products formed on Fe-25 wt.-%Cr steel uncoated and coated with films of (La,Sr)CrO3, (La,Sr)CoO3, (La,Sr)(Co,Fe)O3, Mn1.5Cr1.5O4 and MnCo2O4 in air and the Ar-H2-H2O gas mixture at 1023−1173 K for up to 840 h with regard to their application as SOFC metallic interconnect were investigated. To improve poor electrical conductivity of chromia scales and to suppress chromium vaporization from this scale grown on uncoated steel during oxidation, the perovskite and spinel thick films composed of paste prepared via co-precipitation-calcination and ultrasonic spray pyrolysis methods were applied. Perovskite and spinel coatings decreased the volatilization rate of chromia species in comparison with the value of this parameter corresponding to oxide scales built mainly of chromia formed on uncoated steel. Microstructure investigations by the SEM-EDS method and electrical resistance measurements revealed the significant influence of the formation of multilayer reaction products at the steel/coating interface on the electrical properties of the composite materials used for the construction of the SOFC metallic interconnect.