Concerning the corrosion problem in MgB_2/Al composite material

この論文は国立情報学研究所の学術雑誌公開支援事業により電子化されまし

Resistance of composite materials based on BaCeO3 against the corrosive effects of carbon dioxide and water vapour at intermediate fuel cell operating temperatures

The objective of this work is to analyse the chemical stability of BaCe0.85Y0.15O3−δ –Ce0.85Y0.15O2−δ (BCY15–YDC15) composite materials at 600 °C and to compare the aforementioned chemical stability with that of pure BCY15. The composite powders were obtained by mixing together powders of BCY15 and YDC15 in the following volume fractions: 90 % BCY15 + 10 % YDC15, 70 % BCY15 + 30 % YDC15, 30 % BCY15 + 70 % YDC15, 20 % BCY15 + 80 % YDC15 and 10 % BCY15 + 90 % YDC15. After that both powders and sintered samples of the BCY15 and the BCY15–YDC15 composites were saturated in two different atmospheres at 600 °C: CO2/H2O (3.1 mol% H2O) and N2/H2O (46.8 mol% H2O). The effects of the previously mentioned atmospheres on the physicochemical properties of the samples were investigated via differential thermal analysis (DTA) combined with thermogravimetric analysis (TG). Furthermore, mass spectrometry was used to analyse the chemical composition of the gases released from the samples during the DTA–TG heating process. The surface and cross-section morphology of the samples were examined by scanning electron microscopy. Moreover, the phase composition of each sample was studied via X-ray Diffraction. From the combined analysis, it can be concluded that the addition of YDC15 in the composite samples leads to an increase in resistance against the corrosive effects of CO2. Furthermore, it was determined that all samples maintain stability in the presence of H2O at 600 °C

Interface Reactions between Conductive Ceramic Layers and Fe-Cr Steel Substrates in SOFC Operating Conditions

To improve contact resistance and protect the cathode from chromium poisoning, perovskite (La,Sr)CrO3, (La,Sr)CoO3 and spinel MnCo2O4 coatings were applied onto the surfaces of Fe-25Cr (DIN 50049) steel by means of the screen-printing method. The oxidation process of the coated steels under cyclic-oxidation conditions showed high compactness of the protective layer, good adhesion to the metal substrate, as well as acceptable area specific resistance level for SOFC metallic interconnect materials, which was the result of the structural modification of the coating/steel interface reaction, i.e. the formation of an intermediate, chromia-rich multilayer between the conductive coating and the metal substrate. The cross-sectional morphology and nanostructure of interface products formed during long-term thermal oxidation in air and the H2/H2O gas mixture at 1073K were characterized using SEM-EDS and conventional TEM-SAD. Cr-vaporization tests showed that the perovskite and spinel coatings may play the role of barriers that effectively decrease the volatilization rate of chromia species. [doi:10.2320/matertrans.MB201013

Réactivité à haute température de composés intermétalliques Fe3Al

Fe3Al intermetallic compounds belong to a prospective group of corrosion-resistant and heat-resisting materials. Recent research proved that certain alloy additions introduced to base alloys in small quantities can have significant influence on improving mechanical and corrosion-resistance properties. The goal of this dissertation is to examine the influence of adding third and/or fourth minor element on the heat-resisting properties, and to understand the effects (positive or negative) of minor element addition on the high temperature oxidation mechanism of Fe3Al intermetallic compounds. The influence of selected additions (Zr, Mo, Nb and Cr) was examined on the high-temperature corrosion (degradation) behavior of researched alloys under isothermal conditions in synthetic air and synthetic air enriched with 10% of H2O in temperature range from 900 C to 1200 C. The cyclic oxidation experiments were performed in laboratory air at 1100 C. For understanding the growth mechanism of oxide scale on Fe3Al materials, two-stage oxidation experiments were performed (16O2/18O2) followed by Secondary Ion Mass Spectrometry (SIMS) and Transmission Electron Microscopy (TEM) observations.Les composés intermétalliques de type Fe3Al sont très prometteurs car ils présentent une bonne résistance à la corrosion à haute température. Des études récentes ont montré que l ajout d éléments d additions en faibles teneurs dans ces composés intermétalliques permettait d augmenter considérablement leurs propriétés mécaniques ainsi que leur résistance à la corrosion. L objectif de ce travail est d étudier l influence de ces éléments d addition, mais surtout de comprendre leurs effets et leurs mécanismes d action sur l oxydation à haute température des composés Fe3Al. Ainsi, l influence des éléments Zr, Mo, Nb et Cr a été testée sur le comportement à haute température de Fe3Al sous air synthétique et sous air enrichi en vapeur d eau (10 % en volume) entre 900 et 1200C. Des tests d oxydation en condition de cyclage thermique ont également été menés afin d évaluer l adhérence des produits de corrosion à la surface des composés intermétalliques. Des expériences de marquage isotopique sous 16O2/18O2 suivies d analyses par spectrométrie d ions de masse secondaires et microscopie électronique en transmission ont permis d appréhender les mécanismes d oxydation sur les matériaux dépourvus et contenant les éléments d addition.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Water vapor effect on high-temperature oxidation behavior of Fe3Al intermetallics

Fe3Al intermetallics (Fe3Al, Fe3Al-Zr, Fe3Al-Zr,Mo and Fe3Al-Zr,Mo,Nb) were oxidized at 950 °C in dry and humid (11 vol% water) synthetic air. Thermogravimetric measurements showed that the oxidation rates of the tested intermetallics were lower in humid air than in dry air (especially for Fe3Al-Zr,Mo and Fe3Al-Zr,Mo,Nb). The addition of small amounts of Zr, Mo or Nb improved the kinetics compared with that of the undoped Fe3Al. Fe3Al showed massive spallation, whereas Fe3Al-Zr, Fe3Al-Zr,Mo and Fe3Al-Zr,Mo,Nb produced a flat, adherent oxide layer. The rapid transformation of transient alumina into alpha alumina may explain the decrease in the oxidation rate in humid air