Tomasz Brylewski

Microstructure of Fe–25Cr/(La, Ca)CrO3 composite interconnector in solid oxide fuel cell operating conditions

A 20 μm thick coating of La 0.8 Ca 0.2 CrO 3 perovskite on Fe-25Cr steel substrates was obtained by the screen-printing method. The interaction of the (La, Ca)CrO 3 coating with the steel substrate occurring during oxidation in air at 1073 K for 200h was investigated. The microstructure, phase and chemical analyses of the coating after oxidation were examined. It has been revealed that the metal substrate-coating interfacial zone has a two-layer structure built of mainly FeCr 2 O 4 and LaCrO 3 , which provide the electric contacts between the interconnector material and the film, thus creating conditions for prolonged exploitation of solid oxide fuel cells.

Interfacial Interactions between some La-Based Perovskite Thick Films and Ferritic Steel Substrate with Regard to the Operating Conditions of SOFC

An overview is presented on the oxidation kinetics, electrical properties and microstructure investigations of the oxide products formed on Fe-25 wt.-%Cr steel uncoated and coated with electrical conducting films of (La,Ca)CrO3 or (La,Sr)CoO3 in air and H2/H2O gas mixture at 1023−1173 K for up to 480 hrs with regard to their application as the SOFC metallic interconnect. The application of the Fe-25Cr steel in SOFC operating at 1073 K requires its surface modification to improve the electrical conductivity of chromia scale forming on the uncoated steel surface. The thick films of (La,Ca)CrO3 and (La,Sr)CoO3 with the thickness range of 20−100 μm, coated on the Fe-25Cr steel by screen-printing method helped solve this problem. TEM-SAD, SEM-EDS and impedance spectroscopy investigations have shown significant influence of the multilayer products formation at the substrate steel/coating films interfacial zone on the electrical properties of the metallic interconnect.

The effect of calcination conditions on the superconducting properties of Y−Ba−Cu−O powders

Calcination conditions of the precursor powders, i.e. temperature, type of atmosphere and duration, were determined with a view to obtain superconducting powders with the most advantageous physico-chemical properties. Investigated were powders in the Y−Ba−Cu−O system prepared by the sol-gel method. Thermogravimetric examinations of the powders have revealed that the decomposition kinetics of BaCO3 determines the formation rate of the superconducting YBa2Cu3O7−x (‘123’) phase. It follows from the decomposition kinetics of BaCO3 that the process is the most intensive in argon, whereas in static air and oxygen it is the slowest. The phase composition analysis (XRD) and low-temperature magnetic susceptibility measurements of the calcinated powders, confirm the above mentioned changes in the decomposition kinetics. The reaction of barium carbonate can be completed if the calcination process is conducted at the temperature of 850°C for 25 h, yielding easily sinterable powders for obtaining single-phase superconducting bulk samples with advantageous functional parameters.ZusammenfassungEine kurze Übersicht über die theoretischen Möglichkeiten der Bestimmung von energetischen und thermodynamischen Eigenschaften von chemischen Substanzen in gasförmigen und kondensierten (festen und flüssigen) Phasen wird gegeben. Die Überlegungen umfassen quantenchemische Methoden, die die Auswertung von energetischen Größen und statistischen thermodynamischen Abhängigkeiten ermöglichen, die für die Bestimmung anderer thermodynamischer Charakteristika erforderlich sind. Mögliche Anwendungen dieser Methoden werden ebenfalls diskutiert.

Perovskite and Spinel Functional Coatings for SOFC Metallic Interconnects

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.

High Temperature Corrosion of TiAl - 2-5At-%X (X=Ag,Cr,Nb) Alloys in SO2 and H2S-H2 Atmospheres

The sulphidation and oxidation behaviour of Ar-arc-melted Ti-50Al, Ti-49Al-2Nb, Ti49Al-2Ag, Ti-48Al-3Ag-5Cr and Ti-52Al-3Ag-5Cr alloys were studied at 1173 K in SO2 atmosphere (100 kPa) and in H2S-H2 gas mixture (pS2=1Pa) up to 39 hrs. Comparison of the influence of the applied sulphidizing atmosphere and addition of the third and fourth alloying element (Nb, Cr, Ag) to binary TiAl alloy on sulphidation and oxidation kinetics, microstructure, composition and growth mechanism of the scales formed on the above alloys were investigated. It was found that sulphidation and oxidation reactions followed a parabolic or para-linear rate laws. Investigations in SO2 revealed that TiAlAg alloy is much less resistible to the exposured atmosphere in comparison with other alloy compositions, caused probably by an Al-Ag liquid phase formation. Investigations in H2S-H2 show that TiAlAg and TiAlAgCr alloys sulphidize faster than TiAl and TiAlNb alloys due to formation of an Al-Ag liquid phase on the surface of these alloys. A significant influence of Ag, Nb and Cr additions to TiAl alloy on the microstructure and composition of the formed mixed oxide/sulphide (in SO2) and sulphide (in H2S−H2) scales and alloy surface layers was observed. The scales obtained in both atmospheres were multilayered and heterogenous and these formed in SO2 were composed of TiO2, Al2O3, TiS and Al2S3, while those in H2S-H2 of Ti3S4, TiS1.5, TiS and Al2S3. Marker experiments using platinum were performed in order to obtain information about the growth mechanism of scales in both atmospheres used.

A method of optimizing the rapeseed oil transportation costs in biofuel production installations

Background. Rapeseed oil is the main source of production biofuels in the Polish climatic conditions. This oil in the raw state has a high kinematic viscosity, much higher than the esters derived from it RME. Such a property rapeseed oil generates additional costs during its transport in industrial hydraulic systems. The goal of study was to develop a technology to reduce the viscosity of rapeseed oil by heating it before further pumping between the tanks. Material and methods. The research was raw rapeseed oil prior to transesterification. The simulation tests in the laboratory were performed on a specially designed test bench for testing the properties of a viscous liquid having a volume of 5 liter tank. The oil is heated heater at 5°C temperature range 20÷80°C and determined the cost of its heating HC, the costs of pumping PC, making up the total cost of transport TC. Then the analytical method and graphical establish optimum temperature rapeseed oil during transport in pipelines. Results. Heating the fresh rapeseed oil temperature from 20°C to 80°C causes a significant reduction in the kinematic viscosity from 62 to 10 mm2·s-1. In this temperature range, the cost of oil heating grow faster than the benefits of a lower load the electric motor driving the pump. Conclusions. In the case of small volumes of liquid heating method proposed rapeseed oil preparation tank in order to reduce its viscosity without any recognizable economic benefits. Mathematical analysis showed that the total costs were the smallest in the lower temperature range studied (here To = 20°C). Yet, the method can become profitable for large flows and low temperatures of hydraulic installations operation e.g. in the winter season when a oil puts up a meaningful resistance of flow. This requires further research conducted on an industrial scale.

High Temperature Oxidation of TiAl and TiAl8Nb Alloys in Air

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 kp 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 Ea = 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.