The ‘shrinking core’ model has been applied for the evaluation of hydrogen desorption kinetics during decomposition of magnesium hydride.

A simple model of the hydrogen desorption kinetics of metal hydrides is formulated and solved analytically. The particle surface reaction is assumed to be a rate-controlling-step. Then a volumetric measurement of hydrogen desorption process is evaluated on an example of wet ball milled magnesium hydride, and can be applied generally for any metal hydride.The solution reproduces the shape of experimental curves for desorption process. In the case of surface-controlled kinetics, a volumetric measurement requires a special evaluation of results, predicted by the solution of the model. An improved evaluation of the volumetric measurement of hydrogen desorption from magnesium hydride powders using the model has been demonstrated. (C) Copyright 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Composite materials based on 8wt% yttria partially stabilized zirconia, with additions of gadolinium zirconate, lanthanum lithium hexaaluminate, yttrium aluminum garnet and strontium zirconate were characterized. Samples were fabricated by hot-press sintering at 1550°C. The effect of the secondary phase content on the mechanical properties of the composites was evaluated. Hardness, elastic modulus and fracture toughness of the fabricated composites were determined by means of depth-sensitive indentation testing. The fracture toughness of the samples as determined by the indentation method was found to increase with increasing YSZ content, reaching 3MPa·m0.5 for samples with 80wt% YSZ. The fracture toughness appeared to be affected by thermal expansion coefficient mismatch, crack bridging and crack deflection.

Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) is widely known as a promising candidate material for oxygen transport membranes (OTMs). In order to maximize the oxygen permeation through such a membrane, the membrane layer should be as thin as possible, which requires a porous support. Because of the expansion behavior of BSCF, porous supports of the same material were developed to avoid failure due to mismatches in the thermal expansion coefficients. For the purpose of minimizing concentration polarization in the support pores, the microstructure of these support-layers has been optimized. For that reason supports with a porosity of up to 41% were developed. Membrane curvature caused by different shrinkage rates during co-firing could be minimized by the use of corn starch as pore former. By increasing the support porosity from 26% to 41%, the oxygen permeation of a supported 20 μm membrane in an air–argon gradient at 800 °C was increased by 50%. Compared to a disc membrane of 0.9 mm thickness the permeation enhancement is 90%.

Tape casting is widely used in industrial scale for production of multilayer ceramic capacitors or substrates for different applications. In 2009, it was successfully introduced as standard shaping technology for 3 (BSCF) are shown. The entire scope from the preparation of the used powders, the different manufacturing steps and their optimization potential up to the final tape-cast product will be discussed. The influence of the use of pore forming agents, heat treatment or other parameters during processing will be described in detail. Finally, the option of sequential tape casting of different materials for graded structures as a future step in shaping technology will be presented for different applications.

The morphology of layers of fully yttria-stabilised zirconia (YSZ) deposited by reactive magnetron sputtering was studied with regard to their application as thin electrolytes for solid oxide fuel cells (SOFC). A thin layer of YSZ was deposited on top of anode substrates for SOFC. The substrate comprises the warm-pressed anode itself, which supports the complete cell, and an anode functional layer deposited by vacuum slip casting, which is in direct contact with the electrolyte. From previous experiments it is known that non-assisted reactive DC magnetron sputtering produces layers with rather high leak-rate even when depositing at high temperatures. Residual pores on the substrates' surfaces are responsible for the incomplete coverage by the thin electrolyte and are detrimental to the cell's performance. In the present paper, the effect of increasing bias power applied to the substrate is studied. A clear improvement of the layer morphology and gas-tightness can be observed with increasing bias power. SOFC single cell-tests show art improved performance with regard to standard wet-ceramic processing routes. (C) 2012 Elsevier B.V. All rights reserved.

Yttria partially stabilized zirconia (YSZ) coatings are widely used for thermal barrier coatings (TBCs) to increase operating temperature of gas turbines. In the wavelength range where most of the radiation by walls and combustion gas is emitted within the gas turbine YSZ is semitransparent leading to increasing radiation heat flows into the components at increasing service temperatures. The objective of this work is to optimize the diffuse reflectance of plasma‐sprayed TBCs by improving the coating microstructure such that the reflectance of radiation is increased. As a result, a more efficient thermal screening of the underlying metallic substrate is achieved. In this work, air plasma‐sprayed and suspension plasma‐sprayed (SPS) coatings of 7% YSZ using powder of different grain size distributions and different spray parameters were deposited. The reflectance and transmittance has been investigated in the wavelength range from 0.3 to 2.5 μm. The SPS‐coatings showed the highest reflectance up to 94% at 1.5 μm wavelength. In addition, the scattering and absorption coefficients of the sprayed TBCs calculated with the Kubelka–Munk two flux model showed strong correlation with the measured porosity. By improving the microstructure, we were able to reduce thermal conductivity while increasing scattering of radiation, resulting in lower heat flow and lower temperature at the metallic substrate. These results are strengthened by numerical calculations.

Physical vapor deposition (PVD) technologies allow for a variety of microstructural morphologies. PVD is especially qualified for the production of dense ceramic layers at comparatively moderate substrate temperatures. This paper discusses the physical vapor deposition of SOFC functional layers, comprising perovskites, NiO/8YSZ and composite electrolyte layers, with a thickness between 300 nanometres and several micrometres and lateral dimensions of 100 mm⋅100 mm. Magnetron sputtering and electron beam evaporation were used as PVD techniques, with and without additional ion bombardment of the layers during deposition. Scanning electron microscopy analysis revealed that an additional ion bombardment during layer growth increasingly promotes the creation of a continuous and dense layer morphology instead of a columnar microstructure.

One way to improve the mechanical properties of solid oxide fuel cells is the development of metal supported designs. This type of SOFC offers improved thermal shock resistance, reduced temperature gradients due to the greater thermal conductivity of the metal, and lower operating temperatures. Switching from ceramic supports to metal supports also allows the uses of conventional metal joining and forming techniques and could significantly reduce the material and manufacture costs. However, one persistent problem needs to be solved: inter-diffusion of chemical elements contained in the metal substrates and in the anodes of SOFC leads to degradation, which is to be prevented by protective coatings. In order to address the issues of sintering and delamination for metal supported SOFC, the deposition of gadolinia doped ceria on metal substrates made of Crofer 22 APU has been done by electron beam evaporation and reactive spray deposition technique, as two direct deposition techniques that will not require a sintering step, respectively. Additionally, the effect of ion-assistance on layers made by electron beam evaporation was studied. Because metal supported fuel cells aim at low/intermediate operating temperatures, reducing the thickness of these protective coatings is crucial, since layer thickness is directly correlated to its ohmic resistance. A layer of nickel was applied by magnetron sputtering to prove the effectiveness of the deposited diffusion barrier layers.

A systematic study of room temperature 57Fe-Mössbauer spectra has been undertaken in the quasi-ternary system La0.8Sr0.2(Mn,Fe,Co)O3. The spectra exhibit a wide variety from simple to complex line shapes due to varying magnetic and/or quadrupolar interactions. Most samples are non-magnetic and show a linear variation of isomer shift vs. formal oxidation state. Magnetism seems to depend on a critical amount of Fe3+–Fe3+ interactions. A magnetic phase diagram of the system at room temperature is presented.

Nanostructured gas separation membranes are promising candidates for the separation of CO2 from the flue gas of fossil power plants. Well-defined atomic structures in the range of a few Angstrom are required to separate CO2 from N2 in existing post-combustion power plants, and H2 from CO2 in prospective integrated gasification combined cycle (IGCC) power plants. Today, CO2/N2 and H2/CO2 gas separation with membranes has been demonstrated mainly on a laboratory scale, while less is known about membrane performance and stability under real conditions. To extend the state of knowledge, a test bed was put into operation in the flue gas stream of a hard-coal-fired power plant (EnBW Rheinhafendampfkraftwerk, Karlsruhe), which enabled the long-term functional test of ceramic as well as polymer gas separation membranes for up to 1100h. For the first time, a CO2 enrichment from 12vol.% in the flue gas to 57vol.% in the permeate of a polymer membrane was demonstrated. Due to operating this membrane in direct contact with flue gas, the flow rate was reduced from 0.86 to 0.07m3/m2hbar within the first 400h. This reduction was mainly caused by the deposition of ash particles and gypsum suggesting the need of developing effective membrane protection strategies. In addition, ceramic supported Ti0.5Zr0.5O2 and metal supported Co–SiO2 membranes were tested under the same conditions. Even if demonstration of CO2 gas separation with ceramic membranes requires further modifications of the membrane materials, the long-term exposure in the power plant led to notable results regarding adherence of functional layers and chemical stability.

Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) exhibits high oxygen permeability, which is why it is being discussed for gas separation (oxygen transport membrane, OTM) in zero-emission power plants using oxyfuel technology when the membrane is operated in a clean environment, i.e. no flue gas contact. We investigate the influence of membrane processing on microstructure and oxygen permeation. Pure-phase BSCF powder is synthesized using a modified Pechini method. For comparison, commercially available powder is also used, synthesized by a solid-state reaction. Disk-shaped membranes of various microstructures, i.e. closed porosities and grain sizes, are prepared by uniaxial pressing and sintering of the powders processed in different ways. The powders and membranes are characterized by methods including BET, SEM, XRD, and DSC. The microstructures obtained by different sintering conditions are investigated by SEM and TEM. Sintering at 1150°C leads to incongruent melting of BSCF indicated by DSC. The liquid phase appears at three-phase boundaries grain–grain–air and consists of nearly pure cobalt oxide with small impurities of barium and strontium detected by TEM/EDX analysis. Oxygen permeation of the membranes is measured in an air/Ar gradient depending on temperature and membrane microstructure. The closed porosity of different processed membranes is varied between 2 and 15% with uniform grain sizes in the range of approx. 10μm. The average grain size is increased from 10 to 45μm by increasing the sintering temperature. Neither porosity nor the grain size significantly influences the oxygen permeation rate of 1-mm-thick disks in the investigated parameter range.

A decrease in the operating temperature of solid oxide fuel cells below 700 degrees C results in a significant decrease of the output power. In this temperature regime the ionic resistance of the commonly used electrolyte yttria-stabilized zirconia becomes dominant. Therefore, it is necessary to reduce the thickness of the electrolyte layer to minimize the resistance to ionic flow as long as no alternative electrolyte materials with higher ionic conductivity negligible electronic conductivity and sufficient stability are available.In this paper electron beam physical vapour deposition is discussed as a deposition technology for thin electrolyte layers. An electrolyte composite layer was developed with a lower specific resistance in comparison to an electrolyte layer made by vacuum slip-casting. The purpose of the composite electrolyte was to fulfil both gas tightness and electronic insulation.The performance of fully-assembled anode-supported fuel cells with an electrolyte composite manufactured by electron beam evaporation was 0.93 A/cm(2) at 650 degrees C and 0.7 V. whereas the performance of cells with an electrolyte manufactured by vacuum slip-casting with a sintering step was 0.63 A/cm(2) at 650 degrees C and 0.7 V. The performance improvement was interpreted in terms of a significantly different bulk ionic resistance of the electrolyte layers. (C) 2010 Elsevier B.V. All rights reserved.

Porous NiTi alloys are highly attractive for energy absorbers, damping devices and biomedical implants. In the present work, metal injection moulding (MIM) in combination with the application of a suitable space holder material was used for the production of NiTi parts with well defined pore sizes and porosities in the range of 30-70 vol.%. For comparing the properties, porous titanium and Ti-6Al-4V samples were prepared in the same manner.Focus of the present work was a detailed investigation of the mechanical properties of porous NiTi to estimate its potential regarding the abovementioned applications. For a Ni-rich NiTi alloy with a porosity of 50 vol.%, fully pronounced pseudoelasticity after 6% compression was demonstrated. An energy dissipation of 1.5 MJ/m(3) was measured, which could be directly related to the reversible austenite-martensite phase transformation. At higher deformations, pseudoelasticity becomes more and more superposed by the onset of plastic deformation. Nevertheless, even at deformations of up to 50%, a clearly pronounced amount of pseudoelastic shape recovery still remained. Fatigue of pseudoelasticity was investigated by conducting of up to 230,000 load cycles to 4% compression at a frequency of 1 Hz. (C) 2010 Elsevier B.V. All rights reserved.

Oxides resulting from discrete changes in composition within the quasi-ternary system La0.8Sr0.2CuO2.4(sic)La0.8Sr0.2CoO3 (- delta)-La0.8Sr0.2FeO3 (- delta) were investigated under similar experimental conditions with the objective of obtaining an overview of the variation of the relevant properties for possible applications as cathode contact layer in SOFCs. Twenty-two oxide compositions within this system were systematically selected and synthesized under identical conditions by the Pechini method. The distribution of the different crystallographic phases at 1050 degrees C within this quasi-ternary phase diagram, the DC electrical conductivity at 800 degrees C and the thermal expansion coefficients are presented. Perovskites of different compositions issued from this ternary diagram were tested as cathode contact material between an La0.8Sr0.2FeO3 cathode and a Crofer22APU interconnect by resistance measurements at 800 degrees C. The application of a MnCo1.9Fe0.1O4 spinel protection reduced the interfacial reaction between the Crofer22APU and the cathode contact material. Electrical resistance measurements at 800 degrees C in air up to 1000 h and the analysis by scanning electron microscopy/energy-dispersive X-ray spectroscopy of the sample cross-sections were carried out to verify the Surface stability and the electrical performance. (c) 2009 Elsevier B.V. All rights reserved.

The series of Gd4-xMxAl2O9-x/2 (M = Ca, Sr) with x =0, 0.01, 0.05, 0.10 and 0.25 was prepared by the citrate complexation method. Both Gd4-xCaxAl2O9-x/2 and Gd4-xSrxAl2O9-x/2 show the monoclinic cuspidine structure with space group of P2(1)/c up to 0.05-0.1 and 0.01-0.05 mol for Ca and Sr, respectively. Beyond the substitution limit of Gd4Al2O9, GdAlO3 and SrGd2Al2O7 appear as additional phases. The highest electrical conductivity obtained at 900 degrees C yielded sigma = 1.49 x 10(-4) S/cm for Gd3.95Ca0.05Al2O8.98. In comparison, the conductivity of pure Gd4Al2O9 was sigma = 1.73 x 10(-5) S/cm. The conductivities determined are in a similar range as those of other cuspidine materials investigated previously. The thermal expansion coefficient of Gd4Al2O9 at 1000 degrees C was 7.4 x 10(-6) K-1. The phase transition between 1100 and 1200 degrees C reported earlier changes with increasing substitution of Ca and Sr. (C) 2009 Elsevier B.V. All rights reserved.

Ferritic stainless steels have become promising candidate materials for interconnects in tubular metal-supported solid oxide fuel cell stacks. A number of ferritic alloys containing between 18 and 26 mass% Cr and discrete changes in minor alloying elements and reactive elements were isothermally oxidized at 800 °C in air and their electrical resistance was measured with the objective of obtaining an overview of the properties relevant for applications for cathode side interconnect. The alloys containing Mn showed a (Mn,Cr)3O4 spinel layer on top of a Cr2O3 oxide. The electrical conductivity of the steels forming this kind of oxide layer was higher than the measured for only Cr2O3 former or oxide dispersion strengthened alloys and increased when the alloy contained Ti or Nb. Oxide scale spallation was observed for F18TNb and E-Brite, both containing Si. The influence of different cyclic oxidations was studied for the Crofer22APU steel, showing an irregular oxide growth as well as an increase in conductivity of the oxide scale formed when 12-h cycles were applied.

The aim of the MEM-BRAIN project is the development and integration of gas separation membranes for zero-emission fossil power plants. This will be achieved by selective membranes with high permeability for CO2, O-2 or H-2, so that high-purity CO2 is obtained in a readily condensable form. The project is being implemented by the "MEM-BRAIN" Helmholtz Alliance consisting of research centres, universities and industrial partners.The MEM-BRAIN project focuses on the development, process engineering, system integration and energy systems analysis of different gas separation membranes for the different CO2 capture process routes in fossil power plants.

Perovskites of different compositions were tested as cathode contact material between an La0.8Sr0.2FeO3 cathode and a Crofer22APU interconnect by resistance measurements at 800 °C. The materials tested were LaNi0.6Fe0.4O3 and La0.8Sr0.2FeO3 which are also used as cathodes; La0.8Sr0.2Mn0.5Co0.5O3 and La0.8Sr0.2Mn0.1Co0.3Fe0.6O3, selected for comparing perovskites with different Mn contents; and La0.8Sr0.2Co0.75Fe0.25O3 and La0.8Sr0.2Co0.75Cu0.25O3 for comparing perovskites with high Co content and two possible partial substitutions of the Co. The initial area-specific contact resistance (ASR) was found to depend on the electrical conductivity of the measured perovskites. Time evolution of the ASR depended on the interactions between the contact material and the interconnect, showing the highest degradation rates for LaNi0.6Fe0.4O3 and La0.8Sr0.2FeO3. Chromium from the interconnect reacted with the Sr-containing perovskites forming SrCrO4. With the contact material without strontium chromium-containing perovskites were formed. A reduced interfacial reaction was achieved by application of a MnCo1.9Fe0.1O4 spinel protection layer on Crofer22APU in terms resulting in low and stable ASR.