Thin dense membrane layers, mechanically supported by porous substrates, are considered as the most efficient designs for oxygen supply units used in Oxy-fuel processes and membrane reactors. Based ...on the favorable permeation properties and chemical stability, several materials were suggested as promising membrane and substrate materials: Ba0.5Sr0.5Co0.8Fe0.2O3−δ, La0.6−xSr0.4Co0.2Fe0.8O3−δ (x=0, 0.02) and Ce0.9Gd0.1O1.95−δ. Although membranes operate at elevated temperatures, the ends of tubes in certain three-end concepts remain almost at room temperature. The current work concentrates on the failure potential of these membrane parts, where in a complex device also the highest residual stresses should arise due to differences in thermal expansion. In particular, sensitivity of the materials to subcritical crack growth was assessed since the long-term reliability of the component does not only depend on its initial strength, but also on strength degradation effects. The results were subsequently used as a basis for a strength–probability–time lifetime prediction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The performance and durability of solid oxide fuel cell (SOFC) cathodes consisting of a porous Ce0.9Gd0.1O1.95 (CGO) infiltrated with nitrates corresponding to the nominal compositions ...La0.6Sr0.4Co1.05O3–δ (LSC), LaCoO3–δ (LC), and Co3O4 are discussed. At 600 °C, the polarization resistance, Rp, varied as: LSC (0.062 Ω cm2) < LC (0.079 Ω cm2) < Co3O4 (0.27 Ω cm2). High temperature X‐ray diffraction revealed a number of different phases in LSC and LC. The electrochemical performance of the LSC‐infiltrated CGO cathode was found to depend on the infiltrate firing temperature and is suggested to originate from a complex interplay between the formation, percolation, and surface area of electronically conducting and catalytically active phases. Simplified models that predict the Rp of LSC‐infiltrated CGO were applied and showed that the performance is not only characterized by the nanoscale size of the infiltrate but also from a better surface exchange property. A 450 h test of an LSC‐infiltrated CGO cathode showed an Rp with final degradation rate of only 11 mΩ cm2 kh–1. An SOFC with an LSC‐infiltrated CGO cathode tested for 1,500 h at 700 °C and 0.5 A cm–2 (60% fuel, 20% air utilization) revealed no measurable degradation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
▶ Cerium gadolinium oxide (CGO) tested as membrane material in syngas reactor. ▶ Multi-layer processing and co-sintering of supported CGO thin film membranes. ▶ Measurement of high oxygen fluxes of ...16
ml
min
−1
cm
−2 at 900
°C. ▶ Calculation of non-stoichiometry profile across membrane and mechanical integrity.
Gadolinium doped ceria (Ce
0.1Gd
0.9O
1.95−
δ
, CGO10) was investigated as oxygen separation membrane material for application in syngas production. Planar, thin film CGO10 membranes were fabricated by tape casting and lamination on porous NiO-YSZ supports and subsequent co-sintering. High oxygen fluxes, up to 16
N
ml
cm
−2
min
−1 at 900
°C, were obtained when placing the membrane between air and humidified hydrogen (H
2/H
2O
=
20). Initial experiments for syngas production were performed by testing the CGO10 membrane with methane and steam feed.
The mechanical integrity of CGO10 membranes during operation (heat up, cooling, reduction and re-oxidation) was also investigated. Chemically induced stress in the CGO10 membrane due to harsh reduction of the CGO10 material at high temperatures and very low
pO
2 values can lead to mechanical failure by lattice expansion. Calculations of the oxygen non-stoichiometry profile in the 30
μm thin CGO membrane under operation reveal that due to oxygen permeation in the membrane the largest non-stoichiometry at the permeate (fuel) side is more than a factor of 6 times smaller at 850
°C than that expected for CGO10 at equilibrium. The related relative expansion of the thin film CGO membrane should therefore lie below the expansion limit of 0.1% expected to be critical for mechanical stability and thereby allows for operation at high temperatures and low oxygen partial pressures.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Short chained triesters of glycerol and citric acid were systematically investigated as novel dual-functional dispersants and plasticisers for use in ceramic processing. Additional systematic studies ...on a series of diesters having structural similarities with the citrate and glycerol triesters were performed to further assess the significance of specific functional groups for the stabilisation of suspensions.
The overall purpose of this work consists in simplifying the formulation for ceramic processing slurries while at the same time limiting the environmental impact and toxicity. The use of multifunctional additives reduces the risk of unwanted interactions between different components. Additionally, the possible use of one additive in more than one role opens the opportunity for an overall reduction in the number and amount of chemicals and therefore reduction of costs and risks.
For the citrate ester candidates, different alkoxy groups were tested as well as the acetylation on the hydroxyl group. The glycerol esters differed by the length of the carboxylic chain.
Especially triethyl and tributyl citrate are proposed as promising dual-functional additives for ceramic processing. Specifically, for triethyl citrate the dual-function was finally demonstrated by producing a dense piece of 8YSZ through tape casting and subsequent sintering.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The sintering of asymmetric CGO bi-layers (thin dense membrane on a porous support; Ce0.9Gd0.1O1.95−δ=CGO) with Co3O4 as sintering additive has been optimized by combination of two in situ ...techniques. Optical dilatometry revealed that bi-layer shape and microstructure are dramatically changing in a narrow temperature range of less than 100°C. Below 1030°C, a higher densification rate in the dense membrane layer than in the porous support leads to concave shape, whereas the densification rate of the support is dominant above 1030°C, leading to convex shape. A flat bi-layer could be prepared at 1030°C, when shrinkage rates were similar. In situ van der Pauw measurements on tape cast layers during sintering allowed following the conductivity during sintering. A strong increase in conductivity and in activation energy Ea for conduction was observed between 900 and 1030°C indicating an activation of the reactive sintering process and phase transformation of cobalt oxide.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The densification, delamination and crack growth behavior in a Ce0.9Gd0.1O1.95 (CGO) and (La0.85Sr0.15)0.9MnO3 (LSM) multi-layer ceramic sample was studied using in situ X-ray tomographic microscopy ...(microtomography) to investigate the critical dynamics of crack propagation and delamination in a multilayered sample. Naturally occurring defects, caused by the sample preparation process, are shown not to be critical in sample degradation. Instead defects are nucleated during the debinding step. Crack growth is significantly faster along the material layers than perpendicular to them, and crack growth and delamination only accelerates when sintering occurs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A novel solid oxide cell concept, named as redox solid oxide cell, is proposed in this work. To demonstrate the concept, solid oxide cells with doped-SrTiO3 fuel electrodes and modified NiO-3YSZ fuel ...electrode support were developed to realize the redox-stable solid oxide cells. By modifying the particle characteristics of NiO, 3YSZ, slurry composition and sintering profile, a redox stable and multifunctional NiO-3YSZ fuel electrode support was successfully developed. Furthermore, two different types of doped-SrTiO3 (Sr0.94Ti0.9Nb0.1O3 and La0.49Sr0.31Fe0.03Ni0.03Ti0.94O3) fuel electrode materials were successfully integrated in to the half-cells with redox stable NiO-3YSZ support. Defect free solid oxide cells of 12 cm × 12 cm size were fabricated. The redox stability of these cells was evaluated and compared with the state-of-the-art NiO-3YSZ solid oxide cells at 850 °C. It was clearly demonstrated that the newly developed redox solid oxide cells have superior stability compared to the state-of-the-art cells. In order to establish the potential of the newly developed redox solid oxide cells, the evaluation of the electrochemical performance is required.
•Adapting processing parameters results in redox stable solid oxide cells.•Ceramic fuel electrodes are successfully combined with redox stable cermet supports.•Multifunctional fuel electrode support for high performing solid oxide cells.•Upscalable fabrication processes have been successfully applied.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A systematic screening of plasticisers for a polyvinyl butyral based binder system revealed that dibutyl maleate, dibutyl adipate and Pycal 94 are promising and less toxic alternatives to the very ...harmful but frequently used dibutyl phthalate. Pycal 94 seems especially promising as it unlike the two other candidates did not require a co-plasticiser, such as a polyethylene glycol, thus simplifying the system and reducing the risk of unwanted cross-interactions.
An effective and systematic procedure for substitution of the plasticiser, while maintaining chemical compatibility and mechanical properties, was also demonstrated. Incompatible systems were discarded in an initial broad screening while primary systems were further evaluated based on debinding properties, mechanical properties, flow behavior as well as sintering properties of ceramic tapes. The thermomechanical characterization performed on dried drops of binder and their corresponding tapes show strong similarities in the strain/stress profiles, validating the qualitative method used.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The microstructure, mechanical properties and gas permeability of porous supports of Ce0.9Gd0.1O1.95−δ (CGO) were investigated as a function of sintering temperature and volume fraction of pore ...former for use in planar asymmetric oxygen transport membranes (OTMs). With increasing the pore former content from 11vol% to 16vol%, the gas permeabilities increased by a factor of 5 when support tapes were sintered to comparable densities. The improved permeabilities were due to a more favourable microstructure with larger interconnected pores at a porosity of 45% and a fracture strength of 47±2MPa (m=7). The achieved gas permeability of 2.25×10−15m2 for a 0.4mm thick support will not limit the gas transport for oxygen production but in partial oxidation of methane to syngas at higher oxygen fluxes. For integration of the CGO support layer into a flat, asymmetric CGO membrane, the sintering activity of the CGO membrane was reduced by Fe2O3 addition (replacing Co3O4 as sintering additive).
•Design of porous ceria supports for asymmetric oxygen transport membranes.•Investigation of support microstructure, mechanical properties and gas permeability.•Pore former percolation at constant porosity increases gas permeability significantly.•Dusty gas model predicts gas transport limitations through supports at high fluxes.•Use of sintering aids to co-sinter defect-free multilayers of support and membrane.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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