| 1. |
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| 2. |
- Gao, Zhan, 1981-
(författare)
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Advanced Functional Materials for Intermediate-Temperature Ceramic Fuel Cells
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Low to intermediate-temperature solid oxide fuel cell (SOFC, 500 oC-700 oC) based on doped ceria (DCO) electrolyte has attracted much attention during the last decade. However, DCO suffers from electronic conduction caused byreduction of Ce (IV) to Ce (III) at high temperatures and low oxygen partial pressures and has a high grain-boundary resistivity. Co-doping has been chosen as the focus of this PhD study to investigate the feasibility of overcoming these technical problems. For different purposes, two co-doping strategies have been implemented to improve the properties of the singly doped ceria. Sr addition has been used with the aim of enhancing the ionic conductivity of Ce0.8Sm0.2O2-δ. The Sr addition greatly improves the microstructure of the space charge layers and the space charge potentials. The total conductivity of Sm and Sr co-doped ceria is higher than that of Ce0.8Sm0.2O1.9, and Ce0.8(Sm0.7Sr0.3)0.2O2-δ has the highest total conductivity. Sm and Lu co-doped ceria with composition of Ce1-x(Sm3Lu2)x/5O2-δ was investigated to validate the concept of critical dopant ionic radius. The elastic strain and critical dopant ionic radius may have an immediate effect on the grain bulk ionic conduction characteristics. As the basis of the ceramic electrolyte processing, the effect of the powder synthesis routes, including Polyvinyl alcohol (PVA)-assisted sol-gel process,Polyethylene glycol (PEG)-assisted sol-gel process, citrate sol-gel process and oxalate co-precipitation process (OCP), on the microstructure and the ionic conductivity of the Ce0.85Sm0.075Nd0.075O2-δ (SNDC) electrolyte has beeninvestigated. OCP process results in higher relative density and ionic conductivity, lower grain-boundary resistance and activation energy. Sm0.5Sr0.5CoO3-δ (SSC) cathode was investigated for SOFCs based on Ce0.85Sm0.075Nd0.075O2-δ (SNDC) electrolyte. Kinetics of oxygen reduction reaction (ORR) on porous SSC cathode was investigated by AC impedance spectra. Finally, novel BaZr0.1Ce0.7Y0.2O3-δ (BZCYO)-Ce0.8Y0.2O2-δ (YDC) composite ceramic electrolyte having both proton and oxygen ion conduction was studied. The composite ceramic electrolyte shows an enhanced ionic conductivity and chemical stability against reduction.
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| 3. |
- Gao, Zhan, et al.
(författare)
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Comparative study of Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) electrolyte synthesized by different routes
- 2011
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 509:35, s. 8720-8727
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Tidskriftsartikel (refereegranskat)abstract
- In this work, four different methods, including polyvinyl alcohol (PVA)-assisted sol-gel process, polyethylene glycol (PEG)-assisted sol-gel process, citrate sol-gel process and oxalate coprecipitation process (OCP) are employed to synthesize the Sm and Nd co-doped ceria electrolyte with the composition of Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) (SNDC). The phase structure of the powders can be well indexed with the fluorite-type CeO(2) structure. The morphology of sintered samples indicates that the ceramics can be highly densified. The relative density and the average grain size vary with the synthesis processes and the sintering temperatures. The bulk conductivities are quite close and the OCP-SNDC yields highest grain-boundary conductivities and total conductivities. The results indicate that the OCP process for the powder synthesis results in higher relative density and conductivities, lower grain-boundary resistance and activation energy. Grain-boundary space charge potentials for different specimens are calculated based on the Mott-Schottky model. The synthesis process and sintering temperature have significant effect on the space charge potential and the specific grain-boundary conductivity. (C) 2011 Elsevier B.V. All rights reserved.
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| 4. |
- Gao, Zhan, et al.
(författare)
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Electrical properties of ceria co-doped with Sm3+ and Lu3+electrolyte materials
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Sm and Lu co-doped ceria with compositions of Ce1-x(Sm3Lu2)x/5O2-δ (SLDC, x=0.05, 0.1, 0.15, 0.2) are investigated to validate the concept of critical dopant ionic radius ( rc ), where the number-average dopant ionic radius is designed tomatch the critical dopant ionic radius ( c r ). A variety of techniques including X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to characterize the SLDC powders and the sintered pellets. Electrical properties of different specimens are investigated by using the impedance spectroscopy. The result sdemonstrated that the critical dopant ionic radius concept is not totally valid for Sm-Lu co-doping strategy, even that the co-doping with appropriate chemicalcomposition, Ce0.85(Sm3Lu2)0.03O2-δ, yields higher total conductivity than either Smor Lu-doped ceria. More co-doping strategies need to be studied to test the critical dopant ionic radius concept.
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| 5. |
- Gao, Zhan, et al.
(författare)
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Enhanced ionic conductivity of Ce0.8Sm0.2O2-delta by Sr addition
- 2012
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 208, s. 225-231
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Tidskriftsartikel (refereegranskat)abstract
- Sm and Sr co-doped ceria-based electrolyte with compositions of Ce-0.8(Sm1-xSrx)(0.2)O2-delta (x = 0, 0.3, 0.5, 0.7) are synthesized and investigated with the aim of improving the electrical properties of Ce0.8Sm0.2O2-delta. X-ray diffraction (XRD) and electron microscope (SEM and TEM) techniques are employed to characterize the microstructure of powders and sintered pellets. The ionic conductivity has been examined by the A.C. impedance spectroscopy in air. The Ce-0.8(Sm0.7Sr0.3)(0.2)O2-delta exhibits the highest bulk conductivity among the series, which can be mainly ascribed to the increase of oxygen vacancy concentration. The specific grain-boundary conductivities are observed to increase with the Sr doping content up to x = 0.5. Further increase in Sr concentration will lead to reduced specific grain-boundary conductivities. The total conductivities of all Sm and Sr co-doped ceria are higher than that of Ce0.8Sm0.2O1.9. The results indicate that Sr co-doping opens a new avenue to improve ionic conductivity in Ce0.8Sm0.2O1.9.
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| 6. |
- Gao, Zhan, et al.
(författare)
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Investigation of oxygen reduction reaction kinetics on Sm(0.5)Sr(0.5)CoO(3-delta) cathode supported on Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) electrolyte
- 2011
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 196:22, s. 9195-9203
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Tidskriftsartikel (refereegranskat)abstract
- Sm(0.5)Sr(0.5)CoO(3-delta) (SSC) cathode prepared by a glycine-nitrate process (GNP) is investigated for solid oxide fuel cells (SOFCs) based on Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) (SNDC) electrolyte. SSC forms cubic perovskite structure after being annealed at 1100 degrees C for 5 h. SSC cathode and SNDC electrolyte can retain their own structure and there is no reaction between the two compositions. The microstructure of the cathode and the interfaces between cathodes and SNDC electrolytes are studied by scanning electron microscopy (SEM) after sintering at various temperatures. Impedance spectroscopy measurements reveal that area specific resistances (ASRs) of SSC-SNDC30 cathode are much lower than those of SSC cathode. Kinetics of oxygen reduction reaction (ORR) on porous SSC cathode is investigated by analysis of impedance spectra. Medium-frequency conductivities show no dependency on oxygen partial pressure (Po(2)), which can be attributed to the oxygen ions transfer across the electrode/electrolyte interface. The dependencies of low-frequency conductivities on oxygen partial pressure (Po(2)) vary in the range from ca. 0.31 to ca. 0.34 and increase with the increasing temperatures. The low-frequency electrode process is a mixing process involving oxygen reduction reaction related to atomic oxygen and oxygen ions conduction step together with total charge-transfer step. IR-compensated current density (i)-overpotential (eta) relationship is established and the exchange current densities i(0) originated from high-field approximations are much higher than those of low-field approximations and a.c. impedance data under OCV state. It demonstrates the polarization overpotential has great effect on the kinetics of ORR. The polarization current is observed to increase with time in the long-term stability measurement, which can be ascribed to the propagation process of oxygen vacancies.
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| 7. |
- Gao, Zhan, et al.
(författare)
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Novel BaZr0.1Ce0.7Y0.2O3-δ (BZCYO)-Ce0.8Y0.2O2-δ (YDC) composite ceramic electrolyte for low-temperature SOFCs
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Novel BaZr0.1Ce0.7Y0.2O3-δ (BZCYO)-Ce0.8Y0.2O2-δ (YDC) composite ceramic electrolyte possessing both proton and oxygen ion vacancies conduction was first reported. There are no chemical reactions between the two compositions. The composite ceramic electrolyte shows excellent chemical stability to reduction. BZCYO2-YDC8 exhibits the highest bulk ionic conductivities in the temperature range of 450 oC to 650 oC and total ionic conductivities when the temperatures are higher than 550 oC. The conductivity enhancement mechanism has been discussed. BZCYO-YDC composite ceramics may be promising electrolytes in low-temperature solid oxide fuel cells.a)
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| 8. |
- Justice, A. E., et al.
(författare)
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Genome-wide meta-analysis of 241,258 adults accounting for smoking behaviour identifies novel loci for obesity traits
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Few genome-wide association studies (GWAS) account for environmental exposures, like smoking, potentially impacting the overall trait variance when investigating the genetic contribution to obesity-related traits. Here, we use GWAS data from 51,080 current smokers and 190,178 nonsmokers (87% European descent) to identify loci influencing BMI and central adiposity, measured as waist circumference and waist-to-hip ratio both adjusted for BMI. We identify 23 novel genetic loci, and 9 loci with convincing evidence of gene-smoking interaction (GxSMK) on obesity-related traits. We show consistent direction of effect for all identified loci and significance for 18 novel and for 5 interaction loci in an independent study sample. These loci highlight novel biological functions, including response to oxidative stress, addictive behaviour, and regulatory functions emphasizing the importance of accounting for environment in genetic analyses. Our results suggest that tobacco smoking may alter the genetic susceptibility to overall adiposity and body fat distribution.
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| 9. |
- Kese, K., et al.
(författare)
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Contact residual stress relaxation in soda-lime glass Part I. Measurement using nanoindentation
- 2006
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 26:6, s. 1003-1011
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Tidskriftsartikel (refereegranskat)abstract
- The contact residual stress field created by a Vickers indentation is a micro-size region of high and varying stresses. Stress relaxation studies in such a micro-region may not be accessible to the conventional methods of investigation. In this paper the elastic response during nanoindentation has been used to study the isothermal stress relaxation of a Vickers residual stress field in soda-lime glass at 540 and 630 degrees C. At each temperature, the stress relaxation profile varied from one location of the stress field to the other suggesting non-linear response to stress. Also, the relaxation profiles at identical positions were different for the two temperatures suggesting that the Vickers residual stress field is not a thermorheologically simple region of material.
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| 10. |
- Kese, Kwadwo, et al.
(författare)
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Influence of residual stress on elastic modulus and hardness of soda-lime glass measured by nanoindentation
- 2004
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Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 19:10, s. 3109-3119
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Tidskriftsartikel (refereegranskat)abstract
- The influence of stress on the elastic modulus E and hardness H in soda-lime glass was studied in the Vickers residual stress field by nanoindentation. The Oliver-Pharr method of analysis first gave higher values of E and H, but after correcting for the pileup contact areas around the nanoindents, results consistent with literature values were obtained at regions in the stress field where the stresses were either low or close to zero. Determination of the pileup contact areas was made possible by the use of the atomic force microscope, which has facility for generating cross-section images of the indents. The elastic modulus was found to decrease with stress, which is explained with reference to the influence of applied stresses on the Si-O-Si bond angle. The hardness on the other hand did not depend on the stresses except in the region very close to the edge of the Vickers indent where the stresses are high.
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| 11. |
- Kese, Kwadwo, et al.
(författare)
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Method to account for true contact area in soda-lime glass during nanoindentation with the Berkovich tip
- 2005
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 404:1-2, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- An. empirical relationship for estimating the pile-up contact area from the contact stiffness, S and the contact depth, h(c) has been developed. This was achieved first by using the atomic force microscope to image nanoindents made with the Berkovich indenter in soda-lime glass and approximating the pile-up contact perimeter as a semi-ellipse. Then, by determining the pile-up contact area for several peak indentation loads, a correlation was found between the pile-up contact area and the load used to generate it. The importance of this new method of determining the pile-up contact area is that the need for indent imaging is made completely redundant, since the contact stiffness is a quantity that is routinely obtained during nanoindentation data analysis. Elastic modulus of soda-lime glass of 70 +/- 1.5 GPa is measured with loads ranging from 20 to 500 mN. The hardness measured also falls within the range of values, 5.2-5.9 GPa, normally quoted in the literature for the glass.
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| 12. |
- Kese, K. O., et al.
(författare)
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Contact residual stress relaxation in soda-lime glass Part II. Aspects relating to strength recovery
- 2006
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 26:6, s. 1013-1022
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Tidskriftsartikel (refereegranskat)abstract
- Strength recovery of Vickers indented soda lime glass was measured and compared after annealing at two temperatures: one below and one above T, The atomic force microscope was used to study the cracks. At 540 degrees C, no changes were observed in crack morphology either below the surface or on the surface relative to the pre-anneal state. At 630 degrees C, both sub-surface and surface crack morphology changes were observed. The trends in strength recovery were compared with residual stress relaxation as measured by a new method of stress estimation based on nanoindentation elastic response. At short hold times at 630 degrees C, and regardless of the length of hold time at 540 degrees C, strength recovery of only similar to 30% was measured while at moderately long hold times at 630 similar to C, strong recovery of fracture strength, similar to 132% was measured. Trends in strength recovery above T. are shown to match those of crack tip radius instead of trends in stress relaxation across the residual stress field.
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| 13. |
- Kese, K. O., et al.
(författare)
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Effect of ageing on the electrical resistivities of (Ba0.69Pb0.31)Ti-3 PTCR ceramic thermistors
- 2005
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 31:3, s. 375-378
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Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity of (Ba0.69Pb0.31)TiO3 PTCR ceramic thermistors aged at temperatures of 175, 200, 250 and 300 degrees C, respectively, were measured. When the samples were aged at temperatures of 175 and 200 degrees C, room-temperature resistivity decreased at the initial ageing stage, and then increased with the ageing time. The samples displayed a monotonous rise of the room-temperature resistivity when the ageing treatments were performed at 250 and 300 degrees C. PTCR effects showed different characteristics after different ageing treatments. These ageing characteristics were analyzed by considering interior oxidation and reduction reactions.
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| 14. |
- Kese, Kwadwo O., 1960-
(författare)
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Relaxation and nanomechanical studies of the vickers residual stress field in glass
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Vickers residual stress field (VRSF) in soda-lime glass results from the elastic-plastic contact event that takes place when a Vickers diamond pyramid is loaded onto the surface of the material in an indentation cycle. The importance of elastic-plastic indentation lies in the contact damage that it gives rise to in the surface of the glass. Since such surface flaws can be characterised, with respect to shape and size, they offer the opportunity to study naturally occurring flaws in glass and brittle materials in general. The residual stress field is not passive; rather it exerts a crack opening force on the associated crack system during subsequent strength testing of a Vickers-indented sample through a residual stress field coefficient, c. Besides the strength-controlling properties, the elastic-plastic contact residual stress field is also important as a region where the influence of mechanical excitation on material properties such as hardness, H, and elastic modulus, E, can be studied. This thesis concerns studies that were made to characterise the Vickers residual stress field by first measuring the magnitude and distribution of stresses around it, using nanoindentation with a cube corner tip. With a Berkovich tip in nanoindentation, experiments were conducted in the VRSF to study the dependence of hardness, H and elastic modulus, E, on stresses in soda-lime glass: a strong E dependence on stress was observed, while H was not affected unless the stresses were high. In the process, a method was developed to determine the true contact area during elastic-plastic nanoindentation when the Oliver-Pharr method is used for the data analysis. The observed elastic modulus dependence on stress was then utilised in a study where it was shown that the VRSF responds differently to relaxation annealing on either side of the glass transition temperature. This result was then used to explain strength recovery trends in annealed Vickers-indented glass specimens.
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| 15. |
- LAGERGREN, CARINA, et al.
(författare)
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SYNTHESIS AND PERFORMANCE OF LICOO2 CATHODES FOR THE MOLTEN CARBONATE FUEL CELL
- 1994
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 141:11, s. 2959-2966
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Tidskriftsartikel (refereegranskat)abstract
- A method for fabricating LiCoO2 electrodes has been developed. LiCoO2 powder was synthesized from Li2CO3 and CoCO3 powder by calcining in air at 650-degrees-C. Electrodes were tape cast in a nonaqueous slurry with and without a graphite poreformer. They were sintered in air at temperatures between 700 and 850-degrees-C. Powders and electrodes were characterized by using x-ray diffraction, thermogravimetric analysis, the Brunauer, Emmett, and Teller method, Hg porosimetry, scanning electron microscopy, and a van der Pauw conductivity measurement setup. The electrodes were electrochemically characterized by polarization measurements at different temperatures. Performance of the electrodes, with and without poreformer, respectively, was also determined by measuring polarization curves at different degrees of electrolyte fill.
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| 16. |
- Lapina, Alberto, et al.
(författare)
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Synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 powder by gel combustion route with two-step doping strategy
- 2012
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Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 32:10, s. 2325-2331
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Tidskriftsartikel (refereegranskat)abstract
- A two-step doping strategy was applied to the synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 (LSGM1020) powder by a gel combustion method. The Mg-doped LaGaO 3 powder was prepared in the first step, and Sr incorporation in the Mg-doped LaGaO 3 powder was done in the second step to obtain the final LSGM1020 powder. The two-step procedure is effective in preparing higher purity powders than the traditional one-step procedure. Rietveld refinement of X-ray powder diffraction (XRD) patterns shows that incorporation of Mg in LaGaO 3 in the first step enlarges the LaGaO 3 lattice: this facilitates the incorporation of Sr in the second doping step and thus high purity powder is obtained. Relatively phase pure LSGM1020 powder with only 3.1% of LaSrGaO 4 was obtained after calcination at 1300°C for 5h. Therefore, the two-step doping strategy is an effective procedure for the preparation of LSGM powders with high Sr- and Mg-doping levels.
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| 17. |
- Lapina, Alberto, et al.
(författare)
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Synthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85 powder by gel combustion route with two-step doping strategy
- 2012
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 32:10, s. 2325-2331
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Tidskriftsartikel (refereegranskat)abstract
- A two-step doping strategy was applied to the synthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85(LSGM1020) powder by a gel combustion method. The Mg-doped LaGaO3 powder was prepared in the first step, and Sr incorporation in the Mg-doped LaGaO3 powder was done in the second step to obtain the final LSGM1020 powder. The two-step procedure is effective in preparing higher purity powders than the traditional one-step procedure. Rietveld refinement of X-ray powder diffraction (XRD) patterns shows that incorporation of Mg in LaGaO3 in the first step enlarges the LaGaO3 lattice: this facilitates the incorporation of Sr in the second doping step and thus high purity powder is obtained. Relatively phase pure LSGM1020 powder with only 3.1% of LaSrGaO4 was obtained after calcination at 1300 degrees C for 5 h. Therefore, the two-step doping strategy is an effective procedure for the preparation of LSGM powders with high Sr- and Mg-doping levels.
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| 18. |
- Li, Shuai, et al.
(författare)
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A Polymer Complexing Route for Low Temperature Synthesis of Perovskite Lanthanum Aluminate Powder
- 2010
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Ingår i: HIGH-PERFORMANCE CERAMICS VI. ; 434 - 435, s. 863-867
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Konferensbidrag (refereegranskat)abstract
- Lanthanum aluminate powders were prepared via a polymer complexing method by using PEG as complexing agent. The LaAlO3 powder was characterized by XRD and SEM. The influence of processing parameters such as molar ratio of PEG monomers to metal cations (PEG:Men+) and aging process on the phase purity and powder morphology were investigated. The calcined powder with the PEG:Me ratio larger than 2:1 may contain the secondary phase, namely La2O3. The formation of phase pure LaAlO3 powder occurs when the PEG:Men+ ratio is 1:1 or enough gelation time is involved. Although the phase pure powder is obtained by this PEG method, all the single phase LaAlO3 powders are found to have seriously aggregated particles. The weakly agglomerated powder morphology is only found in the powders which contain La2O3.
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| 19. |
- Li, Shuai, et al.
(författare)
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Doping effect on secondary phases, microstructure and electrical conductivities of LaGaO3 based perovskites
- 2009
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 29:6, s. 1139-1146
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Tidskriftsartikel (refereegranskat)abstract
- The intermediate temperature electrolytes La1-xSrxGa1-yMgyO3-delta (LSGM, where delta=(x+y)/2) with perovskite structure were prepared using a poly(vinyl alcohol) (PVA) solution polymerization method. Three secondary phases were identified by X-ray diffraction, LaSrGaO4, LaSrGa3O7 and La4Ga2O9. The relative amount of these secondary phases depended on the doping compositions. Sr doping produced more Sr rich secondary phases with increasing content, while enhanced solid solubility was observed with Mg addition. Sintered samples showed dense microstructures with well-developed equiaxed grains, and the secondary phases were mainly in the grain boundaries. LaSrGaO4 could not be detected by SEM for the sintered pellets. The oxygen ionic conductivity was enhanced by doping with Sr and Mg. Mg doping showed the increased conductivity activation energy. La0.8Sr0.2Ga0.9Mg0.1O2.85 had the highest ionic conductivity sigma = 0.128 S/cm at 800 degrees C in this work.
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| 20. |
- Li, Shuai, et al.
(författare)
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Lanthanum gallate and ceria composite as electrolyte for solid oxide fuel cells
- 2010
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 492:1-2, s. 392-395
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Tidskriftsartikel (refereegranskat)abstract
- The composite of doped lanthanum gallate (La(0.9)Sr(0.1)Ga(0.8)Mg(0.2)O(2.85), LSGM) and doped ceria (Ce(0.8)Sm(0.2)O(1.9), CSO) was investigated as an electrolyte for solid oxide fuel cell (SOFC). The LSGM-CSO composite was examined by X-ray diffraction (XRD) and impedance spectroscopy. It was found that the sintered LSGM-CSO composite contains mainly fluorite CeO(2) phase and a minority impurity phase, Sm(3)Ga(5)O(12). The LSGM-CSO composite electrolyte shows a small grain boundary response in the impedance spectroscopy as compared to LSGM and CSO pellets. The composite electrolyte exhibits the highest conductivity in the temperature range of 250-600 degrees C, compared to LSGM and CSO. The LSGM-CSO composite can be expected to be an attractive intermediate temperature electrolyte material for solid oxide fuel cells.
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| 21. |
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| 22. |
- Li, Shuai, 1981-
(författare)
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Preparation and characterization of perovskite structure lanthanum gallate and lanthanum aluminate based oxides
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present work was initiated to study the synthesis and properties of lanthanum gallate based oxides as intermediate temperature electrolyte for solid oxide fuel cells. The wet chemical method, polymer complexing route, was used to prepare the precursor powders. To further investigate the polymer complexing method, it was also applied to the preparation of lanthanum aluminate based oxides. Single perovskite phase La0.8Sr0.2Ga0.83Mg0.17O2.815 can be prepared by the polymer complexing method using PVA as complexing agent. The thermal decomposition of the precursor powder undergoes three stages. While complete decomposition of the precursor is obtained at 1000°C. Further investigation of LaGaO3 doped with various amounts Sr or/and Mg was conducted. Three secondary phases were identified by X-ray diffraction, e.g. LaSrGaO4, LaSrGa3O7 and La4Ga2O9. The relative amount of these secondary phases depends on the doping compositions. Sr doping produced more Sr rich secondary phases with increasing content, while enhanced solid solubility was observed with Mg addition. Sintered samples showed dense microstructures with well-developed equiaxed grains, and the secondary phases were mainly in the grain boundaries. The oxygen ionic conductivity was enhanced by doping with Sr and Mg. Mg doping showed the increased activation energy of conductivity. Preliminary study showed that the lanthanum gallate and ceria composite electrolyte is mainly fluorite CeO2 phase after sintering. The minority secondary phase, Sm3Ga5O12, was also detected by XRD. The composite electrolyte showed superior electrical performance. It exhibited the highest conductivity in the temperature range of 250–600°C, compared with lanthanum gallate and ceria specimens. The phase pure perovskite La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 powders can easily be obtained by the polymer method using PVA as complexing agent. No secondary phase was detected after calcination at various temperatures (500–1100°C). The fully crystallized LaAlO3 phase was prepared after calcination at 900°C. Meanwhile the secondary phases were difficult to eliminate in the Sr- and Mg- doped LaGaO3 powder prepared by the same polymer method. It is thus concluded that the polymer, PVA in this work, provides more homogeneous mixing for cations of lanthanum aluminate based oxides, compared with the one for doped lanthanum gallate. The influence of different complexing agents, e.g. PVA and PEG, was investigated in the synthesis of lanthanum aluminate powders. Minority impurity La2O3 existed in the PEG powder, but it could be eliminated after sintering at high temperatures. Although the pure phase LaAlO3 can be easily obtained in PVA powders calcined at 950°C, more seriously aggregated particles existed. PEG showed advantages over PVA in terms of better densification and microstructure control in the sintered products. To select proper polymers in complex oxide synthesis, the agglomeration and morphology of the powder are the most important factors to be considered.
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| 23. |
- Li, Shuai, et al.
(författare)
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Synthesis and characterization of lanthanum aluminate powders via a polymer complexing plus combustion route
- 2012
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Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 132:2-3, s. 309-315
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Tidskriftsartikel (refereegranskat)abstract
- Lanthanum aluminate powders were prepared by a simple polymer complexing plus combustion method using PVA or PEG as complexing agent and fuel. The influence of different polymers on phase purity, powder morphology and sintering performance were investigated. Trace amount impurity La 2O 3 exists in the PEG powder, but it could be eliminated after high temperature sintering. The pure phase LaAlO 3 can be easily obtained in PVA powders calcined at 950 °C even severe aggregation always exists. PEG shows advantages over PVA in terms of the densification and microstructure control during sintering process. The high relative density of 97.0% and homogeneous fine microstructure with grain size < 3 μm can be obtained in the PEG-derived sample sintered at 1600 °C for 5 h. To obtain better quality LaAlO 3 powders through combustion route, PEG is preferred over PVA.
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| 24. |
- Li, Shuai, et al.
(författare)
-
Synthesis of La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 using a polymeric method
- 2009
-
Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 29:6, s. 1133-1138
-
Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 (LSAMC) powders were synthesized via a polymeric method using poly(vinyl alcohol) (PVA). The effect of PVA content on the synthesized powders was studied. When the ratio of positively charged valences (Mn+) to hydroxyl groups (-OH) is 1.5:1, crystalline LaAlO3 could be obtained at such a low calcination temperature as 700 degrees C. While at 900 degrees C the ratio is of less importance, since pure LaAlO3 perovskite could be formed for all powders after calcination at 900 degrees C. Thermal analysis (TG/DTA) was utilized to characterize the thermal decomposition behaviour of precursor powders. The chemical structure of the calcined powder was studied by Fourier transform infrared (FTIR) spectroscopy. The powder morphology and microstructure were examined by SEM. Dense pellets with well-developed submicron microstructures could be formed after sintering at 1450 degrees C for 5 h. Compared with the solid-state reaction method, the sintering temperature is substantially lower for powder prepared by the PVA method. This is due to the ultrafine and highly reactive powder produced.
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| 25. |
- Li, Yi, et al.
(författare)
-
Past, present and future of IEC and IEEE high-voltage and high current testing standards
- 2014
-
Rapport (refereegranskat)abstract
- Recently, IEC and IEEE have published a number of revised and new standards for high-voltage and high-current testing. Significant changes and additions have been introduced to these revised and new standards. CIGRE WG D1.35 has developed a guide to give high-voltage test engineers a broader knowledge of how to apply the latest high-voltage and high-current testing standards. The guide presents a brief account of the history of these standards with the aim to allow readers to gain a better appreciation of the technical background followed by sections summarize the major changes made to the standards in their latest revisions to provide a general picture of the revisions. Finally, some discussion is given on the practical implications of these changes. Practical examples are provided to illustrate some of the new techniques and new procedures. The guide also lists areas of possible improvements to the standards for future revisions.
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| 26. |
- Li, Z. C., et al.
(författare)
-
Electrical properties and ageing characteristics of BaTiO3 ceramics doped by single dopants
- 2005
-
Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 25:4, s. 441-445
-
Tidskriftsartikel (refereegranskat)abstract
- BaTiO3 ceramics doped by single dopants Of SM2O3, Ho2O3, Bi2O3, La2O3, CeO2 and Ta2O5, respectively, were prepared and aged in air. The room-temperature resistivity was measured and the relationship between resistivity change versus ageing time was determined. The electrical resistivity of Bi- and Ta-doped samples decreases at the early ageing stage, and then increases with the ageing time; the other doped ceramics display a monotonous increase of the resistivity with ageing time. The electrical properties and ageing characteristics are analyzed by considering interior oxidation and reduction reactions and the electronegativity of the doping elements.
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| 27. |
- Li, Z. C., et al.
(författare)
-
Synthesis and characterization of La0.85Sr0.15Ga0.85Mg0.15O3-delta electrolyte by steric entrapment synthesis method
- 2006
-
Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 26:12, s. 2357-2364
-
Tidskriftsartikel (refereegranskat)abstract
- Strontium and magnesium doped lanthanum gallate La0.85Sr0.15Ga0.85Mg0.15O3-delta (LSGM) oxygen ionic conducting ceramics were prepared by a steric entrapment synthesis (SES) method, which is a polymeric precursor synthesis method by using polyvinyl alcohol in aqueous solution. The perovskite LSGM phase formed essentially at a calcination temperature of 900 degrees C. Pure and single perovskite LSGM phase with high relative density of 97.1% was obtained after sintering at 1450 degrees C, while the relative density of the LSGM sample sintered at the same temperature by solid state reaction (SSR) method was 80.6% in present experiment. Comparing with SSR synthesis method, the sintering temperature by SES can be reduced at least 100 degrees C. Impedance spectra revealed that the grain-boundary resistivity of LSGM synthesized by SES was smaller than that by SSR method. and the conductivities of the samples by SES were higher than those by SSR method at all measuring temperatures.
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| 28. |
- Li, Z. C., et al.
(författare)
-
Synthesis and characterization of nanostructured Bi2O3-doped cerium oxides fabricated by PVA polymerization process
- 2008
-
Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 34:8, s. 1949-1953
-
Tidskriftsartikel (refereegranskat)abstract
- Bi2O3-doped ceria oxygen-ion conductors were prepared by a wet chemical synthesis method, which is per-formed by polymerization of polyvinyl-alcohol (PVA). The experiments showed that Bi2O3-CeO2 solid solution with 9.2 nm grains and pure fluorite type phase can be synthesized at a calcination temperature of 500 degrees C by PVA polymerization process. X-ray analysis revealed that high density narrostructured bulks could be prepared at a sintering temperature of 900 degrees C, and these bulk samples with an average grain size less than 70 nm could effectively be obtained at various heating rates during sintering. Oxygen-ion conductivity increased with the increase of dopant concentrations between 5 mol% and 15 mol% in present study.
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| 29. |
- Li, Z. C., et al.
(författare)
-
Synthesis of Sm-doped BaTiO3 ceramics and characterization of a secondary phase
- 2005
-
Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5107 .- 1873-4944. ; 116:1, s. 34-39
-
Tidskriftsartikel (refereegranskat)abstract
- Sm2O3-doped barium titanate ceramics with a positive temperature coefficient of resistivity (PTCR) were synthesized by solid-state reaction sintering. The electrical properties are related to the dopant content. The grain size decreases with increasing dopant content. Electron diffraction analysis revealed that a secondary phase with a space group of P6(3)22 and lattice parameters a = 10.6 Angstrom and c = 20.2 Angstrom formed in the ceramics.
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| 30. |
- Li, Z. C., et al.
(författare)
-
Thermal cycle characteristics of PTCR ceramic thermistors
- 2005
-
Ingår i: Sensors and Actuators A-Physical. - 0924-4247 .- 1873-3069. ; 118:1, s. 92-97
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal cycle treatment was performed in BaTiO3 and (Ba, Pb)TiO3 PTCR ceramic thermistors. When the treatment temperatures were higher than the Curie points, the room-temperature resistivities decreased at the initial thermal cycle stage, and then increased further with the thermal cycles. When the treatment temperatures were lower than Curie points, the room-temperature resistivities increased monotonously with the number of thermal cycle. The PTCR effects were also affected by the thermal cycle treatment. The oxygen absorption and oxidation were proposed for the monotonously increasing resistivity. Domain alternation and defect mechanisms were suggested to be the major cause for the resistivity decrease at the initial thermal cycle stage.
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| 31. |
- Li, Zhicheng, et al.
(författare)
-
Influence of AST additives on the stability of PTCR characteristics and microstructure in ferroelectric ceramics
- 2004
-
Ingår i: Journal of materials science. Materials in electronics. - 0957-4522 .- 1573-482X. ; 15:8, s. 561-567
-
Tidskriftsartikel (refereegranskat)abstract
- (Ba0.69Pb0.31)TiO3 ceramics were prepared using Al2O3, SiO2, additives and excess of TiO2 (AST). The characteristics of positive temperature coefficient of resistivity (PTCR) was studied and the corresponding microstructures were investigated using atomic force microscopy and scanning electron microscopy. The results showed that the PTCR effect was related to the AST additives. The maximum value of resistivity in the ceramics with lower content of or without Al2O3 and SiO2 additives was much lower than in those with AST additives. Ceramics with low AST content, which were heated by electric field to a temperature much higher than their Curie temperature, lost the PTCR effect after the electric field stimulation. The microstructure observations revealed that re-crystallization took place in the ceramics with lower content of or without AST additives resulting in the loss of the PTCR effect.
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| 32. |
- Li, Zhicheng, et al.
(författare)
-
Microstructure and PTCR effect of La-doped BaPbO3 ceramics
- 2004
-
Ingår i: Journal of materials science. Materials in electronics. - 0957-4522 .- 1573-482X. ; 15:3, s. 183-186
-
Tidskriftsartikel (refereegranskat)abstract
- La-doped BaPbO3 ceramics were prepared by using BaCO3 and PbO. Electrical properties and microstructure of the ceramics were studied. The results show a thin surface layer with a very low resistivity, and the interior of the ceramics with the characteristics of positive temperature coefficient of resistivity (PTCR). The PTCR behavior was related to the La content. The investigation by scanning electron microscopy and transmission electron microscopy revealed that the low resistivity of the surface layer was due to formation of a nano-size BaPbO3 phase with metallic properties.
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| 33. |
- Murugesan, S., et al.
(författare)
-
Direct evidence for purely silver ion conduction in Cul-doped silver oxysalt superionic systems : Combined electrolysis and EDS studies
- 2007
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 52:28, s. 8064-8068
-
Tidskriftsartikel (refereegranskat)abstract
- Maiden attempt has been made for the direct estimation of the contributions of silver and copper ions to the ionic conductivity in superionic solids obtained in CuI-doped silver oxysalt systems. The application of the combined electrolysis and EDS techniques towards qualitative and quantitative analyses of the mobile ionic species in solid electrolyte systems having more than one possible mobile ion is reported. These studies confirmed that these electrolyte materials are purely Ag+ conducting up to 50 mol% CuI in xCuI-(100-x)[2Ag(2)O-0.7V(2)O(5)-0.3B(2)O(3)] and xCuI-(100 - x)[Ag2O-0.7MoO(3)-0.3WO(3)] systems and small fraction of t(Cu+) exists above 60 mol% CuI. These solid electrolyte materials exhibited a high ionic transport numbers (t(i)) of >0.985 and the t(i) increases when two glass formers are used.
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| 34. |
- Murugesan, S., et al.
(författare)
-
Ion transport studies in CuI-doped silver borovanadate glassy system
- 2008
-
Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093 .- 1873-4812. ; 354:10-11, s. 1066-1073
-
Tidskriftsartikel (refereegranskat)abstract
- In the present report, ionic transport properties and microstructural investigations of superionic materials in a cost-effective glassy system xCuI-(100 - x)[2Ag(2)O-0.7V(2)O(5)-0.3B(2)O(3)], where x = 30, 40, 45, 50 and 60, have been described. The temperature dependent electrical conductivity studies were carried out by ac impedance analysis. The microstructure of the materials studied by SEM indicated the presence of dispersed CuO and AgI micro-crystals in the silver oxysalt glass matrix. High room temperature electrical conductivity of 3.58 x 10(-3) S cm(-1) and low activation energy of 0.24 eV were obtained for the best conducting composition. The ac impedance data were analyzed using impedance and modulus formalisms. These materials show extremely high t(i) value of 0.999 and the ionic conductivity is apparently due to Ag+ ions only. The use of two glass formers helped to form materials with higher T-g, higher thermal stability and better ionic transport properties.
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| 35. |
- Murugesan, S., et al.
(författare)
-
Preparation and characterization of CuI-doped silver borovanadate superionic system
- 2007
-
Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 178:11-12, s. 779-783
-
Tidskriftsartikel (refereegranskat)abstract
- A new cost effective glassy/crystalline superionic system xCul-(100-x)[2Ag(2)O-0.7V(2)O(5)-0.3B(2)O(3)], where x=30, 40, 45, 50 and 60, has been prepared by melt quenching technique and the ionic transport properties were studied. The phase analysis and thermal properties of the samples carried out using XRD, FTIR and DSC techniques confirmed the glassy-crystalline composite nature of the prepared materials. DSC analyses indicated the crystallization of some phases between 130 and 170 degrees C and the subsequent melting of these crystallized phases in the temperature range of 200-250 degrees C. The room temperature electrical conductivity studies were carried out by a.c. impedance analysis. High room temperature electrical conductivity of 3.58 x 10(-3) S cm(-1) was obtained for the best conducting composition. These materials show high t(Ag+) value of 0.997. The use of two glass formers helped to form materials with higher T, higher thermal stability and better ionic transport properties.
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| 36. |
- Ringuede, Armelle, et al.
(författare)
-
Solubility and electrochemical studies of LiFeO2-LiCoO2-NiO materials for the MCFC cathode application
- 2006
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 160:2, s. 789-795
-
Tidskriftsartikel (refereegranskat)abstract
- The dissolution of the state-of-the-art lithiated NiO is still considered as one of the main obstacles to the commercialisation of the molten carbonate fuel cell (MCFC). Development of alternative cathode materials has been considered as a main strategy for solving this problem. Ternary compositions of LiFeO2, LiCoO2 and NiO are expected to decrease the cathode solubility while ensuring a good electrical conductivity and electrochemical activity towards the oxygen reduction. In this work, new material compositions in the LiFeO2-LiCoO2-NiO ternary system were synthesised using Pechini method and investigating their electrical conductivity by the DC four probe method. Then the influence of the cobalt content in the composition was determined in terms of AC impedance analysis and solubility measurements after 200 h of immersion in Li2CO3-Na2CO3 at 650 degrees C. The DC electrical conductivity study reveals the ability of improving the electrical conductivity, adequate for MCFC cathode application, by controlling the Co content of the composition. A special attention was given to the evolution of the open circuit potential as a function of time and to the impedance spectroscopy characterization related to microstructure modifications. Taking into account solubility, electrical conductivity, as well as electrochemical performance in the fuel cell, this study reveals the possibility of using LiFeO2-LiCoO2-NiO ternary materials for MCFC cathode.
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| 37. |
- Smuk, O., et al.
(författare)
-
The effect of copper on secondary phase precipitation in duplex stainless steel - a thermodynamic calculations approach
- 2005
-
Ingår i: Zeitschrift für Metallkunde. - : Walter de Gruyter GmbH. - 0044-3093. ; 96:8, s. 918-923
-
Tidskriftsartikel (refereegranskat)abstract
- Thermodynamic calculations with Thermo-Calc software and the steel database TCFE3 was applied to investigate the precipitation behavior of industrial grades of duplex stainless steels with high copper content, 1.6 and 2.3 wt.%, Duplok 27 and DUP 27, respectively. Well-documented super duplex stainless grade SAF 2507 with copper content of 0.20 wt.% was used as the reference steel. The results of the calculations are compared with the experimental results obtained previously for these steels. It is shown that copper decreases the high-temperature limit of precipitation of sigma and chi phases and reduces the equilibrium amount of precipitated chi phase. Copper addition to a duplex stainless steel facilitates precipitation of chromium nitride phase and stabilizes it at elevated temperatures. The ferrite-austenite balance at high temperatures is also affected in these steels by the copper addition.
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| 38. |
- Smuk, Olena, et al.
(författare)
-
The effect of copper on secondary phase precipitation in duplex stainless steel - a thermodynamic calculations approach
- 2022
-
Ingår i: International Journal of Materials Research - Zeitschrift für Metallkunde. - : WALTER DE GRUYTER GMBH. - 1862-5282 .- 2195-8556. ; 96:8, s. 918-923
-
Tidskriftsartikel (refereegranskat)abstract
- Thermodynamic calculations with Thermo-Calc software and the steel database TCFE3 was applied to investigate the precipitation behavior of industrial grades of duplex stainless steels with high copper content, 1.6 and 2.3 wt.%, Duplok 27 and DUP 27, respectively. Well-documented super duplex stainless grade SAF 2507 with copper content of 0.20 wt.% was used as the reference steel. The results of the calculations are compared with the experimental results obtained previously for these steels. It is shown that copper decreases the high-temperature limit of precipitation of sigma and chi phases and reduces the equilibrium amount of precipitated chi phase. Copper addition to a duplex stainless steel facilitates precipitation of chromium nitride phase and stabilizes it at elevated temperatures. The ferrite-austenite balance at high temperatures is also affected in these steels by the copper addition.
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| 39. |
- Tennakoon, T. M. T. N., et al.
(författare)
-
Performance of LiCoO2 cathodes, prepared using the Pechini method, in molten carbonate fuel cells
- 1997
-
Ingår i: Journal of the Electrochemical Society. ; 144:7, s. 2296-2301
-
Tidskriftsartikel (refereegranskat)abstract
- The Pechini method has successfully been used to fabricate a high-purity, ultrafine, homogeneous LiCoO2 powder. The powder has been used to cast tapes together with a plastic pore former. Sintered tapes show a bimodal pore size distribution comparable to that of state-of-the-art NiO cathodes and a homogeneous distribution of the pores throughout the tape. It is also shown that total porosity can be changed while retaining approximately the same pore size distribution using different sintering temperatures. Cell characterization, in a 3 cm2 lab cell, was performed on three cathodes sintered at 850, 900, and 950°C with total porosity ranging from 57 to 69%. It is concluded that (i) the selected chemical powder preparation technique provides pure, stable LiCoO2 with high surface area and high electrical conductivity and (ii) the cathode sintered at 900°C possesses a compromise of both phase purity, maximum possible porosity, and particle size, and hence gives a cathode polarization of 88 mV for 160 mA/cm2 at 650°C under optimum electrolyte content, which is comparable to state-of-the-art lithiated NiO. However, the voltage loss due to the interface resistance between current collector and electrode is on the order of 100 mV, which leads to a less advantageous total cathode performance.
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| 40. |
- Wijayasinghe, Athula, et al.
(författare)
-
A study on LiCoO2-rich cathode materials for the MCFC based on the LiCoO2-LiFeO2-NiO ternary system
- 2004
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 49:26, s. 4709-4717
-
Tidskriftsartikel (refereegranskat)abstract
- A study performed in LiCoO2-rich LiCoO2-LiFeO2-NiO ternary materials for the molten carbonate fuel cell (MCFC) cathodes is reported in this paper. LiCoO2-LiFeO2-NiO ternary materials are considered as more viable alternatives to lithiated NiO, however, the work reported so far has mainly been focused on ternary compositions rich in LiFeO2 or NiO. The present work was carried out by investigating the electrical conductivity and microstructural characteristics of the new materials first in the form of bulk pellets and then in ex situ sintered porous-gas-diffusion (PGD) cathodes. The material study reveals the ability of preparing LiCoO2-LiFeO2-NiO ternary compositions with adequate electrical conductivity by controlling the LiCoO2 content. A bimodal pore structure, appropriate for the MCFC cathode, could be achieved in sintered cathodes prepared with fine powders and pore formers. Further, the cathode fabrication study indicates the nature of the compromise to be made between the electrical conductivity, phase purity, pore structure and porosity in optimization cathodes for MCFC application. The study shows the possibility of preparing LiCoO2-rich LiCoO2-LiFeO2-NiO cathodes with promising electrical and pore structural characteristics for the MCFC.
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| 41. |
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| 42. |
- Wijayasinghe, A., et al.
(författare)
-
LiFeO2-LiCoO2-NiO cathodes for molten carbonate fuel cells
- 2003
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 150:5, s. A558-A564
-
Tidskriftsartikel (refereegranskat)abstract
- Dissolution of the state-of-the-art lithiated nickel oxide cathode is a major obstacle for the development of molten carbonate fuel cell (MCFC) technology. LiFeO2 and LiCoO2 were reported earlier as the most promising alternative materials; however, they do not satisfactorily substitute for the state-of-the-art cathode material. A solid solution consisting of LiFeO2, LiCoO2, and NiO is expected to posses some desirable properties of these three materials. Powder compositions in the LiFeO2-NiO binary system and a ternary subsystem with a constant 50:50 molar ratio of LiFeO2:NiO were prepared by the Pechini method. After preliminary powder characterizations, the feasibility of new materials for MCFC cathode application was studied. Electrical conductivity and microstructural characteristics were investigated, first in the form of bulk pellets and then in ex situ sintered porous gas diffusion cathodes. Finally, the electrochemical performance of selected cathodes was evaluated by short-time laboratory scale cell operations. The electrical conductivity of the ternary compositions with 50:50 molar ratio of LiFeO2:NiO increases significantly with increasing LiCoO2 content up to about 25 mol %. Further increase of LiCoO2 content decreases conductivity. The cell study indicates the possibility of preparing cathodes suitable for MCFC application with a considerably high LiFeO2 content.
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| 43. |
- Wijayasinghe, A., et al.
(författare)
-
LiFeO2-LiCoO2-NiO materials for Molten Carbonate Fuel Cell cathodes. Part I : Powder synthesis and material characterization
- 2006
-
Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 177:1-2, s. 165-173
-
Tidskriftsartikel (refereegranskat)abstract
- Ternary compositions of LiFeO2LiCoO2 and NiO are expected to posses desirable characteristics for the Molten Carbonate Fuel Cell (MCFC) cathode application. This paper presents a detailed description of the synthesis of LiFeO2-LiCoO2-NiO powders as well as dense sintered materials together with a brief discussion on the common aspects and trends observed in the characterization of these materials for MCFC cathode application. Feasibility of two wet-chemical powder preparation techniques, the Pechini method and the glycine-nitrate method, was investigated to obtain powders with characteristics appropriate for cathode fabrication. Materials in the LiFeO2-NiO binary system and five ternary subsystems, each with a constant molar ratio of LiFeO2/NiO while varying LiCoO2 content, were studied. Powders with characteristics appropriate for MCFC cathode fabrication could be obtained by the Pechini method. The particle size of LiFeO2-LiCoO2-NiO powders considerably depends on the calcination temperature and the material composition. The electrical conductivity study reveals the ability of preparing LiFeO2-LiCoO2-NiO materials with adequate electrical conductivity for MCFC cathode application.
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| 44. |
- Wijayasinghe, A., et al.
(författare)
-
LiFeO2-LiCoO2-NiO materials for Molten Carbonate Fuel Cell cathodes. Part II. Fabrication and characterization of porous gas diffusion cathodes
- 2006
-
Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 177:1-2, s. 175-184
-
Tidskriftsartikel (refereegranskat)abstract
- LiFeO2-LiCoO2-NiO ternary materials are considered as more viable alternatives to lithiated NiO2 in solving the cathode dissolution problem of the Molten Carbonate Fuel Cell (MCFC). This paper presents a detailed description of fabrication and characterization of LiFeO2-LiCoO2-NiO porous gas diffusion cathodes for MCFC, together with a brief discussion on the limitations and trends observed in cathode optimization. Several LiFeO2-LiCoO2-NiO ternary compositions and a LiFeO2-NiO binary composition, were fabricated into porous cathodes by tape casting and sintering. The sintered cathodes were subjected to phase analysis, electrical conductivity and pore structural characterization. A bimodal pore structure, appropriate for the MCFC cathode, could be achieved in sintered cathodes prepared using poreformers and sub-micron size powders. The amount of poreformers significantly influences the pore structure and the electrical conductivity of sintered cathodes. Furthermore, this study indicates the nature of the compromise to be made between the electrical conductivity, phase purity, pore structure and porosity in optimization cathodes for the MCFC application.
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| 45. |
- Zhang, H., et al.
(författare)
-
Fabrication and conductivities of CeO2-based oxygen-ion conductors doped by M2O3 (M=La, Nd, Sm and/or Ga)
- 2008
-
Ingår i: Key Engineering Materials. ; , s. 244-246
-
Konferensbidrag (refereegranskat)abstract
- Ceria oxygen-ion conductors doped with M2O3 (M=La, Nd, Sm and/or Ga) were prepared by a wet chemical method. Phases were analyzed by X-ray diffraction method and conductivities were measured by using AC impedance analyzer. The results showed that Ga2O3-CeO 2 solid solution with 17 nm grains and pure fluorite phase had been obtained even at calcination temperature of 800 °C for 5 hs. Conductivities of Ga2O3-La2O3 co-doped CeO2 were higher than that of Sm2O3-doped CeO2, which was reported having the highest conductivity among CeO2-based oxides.
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| 46. |
- Zhang, H., et al.
(författare)
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Investigation of La9.33Si6O26 oxygen ionic conductor
- 2007
-
Ingår i: Journal of Materials Science & Technology. - 1005-0302. ; 23:5, s. 629-632
-
Tidskriftsartikel (refereegranskat)abstract
- La9.33Si6O26 oxygen ionic conductor was synthesized by solid state reaction method. Its structure was determined by single-crystal X-ray diffraction analysis at room temperature. The results showed that La9.33Si6O26 oxide has the apatite structure with space group P6(3)/m. AC impedance measurements indicated that the oxides sintered in nitrogen have much higher conductivity than those sintered in air. The effects of grain boundaries on the conductivity were discussed.
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