| 1. |
- Magraso, A., et al.
(författare)
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In situ high temperature powder neutron diffraction study of undoped and Ca-doped La28-xW4+xO54+3x/2 (x=0.85)
- 2013
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 1:11, s. 3774-3782
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Tidskriftsartikel (refereegranskat)abstract
- In situ neutron diffraction experiments of 2% Ca-doped and nominally undoped lanthanum tungstate (La28-xW4+xO54+3x/2, with x = 0.85) have been carried out under controlled pD(2)O and pO(2) at elevated temperatures. All the diffraction patterns could be refined using an average cubic fluorite-related structure, in accordance with recent reports. The material exhibits disorder of the oxygen and the cation sublattices. Splitting of the oxygen sites around tungsten from the 32f to 96k Wyckoff position in the Fm (3) over barm space group improves the model and can better represent the oxygen disorder. No phase transition was detected from room temperature up to 800 degrees C under any of the studied conditions. Expansion of the unit cell constants in the presence of water at intermediate and low temperatures was correlated with the formation of protonic defects. The thermal expansion coefficient for lanthanum tungstate is rather linear under all studied conditions (similar to 11 x 10(-6) K-1). The in situ diffraction studies are correlated with dilatometry investigations and conductivity measurements.
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| 2. |
- Froitzheim, Jan, 1981, et al.
(författare)
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Nano coated interconnects for SOFC (NaCoSOFC)
- 2013
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 57:1, s. 2187-2193
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Konferensbidrag (refereegranskat)abstract
- The NaCoSOFC project is focused on the development of nano coatings for SOFC interconnects. The project is sponsored by the Nordic Top Level Research Initiative and has four project partners: Sandvik Materials Technology which is producing coated interconnects, Chalmers University of Technology and the University of Oslo that characterize samples with respect to e.g. corrosion, Cr evaporation and ASR as well as Topsoe Fuel Cell that is testing the developed interconnects in its stacks. The developed coatings are based on a combination of Co with RE elements and exhibit high corrosion resistance, 10 fold decrease in Cr evaporation and ASR values that are approximately 50% of the uncoated material.
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| 3. |
- Knee, Christopher, 1973, et al.
(författare)
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Structural transitions and conductivity of BaPrO3 and BaPr0.9Y0.1O3-d
- 2009
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Ingår i: J. Mater. Chem. - : Royal Society of Chemistry (RSC). ; 19, s. 3238-3247
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Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of the crystal structures of the perovskites BaPrO3 and BaPr0.9Y0.1O3-d has been determined between room temperature and 900 °C using time-of-flight neutron powder diffraction data. The orthorhombic room temperature structures evolve to a primitive cubic cell via three changes of symmetry Pnma -> Imma -> R-3c -> Pm-3m which occur at T~240, ~375, and ~860 °C for BaPrO3. The stability fields of the Pnma and Pm-3m structures are lowered markedly by the presence of yttrium on the B-site. The first and last structural transitions are assigned as continuous events, and analysis of the octahedral tilt angle order parameter suggests the latter is tricritical in nature. The Imma -> R-3c transition is expected to be discontinuous first order and hysteresis effects in dilatometry data support this assignment although no discontinuity is found in the refined structural parameters. Conductivity data collected under dry, oxidising conditions reveal significantly higher conductivity levels in 10% acceptor (Y or Gd) substituted samples compared to undoped BaPrO3. For the acceptor substituted samples electron holes are the dominant charge carriers and the conductivity is weakly influenced by the changing crystal structure. In the undoped BaPrO3, a crossover, probably between extrinsic (impurity-derived) and intrinsic electronic conductivity, coincides with the high temperature rhombohedral to cubic transition.
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| 4. |
- Magraso, A., et al.
(författare)
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Reduced long term electrical resistance in Ce/Co-coated ferritic stainless steel for solid oxide fuel cell metallic interconnects
- 2015
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 40:27, s. 8579-8585
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Tidskriftsartikel (refereegranskat)abstract
- The present study is focused on the influence of selected coatings on a ferritic stainless steel (Sanergy HT (TM), Sandvik) on the evolution of the area specific resistance (ASR) as a function of time at high temperature. The samples are exposed in humidified air at 850 degrees C for up to 4200 h. It combines long-term ASR measurements with the thermogravimetric behavior and microstructural analysis of the cross sections by scanning electron microscopy. The results show that uncoated and Co-coated Sanergy HT (TM) exhibit similar oxidation kinetics and comparable ASRs, while a combined Ce/Co coating improves oxidation resistance and, consequently, reduces the ASR significantly. Other reports have earlier shown that Co- (and Ce/Co)-coated Sanergy HT (TM) reduces the evaporation of volatile chromium species. Overall, the study indicates that Ce/Co-coatings will render substantially improved performance for ferritic steel interconnects for solid oxide fuel cells.
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