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1998 |
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Monday, May 03, 2010, Moor Room 3:00 PM Power Engineering and SOFC 1 |
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Plasma spraying of lanthanum silicate electrolytes for intermediate temperature solid oxide fuel cells |
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Sophie Dru* / CEA Le Ripault, FRANCE Karine Wittmann-Tenèze / CEA-DAM LE RIPAULT, FRANCE Erick Meillot/ CEA-DAM LE RIPAULT, FRANCE Marie-Louise Saboungi/ CRMD, FRANCE Roland Benoit/ CRMD, FRANCE |
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An important task in Solid Oxide Fuel Cell (SOFC) development is to reduce the operating temperature down to 700°C in order to avoid premature ageing of the cell components. At such a temperature, the usual electrolyte materials, like yttria-stabilized zirconia (YSZ), do not present anymore such good performances. Apatite ceramics seem to be interesting alternative SOFC electrolytes due to a high ionic conductivity and a good chemical stability. This work reports the manufacturing and the characterization of apatite La9Sr1Si6O26.5 coating realized by Atmospheric Plasma Spraying (APS) with different plasma gas mixtures. The in-flight particles properties were studied in order to understand plasma forming gas influence on coatings microstructure and composition. From the parametric study of plasma spraying conditions, quite dense apatite coatings were manufactured (only some percents of porosity measured). X-Ray Diffraction (XRD) analysis report that crystallized apatite phase and amorphous are present in all the plasma sprayed coatings. A possible explanation is that particles and substrate temperature is so different during the coating manufacturing that particles are quenched when they spread on the substrate, this phenomenon leads to amorphous formation. A study by scanning electronic microscopy on different coatings revealed chemical contrasts in apatite coatings. An analysis by electron dispersive spectroscopy showed that some areas are either poor in Si or rich in La. They may correspond to the amorphous phases detected by XRD. A sintering step was achieved on plasma sprayed coatings. Their characterization revealed a lower porosity and so a higher gas tightness. The results obtained by XRD showed that the sintering step lead to a complete crystallization of the coating under apatite and La2O3 phases. The apatite coatings ionic conductivity of as-sprayed and sintered coatings was measured by impedance spectroscopy. The ionic conductivity is dependent on the spraying conditions and improves after the sintering step. |