1. Novel processing route of La9.33Si2Ge4O26 electrolytes for SOFCs combining mechanical alloying and microwave hybrid sintering B. Trindade 1 , A. Cavaleiro 1, C. Alves2, F.A.C. Oliveira2 , T. Marcelo2, J. Mascarenhas2 1 CEMUC, Mechanical Engineering Department, University of Coimbra 2 Laboratrio Nacional de Energia e Geologia I.P., Lisboa 1Materiais 2013, Coimbra, Portugal, March 25 27, 2013

2. 2 Advantages over traditional energy conversion systems: cleaner and more efficient fuel adaptability reliability modularity durability CathodeAnode Electrolyte Fuel cell is a device that generates electricity by a chemical reaction. Fuel Cell 3. 3 Traditional: Yttria-stabilised zirconia (YSZ) New Materials: Lanthanum oxides La9.33Si2Ge4O26 The requirements for the electrolyte are: high ionic conductivity very low electronic conductivity high hardness chemical stability thermal expansion coefficient compatibly with the other parts of the cell New Materials Electrolite 4. 4 Microstruture Ionic conductivity Sintering conditions The ionic conductivity varies strongly with the sintering conditions Different sintering conditions will result in diverse microstructure characteristics Microstructure with full density and suitable grain size are essential for a high-performance ionic conductor Summary 5. 5 MillingPre-Milling La2O3 + SiO2 + GeO2 (99.9% purity) 7La2O3:3SiO2:6GeO2 Sintering Microwave (MW) La9.33Si2Ge4O26 Pressing Cold Uniaxial Pressing Milling & Sintering 6. 6 Initial Powders (raw materials) La2O3 SiO2 GeO2 SiO2 GeO2 Intensidade(unid.Arb.) 20 30 40 50 60 La2O3 2 () ICDD 85-1515 ICDD 85-0930 ICDD 83-1344 La2O3 SiO2 GeO2 RESULTS 7. 7 Milling (with premilling) Intensity(arbitraryunits) 2q () 20 25 30 35 40 45 50 55 60 La9.36Si3Ge3O26 (card 75-3458) (300) (202) (200) (111) (002) (102) (210) (211) (112) (213) (222) La9.33Si6O26 (card 49-0443 ) (211) (112) (300) (202) (200) (111) (002) (102) (210) (213) (222) XRD SEM Nanometric apatite phase (20 nm) after milling Nanometric Apatite Phase RESULTS 15h 8. 8 Density and open porosity 0 1 2 3 4 5 6 Density (g.cm-3) Open Porosity (%) 5,36 2,96 RESULTS Theoretical density value of La9.33Si2Ge4O265.446 g.cm-3 9. 9 Microstructure The grain size of MW sample is about 1.9 m Sintered Samples MW 10 m 10. 10 Thermal Expansion Thermal Expansion Coefficient: Temperature-700C Microwave (MW) Values similar to the ones of yttria-stabilized zirconia electrolytes normally used in SOFCs. 11. 11 a b Oxyapatite-based La9.33Si2Ge4O26 samples for SOFC electrolytes have been prepared by conventional and microwave hybrid sintering at 1350C (250C lower than conventional processes) Quite dense samples were obtained independently of the sintering process. Almost full dense sample was obtained by MW powders with promising mechanical properties. The ionic conductivity values of sintered samples did not show any relevant dependence on the different production parameters. Microwave hybrid sintering is a novel suitable process for the densification of La9.33Si2Ge4O26 powders. Conclusions