Apresentação Universidade de Coimbra na 3ª Conferência Anual do Energyin

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 Laboratório 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 (º)
ICDD
85-1515
ICDD
85-0930
ICDD
83-1344
La2O3
SiO2
GeO2
RESULTS

7. 7
Milling (with premilling)
Intensity(arbitraryunits)
2q (º)
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-700ºC
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 1350ºC
(250ºC 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