Yi-Cheng Liou*, Pei-Hung Yeh, Ming-Jih Lin

1. Materials and Austceram 2007 July 4 - 6, 2007, Sydney , Australia La0.9Sr0.1Ga0.57Mn0.43O3 ANODE CERAMICS OF SOLID OXIDE FUEL CELLS PRODUCED USING REACTION-SINTERING PROCESS Yi-Cheng Liou*, Pei-Hung Yeh, Ming-Jih Lin Department of Electronics Engineering, Kun Shan University, Tainan Hsien 71003, Taiwan, R.O.C. *Corresponding author. ycliou@mail.ksu.edu.tw La0.9Sr0.1Ga0.57Mn0.43O3 (LSGM) anode ceramics of solid oxide fuel cells produced using a reaction-sintering process were investigated.Without any calcination involved, the mixture of La2O3, SrCO3, Ga2O3 and MnO2 was pressed and sintered directly. Porous LSGMceramics could be obtained at 1230-1270oC for 2 and 4 hours sintering. Temperatures higher than 1270oC are too high to obtain useful porous LSGM ceramics for 6 h soak time. A lower sintering temperature is needed in preparing LSGM ceramics using a reaction-sintering process than using the conventional solid oxide method. Reaction-sintering process has proven a simple and effective method in preparing LSGM ceramics for applications in solid oxide fuel cell anode. The XRD patterns of LSGM ceramics are shown in figure 1. All the diffraction peaks match with peaks of ICDD PDF # 01-070-8683 (La0.73Sr0.27Ga0.1Mn0.9O3) and no second phases were found. Therefore, the reaction-sintering process is proven effective in preparing LSGM ceramics. This simple process is effective not only in preparing BaTi4O9, Ba5Nb4O15, Sr5Nb4O15, CaNb2O6, NiNb2O6 and Pb-based complex perovskite ceramics but also effective in preparing LSGM ceramics. In Fig. 2, the SEM photographs of LSGM ceramics sintered at 1230oC to 1300oC for 2 h are shown. Porous pellets with fine grains were formed at 1230-1270oC/2 h sintering. Grains >10μm can be easily found in 1300oC/2 h sintering pellets. Pores are needed in anodes of SOFCs for the transformation of fuel gas. The SEM photographs of LSGM ceramics sintered at 1230oC to 1300oC for 4 h are illustrated in figure 3. Porous pellets with fine grains were still found at 1230-1250oC sintering. Grain growth increased clearly in pellets sintered at 1270oC. In our investigation of La0.8Sr0.2Ga0.83Mg0.17O2.815, grains of size less than 4μm were formed in pellets sintered at 1300oC for 2-6 h. This indicates larger grains formed in Mn substituted than in Mg substituted LaSrGaO3 ceramics. Figure 4 shows the SEM photographs of LSGM ceramics sintered at 1230oC to 1300oC for 6 h. Porous pellets with fine grains were found again at 1230-1250oC/6 h sintering. Grains larger than 10μm can be easily found in 1270oC and 1300oC sintering pellets. Anodes of SOFCs must be poroustoallow gastransportto the reaction sites. Amount of pores could be easily controlled by adjusting the sintering temperature or soak time in LSGM ceramics prepared using reaction-sintering process. This method is proven a simple and effective method to obtain useful LSGM anode material for SOFC. The shrinkage percentage of LSGM ceramics sintered at different temperatures and soak times are shown in Fig. 5. It increased from 10-14% at 1230oC to 20-25% at 1300oC and reached a maximum value 24.12% at 1300oC/6 h. The density of LSGM ceramics increased with the sintering temperature and reached a maximum value 6.4 g/cm3 at 1300oC/6 h as shown in Fig. 6. From the discussion above, porous LSGM ceramics could be obtained at 1230-1270oC for 2 and 4 hours sintering. Temperatures higher than 1270oC are too high to obtain useful porous LSGM ceramics for 6 h soak time. In LSGM prepared via conventional solid oxide method, Hsu et al. found the open porosity of LSGM dropped sharply from 30 to 5% at 1350°C/4 h sintering. It implies a lower sintering temperature is needed in preparing LSGM ceramics using a reaction-sintering process. Fig. 2 SEM photographs of LSGM ceramics sintered at (A) 1230oC, (B) 1250oC, (C) 1270oC, and (D) 1300oC for 2 h. Fig. 3 SEM photographs of LSGM ceramics sintered at (A) 1230oC, (B) 1250oC, (C) 1270oC, and (D) 1300oC for 4 h. Fig. 4 SEM photographs of LSGM ceramics sintered at (A) 1230oC, (B) 1250oC, (C) 1270oC, and (D) 1300oC for 6 h. Fig. 6 Density of LSGM ceramics sintered at various temperatures and soak times. Fig. 5 Shrinkage of LSGM ceramics sintered at various temperatures and soak times. Fig. 1 XRD patterns of LSGM ceramics sintered at 1230oC and 1250oC for 2 h. (Standard pattern of La0.73Sr0.27Ga0.1Mn0.9O3: ICDD PDF # 01-070-8683 is used for comparison.)