Yi-Cheng Liou*, Wen-Chou Tsai, Chii-Shyang Huang

1. Materials and Austceram 2007 July 4 - 6, 2007, Sydney , Australia REACTION-SINTERING PROCESS FOR CALCIUM-DOPED LANTHANUM CHROMITE INTERCONNECT CERAMICS OF SOLID OXIDE FUEL CELL Yi-Cheng Liou*, Wen-Chou Tsai, Chii-Shyang Huang Department of Electronics Engineering, KunShan University, Tainan Hsien 71003, Taiwan, R.O.C. *Corresponding author. ycliou@mail.ksu.edu.tw Calcium-doped lanthanum chromite La0.7Ca0.31CrO3 (LCC) interconnect ceramics of solid oxide fuel cellsprepared using a reaction-sintering process were investigated. Without any calcination involved, the mixture of La2O3, CaCO3, and Cr2O3 was pressed and sintered directly. Shrinkage percentage increased from 8-9% at 1100oC to 26-27% at 1250-1300oC. Density increased with sintering temperature and reaches a maximum value 6.01 g/cm3 at 1300oC/6 h. Results indicate that reaction-sintering process could be a proper approach to prepare LaCaCrO3 ceramics for interconnects in solid oxide fuel cells. Fig.1 shows the XRD patterns of the LCC ceramics sintered at 1100oC to 1300oC for 6 h. All the diffraction peaks match the ones of ICDD PDF #00-055-0921 (La0.7Ca0.3CrO3) and no second phases were found even for the sample sintered at 1100oC. Therefore, the reaction-sintering process is proven effective in preparing LCC 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 LCC ceramics. SEM photographs of the LCC ceramics sintered at 1100oC to 1300oC for 2 h are shown in Fig. 2. At sintering temperature lower than 1200oC, the ceramics are porous and loosely constructed. At sintering temperature over 1200oC, we found some grains of rectangular, thin slice, or other shapes. Less porosity is found and grains began to grow and the ceramics were under densification. However, the dominant outline of LCC grains is not clear and the grains grow mildly in size with increasing sintering temperature. Fig. 3 shows SEM photographs of the LCC ceramics sintered at 1100oC to 1300oC for 6 h. These figures illustrated a similar grain growing phenomena to that for 2 h, that is, the LCC ceramics sintered below 1200oC are porous and loosely constructed and the grains grow mildly in size with increasing sintering temperature. Thus an increase of soaking time does not result in much bigger grain size. Shrinkage percentage of LCCceramics increased from 8-9% at 1100oC to 26-27% at 1250-1300oC as shown in Fig. 4. The figure reveals that a temperature of 1200oC is high enough for densification of LCC ceramics. Fig. 5 shows the density of the LCC ceramics sintered at 1100oC to 1300oC for 2-6 h. The density increases linearly with increasing sintering temperatures up to 1200oC. At sintering temperature over 1200oC, the density saturated around 6 g/cm3 regardless of the 2-6 h soaking time. The highest density is 6.01 g/cm3 for samples sintered at 1300oC for 6 h, which corresponds to a relative density of 98.8% if a theoretical density 6.084 g/cm3 of La0.7Ca0.3CrO3 is used. In La0.9Ca0.1CrO3 and La0.8Ca0.2CrO3 prepared using hydrothermalmethod and sintered at 1400oC for 5 h, Rivas-Vázquez and co-workers reported a relative density of 96.8% and 97.7% was obtained, respectively. Since interconnects in solid oxide fuel cells need to be of high density, our reaction-sintering process could be a suitable approach in preparing dense LCC ceramics. Fig. 3 SEM photographs of the LCC ceramics sintered at (A) 1100oC, (B) 1150oC, (C)1200oC, (D) 1250oC, and (E)1300oC for 6 h. Fig. 2 SEM photographs of the LCC ceramics sintered at (A) 1100oC, (B) 1150oC, (C)1200oC, (D) 1250oC, and (E)1300oC for 2 h. Fig. 4 Shrinkage percentage of LCC ceramics sintered at varioustemperatures and soak time. Fig. 5 Density of LCC ceramics sintered at various temperatures and soak time. Fig. 1 XRD patterns of the LCC ceramics with 1wt％ B2O3 addition and sintered at 1100-1300oC for 6h. (La0.7Ca0.3CrO3: ICDD PDF#00-055-0921)