Characterization of Ca2+ Doped Lanthanum Chromate Film Prepared by Plasma-spray Process for Solid Oxide Fuel Cell Separator
Tomoo IWATA
Fuji Electric Corporate Research and Development, Ltd.; 2-2-1 Nagasaka, Yokosuka-shi 240-0101 Japan
Present address: Fuji Electric Co., Ltd.; 1-11-2 Osaki, Shinagawa-ku, Tokyo 141-0032 Japan
A composite ceramic separator of La(Ca) CrO3/La(Sr) MnO3 has been developed for a substrate-type, planar solid oxide fuel cell. La(Ca) CrO3 was plasma-sprayed onto the porous thick La(Sr) MnO3 substrate. As-sprayed films of calcium(II)-doped lanthanum chromate, La0.7Ca0.35Cr0.95O3 and La0.8Ca0.22Cr0.98O3 showed high gas permeability of 10−7 10−6 cm4g−1 s−1 and SEM observation showed surface cracks. After sintering the as-sprayed films at 1473 K for 2 h in air, the sintered films showed no surface cracks and showed improvement of gas permeability of less than 1× 10−8 cm4 g−1 s−1. The peaks of CaCrO4 and La2 CrO6 were observed in the XRD spectra of the powders and as-sprayed films for both components of La(Ca) CrO3. However, those peaks disappeared and the peaks of La2O3 and CaO were observed in the sintered films. The lattice parameters of the sintered films of La0.7Ca0.35Cr0.95O3 were larger than those of the as-sprayed films, whereas those of La0.8Ca0.22Cr0.98O3 were almost same before and after the sintering. WDX-SEM analysis of the sintered films of La0.7Ca0.35Cr0.95O3 showed that CaO precipitated like an island on the surface of the sintered films. During the sintering process, dissolution of CaCrO4 and La2CrO6 seems likely to promote sintering of La(Ca) CrO3. However, La2O3 and CaO precipitated from the melted CaCrO4 and La2CrO6 accompanied with the sintering process of La(Ca) CrO3. Because of the low CaO precipitation in the sintered films, La0.8Ca0.22Cr0.98O3 is considered to be preferable materials for solid oxide fuel cell composite ceramic separators.
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