• PDF / 549,270 Bytes
• 6 Pages / 576 x 792 pts Page_size
• 40 Downloads / 211 Views

DOWNLOAD

REPORT

---

A simple and convenient method for low-temperature synthesis of Lao.84Sr0.i6Mn03 powder is described. The technique involves autoignition of a carboxylate (citrate + acetate)-nitrate gel resulting from a thermally induced anionic oxidation-reduction reaction to yield an ash, which upon calcination produces the desired powder. The resulting powder is pure, homogeneous, and possesses ultrafine particle size of the order of 0.3 to 0.5 //.m. The autoignition is restricted to a particular range of carboxylate to nitrate ratio in the gel. Attempts have been made to understand the ignition process with the help of Thermogravimetry (TG) and Differential Thermal Analysis (DTA) of the samples. The process appears to have a higher degree of reproducibility and a good material yield (more than 96%) suitable for large-scale production.

I. INTRODUCTION High-temperature solid oxide fuel cells (SOFC) have been extensively investigated for the last two decades because of their potential use as clean and efficient power-generating devices. Strontium-doped lanthanum manganite is known to be a very promising cathode material for SOFC's based on stabilized zirconia electrolyte.1 A nominal composition of Lai-jSr^MnC^ (x =£ 0.2) is normally used in present generation SOFC's because of its high electrical conductivity, thermal and chemical stability at the working temperature, and its compatibility with the zirconia electrolyte. 2 ^ However, it is evident that maintaining compositional homogeneity is an important criterion for obtaining many of these properties in a reproducible manner. Hence, the preparation of the compound by chemical methods has attracted a great deal of interest in recent years. Several preparation techniques based on solution chemistry methods, such as the citrate-gel process,5*7 sol-gel process,8'9 co-precipitation technique,10"12 freeze-drying process,12'13 and combustion processes14'15 have been attempted for the preparation of highly homogeneous and fine powders of these perovskite oxide materials. In order to overcome the experimental difficulties associated with the amorphous citrate process, particularly the adherence of the gel to the container wall arising from its sticky nature, a modified process, termed as "autoignition process," has been successfully tried recently for the preparation of fine and homogeneous powders of 123 and bismuth superconducting oxides.16'17 In this process a particular citrate to nitrate ratio is maintained to initiate

^Present address: Ceramic Technological Institute, Bharat Heavy Electricals Ltd., Bangalore, India. 986 http://journals.cambridge.org

J. Mater. Res., Vol. 9, No. 4, Apr 1994 Downloaded: 21 Mar 2015

the self-propagating combustion process between the reducing citrate and oxidizing nitrate group. In the present investigation, the above method is further modified and used for the preparation of lanthanum manganite-based oxides at relatively low temperatures. In addition to the citrate to nitrate ratio, the effect of acetate to nitrate ratio on the self-combustion pr