Sathi R. Nair

Nanocrystalline Electroceramics by Combustion Method

Solution‐combustion is a simple and cost‐effective technique, to synthesize phase pure, nano crystalline powders having high surface area and better sinterability. The potential of combustion technique in synthesizing several electro ceramics, having application in Solid Oxide Fuel Cells (SOFC), has been explored. These nanopowders were characterized in terms of X‐ray diffraction, surface area analysis, electron microscopy, sinterability and conductivity data. The main outcome of this work was preparation of highly sinter‐active powders.

Development of Ca-doped LaCr03 feed material and its plasma coating for SOFC applications

In order to realize SOFC as power generating devices, multiple cells are connected in series through an interconnect material to accumulate the voltage output. The interconnect should have very low permeability for the gases used. A novel solution combustion process has been developed for producing the phase pure, well-sinterable powders of Ca-doped LaCrO3 interconnect material. A process has been developed to produce the coarse granules as a feed material using combustion-synthesized powder for plasma spray through (a) preparation of granules through cold iso-static pressing followed by breaking and sieving (b) sintering of the green granules followed by sieving. The flow ability and deposition efficiency studies on +45-75 and 75-125 μm powders suggested that +45-75 powder is more suitable for the plasma spray coating. The plasma process parameters; plasma power, flow rate of carrier gases and distance between substrate and plasma gun have been optimized to achieve required coating characteristics. The as-produced coating using 20 kW power plasma gun on the porous Sr-doped LaMnO3 cathode substrates has been examined by SEM. An adherent coating of about 100 μm has been observed in the micrographs. No large cracks were observed throughout the coating. However, the coating was not found to be impervious in nature. Also the micrographs showed incomplete melting of the plasma-coated material. The similar experiments were performed using a higher power (≈ 60 Kw) plasma gun. The coated coupons were tested for leakage by checking water penetration. It was found that water did not penetrate for quite a long time. Therefore, the coupon was further tested for leakage by keeping it over a port connected to vacuum pump. The vacuum attained was 7×10-3 mbar and it was maintained for four consecutive days. The SEM studies on the coated sample showed a quite dense coating along with a very few small local pores.