Lanthanum chromite interconnects

The lanthanum chromite interconnect strip is applied along the length of the tube by plasma-spraying. Since this is required to pass through the electrolyte and anode it is necessary to use appropriate masking during their deposition. The connection between cells is made via a soft nickel felt so that no dangerous mechanical stresses are placed on the tubes. 

Doped lanthanum chromite interconnection is deposited in the form of about 85 pm thick, 9 mm wide strip along the air electrode tube length by plasma spraying followed by densification sintering [29]. 

Armstrong, T.R., Hardy, J.S., Simmer, S.P. and Stevenson, J.W. (1999), Optimizing lanthanum chromite interconnects for solid oxide fuel cells. Proceedings of the Sixth International Symposium on Solid Oxide Fuel Cells (SOFC-VI), Eds. S.C. Singhal and M. Dokiya. The Electrochemical Society Proceedings Series, Pennington, NJ, pp. 706-715. 

The result is the formation of a dense and uniform metal oxide layer in which the deposition rate is controlled by the diffusion rate of ionic species and the concentration of electronic charge carriers. This procedure is used to fabricate the thin layer of soHd electrolyte (yttria-stabilized 2irconia) and the interconnection (Mg-doped lanthanum chromite). 

The interconnect material is in contact with both electrodes at elevated temperatures, so chemical compatibility with other fuel cell components is important. Although, direct reaction of lanthanum chromite based materials with other components is typically not a major problem [2], reaction between calcium-doped lanthanum chromite and YSZ has been observed [20-24], but can be minimized by application of an interlayer to prevent calcium migration [25], Strontium doping, rather than calcium doping, tends to improve the resistance to reaction [26], but reaction can occur with strontium doping, especially if SrCr04 forms on the interconnect [27],... 

Lanthanum chromite is the most common base for SOFC interconnects, but chromites of other lanthanide elements have also been used [43, 45, 46, 48, 54, 55], Although the conductivity of calcium-doped gadolinium chromite for low calcium contents is in the upper range of conductivities for lanthanum chromite, other nonlanthanum chromites typically have lower conductivities. However, the use of other lanthanides provides benefits in controlling the phase transformation temperature and in potential cost savings [48],... 

Sakai N, Yokokawa H, Horita T, and Yamaji K. Lanthanum chromite-based interconnects as key materials for SOFC stack development. Int. J. Appl. Ceram. Technol. 2004 l 23-30. 

Fergus JW. Lanthanum chromite based materials for solid oxide fuel cell interconnects. Solid State Ionics 2004 171 1-15. 

Zhong Z. Stoichiometric lanthanum chromite based ceramic interconnects with low sintering temperature. Solid State Ionics 2006 177 757-764. 

Suzuki M, Sasaki H, and Kajimura A. Oxide ion conductivity of doped lanthanum chromite thin film interconnects. Solid State Ionics 1997 96 83-88. 

Cell Interconnect Pt Mn doped cobalt chromite Doped lanthanum chromite Plasma spray 10 X 10 cm/cm °C 100 pm thickness... 

Satisfactory conductivity is maintained up to 1800 °C in air but falls off at low oxygen pressures so that the upper temperature limit is reduced to 1400 °C when the pressure is reduced to 0.1 Pa. A further limitation arises from the volatility of Cr2C>3 which may contaminate the furnace charge. The combination of high melting point, high electronic conductivity and resistance to corrosion has led to the adoption of lanthanum chromite for the interconnect in high temperature solid oxide fuel cells (see Section 4.5.3). 

These requirements are satisfied by a doped lanthanum chromite (see Section 4.1.3) e.g. La (Ca, Mg, Sr, etc.) Cr03. However for SOFCs operating in the temperature range 500-750 °C a stainless steel interconnect plate can be used. 

Fig. 13.22. The monolithic SOFC concept of Argonne National Laboratory. Anode nickel-yttria-stabilized zirconia. Cathode strontium-doped lanthanum manganite. Interconnect doped lanthanum chromite, a, Interconnection b, electron-ion path c, anode d, electrolyte e, cathode. (Reprinted from K. Kordesch,...

Various alloys, cermets as well as lanthanum chromites with different dopants were used as interconnects in SOFC prototypes. The seals having different softening temperatures were elaborated and widely used for gas-tight assembling cells into stacks. 

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