Direct production of porous lanthanum strontium manganite (La(0.8)Sr(0.2)MnO(3)) in a reactive dc thermal plasma spray system

Synthesis of a La_0.8Sr_0.2MnO₃ cathode layer in planar solid oxide fuel cell using a reactive d.c. thermal plasma spray system at atmospheric pressure and lower pressure (0.334 atm.) was proposed and studied. Two preparation methods using a reactive dc thermal plasma spray system were carried out to produce the cathode layer. One is the currently widely used d.c. thermal plasma spray method, which uses the completely prereacted La_0.8Sr_0.2MnO₃ (LSMO) powders with a certain amount of pore former to produce the porous LSMO cathode layer. The second is our newly developed reactive d.c. thermal plasma spray method, which uses only mixed raw materials (La₂O₃, SrCO₃, and MnCO₃) in appropriate ratio to decrease the production cost of the LSMO cathode layer by decreasing process steps. In the case of the current d.c. thermal plasma spray methods, the coated LSMO layer was not completely crystallized due to the coexistence of amorphous phase. A stronger peak of the LSMO phase in our new developed method was obtained after spraying with the raw materials.; CSIRO thermochemical analysis showed that the synthesis of La_0.8 Sr_0.2MnO₃ from the mixed raw materials is possible at the temperature range of 1,300–2,600 K. The LSMO coating layers with well-crystallization and fine open pores were obtained at the stand-off distance of 90 mm and the input power of 35 kW on the mild steel substrate with the feeding rate of 2g/min, and the stand-off distance of 94 mm and the input power of 38 kW with the feeding rate of 2.2 g/min on the zirconia, substrate. Very fine particles (20 nm) from collected powder were examined by TEM. A model for particle vaporization, temperature and velocity profiles, and heat and mass transfer in the reactor was developed. Particle size has the greatest effect to the vaporization. The stand-off distance from the spray gun to the substrate is very important with respect to the temperature and velocity history of plasma flame.; Finally these experiments have successfully demonstrated the direct production of porous lanthanum strontium manganite (La_0.8Sr_0.2MnO ₃) in a reactive d.c. thermal plasma system to decrease the process steps of current plasma spray.