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SYNTHESIS AND CHARACTERIZATION OF LANTHANUM SILICATE APATITE TYPE POWDERS FOR SOFC ELECTROLYTE Daniel Ricco Elias Abstract Solid oxide fuel cell (SOFCs) operating temperature that uses yttria stabilized zirconia (YSZ) as the electrolyte is 1000oC. This high temperature causes serious problems concerning cell life and materials. Therefore, the ionic conductors which have high conductivity at lower temperature are currently researched. Studies have shown that the composition of La10Si6O27 apatite type has high oxygen ionic conductivity, which is comparably higher than that of YSZ, at 500 C, it is therefore a potential candidate as for SOFC electrolyte. The objective of the present work is the development of lanthanum silicate with apatite type synthesis techniques. Novel modified sol–gel routes to synthesize La9.33Si6O26 are proposed. Stoichiometric volumes of Na2SiO3 and LaCl3 solutions were mixed for the formation of Si gel. This gel was calcined at 900 °C, washed, filtered and again thermally treated at 900 °C. In the other route, stoichiometric volumes of Si (Na2SiO3 or TEOS) and La (LaCl3) solutions were used for obtaining Si gel. Then, La hydroxide was precipitated by adding of a base (NaOH or NH4OH) to gel. Then the material was calcined at 900 °C, washed, filtered and again treated at 900 °C. Highly sinterable weakly agglomerated powders have been obtained. XRD patterns of the powders showed the single-phase apatite structure at 900 C. Dense ceramic morphology was observed from the SEM images of surface of the pellets sintered at 1200, 1300 and 1400C for 4h. This low temperature sintering and time of sintering are significant because the conventional method requires superior temperatures of 1700 C to obtain the same dense ceramics. High relative densities higher than 90% was obtained via proposed methods. An Important conclusion is the TEOS, the usual high cost reagent, may be substituted by a cheap price Na2SiO3, to obtain apatite type La9.33Si6O26.

Síntese e caracterização de pós de silicato de lantânio tipo apatita para eletrólito em SOFC