Oxy-apatite reaction sintering of colloidal and classic ceramic processed powders

摘要

Oxy-apatites are promising electrolyte materials for intermediate-temperature solid oxide fuel cells, IT-SOFC. However the requirements of electrolytes make necessary the preparation of dense films with the appropriated composition to show good electrical properties;;in this way, colloidal processing is a key issue. This work involves the application of colloidal processing for four oxygen-excess oxy-apatites, La_(9.67)(Si_6O_(24))O_(2.5), La_(10)(Si_6O_(24))O_3, La_(10)(Si_(5.5)Al_(0.5)O_(24))O_(2.75) and La_(10)(Si_5Al_1O_(24))O_(2.5) and their characterization (phases, microstructure and electrical properties). The results have been compared with those obtained by classical ceramic method to assure the same composition without loosing properties. Samples with the desired compositions were obtained by reaction sintering of La_2O_3, SiO_2 and Al_2O_3. La_(10)(Si_(5.5)Al_(0.5)O_(24))O_(2.75) prepared by colloidal processing and heated at 1923 K showed the highest conductivity value, 3.0 x 10~(-2) S cm~(-1) at 973 K. Furthermore, its residual porosity was very low. On the other hand, La_(10)(Si_6O_(24))O_3 stoichiometry was tried by colloidal and ceramic methods under several experimental conditions. Unfortunately, the obtained oxy-apatite seems to have slightly lower lanthanum content. In spite of previous reports claiming the preparation of stoichiometric La_(10)(Si_6O_(24))O_3, this study cannot support these findings.