Keywords: ceric ammonium nitrate, mixed fuel process, nanocrystalline, cerium, ceria solid solutions, thermal analysis, sintering, dense ceramics, oxide nanoparticles, nanostructures, sintered ceramics, citric acid, glycine, microstructure, nanopowders, nanotechnology
Towards achieving nano-structured sintered ceramics with high stability for SOFC applications: Ce1−xMxO2−δ, M = Gd, Sm: interesting examples
Through selected examples, we have demonstrated the importance of using nanoparticles of oxides to obtain nanostructured sintered ceramics at low sintering temperatures. For this purpose, we have prepared two series of single doped ceria solid solutions of the general formulae Ce1−xMxO2−δ, where M = Gd and Sm and x = 0.05-0.2 using a modified combustion process, namely a mixed fuel process with a mixture of fuels, such as citric acid and glycine. Independent of the nature of the metal ions all the compositions formed doped Ce1−xMxO2−δ ceria in-situ with improved powder properties such as finer particle size and high surface area. Highly reactive powders that could achieve resultant sintered density of ≥98% of the theoretical density were achieved by this synthetic approach. Moreover, the sintered Ce1−xMxO2−δ powders exhibited enhanced densification and controlled grain growth and exhibited nano-sized grains in the sintered microstructures. A correlation could be established between the agglomerate size of the powders and the ultimate grain size of the sintered powder compacts. In addition, these powders have the potential of exhibiting substantial stability against reduction by retaining relatively high density over a wide range of temperatures. The cited examples clearly demonstrate an incremental increase in property, viz., enhanced sinterability of the particles due to nanosize effect.