Mechanically activated self-propagating high-temperature synthesis of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ as an electrolyte for SOFC

In this paper, we report on synthesis of highly pure La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ (LSGM9182) powder with high crystallinity by mechanically activated (MA) self-propagating high-temperature synthesis (SHS), in which the synergy effects of MA and SHS on final and intermediate products were mainly examined. In the experiments, raw materials of La₂O₃, SrCO₃, Ga₂O₃, Mg and NaClO₄ were fractured and well mixed by planetary ball milling for different periods from 0 h to 24 h, then the bottom surface of the green compacts were electrically ignited for producing pure LSGM9182 through the propagation of sustainable exothermic reaction. The final and intermediate products, shortly after MA treatment, were characterized by XRD, SEM, XRF and particle size analyzer. During the planetary ball milling, the raw materials became gradually amorphous due to disordering of crystal structure. Interestingly, the longer milling operation caused the larger particle size of the raw material because nanoparticles, generated by the milling, became easily massed together. More significantly, the MA pretreatment improved a reactivity of the SHS to purify the product. In particular, the combination of MA-SHS with ball milling of 24 h at 300 rpm gave the highest-grade LSGM9182 product of nano-sized primary particles. The results appealed that the SHS after the MA treatment was quite effective for initiating, activating, sustaining and completing the solid-solid reaction synthesis of functional perovskite-type oxide with mild exothermic heat.