Water pressure enhanced sintering of alkaline-earth perovskite ceramics

The alkaline earth-based perovskite ceramics are potential electrolytes for components of electrolysers, fuel cells and CO2/syngas converters. Their high refractariness is an advantage from the chemical stability point of view but involves high sintering temperature (>1450 degrees C), detrimental to the co-sintering procedure required to assemble device components. Since the presence of protonic species is not intrinsic to the perovskite structure, the Ln-modified perovskites have to be successfully protonated by exposition of dense (95-99% theoretical density) ceramic pieces to (pressurized) water. We demonstrate that densification of a AZr(1-x)Ln(x)O(3-delta) ceramic can be enhanced by prior exposition of 1200 to 1300 degrees C pre-fired (porous) ceramics to high water pressure using an autoclave. Autoclave temperature and treatment duration are considered. Thermal expansion measurements reveal that the protonation (200-300 degrees C under 15-80 bar of water vapour) of previously fired (70-80% of the theoretical density) porous perovskite body (SrZr1-xYbxO3, x=0.1) enhances the sintering and allows densification at lower temperature. The gain in temperature reaches 200-300 degrees C. IR and Raman studies show that the film formed on surface consists of (hydrated) alkali-earth oxyhydroxides. Sintering enhancement is assigned to the modification of the material structure close to the grain surface/boundary and to the enhancement of ions mobility at the grain surface/interface. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.