Water pressure enhanced sintering of alkaline-earth perovskite ceramics

Abstract

The alkaline earth-based perovskite ceramics are potential electrolytes for components of electrolysers, fuel cells and CO 2 /syngas converters. Their high refractariness is an advantage from the chemical stability point of view but involves high sintering temperature (>1500°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-δ ceramic can be enhanced by prior exposition of 1200 to 1300°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°C under 15-80 bar of water vapour) of previously fired (70-80% of the theoretical density) porous perovskite body (SrZr 1-x Yb x O 3 , x=0.1) enhances the sintering and allows densification at lower temperature. The gain in temperature reaches 200-300°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 tions mobility at the grain surface/interface.

Chemical Preparation Routes and Lowering the Sintering Temperature of Ceramics

“…The volume of liquid phase favored by the sintering aids is much smaller-a few % or less-and, therefore, being effective requires high packing of grains in the green state in order to maximize the efficiency of the liquid phase. Sintering aids for oxide compositions are primary fluxing agents such as alkali and alkaline earth, boron and bismuth oxides and fluorides [17,106,[159][160][161][162][163][164][165][166][167][168][169][170][171]. The volatility of a sintering aid is an advantage: complete elimination is possible and single-phase final ceramics can be obtained [17,64,65,106,[172][173][174].…”